Image forming apparatus

Abstract

In a configuration where a bias is applied to an electrode member positioned downstream of the primary transfer section, the instability of the intermediate transfer belt's movement is suppressed. [Solution] The image forming apparatus 1 comprises a photoreceptor 11, an intermediate transfer belt 6, a primary transfer member 15, an electrode member 8 provided on the inner circumferential surface side of the intermediate transfer belt 6 downstream of the primary transfer section N1 in the direction of movement of the intermediate transfer belt 6, and a power supply 80 that applies a voltage of the same polarity as the charging polarity of the photoreceptor 11 to the electrode member 8. The electrode member 8 is composed of a surface facing the inner circumferential surface of the intermediate transfer belt 6 and has a contact surface 83 having a contact area that can contact the inner circumferential surface of the intermediate transfer belt 6. The contact surface 83 is provided with a convex portion 81a that forms the contact area, and a concave portion 81b that is recessed in a direction away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a, and which forms a non-contact area that is away from the inner circumferential surface of the intermediate transfer belt 6 when the contact area contacts the intermediate transfer belt 6.

Description

[Technical Field]

[0001] The present invention relates to image forming apparatus such as photocopiers, printers, facsimile machines, or multifunction devices that have multiple functions among these, using electrophotographic or electrostatic recording methods. [Background technology]

[0002] Image forming devices such as color copiers, color printers, and color multifunction devices using electrophotography have become mainstream due to their advantages such as miniaturization of the device body and relatively easy compatibility with various recording materials. Image forming devices using the intermediate transfer method generally have a configuration comprising multiple photosensitive drums and an intermediate transfer belt. In this image forming device, toner images formed on the multiple photosensitive drums are sequentially electrostatically transferred onto the intermediate transfer belt in the primary transfer section. The toner images transferred onto the intermediate transfer belt are then electrostatically transferred onto a recording material such as paper in the secondary transfer section. When referring to the arrangement of components around the primary transfer section, upstream and downstream refer to the upstream and downstream directions of transport of the intermediate transfer belt unless otherwise specified.

[0003] In the image forming apparatus described above, the toner on the intermediate transfer belt tends to become charged due to discharge between the intermediate transfer belt and the photosensitive drum downstream of the primary transfer section. This increased charge on the intermediate transfer belt can make it difficult to transfer the toner to the recording material in the secondary transfer section. For example, a larger secondary transfer electric field required to transfer the toner to the recording material in the secondary transfer section can worsen the granularity of the image or make it difficult to uniformly transfer toner to embossed paper or other materials with uneven surfaces.

[0004] In Patent Document 1, a conductive contact plate is provided downstream of the primary transfer section and on the inner circumferential surface side of the intermediate transfer belt, and a bias of the same polarity as the charging polarity of the photosensitive drum is applied to this contact plate. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-57963 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] To suppress the increase in toner charge downstream of the primary transfer section as described above, it is effective to suppress discharge downstream of the primary transfer section. Furthermore, to suppress this discharge, it is effective to reduce the potential difference between the photosensitive drum after passing through the primary transfer section and the intermediate transfer belt. To achieve this, it is effective to place a conductive electrode member downstream of the primary transfer section and on the inner surface of the intermediate transfer belt, and to apply a bias to this electrode member with the same polarity as the charge polarity of the photosensitive drum.

[0007] However, when a relatively high bias is applied to the electrode member, the electrostatic attraction force between the intermediate transfer belt and the electrode member increases, which can cause the intermediate transfer belt to run unstably.

[0008] Therefore, an object of the present invention is to suppress instability in the running performance of the intermediate transfer belt in a configuration in which a bias is applied to an electrode member placed downstream of the primary transfer section. [Means for solving the problem]

[0009] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a photoreceptor capable of being charged to a predetermined polarity and carrying a toner image; a circumferentially movable intermediate transfer belt for transporting the toner image primary transferred from the photoreceptor to a recording material for secondary transfer; a primary transfer member that contacts the inner circumferential surface of the intermediate transfer belt to form a primary transfer section where the photoreceptor and the intermediate transfer belt come into contact, and to which a voltage is applied to transfer a toner image from the photoreceptor to the intermediate transfer belt in the primary transfer section; and an electrode member provided on the inner circumferential surface side of the intermediate transfer belt downstream of the primary transfer section in the direction of movement of the intermediate transfer belt. The image forming apparatus comprises a power supply that applies a voltage of the same polarity as the predetermined polarity to the electrode member, wherein the electrode member is composed of a surface facing the inner circumferential surface of the intermediate transfer belt and has a contact surface having a contact region that can contact the inner circumferential surface of the intermediate transfer belt, the contact surface having a convex portion that forms the contact region and a recess that is recessed in a direction away from the inner circumferential surface of the intermediate transfer belt relative to the convex portion, and which forms a non-contact region that is away from the inner circumferential surface of the intermediate transfer belt when the contact region contacts the intermediate transfer belt. [Effects of the Invention]

[0010] According to the present invention, in a configuration in which a bias is applied to an electrode member positioned downstream of the primary transfer section, it is possible to suppress instability in the running performance of the intermediate transfer belt. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus. [Figure 2] This is a schematic block diagram of the control system of an image forming apparatus. [Figure 3] These are schematic cross-sectional and perspective views of the potential regulating member. [Figure 4] This is a schematic cross-sectional view of another example of a potential regulating member. [Figure 5] This is a schematic cross-sectional view of another example of a potential regulating member. [Figure 6]It is a schematic cross-sectional view for explaining the arrangement of the potential regulating member. [Figure 7] It is a plan view and a cross-sectional view showing the surface shape of the potential regulating member of Example 1. [Figure 8] It is a plan view and a cross-sectional view showing the surface shape of the potential regulating member of Example 2. [Figure 9] It is a plan view and a cross-sectional view showing the surface shape of the potential regulating member of Example 3. [Figure 10] It is a plan view and a cross-section showing the surface shape of the potential regulating member of Example 4. [Figure 11] It is a plan view and a cross-sectional view showing the surface shape of the potential regulating member of Example 5. [Figure 12] It is a plan view and a cross-sectional view showing the surface shape of the potential regulating member of another example. [Figure 13] It is a schematic cross-sectional view near the primary transfer section for explaining the problem.

Mode for Carrying Out the Invention

[0012] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0013] [Example 1] 1. Overall Configuration and Operation of the Image Forming Apparatus First, the overall configuration 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 adopting an intermediate transfer method, which can form a full-color image on a sheet-like recording material S using an electrophotographic method.

[0014] The image forming apparatus 1 comprises an image forming unit 2, a control unit 3, a recording material S feeding unit 4, and a recording material S discharge unit 5. Inside the image forming apparatus 1, there is also a temperature sensor 71 (Figure 2) capable of detecting the internal temperature and a humidity sensor 72 (Figure 2) capable of detecting the internal humidity. The image forming apparatus 1 can form an image on the recording material S based on image information (image signals) acquired by a document reader (not shown) provided in or connected to the image forming apparatus 1. Furthermore, the image forming apparatus 1 can form an image on the recording material S based on image information (image signals) from external devices (not shown) such as a personal computer (host device), digital camera, or smartphone connected to the image forming apparatus 1. The recording material (transfer material, recording medium, sheet) S is one on which an image is formed using toner. Specific examples of recording material S include plain paper, cardboard, gloss-coated paper, matte-coated paper, embossed paper, or substitutes for plain paper such as synthetic resin sheets (synthetic paper) or overhead projector sheets (resin film). Here, recording material S is sometimes referred to as "paper" (e.g., "paper," "embossed paper," "high-resistance paper"), but even in that case, recording material S includes materials other than paper or materials that include materials other than paper.

[0015] The image forming unit 2 forms an image on the recording material S supplied from the feeding unit 4 based on image information. The image forming unit 2 includes image forming units 10y, 10m, 10c, and 10k, toner bottles 18y, 18m, 18c, and 18k, exposure devices 13y, 13m, 13c, and 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 each form toner images of yellow (y), magenta (m), cyan (c), and black (k), respectively. In addition, elements with the same or corresponding functions or configurations provided for each color may be described collectively by omitting the suffixes y, m, c, and k that indicate that they are elements for any of the colors. Furthermore, the image forming apparatus 1 can also form monochrome images, such as a monochrome black image, or multicolor images using image forming units 10 for several of the desired single colors or four colors.

[0016] The image forming unit 10 has a photosensitive drum 11, which is a drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) that serves as an image carrier. The image forming unit 10 also has a charging roller 12, which is a roller-shaped charging member that serves as a charging means. The image forming unit 10 also has a developing device 14 as a developing means. The image forming unit 10 also has a pre-exposure device 16 as a static elimination means. The image forming unit 10 also has a drum cleaning device 17 as a photoreceptor cleaning means. The image forming unit 10 forms a toner image on the intermediate transfer belt 6, which will be described later.

[0017] The photosensitive drum 11 is movable (rotatable) and carries an electrostatic image (electrostatic latent image) or toner image. In this embodiment, the photosensitive drum 11 is a drum-type photoreceptor equipped with a negatively charged organic photoreceptor (OPC), and has an outer diameter of 30 mm. This photosensitive drum 11 can be charged to a negative polarity as a predetermined polarity. In this embodiment, the photosensitive drum 11 has an aluminum cylinder as a substrate and a surface layer (photosensitive layer) formed on its surface. In this embodiment, the surface layer has three layers, which are coated and laminated on the substrate in the following order: an undercoat layer, a photocharge generation layer, and a charge transport layer. When the image forming operation is started, the photosensitive drum 11 is rotated by a drive motor (not shown) as a driving means at a predetermined peripheral speed (process speed) in the direction of arrow R1 in the figure (counterclockwise direction).

[0018] 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 rotates in conjunction with the rotation of the photosensitive drum 11. A charging power supply 73 (Figure 2), which serves as a means for applying a charging voltage (charging voltage application unit), is connected to the charging roller 12. During the charging process, the charging power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 12.

[0019] The surface of the charged photosensitive drum 11 is scanned and exposed by the exposure device 13 based on image information, and 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 laser light according to the separated color image information output from the control unit 3 and scans and exposes the surface (outer surface) of the photosensitive drum 11.

[0020] The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by the toner supplied by the developing device 14, and a toner image (toner image, developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 is a two-component developing device that uses a two-component developer comprising toner (non-magnetic toner particles) and carrier (magnetic carrier particles) as the developer. The developing container (developing container body) 14b of the developing device 14 contains the two-component developer, and an amount of toner corresponding to the consumed toner is replenished from the toner bottle 18. The developing device 14 has a developing sleeve 14a as a developing member (developer carrier). The developing sleeve 14a is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). Inside the developing sleeve 14a, a magnet roller (not shown), which is a roller-shaped magnet serving as a magnetic field generating means (magnetic field generating member), is fixed to the developing container 14b so as not to rotate. The developing sleeve 14a carries a two-component developer and transports it to the developing area facing the photosensitive drum 11. In the developing area, toner moves from the two-component developer on the developing sleeve 14a to the image portion of the electrostatic image on the photosensitive drum 11 and adheres to it. A developing power supply 74 (Figure 2), which serves as a developing voltage application means (developing voltage application unit), is connected to the developing sleeve 14a. During development, the developing power supply 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 14a. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 11 (negative polarity in this embodiment) adheres to the exposed area (image portion) on the photosensitive drum 11, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse developing method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0021] An intermediate transfer unit 20 is positioned opposite four photosensitive drums 11y, 11m, 11c, and 11k. The intermediate transfer unit 20 has an intermediate transfer belt 6, which is an endless belt that serves as an intermediate transfer body. The intermediate transfer belt 6 is wrapped around and stretched over a plurality of tension rollers: drive rollers 21, tension rollers 22, and secondary transfer inner rollers 23. The intermediate transfer belt 6 is movable (rotatable, circumferential) carrying the toner image. The intermediate transfer belt 6 is driven by a drive motor (not shown) which rotates the drive rollers 21, and rotates (circumferentially moves) in the direction of arrow R2 in the figure (clockwise) at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drum 11. The tension rollers 22 control the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 is subjected to a biasing force from a tension spring (not shown) composed of a compression coil spring, which is a biasing member acting as a biasing means. This force pushes the intermediate transfer belt 6 from the inner circumferential surface (back side) to the outer circumferential surface (front side). This force applies a tension of approximately 2 to 5 kgf to the intermediate transfer belt 6 in its conveying direction (process progression direction, movement direction). The secondary transfer inner roller 23, together with the secondary transfer outer roller 25 (described later), constitutes the secondary transfer apparatus 26. On the inner circumferential surface side of the intermediate transfer belt 6, primary transfer rollers 15y, 15m, 15c, and 15k, which are roller-type primary transfer members acting as primary transfer means, are arranged corresponding to each photosensitive drum 11y, 11m, 11c, and 11k. In this embodiment, the primary transfer roller 15 is positioned opposite the photosensitive drum 11 and sandwiches the intermediate transfer belt 6 between itself and the photosensitive drum 11. The primary transfer roller 15 is pressed toward the photosensitive drum 11 and comes into contact with the photosensitive drum 11 via the intermediate transfer belt 6, forming a primary transfer portion (primary transfer nip portion) N1, which is the contact point between the photosensitive drum 11 and the intermediate transfer belt 6.

[0022] The toner image formed on the photosensitive drum 11 is transferred (primary transfer) to the rotating intermediate transfer belt 6 in the primary transfer unit N1 by the action of the primary transfer roller 15. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are sequentially superimposed on the intermediate transfer belt 6 in a multiple transfer process. A primary transfer power supply 75 (Figure 2), which serves as a primary transfer voltage application means (primary transfer voltage application unit), is connected to the primary transfer roller 15. During primary transfer, the primary transfer power supply 75 applies a primary transfer voltage (primary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, to the primary transfer roller 15. As a result, the toner image formed with negatively polarized toner on the photosensitive drum 11 is primary transferred to the intermediate transfer belt 6. The primary transfer power supply 75 is connected to a voltage detection sensor 75a (Figure 2), which serves as a voltage detection means (voltage detection unit) for detecting its output voltage, and a current detection sensor 75b (Figure 2), which serves as a current detection means (current detection unit) for detecting its output current. In this embodiment, for example, a primary transfer voltage of about 1 to 2 [kV] is applied to the primary transfer roller 15 (regarding the numerical range, "~" indicates a range that includes the numbers before and after it. The same applies hereinafter.). In this embodiment, the primary transfer voltage is controlled to a constant voltage. In this embodiment, the primary transfer power supplies 75y, 75m, 75c, and 75k are provided independently for each of the primary transfer rollers 15y, 15m, 15c, and 15k. In this embodiment, the primary transfer voltage applied to each of the primary transfer rollers 15y, 15m, 15c, and 15k can be controlled individually.

[0023] In this embodiment, the primary transfer roller 15 has a core metal and an elastic layer of ion-conductive foamed rubber (NBR rubber) formed around the core metal. The outer diameter of the primary transfer roller 15 is, for example, 15 to 20 mm. The primary transfer roller 15 has an electrical resistance value of 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of [Ω] (N / N measurement at 23°C, 50%RH, 2kV applied) can be suitably used.

[0024] In this embodiment, the intermediate transfer belt 6 is an endless belt having a two-layer structure in which a base layer and a surface layer are laminated in that order from the inner circumferential surface to the outer circumferential surface. The material constituting the base layer is a resin such as polyimide or polycarbonate, and a material containing an appropriate amount of carbon black as an antistatic agent can be suitably used. The thickness of the base layer is, for example, 0.05 to 0.15 [mm]. The material constituting the surface layer can be, for example, CR rubber imparted with carbon black for conductivity, or the like. The thickness of the surface layer is, for example, 0.200 to 0.300 [mm]. In this embodiment, the volume resistivity of the intermediate transfer belt 6 is 5 × 10⁻⁶. 8 ~1 × 10 14 The resistance is [Ω·cm] (23℃, 50%RH). In this embodiment, the intermediate transfer belt 6 has a two-layer structure, but it may also have a single-layer structure of the same material as the base layer described above. The surface layer may also be a resin coating layer with a thickness of about 0.002 to 0.01 [mm] containing a resin such as fluororesin. Furthermore, the intermediate transfer belt 6 may have a multilayer structure of three or more layers.

[0025] A secondary transfer outer roller 25, which is a roller-type secondary transfer member serving as a secondary transfer means, is positioned on the outer circumferential surface of the intermediate transfer belt 6. The secondary transfer outer roller 25, as a secondary transfer member, together with the secondary transfer inner roller 23, which serves as a counter member (counter electrode), constitutes the secondary transfer apparatus 26. The secondary transfer outer roller 25 is pressed toward the secondary transfer inner roller 23 and contacts the secondary transfer inner roller 23 via the intermediate transfer belt 6, forming a secondary transfer section (secondary transfer nip section) N2, which is the contact point between the intermediate transfer belt 6 and the secondary transfer outer roller 25. The toner image formed on the intermediate transfer belt 6 is transferred (secondary transfer) in the secondary transfer section N2 to the recording material S, which is being transported sandwiched between the intermediate transfer belt 6 and the secondary transfer outer roller 25, by the action of the secondary transfer apparatus 26. A secondary transfer power supply 76 (Figure 2), which serves as a secondary transfer voltage application means (secondary transfer voltage application section), is connected to the secondary transfer outer roller 25. During secondary transfer, the secondary transfer power supply 76 applies a secondary transfer voltage (secondary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the secondary transfer outer roller 25 of the normal charging polarity of the toner. As a result, the toner image formed by the negatively polarized toner on the intermediate transfer belt 6 is secondary transferred onto the recording material S. The secondary transfer power supply 76 is connected to a voltage detection sensor 76a (Figure 2) as a voltage detection means (voltage detection unit) for detecting its output voltage, and a current detection sensor 76b (Figure 2) as a current detection means (current detection unit) for detecting its output current. The core metal of the secondary transfer inner roller 23 is connected to ground potential. In this embodiment, for example, a secondary transfer voltage of about 1 to 6.5 [kV] is applied to the secondary transfer outer roller 25, and a secondary transfer current of about 15 to 100 [μA] flows through the secondary transfer unit N2, thereby secondary transferring the toner image on the intermediate transfer belt 6 onto the recording material S. In this embodiment, the secondary transfer voltage is controlled to a constant voltage. Alternatively, a secondary transfer voltage, which is a DC voltage with the same polarity as the normal charging polarity of the toner, may be applied from the secondary transfer power supply 76 to the secondary transfer inner roller 23, which serves as a secondary transfer member, thereby connecting the secondary transfer outer roller 25, which serves as a counter member, to ground potential.

[0026] The recording material S is transported from the feeding unit 4 towards the secondary transfer unit N2 in parallel with the toner image formation operation on the intermediate transfer belt 6. The recording material S is housed in a cassette 41, which serves as the recording material housing of the feeding unit 4. The recording material S housed in the cassette 41 is separated one sheet at a time by feeding rollers 42 and other feeding members of the feeding unit 4 and fed out of the cassette 41. This recording material S is then transported by transport rollers 43 and other transport members of the feeding unit 4 to a register roller (pair of register rollers) 19, which serves as a transport member in the transport path 44 of the recording material S. Then, the recording material S is transported to the secondary transfer unit N2 by the register roller 19, in timing with the toner image on the intermediate transfer belt 6. Although only one cassette 41 is shown in Figure 1, the image forming apparatus 1 may have multiple cassettes 41. Furthermore, the feeding unit 4 may also be configured to feed recording material S from a recording material storage unit (recording material placement unit) separate from the cassette 41, such as a manual feed tray.

[0027] In this embodiment, the secondary transfer outer roller 25 has a core metal and an elastic layer of ion-conductive foamed rubber (NBR rubber) formed around the core metal. The outer diameter of the secondary transfer outer roller 25 is, for example, 20 to 25 mm. Furthermore, the electrical resistance value of the secondary transfer outer roller 25 is 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of [Ω] (N / N measurement at 23°C, 50%RH, 2kV applied) can be suitably used.

[0028] The recording material S onto which the toner image has been transferred is transported to a fixing device 27, which serves as a fixing means. The fixing device 27 includes a fixing roller 27a and a pressure roller 27b. The fixing roller 27a has a built-in heater as a heating means. The pressure roller 27b presses against the fixing roller 27a to form a fixing section (fixing nip section). The fixing device 27 heats and pressurizes the recording material S, which carries the unfixed toner image, by sandwiching it between the fixing roller 27a and the pressure roller 27b and transporting it, thereby fixing (melting and solidifying) the toner image onto the recording material S. The temperature of the fixing roller 27a (fixing temperature) is detected by a fixing temperature sensor 77 (Figure 2). The recording material S with the fixed toner image is transported by a discharge roller 51, etc., in the discharge section 5 and discharged (output) from a discharge port (not shown) onto a discharge tray 52 located outside the main body 1a of the image forming apparatus 1.

[0029] The surface of the photosensitive drum 11 after primary transfer is destaticized by the pre-exposure device 16. Furthermore, toner remaining on the photosensitive drum 11 during primary transfer (primary transfer residue toner) that was not transferred to the intermediate transfer belt 6 is removed and collected by the drum cleaning device 17. In this embodiment, the drum cleaning device 17 uses a cleaning blade as a cleaning member to scrape the primary transfer residue toner from the surface of the rotating photosensitive drum 11 and collect it in a collection container (not shown). The cleaning blade is a plate-shaped member that contacts the photosensitive drum 11 with a predetermined pressing force. The cleaning blade contacts the surface of the photosensitive drum 11 in a counter-direction relative to the rotation direction of the photosensitive drum 11, with its free end facing upstream in the rotation direction of the photosensitive drum 11. Additionally, any deposits such as toner remaining on the intermediate transfer belt 6 during secondary transfer (secondary transfer residue toner) that was not transferred to the recording material S are removed and collected by the belt cleaning device 24, which serves as an intermediate transfer body cleaning means.

[0030] The image forming unit 10 may be integrally formed as a detachable cartridge (process cartridge) attached to the main body 1a of the image forming apparatus 1. In this embodiment, the intermediate transfer unit 20 is composed of an intermediate transfer belt 6, tension rollers for the intermediate transfer belt 6, each primary transfer roller 15, a belt cleaning device 24, and each potential regulating member 8, which will be described later. The intermediate transfer unit 20 may be integrally formed as detachable from the main body 1a of the apparatus.

[0031] 2. Control Configuration Next, the configuration of the control system of the image forming apparatus 1 in this embodiment will be described. Figure 2 is a block diagram showing the schematic configuration of the control system of the image forming apparatus 1 in this embodiment.

[0032] The image forming apparatus 1 is equipped with a control unit 3 (control circuit) as a control means. The control unit 3 is composed of a CPU 31 as an arithmetic processing means, a ROM 32 and RAM 33 as storage means, and an input / output circuit (I / F) (not shown) that performs signal input and output between the control unit 3 and external devices. The ROM 32 stores programs that control each part of the image forming apparatus 1. The RAM 33 temporarily stores control-related data. The CPU 31 is a microprocessor that oversees the overall control of the image forming apparatus 1 and is the main component of the system controller. The CPU 31 is connected to each part, such as the feeding unit 4, the image forming unit 2, and the ejection unit 5, and exchanges signals with these parts and controls the operation of these parts. The ROM 32 stores image forming control sequences for forming images on the recording material S.

[0033] The control unit 3 is connected to, for example, a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, a secondary transfer power supply 76, and a potential regulating power supply 80 (described later), and these are each controlled by signals from the control unit 3. Although not shown in the figures, in this embodiment, the charging power supply 73, the developing power supply 74, the primary transfer power supply 75, and the potential regulating power supply 80 are each provided independently for each image forming unit 10. The control unit 3 is also connected to a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, and a fixing temperature sensor 77. Signals (information) indicating the detection results of each sensor are input to the control unit 3. The control unit 3 is also connected to an operation unit 70. The operation unit 70 has an input unit consisting of operation buttons (keys) as an input means, and a display unit 70a consisting of a liquid crystal panel (display) as a display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. Users and service personnel can operate the operation unit 70 to cause the image forming apparatus 1 to execute a job (a series of operations that form and output an image on one or more recording materials S with a single start command). The control unit 3 receives signals from the operation unit 70 and operates various devices of the image forming apparatus 1. The image forming apparatus 1 can also execute jobs in response to signals from external devices such as a personal computer, rather than from the operation unit 70.

[0034] 3. Overview of the problem and solutions Next, the problems in this embodiment will be described. For convenience, unless otherwise specified, the magnitude (high or low) of voltage and potential will refer to the magnitude (high or low) when compared in absolute value. Furthermore, regarding the arrangement of the primary transfer unit N1, photosensitive drum 11, primary transfer roller 15, and the potential regulating member 8 described later, unless otherwise specified, upstream and downstream will refer to upstream and downstream in the transport direction (process progression direction, movement direction) of the intermediate transfer belt 6.

[0035] As mentioned above, in the intermediate transfer type image forming apparatus 1, it is difficult to uniformly transfer toner images to, for example, embossed paper with an uneven surface. Embossed paper is paper (fancy paper) that has patterns created by raising or pressing on the surface of the paper. In particular, transferring toner images to the recesses of embossed paper is difficult because a gap is created between the intermediate transfer belt 6 and the embossed paper in the secondary transfer section N2, requiring a relatively large transfer electric field. Furthermore, if the secondary transfer electric field is increased to improve the transferability of toner images to the recesses of embossed paper, if the transfer electric field becomes too large in areas other than the recesses, transfer defects may occur where toner is not partially transferred to halftone images, etc.

[0036] The toner on the intermediate transfer belt 6 experiences an increase in charge due to a discharge between the intermediate transfer belt 6 and the photosensitive drum 11 downstream of the primary transfer section N1. More specifically, after receiving the above discharge, the distribution of the toner's charge tends to broaden compared to the distribution during development, and the average value of the charge tends to increase. Furthermore, because the charge increases in this way, the mirroring force between the intermediate transfer belt 6 and the toner increases, making it more difficult to transfer the toner image to the recording material S in the secondary transfer section N2, and thus making it more difficult to transfer the toner image to the recesses of the embossed paper.

[0037] By suppressing the above-mentioned discharge and preventing an increase in the charge amount of toner on the intermediate transfer belt 6, the transferability of toner images to recording materials S, such as embossed paper, which are relatively difficult to transfer toner images to, can be improved. To suppress the above-mentioned discharge, it is effective to reduce the potential difference between the photosensitive drum 11 after passing through the primary transfer section N1 and the intermediate transfer belt 6. To achieve this, it is effective to place a potential regulating member 8, which is an electrode member, on the inner circumferential surface (back surface) side of the intermediate transfer belt 6 downstream of the primary transfer section N1, and to apply a voltage with the same polarity as the charge polarity of the photosensitive drum 11 to this potential regulating member 8. In particular, by placing the potential regulating member 8 in contact with the inner circumferential surface of the intermediate transfer belt 6 and applying a voltage with the same polarity as the charge polarity of the photosensitive drum 11 to this potential regulating member 8, the above-mentioned discharge can be suppressed more effectively.

[0038] Furthermore, the above-mentioned discharge often occurs in a range of approximately 0.3 to 1.5 mm downstream from the primary transfer section N1. In contrast, by applying a voltage with the same polarity as the charge polarity of the photosensitive drum 11 to the potential regulating member 8, it is believed that 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 regulating member 8. Moreover, in the transport direction of the intermediate transfer belt 6, the effect of suppressing the above-mentioned discharge is greater when the potential regulating member 8 is in contact with the intermediate transfer belt 6 over a wide surface area than when it is in contact with the intermediate transfer belt 6 at a point (line) area. In addition, by making the potential regulating member 8 in contact with the intermediate transfer belt 6 over a surface area, the contact state between the intermediate transfer belt 6 and the potential regulating member 8 can be stabilized. This is thought to be because an electrostatic attraction force acts between the intermediate transfer belt 6 and the potential regulating member 8. Therefore, it is more preferable to make the potential regulating member 8 in surface contact with the intermediate transfer belt 6.

[0039] Here, surface contact (contact across a surface) does not mean only when the entire surface of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 (the surface facing the inner circumferential surface of the intermediate transfer belt 6 and having a contact area capable of contacting the inner circumferential surface) is in continuous contact. Surface contact (contact across a surface) also includes cases where the contact area is reduced by an uneven surface shape, as will be explained in more detail later. In other words, surface contact (contact across a surface) does not include cases where contact is made only linearly in a direction intersecting the transport direction of the intermediate transfer belt 6 within a range narrower than the contact width (approximately 5 to 50 mm), as will be explained in more detail later. Therefore, surface contact (contact across a surface) includes not only cases where substantially the entire area is in continuous contact within the contact width region, as will be explained in more detail later, but also cases where the area capable of contacting the inner circumferential surface of the intermediate transfer belt 6 (contact area), formed by the uneven shape described later, is distributed substantially uniformly within the contact width region. Furthermore, as will be described later, this also includes cases where a nonwoven fabric or the like is provided on the contact surface 83 having an uneven shape, and a large number of contact points are distributed within the region of the aforementioned contact width.

[0040] Furthermore, in order to effectively suppress discharge downstream of the primary transfer section N1, it is desirable to bring the potential regulating member 8 closer to the primary transfer section N1 and to increase the bias of the same polarity as the charge polarity of the photosensitive drum 11 applied to the potential regulating member 8.

[0041] In other words, it is desirable that the potential regulating member 8 be in surface contact with the inner circumferential surface of the intermediate transfer belt 6, as close as possible to the primary transfer section N1, and that a relatively high bias of the same polarity as the charging polarity of the photosensitive drum 11 be applied.

[0042] As described above, applying a bias to the potential regulating member 8 causes the intermediate transfer belt 6 to be electrostatically attracted to the potential regulating member 8. Furthermore, the higher the bias applied to the potential regulating member 8, the greater the electrostatic attraction between the intermediate transfer belt 6 and the potential regulating member 8, which reduces the sliding properties between the intermediate transfer belt 6 and the potential regulating member 8 and tends to make the running performance of the intermediate transfer belt 6 unstable. In other words, if the electrostatic attraction between the potential regulating member 8 and the intermediate transfer belt 6 is strong during the image formation operation (while the intermediate transfer belt 6 is running), the running performance of the intermediate transfer belt 6 may decrease. As shown in Figure 13, the intermediate transfer belt 6 may slacken upstream of the primary transfer section N1, starting from the region where the potential regulating member 8 and the intermediate transfer belt 6 are electrostatically attracted (dotted line in the figure). As a result, for example, gap discharge may occur between the photosensitive drum 11 and the intermediate transfer belt 6, causing the polarity of some of the toner in the toner image to reverse and preventing it from being transferred to the intermediate transfer belt 6, potentially resulting in "image white spots."

[0043] In contrast, in this embodiment, the surface shape of the surface of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 (the surface that faces the inner circumferential surface of the intermediate transfer belt 6 and has a contact area that can contact the inner circumferential surface) is made into an uneven surface shape. It was found that by reducing the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6, the electrostatic attraction force between the potential regulating member 8 and the intermediate transfer belt 6 can be suppressed, thereby suppressing a decrease in the running performance of the intermediate transfer belt 6.

[0044] 4. Potential regulating member Next, the configuration of the potential regulating member 8 in this embodiment will be described.

[0045] As shown in Figure 1, in this embodiment, the image forming apparatus 1 has potential regulating members 8y, 8m, 8c, and 8k, which are electrode members, positioned downstream of each primary transfer section N1y, N1m, N1c, and N1k, in contact with the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for each primary transfer section N1y, N1m, N1c, and N1k are substantially identical in configuration.

[0046] The shape of the potential regulating member 8 in this embodiment will now be described. Figure 3(a) is a schematic cross-sectional view of the potential regulating member 8 in this embodiment (a cross-section approximately perpendicular to the rotation axis direction of the photosensitive drum 11), and Figure 3(b) is a schematic perspective view of the potential regulating member 8.

[0047] In this embodiment, the potential regulating member 8 has a planar first portion 81 that is arranged along the width direction of the intermediate transfer belt 6 (a direction substantially perpendicular to the transport direction and substantially parallel to the rotation axis direction of the photosensitive drum 11). In this embodiment, the potential regulating member 8 also has a planar second portion 82 that is arranged along the width direction of the intermediate transfer belt 6 and extends in a direction that intersects (substantially perpendicular in this embodiment) with the plane of the first portion 81. In this embodiment, the surface of the first portion 81 of the potential regulating member 8 that faces the intermediate transfer belt 6 constitutes a contact surface 83 that contacts the inner circumferential surface of the intermediate transfer belt 6 (a surface that faces the inner circumferential surface of the intermediate transfer belt 6 and has a contact area that can contact the inner circumferential surface). In this embodiment, the contact surface 83 of the potential regulating member 8 is substantially planar. However, as will be described in detail later, in this embodiment, the contact surface 83 of the potential regulating member 8 is provided with an uneven shape. In other words, in this embodiment, the first portion 81 that constitutes the contact surface 83 of the potential regulating member 8 is a flat plate. Thus, in this embodiment, the potential regulating member 8 is composed of a member with a cross-section that is substantially L-shaped and substantially perpendicular to the rotation axis direction of the photosensitive drum 11.

[0048] Here, in a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, the upstream end of the contact surface 83 is defined as "A (or upstream end A)," and the downstream 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 end of the potential regulating member 8, and the downstream end B of the contact surface 83 corresponds to the downstream end of the potential regulating member B. As described above, in order to more effectively suppress discharge between the intermediate transfer belt 6 and the photosensitive drum 11 by the action of the electric field formed in the space between the photosensitive drum 11 and the potential regulating member 8, it is preferable to make the potential regulating member 8 in surface contact with the intermediate transfer belt 6. From this viewpoint, the length between line segments A and B, that is, the "contact width," which is the length of the contact surface 83 in the conveying direction of the intermediate transfer belt 6, is preferably 5 [mm] or more. The longer the length between line segments A and B, the greater the effect of suppressing the discharge, but if it is made too long, it may become difficult to make the potential regulating member 8 stably contact the intermediate transfer belt 6 due to the influence of part precision, etc. The length between line segments A and B is often sufficient at 50 mm or less, and is typically 30 mm or less. In other words, the length between line segments A and B is preferably around 5 to 50 mm, and is typically around 5 to 30 mm. From another perspective, the length between line segments A and B is often sufficient at half the distance between adjacent photosensitive drums 11 in a cross section approximately perpendicular to the rotation axis direction of the photosensitive drum 11. In this embodiment, a potential regulating member 8 with a length between line segments A and B of 25 mm is used. In this embodiment, the distance between the photosensitive drums 11 in a cross section approximately perpendicular to the rotation axis direction of the photosensitive drum 11 is approximately 100 mm.

[0049] A potential regulating power supply 80, which serves as a potential regulating voltage application means (potential regulating voltage application unit), is connected to the potential regulating member 8. In this embodiment, the potential regulating power supply 80 is connected to the second portion 82 of the potential regulating member 8. During the primary transfer in the image forming operation, at least, a potential regulating voltage (potential regulating bias), which is a DC voltage with the same polarity as the charge polarity of the photosensitive drum 11, is applied to the potential regulating member 8 by the potential regulating power supply 80. The primary transfer is, more specifically, the period during which the primary transfer voltage is applied, and even more specifically, the period during which the image region (the region on which the toner image can be transferred) on the intermediate transfer belt 6 passes through the primary transfer unit N1. This makes it possible to suppress discharge between the intermediate transfer belt 6 and the photosensitive drum 11 downstream of the primary transfer unit N1. In this embodiment, the potential regulating voltage is a DC voltage with negative polarity. Furthermore, in the configuration of this embodiment, the potential limiting voltage is preferably around -500 to -8000 [V], more preferably around -1000 to -5000 [V], and typically around -1000 to -3000 [V].

[0050] The potential regulating member 8 is a member that is long in the width direction of the intermediate transfer belt 6. Preferably, the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction (along the width direction of the intermediate transfer belt 6) is longer than the maximum image width in the width direction of the intermediate transfer belt 6. The maximum image width is the length of the image area of ​​the largest image that can be formed by the image forming apparatus 1 in the width direction of the intermediate transfer belt 6. In this embodiment, the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction is longer than the above-mentioned maximum image width and is also longer than the width of the portion of the primary transfer roller 15 that contacts the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6. In other words, in this embodiment, both the range of the above-mentioned maximum image width and the range of the width of the portion of the primary transfer roller 15 that contacts the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6 are within the range of the longitudinal length of the contact surface 83 of the potential regulating member 8. As a result, regardless of the length of the toner image transferred to the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6, the effect of suppressing the increase in the charge amount of toner on the intermediate transfer belt 6 by suppressing the discharge described above can be obtained. On the other hand, in this embodiment, the longitudinal length of the potential regulating member 8 is shorter than the width of the intermediate transfer belt 6. In other words, in this embodiment, the range of the longitudinal length of the potential regulating member 8 is within the range of the width of the intermediate transfer belt 6. This makes it possible to suppress discharge between the potential regulating member 8 and surrounding members of the intermediate transfer belt 6, which may occur if the longitudinal end of the potential regulating member 8 protrudes beyond the widthwise end of the intermediate transfer belt 6. As a result, the possibility that the effect of the potential regulating member 8 in suppressing discharge between the intermediate transfer belt 6 and the photosensitive drum 11 will be reduced can be reduced.

[0051] The potential regulating member 8 can be composed of, for example, only one conductive material (material). In this embodiment, the potential regulating member 8 is substantially composed of only a conductive metal such as SUS (stainless steel). More specifically, in this embodiment, the potential regulating member 8 is formed by bending a metal plate (sheet metal) such as SUS to form a first portion 81 and a second portion 82. The thickness of the sheet metal used for the potential regulating member 8 may be, for example, about 0.5 to 5 mm, typically about 1 to 3 mm. By performing such bending, the strength of the potential regulating member 8 can be increased. In this embodiment, neither the first portion 81 nor the second portion 82 of the potential regulating member 8 substantially deform in the usage state of the image forming apparatus 1. However, the present invention is not limited to such a mode, and the potential regulating member 8 may be composed of two or more materials.

[0052] Note that a conductive material (conductor) generally refers to a material (substance) having a resistivity of 10 -6 (Ω·m) or less, typically about 10 -8 (Ω·m). Also, a non-conductive material (insulator) generally refers to a material (substance) having a resistance value of 10 8 (Ω·m) or more, preferably 10 10 (Ω·m) or more. However, typically, an insulator has a resistivity of 10 16 (Ω·m) or less.

[0053] Figure 4 is a schematic cross-sectional view of another example of the potential regulating member 8 (a cross-section approximately perpendicular to the rotation axis direction of the photosensitive drum 11). For example, as shown in Figure 4, it can have a configuration having a base 84 having the same shape as the potential regulating member 8 shown in Figure 3, and a surface layer 85 provided on the surface of the base 84. The surface layer 85 that constitutes the contact surface 83 that contacts the intermediate transfer belt 6 and the connection part with the potential regulating power supply 80 is made of a conductive material, for example, metal or a conductive resin. The surface layer 85 may have the same configuration as the potential regulating member 8 shown in Figure 3. The base 84 may be made of a conductive material, but it may also be made of a non-conductive (electrically insulating) material, for example, a non-conductive resin. The base 84 and the surface layer 85 can be fixed together by any fixing means such as adhesive bonding or welding.

[0054] Figure 5 is a schematic cross-sectional view of yet another example of the potential regulating member 8 (a cross-section approximately perpendicular to the rotation axis direction of the photosensitive drum 11). For example, as shown in Figure 5, the contact surface 83 of the potential regulating member 8 that contacts the intermediate transfer belt 6 may be made of a conductive nonwoven fabric 86. In the example shown in Figure 5, the conductive nonwoven fabric 86 is provided on the contact surface 83 of the potential regulating member 8 with the configuration shown in Figure 4, but the conductive nonwoven fabric 86 may also be provided on the contact surface 83 of the potential regulating member 8 with the configuration shown in Figure 3. In other words, the potential regulating member 8 may be formed using different materials for the base to which the voltage is applied and the surface layer that contacts the inner circumferential surface of the intermediate transfer belt 6. The conductive nonwoven fabric 86 can be fixed by any fixing means such as a conductive adhesive. Alternatively, instead of the nonwoven fabric 86, felt or pile fabric (cut pile fabric (velvet, brush) or loop pile fabric (terry cloth)) made using conductive fibers, or a sponge (foamed elastic body) made using conductive rubber material may be used. In this way, by making the contact surface 83 of the potential regulating member 8 that contacts the intermediate transfer belt 6 out of a flexible or elastic material, the possibility of scratches occurring on the inner surface of the intermediate transfer belt 6 due to friction between the inner surface of the intermediate transfer belt 6 and the potential regulating member 8 can be reduced.

[0055] 5. Arrangement of potential regulating members Next, the arrangement of the potential regulating members 8 in this embodiment will be described. In this embodiment, the arrangement of the potential regulating members 8 provided for each primary transfer section N1y, N1m, N1c, and N1k is substantially the same. Figure 6 is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) illustrating the arrangement of the potential regulating members 8 provided between two adjacent primary transfer sections N1 in the transport direction of the intermediate transfer belt 6. As an example, Figure 6 shows the potential regulating members 8c provided between the cyan and black primary transfer sections N1c and N1k.

[0056] 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 this embodiment, the primary transfer roller 15 is positioned offset downstream of the photosensitive drum 11. In this embodiment, the offset amount X1 is 3 mm. The offset amount X1 is the distance between the rotation center of the photosensitive drum 11 and the rotation center of the primary transfer roller 15 in a direction along (approximately parallel to) the common tangent line on the side of the multiple photosensitive drums 11 that contact the intermediate transfer belt 6, in a cross-section approximately perpendicular to the rotation axis direction of the photosensitive drum 11. The primary transfer roller 15 may also be positioned without offset relative to the photosensitive drum 11, or it may be positioned offset upstream of the photosensitive drum 11.

[0057] Here, in order to explain the arrangement of the potential regulating member 8, we will assume the case where the potential regulating member 8 is removed. In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, we define the straight line L as the straight line through which the tensioned surface on the inner circumferential side of the intermediate transfer belt 6 downstream of the primary transfer section N1 passes when the potential regulating member 8 is absent. More specifically, this straight line L corresponds to the tensioned surface in a state where only the potential regulating member 8 is substantially removed from the configuration of the image forming apparatus 1 in the state of image forming operation (however, the photosensitive drum 11 and the intermediate transfer belt 6 are stopped). In other words, the straight line L corresponds to the tensioned surface in a state where the tensioned state of the intermediate transfer belt 6 is in a state where image forming is possible (primary transfer of the toner image from the photosensitive drum 11 to the intermediate transfer belt 6 is possible), and the intermediate transfer belt 6 is stopped (stationary). Furthermore, on the straight line L, the point where the inner surface of the intermediate transfer belt 6 separates from the tensioning member immediately upstream of the potential regulating member 8 is defined as "C (or upstream tensioning part C)," and the point where it separates from the tensioning member immediately downstream of the potential regulating member 8 is defined as "D (or downstream tensioning part D)." In Figure 6, the straight line L is schematically shown as approximately horizontal, but if the elastic layer of the primary transfer roller 15 deforms and the surface of the primary transfer roller 15 is lifted towards the photosensitive drum 11, the straight line L may be inclined downwards in the figure as it goes downstream.

[0058] In this embodiment, the tensioning member immediately upstream of the potential regulating member 8 is the primary transfer roller 15, and the upstream tensioning portion C is the position on the inner surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the primary transfer roller 15. However, the tensioning member immediately upstream of the potential regulating member 8 is not limited to the primary transfer roller 15. For example, if the primary transfer roller 15 is offset upstream of the photosensitive drum 11, the upstream tensioning portion C is the position on the inner surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the photosensitive drum 11.

[0059] In this embodiment, the tension member immediately downstream of the potential regulating member 8 is the photosensitive drum 11m, 11c, and 11k, which are located adjacent to the downstream side of the primary transfer sections N1y, N1m, and N1c for yellow, magenta, and cyan, respectively. The downstream tension member D is the position on the inner surface of the intermediate transfer belt 6 at the point where the intermediate transfer belt 6 separates from the photosensitive drum 11m, 11c, and 11k. However, the tension member immediately downstream of the potential regulating member 8 is not limited to the photosensitive drum 11. For example, if the primary transfer roller 15 is offset upstream of the photosensitive drum 11, the downstream tension member D is the position on the inner surface of the intermediate transfer belt 6 at the point where the intermediate transfer belt 6 separates from the primary transfer roller 15. In this embodiment, for the furthest downstream primary transfer section N1k for black, the tension member immediately downstream is the tension roller (tension roller in this embodiment) 22. The downstream tensioning section D is the position on the inner surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the tensioning roller 22.

[0060] Furthermore, for any primary transfer section N1, if there is another tension roller that restricts the orientation of the intermediate transfer belt 6 during the image forming operation as the tension member immediately downstream of the potential regulating member 8, the straight line L and the downstream tension section D are defined with respect to that tension roller. Also, even if a scraper or brush, rather than a tension roller, is in contact with the inner surface of the intermediate transfer belt 6 for purposes such as cleaning the inner surface of the intermediate transfer belt 6, it can be considered the immediately downstream tension member if it restricts the orientation of the intermediate transfer belt 6 during the image forming operation. Scrapers are generally composed of sheet-like or film-like materials.

[0061] As shown in Figure 6, the potential regulating member 8 is positioned downstream of the primary transfer section N1 and close to the primary transfer section 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. In this case, the closer the upstream end A is to the primary transfer section N1, the greater the effect of the potential regulating member 8 in suppressing discharge between the intermediate transfer belt 6 and the photosensitive drum 11. In this embodiment (Figure 6), the potential regulating member 8 is positioned downstream of the primary transfer section N1 such that the distance X2 from the primary transfer roller 15 to the upstream end A is about 8 [mm]. Here, distance X2 is the distance between the rotation center of the primary transfer roller 15 and the upstream end A in a direction along (approximately parallel to) the common tangent line on the side of the multiple photosensitive drums 11 that contact the intermediate transfer belt 6, in a cross-section approximately perpendicular to the rotation axis direction of the photosensitive drum 11. In other words, in this embodiment, in the direction along the common tangent, the distance from the rotation center of the primary transfer roller 15 to the upstream end A is smaller than the distance (radius) from the rotation center of the primary transfer roller 15 to the outer circumference of the primary transfer roller 15. Although not limited to this, the above distance X2 is preferably about 1 to 20 mm, and typically about 1 to 10 mm.

[0062] In this embodiment, the potential regulating member 8 is pressed against the inner circumferential surface of the intermediate transfer belt 6 at both ends in its longitudinal direction by compression springs 87, which are biasing members composed of compression coil springs. At this time, the contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 is positioned to penetrate further toward the photosensitive drum 11 than the straight line L. This allows the potential regulating member 8 to contact the intermediate transfer belt 6 more stably, even if undulation or vibration occurs in the intermediate transfer belt 6 during the image forming operation (while the intermediate transfer belt 6 is running). In this embodiment, the pressing force of the compression springs 87 is set (adjusted) so that the upstream end A and downstream end B of the contact surface 83 of the potential regulating member 8 penetrate approximately 0.5 [mm] toward the photosensitive drum 11 relative to the straight line L. By allowing the contact surface 83 of the potential regulating member 8 to penetrate the straight line L toward the photosensitive drum 11 in this manner, even if undulation or vibration occurs in the intermediate transfer belt 6 during the image forming operation (while the intermediate transfer belt 6 is running), the potential regulating member 8 can be more stably brought into surface contact with the intermediate transfer belt 6. Although not limited to this, the penetration depth of the contact surface 83 of the potential regulating member 8 toward the straight line L is preferably about 0.3 to 5 mm, more preferably about 0.5 to 3 mm, and typically about 0.5 to 1.0 mm. If this penetration depth is too small, it may become difficult to stably bring the potential regulating member 8 into contact with the intermediate transfer belt 6. Conversely, if this penetration depth is too large, it may become difficult to stably transport the intermediate transfer belt 6, or discharge between the intermediate transfer belt 6 and the photosensitive drum 11 may increase.

[0063] Here, in a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, the straight line passing through the upstream end A and the downstream end B of the contact surface 83 is defined as straight line M. In this case, it is preferable that straight line M does not intersect with the line segment CD in straight line L. This allows for more reliable surface contact between the intermediate transfer belt 6 and the potential regulating member 8 when the contact surface 83 of the potential regulating member 8 is planar. If straight line M intersects with the line segment CD in straight line L, it is possible that only one of the ends of the potential regulating member 8 on the upstream end A side or the end of the potential regulating member 8 on the downstream end B side can contact the inner circumferential surface of the intermediate transfer belt 6. In this case, it may become difficult to enhance the discharge suppression effect through surface contact. Also, in Figure 6, the potential regulating member 8 is arranged so that straight line M and straight line L are substantially parallel, but the potential regulating member 8 may be arranged so that straight line M is tilted relative to straight line L, as long as straight line M does not intersect with the line segment CD in straight line L.

[0064] Furthermore, the contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 is not limited to being flat. For example, the potential regulating member 8 may be made of a curved plate or the like, with a cross-section that is substantially perpendicular to the rotation axis direction of the photosensitive drum 11 and curved in a convex shape toward the photosensitive drum 11, and the contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 may be a curved surface that is convex toward the photosensitive drum 11. By making the contact portion (contact surface) of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 a curved shape, the stress when rubbing against the intermediate transfer belt 6 can be reduced. The contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 may also be curved by using a roller-shaped potential regulating member 8.

[0065] Furthermore, in this embodiment, embossed paper was given as an example of a recording material S that is relatively difficult to transfer toner images onto, but similar effects can be expected with recording materials with relatively high electrical resistance (high-resistance paper), such as synthetic paper mainly composed of synthetic resin or resin film.

[0066] 6. Surface shape of the potential regulating member Next, the surface shape of the potential regulating member 8 in this embodiment will be described further.

[0067] As mentioned above, when a relatively high bias is applied to the potential regulating member 8, the electrostatic attraction force between the intermediate transfer belt 6 and the potential regulating member 8 increases, which can cause the intermediate transfer belt 6 to run unstably. As a result, for example, gap discharge may occur upstream of the primary transfer section N1 (Figure 13), potentially causing "image whiteout."

[0068] The bias applied to the potential regulating member 8 can be determined, for example, as follows. The bias applied to the potential regulating member 8 is desirable to be highly effective in suppressing the increase in toner charge due to discharge downstream of the primary transfer unit N1. Furthermore, the bias applied to the potential regulating member 8 is desirable to be such that the primary transfer efficiency does not fall below a target value due to the current flowing from the primary transfer unit N1 to the potential regulating member 8, or the potential difference between the primary transfer voltage applied to the primary transfer unit N1 and the potential regulating voltage applied to the potential regulating member 8. The setting value of the bias applied to the potential regulating member 8 that can sufficiently suppress discharge downstream of the primary transfer unit N1 while maintaining primary transfer performance can be determined in advance through experiments or other means. The higher the bias, the higher the likelihood of the aforementioned gap discharge occurring.

[0069] Therefore, even when the bias applied to the potential regulating member 8 is relatively high, it is desirable to reduce the electrostatic attraction force generated between the intermediate transfer belt 6 and the potential regulating member 8 and stabilize the running performance of the intermediate transfer belt 6. In order to reduce the electrostatic attraction force generated between the intermediate transfer belt 6 and the potential regulating member 8, it is effective to reduce the contact area between the contact surface 83 of the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6.

[0070] Figure 7 is a schematic diagram showing the surface shape of the contact surface 83 of the potential regulating member 8 in this embodiment. The potential regulating member 8 has the configuration described with reference to Figure 3, and the first portion 81 is made of sheet metal with a thickness of approximately 2 mm. In Figure 7, the second portion 82 of the potential regulating member 8 is not shown, and a part of the contact surface 83 is schematically shown. Figure 7(a) is a schematic plan view of the contact surface 83 of the potential regulating member 8 as seen from the inner circumferential surface side of the intermediate transfer belt 6. Figure 7(b) is a schematic cross-sectional view (cross-sectional view AA in Figure 7(a)) of the potential regulating member 8 cut in the direction of transport of the intermediate transfer belt 6.

[0071] In Figure 7, with respect to the image forming apparatus 1 or its elements (such as the intermediate transfer belt 6), the front side of the paper in Figure 1 is referred to as the "front side," and the back side of the paper is referred to as the "rear side." The straight line connecting the front side and the rear side is assumed to be approximately parallel to the rotation axis direction of the photosensitive drum 11 (the width direction of the intermediate transfer belt 6). In Figure 7, the transport direction of the intermediate transfer belt 6 is defined as the "X direction" (the direction from downstream to upstream is the positive direction). In Figure 7, the width direction of the intermediate transfer belt 6 (the direction perpendicular to the X direction) is defined as the "Y direction" (the direction from front to rear is the positive direction). In Figure 7, the direction perpendicular to the X and Y directions is defined as the Z direction (the direction from the potential regulating member 8 side (bottom side) to the intermediate transfer belt 6 side (top side) is the positive direction). In Figures 9 to 12, which will be described later, the X, Y, and Z directions will be the same as described above.

[0072] In this embodiment, the contact surface 83 of the potential regulating member 8 has a convex portion 81a and a concave portion 81b. The convex portion 81a protrudes toward the inner circumferential surface of the intermediate transfer belt 6 relative to the concave portion 81b. The concave portion 81b is recessed (retracted) toward away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a. The concave portion 81b forms a non-contact region (separated region) that is separated from the inner circumferential surface of the intermediate transfer belt 6 when the contact region formed by the convex portion 81a on the contact surface 83 comes into contact with the inner circumferential surface of the intermediate transfer belt 6. For convenience, the concave portion 81b is shown as dots in Figure 7(a). The surface (top) of the convex portion 81a facing the inner circumferential surface of the intermediate transfer belt 6 constitutes a contact region that can contact the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the contact surface 83 of the potential regulating member 8 has a surface shape in which a plurality of independent convex portions 81a protrude toward the inner circumferential surface of the intermediate transfer belt 6. Here, this type of surface shape is also referred to as an "embossed shape." In this embodiment, the surface formed by the multiple protrusions 81a is substantially flat.

[0073] The reduction in contact area (%) is defined as the ratio of the reduction in contact area due to the provision of an uneven shape on the contact surface 83 of the potential regulating member 8 to the contact area of ​​the inner circumferential surface of the intermediate transfer belt 6 when the contact surface 83 of the potential regulating member 8 does not have an uneven shape. The contact area when the above uneven shape is not provided corresponds to the contact area when the area corresponding to the recess 81b is flush with the convex portion 81a. In this case, the reduction in contact area is preferably 10% or more, and more preferably 20% or more. If the reduction in contact area is too small, it becomes difficult to sufficiently suppress the electrostatic attraction force between the potential regulating member 8 and the intermediate transfer belt 6 and to prevent a decrease in the running performance of the intermediate transfer belt 6. On the other hand, the reduction in contact area is preferably 70% or less, and more preferably 50% or less. If the reduction in contact area is too large, the processing accuracy of the potential regulating member 8 (especially the contact area that can contact the inner circumferential surface of the intermediate transfer belt 6) may decrease. In other words, the reduction in contact area is preferably 10-70%, and more preferably 20-50%. Our studies have shown that by setting the reduction in contact area within this range, the electrostatic attraction force between the potential regulating member 8 and the intermediate transfer belt 6 can be sufficiently suppressed, thereby preventing a decrease in the running performance of the intermediate transfer belt 6. Furthermore, our studies have shown that within this range of contact area reduction, the effect of suppressing discharge between the photosensitive drum 11 and the intermediate transfer belt 11 can also be maintained. Here, the reduction in contact area can also be defined as the ratio of the area of ​​the non-contact region on the contact surface 83 to the area of ​​the contact surface 83 when viewed from the inner circumferential surface side of the intermediate transfer belt 6 in a direction substantially perpendicular to it. More specifically, the contact surface 83 of the potential regulating member 8 is a surface facing the inner circumferential surface of the intermediate transfer belt 6, and has a contact region capable of contacting the inner circumferential surface of the intermediate transfer belt 6.

[0074] In other words, the contact area (%), which is the ratio of the contact area when the contact surface 83 of the potential regulating member 8 has an uneven shape to the contact area when the contact surface 83 of the potential regulating member 8 has an uneven shape, is preferably 30-90%, and more preferably 50-80%. Here, the contact area can also be expressed as the ratio of the area of ​​the region on the contact surface 83 that can contact the inner surface of the intermediate transfer belt 6 (contact region) to the area of ​​the contact surface 83 when the contact surface 83 is viewed from the inner surface side of the intermediate transfer belt 6 in a direction substantially perpendicular to it.

[0075] The reduction in contact area is preferably within the above range, both over the entire contact surface 83 of the potential regulating member 8 and in a portion of the contact surface 83 of the potential regulating member 8. It is more preferable that the reduction in contact area over the entire area and the reduction in contact area in the portion of the area are approximately the same. Even if there is a variation in the reduction in contact area that is within the margin of error (for example, a variation of ±15% or less), this is included in the above-mentioned approximately the same. In other words, the reduction in contact area (%) can be defined as the ratio of the area of ​​the non-contact area in a unit area to the area of ​​the unit area when the contact surface 83 is viewed from the inner circumferential surface side of the intermediate transfer belt 6. And it is preferable that this reduction in contact area (%) is within the above range. The above-mentioned unit area is, for example, the front half and the rear half of the area in the width direction of the intermediate transfer belt 6 (the longitudinal direction of the potential regulating member 8). The above-mentioned unit area is, for example, each area when a predetermined shape (for example, a square with sides of 10 mm) is taken at an arbitrary position on the contact surface 83. In other words, even if the contact surface 83 of the potential regulating member 8 has an uneven shape, it is preferable that the contact area that can come into contact with the inner circumferential surface of the intermediate transfer belt 6 is distributed substantially uniformly.

[0076] In this embodiment, the contact surface 83 of the potential regulating member 8 has rows of multiple independent protrusions 81a arranged regularly (at approximately equal intervals in this embodiment) along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment), and rows of multiple rows arranged regularly (at approximately equal intervals in this embodiment) along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment). In this embodiment, each protrusion 81a in each row in the width direction of the intermediate transfer belt 6 is provided so as not to overlap with the protrusions 81a of adjacent rows in the conveying direction of the intermediate transfer belt 6. Furthermore, in this embodiment, when viewed from the inner circumferential surface side of the intermediate transfer belt 6, the protrusions 81a have a substantially square shape with sides extending along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment) and sides extending along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment). If the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 can be sufficiently reduced (preferably achieving the above-mentioned reduction in contact area), the size and spacing (pitch) of the protrusions 81a can be set as appropriate. The spacing (pitch) d1 of the protrusions 81a in the transport direction (and width direction) of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, in this embodiment, the surface (top) of the protrusion 81a that faces (contacts) the inner circumferential surface of the intermediate transfer belt 6 is flat. Also, the length (width) w1 of one side of the protrusion 81a when viewed from the inner circumferential surface side of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, the height h1 of the protrusion 81a can be, for example, about 0.05 to 1 mm, and in the configuration of this embodiment, it is preferable to be about 0.05 to 0.5 mm from the viewpoint of processing accuracy, etc. Furthermore, it is preferable that the height h1 of the protrusions 81a is substantially constant within the contact surface 83, that is, that a substantially flat surface is formed by the tops of the multiple protrusions 81a. Note that even if there is a variation of an error-sized amount (for example, a variation of ±15% or less) in the height of the protrusions (depth of the recesses), this is included in the condition that the height of the protrusions (depth of the recesses) is substantially constant. In addition, in this embodiment, the area of ​​the recess 81b is equal to the area other than the protrusions 81a, and its bottom surface does not have to be flat.

[0077] The uneven shape of the contact surface 83 of the potential regulating member 8 reduces the contact area between the potential regulating member 8 and the inner surface of the intermediate transfer belt 6.

[0078] In this embodiment, the protrusion 81a has a substantially square shape when viewed from the inner circumferential surface side of the intermediate transfer belt 6, but the shape of the protrusion 81a is not limited to this. The shape is arbitrary as long as the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 is sufficiently reduced (preferably achieving the above-mentioned reduction in contact area). For example, this shape may be a polygon such as a triangle, quadrilateral (square, rectangle), pentagon, hexagon, or rhombus, or a circle, ellipse, or oblong. Furthermore, all of the protrusions 81a may be substantially the same shape, or at least some may have different shapes. In this embodiment, if the shape of the protrusion 81a is circular, for example, its diameter can be made equivalent to the length of one side of the square protrusion 81a in this embodiment. Also, in this embodiment, if the shape of the protrusion 81a is a polygon other than a square or a circle, for example, the diameter of its circumscribed circle can be made equivalent to the length of one side of the square protrusion 81a in this embodiment.

[0079] Furthermore, an uneven shape can be formed on the contact surface 83 of the potential regulating member 8 by any available method. Examples of such methods include press working, cutting, polishing, and chemical surface treatment (etching). Multiple processing methods may be used in combination. In this embodiment, an uneven shape was formed on the contact surface 83 by press working the first portion 81 of the potential regulating member 8, which is made of sheet metal with a thickness of approximately 2 mm.

[0080] As described above, according to this embodiment, even when a relatively high bias is applied to the potential regulating member 8, it is possible to reduce the electrostatic attraction force between the intermediate transfer belt 6 and the potential regulating member 8, thereby suppressing instability in the running of the intermediate transfer belt 6. Therefore, according to this embodiment, in a configuration in which a bias is applied to the potential regulating member 8 located downstream of the primary transfer section N1, it is possible to suppress instability in the running performance of the intermediate transfer belt 6.

[0081] [Example 2] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0082] In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for each primary transfer section N1y, N1m, N1c, and N1k have substantially the same configuration. However, in this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 differs from that of Embodiment 1. This will be explained in detail below.

[0083] Figure 8 is a schematic diagram showing the surface shape of the contact surface 83 of the potential regulating member 8 in this embodiment. The potential regulating member 8 has the configuration described with reference to Figure 3, and the first portion 81 is made of sheet metal with a thickness of approximately 2 mm. In Figure 8, the second portion 82 of the potential regulating member 8 is not shown, and a part of the contact surface 83 is schematically shown. Figure 8(a) is a schematic plan view of the contact surface 83 of the potential regulating member 8 as seen from the inner circumferential surface side of the intermediate transfer belt 6. Figure 8(b) is a schematic cross-sectional view (BB cross-section in Figure 8(a)) of the potential regulating member 8 cut in the width direction of the intermediate transfer belt 6.

[0084] In this embodiment, the contact surface 83 of the potential regulating member 8 has a convex portion 81a and a concave portion 81b. The convex portion 81a protrudes toward the inner circumferential surface of the intermediate transfer belt 6 relative to the concave portion 81b. The concave portion 81b is recessed toward the direction away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a. For convenience, in Figure 8(a), the concave portion 81b is marked with dots. The surface (top) of the convex portion 81a facing the inner circumferential surface of the intermediate transfer belt 6 constitutes a contact area that can contact the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the contact surface 83 of the potential regulating member 8 has a surface shape in which a plurality of strip-shaped convex portions 81a extending along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment) protrude toward the inner circumferential surface of the intermediate transfer belt 6. Here, such a surface shape is also called a "horizontal strip shape". This surface shape can also be described as a surface shape in which multiple strip-shaped recesses 81b extending along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment) are recessed from the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the surface formed by the multiple protrusions 81a is substantially flat.

[0085] In this embodiment, the contact surface 83 of the potential regulating member 8 has multiple protrusions 81a that extend linearly along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment), and multiple protrusions 81a that are regularly spaced (approximately equally spaced in this embodiment) along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment). The size and spacing (pitch) of the protrusions 81a can be set as appropriate, provided that the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 is sufficiently reduced (preferably achieving the contact area reduction amount described in Embodiment 1). The spacing (pitch) d2 of the protrusions 81a in the width direction of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, in this embodiment, the surface (top) of the protrusion 81a that faces (contacts) the inner circumferential surface of the intermediate transfer belt 6 is flat. Furthermore, the width w2 of the protrusions 81a in the width direction of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable that it be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, the height h2 of the protrusions 81a can be, for example, about 0.05 to 1 mm, and in the configuration of this embodiment, it is preferable that it be about 0.05 to 0.5 mm from the viewpoint of processing accuracy, etc. Furthermore, it is preferable that the height h2 of the protrusions 81a be substantially constant within the contact surface 83, that is, that a substantially flat surface is formed by the tops of the multiple protrusions 81a. Also, in this embodiment, the area of ​​the recess 81b is equal to the area other than the protrusions 81a, and its bottom surface does not have to be flat.

[0086] Even if the contact surface 83 of the potential regulating member 8 has such an uneven shape, the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 can be reduced, similar to Example 1.

[0087] Furthermore, as described in Example 1, an uneven shape can be formed on the contact surface 83 of the potential regulating member 8 by any available method. In this embodiment, an uneven shape was formed on the contact surface 83 by press-forming the first portion 81 of the potential regulating member 8, which is made of sheet metal with a thickness of approximately 2 mm.

[0088] As described above, with the configuration of this embodiment, similar to that of Embodiment 1, it is possible to suppress instability in the running performance of the intermediate transfer belt 6 in a configuration in which a bias is applied to the potential regulating member 8 located downstream of the primary transfer section N1.

[0089] [Example 3] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatuses in Embodiments 1 and 2. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatuses in Embodiments 1 and 2 are denoted by the same reference numerals as in Embodiments 1 and 2, and detailed descriptions are omitted.

[0090] In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for each primary transfer section N1y, N1m, N1c, and N1k have substantially the same configuration. However, in this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 differs from that of embodiments 1 and 2. This will be explained in detail below.

[0091] Figure 9 is a schematic diagram showing the surface shape of the contact surface 83 of the potential regulating member 8 in this embodiment. The potential regulating member 8 has the configuration described with reference to Figure 3, and the first portion 81 is made of sheet metal with a thickness of approximately 2 mm. In Figure 9, the second portion 82 of the potential regulating member 8 is not shown, and a part of the contact surface 83 is schematically shown. Figure 9(a) is a schematic plan view of the contact surface 83 of the potential regulating member 8 as seen from the inner circumferential surface side of the intermediate transfer belt 6. Figure 9(b) is a schematic cross-sectional view (CC cross-section in Figure 9(a)) of the potential regulating member 8 cut in the direction of transport of the intermediate transfer belt 6.

[0092] In this embodiment, the contact surface 83 of the potential regulating member 8 has a convex portion 81a and a concave portion 81b. The convex portion 81a protrudes toward the inner circumferential surface of the intermediate transfer belt 6 relative to the concave portion 81b. The concave portion 81b is recessed toward the direction away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a. For convenience, in Figure 9(a), the concave portion 81b is marked with dots. The surface (top) of the convex portion 81a facing the inner circumferential surface of the intermediate transfer belt 6 constitutes a contact area that can contact the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the contact surface 83 of the potential regulating member 8 has a surface shape in which a plurality of strip-shaped convex portions 81a extending along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment) protrude toward the inner circumferential surface of the intermediate transfer belt 6. Here, such a surface shape is also called a "vertical strip shape". This surface shape can also be described as a surface shape in which multiple strip-shaped recesses 81b extending along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment) are recessed from the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the surface formed by the multiple protrusions 81a is substantially flat.

[0093] In this embodiment, the contact surface 83 of the potential regulating member 8 has multiple protrusions 81a that extend linearly along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment), and are arranged regularly (approximately equally spaced in this embodiment) along the transport direction of the intermediate transfer belt 6 (approximately parallel in this embodiment). The size and spacing (pitch) of the protrusions 81a can be set as appropriate, provided that the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 can be sufficiently reduced (preferably achieving the contact area reduction amount described in Embodiment 1). The spacing (pitch) d3 of the protrusions 81a in the transport direction of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable that it be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, in this embodiment, the surface (top) of the protrusion 81a that faces (contacts) the inner circumferential surface of the intermediate transfer belt 6 is flat. Furthermore, the width w3 of the protrusions 81a in the conveying direction of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable that it be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Also, the height h3 of the protrusions 81a can be, for example, about 0.05 to 1 mm, and in the configuration of this embodiment, it is preferable that it be about 0.05 to 0.5 mm from the viewpoint of processing accuracy, etc. Furthermore, it is preferable that the height h3 of the protrusions 81a is substantially constant within the contact surface 83, that is, a substantially flat surface is formed by the tops of the multiple protrusions 81a. Also, in this embodiment, the area of ​​the recess 81b is equal to the area other than the protrusions 81a, and its bottom surface does not have to be flat.

[0094] Even if the contact surface 83 of the potential regulating member 8 has such an uneven shape, the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 can be reduced, similar to Examples 1 and 2.

[0095] Furthermore, as described in Example 1, an uneven shape can be formed on the contact surface 83 of the potential regulating member 8 by any available method. In this embodiment, an uneven shape was formed on the contact surface 83 by press-forming the first portion 81 of the potential regulating member 8, which is made of sheet metal with a thickness of approximately 2 mm.

[0096] As described above, the configuration of this embodiment, like that of embodiments 1 and 2, can suppress instability in the running performance of the intermediate transfer belt 6 in a configuration in which a bias is applied to the potential regulating member 8 located downstream of the primary transfer section N1.

[0097] Furthermore, in this embodiment, the uneven shape of the contact surface 83 is formed such that, at any position on the contact surface 83 in the width direction of the intermediate transfer belt 6, a contact area with the inner circumferential surface of the intermediate transfer belt 6 exists in at least a portion of the conveying direction of the intermediate transfer belt 6. Further effects of the surface shape of the contact surface 83 of the potential regulating member 8 will be explained in Embodiment 4.

[0098] [Example 4] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatuses in Embodiments 1 to 3. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatuses in Embodiments 1 to 3 are denoted by the same reference numerals as in Embodiments 1 to 3, and detailed descriptions are omitted.

[0099] In this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 differs from that of embodiments 1 and 2. Furthermore, this embodiment will also describe a problem different from that described in embodiment 1, and its solution.

[0100] In an intermediate transfer type image forming apparatus 1, foreign matter such as toner, external additives, and paper dust that seeps around from spaces near both ends of the intermediate transfer belt 6 in the width direction may adhere to the inner surface of the intermediate transfer belt 6. Furthermore, for example, if sponge is used as the material for the primary transfer roller 15 or the secondary transfer inner roller 23, substances seeping from the sponge may adhere to the inner surface of the intermediate transfer belt 6 as foreign matter. In areas where such foreign matter adheres to the inner surface of the intermediate transfer belt 6, the transfer efficiency may decrease, potentially preventing the toner image from being properly transferred to the recording material S and resulting in a decrease in image quality. Therefore, it is desirable to remove foreign matter from the inner surface of the intermediate transfer belt 6.

[0101] In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for each primary transfer section N1y, N1m, N1c, and N1k have substantially the same configuration. However, in this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 differs from that of embodiments 1 to 3. In this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 is designed to reduce the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6, and is also advantageous for removing foreign matter from the inner circumferential surface of the intermediate transfer belt 6. This will be explained in detail below.

[0102] Figure 10 is a schematic diagram showing the surface shape of the contact surface 83 of the potential regulating member 8 in this embodiment. The potential regulating member 8 has the configuration described with reference to Figure 3, and the first portion 81 is made of sheet metal with a thickness of approximately 2 mm. In Figure 10, the second portion 82 of the potential regulating member 8 is not shown, and a part of the contact surface 83 is schematically shown. Figure 10(a) is a schematic plan view of the contact surface 83 of the potential regulating member 8 as seen from the inner circumferential surface side of the intermediate transfer belt 6. Figure 10(b) is a schematic cross-sectional view (DD cross-section in Figure 10(a)) of the potential regulating member 8 cut in the width direction of the intermediate transfer belt 6.

[0103] In this embodiment, the contact surface 83 of the potential regulating member 8 has a convex portion 81a and a concave portion 81b. The convex portion 81a protrudes toward the inner circumferential surface of the intermediate transfer belt 6 relative to the concave portion 81b. The concave portion 81b is recessed toward the direction away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a. For convenience, in Figure 10(a), the concave portion 81b is marked with dots. The surface (top) of the convex portion 81a facing the inner circumferential surface of the intermediate transfer belt 6 constitutes a contact area that can contact the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the contact surface 83 of the potential regulating member 8 has a surface shape in which a plurality of strip-shaped convex portions 81a extending at an angle with respect to the transport direction of the intermediate transfer belt 6 protrude toward the inner circumferential surface of the intermediate transfer belt 6. Here, such a surface shape is also called an "inclined shape". This surface shape can also be described as a surface shape in which multiple strip-shaped recesses 81b, which extend at an angle with respect to the conveying direction of the intermediate transfer belt 6, are recessed from the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the surface formed by the multiple protrusions 81a is substantially flat.

[0104] In this embodiment, the contact surface 83 of the potential regulating member 8 has multiple protrusions 81a that extend linearly along the conveying direction of the intermediate transfer belt 6 (approximately parallel in this embodiment), and are regularly spaced (approximately equally spaced in this embodiment) along the width direction of the intermediate transfer belt 6. However, in this embodiment, the protrusions 81a extend at an angle with respect to the conveying direction of the intermediate transfer belt 6. Furthermore, in this embodiment, the multiple protrusions 81a are formed such that at any position on the contact surface 83 in the width direction of the intermediate transfer belt 6, a contact area with the inner circumferential surface of the intermediate transfer belt 6 exists in at least a portion of the conveying direction of the intermediate transfer belt 6. In other words, in this embodiment, the protrusions 81a are formed such that at least a portion of each adjacent protrusion 81a overlaps in the width direction of the intermediate transfer belt 6. The size and spacing (pitch) of the protrusions 81a can be set as appropriate, provided that the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 can be sufficiently reduced (preferably achieving the contact area reduction amount described in Embodiment 1). Furthermore, as described above, if at least a portion of each adjacent protrusion 81a overlaps in the width direction of the intermediate transfer belt 6, the angle that the direction in which the protrusion 81a extends makes with the conveying direction of the intermediate transfer belt 6 can be set as appropriate. The spacing (pitch) d4 of the protrusions 81a in the width direction of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 0.5 to 2 mm from the viewpoint of processing accuracy, etc. Also, in this embodiment, the surface (top) of the protrusion 81a that faces (contacts) the inner circumferential surface of the intermediate transfer belt 6 is flat. Also, the width w4 of the protrusion 81a in a direction substantially perpendicular to the direction in which the protrusion 81a extends can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 0.1 to 1 mm from the viewpoint of processing accuracy, etc. Furthermore, the height h4 of the protrusion 81a can be, for example, about 0.05 to 1 mm, and in the configuration of this embodiment, it is preferable that it be about 0.05 to 0.5 mm from the viewpoint of processing accuracy. Also, it is preferable that the height h4 of the protrusion 81a is substantially constant within the contact surface 83, that is, that a substantially flat surface is formed by the tops of the multiple protrusions 81a.Furthermore, the angle that the direction in which the protrusion 81a extends makes with the conveying direction of the intermediate transfer belt 6 can be, for example, about 5 to 45 degrees, and is preferably about 10 to 30 degrees. Also, in this embodiment, the area of ​​the recess 81b is equal to the area other than the protrusion 81a, and its bottom surface does not have to be flat.

[0105] The uneven shape of the contact surface 83 of the potential regulating member 8 reduces the contact area between the potential regulating member 8 and the inner surface of the intermediate transfer belt 6, similar to Examples 1 to 3. Furthermore, by overlapping at least a portion of adjacent protrusions 81a in the width direction of the intermediate transfer belt 6, foreign matter can be scraped off by the protrusions 81a over substantially the entire width direction of the intermediate transfer belt 6 (the area in contact with the contact surface 83). Additionally, by making the protrusions 81a inclined with respect to the transport direction of the intermediate transfer belt 6, the retention of foreign matter on the potential regulating member 8 is suppressed. At least a portion of the foreign matter removed from the inner surface of the intermediate transfer belt 6 by the potential regulating member 8 is then moved in the transport direction of the intermediate transfer belt 6 along the uneven shape of the contact surface 83 as the intermediate transfer belt 6 moves, for example, and is removed from the potential regulating member 8. The image forming apparatus 1 may have a storage section (not shown) for accommodating foreign matter that is removed from the potential regulating member 8 and falls, for example, due to gravity. The configuration in this embodiment, in which foreign matter is removed from the inner surface of the intermediate transfer belt 6 by the potential regulating member 8, is particularly effective when a dedicated cleaning member (scraper or brush) for cleaning the inner surface of the intermediate transfer belt 6 is not provided.

[0106] Furthermore, as described in Example 1, an uneven shape can be formed on the contact surface 83 of the potential regulating member 8 by any available method. In this embodiment, an uneven shape was formed on the contact surface 83 by press-forming the first portion 81 of the potential regulating member 8, which is made of sheet metal with a thickness of approximately 2 mm.

[0107] In Example 3, the uneven shape of the contact surface 83 is formed such that, at any position on the contact surface 83 in the width direction of the intermediate transfer belt 6, there is a contact area with the inner circumferential surface of the intermediate transfer belt 6 in at least a portion of the conveying direction of the intermediate transfer belt 6. However, in Example 3, since the protrusions 81a extend in a direction substantially perpendicular to the conveying direction of the intermediate transfer belt 6, foreign matter is more likely to remain on the potential regulating member 8 compared to this embodiment. Therefore, from the viewpoint of removing foreign matter from the inner circumferential surface of the intermediate transfer belt 6, the uneven shape of this embodiment is preferable.

[0108] As described above, the configuration of this embodiment, like that of embodiments 1 to 3, can suppress instability in the running performance of the intermediate transfer belt 6 when a bias is applied to the potential regulating member 8 located downstream of the primary transfer section N1. Furthermore, the configuration of this embodiment is advantageous for removing foreign matter from the inner circumferential surface of the intermediate transfer belt 6 using the potential regulating member 8.

[0109] [Example 5] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatuses in Embodiments 1 to 4. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatuses in Embodiments 1 to 4 are denoted by the same reference numerals as in Embodiments 1 to 3, and detailed descriptions are omitted.

[0110] In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for each primary transfer section N1y, N1m, N1c, and N1k have substantially the same configuration. However, in this embodiment, the surface shape of the contact surface 83 of the potential regulating member 8 differs from that of Embodiments 1 to 4. This will be explained in detail below.

[0111] Figure 11 is a schematic diagram showing the surface shape of the contact surface 83 of the potential regulating member 8 in this embodiment. The potential regulating member 8 has the configuration described with reference to Figure 3, and the first portion 81 is made of sheet metal with a thickness of approximately 2 mm. In Figure 11, the second portion 82 of the potential regulating member 8 is not shown. Figure 11(a) is a schematic plan view of the contact surface 83 of the potential regulating member 8 as seen from the inner circumferential surface side of the intermediate transfer belt 6. Figure 11(b) is a schematic cross-sectional view (EE cross-sectional view in Figure 11(a)) of the potential regulating member 8 cut in the width direction of the intermediate transfer belt 6.

[0112] In this embodiment, the contact surface 83 of the potential regulating member 8 has a convex portion 81a and a concave portion 81b. The convex portion 81a protrudes toward the inner circumferential surface of the intermediate transfer belt 6 relative to the concave portion 81b. The concave portion 81b is recessed toward the direction away from the inner circumferential surface of the intermediate transfer belt 6 relative to the convex portion 81a. For convenience, in Figure 11(a), the concave portion 81b is marked with dots. The surface of the convex portion 81a facing the inner circumferential surface of the intermediate transfer belt 6 constitutes a contact area that can contact the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the contact surface 83 of the potential regulating member 8 has a surface shape in which a plurality of independent concave portions 81b are recessed toward the direction away from the inner circumferential surface of the intermediate transfer belt 6. Here, such a surface shape is also called a kind of "embossed shape (or debossed shape)". In this embodiment, the area of ​​the remaining contact surface 83 in which the plurality of concave portions 81b are formed is substantially flat.

[0113] In this embodiment as well, similar to embodiments 1 to 4, the reduction in contact area due to the provision of an uneven shape on the contact surface 83 of the potential regulating member 8 is preferably 10 to 70%, and more preferably 20 to 50%. In this embodiment as well, even if the contact surface 83 of the potential regulating member 8 has an uneven shape, the contact area that can contact the inner circumferential surface of the intermediate transfer belt 6 is distributed substantially uniformly. As in this embodiment, a surface shape in which the original flat surface of the contact surface 83 constitutes the contact area with the inner circumferential surface of the intermediate transfer belt 6 has the advantage of making it easier to mechanically achieve flatness of the contact area.

[0114] In this embodiment, the contact surface 83 of the potential regulating member 8 has rows of independent recesses 81b arranged regularly (at approximately equal intervals in this embodiment) along the width direction of the intermediate transfer belt 6 (approximately parallel in this embodiment), and rows of these recesses 81b arranged along the transport direction of the intermediate transfer belt 6 (approximately parallel in this embodiment). In this embodiment, the recesses 81b in each row in the transport direction of the intermediate transfer belt 6 are arranged such that at least a portion of each recess 81a in adjacent rows overlaps in the width direction of the intermediate transfer belt 6. Thus, in this embodiment, the recesses 81b on the contact surface 83 are arranged in a staggered pattern (staggered embossing). Also, in this embodiment, the recesses 81b have an approximately circular shape when viewed from the inner circumferential surface side of the intermediate transfer belt 6. The size and spacing (pitch) of the recesses 81b can be set as appropriate, provided that the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 is sufficiently reduced (preferably achieving the above-mentioned reduction in contact area). The spacing (pitch) d5 of the recesses 81a in the conveying direction (and width direction) of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 1 to 3 mm from the viewpoint of processing accuracy. The diameter w5 of the recesses 81b when viewed from the inner circumferential surface side of the intermediate transfer belt 6 can be, for example, about 0.1 to 3 mm, and in the configuration of this embodiment, it is preferable to be about 1 to 3 mm from the viewpoint of processing accuracy. The depth h5 of the recesses 81b (height of the protrusions 81a) can be, for example, about 0.05 to 1 mm, and in the configuration of this embodiment, it is preferable to be about 0.05 to 0.5 mm from the viewpoint of processing accuracy. Furthermore, it is preferable that the depth h5 of the recesses 81b be substantially constant within the contact surface 83. The bottom surface of the recesses 81b does not have to be flat. Furthermore, in this embodiment, the area of ​​the protrusions 81b is equal to the area other than the recesses 81b, and the surface facing the intermediate transfer belt 6 is flat.

[0115] The uneven shape of the contact surface 83 of the potential regulating member 8 reduces the contact area between the potential regulating member 8 and the inner surface of the intermediate transfer belt 6. Furthermore, the uneven shape of this embodiment has the advantage of making it easier to achieve flatness in the contact area of ​​the contact surface 83 that can come into contact with the inner surface of the intermediate transfer belt 6.

[0116] In this embodiment, the recess 81b has a substantially circular shape when viewed from the inner circumferential surface side of the intermediate transfer belt 6, but the shape of the recess 81b is not limited to this. The shape is arbitrary as long as the contact area between the potential regulating member 8 and the inner circumferential surface of the intermediate transfer belt 6 is sufficiently reduced (preferably achieving the above-mentioned reduction in contact area). For example, the shape may be a polygon such as a triangle, quadrilateral (square, rectangle), pentagon, hexagon, or rhombus, or a circle, ellipse, or oblong. Also, all of the recesses 81b may be substantially the same shape, or at least some may have different shapes. In this embodiment, if the shape of the recess 81b is a shape other than a circle, such as a polygon, for example, the diameter of its circumscribed circle can be made equivalent to the diameter of the circular recess 81b in this embodiment.

[0117] Furthermore, as described in Example 1, an uneven shape can be formed on the contact surface 83 of the potential regulating member 8 by any available method. In this embodiment, an uneven shape was formed on the contact surface 83 by press working the first portion 81 of the potential regulating member 8, which is made of sheet metal with a thickness of approximately 2 mm. This press working can be performed, for example, in the same manner as harp piercing of sheet metal.

[0118] As described above, the configuration of this embodiment, like that of embodiments 1 to 4, can suppress instability in the running performance of the intermediate transfer belt 6 when a bias is applied to the potential regulating member 8 located downstream of the primary transfer section N1. Furthermore, the configuration of this embodiment makes it easier to achieve flatness in the contact area of ​​the potential regulating member 8 that can contact the inner circumferential surface of the intermediate transfer belt 6.

[0119] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0120] In Examples 1 to 5, the surface shape of the contact surface 83 was described assuming that the potential regulating member 8 is composed only of a conductive metal such as SUS (stainless steel). However, as explained in Example 1, the configuration of the potential regulating member 8 is not limited to this. For example, as shown in Figure 4, the potential regulating member 8 may have a base portion 84 having the same shape as the potential regulating member 8 shown in Figure 3, and a conductive surface layer 85 made of metal or a conductive resin provided on the surface of the base portion 84. In this configuration, the surface layer 85 only needs to have an uneven shape (such as an "embossed shape," "horizontal band shape," "vertical band shape," or "inclined shape") as described in Examples 1 to 5. This makes it possible to reduce the electrostatic adsorption force between the intermediate transfer belt 6 and the potential regulating member 8, similar to Examples 1 to 5. Also, for example, as shown in Figure 5, the contact surface 83 of the potential regulating member 8 may be made of a conductive nonwoven fabric 86 or the like. In this configuration, the same effects as in Examples 1 to 5 can be obtained by fixing a conductive nonwoven fabric 86 or the like to the protrusions 81a of the surface layer 85 which has an uneven shape (such as an embossed shape, a horizontal band shape, a vertical band shape, or an inclined shape) as described in Examples 1 to 5. In this case, the reduction in contact area when the surface layer 85 has an uneven shape and the nonwoven fabric 86 or the like is provided on the protrusions 81a can be defined as the reduction in contact area (%). This reduction in contact area (%) can be considered to be substantially the same as the reduction in contact area (%) when the surface layer 85 has an uneven shape and the nonwoven fabric 86 or the like is provided on the protrusions 81a, compared to the contact area of ​​the contact surface 83 with the inner circumferential surface of the intermediate transfer belt 6 when the nonwoven fabric 86 or the like is provided on the surface layer 85 which does not have an uneven shape. However, this reduction in contact area (%) can be considered to be substantially the same as the reduction in contact area (%) when the surface layer 85 with an uneven shape is assumed to be the contact surface 83.

[0121] Furthermore, the surface shape of the contact surface 83 of the potential regulating member 8 may be, for example, the surface shape shown in Figures 12(a) and (b). Figures 12(a) and (b) are schematic plan views of the contact surface 83 of the potential regulating member 8 of another example, as seen from the inner circumferential surface side of the intermediate transfer belt 6. For convenience, dots are shown on the recess 81b in Figure 12(a). In the example shown in Figure 12(a), the potential regulating member 8 has a convex portion 81a similar to that of Embodiment 1, and the convex portions 81a of each row in the transport direction of the intermediate transfer belt 6 are arranged such that at least a portion of the convex portions 81a of adjacent rows overlap in the width direction of the intermediate transfer belt 6. Also, in the example shown in Figure 12(b), the area of ​​the recess 81b in Embodiment 5 is the convex portion 81a, and the area of ​​the convex portion 81a in Embodiment 5 is the recess 81b. In the example shown in Figure 12(b), the protrusions 81a of each row in the conveying direction of the intermediate transfer belt 6 are arranged such that at least a portion of the protrusions 81a of adjacent rows overlap in the width direction of the intermediate transfer belt 6. Thus, in the examples shown in Figures 12(a) and (b), the protrusions 81a are arranged in a staggered pattern on the contact surface 83 (staggered embossing). This surface shape is advantageous for removing foreign matter from the inner circumferential surface of the intermediate transfer belt 6 by the potential regulating member 8. Furthermore, since the protrusions 81a do not extend continuously along the width direction of the intermediate transfer belt 6, the retention of foreign matter on the potential regulating member 8 is suppressed.

[0122] Furthermore, in the above-described embodiment, the uneven shape of the contact surface of the potential regulating member 8 was provided in a regular pattern, but it may also be provided in an irregular (random) pattern. In this case as well, it is preferable that the reduction in contact area (%) is the same as in the above-described embodiment.

[0123] Furthermore, the surface shape of the contact surface of a potential regulating member provided with respect to at least some of the multiple image forming units may differ from the surface shape of the contact surface of a potential regulating member provided with respect to at least some of the other image forming units. The surface shape of the contact surface may differ for each potential regulating member provided with respect to each image forming unit.

[0124] Furthermore, in the above-described embodiment, the potential regulating member 8 was configured to have a first portion 81 and a second portion 82, but the potential regulating member 8 may be composed of, for example, a flat plate corresponding to the first portion 81 in the above-described embodiment. Also, the potential regulating member 8 may take other forms, such as a block-shaped member with a rectangular cross-section.

[0125] Furthermore, although the primary transfer member in the above-described embodiment was a roller-shaped member, it may also be a brush-shaped member, a sheet-shaped member, a pad-shaped member, or the like.

[0126] Furthermore, in the above-described embodiment, the potential regulating power supply was provided independently for each image forming unit, but it may be shared with multiple image forming units (or all of them). The same applies to the charging power supply, developing power supply, and primary transfer power supply.

[0127] Furthermore, although the predetermined charging polarity of the photoreceptor was negative in the above-described embodiment, it is not limited to this, and the predetermined charging polarity of the photoreceptor may be positive. Similarly, although the normal charging polarity of the toner was negative in the above-described embodiment, the normal charging polarity of the toner may be positive. When the predetermined charging polarity of the photoreceptor and the normal charging polarity of the toner are positive, the various applied voltages may be appropriately changed, for example, by setting them to the opposite polarity to those in the above-described embodiment, in accordance with the above-described embodiment.

[0128] Furthermore, the image forming apparatus can be configured to have a potential regulating member with respect to at least one of the multiple image forming units. In other words, the image forming apparatus can be configured to have a potential regulating member provided on the inner circumferential surface side of the intermediate transfer belt immediately downstream of at least one of the multiple primary transfer units.

[0129] Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming full-color images; it may also be an image forming apparatus capable of forming only monochrome (black and white or monocolor) images. [Explanation of Symbols]

[0130] 1. Image forming apparatus 6. Intermediate transfer belt 8. Potential regulating member (electrode member) 11. Photosensitive drum (photoconductor) 15. Primary transfer roller (primary transfer member) 80. Potential-regulated power supply

Claims

1. A photoreceptor that can be charged to a predetermined polarity and carries a toner image, A circulating intermediate transfer belt for transporting the toner image, which has been primarily transferred from the photoreceptor, to a recording material for secondary transfer, A primary transfer member is provided, which contacts the inner circumferential surface of the intermediate transfer belt to form a primary transfer section in which the photoreceptor and the intermediate transfer belt come into contact, and to which a voltage is applied to transfer a toner image from the photoreceptor to the intermediate transfer belt in the primary transfer section. An electrode member provided on the inner circumferential surface side of the intermediate transfer belt downstream of the primary transfer section in the direction of movement of the intermediate transfer belt, A power supply that applies a voltage with the same polarity as the predetermined polarity to the electrode member, It has, The electrode member is composed of a surface facing the inner circumferential surface of the intermediate transfer belt, and has a contact surface with a contact area that can contact the inner circumferential surface of the intermediate transfer belt. The image forming apparatus is characterized in that the contact surface is provided with a convex portion that forms the contact region, and a recess that is recessed in a direction away from the inner circumferential surface of the intermediate transfer belt relative to the convex portion, and which forms a non-contact region that is away from the inner circumferential surface of the intermediate transfer belt when the contact region comes into contact with the intermediate transfer belt.

2. The image forming apparatus according to claim 1, characterized in that the surface formed by the contact region is planar.

3. The image forming apparatus according to claim 1, characterized in that, when the contact surface is viewed from the inner circumferential surface side of the intermediate transfer belt, the ratio of the area of ​​the non-contact area in a unit region to the area of ​​a unit region at any position on the contact surface is 10% or more and 70% or less.

4. The image forming apparatus according to claim 3, characterized in that the aforementioned ratio is 20% or more and 50% or less.

5. The image forming apparatus according to claim 1, characterized in that a plurality of independent protrusions are provided on the contact surface.

6. The image forming apparatus according to claim 5, characterized in that the plurality of protrusions are provided such that the contact area exists on at least a portion of the contact surface in the direction of movement at any position on the contact surface in a direction substantially perpendicular to the direction of movement.

7. The image forming apparatus according to claim 1, characterized in that the contact surface is provided with a plurality of protrusions that extend linearly along the direction of movement.

8. The image forming apparatus according to claim 1, characterized in that the contact surface is provided with a plurality of protrusions that extend linearly along a direction substantially perpendicular to the direction of movement.

9. The image forming apparatus according to claim 1, characterized in that the contact surface is provided with a plurality of protrusions that extend linearly and are inclined with respect to the direction of movement.

10. The image forming apparatus according to claim 9, characterized in that the plurality of protrusions are provided such that at least a portion of each adjacent protrusion overlaps in a direction substantially perpendicular to the direction of movement.

11. The image forming apparatus according to claim 1, characterized in that a plurality of independent recesses are provided on the contact surface.

12. The image forming apparatus according to claim 11, characterized in that the plurality of recesses are provided such that the contact area exists on at least a portion of the contact surface in the direction of movement at any position on the contact surface in a direction substantially perpendicular to the direction of movement.

13. The image forming apparatus according to any one of claims 1 to 12, comprising: a plurality of photoreceptors arranged along the direction of movement; a plurality of primary transfer members provided corresponding to each of the plurality of photoreceptors; and an electrode member provided on the inner circumferential surface side of the intermediate transfer belt immediately downstream of at least one of the primary transfer sections in the direction of movement.

Images