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 device

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 technique

As an image forming apparatus such as a color copier, a color printer or a color multifunction machine using an electronic photographic type, an image forming apparatus of an intermediate transfer type has become mainstream because the image forming apparatus has the advantages of miniaturization of the main assembly of the apparatus and relatively easy adaptation to various recording materials. An image forming apparatus of an intermediate transfer type generally includes a configuration in which a plurality of photosensitive drums and an intermediate transfer belt are provided. In addition, in such an image forming apparatus, the toner image formed on the photosensitive drum is electrostatically transferred to the intermediate transfer belt one after another, and then the toner image on the intermediate transfer belt is electrostatically transferred to a recording material such as paper by secondary transfer.

In the image forming apparatus as described above, it is difficult to uniformly transfer a toner image onto, for example, embossed paper having an uneven surface, etc. In particular, transferring a toner image onto a recessed portion of the embossed paper tends to become difficult due to the need for a relatively large transfer electric field (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 a secondary transfer voltage in the form of a DC voltage biased with an AC voltage, the quality of micro images such as fine lines tends to be degraded due to toner scattering. For this reason, it has been desired to improve the transfer performance of a toner image onto a recording material such as embossed paper (on which it is relatively difficult to transfer a toner image), even in the case of using a secondary transfer voltage consisting only of a DC voltage.

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

Summary of the invention

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

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

According to one aspect of the present invention, there is provided an image forming device, comprising: a first image bearing member, the first image bearing member being configured to bear a toner image; a second image bearing member, the second image bearing member being configured to bear a toner image; an intermediate transfer belt, the toner image being transferred from the first image bearing member and the second image bearing member to the intermediate transfer belt, wherein the first image bearing member is provided adjacent to the second image bearing member on the upstream side of the second image bearing member relative to the moving direction of the intermediate transfer belt; a first transfer member, the first transfer member being provided downstream of the first image bearing member relative to the moving direction of the intermediate transfer belt and being configured to transfer the toner image from the first image bearing member to the intermediate transfer belt in a first transfer portion under application of a first transfer voltage; and a second transfer member, the second transfer member being provided downstream of the second image bearing member relative to the moving direction of the intermediate transfer belt and being configured to transfer the toner image from the first image bearing member to the intermediate transfer belt in a second transfer portion. Under the application of a transfer voltage, the colorant image is transferred from the second image bearing member to the intermediate transfer belt in the second transfer portion; and an electrode member, which is provided downstream of the first transfer portion and upstream of the second transfer portion relative to the moving direction of the intermediate transfer belt, and includes a contact portion that contacts the inner surface of the intermediate transfer belt, wherein a voltage of a polarity opposite to the 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 the common tangent 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 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 the intersection 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 so 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.

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

BRIEF DESCRIPTION OF THE 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 cross-sectional view and a perspective view of the potential adjusting member, respectively.

FIG. 4 is a cross-sectional view of a potential adjusting member in another example.

FIG. 5 is a cross-sectional view of a potential adjusting member in another example.

FIG. 6 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 7 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 8 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

Parts (a) and (b) of FIG. 9 are cross-sectional views each for illustrating the arrangement of the potential adjusting member.

FIG. 10 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 11 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 12 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 13 is a diagram for illustrating the effect of the potential adjusting member.

Parts (a) and (b) of FIG. 14 are photographic diagrams for illustrating the effect of the potential adjusting member.

FIG. 15 is a diagram for illustrating the effect of the potential adjusting member.

Parts (a) and (b) of FIG. 16 are a cross-sectional view and a perspective view, respectively, of a potential adjusting member in another embodiment.

FIG. 17 is a cross-sectional view for illustrating the arrangement of the potential adjusting member.

FIG. 18 is a cross-sectional view for illustrating a potential adjusting member in another example.

Parts (a) and (b) of FIG. 19 are a cross-sectional view and a perspective view, respectively, for illustrating a potential adjusting member in another embodiment.

Detailed ways

Hereinafter, 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 the 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 adopting an intermediate transfer type.

The image forming apparatus 1 includes an image forming portion 2, a controller 3, a feeding portion 4 of a 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 can form an image on the recording material S based on image information (image signal) acquired by an original reading device (not shown) provided on the image forming apparatus 1 or connected to the image forming apparatus 1. In addition, the image forming apparatus 1 can form 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, matte coated paper, embossed paper, or a synthetic resin sheet (synthetic paper) as a substitute for plain paper or the like, and an overhead projector sheet (resin film). 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 materials other than paper or is formed by materials containing materials other than paper.

The image forming part 2 forms an image on the recording material S fed from the feeding part 4 based on the image information. The image forming part 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 structure provided for each color will be described uniformly by omitting the suffixes y, m, c, and k of the elements respectively used to represent the associated colors. In addition, the image forming apparatus 1 can also form a monochrome image (such as a (single) black image) or a multi-color image, for example, by using the image forming unit 10 for a desired single color or some of the four colors.

The image forming unit 10 includes a photosensitive drum 11 as an image bearing member, which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member). In addition, the image forming portion 10 includes a charging roller 12 as a charging member, which is a roller-type charging member. In addition, the image forming portion 10 includes a developing device 14 as a developing member. In addition, the image forming portion 10 includes a pre-exposure device 16 as a discharge (charge elimination) member. In addition, a drum cleaning device 17 serves as a photosensitive member cleaning member. 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 substrate and a surface layer formed on the surface of the substrate. In this embodiment, as the surface layer, three layers of a primer layer, a photocharge generating layer, and a charge transporting layer sequentially coated and laminated on the substrate are provided. When the image forming operation starts, the photosensitive drum 11 is rotationally driven by a driving motor (not shown) as a driving member at a predetermined circumferential speed (processing speed) in the direction indicated by the arrow R1 in the figure (counterclockwise).

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 source 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 the image information, so that an electrostatic image is formed on the photosensitive drum 11. In this embodiment, the exposure device 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 (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 using a two-component developer including a toner (non-magnetic toner particles) and a carrier (magnetic carrier particles) as a developer. In a developing container (developing body) 14b of the developing device 14, the two-component developer is accommodated, and the toner is supplied from the toner bottle 18 in an amount corresponding to the consumption of the toner. The developing device 14 includes a developing sleeve 14a as a developing member (developer carrying member). The developing sleeve 14a is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment), for example. Inside the developing sleeve 14a, a magnetic roller (not shown) as a magnetic field generating component (magnetic field generating member) is fixed and arranged not to rotate relative to the developing container 14b, and the magnetic roller (not shown) is a roller-shaped magnet. 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 developing area, the toner moves from the two-component developer on the developing sleeve 14a to and is deposited on the image portion of the electrostatic image on the photosensitive drum 1. A developing power source 74 (FIG. 2) as a developing voltage applying component (developing voltage applying portion) is connected to the developing sleeve 14a. The developing power source 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 whose absolute value of potential is reduced by being exposed after being uniformly charged, the toner charged to the same polarity as the charge polarity of the photosensitive drum 11 (negative polarity in this embodiment) is deposited (reverse 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 polarity.

The intermediate transfer unit 20 is arranged to be opposite to the four photosensitive drums 11y, 11m, 11c and 11k. 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 as a plurality of stretch 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 the driving force is transmitted to the intermediate transfer belt 6, so that the intermediate transfer belt 6 rotates (circulates and moves) in the arrow R2 direction (clockwise direction) in Figure 1 at a predetermined circumferential speed corresponding to the circumferential speed of the photosensitive drum 1. The tension of the intermediate transfer belt 6 is controlled to be constant by the tension roller 22. The tension roller 22 is subjected to a force that pushes the intermediate transfer belt 6 from the inner peripheral surface (back side) side toward the outer peripheral surface (front side) side by the urging force of a tension spring (not shown) composed of a compression coil spring as an urging member, which is an urging member. By this force, a tension of about 2 to 5 kg is applied in the feeding direction (processing progress direction, moving direction) of the intermediate transfer belt 6. The inner secondary transfer roller 23 constitutes a secondary transfer device 26 in combination with the outer secondary transfer roller 25 described below. On the inner peripheral surface side of the intermediate transfer belt 6, primary transfer rollers 15y, 15m, 15c, 15k as primary transfer members are provided corresponding to 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 to be opposed to the photosensitive drums 11 and to nip the intermediate transfer belt 6 between themselves and the photosensitive drums 11. Each of the primary transfer rollers 15 is pressed toward the photosensitive drums 11 and contacts the photosensitive drums 11 via the intermediate transfer belt 6, and a primary transfer portion (primary transfer nip) N1 which is a contact portion between the photosensitive drums 11 and the intermediate transfer belt 6 is formed.

The toner image formed on the photosensitive drum 11 is transferred (primary transfer) to 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 drum 11 are multi-transferred so as to be sequentially superimposed on the intermediate transfer belt 6. A primary transfer power source 75 (FIG. 2) as a primary transfer voltage applying member (primary transfer voltage applying portion) is connected to the primary transfer roller 15. During the primary transfer, the primary transfer power source 75 applies a primary transfer voltage (primary transfer bias) to the primary transfer roller 15, which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive polarity in this embodiment). Thus, the negative polarity toner image on the photosensitive drum 11 is primary transferred to the intermediate transfer belt 6. A voltage detection sensor 75a (FIG. 2) as a voltage detection component (voltage detection portion) detecting its output voltage and a current detection sensor 75b (FIG. 2) as a current detection component (current detection portion) detecting its output current are connected to the primary transfer voltage source 75. In this embodiment, for example, a primary transfer voltage of about 1 to 2 kV is applied to the primary transfer roller 15 ("1 to 2 kV" means a range including 1 kV and 2 kV, and the same applies hereinafter). In addition, 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 voltage applied to the primary transfer rollers 15y, 15m, 15c, and 15k can 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 on the periphery of the core metal. The outer diameter of the primary transfer roller 15 is, for example, 15 to 20 mm. In addition, as the primary transfer roller 15, a roller having a resistance value of 1x10 ⁵ to 1x10 ⁸ Ω (N/N (23°C, 50%RH) condition, 2kV applied) can be preferably used.

In addition, in this embodiment, the intermediate transfer belt 6 is an endless belt having a two-layer structure, which includes a base layer and a surface layer in order from the inner peripheral surface side toward the outer peripheral surface side. As a material constituting the base layer, a resin such as polyimide and polycarbonate containing an appropriate amount of carbon black as an antistatic agent can be appropriately used. The thickness of the base layer is, for example, 0.05 to 0.15 mm. As a material constituting the surface layer, a resin such as chloroprene rubber (CR) imparted with conductivity can be used. The thickness of the surface layer is, for example, 0.200 to 0.300 mm. In this embodiment, the intermediate transfer belt 6 has a volume resistivity of 5x10 ⁸ to 1x10 ¹⁴ Ω·cm (23°C, 50%RH). Incidentally, in this embodiment, a two-layer structure is adopted in the intermediate transfer belt 6, but a single-layer structure of a material corresponding to the material of the above-mentioned base layer can also be adopted. In addition, the surface layer can also be formed as a resin coating layer containing a resin material such as a fluorine-containing resin and 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 member is disposed, which is a roller-type secondary transfer member. The outer secondary transfer roller 25 as a secondary transfer member cooperates with the inner secondary transfer roller 23 as a counter member (counter electrode) to form a secondary transfer device 26. The outer secondary transfer roller 25 is pressed toward 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 as 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) to the recording material S sandwiched and fed by the intermediate transfer belt 6 and the outer secondary transfer roller 25 in the secondary transfer portion N2 by the action of the secondary transfer device 26. A secondary transfer power source 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 the secondary transfer, the secondary transfer power source 76 applies a secondary transfer voltage (secondary transfer bias) to the outer secondary transfer roller 25, which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive polarity in this embodiment). Thus, the toner image of 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 member (voltage detection portion) for detecting its output voltage and a current detection sensor 76b (FIG. 2) as a current detection member (current detection portion) for detecting its output current are connected to the secondary transfer power source 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 6.5 kV 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 to the recording material S. In this embodiment, the secondary transfer voltage is subjected to constant voltage control. Incidentally, the following configuration may also be adopted: in this configuration, a secondary transfer voltage is applied from the secondary transfer power source 76 to the inner secondary transfer roller 23 as the secondary transfer member, so that the outer secondary transfer roller 25 as the counter member is connected to the ground potential, and the secondary transfer voltage is a DC voltage of the same polarity as the normal charge polarity of the toner.

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 box 41 as a recording material accommodating portion of the feeding portion 4. The recording material S accommodated in the box 41 is separated and fed one by one from the box 41 by a feeding 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 passage 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 in sync with the toner image on the intermediate transfer belt 6. Incidentally, in FIG. 1 , only one box 41 is illustrated, but the image forming apparatus 1 may also include a plurality of boxes 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 placement portion) other than the box 41, such as a manual feed tray or the like.

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 25 mm. In addition, as the outer secondary transfer roller 25, a roller having a resistance value of 1x10 ⁵ to 1x10 ⁸ Ω (measured at N/N (23°C, 50%RH), 2 kV applied) can 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 pressure roller 27b. A heater as a heating member is included in the fixing roller 27a. The pressure 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 clamping and feeding the recording material S between the fixing roller 27a and the pressure roller 27b, thereby fixing (melting and adhering) the toner image on the recording material S. Incidentally, the temperature (fixing temperature) of the fixing roller 27a is detected by a fixing temperature sensor 77 (FIG. 2). The recording material S on which the toner image is fixed is fed by a discharge roller pair 51 or the like, and is discharged (output) through a discharge opening (not shown) to 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 device 16. In addition, the toner (primary transfer residual toner) remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 6 during the primary transfer is removed from the surface of the photosensitive drum 11 and collected by the drum cleaning device 17. 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-shaped member that contacts the photosensitive drum 11 with a predetermined pressure. The cleaning blade contacts the surface of the photosensitive drum 11 in the opposite direction to the rotation direction of the photosensitive drum 11 so that its front end on the free end side faces the upstream side of the rotation direction of the photosensitive drum 11. In addition, deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 6 without being transferred onto the recording material S during secondary transfer are removed from the surface of the intermediate transfer belt 6 by the belt cleaning device 24 as an intermediate transfer member cleaning means and collected.

Incidentally, the image forming unit 10 may constitute a cartridge (process cartridge) integrally and 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, a stretching roller for the intermediate transfer belt 6, respective primary transfer rollers 15, a belt cleaning device 24, and a potential adjusting member 8 described below, etc. The intermediate transfer unit 20 may be integrally and detachably mounted to the apparatus main assembly 1a.

2. Control composition

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 component. The controller 3 is composed of a CPU 31 as a computing component, a ROM 32 as a storage component, a RAM 33 as a storage component, 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 various parts of the image forming apparatus 1. The RAM 33 temporarily stores data on the 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 various parts such as a feeding part 4, an image forming part 2, a discharge part 5, etc., and not only exchanges signals with these parts, but also controls the operation of each of these parts. The ROM 32 stores an image formation control sequence for forming an image on a recording material S.

The charging power source 73, the developing power source 74, the primary transfer power source 75, the secondary transfer power source 76, and the potential adjustment power source 80 described below, which are controlled by a signal from the controller 3, are respectively connected to the controller 3. Incidentally, although omitted from the illustration, in this embodiment, each of the charging power source 73, the developing power source 74, the primary transfer power source 75, and the potential adjustment power source 80 is provided independently of the associated image forming unit 10. In addition, the temperature sensor 71, the humidity sensor 72, the voltage detection sensor 75a and the current detection sensor 75b of the primary transfer voltage source 75, the voltage detection sensor 76a and the current detection sensor 76b of the secondary transfer voltage source 76, and the fixing temperature sensor 77, etc. 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 composed of operation buttons (keys) and the like as an input component, and a display portion 70a composed of a liquid crystal panel (display) and the like as a display component. By the way, in this embodiment, the display portion 70a is configured as a touch panel and also has a function as an input component. An operator such as a user or a service personnel operates the operation portion 70, and thus can cause the image forming device 1 to perform a job (described later). A series of operations for forming and outputting an image on a single recording material S or forming and outputting an image on a plurality of recording materials S by a single start instruction. The controller 3 receives a signal from the operation portion 70 and operates various devices of the image forming device 1. In addition, the image forming device 1 can also perform a job relying on a signal from, for example, an external device such as a personal computer, rather than from the operation unit 70.

3. Summary of Problems and Solutions

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

As described above, in the image forming apparatus 1 of the intermediate transfer type, it is difficult to uniformly transfer the toner image onto, for example, embossed paper having an uneven surface. Incidentally, embossed paper is paper (fancy paper) to which an uneven pattern is provided by using a method such as expansion 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 recessed 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 tends 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 recessed portion of the embossed paper, in the case where the transfer electric field becomes too large at a portion other than the recessed portion, there is a possibility that improper transfer occurs in which the toner is partially not transferred onto the halftone image.

When the present inventors conducted research, 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 increased. Specifically, it was found that the toner was subjected to discharge, and thus the average value of the charge amount increased when the toner charge amount distribution became wider than the toner charge amount distribution during development. In addition, it was found that the charge amount increased as described above, and thus the mirror image force between the toner and the intermediate transfer belt 6 increased and the transfer electric field necessary to transfer the toner onto the recording material S in the secondary transfer portion N2 became larger, and thus it became more difficult to transfer the toner image onto the recessed portion of the embossed paper.

Therefore, the present inventors have conducted intensive studies and found that the transfer performance of the toner image onto a recording material S such as embossed paper (to which the transfer of the toner image is relatively difficult) can be improved by suppressing the above-mentioned discharge and the increase in the charge amount of the toner on the intermediate transfer belt 6. That is, it was found that in order to suppress the above-mentioned discharge, it is effective to apply a voltage of the same polarity as the charge polarity of the photosensitive drum 11 to the potential adjusting member 8, which is 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-mentioned discharge can be effectively suppressed by applying a voltage of the same polarity as the charge polarity of the photosensitive drum 11 to the potential adjusting member 8 disposed in contact with the inner peripheral surface of the intermediate transfer belt 6. Incidentally, the potential adjusting 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), 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 the curling (inclination) of the intermediate transfer belt 6 caused by the stretching roller or the steering operation for controlling the displacement (meandering) of the intermediate transfer belt 6. 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 adjustment member 8 fluctuates or disappears, the above-mentioned discharge suppression effect cannot be stably obtained. That is, in the effect of improving the transfer performance of the toner image by suppressing the above-mentioned discharge, there is a possibility that the in-plane non-uniformity of the image occurs. On the other hand, it is found that the contact portion of the potential adjustment member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is made to enter the photosensitive drum 11 side more than the stretching surface of the intermediate transfer belt 6 on the inner peripheral surface side in the position downstream of the primary transfer portion N1 in the absence of the potential adjustment member 8, so that the potential adjustment member 8 can also be more stably contacted with the intermediate transfer belt 6 during the image forming operation.

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

Thus, it is found that it is preferable that the potential adjusting member 8 is in surface contact with the intermediate transfer belt 6 more stably during the image forming operation. Here, surface contact (contact at the surface) means that the contact does not include a case where the potential adjusting member 6 is in contact with the intermediate transfer belt 6 only in a linear shape with respect to a direction intersecting with the feeding direction of the intermediate transfer belt 6 in a range narrower than the contact width (approximately 5 to 50 mm) described in detail below. Thus, the surface contact, for example, includes not only a case where substantially the entire area of the potential adjusting member 8 is in continuous and close contact with the intermediate transfer belt 6 in the contact width described in detail below, but also a case where many contact points are substantially uniformly distributed in the above range as in the case of nonwoven fabrics, etc. In the following, it will be described in more detail.

4. Potential adjustment components

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

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

In this embodiment, the potential adjusting 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 adjusting 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 flat surface of the first portion 81. In this embodiment, the contact surface 83 of the first portion 81 of the potential adjusting member 8 (which is a contact portion that contacts 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 adjusting 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 adjusting member 8, and the downstream end B of the contact surface 83 corresponds to the downstream side end of the potential adjusting member 8. As described above, by the action of the electric field formed in the space between the photosensitive drum 11 and the potential adjusting member 8, in order to more effectively suppress the discharge between the intermediate transfer belt 6 and the photosensitive drum 11, the potential adjusting member 8 may preferably be in surface contact with the intermediate transfer belt 6. 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 preferably be 5 mm or more. As the length of line segment AB increases, the above-mentioned electric field suppression effect becomes greater, but it can be considered that when the length becomes too long, stable contact between the potential adjustment member 8 and the intermediate transfer belt 6 becomes difficult due to the influence of (component) component accuracy, etc.

When the length of the line segment AB is 50 mm or less, and typically 30 mm or less, the length is insufficient in many cases. That is, the length of the line segment AB may be suitably about 5 to 50 mm, typically about 5 to 30 mm. From another point of view, it can be said that in many cases it is sufficient 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 drum 11. In this embodiment, a potential adjusting member 8 having a length of 25 mm for the line segment AB 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 drum 11 is about 100 mm.

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

The potential adjusting member 8 is a member that is long in the width direction of the intermediate transfer belt 6. The length of the contact surface 83 of the potential adjusting member 8 in the longitudinal direction (the 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 device 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 adjusting member 8 in the longitudinal direction is longer than the above-mentioned 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 primary transfer roller 15 contacting 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 adjusting member 8 in the longitudinal direction.

Thus, regardless of the length of the toner image transferred onto the intermediate transfer belt 6 relative to the width direction of the intermediate transfer belt 6, 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-mentioned charge. On the other hand, in this embodiment, the length of the potential adjusting 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 adjusting 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 of the potential adjusting member 8 relative to the longitudinal direction protrudes more than the end of the intermediate transfer belt 6 relative to the width direction, the possibility that discharge occurs to the potential adjusting member 8 and the members around the intermediate transfer belt 8, so that the effect of suppressing the discharge becomes smaller can be reduced.

The potential adjusting member 8 may be composed only of a single material having conductivity, for example. In this embodiment, the potential adjusting member 8 is basically composed only of a metal having conductivity, such as SUS (stainless steel). Specifically, in this embodiment, the potential adjusting member 8 is formed by subjecting a plate (metal plate) made of a metal such as SUS to bending to form a first portion 81 and a second portion 82. By subjecting the metal plate to bending in this way, the strength of the potential adjusting member 8 can be increased. In this embodiment, each of the first portion 81 and the second portion 82 of the potential adjusting member 8 is substantially not deformed in the use state of the image forming device 1. However, the present invention is not limited to such an embodiment, but the potential adjusting 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 adjusting member 8. For example, as shown in FIG. 4, a configuration may be adopted in which a base 84 having a shape similar to that of the potential adjusting 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 source 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 another example of the potential adjustment member 8. For example, as shown in FIG. 5, the contact surface 83 of the potential adjustment member 8 that contacts the intermediate transfer belt 6 can also be formed by a conductive nonwoven fabric 86. Incidentally, in FIG. 5, the conductive nonwoven fabric 86 is provided on the contact surface 83 of the potential adjustment member 8 having the structure shown in FIG. 4, but the conductive nonwoven fabric 86 can also be provided on the contact surface 83 of the potential adjustment member 8 having the structure shown in FIG. 3. The conductive nonwoven fabric 86 can be fixed by any fixing means such as a conductive adhesive. In addition, instead of the nonwoven fabric 86, a felt, a pile fabric (external pile fabric (velvet, brush) or a terry pile fabric (terry cloth)) composed of conductive fibers, or a sponge (elastic foam member) composed of a conductive rubber material can also be used. Therefore, the contact surface 83 of the potential adjusting member 8 that contacts the intermediate transfer belt 6 is made of a flexible material or an elastic material, so that the possibility of the occurrence of scratches 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 adjusting member 8 can be reduced.

5. Arrangement of potential adjustment components

Next, the arrangement of the potential adjusting member 8 in this embodiment will be described. FIG. 6 is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for illustrating the arrangement of the potential adjusting 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, the potential adjusting member 8c provided between the primary transfer portion N1c for cyan and the primary transfer portion N1k for black is shown (hereinafter the same applies to FIGS. 7, 10, 11, and 12).

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

Here, in order to explain the arrangement of the potential adjusting member 8, a case where the potential adjusting member 8 is removed is assumed. In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line along which the stretched surface of the intermediate transfer belt on the inner peripheral surface side in the portion downstream of the primary transfer portion N1 in the absence of the potential adjusting member 8 passes is defined as a straight line L. Incidentally, specifically, this straight line L corresponds to the stretched surface in a state where only the potential adjusting 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 can be regarded as a common tangent (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 influence reaches a negligible degree). In addition, on the straight line L, a portion where the inner peripheral surface of the intermediate transfer belt 6 is separated from the tensile member closest to the upstream side of the potential adjusting member 8 is defined as "C (or upstream tensile portion C)", and a portion where the inner peripheral surface of the intermediate transfer belt 6 is separated from the tensile member closest to the downstream side of the potential adjusting member 8 is defined as "D (or downstream tensile 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 rises 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 figure.

In this embodiment, the tensile member closest to the upstream side of the potential adjusting 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 tensile portion C. However, the tensile member closest to the upstream side of the potential adjusting 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 relative 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 tensile portion C. Incidentally, FIG. 7 is a cross-sectional view similar to FIG. 6 in the case where the primary transfer roller 15 is offset and disposed on the upstream side relative to the photosensitive drum 11.

In addition, in this embodiment, the most proximate stretching member on the downstream side of the potential adjusting member 8 is the photosensitive drums 11m, 11c, and 11k disposed adjacent to the potential adjusting member 8 on the downstream side of the potential adjusting member 8 for the primary transfer portions N1y, N1m, and N1c for yellow, magenta, and cyan, respectively. In addition, the position on the inner peripheral surface of the intermediate transfer belt 6 at a portion corresponding to the portion where the intermediate transfer belt 6 is separated from the associated one of the photosensitive drums 11m, 11c, and 11k is the downstream stretching portion D. However, the most proximate stretching member on the downstream side of the potential adjusting 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 relative to the photosensitive drum 11, the 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 primary transfer roller 15 is the downstream stretching portion D. In addition, in this embodiment, for the most downstream primary transfer portion N1k for black, as shown in FIG. 8 , the most proximate stretching member on its downstream side is the stretching roller (in this embodiment, the tension roller) 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 separates from the stretching roller 22 is a downstream stretching portion D. Incidentally, FIG. 8 is a cross-sectional view similar to FIG. 6 regarding the potential adjusting member 8 provided to the most downstream primary transfer portion N1k.

In addition, for each of the primary transfer portions N1, as the tensile member closest to the downstream side of the potential adjusting member 8, in the case where there is another tensile roller for adjusting the posture of the intermediate transfer belt 6 during the image forming operation, the straight line L and the downstream tensile portion D are defined based on the tensile roller thereof. In addition, in the case where not the tensile roller but a scraper or a brush contacts 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 a similar purpose, when the scraper or the brush adjusts the posture of the intermediate transfer belt 6, the scraper or the brush can be regarded as the tensile member closest to the downstream side of the potential adjusting member 8. The scraper is generally composed of a sheet-like or film-like member.

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-mentioned charge suppression effect becomes greater. In this embodiment ( FIG. 6 ), the potential regulating member 8 is disposed in a position downstream of the primary transfer portion N1 so that the distance X2 from the primary transfer roller 15 to the upstream end A becomes about 8 mm. Here, the distance X2 is the distance between the rotation center of the primary transfer roller 15 and the upstream end A in the direction of the common tangent along the side where the plurality of photosensitive drums 11 contact the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 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 preferably be approximately 1 to 20 mm, typically approximately 1 to 10 mm.

In addition, in this embodiment, the potential adjusting 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 pressurizing spring 87 (part (b) of FIG. 3 ) composed of a compression coil spring (which is an urging member) as an urging member. At this time, the contact portion of the potential adjusting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is made to enter the photosensitive drum 11 side relative to the straight line L. Thus, even in the case where a fluctuation or fluctuation occurs on the intermediate transfer belt 6 during the image forming operation (during the travel of the intermediate transfer belt 6), the potential adjusting member 8 can be in contact with the intermediate transfer belt 6 more stably. Although the potential adjusting member 8 is not limited to this, the amount of entry of the contact surface 83 of the potential adjusting member 8 to the straight line L may preferably be about 0.3 to 5 mm, typically about 0.5 to 3 mm (for example, about 0.5 mm). When this entry amount is too small, there is a possibility that the potential adjusting member 8 cannot be stably contacted with the intermediate transfer belt 6. When the entry amount is too large, there is a possibility that stable feeding (conveying) 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 each of the upstream end A and the downstream end B of the contact surface 83 of the contact portion of the potential adjustment member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 enters the photosensitive drum 11 side by the following entry amount to the straight line L. In this embodiment, as described above, the primary transfer roller 15 is disposed so as to be offset toward the downstream side of the photosensitive drum 11. Parts (a) and (b) of FIG. 9 are cross-sectional views (cross sections substantially perpendicular to the rotation axis direction of the photosensitive drum 11) each showing the vicinity of a single primary transfer portion N1 in an enlarged state in order to explain the entry amount of the contact surface 83 of the potential adjustment member 8 to the straight line L. Here, in the cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 1, a straight line passing through the intersection between the straight line L and the straight line P and perpendicular to the straight line P is defined as a clamping line Q, and the straight line P connects the rotation axis center of the photosensitive drum 11 and the rotation axis center of the primary transfer roller 15. Here, the intersection between the straight line L and the straight line P can be substantially regarded as the intersection between the straight line P and the photosensitive drum 11. For this reason, the clamping line Q can be regarded as a straight line that passes through the intersection (nip portion) between the straight line P and the photosensitive drum 1 and is perpendicular to the straight line P. In this embodiment, the upstream end A and the downstream end B of the contact surface 83, which is the contact portion of the potential adjusting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6, are made to enter the photosensitive drum 11 side relative to the straight line P, but are not made to enter the clamping line Q (part (a) of Figure 9). That is, the contact surface 83 of the potential adjusting member 8 is located on the photosensitive drum 11 side relative to the straight line L, and is located on the primary transfer roller 15 side relative to the clamping line Q. When the contact surface 83 of the potential adjusting member 8 is made to enter the photosensitive drum 11 side relative to the clamping 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 Figure 9). In this case, the small gap area between the photosensitive drum 1 and the intermediate transfer belt 6 is enlarged, 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 the 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 is deteriorated as described above. When the case where the potential adjusting member 8 is entered into the nip line Q is taken as 100%, the entry amount of the potential adjusting member 8 to the straight line L may be preferably 5% or more and 800% or less, more preferably 10% or more and 50% or less, and in this embodiment, 30%.

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

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 with the line segment CD of the straight line. Thus, in the case where the contact surface 83 of the potential adjustment member 8 is a flat surface, the intermediate transfer belt 6 and the potential adjustment member 8 can be more reliably in surface contact with each other. As shown in Figure 10 or Figure 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 one of the end portion on the upstream end A side of the potential adjustment member 8 (Figure 11) and the end portion on the downstream end B side of the potential adjustment member 8 (Figure 10) can 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 suppression effect by surface contact. Incidentally, each of Figures 10 and 11 is a cross-sectional view similar to Figure 6 in the case where the straight line M intersects with the line segment CD of the straight line L. 10 shows a case where the straight line M is inclined relative 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 relative 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 adjusting member 8 is disposed so 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 adjusting member 8 may be disposed so that the straight line M is inclined relative to the straight line L. In particular, as shown in FIG. 12 , the straight line M is inclined relative 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 laying the intermediate transfer belt 6 in the vicinity of the upstream end A can be made small. Therefore, this case is advantageous for reducing the possibility of scratches 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 results of verification of the effect of this embodiment will be described. Verification was performed on two points that an increase in the charge amount of toner can be suppressed and transfer performance of toner to embossed paper can be improved.

Specifically, the following experiment was conducted. In the image forming device 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 330 mm, and the width of the secondary transfer portion N2 (i.e., the length of the intermediate transfer belt 6 in the width direction) is 340 mm. In addition, the image forming device 1 operates at a process speed (circumferential speed of the photosensitive drum 11) of 180 mm/s. Then, a solid image of A4 size is formed on the photosensitive drum 11c, and the toner image is transferred once to 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 the primary transfer portion N1k for black, and then is secondarily transferred onto the embossed paper in the secondary transfer portion N2. The primary transfer voltage is subjected to constant voltage control by the controller 3 with a voltage set so that the primary transfer current in the primary transfer portion N1 becomes 20 μA as a target current. Furthermore, 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 operation is performed in a state where the potential adjusting member 8 (8c, 8k) is removed ("without the potential adjusting member") and in a state where the potential adjusting member 8 (8c, 8k) is installed according to this embodiment and a potential adjusting voltage of -3000V is applied thereto by the potential adjusting power supply 80 ("with the potential adjusting member"). As embossed paper, "Rezak 66" (trade name, manufactured by Tokushu Tokai Paper Co., Ltd) with a basis weight of 302g/ ^cm2 is used. Then, the change in the charge amount of the colorant in each of the case of "with the potential adjusting member" and the case of "without the potential adjusting member" is measured. Incidentally, the charge amount of the colorant is calculated by measuring the charge per unit weight (mass) using the attraction method commonly used in this field. This method calculates the charge amount [μC/g] by measuring the weight [g] and charge amount [μC] of the attracted colorant, and thus the average charge amount of the colorant can be grasped. In addition, the images on the above-mentioned embossed paper after fixing in the case where the potential adjusting member existed ("with potential adjusting member") and in the case where the potential adjusting member did not exist ("without potential adjusting member") were compared with each other.

Figure 13 is a diagram showing the measurement results of the change in the charge amount of the colorant in each of the cases where there is a potential adjusting member and the case where there is no potential adjusting member. As shown in Figure 13, the charge amount of the colorant on the photosensitive drum 11c for cyan is -23μC/g. Based on this charge amount of the colorant, the change in the charge amount of the colorant in each of the following states is measured. First, the charge amount of the colorant on the intermediate transfer belt 6 after the primary transfer in the primary transfer part N1c for cyan and before reaching the primary transfer part N1k for black is measured ("on the belt after the cyan primary transfer (N1c)"). In addition, the charge amount of the colorant on the intermediate transfer belt 6 after passing through the primary transfer part N1k for black and before reaching the secondary transfer part N2 is measured ("on the belt after the black primary transfer (N1k)"). As a result, it was found that although the charge amount of the colorant increased (its absolute value became larger) both in the presence and absence of the potential adjusting member, the increase in the charge amount of the colorant could be suppressed in the presence of the potential adjusting member compared to in the absence of the potential adjusting member.

Parts (a) and (b) of Figure 14 are photographic diagrams showing, in a comparative manner, images on embossed paper after fixing in the absence of a potential adjusting member and in the presence of a potential adjusting member, respectively. Part (a) of Figure 14 shows an image in the absence of a potential adjusting member, and part (b) of Figure 14 shows an image in the presence of a potential adjusting member. As shown in part (a) of Figure 14, in the absence of a potential adjusting member, the toner cannot be transferred to the recessed portion of the surface of the embossed paper, so that white leakage is obvious in some cases. On the other hand, as shown in part (b) of Figure 14, in the presence of a potential adjusting member, it is found that the toner can be fully transferred to the recessed 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 a potential adjusting member, the transfer performance of the toner image to the recessed portion of the embossed paper can be improved while reducing the possibility of improper transfer on the halftone image at a portion of the embossed paper other than the recessed portion due to an excessively large 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 on the downstream side of the primary transfer portion N1 and thus the charge amount increases whenever the toner passes through the primary transfer portion N1. For this reason, the toner transferred onto the intermediate transfer belt 6 in the upstream primary transfer portion N1 is large in the number of times the toner passes through the downstream primary transfer portion N1, so that it can be said that the charge amount is more likely to increase. Thus, in this embodiment, the potential adjusting member 8 is provided to all four primary transfer portions N1, but the potential adjusting member 8 may also be provided only to a single or a plurality of upstream primary transfer portions N1, and not to all four primary transfer portions N1. For example, the potential adjusting member 8 may be provided only to the most upstream primary transfer portion N1y, or only to the most upstream primary transfer portion N1y and the primary transfer portion N1m (and further the primary transfer portion N1c) adjacent to the primary transfer portion N1y on the downstream side.

In addition, 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 surface contact of the potential adjusting member 8 with the intermediate transfer belt 6. Specifically, FIG. 15 shows the simulation results under the following conditions. As the potential adjusting member 8, a test potential adjusting member 8 composed of a flat plate similar to the first portion 81 of the potential adjusting member 8 in this embodiment is assumed. In addition, the indicators 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) A case where the end portion corresponding to the upstream end A is brought close to the inner peripheral surface of the intermediate transfer belt 6 in a dotted (line) shape (separated by about 0.4 mm) (the potential adjusting member 8 is arranged at a certain angle with respect to the intermediate transfer belt 6 ).

(2) A case where the portion from the end portion corresponding to the upstream end A to the end portion corresponding to the downstream end B is brought close to the intermediate transfer belt 6 in a planar shape (separated by about 0.4 mm).

(3) A case where the end portion corresponding to the upstream end A contacts the inner peripheral surface of the intermediate transfer belt 6 in a dot (line) shape (the potential adjusting member 8 is arranged at a certain angle with respect to the intermediate transfer belt 6 ).

(4) A case where the portion from the end portion corresponding to the upstream end A to the end portion corresponding to the downstream end B is in contact with the intermediate transfer belt 6 in a planar shape.

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

As shown in FIG. 15 , when the potential adjusting member 8 is separated from the intermediate transfer belt 6 (the above (1) and (2)), the above effect of suppressing discharge becomes smaller. That is, it is understood that the potential adjusting member 8 is made to enter the intermediate transfer belt 6 further than the stretched surface, and is also stably in contact with the intermediate transfer belt 6 during the image forming operation (during the travel of the intermediate transfer belt 6) (the above (3) and (4)), so the above effect of suppressing discharge can be stably obtained. In addition, as shown in FIG. 15 , it is understood that the corresponding effect can also be obtained in the case where the potential adjusting 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 discharge is greater in the case where the potential adjusting member 8 is in surface contact with the intermediate transfer belt 6 than in the case where the potential adjusting 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 is a tendency that the effect of suppressing discharge becomes greater by increasing the potential adjusting voltage of the same polarity as the charge polarity of the photosensitive drum 11 (by making its absolute value large). As described above, in the configuration of this embodiment, the potential adjustment voltage may preferably be approximately -1000 to -3000V.

Thus, in this embodiment, the image forming apparatus 1 includes a photosensitive member 11 which can be charged to a predetermined polarity and carries a toner image, an intermediate transfer belt 6 which is circumferentially movable and is stretched by a plurality of stretching rollers and conveys the toner image for secondarily transferring the toner image primarily transferred from the photosensitive member 11 in the primary transfer portion N1 to a recording material in the secondary transfer portion N2, and a recording medium which is provided corresponding to the photosensitive member 11 and is formed in which the photosensitive member 11 and the intermediate transfer belt 6 are in contact with each other with the inner peripheral surface of the intermediate transfer belt 6 being in contact with each other and the toner image is transferred from the photosensitive member 11 under application of a voltage. 11 is transferred to the primary transfer portion N1 on the intermediate transfer belt 6, an electrode member 8 is in close contact with the inner peripheral surface of the intermediate transfer belt 6 on the downstream side of the primary transfer member 15 with respect to the moving direction of the intermediate transfer belt 6, and a power supply 80 for applying a voltage of the same polarity as a predetermined polarity to the electrode member 8, wherein the electrode member 8 is arranged so that its contact portion 83 contacting the inner peripheral surface of the intermediate transfer belt 6 enters the photosensitive member side relative to the stretched 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 P passing through the intersection between 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 followed and a straight line perpendicular to the straight line P is a nip line Q, the contact portion 83 is further on the photosensitive member side than the straight line L and further 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 preferred 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 the upstream end A, the downstream side end of the contact portion 83 with respect to the moving direction is the downstream end B, the position where the posture of the intermediate transfer belt 6 is adjusted immediately upstream of the electrode member 8 with respect to the moving direction on the straight line L is the upstream extension portion C, the position where the posture of the intermediate transfer belt 6 is adjusted immediately downstream of the electrode member with respect to the moving direction on the straight line L is the downstream stretching portion D, and a straight line passing through the upstream end A and the downstream end B is a straight line M, the electrode member 8 is disposed so that the straight line M does not intersect with 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 5 mm or more and 50 mm or less. In addition, in a preferred form, the image forming device 1 includes a plurality of drum-shaped photosensitive members 11, and the length of the contact portion 83 in the moving direction is not greater than half of the center (inter-axial) distance between 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 composed of, for example, conductive fibers. In addition, the image forming device 1 may have a plurality of photosensitive members 11 disposed along the moving direction, a plurality of primary transfer members 15 provided corresponding to the plurality of photosensitive members 11, and an electrode member 8 provided to contact the inner peripheral surface of the intermediate transfer belt 6 in close proximity to at least one primary transfer member 15 with respect to the downstream side of the moving direction. In this embodiment, the image forming device 1 includes a plurality of electrode members 8 provided to contact the intermediate transfer belt 6 in close proximity to all of the plurality of primary transfer members 15 with respect to the downstream side of the moving direction.

As described above, according to this embodiment, by the action of the potential adjusting member 8 , the 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 it is relatively difficult to transfer the toner image, embossed paper is cited as an example, but similar effects can be expected on a recording material (high resistance paper) whose resistance is relatively high, such as 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 of using a voltage in the form of a DC voltage biased with an AC voltage as the secondary transfer voltage in order to output a good image, it is advantageous to promote the transfer of the toner image onto the 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 functions or structures that are the same as or correspond to those of the image forming apparatus of Embodiment 1 are denoted by the same reference numerals or symbols as those of Embodiment 1, and their detailed description will be omitted.

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

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

In this embodiment, the potential adjusting member 8 is composed of a curved plate which is provided along the width direction of the intermediate transfer belt 6 and is curved in a curved shape convex 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 adjusting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6, is a curved surface convex toward the photosensitive drum 11. Therefore, by forming the contact surface 83 into a curved surface shape, the stress when the contact surface 83 slides with the intermediate transfer belt 6 is alleviated, so that the possibility of scratches on the inner peripheral surface of the intermediate transfer belt 6 can be reduced.

A potential adjusting power source 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 adjusting voltage similar to that in Embodiment 1 is applied to the potential adjusting member 8. Thus, 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.

Similar to Embodiment 1, the potential adjusting member 8 in this embodiment is a member that is long in the width direction of the intermediate transfer belt 6. In this embodiment, the length of the contact surface 83 of the potential adjusting 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 contacting 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 adjusting member 8 in the longitudinal direction is shorter than the width of the intermediate transfer belt 6.

In addition, similar to Embodiment 1, the potential adjusting member 8 in this embodiment may be composed of only a single material having conductivity, for example. In this embodiment, the potential adjusting member 8 is basically composed of only a metal having conductivity, such as SUS. However, similar to what is described in Embodiment 1, the potential adjusting member 8 may also be composed of two or more materials.

For example, similarly to the potential adjusting member 8 shown in FIG. 4 , as a configuration including a base and a surface layer, the surface layer constituting the contact surface 83 may be formed of a conductive material, and the base may be formed of a non-conductive material.

In addition, for example, similar to the potential adjustment member 8 shown in FIG5 , the contact surface 83 may also be formed of a conductive nonwoven fabric, etc. Therefore, the contact surface 83 of the potential adjustment member 8, which is a curved surface, is composed of a flexible material or an elastic material, and thus the possibility of the occurrence of scratches on the inner peripheral surface of the intermediate transfer belt 6 caused by the friction (sliding) between the inner peripheral surface of the intermediate transfer belt 6 and the potential adjustment member 8 can be further reduced.

Next, the arrangement of the potential adjusting member 8 in this embodiment will be described. FIG. 17 is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for illustrating the arrangement of the potential adjusting 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, the potential adjusting member 8c provided between the primary transfer portion N1c for cyan and the primary transfer portion N1k for black is shown (hereinafter the same applies to FIG. 18).

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

Here, the straight line L is defined similarly to that in Example 1. In addition, the above-mentioned upstream stretching portion C and the above-mentioned downstream stretching portion D are defined similarly to that in Example 1. In addition, similarly to Example 1, the upstream end of the contact surface 83 is defined as the upstream end A, and the downstream end of the contact surface 83 is defined as the 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 adjusting member 8, respectively. In this embodiment, the upstream side end of the potential adjusting member 8 is separately 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 adjusting member 8 may also coincide with each other.

Similar to Embodiment 1, the potential adjustment member 8 is deployed 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-mentioned charge suppression effect becomes greater. In this embodiment (Figure 17), the potential adjustment member 8 is deployed in a position downstream of the primary transfer portion N1 so that the distance X2 from the primary transfer roller 15 to the upstream end E of the member becomes about 8mm. Here, the distance X2 is the distance between the rotation center of the primary transfer roller 15 and the upstream end E of the member in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11 in the direction of the common tangent along the side where the plurality of photosensitive drums 11 contact the intermediate transfer belt 6.

In addition, in this embodiment, the potential adjusting member 8 is pressed against the inner peripheral surface of the intermediate transfer belt 6 by the pressing spring 87 (part (b) of FIG. 16 ) at each of the opposite ends thereof with respect to the longitudinal direction thereof. 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 relative to the straight line L. Similar to Embodiment 1, the contact width X3 as the length of the contact surface 83 in the feeding direction of the intermediate transfer belt 6, which is the contact portion of the potential adjusting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6, may preferably be about 5 to 50 mm, typically about 5 to 30 mm. That is, in this embodiment, in the curved surface of the potential adjusting member 8 on the intermediate transfer belt 6 side, the region (contact surface 83) from the upstream end A to the downstream end B of the range 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 relative to the straight line L.

Therefore, by making the contact surface 83 of the potential adjusting member 8 enter the photosensitive drum 11 side relative to the straight line L, even in the case where a fluctuation or vibration occurs on the intermediate transfer belt 6 during the image forming operation (during the travel of the intermediate transfer belt 6), the potential adjusting member 8 can be in stable surface 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 convex toward the photosensitive drum 11, the intermediate transfer belt 6 and the potential adjusting member 8 can be more reliably in surface contact with each other by making the contact surface 83 itself enter toward the photosensitive drum 11 side relative to the straight line L in the above-mentioned 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 is convex toward the photosensitive member side.

As described above, by the configuration of this embodiment, it is also possible to obtain effects similar to those of Embodiment 1. In addition, according to the configuration of this embodiment, the intermediate transfer belt 6 and the potential adjusting member 8 can be brought into surface contact with each other more easily.

Incidentally, in this embodiment, the contact surface 83 is made a curved surface by forming the potential adjusting member 8 using a curved plate, but as shown in FIG18 , the contact surface 83 may also be made a curved surface by using a roller-shaped potential adjusting member 83. In this case, the roller-shaped potential adjusting member 8 may be rotatable, or may be a fixed and non-rotating device. In addition, this roller-shaped potential adjusting member 8 may be composed of, for example, a metal roller, but may also be composed of two or more materials similarly to that described in Example 1. For example, similar to the potential adjusting member 8 shown in FIG4 , a composition including a base and a surface layer is adopted, so that the surface layer constituting the contact surface 83 may be formed of a conductive material, and the base may be formed of a conductive material or a non-conductive material. In addition, for example, similar to the potential adjusting member 8 shown in FIG5 , the contact surface 83 may be formed of a conductive nonwoven fabric.

[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 their detailed description will be omitted.

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

The composition of the potential adjustment member 8 in this embodiment will be described. Part (a) of Figure 19 is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) of the potential adjustment member 8 in this embodiment. In addition, part (b) of Figure 19 is a perspective view of the potential adjustment member 8 in this embodiment. In this embodiment, the potential adjustment 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 of the 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 adjustment power supply 80 is connected to the contact member 89. In addition, in this embodiment, the end of the support member 88 on the primary transfer roller 15 side relative 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 relative to the feeding direction. The purpose of providing the protruding portion 88 a is to prevent discharge in the space between the primary transfer roller 15 and the contact member 89 .

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 supporting member 88 toward the intermediate transfer belt 6, so as to reliably contact the intermediate transfer belt 6 even when the supporting member 88 is provided with the protruding portion 88a. 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 end portions with respect to the longitudinal direction thereof by a pressurizing spring 87 constituted of a compression coil spring (which is an urging member) as an urging member. In this embodiment, this pressurizing spring 87 is provided between the contact member 89 and the supporting member 88, and urges the contact member 89 in a direction toward the intermediate transfer belt 6 from its back surface (the surface opposite to the contact surface 83).

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

In addition, the supporting member 88 may be pressed toward the intermediate transfer belt 6 by an urging member as an urging part. For example, a configuration is adopted in which the supporting member 88 is pressed toward the inner peripheral surface of the intermediate transfer belt 6 by an urging member at each of its opposing portions with respect to the longitudinal direction thereof. Moreover, thereby, the contact member 89 may 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 supporting member 88.

Therefore, the image forming apparatus 1 includes an urging member 87 for urging the electrode member (contact member) 89 in a direction from the back side 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 urging member 87 can be constituted by using an elastically deformable spring, sponge, or nonwoven fabric.

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

[Other embodiments]

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

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

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

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

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

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 monochrome (white/black or monochrome) 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, on which it is relatively difficult to transfer a toner image in an intermediate transfer type image forming apparatus.

While the present 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 device, 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 the toner image is 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 the moving direction of the intermediate transfer belt and configured to transfer the toner image from the first image bearing member to 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 the moving direction of the intermediate transfer belt and configured to transfer the toner image from the second image bearing member to 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 contacting 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, In which, in a cross section perpendicular to the rotation axis of the first image bearing member, when the common tangent between the first transfer member on the intermediate transfer belt side and the second image bearing member 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 the intersection 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 so 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. An image forming device according to claim 1, wherein, in a cross section perpendicular to the direction of the rotation axis of the first image bearing member, in a vertical direction perpendicular to the direction along the common tangent between the first image bearing member and the second image bearing member, when the amount of entry of the contact portion into the straight line Q is 100%, the amount of entry of the contact portion into the straight line L is greater than 5% and less than 80%. 3. An image forming device according to claim 1, wherein, in a cross section perpendicular to the direction of the rotation axis of the first image bearing member, in a vertical direction perpendicular to the direction along the common tangent between the first image bearing member and the second image bearing member, when the amount of entry of the contact portion into the straight line Q is 100%, the amount of entry of the contact portion into the straight line L is greater than 10% and less than 50%. 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 surface. 6 . The image forming apparatus according to claim 1 , wherein the contact portion is a curved surface 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 5 mm or more and 50 mm or less. 8. An 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 greater 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 at 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 an urging member configured to urge 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, sponge, or nonwoven fabric.