CN118057245A - Image forming apparatus having a plurality of image forming units - Google Patents

Abstract

The present invention relates to an image forming apparatus. In a cross section perpendicular to the rotation axis of the first image bearing member, when a common tangent line between the first image bearing member and the second image bearing member on the intermediate transfer belt side is a straight line L, a straight line passing through the rotation center of the first image bearing member and the rotation center of the first transfer member is a straight line P, and a straight line passing through an intersection point between the straight line P and the first image bearing member and perpendicular to the straight line P is a straight line Q, the electrode member is configured such that a contact portion contacting the inner surface of the belt is located more on the first image bearing member side than the straight line L and more on the first transfer member side than the straight line Q.

Description

Image forming apparatus having a plurality of image forming units

Technical Field

The present invention relates to an image forming apparatus using an electrophotographic type or an electrostatic recording type, such as a copying machine, a printer, a facsimile machine, or a multifunctional machine having a plurality of functions of these machines.

Background

As an image forming apparatus using an electrophotographic type such as a color copier, a color printer, or a color multifunction machine, an intermediate transfer type image forming apparatus has become mainstream because the image forming apparatus has advantages of miniaturization of an apparatus main assembly and relatively easy adaptation to various recording materials. An image forming apparatus of the intermediate transfer type generally includes a constitution provided with a plurality of photosensitive drums and an intermediate transfer belt. In addition, in such an image forming apparatus, the toner images formed on the photosensitive drums are sequentially electrostatically primary-transferred onto the intermediate transfer belt, and then the toner images on the intermediate transfer belt are electrostatically secondary-transferred onto a recording material such as paper.

In the image forming apparatus as described above, it is difficult to uniformly transfer the toner image onto, for example, an embossed paper (embossed paper) or the like having an uneven surface. In particular, transferring the toner image onto the concave portion of the embossed paper tends to become difficult because of the relatively large transfer electric field required (because a gap is formed between the intermediate transfer belt and the embossed paper in the secondary transfer portion).

On the other hand, in japanese laid-open patent application No.2006-267486, a technique of using a secondary transfer voltage in the form of a DC voltage biased with an AC voltage is proposed.

However, in the case of using the secondary transfer voltage in the form of a DC voltage biased with an AC voltage, the quality of a microimage such as a thin line tends to be lowered due to scattering of toner. For this reason, it has been desired to improve the transfer performance of a toner image onto a recording material such as an embossed paper, on which it is relatively difficult to transfer the toner image, even in the case of using a secondary transfer voltage containing only a DC voltage.

Incidentally, in the above, as a recording material on which it is relatively difficult to transfer a toner image, an embossed paper is exemplified, but this is also true for a recording material (high-resistance paper) having a relatively high resistance such as a synthetic paper formed mainly of a synthetic resin material, or a resin film. In addition, the present invention does not exclude the use of a secondary transfer voltage of a DC voltage biased with an AC voltage.

Disclosure of Invention

A main object of the present invention is to provide an image forming apparatus capable of improving transfer performance of a toner image onto a recording material such as embossed paper, which is relatively difficult to transfer the toner image thereon in an image forming apparatus of an intermediate transfer type.

This object has been achieved by an image forming apparatus according to the present invention.

According to an aspect of the present invention, there is provided an image forming apparatus including: a first image bearing member configured to bear a toner image; a second image bearing member configured to bear a toner image; an intermediate transfer belt onto which toner images are transferred from the first image bearing member and the second image bearing member, wherein the first image bearing member is provided adjacent to the second image bearing member on an upstream side of the second image bearing member with respect to a moving direction of the intermediate transfer belt; a first transfer member provided downstream of the first image bearing member with respect to a moving direction of the intermediate transfer belt and configured to transfer a toner image from the first image bearing member onto the intermediate transfer belt in a first transfer portion under application of a first transfer voltage; a second transfer member provided downstream of the second image bearing member with respect to a moving direction of the intermediate transfer belt and configured to transfer a toner image from the second image bearing member onto the intermediate transfer belt in a second transfer portion under application of a second transfer voltage; and an electrode member provided downstream of the first transfer portion and upstream of the second transfer portion with respect to a moving direction of the intermediate transfer belt and including a contact portion that contacts an inner surface of the intermediate transfer belt, wherein a voltage of a polarity opposite to that of the first transfer voltage is applied to the electrode member, wherein, in a cross section perpendicular to a rotation axis of the first image bearing member, a common tangent line between the first transfer member and the second image bearing member on an intermediate transfer belt side is a straight line L, a straight line passing through a rotation center of the first image bearing member and a rotation center of the first transfer member is a straight line P, and a straight line passing through an intersection point between the straight line P and the first image bearing member and perpendicular to the straight line P is a straight line Q, the electrode member is configured such that the contact portion is located on the first image bearing member side and on the first transfer member side than the straight line Q.

Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

Fig. 1 is a schematic cross-sectional view of an image forming apparatus.

Fig. 2 is a block diagram showing a control system of the image forming apparatus.

Parts (a) and (b) of fig. 3 are a sectional view and a perspective view, respectively, of the potential regulating member.

Fig. 4 is a sectional view of a potential regulating member in another example.

Fig. 5 is a sectional view of a potential adjusting member in another example.

Fig. 6 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 7 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 8 is a sectional view for illustrating the arrangement of the potential regulating member.

Parts (a) and (b) of fig. 9 are sectional views each for illustrating the arrangement of the potential regulating member.

Fig. 10 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 11 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 12 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 13 is a diagram for illustrating the effect of the potential regulating member.

Parts (a) and (b) of fig. 14 are photo diagrams for illustrating the effect of the potential regulating member.

Fig. 15 is a diagram for illustrating the effect of the potential regulating member.

Parts (a) and (b) of fig. 16 are a sectional view and a perspective view, respectively, of the potential regulating member in another embodiment.

Fig. 17 is a sectional view for illustrating the arrangement of the potential regulating member.

Fig. 18 is a sectional view for illustrating a potential adjusting member in another example.

Parts (a) and (b) of fig. 19 are a sectional view and a perspective view, respectively, for illustrating the potential regulating member in another embodiment.

Detailed Description

In the following, an image forming apparatus according to the present invention will be described in more detail with reference to the accompanying drawings.

Example 1

1. Overall structure and operation of image forming apparatus

First, the overall structure and operation of the image forming apparatus of this embodiment will be described. Fig. 1 is a schematic cross-sectional view of an image forming apparatus 1 of this embodiment. The image forming apparatus 1 of this embodiment is a tandem type full-color printer capable of forming a full-color image on a sheet-like recording material S by using an electrophotographic type and employing an intermediate transfer type.

The image forming apparatus 1 includes an image forming portion 2, a controller 3, a feeding portion 4 of the recording material S, and a discharging portion 5 of the recording material S. In addition, inside the image forming apparatus 1, a temperature sensor 71 (fig. 2) capable of detecting the temperature inside the apparatus and a humidity sensor 72 (fig. 2) capable of detecting the humidity inside the apparatus are provided. The image forming apparatus 1 is capable of forming an image on a recording material S based on image information (image signal) acquired by an original reading apparatus (not shown) provided on the image forming apparatus 1 or connected to the image forming apparatus 1. In addition, the image forming apparatus 1 is capable of forming an image on the recording material S based on image information (image signal) from an external device (not shown) such as a personal computer (host device), a digital camera, or a smart phone connected to the image forming apparatus 1. Incidentally, the recording material (transfer material, recording medium sheet) S is a material on which a toner image is formed, and specific examples thereof include plain paper, thick paper, glossy coated paper, matt coated paper, embossed paper, or synthetic resin sheets (synthetic paper) as substitutes for plain paper or the like, and overhead projector sheets (resin films). Here, the recording material S is referred to as "paper" ("paper", "embossed paper", "high-resistance paper", etc.) in some cases, but even in that case, the recording material S includes a material other than paper or a recording material formed of a material containing a material other than paper.

The image forming portion 2 forms an image on the recording material S fed from the feeding portion 4 based on the image information. The image forming portion 2 includes image forming units 10y, 10m, 10c, 10k, toner bottles 18y, 18m, 18c, 18k, exposure devices 13y, 13m, 13c, 13k, an intermediate transfer unit 20, a secondary transfer device 26, and a fixing device 27. The image forming units 10Y, 10M, 10C, and 10K form toner images of colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In some cases, elements having the same or corresponding functions of the structures provided for the respective colors will be collectively described by omitting suffixes y, m, c, and k respectively for the elements representing the associated colors. In addition, the image forming apparatus 1 can also form a monochrome image such as a (single) black image or a multicolor image by using the image forming unit 10 for a desired single color or some of four colors, for example.

The image forming unit 10 includes a photosensitive drum 11 as an image bearing member, the photosensitive drum 11 being a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member). Further, the image forming portion 10 includes a charging roller 12 as a charging member, and the charging roller 12 is a roller-type charging member. Further, the image forming portion 10 includes a developing device 14 as a developing member. Further, the image forming section 10 includes a pre-exposure device 16 as a discharging (charge eliminating) member. Further, the drum cleaning device 17 serves as a photosensitive member cleaning means. The image forming unit 10 forms a toner image on an intermediate transfer belt 6 described below.

The photosensitive drum 11 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 11 is a negatively chargeable organic photosensitive member (OPC) having an outer diameter of 30 mm. The photosensitive drum 11 has an aluminum cylinder as a base and a surface layer formed on the surface of the base. In this embodiment, as the surface layer, three layers of an undercoat layer, a photoelectric charge generation layer, and a charge transport layer, which are sequentially coated and laminated on a substrate, are provided. When the image forming operation starts, the photosensitive drum 11 is rotationally driven at a predetermined peripheral speed (process speed) in a direction indicated by an arrow R1 (counterclockwise) in the drawing by a drive motor (not shown) as a driving member.

The surface of the rotating photosensitive drum 11 is uniformly charged by the charging roller 12. In this embodiment, the charging roller 12 is a rubber roller that contacts the surface of the photosensitive drum 11 and is rotated by the rotation of the photosensitive drum 11. A charging power source 73 (fig. 2) as a charging voltage applying member (charging voltage applying portion) is connected to the charging roller 12. The charging power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 12 during the charging process.

The surface of the charged photosensitive drum 11 is scanned and exposed by the exposure device 13 according to image information, so that an electrostatic image is formed on the photosensitive drum 11. In this embodiment, the exposure apparatus 13 is a laser scanner. The exposure device 13 emits a laser beam according to the separated color image information output from the controller 3, and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 11.

The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by supplying toner thereto by the developing device 14, so that a toner image (developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 is a two-component developing device that uses a two-component developer including toner (non-magnetic toner particles) and carrier (magnetic carrier particles) as the developer. In a developing container (developing main body) 14b of the developing device 14, a two-component developer is accommodated, and an amount of toner corresponding to the consumption amount of toner is supplied from a toner bottle 18. The developing device 14 includes a developing sleeve 14a as a developing member (developer carrying member). The developing sleeve 14a is made of, for example, a nonmagnetic material such as aluminum or nonmagnetic stainless steel (aluminum in this embodiment). Inside the developing sleeve 14a, a magnet roller (not shown), which is a roller-shaped magnet, as a magnetic field generating member (magnetic field generating member) is fixed and arranged so as not to rotate relative to the developing container 14 b. The developing sleeve 14a carries the two-component developer and conveys it to a developing area opposite to the photosensitive drum 11. Then, in the development region, the toner moves from the two-component developer on the development sleeve 14a to and deposits on the image portion of the electrostatic image on the photosensitive drum 1. A developing power supply 74 (fig. 2) as a developing voltage applying member (developing voltage applying portion) is connected to the developing sleeve 14a. The developing power supply 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 14a during development. In this embodiment, on the exposed portion (image portion) of the photosensitive drum 11 reduced in the absolute value of the potential by being exposed after being uniformly charged, the toner charged to the same polarity (negative polarity in this embodiment) as that of the photosensitive drum 11 is deposited (reversal development type). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative.

The intermediate transfer unit 20 is arranged opposite to the four photosensitive drums 11y, 11m, 11c, and 11 k. The intermediate transfer unit 20 includes an intermediate transfer belt 6 composed of an endless belt as an intermediate transfer member. The intermediate transfer belt 6 is wound and stretched around a driving roller 21, a tension roller 22, and an inner secondary transfer roller 23, which are a plurality of stretching rollers. The intermediate transfer belt 6 is movable (rotatable) while carrying the toner image. The driving roller 21 is rotationally driven by a driving motor (not shown) as a driving member, so that a driving force is transmitted to the intermediate transfer belt 6, and thus the intermediate transfer belt 6 rotates (circulates and moves) in the arrow R2 direction (clockwise direction) in fig. 1 at a predetermined circumferential speed corresponding to the circumferential speed of the photosensitive drum 1. The tension roller 22 controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 is subjected to a force that urges the intermediate transfer belt 6 from the inner peripheral surface (back surface) side toward the outer peripheral surface (front surface) side by an urging force of a tension spring (not shown) constituted by a compression coil spring as an urging member. By this force, a tension of about 2 to 5kg is applied in the feeding direction (the process proceeding direction, the moving direction) of the intermediate transfer belt 6. The inside secondary transfer roller 23 constitutes a secondary transfer apparatus 26 in combination with an outside secondary transfer roller 25 described below. Primary transfer rollers 15y, 15m, 15c, 15k as primary transfer means are provided on the inner peripheral surface side of the intermediate transfer belt 6 in correspondence with the photosensitive drums 11y, 11m, 11c, 11k, respectively, and these primary transfer rollers 15y, 15m, 15c, 15k are roller-type primary transfer members. In this embodiment, the primary transfer rollers 15 are disposed opposite to the photosensitive drums 11 and nip (nip) the intermediate transfer belt 6 between themselves and the photosensitive drums 11. Each of the primary transfer rollers 15 is pressed against the photosensitive drum 11 and contacts the photosensitive drum 11 via the intermediate transfer belt 6, and forms a primary transfer portion (primary transfer nip) N1 that is a contact portion between the photosensitive drum 11 and the intermediate transfer belt 6.

The toner image formed on the photosensitive drum 11 is transferred (primary transfer) onto the intermediate transfer belt 6 in the primary transfer portion N1 by the action of the primary transfer roller 15. For example, when a full-color image is formed, the yellow, magenta, cyan, and black toner images formed on the photosensitive drums 11 are multiply transferred so as to be sequentially superimposed on the intermediate transfer belt 6. A primary transfer power supply 75 (fig. 2) as a primary transfer voltage applying member (primary transfer voltage applying portion) is connected to the primary transfer roller 15. During primary transfer, the primary transfer power supply 75 applies a primary transfer voltage (primary transfer bias) to the primary transfer roller 15, which is a DC voltage having a polarity (positive polarity in this embodiment) opposite to the normal charge polarity of the toner. Thereby, the toner image of the negative polarity on the photosensitive drum 11 is primary-transferred onto the intermediate transfer belt 6. A voltage detection sensor 75a (fig. 2) as a voltage detection means (voltage detection portion) that detects an output voltage thereof and a current detection sensor 75b (fig. 2) as a current detection means (current detection portion) that detects an output current thereof are connected to the primary transfer voltage source 75. In this embodiment, for example, a primary transfer voltage of about 1 to 2kV is applied to the primary transfer roller 15 ("1 to 2kV" means a range including 1kV and 2kV, and the same applies hereinafter). Further, in this embodiment, the primary transfer voltage is subjected to constant voltage control. In this embodiment, primary transfer voltage sources 75y, 75m, 75c, and 75k are independently provided to the primary transfer rollers 15y, 15m, 15c, and 15k, respectively. In addition, in this embodiment, the primary transfer voltages applied to the primary transfer rollers 15y, 15m, 15c, and 15k may be individually controlled.

Here, in this embodiment, the primary transfer roller 15 has a core metal and an elastic layer of ion-conductive foam rubber (NBR rubber) formed at the periphery of the core metal. The outer diameter of the primary transfer roller 15 is, for example, 15 to 20mm. Further, as the primary transfer roller 15, a roller having a resistance value of 1×10 ⁵ to 1×10 ⁸ Ω (N/N (23 ℃,50% rh) condition, application of 2 kV) can be preferably used.

In addition, in this embodiment, the intermediate transfer belt 6 is an endless belt having a two-layer structure including a base layer and a surface layer in this order from the inner peripheral surface side toward the outer peripheral surface side. As a material constituting the base layer, resins such as polyimide and polycarbonate, in which an appropriate amount of carbon black is contained as an antistatic agent, can be suitably used. The thickness of the base layer is, for example, 0.05 to 0.15mm. As a material constituting the surface layer, a resin such as Chloroprene Rubber (CR) to which conductivity is imparted may be used. The thickness of the surface layer is, for example, 0.200 to 0.300mm. In this embodiment, the intermediate transfer belt 6 has a volume resistivity of 5×10 ⁸ to 1×10 ¹⁴ Ω·cm (23 ℃,50% rh). Incidentally, in this embodiment, a two-layer structure is employed in the intermediate transfer belt 6, but a single-layer structure of a material corresponding to the material of the above-described base layer may also be employed. In addition, the surface layer may also be formed to contain a resin material such as a fluorine-containing resin, a resin coating layer having a thickness of about 0.002 to 0.01 mm. In addition, the intermediate transfer belt 6 may have a multilayer structure of three or more layers.

On the outer peripheral surface side of the intermediate transfer belt 6, an outer secondary transfer roller 25 as a secondary transfer means is disposed, and the outer secondary transfer roller 25 is a roller-type secondary transfer member. The outer secondary transfer roller 25 as a secondary transfer member constitutes a secondary transfer device 26 in cooperation with the inner secondary transfer roller 23 as an opposing member (opposing electrode). The outer secondary transfer roller 25 is pressed against the inner secondary transfer roller 23, and contacts the inner secondary transfer roller 23 via the intermediate transfer belt 6, and forms a secondary transfer portion (secondary transfer nip) N2 that is a contact portion between the intermediate transfer belt 6 and the outer secondary transfer roller 25. The toner image formed on the intermediate transfer belt 6 is transferred (secondary transfer) in the secondary transfer portion N2 by the action of the secondary transfer apparatus 26 onto the recording material S nipped and fed by the intermediate transfer belt 6 and the outer secondary transfer roller 25. A secondary transfer power supply 76 (fig. 2) as a secondary transfer voltage applying member (secondary transfer voltage applying portion) is connected to the outer secondary transfer roller 25. During secondary transfer, the secondary transfer power supply 76 applies a secondary transfer voltage (secondary transfer bias) which is a DC voltage having a polarity (positive polarity in this embodiment) opposite to the normal charge polarity of the toner to the outer secondary transfer roller 25. Thereby, the toner image of the negative polarity on the intermediate transfer belt 6 is secondarily transferred onto the recording material S. A voltage detection sensor 76a (fig. 2) as a voltage detection means (voltage detection portion) for detecting an output voltage thereof and a current detection sensor 76b (fig. 2) as a current detection means (current detection portion) for detecting an output current thereof are connected to the secondary transfer power supply 76. In addition, the core metal of the inner secondary transfer roller 23 is connected to the ground potential. In this embodiment, for example, a secondary transfer voltage of about 1 to 6.5kV is applied to the secondary transfer roller 25, and a current of about 15 to 100 μa is caused to flow through the secondary transfer portion N2, so that the toner image on the intermediate transfer belt 6 is secondarily transferred onto the recording material S. In this embodiment, the secondary transfer voltage is subjected to constant voltage control. Incidentally, the following constitution may also be adopted: in this configuration, a secondary transfer voltage, which is a DC voltage of the same polarity as the normal charge polarity of the toner, is applied from the secondary transfer power supply 76 to the inner secondary transfer roller 23 as the secondary transfer member so that the outer secondary transfer roller 25 as the opposing member is connected to the ground potential.

The recording material S is fed from the feeding portion 4 toward the secondary transfer portion N2 in parallel with the forming operation of the toner image on the intermediate transfer belt 6. The recording material S is accommodated in a cassette 41 as a recording material accommodating portion of the feeding portion 4. The recording materials S accommodated in the cassette 41 are separated from the cassette 41 one by one and fed by a feed roller 42 or the like. This recording material S is conveyed by a conveying roller 43 or the like as a conveying member of the feeding portion 4 to a registration roller pair 19 as a conveying member provided on a conveying path 44 of the recording material S. Then, this recording material S is conveyed to the secondary transfer portion N2 by the registration roller pair 19 by being in line with the toner image on the intermediate transfer belt 6. Incidentally, in fig. 1, only one cartridge 41 is illustrated, but the image forming apparatus 1 may also include a plurality of cartridges 41. In addition, the feeding unit 4 may also be capable of feeding the recording material S from a recording material accommodating portion (recording material mounting portion) other than the cassette 41, such as a manual feeding tray.

Here, in this embodiment, the outer secondary transfer roller 25 includes a core metal and an elastic layer of ion-conductive foam rubber (NBR rubber) formed around the core metal. The outer diameter of the outer secondary transfer roller 25 is, for example, 20 to 25mm. Further, as the outside secondary transfer roller 25, a roller having a resistance value of 1x10 ⁵ to 1x10 ⁸ Ω (measured at N/N (23 ℃,50% rh), applied at 2 kV) may be preferably used.

The recording material S on which the toner image has been transferred is fed to a fixing device 27 as a fixing member. The fixing device 27 includes a fixing roller 27a and a pressing roller 27b. The fixing roller 27a includes a heater as a heating member. The pressing roller 27b is pressed against the fixing roller 27a and forms a fixing portion (fixing nip). The fixing device 27 heats and pressurizes the recording material S carrying the unfixed toner image by sandwiching and feeding the recording material S between the fixing roller 27a and the pressing roller 27b, thereby causing the toner image to be fixed (fusion-adhered) on the recording material S. Incidentally, the temperature of the fixing roller 27a (fixing temperature) is detected by a fixing temperature sensor 77 (fig. 2). The recording material S having the toner image fixed thereon is fed by a discharge roller pair 51 or the like, and is discharged (output) through a discharge opening (not shown) onto a discharge tray 52 provided outside the apparatus main assembly 1a of the image forming apparatus 1.

The surface of the photosensitive drum 11 after the primary transfer is discharged by the pre-exposure apparatus 16. Further, the toner (primary transfer residual toner) which is not transferred onto the intermediate transfer belt 6 during primary transfer but remains on the photosensitive drum 11 is removed from the surface of the photosensitive drum 11 by the drum cleaning device 17 and collected. In this embodiment, the drum cleaning device 17 scrapes off the primary transfer residual toner from the surface of the rotating photosensitive drum 11 by a cleaning blade as a cleaning member, and collects the primary transfer residual toner in a collector (not shown). The cleaning blade is a plate-like member that contacts the photosensitive drum 11 at a predetermined pressure. The cleaning blade contacts the surface of the photosensitive drum 11 in the opposite direction to the rotational direction of the photosensitive drum 11 such that its front end on the free end side faces the upstream side of the rotational direction of the photosensitive drum 11. In addition, deposits such as toner (secondary transfer residual toner) that has not been transferred onto the recording material S during secondary transfer and remains on the intermediate transfer belt 6 are removed and collected from the surface of the intermediate transfer belt 6 by the belt cleaning device 24 as an intermediate transfer member cleaning means.

Incidentally, the image forming unit 10 may constitute a cartridge (process cartridge) integrally detachably mounted to the apparatus main assembly 1a of the image forming apparatus 1. In this embodiment, the intermediate transfer unit 20 is constituted by the intermediate transfer belt 6, tension rollers for the intermediate transfer belt 6, respective primary transfer rollers 15, a belt cleaning device 24, and a potential adjusting member 8 described below, and the like. The intermediate transfer unit 20 may be integrally detachably mounted to the apparatus main assembly 1a.

2. Control structure

Fig. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a controller 3 (control circuit) as a control means. The controller 3 is constituted by including a CPU 31 as a computing means, a ROM 32 as a storage means, a RAM 33 as a storage means, and an input/output circuit (I/F) (not shown) for inputting/outputting signals between itself and an external device. The ROM 32 stores programs and the like for controlling the respective portions of the image forming apparatus 1. The RAM 33 temporarily stores data on control. The CPU 31 is a microprocessor that controls the entire image forming apparatus 1 and is a main part of a system controller. The CPU 31 is connected to respective sections such as the feeding section 4, the image forming section 2, the discharging section 5, and the like, and exchanges signals with these sections, but also controls the operation of each of these sections. The ROM 32 stores an image formation control sequence for forming an image on the recording material S.

A charging power supply 73, a developing power supply 74, a primary transfer power supply 75, a secondary transfer power supply 76, and a potential adjusting power supply 80 described below, which are controlled by signals from the controller 3, are connected to the controller 3, respectively. Incidentally, although omitted from illustration, in this embodiment, each of the charging power supply 73, the developing power supply 74, the primary transfer power supply 75, and the potential adjusting power supply 80 is provided independently of the associated image forming unit 10. Further, a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer voltage source 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer voltage source 76, a fixing temperature sensor 77, and the like are connected to the controller 3. A signal (information) indicating the detection result of the associated sensor. In addition, the operation unit 70 is connected to the controller 3.

Then, the operation unit 70 includes an input portion constituted by operation buttons (keys) or the like as an input means, and a display portion 70a constituted by a liquid crystal panel (display) or the like as a display means. Incidentally, in this embodiment, the display portion 70a is constituted as a touch panel, and also has a function as an input member. An operator such as a user or a service person operates the operation portion 70, and thus the image forming apparatus 1 can be caused to execute a job (described later). A series of operations for forming and outputting an image on a single recording material S or forming and outputting images on a plurality of recording materials S by a single start instruction. The controller 3 receives signals from the operation section 70 and operates various devices of the image forming apparatus 1. Further, the image forming apparatus 1 may also execute a job depending on a signal from an external device such as a personal computer, for example, instead of from the operation unit 70.

3. Summary of problems and solutions

Next, a problem in the image forming apparatus 1 of the intermediate transfer type will be further described. Incidentally, for convenience, unless otherwise mentioned, the magnitudes of the voltage and the potential (high/low) refer to the magnitudes (high/low) in the case where the values thereof are compared with each other in absolute value. In addition, regarding the arrangement of the primary transfer portion N1, the photosensitive drum 11, the primary transfer roller 15, and the potential adjusting member 8 and the like described later, upstream and downstream refer to upstream and downstream with respect to the feeding direction (process proceeding direction, moving direction) of the intermediate transfer belt 6 unless otherwise mentioned.

As described above, in the image forming apparatus 1 of the intermediate transfer type, it is difficult to uniformly transfer the toner image on, for example, an embossed paper having an uneven surface. Incidentally, the embossed paper is paper (fancy paper) provided with an uneven pattern by using a method such as swelling or embossing on the surface of the paper. In particular, a relatively large transfer electric field is required to transfer the toner image onto the concave portion of the embossed paper (because a gap is formed between the intermediate transfer belt 6 and the embossed paper in the secondary transfer portion N2), and thus it is easy to become difficult. In addition, when the secondary transfer electric field is made large in order to improve the transfer performance of the toner image on the concave portion of the embossed paper, there is a possibility that improper transfer occurs in which the toner is not partially transferred onto the halftone image in the case where the transfer electric field becomes excessively large at a portion other than the concave portion.

When the present inventors studied, it was found that the toner on the intermediate transfer belt 6 was subjected to discharge between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer portion N1, and thus the charge amount was increased. Specifically, it was found that the toner was subjected to discharge, and therefore the average value of the electric charges increased when the electric charge amount distribution of the toner became wider than that during development. Further, it was found that the charge amount increases as described above, so that the mirror force between the toner and the intermediate transfer belt 6 increases and the transfer electric field necessary to transfer the toner onto the recording material S in the secondary transfer portion N2 becomes large, and thus it becomes more difficult to transfer the toner image onto the concave portion of the embossed paper.

Accordingly, the present inventors have made intensive studies and found that by suppressing the above-described discharge and the increase in the charge amount of the toner on the intermediate transfer belt 6, the transfer performance of the toner image onto a recording material S such as an embossed paper (transfer of the toner image thereto is relatively difficult) can be improved. That is, it was found that it is effective to apply a voltage of the same polarity as that of the charge of the photosensitive drum 11 to the potential regulating member 8 in order to suppress the above-described discharge, the potential regulating member 8 being an electrode member provided on the inner peripheral surface (back surface) side of the intermediate transfer belt 6 in a position downstream of the primary transfer portion N1. In particular, it was found that the above-described discharge can be effectively suppressed by applying a voltage of the same polarity as that of the charge of the photosensitive drum 11 to the potential regulating member 8 disposed in contact with the inner peripheral surface of the intermediate transfer belt 6. Incidentally, the potential regulating member 8 is disposed downstream of the primary transfer portion N1 and adjacent to the primary transfer portion N1 so as not to contact the primary transfer roller 15 and not to contact the photosensitive drum 11 via the intermediate transfer belt 6.

Here, in the image forming apparatus 1, during the image forming operation (during the travel of the intermediate transfer belt 6), the fluctuation or vibration of the intermediate transfer belt 6 is generated between the stretching members in some cases. This phenomenon occurs in some cases due to curling (tendency) of the intermediate transfer belt 6 caused by the tension roller, a steering operation for controlling displacement (meandering) of the intermediate transfer belt 6, or the like. In addition, due to such fluctuation or vibration of the intermediate transfer belt 6, when the contact state (contact area) between the intermediate transfer belt 6 and the potential regulating member 8 fluctuates or is eliminated, the above-described discharge suppressing effect cannot be stably obtained. That is, in the effect of improving the transfer performance of the toner image by suppressing the above-described discharge, there is a possibility that in-plane unevenness of the image occurs. On the other hand, it was found that the contact portion of the potential regulating member 8 contacting the inner peripheral surface of the intermediate transfer belt 6 was made to enter the photosensitive drum 11 side more than the stretched surface of the intermediate transfer belt 6 in the position downstream of the primary transfer portion N1 in the absence of the potential regulating member 8, and therefore the potential regulating member 8 could also be brought into contact with the intermediate transfer belt 6 more stably during the image forming operation.

In addition, according to the studies of the present inventors, in many cases, the above-described discharge occurs in a range of about 0.3 to 1.5mm from the primary transfer portion N1 toward the downstream side. On the other hand, it is considered that by applying a voltage of the same polarity as that of the charge of the photosensitive drum 11 to the potential regulating member 8, the above-described discharge can be suppressed by the action of an electric field formed in the space between the photosensitive drum 11 and the potential regulating member 8. In addition, it was found that the above-described discharge suppressing effect is greater in the case where the potential regulating member 8 is in surface contact with the intermediate transfer belt 6 with a certain width with respect to the feeding direction of the intermediate transfer belt 6 than in the case where the potential regulating member 8 is in contact with the intermediate transfer belt point (line) with respect to the feeding direction of the intermediate transfer belt 6.

Therefore, it was found preferable that the potential regulating member 8 is more stably in surface contact with the intermediate transfer belt 6 during the image forming operation. Here, the surface contact (contact at the surface) means that the contact does not include a case where the potential regulating member 6 contacts the intermediate transfer belt 6 only in a line shape with respect to a direction intersecting the feeding direction of the intermediate transfer belt 6 in a range narrower than a contact width (about 5 to 50 mm) specifically described below. Thus, the surface contact includes, for example, not only a case where substantially the entire area of the potential regulating member 8 is continuously and closely contacted with the intermediate transfer belt 6 with a contact width specifically described below, but also a case where a number of contact points are substantially uniformly distributed in the above-described range as in the case of a nonwoven fabric or the like. In the following, description will be made in more detail.

4. Potential regulating member

Next, the constitution of the potential regulating member 8 in this embodiment will be described. As shown in fig. 1, the image forming apparatus 1 of this embodiment provides potential regulating members 8y, 8m, 8c, and 8k as electrode members in contact with the inner peripheral surface of the intermediate transfer belt 6 on the downstream sides of the primary transfer portions N1y, N1m, N1c, and N1k, respectively. In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided in the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same constitution.

The shape of the potential regulating member 8 in this embodiment will be described. Part (a) of fig. 3 is a sectional view of the potential regulating member 8 in this embodiment (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11). In addition, part (b) of fig. 3 is a perspective view of the potential regulating member 8 in this embodiment.

In this embodiment, the potential regulating member 8 includes a planar first portion 81 provided along the width direction of the intermediate transfer belt 6 (a direction substantially perpendicular to the feeding direction, a direction substantially parallel to the rotation axis direction of the photosensitive drum 11). In addition, in this embodiment, the potential regulating member 8 includes a planar second portion 82 provided along the width direction of the intermediate transfer belt 6 and extending in a direction substantially perpendicular to the planar surface of the first portion 81. In this embodiment, the contact surface 83 of the first portion 81 of the potential regulating member 8 (which is a contact portion contacting the inner peripheral surface of the intermediate transfer belt 6) is a flat surface. That is, in this embodiment, the first portion 81 constituting the contact surface 83 of the potential regulating member 8 is a flat plate.

Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, the upstream side end of the contact surface 83 is defined as "a (or upstream end a)", and the downstream side end of the contact surface 83 is defined as "B (or downstream end B)". In this embodiment, the upstream end a of the contact surface 83 corresponds to the upstream-side end of the potential regulating member 8, and the downstream end B of the contact surface 83 corresponds to the downstream-side end of the potential regulating member 8. As described above, by the action of the electric field formed in the space between the photosensitive drum 11 and the potential regulating member 8, the potential regulating member 8 can preferably be in surface contact with the intermediate transfer belt 6 in order to more effectively suppress the discharge between the intermediate transfer belt 6 and the photosensitive drum 11. From this point of view, the length of the line segment AB (between a and B), that is, the "contact width" (which is the length of the contact surface 83 in the feeding direction of the intermediate transfer belt 6) may be preferably 5mm or more. As the length of the line segment AB is longer, the effect of suppressing the electric field described above becomes larger, but it is considered that when the length becomes excessively long, stable contact of the potential regulating member 8 with the intermediate transfer belt 6 becomes difficult due to the influence of the (component part) component part accuracy or the like.

When the length of the line segment AB is 50mm or less, and typically 30mm or less, the length is insufficient in many cases. That is, the length of the line segment AB may suitably be about 5 to 50mm, typically about 5 to 30mm. From another point of view, it can be said that it is sufficient in many cases that the length of the line segment AB is not more than half of the center distance between adjacent photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11. In this embodiment, the potential regulating member 8 of which the length of the line segment AB is 25mm is used. Incidentally, in this embodiment, the center distance between the photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11 is about 100mm.

A potential adjusting power supply 80 as a potential adjusting voltage applying part (potential adjusting voltage applying section) is connected to the potential adjusting member 8. In this embodiment, the potential adjusting power supply 80 is connected to the second portion 82 of the potential adjusting member 8. At least at the time of primary transfer during an image forming operation, a potential adjustment voltage (potential adjustment bias) which is a DC voltage of the same polarity as that of the charge of the photosensitive drum 11 is applied to the potential adjustment member 8 by the potential adjustment power supply 80. The time of primary transfer is specifically a period during which a primary transfer voltage is applied, and more specifically, a period during which an image area (an area onto which a toner image can be transferred) on the intermediate transfer belt 6 passes through the primary transfer portion N1. Thereby, the discharge between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer portion N1 can be suppressed. In this embodiment, the potential regulating voltage is a DC voltage of negative polarity. In addition, in the constitution of this embodiment, the potential regulating voltage may be preferably about-500 to-5000V, more preferably-1000 to-3000V.

The potential adjusting member 8 is a member long in the width direction of the intermediate transfer belt 6. The length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction (direction along the width direction of the intermediate transfer belt 6) may preferably be longer than the maximum image width in the width direction of the intermediate transfer belt 6. Incidentally, the maximum image width is the length of the image area of the maximum image that can be formed by the image forming apparatus 1 with respect to the width direction of the intermediate transfer belt 6. In this embodiment, the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction is longer than the above-described maximum image width and the width of the primary transfer roller 15 contacting the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6. That is, in this embodiment, each of the range of the maximum image width and the range of the contact of the primary transfer roller 15 with the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6 falls within the range of the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction.

Thus, the effect of suppressing the increase in the charge amount of the toner on the intermediate transfer belt 6 can be obtained by suppressing the above-described charge, regardless of the length of the toner image transferred onto the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6. On the other hand, in this embodiment, the length of the potential regulating member 8 in the longitudinal direction is shorter than the width of the intermediate transfer belt 6. That is, in this embodiment, the range of the length of the potential regulating member 8 in the longitudinal direction falls within the range of the width of the intermediate transfer belt 6. Thus, in the case where the end portion of the potential adjusting member 8 with respect to the longitudinal direction is projected from the end portion of the intermediate transfer belt 6 with respect to the width direction, discharge to the potential adjusting member 8, members around the intermediate transfer belt 8, and the like occurs, so that the possibility of suppressing the effect of the discharge becomes small can be reduced.

The potential regulating member 8 may be constituted of only a single material having conductivity, for example. In this embodiment, the potential regulating member 8 is substantially composed of only a metal having conductivity such as SUS (stainless steel). Specifically, in this embodiment, the potential regulating member 8 is constituted by subjecting a plate material (metal plate) made of a metal such as SUS to bending to form the first portion 81 and the second portion 82. By thus subjecting the metal plate to bending, the strength of the potential regulating member 8 can be increased. In this embodiment, each of the first portion 81 and the second portion 82 of the potential regulating member 8 is substantially not deformed in the use state of the image forming apparatus 1. However, the present invention is not limited to such an embodiment, but the potential regulating member 8 may also be composed of two or more materials.

Fig. 4 is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) in another example of the potential regulating member 8. For example, as shown in fig. 4, a constitution may be adopted in which a base 84 having a shape similar to that of the potential regulating member 8 shown in fig. 3 and a surface layer 85 formed on the base 84 are provided. The contact surface 83 contacting the intermediate transfer belt 6 and the surface layer 85 constituting the connection portion with the potential adjusting power supply 80 are formed of a conductive material such as a metal or a conductive resin material. The base 84 may be formed of a conductive material, but may also be formed of a non-conductive material such as a non-conductive resin material. The base 84 and the surface layer 85 may be fixed by any fixing means such as an adhesive or welding.

In addition, fig. 5 is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) in still another example of the potential regulating member 8. For example, as shown in fig. 5, the contact surface 83 of the potential regulating member 8 that contacts the intermediate transfer belt 6 may also be formed of a conductive nonwoven fabric 86. Incidentally, in fig. 5, the conductive nonwoven 86 is provided on the contact surface 83 of the potential regulating member 8 having the constitution shown in fig. 4, but the conductive nonwoven 86 may also be provided on the contact surface 83 of the potential regulating member 8 having the constitution shown in fig. 3. The conductive nonwoven 86 may be secured by any securing means such as a conductive adhesive. In addition, instead of the nonwoven fabric 86, a felt using conductive fibers, a raised fabric (outer raised fabric (velvet, brush) or terry raised fabric (terry cloth)), or a sponge using a conductive rubber material (elastic foam member) may be used. Therefore, the contact surface 83 of the potential regulating member 8 that contacts the intermediate transfer belt 6 is composed of a flexible material or an elastic material, so that the possibility of occurrence of a flaw on the inner peripheral surface of the intermediate transfer belt 6 caused by friction (sliding) between the inner peripheral surface of the intermediate transfer belt 6 and the potential regulating member 8 can be reduced.

5. Arrangement of potential regulating members

Next, the arrangement of the potential regulating member 8 in this embodiment will be described. Fig. 6 is a sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for illustrating the arrangement of the potential regulating member 8 provided between two primary transfer portions N1 adjacent to each other in the feeding direction of the intermediate transfer belt 6. In fig. 6, as an example, a potential adjusting member 8c provided between a primary transfer portion N1c for cyan and a primary transfer portion N1k for black (hereinafter, the same applies to fig. 7, 10, 11, and 12) is shown.

In this embodiment, the outer diameter of the photosensitive drum 11 is 30mm, the outer diameter of the primary transfer roller 15 is 18mm, and the thickness of the intermediate transfer belt 6 is 0.350mm. In addition, in this embodiment, the primary transfer roller 15 is offset toward the downstream side with respect to the photosensitive drum 11. In this embodiment, the offset X1 is 3mm. Incidentally, the offset X1 is a distance between the rotation center of the photosensitive drum 11 and the rotation center of the associated primary transfer roller 15 in a direction along a common tangent line of one side of the plurality of photosensitive drums 15 contacting the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11.

Here, for the purpose of explaining the arrangement of the potential regulating member 8, a case is assumed in which the potential regulating member 8 is removed. In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line along which the stretching surface on the inner peripheral surface side passes in a portion downstream of the primary transfer portion N1 in the absence of the potential regulating member 8 is defined as a straight line L. Incidentally, specifically, this straight line L corresponds to a stretched surface in a state where only the potential regulating member 8 is substantially removed from the constitution of the image forming apparatus 1 in a state during the image forming operation (however, the photosensitive drum 11 and the intermediate transfer belt 6 are at rest). For example, the straight line L between the photosensitive drum 11c and the photosensitive drum 11k may be regarded as a common tangent line (on the intermediate transfer belt 6 side) of the primary transfer roller 15c of the upstream station and the photosensitive drum 11k of the downstream station (strictly speaking, in the case where the primary transfer roller 15 has an elastic layer as in the case of a sponge roller, the primary transfer roller 15 is deformed, but this effect is to a negligible extent). In addition, on the straight line L, a portion of the inner peripheral surface of the intermediate transfer belt 6 separated from the stretching member closest to the upstream side of the potential regulating member 8 is defined as "C (or upstream stretching portion C)", and a portion of the inner peripheral surface of the intermediate transfer belt 6 separated from the stretching member closest to the downstream side of the potential regulating member 8 is defined as "D (or downstream stretching portion D)". Incidentally, in fig. 6, the straight line L is schematically shown as being substantially horizontal, but in the case where the surface of the primary transfer roller 15 is raised toward the photosensitive drum 11 side due to deformation of the elastic layer of the primary transfer roller 15 or the like, the straight line L may be inclined downward toward the downstream side in the drawing.

In this embodiment, the stretching member closest to the upstream side of the potential regulating member 8 is the primary transfer roller 15, and the position on the inner peripheral surface of the intermediate transfer belt 6 at the portion where the intermediate transfer belt 6 is separated from the primary transfer roller 15 is the upstream stretching portion C. However, the stretching member closest to the upstream side of the potential regulating member 8 is not limited to the primary transfer member 15. For example, as shown in fig. 7, in the case where the primary transfer roller 15 is offset and disposed on the upstream side with respect to the photosensitive drum 11, the position on the inner peripheral surface of the intermediate transfer belt 6 at the portion corresponding to the portion where the intermediate transfer belt 6 is separated from the photosensitive drum 11 is the upstream stretched portion C. Incidentally, fig. 7 is a sectional view similar to fig. 6 in the case where the primary transfer roller 15 is offset and disposed on the upstream side with respect to the photosensitive drum 11.

In addition, in this embodiment, the stretching members closest to the downstream side of the potential regulating member 8 are photosensitive drums 11m, 11c, and 11k disposed adjacent to the potential regulating member 8 on the downstream side of the potential regulating member 8 for the primary transfer portions N1y, N1m, and N1c for yellow, magenta, and cyan, respectively. In addition, a position on the inner peripheral surface of the intermediate transfer belt 6 at a portion corresponding to a portion where the intermediate transfer belt 6 is separated from an associated one of the photosensitive drums 11m, 11c, and 11k is a downstream stretching portion D. However, the stretching member closest to the downstream side of the potential regulating member 8 is not limited to the photosensitive drum 11. For example, as shown in fig. 7, in the case where the primary transfer roller 15 is offset and disposed on the upstream side with respect to the photosensitive drum 11, the position on the inner peripheral surface of the intermediate transfer belt 6 at the portion where the intermediate transfer belt 6 is separated from the primary transfer roller 15 is the downstream stretching portion D. In addition, in this embodiment, as shown in fig. 8, for the downstream-most primary transfer portion N1k for black, the stretching member whose downstream side is closest is a stretching roller (tension roller in this embodiment) 22. In addition, a position on the inner peripheral surface of the intermediate transfer belt 6 at a portion where the intermediate transfer belt 6 is separated from the tension roller 22 is a downstream tension portion D. Incidentally, fig. 8 is a sectional view similar to fig. 6 with respect to the potential regulating member 8 provided to the downstream-most primary transfer portion N1 k.

In addition, for each of the primary transfer portions N1, as a stretching member closest to the downstream side of the potential adjusting member 8, in the case where there is another stretching roller for adjusting the posture of the intermediate transfer belt 6 during the image forming operation, the straight line L and the downstream stretching portion D are defined based on the stretching rollers thereof. In addition, in the case where not the tension roller but the doctor blade or the brush is in contact with the inner peripheral surface of the intermediate transfer belt 6 for the purpose of cleaning the inner peripheral surface of the intermediate transfer belt 6 or for the similar purpose, when the doctor blade or the brush adjusts the posture of the intermediate transfer belt 6, the doctor blade or the brush may be regarded as the tension member closest to the downstream side of the potential adjusting member 8. Doctor blades are generally constructed of sheet-like or film-like members.

As shown in fig. 6, the potential regulating member 8 is disposed downstream of the primary transfer portion N1 and close to the primary transfer portion N1 so as not to contact the primary transfer roller 15 and contact the photosensitive drum 11 via the intermediate transfer belt 6. At this time, as the upstream end a is closer to the primary transfer portion N1, the above-described charge suppressing effect becomes larger. In this embodiment (fig. 6), the potential regulating member 8 is disposed in a position downstream of the primary transfer portion N1 such that the distance X2 from the primary transfer roller 15 to the upstream end a becomes about 8mm. Here, the distance X2 is a distance between the rotation center of the primary transfer roller 15 and the upstream end a in a direction along a common tangent to the side of the plurality of photosensitive drums 11 contacting the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11. That is, in this embodiment, the distance from the rotation center of the primary transfer roller 15 to the upstream end a is shorter than the distance (radius) from the rotation center of the primary transfer roller 15 to the outer periphery of the primary transfer roller 15. The distance X2 is not limited thereto, but may be preferably about 1 to 20mm, typically about 1 to 10mm.

In addition, in this embodiment, the potential regulating member 8 is pressed against the inner peripheral surface of the intermediate transfer belt 6 at each of its opposite ends with respect to the longitudinal direction thereof by a pressing spring 87 (part (b) of fig. 3) constituted by a compression coil spring, which is a pushing member, as a pushing means. At this time, the contact portion of the potential regulating member 8 contacting the inner peripheral surface of the intermediate transfer belt 6 is brought into the photosensitive drum 11 side with respect to the straight line L. Thereby, even in the event of fluctuation or waving on the intermediate transfer belt 6 during the image forming operation (during the traveling of the intermediate transfer belt 6), the potential regulating member 8 can be brought into more stable contact with the intermediate transfer belt 6. Although the potential regulating member 8 is not limited thereto, the amount of entry of the contact surface 83 of the potential regulating member 8 into the straight line L may be preferably about 0.3 to 5mm, typically about 0.5 to 3mm (e.g., about 0.5 mm). When this amount of entry is excessively small, there is a possibility that the potential regulating member 8 and the intermediate transfer belt 6 cannot be stably contacted. When the amount of entry is excessively large, there is a possibility that stable feeding (conveyance) of the intermediate transfer belt 6 becomes difficult.

In particular, in this embodiment, the pressing force of the pressing spring 87 is set (adjusted) so that an amount of entry into the photosensitive drum 11 side below each of the upstream end a and the downstream end B of the contact surface 83, which is a contact portion of the potential regulating member 8 contacting the inner peripheral surface of the intermediate transfer belt 6, into the straight line L. In this embodiment, as described above, the primary transfer roller 15 is disposed offset toward the downstream side of the photosensitive drum 11. Parts (a) and (b) of fig. 9 are sectional views (cross sections substantially perpendicular to the rotation axis direction of the photosensitive drum 11) each showing the vicinity of the single primary transfer portion N1 in an enlarged state so as to explain the amount of entry of the contact surface 83 of the potential regulating member 8 into the straight line L. Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 1, a straight line passing through an intersection point between a straight line L and a straight line P connecting the rotation axis center of the photosensitive drum 11 and the rotation axis center of the primary transfer roller 15 and perpendicular to the straight line P is defined as a nip line Q. Here, the intersection point between the straight line L and the straight line P can be basically regarded as the intersection point between the straight line P and the photosensitive drum 11. For this reason, the nip line Q may be regarded as a straight line passing through an intersection (nip) between the straight line P and the photosensitive drum 1 and being perpendicular to the straight line P. In this embodiment, the upstream end a and the downstream end B of the contact surface 83, which are contact portions of the potential regulating member 8 contacting the inner peripheral surface of the intermediate transfer belt 6, are made to enter the photosensitive drum 11 side with respect to the straight line P, but are not made to enter the nip line Q (portion (a) of fig. 9). That is, the contact surface 83 of the potential regulating member 8 is located on the photosensitive drum 11 side with respect to the straight line L, and on the primary transfer roller 15 side with respect to the nip line Q. When the contact surface 83 of the potential regulating member 8 is brought into the photosensitive drum 11 side with respect to the nip line Q, the intermediate transfer belt 6 becomes a shape in which the intermediate transfer belt 6 is wound around the photosensitive drum 11 (part (b) of fig. 9). In this case, the minute gap area between the photosensitive drum 1 and the intermediate transfer belt 6 expands, so that the discharge amount increases. That is, in this case, the distance between the photosensitive drum 11 and the intermediate transfer belt 6 is not easily increased relative to the distance from the primary transfer portion N1 on the downstream side of the primary transfer portion N1, so that the area in which discharge between the photosensitive drum 11 and the intermediate transfer belt 6 can occur increases. This discharge increases the charge amount of the toner on the intermediate transfer belt 6, so that the secondary transfer becomes worse as described above. When the case where the potential regulating member 8 is caused to enter the clamp line Q is regarded as 100%, the entering amount of the potential regulating member 8 into the straight line L may be preferably 5% or more and 800% or less, more preferably 10% or more and 50% or less, and is 30% in this embodiment.

The above description may also be modified as follows. That is, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11, a direction along a common tangent line to a side of the plurality of photosensitive drums 11 contacting the intermediate transfer belt 6 is referred to as a perpendicular direction. At this time, with respect to this vertical direction, the entrance rate of the contact surface 83 of the potential regulating member 8 from the straight line L to the straight line Q may be preferably 5% or more and 80% or less, more preferably 10% or more and 50% or less, and 30% in this embodiment.

Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line passing through the upstream end a and the downstream end B of the contact surface 83 is defined as a straight line M. At this time, it is preferable to prevent the straight line M from intersecting the line segment CD of the straight line. Thus, in the case where the contact surface 83 of the potential regulating member 8 is a flat surface, the intermediate transfer belt 6 and the potential regulating member 8 can be more reliably brought into surface contact with each other. As shown in fig. 10 or 11, in the case where the straight line M intersects with the line segment CD of the straight line L, there is a possibility that only either one of the end portion on the upstream end a side of the potential regulating member 8 (fig. 11) and the end portion on the downstream end B side of the potential regulating member 8 (fig. 10) may contact the inner peripheral surface of the intermediate transfer belt 6. In this case, there is a possibility that it becomes difficult to enhance the discharge suppressing effect by the surface contact. Incidentally, each of fig. 10 and 11 is a sectional view similar to fig. 6in the case where the straight line M intersects with the line segment CD of the straight line L. Fig. 10 shows a case where the straight line M is inclined with respect to the straight line L so that the upstream end a side is closer to the straight line L than the downstream end B side, and fig. 11 shows a case where the straight line M is inclined with respect to the straight line L so that the downstream end B side is closer to the straight line L than the upstream end a side.

In addition, in fig. 6, the potential regulating member 8 is disposed such that the straight line M and the straight line L are substantially parallel to each other, but when the straight line M falls within a range in which the straight line M does not intersect the line segment CD of the straight line L, the potential regulating member 8 may be disposed such that the straight line M is inclined with respect to the straight line L. In particular, as shown in fig. 12, the straight line M is inclined with respect to the straight line L so that the upstream end a side is closer to the straight line L than the downstream end B side, so that the curvature generated on the intermediate transfer belt 6 due to the intermediate transfer belt 6 laid in the vicinity of the upstream end a can be made small. Thus, this case is advantageous for reducing the possibility of occurrence of flaws on the inner peripheral surface of the intermediate transfer belt 6 due to friction (sliding) with the potential adjusting member 8.

6. Effect confirmation

Next, the result of verification of the effect of this embodiment will be described. Verification is performed at two points that an increase in the charge amount of the toner can be suppressed and the transfer performance of the toner to the embossed paper can be improved.

Specifically, the following experiment was performed. In the image forming apparatus 1 according to this embodiment, the width of the primary transfer portion N1 (i.e., the length of the intermediate transfer belt 6 in the width direction) is 330mm, and the width of the secondary transfer portion N2 (i.e., the length of the intermediate transfer belt 6 in the width direction) is 340mm. In addition, the image forming apparatus 1 operates at a process speed of 180mm/s (peripheral speed of the photosensitive drum 11). Then, a real image of A4 size is formed on the photosensitive drum 11c, and the toner image is primary-transferred onto the intermediate transfer belt 6 in the primary transfer portion N1c for cyan. Thereafter, the toner image is conveyed on the intermediate transfer belt 6 and passes through a primary transfer portion N1k for black, and is then secondarily transferred onto the embossed paper in a secondary transfer portion N2. The primary transfer voltage is subjected to constant voltage control by the controller 3 at a voltage set to make the primary transfer current in the primary transfer portion N1 become 20 μa as a target current. Further, the secondary transfer voltage is subjected to constant voltage control by the controller 3 at a voltage set so that the secondary transfer current in the secondary transfer portion N2 becomes 30 μa as a target current.

The above-described operation is performed in a state where the potential regulating members 8 (8 c,8 k) are removed ("without potential regulating members") and in a state where the potential regulating members 8 (8 c,8 k) are mounted according to this embodiment and a potential regulating voltage of-3000V is applied thereto by the potential regulating power supply 80 ("with potential regulating members"). As the embossed paper, "Rezak 66" (trade name, manufactured by Tokushu Tokai Paper co., ltd) having a basis weight of 302g/cm ² was used. Then, a change in the charge amount of the toner in each of the case of "having the potential adjusting member" and the case of "having no potential adjusting member" was measured. Incidentally, the charge amount of the toner is calculated by measuring the charge per unit weight (mass) by using an attraction method commonly used in this field. This method calculates the amount of charge [ μc/g ] by measuring the weight [ g ] and the amount of charge [ μc ] of the attracted toner, and thus can grasp the average amount of charge of the toner. In addition, images on the above-described embossed paper after fixing in the presence of the potential adjusting member ("with the potential adjusting member") and in the absence of the potential adjusting member ("without the potential adjusting member") are compared with each other.

Fig. 13 is a diagram showing measurement results of changes in the charge amount of the toner in each of the case where the potential adjusting member is present and the case where the potential adjusting member is not present. As shown in fig. 13, the charge amount of the toner on the photosensitive drum 11C for cyan is-23 μc/g. Based on this charge amount of the toner, a change in the charge amount of the toner in each of the following states is measured. First, the charge amount of the toner on the intermediate transfer belt 6 after the primary transfer in the primary transfer portion N1c for cyan and before reaching the primary transfer portion N1k for black ("on the belt after the primary transfer (N1 c) for cyan") is measured. In addition, the charge amount of the toner on the intermediate transfer belt 6 after passing through the primary transfer portion N1k for black and before reaching the secondary transfer portion N2 ("on the belt after the primary transfer (N1 k) for black") was measured. As a result thereof, it was found that although the charge amount of the toner increases (its absolute value becomes large) both in the case where the potential regulating member is present and in the case where the potential regulating member is not present, the increase in the charge amount of the toner can be suppressed in the case where the potential regulating member is present as compared with the case where the potential regulating member is not present.

Parts (a) and (b) of fig. 14 are photo diagrams showing images on embossed paper after fixing in the absence of a potential adjusting member and in the presence of a potential adjusting member, respectively, in a comparative manner. Part (a) of fig. 14 shows an image in the case where the potential regulating member is not present, and part (b) of fig. 14 shows an image in the case where the potential regulating member is present. As shown in part (a) of fig. 14, in the absence of the potential regulating member, the toner cannot be transferred onto the concave portion of the surface of the embossed paper, so that white leakage is noticeable in some cases. On the other hand, as shown in part (b) of fig. 14, in the presence of the potential regulating member, it was found that the toner can be sufficiently transferred onto the concave portion of the surface of the embossed paper, so that the transfer of the toner image can be performed more uniformly. That is, in the presence of the potential adjusting member, it is possible to improve the transfer performance of the toner image onto the concave portion of the embossed paper while reducing the possibility of occurrence of improper transfer on the halftone image at the portion of the embossed paper other than the concave portion due to the excessive secondary transfer electric field.

Incidentally, as understood from fig. 13, there is a possibility that the toner on the intermediate transfer belt 6 is subjected to discharge between the intermediate transfer belt 6 and the photosensitive drum 11 at the downstream side of the primary transfer portion N1 every time the toner passes through the primary transfer portion N1 and thus the charge amount increases. For this reason, the toner transferred onto the intermediate transfer belt 6 in the upstream side primary transfer portion N1 is larger in the number of times the toner passes through the downstream side primary transfer portion N1, so that it can be said that the charge amount is more liable to increase. Thus, in this embodiment, the potential regulating member 8 is provided for all four primary transfer portions N1, but the potential regulating member 8 may be provided for only a single or a plurality of upstream primary transfer portions N1, not for all four primary transfer portions N1. For example, the potential regulating member 8 may be provided only for the most upstream primary transfer portion N1y, or only for the most upstream primary transfer portion N1y and the primary transfer portion N1m (and further the primary transfer portion N1 c) adjacent to the primary transfer portion N1y on the downstream side.

Fig. 15 is a diagram for illustrating the effect of the potential adjusting member 8 entering the stretched surface of the intermediate transfer belt 6 and the effect of the potential adjusting member 8 coming into contact with the surface of the intermediate transfer belt 6. Specifically, fig. 15 shows simulation results under the following conditions. As the potential adjusting member 8, a test potential adjusting member 8 constituted by a flat plate similar to the first portion 81 of the potential adjusting member 8 in this embodiment is assumed. In addition, the indexes of the discharge amount between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer portion N1 in each of the following cases (1) to (4) are compared with each other.

(1) The end corresponding to the upstream end a is brought close to the inner peripheral surface of the intermediate transfer belt 6 in a dot (line) shape (spaced about 0.4mm apart) (the potential regulating member 8 is disposed at an angle with respect to the intermediate transfer belt 6).

(2) The portion from the end corresponding to the upstream end a to the end corresponding to the downstream end B is brought close to the intermediate transfer belt 6 (spaced about 0.4mm apart) in a planar shape.

(3) The end corresponding to the upstream end a is in contact with the inner peripheral surface of the intermediate transfer belt 6 in a dot (line) shape (the potential regulating member 8 is disposed at an angle with respect to the intermediate transfer belt 6).

(4) A portion from the end corresponding to the upstream end a to the end corresponding to the downstream end B contacts the intermediate transfer belt 6 in a planar shape.

Incidentally, as an index of the discharge amount, a width (distance from the primary transfer portion N1) of the intermediate transfer belt 6 with respect to the feeding direction in a region where discharge occurs in a position downstream of the primary transfer portion N1 in the case where a predetermined primary transfer voltage is applied to the primary transfer roller 15 is used. As the width of the region where the discharge occurs is larger, the discharge amount between the intermediate transfer belt 6 and the photosensitive drum 11 in a position downstream of the primary transfer portion N1 becomes larger, so that it can be said that the possibility of an increase in the charge amount of the toner increases. In addition, the case where the potential regulating member 8 is not in contact with the intermediate transfer belt 6 as in the above-described cases (1) and (2) is a case where a fluctuation or vibration occurs on the intermediate transfer belt 6 during the image forming operation (during the traveling of the intermediate transfer belt 6) and thus the potential regulating member 8 is separated from the intermediate transfer belt 6. Incidentally, regarding the constitution of the photosensitive drum 11, the intermediate transfer belt 6, and the primary transfer roller 15, and the condition of the primary transfer voltage, a case similar to that in the image forming apparatus 1 of this embodiment is assumed. In fig. 15, the ordinate represents the above-described discharge amount, and the abscissa represents the potential adjustment voltage. In addition, "REF" in fig. 15 shows a case where the potential regulating member 8 is not provided.

As shown in fig. 15, when the potential regulating member 8 is separated from the intermediate transfer belt 6 (the above-described (1) and (2)), the above-described effect of suppressing discharge becomes small. That is, it is understood that the potential regulating member 8 is made to enter the intermediate transfer belt 6 more than the stretched surface, and is also in stable contact with the intermediate transfer belt 6 during the image forming operation (during the traveling of the intermediate transfer belt 6) (the above-described (3) and (4)), so that the above-described effect of suppressing discharge can be stably obtained. In addition, as shown in fig. 15, it is understood that a corresponding effect can be obtained also in the case where the potential regulating member 8 is in point (line) contact with the intermediate transfer belt 6. However, as shown in fig. 15, it is understood that the effect of suppressing the discharge is greater in the case where the potential regulating member 8 is in surface contact with the intermediate transfer belt 6 than in the case where the potential regulating member 8 is in point (line) contact with the intermediate transfer belt 6. In addition, as shown in fig. 15, it is understood that there are the following tendencies: by increasing the potential regulating voltage of the same polarity as the charge polarity of the photosensitive drum 11 (by making the absolute value thereof large), the effect of suppressing discharge becomes greater. As described above, in the constitution of this embodiment, the potential regulating voltage may be preferably about-1000 to-3000V.

Thus, in this embodiment, the image forming apparatus 1 includes the photosensitive member 11 chargeable to a predetermined polarity and carrying the toner image, the circumferentially movable intermediate transfer belt 6 stretched by the plurality of stretching rollers and conveying the toner image for secondary transfer of the toner image primary-transferred from the photosensitive member 11 to the recording material in the primary transfer portion N1 in the secondary transfer portion N2, the primary transfer member 15 provided in correspondence with the photosensitive member 11 and forming the primary transfer portion N1 in which the photosensitive member 11 and the intermediate transfer belt 6 are in contact with each other in contact with the inner peripheral surface of the intermediate transfer belt 6 and the toner image is transferred from the photosensitive member 11 to the intermediate transfer belt 6 under an applied voltage, An electrode member 8 in close proximity to the downstream side of the primary transfer member 15 with respect to the moving direction of the intermediate transfer belt 6 contacts the inner peripheral surface of the intermediate transfer belt 6, and a power source 80 for applying a voltage of the same polarity as a predetermined polarity to the electrode member 8, wherein the electrode member 8 is disposed such that a contact portion 83 thereof contacting the inner peripheral surface of the intermediate transfer belt 6 enters the photosensitive member side with respect to a stretching surface of the inner peripheral surface side of the intermediate transfer belt 6 on the downstream side of the primary transfer portion N1 in the absence of the electrode member 8. In this embodiment, in a cross section substantially perpendicular to the width direction of the intermediate transfer belt 6, when a straight line passing through an intersection point between a straight line P connecting the rotation axis center of the rotatable photosensitive member 1 and the rotation axis center of the rotatable primary transfer member 15 and a straight line L along which the inner peripheral surface side stretching surface of the intermediate transfer belt 6 on the downstream side of the primary transfer portion N1 in the absence of the electrode member 8 is located and which is perpendicular to the straight line P is a nip line Q, the contact portion 83 is on the photosensitive member side than the straight line L and on the primary transfer member side than the nip line Q. In this embodiment, the contact portion 83 surface contacts the inner peripheral surface of the intermediate transfer belt 6. In addition, in this embodiment, the contact surface 83 is a flat surface. Here, in a preferable form, in a cross section substantially perpendicular to the width direction of the intermediate transfer belt 6, when the inner peripheral surface side stretching surface of the intermediate transfer belt 6 on the downstream side of the primary transfer portion N1 in the absence of the electrode member 8 is a straight line L, the upstream side end of the contact portion 83 with respect to the moving direction is an upstream end a, the downstream side end of the contact portion 83 with respect to the moving direction is a downstream end B, the position at which the posture of the intermediate transfer belt 6 on the upstream side of the electrode member 8 with respect to the moving direction on the straight line L is adjusted is an upstream extending portion C, the position at which the posture of the intermediate transfer belt 6 on the downstream side of the electrode member with respect to the moving direction on the straight line L is adjusted is a downstream stretching portion D, And the straight line passing through the upstream end a and the downstream end B is the straight line M, the electrode member 8 is disposed so that the straight line M does not intersect the line segment CD on the straight line L. In a preferred form, the length of the contact portion 83 in the moving direction is 5mm or more and 50mm or less. In addition, in a preferred form, the image forming apparatus 1 includes a plurality of drum-shaped photosensitive members 11, and the length of the contact portion 83 in the moving direction is not more than half of the center (inter-axis) distance between the adjacent photosensitive members 11 in a cross section substantially perpendicular to the width direction of the intermediate transfer belt 6. In this embodiment, the contact portion 83 is composed of a conductive material. In particular, in this embodiment, the contact portion 83 is composed of a conductive metal. However, the contact portion 83 may also be constituted of, for example, conductive fibers. In addition, the image forming apparatus 1 may have a plurality of photosensitive members 11 disposed along the moving direction, a plurality of primary transfer members 15 provided respectively corresponding to the plurality of photosensitive members 11, and an electrode member 8 provided so as to abut against an inner peripheral surface of the intermediate transfer belt 6 on a downstream side of the at least one primary transfer member 15 with respect to the moving direction. In this embodiment, the image forming apparatus 1 includes the plurality of electrode members 8 provided so as to abut against the downstream-side contact intermediate transfer belt 6 with respect to the moving direction of all of the plurality of primary transfer members 15.

As described above, according to this embodiment, by the action of the potential regulating member 8, an increase in the charge amount of the toner is suppressed, so that the transfer performance of the toner image onto the embossed paper can be improved.

Incidentally, in this embodiment, as the recording material S on which transfer of the toner image is relatively difficult, an embossed paper is exemplified, but similar effects can be expected also on a recording material (high-resistance paper) having a relatively high resistance such as a synthetic paper or a resin film mainly including a synthetic resin material. In addition, in this embodiment, only a DC voltage is used as the secondary transfer voltage, but in the case where a voltage in the form of a DC voltage biased with an AC voltage is used as the secondary transfer voltage in order to output a good image, it is advantageous to promote transfer of a toner image onto a recording material according to this embodiment.

Example 2

Next, another embodiment of the present invention will be described. The basic structure and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or structures as those of the image forming apparatus of embodiment 1 are denoted by the same reference numerals or symbols as those of embodiment 1, and detailed description thereof will be omitted.

In this embodiment, similarly to embodiment 1, on the downstream sides of the primary transfer portions N1y, N1m, N1c, and N1k, potential regulating members 8y, 8m, 8c, and 8k are provided in contact with the inner peripheral surface of the intermediate transfer belt 6, respectively. In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided in the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same constitution. In addition, in this embodiment, the shape of the potential regulating member 8 is different from the shape of the potential regulating member 8 in embodiment 1.

First, the shape of the potential regulating member 8 in this embodiment will be described. Part (a) of fig. 16 is a sectional view of the potential regulating member 8 in this embodiment (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11). In addition, part (b) of fig. 16 is a perspective view of the potential regulating member 8 in this embodiment.

In this embodiment, the potential regulating member 8 is constituted by a curved plate provided along the width direction of the intermediate transfer belt 6 and curved in a curved shape protruding toward the photosensitive drum 11 side in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11. In this embodiment, the contact surface 83, which is a contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6, is a curved surface that protrudes toward the photosensitive drum 11. Therefore, by shaping the contact surface 83 into a curved surface shape, the stress at the time of sliding of the contact surface 83 and the intermediate transfer belt 6 is reduced, so that the possibility of occurrence of flaws on the inner peripheral surface of the intermediate transfer belt 6 can be reduced.

The potential adjusting power supply 80 is connected to the potential adjusting member 8. In this embodiment, at least at the time of primary transfer during the image forming operation, a potential adjustment voltage similar to that in embodiment 1 is applied to the potential adjustment member 8. Thereby, the discharge between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer portion N1 can be suppressed.

The potential adjusting member 8 in this embodiment is a member long in the width direction of the intermediate transfer belt 6, similarly to that in embodiment 1. In this embodiment, the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction is longer than the maximum image width of the intermediate transfer belt 6 with respect to the width direction and the width of the primary transfer roller 15 in contact with the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6. On the other hand, in this embodiment, the length of the potential regulating member 8 in the longitudinal direction is shorter than the width of the intermediate transfer belt 6.

In addition, similarly as in embodiment 1, the potential regulating member 8 in this embodiment may be constituted of only a single material having conductivity, for example. In this embodiment, the potential regulating member 8 is substantially composed of only a metal having conductivity such as SUS. However, similarly to that described in embodiment 1, the potential regulating member 8 may also be composed of two or more materials.

For example, as a constitution including a base and a surface layer, the surface layer constituting the contact face 83 may be formed of a conductive material, and the base may be formed of a nonconductive material, similarly to the potential regulating member 8 shown in fig. 4.

In addition, for example, the contact surface 83 may also be formed of a conductive nonwoven fabric or the like, similarly to the potential regulating member 8 shown in fig. 5. Therefore, the contact surface 83 of the potential regulating member 8, which is a curved surface, is composed of a flexible material or an elastic material, and thus the possibility of occurrence of a flaw on the inner peripheral surface of the intermediate transfer belt 6 caused by friction (sliding) between the inner peripheral surface of the intermediate transfer belt 6 and the potential regulating member 8 can be further reduced.

Next, the arrangement of the potential regulating member 8 in this embodiment will be described. Fig. 17 is a sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for illustrating the arrangement of the potential regulating member 8 provided between two primary transfer portions N1 adjacent to each other in the feeding direction of the intermediate transfer belt 6. In fig. 17, as an example, a potential adjusting member 8c provided between a primary transfer portion N1c for cyan and a primary transfer portion N1k for black (hereinafter, the same applies to fig. 18) is shown.

In this embodiment, similarly to embodiment 1, the outer diameter of the photosensitive drum 11 is 30mm, the outer diameter of the primary transfer roller 15 is 18mm, and the thickness of the intermediate transfer belt 6 is 0.350mm. In addition, in this embodiment, the primary transfer roller 15 is offset toward the downstream side with respect to the photosensitive drum 11. The offset X1 is 3mm.

Here, the straight line L is defined similarly to that in embodiment 1. Further, the above upstream stretching section C and the above downstream stretching section D are defined similarly to those in example 1. Further, similarly as in embodiment 1, the upstream end portion of the contact surface 83 is defined as an upstream end a, and the downstream end portion of the contact surface 83 is defined as a downstream end B. Incidentally, in this embodiment, the upstream end a and the downstream end B do not necessarily correspond to the upstream-side end and the downstream-side end of the potential regulating member 8, respectively. In this embodiment, the upstream-side end of the potential regulating member 8 is individually defined as "E (or member upstream end E)". The upstream end a of the contact surface 83 and the member upstream end E of the potential regulating member 8 may also coincide with each other.

Similarly as in embodiment 1, the potential regulating member 8 is disposed downstream of the primary transfer portion N1 and close to the primary transfer portion N1 so as not to contact the primary transfer roller 15 and contact the photosensitive drum 11 via the intermediate transfer belt 6. At this time, as the upstream end a is closer to the primary transfer portion N1, the above-described charge suppressing effect becomes larger. In this embodiment (fig. 17), the potential regulating member 8 is disposed in a position downstream of the primary transfer portion N1 such that the distance X2 from the primary transfer roller 15 to the member upstream end E becomes about 8mm. Here, the distance X2 is a distance between the rotation center of the primary transfer roller 15 and the member upstream end E in a direction along a common tangent to a side of the plurality of photosensitive drums 11 contacting the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11.

In addition, in this embodiment, the potential regulating member 8 is pressed against the inner peripheral surface of the intermediate transfer belt 6 at each of its opposite ends with respect to its longitudinal direction by a pressing spring 87 (part (b) of fig. 16). At this time, in this embodiment, the pressing force of the pressing spring 87 is set (adjusted) so that the upstream end a and the downstream end B of the contact surface 83 enter the photosensitive drum 11 side with respect to the straight line L. Similar to that in embodiment 1, the contact width X3, which is the length of the contact surface 83 in the feeding direction of the intermediate transfer belt 6, may be preferably about 5 to 50mm, typically about 5 to 30mm, the contact surface 83 being a contact portion of the potential regulating member 8 contacting the inner peripheral surface of the intermediate transfer belt 6. That is, in this embodiment, in the curved surface of the potential regulating member 8 on the intermediate transfer belt 6 side, the region (contact surface 83) ranging from the upstream end a to the downstream end B of the contact width as described above contacts the inner peripheral surface of the intermediate transfer belt 6 and enters the photosensitive drum 11 side with respect to the straight line L.

Therefore, the contact surface 83 of the potential regulating member 8 is brought into the photosensitive drum 11 side with respect to the straight line L, and even in the event of a fluctuation or vibration on the intermediate transfer belt 6 during the image forming operation (during the traveling of the intermediate transfer belt 6), the potential regulating member 8 can be brought into stable ground contact with the intermediate transfer belt 6. In addition, as in this embodiment, in the case where the contact surface 83 is a curved surface that bulges toward the photosensitive drum 11, the intermediate transfer belt 6 and the potential adjusting member 8 can be more reliably brought into surface contact with each other by bringing the contact surface 83 itself toward the photosensitive drum 11 side with respect to the straight line L in the above-described manner.

Therefore, in this embodiment, the contact portion 83 of the electrode member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is a curved surface that protrudes toward the photosensitive member side.

As described above, with the constitution of this embodiment, effects similar to those of embodiment 1 can also be obtained. In addition, according to the constitution of this embodiment, the intermediate transfer belt 6 and the potential regulating member 8 can be more easily brought into surface contact with each other.

Incidentally, in this embodiment, the contact surface 83 is made a curved surface by constituting the potential regulating member 8 with a curved plate, but as shown in fig. 18, the contact surface 83 may also be made a curved surface by using a roller-shaped potential regulating member 83. In this case, the roller-shaped potential regulating member 8 may be rotatable, or may be a device that is fixed without rotation. In addition, this roller-shaped potential regulating member 8 may be constituted by, for example, a metal roller, but may also be constituted by two or more materials similarly as described in embodiment 1. For example, similar to the potential regulating member 8 shown in fig. 4, a constitution including a base portion and a surface layer is employed, so that the surface layer constituting the contact surface 83 can be formed of a conductive material, and the base portion can be formed of a conductive material or a nonconductive material. In addition, for example, the contact surface 83 may be formed of a conductive nonwoven fabric, similarly to the potential regulating member 8 shown in fig. 5.

Example 3

Next, another embodiment of the present invention will be described. The basic structure and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or structures as those of the image forming apparatus of embodiment 1 are denoted by the same reference numerals or symbols as those of embodiment 1, and detailed description thereof will be omitted.

In this embodiment, similarly to embodiment 1, on the downstream sides of the primary transfer portions N1y, N1m, N1c, and N1k, potential regulating members 8y, 8m, 8c, and 8k are provided in contact with the inner peripheral surface of the intermediate transfer belt 6, respectively. In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided in the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same constitution. In addition, in this embodiment, the constitution of the potential adjusting member 8 is different from that of the potential adjusting member 8 in embodiment 1.

The constitution of the potential adjusting member 8 in this embodiment will be described. Part (a) of fig. 19 is a sectional view of the potential regulating member 8 in this embodiment (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11). In addition, part (b) of fig. 19 is a perspective view of the potential regulating member 8 in this embodiment. In this embodiment, the potential regulating member 8 is constituted by including a conductive contact member 89 and a non-conductive support member 88 for supporting the contact member 89. In this embodiment, the contact member 89 as an electrode member is constituted by a flat plate provided along the width direction of the intermediate transfer belt 6. In this embodiment, the contact surface 83, which is a contact portion of the contact member 89 that contacts the inner peripheral surface of the intermediate transfer belt 6, is a flat surface. In addition, the potential regulating power supply 80 is connected to the contact member 89. In addition, in this embodiment, the end of the supporting member 88 on the primary transfer roller 15 side with respect to the direction along the feeding direction of the intermediate transfer belt 6 is provided with a protruding portion 88a so as to shield the space between the primary transfer roller 15 and the contact member 89 with respect to the feeding direction. The purpose of the projection 88a is to prevent the space between the primary transfer roller 15 and the contact member 89 from discharging.

In this embodiment, the contact member 89 is pressed against the inner peripheral surface of the intermediate transfer belt 6 in such a manner that the contact member 89 is pushed out from the support member 88 toward the intermediate transfer belt 6, so as to reliably ground-contact the intermediate transfer belt 6 even when the support member 88 is provided with the protruding portion 88 a. In this embodiment, the contact member 89 is pressed against the inner peripheral surface of the intermediate transfer belt 6 at each of its opposite ends with respect to the longitudinal direction thereof by a pressing spring 87 constituted by a compression coil spring (which is a pushing member) as a pushing means. In this embodiment, this pressing spring 87 is provided between the contact member 89 and the supporting member 88, and urges the contact member 89 in a direction from the back surface thereof (the surface opposite to the contact surface 83) toward the intermediate transfer belt 6.

Incidentally, the urging member as the urging means is not limited to the pressing spring 87, but a material having elastically deformable property (elasticity) such as sponge or nonwoven fabric may be used.

In addition, the supporting member 88 may be pressed against the intermediate transfer belt 6 by a pushing member as a pushing means. For example, a constitution is adopted in which the supporting member 88 is pressed toward the inner peripheral surface of the intermediate transfer belt 6 by a pushing member at each of its opposite portions with respect to the longitudinal direction thereof. Further, thereby, the contact member 89 can be pressed against the inner peripheral surface of the intermediate transfer belt 6. In this case, the contact member 89 may be fixed to the support member 88.

Accordingly, the image forming apparatus 1 includes a pushing member 87 for pushing the electrode member (contact member) 89 in a direction from the back surface thereof toward the intermediate transfer belt 6 so that the contact portion (contact surface) 83 contacts the inner peripheral surface of the intermediate transfer belt 6. This pushing member 87 may be constructed by using an elastically deformable spring, sponge, or nonwoven fabric.

As described above, with the constitution of this embodiment, effects similar to those of embodiment 1 can also be obtained. In addition, according to the constitution of this embodiment, the intermediate transfer belt 6 and the potential regulating member 8 (contact member 89) can be more easily brought into surface contact with each other.

Other embodiments

As described above, the present invention is described based on specific embodiments, but is not limited to the above-described embodiments.

In the above-described embodiment, the potential adjustment power supply is independently provided for each of the image forming units, but may be made common to a plurality (or all) of the image forming units.

The same applies to the charging power supply, the developing power supply, and the primary transfer power supply.

In addition, in this embodiment, the potential regulating member (electrode member) whose contact surface contacting the intermediate transfer belt is a flat surface is a plate-like member formed of a metal plate or the like, but may be another form such as a block-like member having, for example, a rectangular cross section. The same applies to the potential regulating member (electrode member) whose contact surface contacting the intermediate transfer belt is a curved surface.

In addition, in the above-described embodiment, the predetermined charge polarity of the photosensitive member is a negative polarity, but is not limited thereto. The predetermined charge polarity of the photosensitive member may also be a positive polarity. Similarly, in the above-described embodiment, the normal charge polarity of the toner is the negative polarity, but may be the positive polarity. According to the above-described embodiments, various applied voltages in the case where the predetermined charge polarity of the photosensitive member and the normal charge polarity of the toner are positive polarities may only need to be appropriately changed so that these polarities are changed to the polarities opposite to those in the above-described embodiments.

In addition, the image forming apparatus is not limited to an image forming apparatus capable of forming a full-color image, but may be an image forming apparatus capable of forming only a single-color (white/black or single-color) image.

According to the present invention, it is possible to improve the transfer performance of a toner image onto a recording material such as embossed paper, which is relatively difficult to transfer the toner image in an image forming apparatus of an intermediate transfer type.

While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims (14)

1. An image forming apparatus comprising:

A first image bearing member configured to bear a toner image;

A second image bearing member configured to bear a toner image;

An intermediate transfer belt onto which toner images are transferred from the first image bearing member and the second image bearing member, wherein the first image bearing member is provided adjacent to the second image bearing member on an upstream side of the second image bearing member with respect to a moving direction of the intermediate transfer belt;

A first transfer member provided downstream of the first image bearing member with respect to a moving direction of the intermediate transfer belt and configured to transfer a toner image from the first image bearing member onto the intermediate transfer belt in a first transfer portion under application of a first transfer voltage;

A second transfer member provided downstream of the second image bearing member with respect to a moving direction of the intermediate transfer belt and configured to transfer a toner image from the second image bearing member onto the intermediate transfer belt in a second transfer portion under application of a second transfer voltage; and

An electrode member provided downstream of the first transfer portion and upstream of the second transfer portion with respect to a moving direction of the intermediate transfer belt and including a contact portion that contacts an inner surface of the intermediate transfer belt, wherein a voltage of a polarity opposite to a polarity of the first transfer voltage is applied to the electrode member,

Wherein, in a cross section perpendicular to the rotation axis of the first image bearing member, when a common tangent line between the first transfer member and the second image bearing member on the intermediate transfer belt side is a straight line L, a straight line passing through the rotation centers of the first image bearing member and the first transfer member is a straight line P, and a straight line passing through an intersection point between the straight line P and the first image bearing member and perpendicular to the straight line P is a straight line Q, the electrode member is configured such that the contact portion is located more on the first image bearing member side than the straight line L and more on the first transfer member side than the straight line Q.

2. The image forming apparatus according to claim 1, wherein, in a cross section perpendicular to a rotation axis direction of the first image bearing member, an entering amount of the contact portion into the straight line L is 5% or more and 80% or less when the entering amount at the time of the contact portion into the straight line Q is 100% in a perpendicular direction perpendicular to a direction along a common tangential line between the first image bearing member and the second image bearing member.

3. The image forming apparatus according to claim 1, wherein, in a cross section perpendicular to a rotation axis direction of the first image bearing member, an entering amount of the contact portion into the straight line L is 10% or more and 50% or less when the entering amount at the time of the contact portion into the straight line Q is 100% in a perpendicular direction perpendicular to a direction along a common tangent line between the first image bearing member and the second image bearing member.

4. The image forming apparatus according to claim 1, wherein the contact portion contacts an inner peripheral surface of the intermediate transfer belt at a surface thereof.

5. The image forming apparatus according to claim 1, wherein the contact portion is a flat face.

6. The image forming apparatus according to claim 1, wherein the contact portion is a curved surface that is convex toward the first image bearing member.

7. The image forming apparatus according to claim 1, wherein a length of the contact portion in a moving direction of the intermediate transfer belt is 5mm or more and 50mm or less.

8. The image forming apparatus according to claim 1, wherein a length of the contact portion in a moving direction of the intermediate transfer belt is not more than half a center distance between the first image bearing member and the second image bearing member in a cross section substantially perpendicular to a width direction of the intermediate transfer belt.

9. The image forming apparatus according to claim 1, wherein the contact portion is formed of a conductive material.

10. The image forming apparatus according to claim 9, wherein the contact portion is formed of a conductive metal.

11. The image forming apparatus according to claim 9, wherein the contact portion is formed of conductive fibers.

12. The image forming apparatus according to claim 1, wherein the electrode member includes a non-conductive supporting portion for supporting the contact portion, and the supporting portion is provided to contact the intermediate transfer belt on an upstream side of the contact portion with respect to a moving direction of the intermediate transfer belt.

13. The image forming apparatus according to claim 1, further comprising a pushing member configured to push the electrode member from a rear surface of the electrode member in a direction toward the intermediate transfer belt so that the contact portion contacts an inner peripheral surface of the intermediate transfer belt.

14. The image forming apparatus according to claim 13, wherein the urging member is formed of an elastically deformable spring, a sponge, or a nonwoven fabric.