Image forming apparatus

Abstract

An image forming apparatus is disclosed. An image forming apparatus includes a photosensitive member, an intermediate transfer belt, a primary transfer member, an electrode member, a first applying portion configured to apply a bias voltage having a polarity opposite to a predetermined polarity to the primary transfer member, a second applying portion configured to apply a bias voltage having a polarity opposite to the predetermined polarity to the primary transfer member, and a controller. The second applying section is configured to apply a bias voltage having the same polarity as a predetermined polarity to the electrode member, and the controller is configured to control the second applying section so as to change the bias voltage applied to the electrode member based on a type of recording material.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus using an electrophotographic type or an electrostatic recording type, such as a copying machine, a printer, a facsimile machine, or a multifunctional machine having multiple functions of these machines, printers, and facsimile machines. Background Art

[0002] As an image forming device such as a color copier, a color printer or a color multifunction machine using an electronic photography type, an intermediate transfer type image forming device has become mainstream because it has the advantages of making it relatively easy to reduce the size of the main component of the device and adapt to various recording materials. An intermediate transfer type image forming device generally includes a plurality of photosensitive drums and an intermediate transfer belt. In addition, the colorant image formed on the photosensitive drum is continuously electrostatically transferred once to the intermediate transfer belt in the primary transfer section. In addition, the colorant image once transferred on the intermediate transfer belt is electrostatically transferred secondarily to a recording material such as paper in the secondary transfer section. By the way, with respect to the arrangement of components around the primary transfer section, etc., "upstream" and "downstream" refer to "upstream" and "downstream" respectively relative to the conveying direction of the intermediate transfer belt.

[0003] In such an image forming device, the toner on the intermediate transfer belt has the following tendency: on the downstream side of the primary transfer section, the toner is subjected to discharge between the intermediate transfer belt and the photosensitive drum and the charge amount increases. Then, when the inventor of the present invention conducted research, it was found that the mirror force between the toner and the intermediate transfer belt increases with the increase in the charge amount, so it becomes difficult to transfer the toner to the recording material in the secondary transfer section. For example, since a gap is generated between the intermediate transfer belt and the recording material in the secondary transfer section and a relatively large secondary transfer electric field is required, it is difficult to transfer the toner uniformly to the embossed paper with surface unevenness. For this reason, when the charge amount of the toner on the intermediate transfer belt increases, it becomes more difficult to transfer uniformly to the embossed paper with surface unevenness. In addition, with respect to the secondary-color toner image, when the toner image transferred on the intermediate transfer belt in the primary transfer section on the upstream side passes through the primary transfer section on the downstream side, the toner image is further subjected to discharge. For this reason, a difference in the charge amount of the toner on the intermediate transfer belt occurs between the secondary color and the single color (monochrome), whereby in some cases, it becomes difficult to set a secondary transfer bias suitable for secondary transfer (secondary transfer latitude becomes narrower).

[0004] Here, in Japanese Patent Application (JP-A) No. 2003-57963, a configuration is disclosed in which a conductive contact plate is provided on the downstream side of the primary transfer portion and the inner peripheral surface side of the intermediate transfer belt, and a bias having the same polarity as the charge polarity of the photosensitive drum is applied to the contact plate.

[0005] In order to suppress an increase in the charge amount of the toner on the downstream side of the primary transfer portion as described above, it is effective to suppress discharge on the downstream side of the primary transfer portion.

[0006] JP-A No. 2003-57963 does not mention suppressing the discharge on the downstream side of the primary transfer portion. However, when the present inventors conducted research, it was found that in order to suppress the discharge on the downstream side of the primary transfer portion, it is effective to provide a potential limiting member as a conductive electrode member on the downstream side and the inner peripheral surface side of the primary transfer portion, and then apply a bias voltage (potential limiting bias) having the same polarity as the charge polarity of the photosensitive drum to the potential limiting member.

[0007] By suppressing the discharge between the intermediate transfer belt and the photosensitive drum on the downstream side of the primary transfer section, the increase in the charge amount of the toner on the intermediate transfer belt can be suppressed, and for example, the toner can be easily transferred uniformly to embossed paper having surface unevenness, etc. In addition, the difference in the charge amount of the toner becomes smaller between the secondary color and the single color, etc., so it becomes easy to ensure the secondary transfer latitude.

[0008] However, recently, the diversification of recording material types is developing, and especially in the commercial printing industry, in many cases, not only ordinary paper is used, but also coated paper with low surface unevenness due to coating with a coating agent and synthetic paper using a resin-type substrate are used. Such coated paper and synthetic paper usually have a high resistance value (volume resistivity) compared with ordinary paper due to the influence of the material used for surface treatment or the material used as the substrate. In the case of using such recording materials, in order to ensure the secondary transfer properties, there is a tendency that the secondary transfer bias is set high (large absolute value). For this reason, when the potential limiting bias applied to the potential limiting member becomes insufficient, the effect of suppressing the increase in the amount of charge of the colorant becomes insufficient, so that in some cases, the phenomenon of the colorant being dispersed by the electric field in the secondary transfer portion (or near its upstream side) is easily caused (herein, this phenomenon is simply referred to as "dispersion (phenomenon)"). In addition, when the smoothness of the recording material is high, in some cases, it is easy for the retention force of the colorant on the intermediate transfer belt to be reduced, and the colorant image to be disturbed by the friction between the intermediate transfer belt and the recording material (herein, this phenomenon is simply referred to as "image interference"). Summary of the invention

[0009] A main object of the present invention is to suppress image defects such as scattering that can occur depending on the type of recording material in a configuration capable of suppressing an increase in the charge amount of toner on an intermediate transfer member by applying a bias to an electrode member provided downstream of a primary transfer portion.

[0010] This object is achieved by an image forming apparatus according to the present invention.

[0011] According to one aspect of the present invention, there is provided an image forming device, the image forming device comprising: a photosensitive member, the photosensitive member being charged to a predetermined polarity and being configured to carry a toner image; an intermediate transfer belt, the toner image being transferred from the photosensitive member to the intermediate transfer belt in a primary transfer section; a primary transfer member, the primary transfer member forming the primary transfer section, the photosensitive member and the intermediate transfer belt being in contact with each other in the primary transfer section, the primary transfer member being in contact with an inner peripheral surface of the intermediate transfer belt, and the primary transfer member being configured to transfer the toner image to the intermediate transfer belt under application of a transfer bias voltage. transfer from the photosensitive member to the intermediate transfer belt; an electrode member, the electrode member being in contact with the inner peripheral surface of the intermediate transfer belt at the downstream side of the primary transfer portion relative to the moving direction of the intermediate transfer belt; a first applying portion, the first applying portion being configured to apply a bias voltage having a polarity opposite to the predetermined polarity to the primary transfer member; a second applying portion, the second applying portion being configured to apply a bias voltage having a polarity identical to the predetermined polarity to the electrode member; and a controller, the controller being configured to control the second applying portion so as to change the bias voltage applied to the electrode member based on the type of recording material.

[0012] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic cross-sectional view of an image forming apparatus.

[0014] Figure 2 is a schematic block diagram showing a control system of the image forming apparatus.

[0015] Figure 3 Parts (a) and (b) are a cross-sectional view and a perspective view of the potential limiting member, respectively.

[0016] Figure 4 is a cross-sectional view of a potential limiting member in another example.

[0017] Figure 5 is a cross-sectional view of a potential limiting member in another example.

[0018] Figure 6 is a cross-sectional view for illustrating the arrangement of the potential limiting member.

[0019] Figure 7 It is a flow chart of one-time transfer ATVC.

[0020] Figure 8 is a schematic graph of voltage-current characteristics obtained by primary transfer ATVC.

[0021] Fig. 9 is a schematic cross-sectional view for illustrating dispersion and image interference.

[0022] Fig.10 is a flowchart illustrating an example of a process for adjusting a potential limit bias.

[0023] Fig.11 Parts (a) and (b) of FIG. 1 are schematic diagrams for illustrating arrangements of examples of a recording material selection screen and a recording material setting screen, respectively.

[0024] Fig.12 Parts (a) and (b) of FIG. 1 are schematic diagrams of an example and another example of a secondary transfer bias adjustment screen, respectively.

[0025] Fig.13 is a schematic diagram of an example of a secondary transfer bias adjustment image.

[0026] Fig.14 This is a diagram showing an example of a potential limiting bias adjustment screen.

[0027] Fig.15 This is a diagram showing an example of a potential limiting bias adjustment screen.

[0028] Fig.16 FIG. 1 is a diagram showing another example of the potential limiting bias adjustment screen.

[0029] Fig.17 This is a diagram showing another example of the potential limiting bias adjustment screen.

[0030] Fig.18 is a graph for illustrating changes in the relationship between the output voltage of the primary transfer power source and the current passing through the primary transfer power source caused by the potential limiting bias.

[0031] Fig.19 is a flow chart of another example of a process for adjusting a potential limiting bias.

[0032] Fig. 20 It is a schematic diagram for illustrating the current path around the primary transfer section.

[0033] Fig.21 is a schematic block diagram of another example of the control system of the image forming apparatus.

[0034] Fig. 22 is a timing chart for illustrating correction control of the primary transfer bias. DETAILED DESCRIPTION

[0035] Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the accompanying drawings.

[0036] [Example 1]

[0037] 1. Overall structure and operation of image forming apparatus

[0038] First, the overall structure and operation of the image forming apparatus of this embodiment will be described. Figure 1 : is a schematic cross-sectional view of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 of this embodiment is a tandem type full color printer capable of forming a full color image on a sheet-like recording material S by using an electrophotographic type and adopting an intermediate transfer type.

[0039] The image forming apparatus 1 includes an image forming section 2, a controller 3, a feeding section 4 for recording material S, and a discharging section 5 for recording material S. In addition, a temperature sensor 71 ( Figure 2 ) and a humidity sensor 72 ( Figure 2 ). The image forming device 1 is capable of forming an image on a recording material S based on image information (image signal) acquired by a manuscript reading device (not shown) provided on or connected to the image forming device 1. In addition, the image forming device 1 is capable of forming an image on a recording material S based on image information (image signal) from an external device (not shown) such as a personal computer (host device), a digital camera, or a smart phone connected to the image forming device 1. Incidentally, the recording material (transfer material, recording medium, sheet) S is a material for forming an image with a toner, and specific examples thereof include plain paper, thick paper, glossy coated paper, matte coated paper, embossed paper, or synthetic resin sheets (synthetic paper) and overhead projector sheets (resin films) as substitutes for plain paper, etc. Here, in some cases, the recording material S is referred to as "paper" ("paper", "embossed paper", "high resistance paper", etc.), but even in this case, the recording material S includes materials other than paper or a recording material formed by a material containing materials other than paper.

[0040] The image forming section 2 forms an image on the recording material S fed from the feeding section 4 based on the image information. The image forming section 2 includes image forming units 10y, 10m, 10c, 10k, toner bottles 18y, 18m, 18c, 18k, exposure devices 13y, 13m, 13c, 13k, an intermediate transfer unit 20, a secondary transfer device 26, and a fixing device 27. The image forming units 10y, 10m, 10c, and 10k form toner images of yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively. In some cases, elements having the same or corresponding functions of structures provided for respective colors will be collectively described by omitting the suffixes y, m, c, and k for the elements respectively representing the associated colors. In addition, the image forming apparatus 1 can also form a monochrome image or a multicolor image such as a (single) black image, for example, by using the image forming unit 10 for a desired single color or some of the four colors.

[0041] The image forming unit 10 includes a photosensitive drum 11 which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image bearing member. In addition, the image forming unit 10 includes a charging roller 12 which is a roller-type charging member as a charging member. In addition, the image forming unit 10 includes a developing device 14 as a developing member. In addition, the image forming unit 10 includes a pre-exposure device 16 as a discharge (charge elimination) member. In addition, the image forming unit 10 includes a drum cleaning device 17 as a photosensitive member cleaning member. The image forming unit 10 forms a toner image on an intermediate transfer belt 6 described later.

[0042] The photosensitive drum 11 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 11 is a negatively chargeable organic photosensitive member (OPC) having an outer diameter of 30 mm. The photosensitive drum 11 has an aluminum cylinder as a substrate and a surface layer formed on the surface of the substrate. In this embodiment, as the surface layer, three layers of a primer layer, a photocharge generating layer, and a charge transport layer sequentially applied and laminated on the substrate are provided. When the image forming operation starts, the photosensitive drum 11 is rotationally driven at a predetermined circumferential speed (processing speed) in the direction indicated by the arrow R1 in the figure (counterclockwise) by a driving motor (not shown) as a drive.

[0043] 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 due to the rotation of the photosensitive drum 11. The charging power source 73 ( Figure 2 ) is connected to the charging roller 12. The charging power source 73 applies a predetermined charging bias (charging voltage) to the charging roller 12 during a charging process.

[0044] The exposure device 13 scans and exposes the surface of the charged photosensitive drum 11 based on the image information, so that an electrostatic image is formed on the photosensitive drum 11. In this embodiment, the exposure device 13 is a laser scanner. The exposure device 13 emits laser light according to the separated color image information output from the controller 3, and scans and exposes the surface (peripheral surface) of the photosensitive drum 11.

[0045] The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by supplying toner to it by the developing device 14, so that a toner image (developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 is a two-component developing device that uses a two-component developer including a toner (non-magnetic toner particles) and a carrier (magnetic carrier particles) as a developer. In a developing container (developing body) 14b of the developing device 14, the two-component developer is accommodated, and the toner is supplied from the toner bottle 18 in an amount corresponding to the consumption of the toner. The developing device 14 includes a developing sleeve 14a as a developing member (developer carrying member). The developing sleeve 14a is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (in this embodiment, aluminum), for example. Inside the developing sleeve 14a, a magnet roller (not shown) is fixed and arranged not to rotate relative to the developing container 14b, and the magnet roller is a roller-shaped magnet as a magnetic field generating component (magnetic field generating member). The developing sleeve 14a carries the two-component developer and conveys it to a developing area opposite to the photosensitive drum 11. Then, in the developing area, the toner moves from the two-component developer on the developing sleeve 14a and is deposited on the image portion of the electrostatic image on the photosensitive drum 11. The developing power source 74 ( Figure 2 ) is connected to the developing sleeve 14a. The developing power source 74 applies a predetermined developing bias (developing voltage) to the developing sleeve 14a during development. In this embodiment, on the exposed portion (image portion) of the photosensitive drum 11 whose absolute value of potential is reduced due to exposure after being uniformly charged, a toner charged to the same polarity as the charge polarity of the photosensitive drum 11 (in this embodiment, negative polarity) is deposited (reversal development type). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative polarity.

[0046] The intermediate transfer unit 20 is arranged to be opposite to the four photosensitive drums 11y, 11m, 11c and 11k. The intermediate transfer unit 20 includes an intermediate transfer belt 6 composed of an endless belt as an intermediate transfer member. The intermediate transfer belt 6 is wound around and stretched by a driving roller 21, a tension roller 22 and an inner secondary transfer roller 23 as a plurality of stretching rollers. The intermediate transfer belt 6 is movable (rotatable) while carrying the colorant image. The driving roller 21 is rotationally driven by a driving motor (not shown) as a driving member, so that the driving force is transmitted to the intermediate transfer belt 6, and thus the intermediate transfer belt 6 is rotated at a predetermined circumferential speed corresponding to the circumferential speed of the photosensitive drum 1. Figure 1 2 and 3. The tension roller 22 rotates (circulates and moves) in the direction of arrow R2 (clockwise) in FIG. 2. The tension roller 22 controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 is subjected to a force that pushes the intermediate transfer belt 6 from the inner peripheral surface (back side) side toward the outer peripheral surface (front side) side by the urging force of a tension spring (not shown) composed of a compression coil spring of a urging member as a urging member. By this force, a tension of about 2 kg to 5 kg is applied in the conveying direction (processing progress direction, moving direction) of the intermediate transfer belt 6. The inner secondary transfer roller 23 constitutes a secondary transfer device 26 in combination with the outer secondary transfer roller 25 described later. On the inner peripheral surface side of the intermediate transfer belt 6, the primary transfer rollers 15y, 15m, 15c, 15k of the roller-type primary transfer member as the primary transfer member are respectively arranged corresponding to the photosensitive drums 11y, 11m, 11c, 11k. In this embodiment, the primary transfer rollers 15 are disposed opposite to the photosensitive drums 11, and sandwich the intermediate transfer belt 6 between themselves and the photosensitive drums 11. Each of the primary transfer rollers 15 is pressed toward the photosensitive drums 11, and contacts the photosensitive drums 11 through the intermediate transfer belt 6, and forms a primary transfer portion (primary transfer nip) N1 which is a contact portion between the photosensitive drums 11 and the intermediate transfer belt 6. The stretching rollers other than the driving roller 21 and the primary transfer rollers 15 rotate as the intermediate transfer rollers 6 rotate.

[0047] The toner image formed on the photosensitive drum 11 is transferred (primary transfer) to the intermediate transfer belt 6 in the primary transfer section N1 by the action of the primary transfer roller 15. For example, when a full-color image is formed, the yellow, magenta, cyan, and black toner images formed on the photosensitive drum 11 are transferred multiple times so as to be sequentially superimposed on the intermediate transfer belt 6. The primary transfer power source 75 ( Figure 2) is connected to the primary transfer roller 15. During the primary transfer, the primary transfer power source 75 applies a primary transfer bias (primary transfer voltage) which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (in this embodiment, a positive polarity) to the primary transfer roller 15. Thus, the toner image of negative polarity on the photosensitive drum 11 is primarily transferred onto the intermediate transfer belt 6. The voltage detection sensor 75a ( Figure 2 ) and a current detection sensor 75b ( Figure 2 ) is connected to a primary transfer power source 75. In this embodiment, for example, a primary transfer bias of about 1 kV to 2 kV is applied to the primary transfer roller 15 ("1 kV to 2 kV" means a range including 1 kV and 2 kV, and the same applies hereinafter). In addition, in this embodiment, the primary transfer bias is subjected to constant voltage control. In this embodiment, primary transfer power sources 75y, 75m, 75c, and 75k are separately provided for the primary transfer rollers 15y, 15m, 15c, and 15k, respectively. In addition, in this embodiment, the primary transfer bias applied to the primary transfer rollers 15y, 15m, 15c, and 15k can be controlled separately.

[0048] Here, in this embodiment, the primary transfer roller 15 has a core metal and an elastic layer of ion conductive foam rubber (NBR rubber) formed on the periphery of the core metal. The outer diameter of the primary transfer roller 15 is, for example, 15 mm to 20 mm. In addition, as the primary transfer roller 15, a rubber having a resistance value of 1×10 5 Up to 1×10 8 Ω(N / N (23°C, 50% RH) condition, 2 kV applied) roller.

[0049] In addition, in this embodiment, the intermediate transfer belt 6 is an endless belt having a double-layer structure including a base layer and a surface layer in order from the inner peripheral surface side toward the outer peripheral surface side. As a material constituting the base layer, a resin such as polyimide or polycarbonate containing an appropriate amount of carbon black as an antistatic agent can be appropriately used. The thickness of the base layer is, for example, 0.05 mm to 0.15 mm. As a material constituting the surface layer, a resin such as chloroprene rubber (CR) to which conductivity is imparted by carbon black can be appropriately used. The thickness of the surface layer is, for example, 0.200 mm to 0.300 mm. In this embodiment, the intermediate transfer belt 6 has a volume resistivity of 5×10 8 Up to 1×10 14Ω.cm (23°C, 50%RH). Incidentally, in this embodiment, a double-layer structure is adopted in the intermediate transfer belt 6, but a single-layer structure of a material corresponding to the material of the above-mentioned base layer may also be adopted. In addition, the surface layer may also be formed as a resin coating layer having a thickness of about 0.002 mm to 0.01 mm containing a resin material such as a fluorine-containing resin. In addition, the intermediate transfer belt 6 may have a multilayer structure of three or more layers.

[0050] On the outer peripheral surface side of the intermediate transfer belt 6, an outer secondary transfer roller 25 is disposed, and the outer secondary transfer roller 25 is a roller-type secondary transfer member as a secondary transfer component. The outer secondary transfer roller 25 as a secondary transfer member cooperates with the inner secondary transfer roller 23 as an opposing member (opposing electrode) to form a secondary transfer device 26. The outer secondary transfer roller 25 is pressed toward the inner secondary transfer roller 23, and contacts the inner secondary transfer roller 23 through the intermediate transfer belt 6, and forms a secondary transfer portion (secondary transfer clamping portion) N2 as a contact portion between the intermediate transfer belt 6 and the outer secondary transfer roller 25. In the secondary transfer portion N2, by the action of the secondary transfer device 26, the colorant image formed on the intermediate transfer belt 6 is transferred (secondary transfer) to the recording material S clamped and conveyed by the intermediate transfer belt 6 and the outer secondary transfer roller 25. As a secondary transfer bias applying component (secondary transfer bias applying portion) ( Figure 2 ) is connected to the outer secondary transfer roller 25. During the secondary transfer, the secondary transfer power supply 76 applies a secondary transfer bias (secondary transfer voltage) which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (in this embodiment, a positive polarity) to the outer secondary transfer roller 25. Thus, the toner image of negative polarity on the intermediate transfer belt 6 is secondarily transferred onto the recording material S. The voltage detection sensor 76a ( Figure 2 ) and a current detection sensor 76b ( Figure 2) is connected to the secondary transfer power supply 76. In addition, the core metal of the inner secondary transfer roller 23 is connected to the ground potential. In this embodiment, for example, a secondary transfer voltage of about 1kV to 6.5kV is applied to the secondary transfer roller 25, and a current of about 15μA to 100μA is passed through the secondary transfer portion N2, so that the colorant image on the intermediate transfer belt 6 is secondarily transferred to the recording material S. In this embodiment, the secondary transfer bias is subjected to constant voltage control. Incidentally, the following structure can also be adopted: a secondary transfer bias as a DC voltage with the same polarity as the normal charge polarity of the colorant is applied from the secondary transfer power supply 76 to the inner secondary transfer roller 23 as the secondary transfer member, so that the outer secondary transfer roller 25 as the opposing member is connected to the ground potential. The outer secondary transfer roller 25 can be configured to rotate with the rotation of the intermediate transfer belt 6, or can also be configured to be rotationally driven by a driving member.

[0051] The recording material S is fed from the feeding section 4 toward the secondary transfer section N2 in parallel with the formation operation of the colorant image on the intermediate transfer belt 6. The recording material S is contained in a box 41 as a recording material containing section of the feeding section 4. The recording material S contained in the box 41 is separated and fed one by one from the box 41 by a feeding roller 42 or the like as a feeding member of the feeding section 4. The recording material S is conveyed by a conveying roller 43 or the like as a conveying member of the feeding section 4 to an alignment roller pair 19 as a conveying member provided on a conveying passage (conveying path) 44 for the recording material S. Then, the recording material S is conveyed to the secondary transfer section N2 by the alignment roller pair 19 in synchronization with the colorant image on the intermediate transfer belt 6. Incidentally, in Figure 1 In the figure, only one cassette 41 is illustrated, but the image forming apparatus 1 may include a plurality of cassettes 41. Furthermore, the feeding section 4 may be capable of feeding the recording material S also from a recording material accommodating section (recording material mounting section) other than the cassette 41 such as a manual feed tray or the like.

[0052] Here, in this embodiment, the outer secondary transfer roller 25 includes a core metal and an elastic layer of ion conductive foam rubber (NBR rubber) formed around the core metal. The outer diameter of the outer secondary transfer roller 25 is, for example, 20 mm to 25 mm. In addition, as the outer secondary transfer roller 25, a roller with a resistance value of 1×10 5 Up to 1×10 8 Ω (measured at N / N (23°C, 50% RH), 2 kV applied) of the roller.

[0053] The recording material S to which the toner image has been transferred is fed to a fixing device 27 as a fixing member. The fixing device 27 includes a fixing roller 27a and a pressure roller 27b. The fixing roller 27a includes a heater as a heating member therein. The pressure roller 27b is in pressure contact with the fixing roller 27a and forms a fixing portion (fixing nip portion). The fixing device 27 heats and pressurizes the recording material S by sandwiching and conveying the recording material S carrying the unfixed toner image between the fixing roller 27a and the pressure roller 27b, thereby fixing (melting, adhering) the toner image on the recording material S. Incidentally, the fixing temperature sensor 77 ( Figure 2 ) detects the temperature (fixing temperature) of the fixing roller 27a. The recording material S with the toner image fixed thereon is conveyed by the discharge roller pair 51 and the like in the discharge section 5, and is discharged (output) through a discharge opening (not shown) onto a discharge tray 52 provided outside the apparatus main assembly 1a of the image forming apparatus 1.

[0054] Here, in the case of single-sided printing in which an image is formed on one side (surface) of the recording material S, as described above, the recording material S on which the toner image is formed is discharged toward the discharge tray 52 through the discharge section 5. In addition, the image forming apparatus 1 of this embodiment includes a two-sided (double-sided) mechanism 60 capable of realizing two-sided (double-sided) printing (automatic two-sided printing) in which images are formed on both sides of the recording material S. In the case of two-sided printing, the recording material S on which the toner image is formed on the first side (surface) as described above is guided to the reverse conveying path 61 by the reverse conveying roller pair 62 and the like. The recording material S conveyed to the reverse conveying path 61 is reversed in the conveying direction and guided to the two-sided conveying path 63, and then after being conveyed to the registration roller pair 19 by the two-sided conveying roller pair 64 as a two-sided conveying member, it is supplied toward the secondary transfer section N2 again. Then, the toner image is transferred to the second side (surface) of the recording material S and fixed on the recording material S, and then discharged to the discharge tray 52 through the discharge section 5. The double-side mechanism 60 is composed of a reversing conveying roller pair 62 , a reversing conveying path 61 , a double-side conveying path 63 , a double-side conveying roller pair 64 , and the like.

[0055] The surface of the photosensitive drum 11 after the primary transfer is discharged by the pre-exposure device 16. In addition, the toner (primary transfer residual toner) remaining on the photosensitive drum 11 during the primary transfer and not transferred to the intermediate transfer belt 6 is removed from the surface of the photosensitive drum 11 by the drum cleaning device 17 and collected. In this embodiment, the drum cleaning device 17 scrapes off the primary transfer residual toner from the surface of the rotating photosensitive drum 11 by a cleaning blade as a cleaning member, and collects the primary transfer residual toner in a 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 direction opposite to the rotation direction of the photosensitive drum 11 so that its front end on the free end side faces the upstream side of the rotation direction of the photosensitive drum 11. Furthermore, deposited matter such as toner remaining on the intermediate transfer belt 6 during the secondary transfer without being transferred onto the recording material S (secondary transfer residual toner) and the like are removed from the surface of the intermediate transfer belt 6 and collected by a belt cleaning device 24 as an intermediate transfer member cleaning component.

[0056] Incidentally, the image forming unit 10 may constitute a cartridge (processing cartridge) integrally and detachably mountable to the apparatus main assembly 1a. In this embodiment, the intermediate transfer unit 20 is constituted by the intermediate transfer belt 6, a stretching roller for the intermediate transfer belt 6, each primary transfer roller 15, a belt cleaning device 24, and a potential limiting member 8 described later, etc. The intermediate transfer unit 20 may be integrally and detachably mountable to the apparatus main assembly 1a.

[0057] 2. Control composition

[0058] Figure 2 3 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a controller (control circuit) 3 as a control component. The controller 3 is composed of a CPU 31 as a computing component, a storage unit 35 as a storage component, and an input / output circuit (I / F) (not shown) for inputting / outputting signals between itself and an external device. The storage unit 35 is composed of a ROM (including a rewritable ROM) 32, a RAM 33, a non-volatile memory 34, etc. The ROM 32 stores programs for controlling various parts of the image forming apparatus 1, etc. The RAM 33 temporarily stores data about the control. The non-volatile memory 34 stores various setting information, usage history information, etc. The CPU 31 is a microprocessor that controls the entire image forming apparatus 1 and is a main part of the system controller. The CPU 31 is connected to various parts such as the feeding part 4, the image forming part 2, the discharge part 5, etc., and not only exchanges signals with these parts, but also controls the operation of each of these parts. The ROM 32 stores an image forming control sequence for forming an image on the recording material S.

[0059] A charging power source 73, a developing power source 74, a primary transfer power source 75, a secondary transfer power source 76, and a potential limiting power source 80 described later, which are respectively controlled by signals from the controller 3, are connected to the controller 3. Incidentally, although omitted in the illustration, in this embodiment, each of the charging power source 73, the developing power source 74, the primary transfer power source 75, and the potential limiting power source 80 is provided independently of the associated image forming unit 10. In addition, a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power source 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power source 76, a fixing temperature sensor 77, and the like are connected to the controller 3. Signals (information) indicating detection results of the associated sensors are input to the controller 3.

[0060] In addition, the operation unit 70 is connected to the controller 3. The operation unit 70 includes an input unit composed of operation buttons (keys) and the like as input means and a display unit 70a composed of a liquid crystal panel (display) and the like as a display means. Incidentally, in this embodiment, the display unit 70a is configured as a touch panel and also has a function as an input means. The operation unit 70 (display unit 70a) can display various setting screens and the like by the control of the control unit 3. In addition, an operator such as a user or a service person operates the operation unit 70, and thus can perform input of various settings to the controller 3, input of a start instruction of a job described later, and the like. The controller 3 receives a signal from the operation unit 70, and can perform registration of various settings to the storage unit 35 and control of operations of various devices of the image forming apparatus 1. Incidentally, the image forming apparatus 1 can also perform jobs and register various settings based on signals from, for example, an external device such as a personal computer instead of from the operation unit 70.

[0061] Here, the image forming device 1 performs a job (printing job, image forming operation), which is a series of operations for forming and outputting an image on a single recording material S or a plurality of recording materials stored by a single start instruction. Generally, the job includes an image forming step, a pre-rotation step, a sheet (paper) spacing step in the case where an image is formed on a plurality of recording materials S, and a post-rotation step. The image forming step is a period of time in which the formation of an electrostatic image, the formation of a toner image, the primary transfer of the toner image, and the secondary transfer of the toner image are performed on the recording material S, and during image formation (image forming period) refers to this period. Specifically, at the position of the steps of performing the formation of an electrostatic image, the formation of a toner image, the primary transfer of the toner image, and the secondary transfer of the toner image, the timing during image formation is different from each other. The pre-rotation step is a period of time of preparatory operations before the image forming step from the input of the start instruction until the actual start of image formation. The paper interval step (recording material interval step, image interval step) is a period corresponding to the interval between the recording material S and the subsequent recording material S when continuously forming images (continuous printing, continuous image formation) on a plurality of recording materials S. The post-rotation step is a period of time in which a post-operation (preparation operation) after the image forming step is performed. The non-image forming period (non-image forming period) is a period other than the image forming period, and includes the pre-rotation step, paper interval step, and post-rotation step as described above, and in addition, includes a pre-multi-rotation step of a preparatory operation during power (switching) on ​​of the image forming apparatus 1 or during recovery from a sleep state.

[0062] The kind of recording material S encompasses the distinction of recording materials S classified by information on any of the following recording materials S: attributes (so-called paper kind categories) based on general features (basis weight, thickness, surface properties, light reflection / light transmission characteristics, etc.) such as plain paper, high-quality paper, glossy paper (glossy paper), coated paper, embossed paper, thick paper, thin paper, rough paper, etc.; numerical values ​​and numerical ranges such as basis weight, thickness, rigidity, etc.; brand (including manufacturer, trade name, product name, etc.); or a combination of these factors; etc. That is, for each of the recording materials S distinguished by the information on the recording material S, it can be regarded as constituting a kind of recording material S. For the image forming apparatus 1, for example, for each kind of recording material S classified by paper kind category and basis weight, image forming conditions (transfer conditions, fixing conditions, process speed, etc.) corresponding to the associated kind are set.

[0063] 3. Problems with the nature of secondary transfer

[0064] Next, the problem in the secondary transfer property will be further described. Incidentally, for the sake of convenience, unless otherwise mentioned, the magnitude (high / low) of the voltage and the potential refers to the magnitude (high / low) when the values ​​thereof are compared with each other in terms of absolute values. In addition, with regard to the arrangement of the primary transfer section N1, the photosensitive drum 11, the primary transfer roller 15, and the potential limiting member 8 described later, etc., unless otherwise mentioned, the upstream and downstream refer to the upstream and downstream with respect to the conveying direction (process progress direction, moving direction) of the intermediate transfer belt 6.

[0065] As described above, the toner on the intermediate transfer belt 6 has a tendency that the amount of its charge increases by being subjected to discharge between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer section N1. When the inventors conducted research, it was found that the mirror force between the toner and the intermediate transfer belt 6 increases due to the increase in the amount of charge of the toner on the intermediate transfer belt 6, and therefore it becomes difficult to transfer the toner to the recording material S in the secondary transfer section N2. For example, as described above, it becomes difficult to uniformly transfer the toner onto embossed paper or the like having surface unevenness. Incidentally, embossed paper is paper (fancy paper) that provides an uneven pattern by using a method such as embossing or embossing on the surface of the paper. In addition, for example, due to the difference in the amount of charge of the toner on the intermediate transfer belt 6 generated between the secondary color and the single color, it becomes difficult to set a secondary transfer bias suitable for the secondary transfer (the secondary transfer latitude becomes narrower).

[0066] In order to suppress the increase in the charge amount of the toner on the downstream side of the primary transfer section N1 as described above, it is effective to suppress the discharge on the downstream side of the primary transfer section N1. In addition, when the inventors conducted research, it was found that in order to suppress the discharge on the downstream side of the primary transfer section N1, it is effective to provide a potential limiting member as a conductive electrode member on the downstream side and the inner peripheral surface side of the primary transfer section N1 and apply a bias voltage having the same polarity as the charge polarity of the photosensitive drum 11 to the potential limiting member.

[0067] 4. Potential limiting components

[0068] Next, the configuration of the potential limiting member 8 in this embodiment will be described. Figure 1 As shown in FIG. 1 , in the image forming apparatus 1 of this embodiment, potential limiting members 8y, 8m, 8c, and 8k as electrode members are respectively provided on the downstream side of the primary transfer portions N1y, N1m, N1c, and N1k in contact with the inner peripheral surface of the intermediate transfer belt 6. In this embodiment, the potential limiting members 8y, 8m, 8c, and 8k respectively provided in the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same configuration.

[0069] The shape of the potential limiting member 8 in this embodiment will be described. Figure 3Part (a) is a cross-sectional view of the potential limiting member 8 in this embodiment (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11). Figure 3 Part (b) is a perspective view of the potential limiting member 8 in this embodiment.

[0070] In this embodiment, the potential limiting member 8 includes a planar first portion 81 provided along the width direction of the intermediate transfer belt 6 (a direction substantially perpendicular to the conveying direction, a direction substantially parallel to the rotation axis direction of the photosensitive drum 11). Furthermore, in this embodiment, the potential limiting member 8 includes a planar second portion 82 provided along the width direction of the intermediate transfer belt 6 and extending in a direction substantially perpendicular to the flat surface of the first portion 81. In this embodiment, the contact surface 83 of the first portion 81 of the potential limiting member 8, which is a contact portion that contacts the inner peripheral surface of the intermediate transfer belt 6, is a flat surface. That is, in this embodiment, the first portion 81 constituting the contact surface 83 of the potential limiting member 8 is a flat plate.

[0071] Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, the upstream side end of the contact surface 83 is defined as "A (or upstream end A)", and the downstream side end of the contact surface 83 is defined as "B (or downstream end B)". In this embodiment, the upstream end A of the contact surface 83 corresponds to the upstream side end of the potential limiting member 8, and the downstream end B of the contact surface 83 corresponds to the downstream side end of the potential limiting member 8. By the action of the electric field formed in the space between the photosensitive drum 11 and the potential limiting member 8, in order to more effectively suppress the discharge between the intermediate transfer belt 6 and the photosensitive drum 11, the potential limiting member 8 may preferably be in contact with the surface of the intermediate transfer belt 6. From this viewpoint, the length of the line segment AB (between A and B) - that is, the "contact width" which is the length of the contact surface 83 in the conveying direction of the intermediate transfer belt 6 may preferably be 5 mm or more. The longer the length of the line segment AB, the greater the above-mentioned effect of suppressing the electric field becomes, but it will be considered that when the length becomes too long, stable contact of the potential limiting member 8 with the intermediate transfer belt 6 becomes difficult due to the influence of (assembly) parts accuracy, etc. In many cases where the length of the line segment AB is 50 mm or less and typically 30 mm or less, the length is insufficient.

[0072] That is, the length of the line segment AB may be appropriately about 5 mm to 50 mm, and typically about 5 mm to 30 mm. From another point of view, it can be said that in many cases, it is sufficient that the length of the line segment AB does not exceed half of the center distance between adjacent photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11. In this embodiment, the potential limiting member 8 having a length of 25 mm of the line segment AB is used. Incidentally, in this embodiment, the center distance between the photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11 is about 100 mm.

[0073] A potential limiting power source 80 as a potential limiting bias applying component (potential limiting bias applying portion) is connected to the potential limiting member 8. In this embodiment, the potential limiting power source 80 is connected to the second portion 82 of the potential limiting member 8. At least at the time of primary transfer during the image forming operation, a potential limiting bias (potential limiting voltage) is applied to the potential limiting member 8 by the potential limiting power source 80, and the potential limiting bias is a DC voltage having the same polarity as the charge polarity of the photosensitive drum 11. The time of the primary transfer is specifically a period of time during which the primary transfer bias is applied, and more specifically, a period of time during which the image area (area to which the toner image can be transferred) on the intermediate transfer belt 6 passes through the primary transfer section N1. Thus, discharge between the intermediate transfer belt 6 and the photosensitive drum 11 on the downstream side of the primary transfer section N1 can be suppressed. In this embodiment, the potential limiting bias is a DC voltage of negative polarity. In this embodiment, the potential limiting bias is subjected to constant voltage control. Furthermore, in the configuration of this embodiment, the potential limiting bias voltage (constant voltage of positive polarity) may preferably be approximately -500V to -3000V.

[0074] The potential limiting member 8 is a member that is long in the width direction of the intermediate transfer belt 6. The length of the contact surface 83 of the potential limiting member 8 in the longitudinal direction (the direction along the width direction of the intermediate transfer belt 6) may preferably be longer than the maximum image width in the width direction of the intermediate transfer belt 6. Incidentally, the maximum image width is the length of the image area of ​​the maximum image that can be formed by the image forming device 1 with respect to the width direction of the intermediate transfer belt 6. In this embodiment, the length of the contact surface 83 of the potential limiting member 8 in the longitudinal direction is longer than the above-mentioned maximum image width and longer than the width of the primary transfer roller 15 in contact with the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6. That is, in this embodiment, each of the range of the maximum image width and the range of the primary transfer roller 15 in contact with the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6 falls within the range of the length of the contact surface 83 of the potential limiting member 8 in the longitudinal direction.

[0075] Thus, regardless of the length of the toner image transferred onto the intermediate transfer belt 6 with respect to the width direction of the intermediate transfer belt 6, the effect of suppressing the increase in the charge amount of the toner on the intermediate transfer belt 6 by suppressing the above-mentioned discharge can be obtained. On the other hand, in this embodiment, the length of the potential limiting member 8 in the longitudinal direction is shorter than the width of the intermediate transfer belt 6. That is, in this embodiment, the range of the length of the potential limiting member 8 in the longitudinal direction falls within the range of the width of the intermediate transfer belt 6. Thus, in the case where the end of the potential limiting member 8 with respect to the longitudinal direction protrudes more than the end of the intermediate transfer belt 6 with respect to the width direction, discharge occurs to the potential limiting member 8 and the members around the intermediate transfer belt 6, so that the possibility of reducing the effect of suppressing the discharge can be reduced.

[0076] The potential limiting member 8 may be composed, for example, of only a single material having conductivity. In this embodiment, the potential limiting member 8 is basically composed of only a metal having conductivity, such as SUS (stainless steel). Specifically, in this embodiment, the potential limiting member 8 is formed by subjecting a plate (metal plate) made of metal such as SUS to bending to form a first portion 81 and a second portion 82. In this embodiment, each of the first portion 81 and the second portion 82 of the potential limiting member 8 is substantially not deformed in the use state of the image forming apparatus 1. By thus subjecting the metal plate to bending, the strength of the potential limiting member 8 can be increased. However, the present invention is not limited to such an embodiment, and the potential limiting member 8 may also be composed of two or more materials.

[0077] Figure 4 : is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) in another example of the potential limiting member 8. For example, Figure 4 As shown in , the following configuration can be adopted: set up with Figure 3 8 and a surface layer 85 formed on the base 84. The contact surface 83 in contact with the intermediate transfer belt 6 and the surface layer 85 constituting the connection portion with the potential limiting power supply 80 are formed of a conductive material such as metal or a conductive resin material. The base 84 may be formed of a conductive material, but may also be formed of a non-conductive material such as a non-conductive resin material. The base 84 and the surface layer 85 may be fixed by any fixing means such as an adhesive or welding.

[0078] also, Figure 5 : is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) in still another example of the potential limiting member 8. For example, Figure 5 As shown in FIG. 8 , the contact surface 83 of the potential limiting member 8 that contacts the intermediate transfer belt 6 may also be formed of a conductive nonwoven fabric 86. Figure 5In the embodiment, the conductive nonwoven fabric 86 is provided on a Figure 4 The potential limiting member 8 is shown in the structure shown in FIG. 1 , but it can also be set on the contact surface 83 of the potential limiting member 8 having Figure 3 On the contact surface 83 of the potential limiting member 8 of the structure shown in the figure. The conductive nonwoven fabric 86 can be fixed by any fixing means such as a conductive adhesive. In addition, the nonwoven fabric 86 can also be replaced by a felt, a pile fabric (external pile fabric (velvet, brush) or a loop pile fabric (towel)) made of conductive fibers, or a sponge (elastic foam member) made of a conductive rubber material or the like. Therefore, the contact surface 83 of the potential limiting member 8 that contacts the intermediate transfer belt 6 is composed of a flexible material or an elastic material, so that the possibility of the occurrence of damage marks on the inner peripheral surface of the intermediate transfer belt 6 caused by the friction (sliding) between the inner peripheral surface of the intermediate transfer belt 6 and the potential limiting member 8 can be reduced.

[0079] Next, the arrangement of the potential limiting member 8 in this embodiment will be described. Figure 6 2 is a cross-sectional view (a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for illustrating the arrangement of the potential limiting member 8 provided between two primary transfer portions N1 adjacent to each other in the conveying direction of the intermediate transfer belt 6. Figure 6 , as an example, the potential limiting member 8 c provided between the primary transfer portion N1 c for cyan and the primary transfer portion N1 k for black is shown.

[0080] In this embodiment, the outer diameter of the photosensitive drum 11 is 30 mm, the outer diameter of the primary transfer roller 15 is 18 mm, and the thickness of the intermediate transfer belt 6 is 0.350 mm. In addition, in this embodiment, the primary transfer roller 15 is offset toward the downstream side relative to the photosensitive drum 11. In this embodiment, the offset amount X1 is 3 mm. Incidentally, the offset amount X1 is the distance between the rotation center of the photosensitive drum 11 and the rotation of the associated primary transfer roller 15 in the direction of the common tangent line along the side where the plurality of photosensitive drums 11 contact the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11.

[0081] Here, in order to illustrate the configuration of the potential limiting member 8, it is assumed that the potential limiting member 8 is removed. In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line through which the stretching surface of the intermediate transfer belt on the inner peripheral surface side in the portion downstream of the primary transfer portion N1 in the absence of the potential limiting member 8 passes is defined as a straight line L. Incidentally, specifically, this straight line L corresponds to the stretching surface in a state in which only the potential limiting member 8 is substantially removed from the configuration of the image forming device 1 in a state during the image forming operation. In addition, on the straight line L, a portion of the inner peripheral surface of the intermediate transfer belt 6 separated from the nearest stretching member on the upstream side of the potential limiting member 8 is defined as “C (or upstream stretching portion C)”, and a portion of the inner peripheral surface of the intermediate transfer belt 6 separated from the nearest stretching member on the downstream side of the potential limiting member 8 is defined as “D (or downstream stretching portion D)”. Incidentally, in Figure 6 , the straight line L is schematically shown substantially horizontally, but in the case where the surface of the primary transfer roller 15 rises toward the photosensitive drum 11 side due to deformation of the elastic layer of the primary transfer roller 15 or the like, the straight line L may be inclined downward toward the downstream side in the figure.

[0082] In this embodiment, the closest stretching member on the upstream side of the potential restricting member 8 is the primary transfer roller 15, and the position on the inner peripheral surface of the intermediate transfer belt 6 at the portion where the intermediate transfer belt 6 is separated from the primary transfer roller 15 is the upstream stretching portion C. However, the closest stretching member on the upstream side of the potential restricting member 8 is not limited to the primary transfer member 15. For example, in the case where the primary transfer roller 15 is offset toward the upstream side relative to the photosensitive drum 11 and disposed on the upstream side, the position on the inner peripheral surface of the intermediate transfer belt 6 at the portion corresponding to the portion where the intermediate transfer belt 6 is separated from the photosensitive drum 11 is the upstream stretching portion C.

[0083] Furthermore, in this embodiment, the closest stretching member on the downstream side of the potential restricting member 8 is the photosensitive drums 11m, 11c, and 11k disposed adjacent to the potential restricting member 8 on the downstream side of the potential restricting member 8 of the primary transfer portions N1y, N1m, and N1c for yellow, magenta, and cyan, respectively. Furthermore, the position on the inner peripheral surface of the intermediate transfer belt 6 at a portion corresponding to a portion where the intermediate transfer belt 6 is separated from an associated one of the photosensitive drums 11m, 11c, and 11k is the downstream stretching portion D. However, the closest stretching member on the downstream side of the potential restricting member 8 is not limited to the photosensitive drum 11. For example, in the case where the primary transfer roller 15 is offset toward the upstream side relative to the photosensitive drum 11 and disposed on the upstream side, the position on the inner peripheral surface of the intermediate transfer belt 6 at a portion where the intermediate transfer belt 6 is separated from the primary transfer roller 15 is the downstream stretching portion D. Further, in this embodiment, for the most downstream primary transfer portion N1k for black, the closest stretching member on its downstream side is the stretching roller (in this embodiment, the tension roller) 22. Furthermore, a position on the inner peripheral surface of the intermediate transfer belt 6 at a portion where the intermediate transfer belt 6 is separated from the stretching roller 22 is a downstream stretching portion D.

[0084] In addition, for each of the primary transfer sections N1, as the closest stretching member on the downstream side of the potential limiting member 8, in the case where there is another stretching roller for limiting the posture of the intermediate transfer belt 6 during the image forming operation, the straight line L and the downstream stretching portion D are defined based on its stretching roller. Furthermore, in the case where a stretching roller, a scraper, or a brush is brought into contact with the outer peripheral surface of the intermediate transfer belt 6 for the purpose of cleaning the inner peripheral surface of the intermediate transfer belt 6 or for the like, when the scraper or the brush limits the posture of the intermediate transfer belt 6, the scraper or the brush can be regarded as the closest stretching member on the downstream side of the potential limiting member 8. The scraper is generally composed of a sheet-like or film-like member.

[0085] like Figure 6 As shown in , the potential limiting member 8 is disposed 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. At this time, the closer the upstream end A is to the primary transfer section N1, the greater the above-mentioned charge suppression effect becomes. In this embodiment ( Figure 6), the potential limiting member 8 is disposed in a position downstream of the primary transfer portion N1 so that the distance X2 from the primary transfer roller 15 to the upstream end A becomes about 8 mm. Here, the distance X2 is the distance between the rotation center of the primary transfer roller 15 and the upstream end A in the direction of the common tangent along the side where the plurality of photosensitive drums 11 are in contact with the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11. That is, in this embodiment, in the direction along the above-mentioned common tangent, the distance from the rotation center of the primary transfer roller 15 to the upstream end A is shorter than the distance (radius) from the rotation center of the primary transfer roller 15 to the outer periphery of the primary transfer roller 15. The distance X2 is not limited thereto, but may preferably be about 1 mm to 20 mm, typically about 1 mm to 10 mm.

[0086] Furthermore, in this embodiment, the potential limiting member 8 is provided at each of its opposite end portions with respect to its longitudinal direction with a pressurizing spring 87 ( Figure 3 The portion (b) of the potential limiting member 8 is pressed against the inner peripheral surface of the intermediate transfer belt 6. At this time, the contact portion of the potential limiting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is brought into the photosensitive drum 11 side relative to the straight line L. Thus, even in the case where a fluctuation or vibration occurs on the intermediate transfer belt 6 during the image forming operation (during the travel of the intermediate transfer belt 6), the potential limiting member 8 can be brought into contact with the intermediate transfer belt 6 more stably. In this embodiment, the pressing force of the pressing spring 87 is set (adjusted) so that each of the upstream end A and the downstream end B of the contact surface 83, which is the contact portion of the potential limiting member 8 with the inner peripheral surface of the intermediate transfer belt 6, enters the photosensitive drum 11 side by about 0.5 mm relative to the straight line L. Therefore, by bringing the contact surface 83 of the potential limiting member 8 into the photosensitive drum 11 side relative to the straight line L, even in the case where a fluctuation or vibration occurs on the intermediate transfer belt 6 during the image forming operation (during the travel of the intermediate transfer belt 6), the potential limiting member 8 can be brought into contact with the intermediate transfer belt 6 more stably. Although the potential limiting member 8 is not limited thereto, the amount of entry of the contact surface 83 of the potential limiting member 8 into the straight line L may preferably be about 0.3 mm to 5 mm, typically about 0.5 mm to 3 mm. When the entry amount is too small, it may be difficult for the potential limiting member 8 to stably contact the intermediate transfer belt 6. When the entry amount is too large, it may be difficult to stably feed (convey) the intermediate transfer belt 6.

[0087] Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line passing through the upstream end A and the downstream end B of the contact surface 83 is defined as a straight line M. At this time, it is preferable to prevent the straight line M from intersecting with the line segment CD of the straight line L. Thus, in the case where the contact surface 83 of the potential limiting member 8 is a flat surface, the intermediate transfer belt 6 and the potential limiting member 8 can be more reliably in surface contact with each other. In the case where the straight line M intersects with the line segment CD of the straight line L, there is a possibility that only either one of the end of the potential limiting member 8 on the upstream end A side and the end of the potential limiting member 8 on the downstream end B side can be in contact with the inner peripheral surface of the intermediate transfer belt 6. In this case, it is possible that it becomes difficult to enhance the discharge suppression effect by surface contact.

[0088] In addition, Figure 6 In the embodiment, the potential limiting member 8 is disposed so that the straight line M and the straight line L are substantially parallel to each other, but when the straight line M falls within a range in which the straight line M does not intersect the line segment CD of the straight line L, the potential limiting member 8 may be disposed so that the straight line M is inclined relative to the straight line L. For example, the straight line M is inclined relative to the straight line L so that the upstream end A side is closer to the straight line L than the downstream end B side, so that the curvature generated on the intermediate transfer belt 6 due to the arrangement of the intermediate transfer belt 6 near the upstream end A can be made small. Therefore, this case is advantageous in reducing the possibility of occurrence of damage marks on the inner peripheral surface of the intermediate transfer belt 6 due to friction (sliding) with the potential limiting member 8.

[0089] Incidentally, the contact portion of the potential limiting member 8 with the inner peripheral surface of the intermediate transfer belt 6 is not limited to a flat surface. For example, the potential limiting member 8 is composed of a curved plate that is curved in a convex curved shape toward the photosensitive drum 11 side in a cross section substantially perpendicular to the rotation axis direction, and the contact portion of the potential limiting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 may be a convex curved surface toward the photosensitive drum 11 side. Therefore, the contact portion (contact surface) of the potential limiting member 8 that contacts the inner peripheral surface has a curved surface, so that the stress when the potential limiting member 8 slides with the intermediate transfer belt 6 can be alleviated. By using a roller-shaped potential limiting member 8, the contact portion of the potential limiting member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 can also have a curved surface.

[0090] Here, in this embodiment, the default value of the potential limiting bias is set in advance according to the kind of recording material S. Incidentally, in this embodiment, for each kind of recording material S, the default value of the potential limiting bias is set according to the environment (temperature, humidity), and then stored in the storage section 35 (ROM 32 or nonvolatile memory 34). In this embodiment, for example, in a predetermined environment (e.g., normal temperature / normal humidity environment: 23°C / 50%RH), for general-purpose plain paper (e.g., basis weight: 64-75 g / m2 ), the default value of the potential limit bias is set to -1500V.

[0091] In addition, for example, in the above-mentioned predetermined environment, for embossed paper, the default value of the potential limiting bias is set to -3000 V. Similarly, in the above-mentioned environment, for double-sided coated paper (e.g., basis weight: 106-128 g / m 2 ) or synthetic paper, the default value of the potential limit bias is set to -3000V.

[0092] 5. One-time transfer ATVC

[0093] Next, the control of the primary transfer bias in this embodiment will be described. Incidentally, in this embodiment, the control of the primary transfer bias is similar between the primary transfer sections N1y, N1m, N1c, and N1k, and is individually performed in a synchronized manner. In this embodiment, the description will be made by focusing on a single primary transfer section.

[0094] In this embodiment, in the image forming apparatus 1, a constant voltage is applied to the primary transfer portion N1 (primary transfer roller 15) so that the toner image is transferred from the photosensitive drum 11 to the intermediate transfer belt 6. In addition, in this embodiment, the image forming apparatus 1 adopts ATVC (active transfer voltage control) as a type of voltage condition for applying a primary transfer bias to the primary transfer portion N1 (primary transfer roller 15) during image formation (during primary transfer). In the ATVC of the primary transfer portion N1 (hereinafter, also referred to as "primary transfer ATVC"), in order to obtain the primary transfer bias during image formation (during primary transfer) according to the total resistance value of the primary transfer portion N1 composed of the intermediate transfer belt 6 and the primary transfer roller 15, a test bias (test voltage, test current) is used to obtain voltage-current characteristics. The primary transfer ATVC is executed by control by the controller 3.

[0095] In the primary transfer ATVC, during the non-image formation period in which there is no toner image in the primary transfer section N1, a predetermined voltage or a predetermined current is supplied from the primary transfer power supply 75 to the primary transfer section N1 (primary transfer roller 15) as a test bias. The setting value of the predetermined voltage or the predetermined current as the test bias is one level or a plurality of levels. In addition, when the test bias as the predetermined voltage is supplied, the current flowing through the primary transfer roller 15 (primary transfer power supply 75) is detected by the current detection sensor 75b. Alternatively, when the test bias as the predetermined current is supplied, the voltage applied to the primary transfer roller 15 (the output voltage of the primary transfer power supply 75) is detected by the voltage detection sensor 75a. Thus, the voltage-current characteristic according to the impedance (total resistance value) of the primary transfer section N1 is obtained. Based on the voltage-current characteristic, the voltage required to flow the primary transfer current suitable for the primary transfer of the toner according to the impedance (total resistance value) of the primary transfer section N1 is calculated. Then, during image formation (during primary transfer), a primary transfer bias is applied to the primary transfer roller 15 under constant voltage control in which the calculated voltage is used as a target voltage.

[0096] Figure 7 : is a flow chart of the primary transfer ATVC in this embodiment. Figure 8 is a graph schematically showing voltage-current characteristics obtained in the primary transfer ATVC.

[0097] When the primary transfer ATVC starts, the controller 3 causes the primary transfer power supply 75 to apply the target voltage (set voltage) V1 [V] determined by the previous primary transfer ATVC to the primary transfer roller 15 while applying a charging bias close to the charging bias during normal image formation to the charging roller 12. Then, the controller 3 causes the current detection sensor 75b to acquire the detection current I1 (S101). Incidentally, in the absence of a target voltage determined by the previous primary transfer ATVC, only the predetermined target voltage V1 may need to be used. Then, the controller 3 compares the acquired detection current I1 [μA] with the target current I0 [μA], and determines whether I1 is I0 or greater (I0 ≤ I1) (S102). The target current I0 is stored in the storage unit 35 (ROM 32) after obtaining an appropriate value based on, for example, the environment (temperature, humidity) in advance based on experiments, etc. Then, in the case where I1 is not I0 or greater - that is, I1 is less than I0 (I0>I1), the controller 3 causes the power supply to apply V2 (=V1+α) [V) obtained by adding a predetermined voltage value α [V] to the above-mentioned V1 to the primary transfer roller 15. Then, the controller 3 causes the current detection sensor 75b to acquire the detection current I2 (S103). On the other hand, in the case where I1 is I0 or greater (I0≤I1), the controller 3 causes the power supply to apply V2 (=V1-α) [V) obtained by subtracting a predetermined voltage value α [V] from the above-mentioned V1 to the primary transfer roller 15. Then, the controller 3 causes the current detection sensor 75b to acquire the detection current I2 (S104). Figure 8 An example of a case where I0>I1 is shown, and V2=V1+α[V] holds. Next, the controller 3 performs linear interpolation using the detection currents I2 and I1, and determines a target voltage V0 corresponding to the target current I0 (S105). Then, during image formation (during primary transfer), the primary transfer bias applied to the primary transfer portion N1 (primary transfer roller 15) is subjected to constant voltage control at the determined target voltage V0.

[0098] Incidentally, in the single transfer ATVC, a test bias subjected to constant current control at a predetermined current (e.g., target current I0) may be used, or both a test bias subjected to constant current control at a predetermined current and a test bias subjected to constant voltage control at a predetermined voltage may be used. Here, constant current control is a control in which the output of a power supply is adjusted so that the current supplied to a supply object becomes substantially constant at a target current. In addition, constant voltage control is a control in which the output of a power supply is adjusted so that the voltage applied to an application object becomes substantially constant at a target voltage. In addition, the test bias may be one level (e.g., a test bias corresponding to the target current I0), or may be three levels or more.

[0099] In addition, the voltage-current characteristic is not limited to being calculated once by linear approximation, but can also be obtained by curve approximation. In addition, in this embodiment, the transfer ATVC is performed once in the pre-rotation step (or in the post-rotation step) as in the non-image formation period. However, the present invention is not limited to this, but if the execution timing is during the non-image formation period, for example, the transfer ATVC can be performed once in the paper interval step at a predetermined frequency (per a predetermined number of sheets subjected to image formation) during continuous image formation. In addition, in this embodiment, also during the non-image formation period, similarly to the image formation period, a potential limiting bias is applied to the potential limiting member 8 by constant voltage control.

[0100] As in this embodiment, in the case where an ion conductive foam rubber is used as the material of the primary transfer member or in similar cases, the resistance value of the primary transfer member changes depending on the environment and the state of use. When the resistance value of the primary transfer member changes, the current required for transferring the toner changes, and therefore, it is necessary to appropriately perform the primary transfer ATVC. In this embodiment, in the case where the temperature changes by 3°C or more (increases or decreases by 3°C or more) relative to the ambient temperature when the previous primary transfer ATVC was performed, the primary transfer ATVC is performed again at the subsequent pre-rotation timing. In addition, in this embodiment, in the case where printing of 500 images is performed after the previous transfer ATVC is performed, the primary transfer ATVC is performed again at the subsequent pre-rotation timing. On the other hand, it will be considered that the primary transfer ATVC is performed before each image formation, but in this case, the FCOT (first copy output time) becomes longer, so the execution of such a primary transfer ATVC is not preferred.

[0101] Incidentally, also, regarding the secondary transfer section N2, during the non-image formation period in which the toner image and the recording material S are not present in the secondary transfer section N2, an ATVC roughly similar to the above-mentioned primary transfer ATVC is performed (herein, this ATVC is also referred to as "secondary transfer ATVC"). In the secondary transfer ATVC, the base voltage (secondary transfer partial voltage (shared voltage)) of the secondary transfer bias during image formation (during secondary transfer) according to the resistance value of the secondary transfer section N2 (mainly, the outer secondary transfer roller 25) is obtained. Based on the base voltage and the recording material partial voltage according to the type of the recording material S, the target voltage of the secondary transfer bias during image formation (during secondary transfer) is determined. Then, during image formation (during secondary transfer), the secondary transfer bias applied to the secondary transfer section N2 (outer secondary transfer roller 25) is subjected to constant voltage control at the determined target voltage. In this embodiment, the secondary transfer ATVC is performed in the pre-rotation step of the job (or in the pre-multi-rotation step) as in the non-image forming period. However, the present invention is not limited thereto, but if the execution timing is during the non-image forming period, for example, the secondary transfer ATVC can be performed in the paper interval step at a predetermined frequency (per a predetermined number of sheets subjected to image forming) during continuous image forming.

[0102] 6. Adjustment of potential limiting bias

[0103] Next, the adjustment (correction) of the potential limiting bias in this embodiment will be described. Incidentally, regarding the recording material S, unless otherwise specified, the leading end and the trailing end refer to the leading end and the trailing end with respect to the conveying direction of the recording material S when the recording material S passes through the secondary transfer portion N2, respectively.

[0104] As described above, in order to suppress the increase in the charge amount of the toner on the intermediate transfer belt 6 by suppressing the discharge on the downstream side of the primary transfer section N1, it is effective to apply a potential limiting bias having the same polarity as the charge polarity of the photosensitive drum 11 to the potential limiting member 8. Thus, for example, the toner can be easily transferred uniformly onto embossed paper having surface unevenness. In addition, the difference in the charge amount of the toner is made small between the secondary color and the single color, making it easy to ensure the secondary transfer latitude.

[0105] However, as described above, in the case of using a recording material S having a relatively high resistance value such as coated paper or synthetic paper (hereinafter, the paper is also referred to as "high resistance paper"), when the charge amount of the colorant on the intermediate transfer belt 6 is reduced and the holding force of the colorant on the intermediate transfer belt 6 is reduced when a potential limiting bias is applied to the potential limiting member 8, "dispersion" and "image interference" are likely to occur in some cases.

[0106] That is, as described above, in this embodiment, each kind of recording material S, such as a representative recording material, is selected, so that the default value of the potential limiting bias is set in advance. However, it is assumed that the commercially available recording material S includes a recording material having properties different from those of the representative recording material. For this reason, under the default value of the potential limiting bias, the amount of charge of the toner on the intermediate transfer belt 6 becomes too low, so that the electrostatic holding force between the intermediate transfer belt 6 and the toner may become too low. In the case where the recording material S used by the user is a high-resistance paper such as coated paper or synthetic paper, in order to ensure the secondary transfer properties, there is a tendency to set the secondary transfer bias high (large absolute value). In this state, when the high-resistance sheet is conveyed toward the secondary transfer portion N2, at a portion where the behavior of the recording material S is unstable, such as the front end or rear end of the recording material S, in some cases, "dispersion" occurs. This is because the interval between the recording material S and the intermediate transfer belt 6 changes at the portion where the behavior of the recording material S is unstable and thus the magnitude of the electric field applied to the toner changes. In addition, “image disturbance” occurs in some cases without being limited to the leading and trailing ends of the recording material S. This is because the intermediate transfer belt 6 and the recording material S slide against each other in a state where the holding force of the toner on the intermediate transfer belt 6 is reduced.

[0107] Fig. 9 Part (a) is a schematic diagram showing dispersion that occurs at the leading and trailing ends of a recording material S when a halftone image (e.g., a halftone image having an area ratio of 50% at the image portion) is formed on the entire surface of the recording material S. Dispersion has a tendency to be easily noticeable in a halftone image, and generally, a portion where dispersion occurs appears darker in density than a portion where dispersion does not occur. This is because the dispersed toner is disposed at the position where the toner should originally be disposed in the halftone image. Fig. 9 The reason why the shapes of the scattered parts appear different between the front end and the rear end in part (a) is due to the difference in posture and shape (fluctuation) of the recording material S during transportation. Fig. 9 Part (b) of FIG. 1 is a schematic diagram showing image noise occurring at a portion of the recording material S in the case where a halftone image (e.g., a halftone image having an area ratio of 50% at the image portion) is formed on the entire surface of the recording material S. Image noise has a tendency to be easily noticeable in a halftone image, and for reasons similar to those in the case of the above-mentioned dispersion, generally, the portion where the image noise occurs appears dark in density compared to the portion where the image noise does not occur. Fig. 9In part (b), the reason why image interference occurs from the front end of the recording material S to a certain position on the rear end side and does not occur from this position to the rear end of the recording material S is that the rear end of the recording material S passes through the positioning roller pair 19 and thus the followability of the recording material S to the intermediate transfer belt 6 is improved, etc.

[0108] "Dispersion" and "image interference" are affected by the amount of charge of the toner on the intermediate transfer belt 6, and are also easily affected by the type of recording material S, image duty ratio (image ratio, print ratio), etc. For this reason, it is preferable that the value of the potential limiting bias voltage can be freely adjusted according to the type of recording material S, the pattern of the output image, etc., so that the user can obtain the desired effect.

[0109] Therefore, in this embodiment, the image forming apparatus 1 is configured so that the user can adjust the potential limit bias value. In particular, in this embodiment, in the image forming apparatus 1, a default value of the potential limit bias is preset according to the type of the recording material S. Furthermore, in this embodiment, the image forming apparatus 1 is configured so that the user can adjust the potential limit bias value from the default value to a desired value.

[0110] Fig.10 1 is a flowchart showing an example of a process in which a user adjusts the potential limit bias of the recording material S for image formation. In this embodiment, a case where a user performs an adjustment-related operation such as inputting an adjustment value into the operation section 70 of the image forming apparatus 1 or the like will be described as an example.

[0111] First, the user outputs an image on the prepared recording material S ( S201 ), and checks whether the potential limit bias value previously set for the recording material S is appropriate ( S202 ).

[0112] At this time, before outputting the image, the user may select a display such as the one displayed on the operation unit 70 (display unit 70a). Fig.11 The type of recording material S corresponding to the type of recording material S prepared is specified in the recording material selection screen 200 shown in part (a) of FIG. 1 . Thus, an image is output under the image forming conditions (voltage conditions of the secondary transfer bias, voltage conditions of the potential limiting bias, fixing conditions, process speed, etc.) pre-set for the type of recording material S. Fig.11 In the recording material selection screen 200 shown in part (a), information about the recording material S (paper type category, basic weight, size, etc.) 201 pre-stored in the storage unit 35 in association with the paper feeding unit 4 (box 41, etc.) and a selection button 202 for selecting the type of recording material S to be used are displayed.

[0113] In a case where the secondary transfer bias value set in advance is not optimal, the user performs adjustment of the secondary transfer bias ( S203 to S205 ).

[0114] At this time, the user can Fig.11 The type of recording material S for which the user desires to adjust the secondary transfer bias is specified in the recording material setting screen 300 shown in part (b) of the drawing, and the sequence proceeds to the adjustment of the secondary transfer bias. Fig.11 In the recording material setting screen 300 shown in part (b) of the present invention, an adjustment button 301 is displayed in association with a paper type category 303 of the recording material S pre-registered in the storage unit 35. The user operates the adjustment button 301 corresponding to the paper type category of the recording material S for which the user desires to adjust the image forming conditions, and can proceed to the adjustment screen of the secondary transfer bias. Fig.11 In the recording material setting screen 300 shown in part (b) of the drawing, by operating the adjustment button 301, the user can also proceed to an adjustment screen of another image forming condition such as a potential limiting bias adjustment screen described later in addition to the secondary transfer bias adjustment screen. Fig.11 In the recording material setting screen 300 shown in part (b) of the present invention, a copy button 302 is provided so that desired settings can be individually registered while retaining the default settings. For example, in the copied paper type category 303, its name is registered as another name in the storage section 35, and the default settings except for the image forming conditions changed in the settings are retained.

[0115] The user operates the adjustment button 301 in the recording material setting screen 300 so that Fig.12 The secondary transfer bias adjustment screen 400 shown in part (a) of FIG. 7 is displayed at the operation section 70 (display section 70a). Fig.12In the secondary transfer bias adjustment screen 400 shown in part (a) of the embodiment, there is an adjustment value display section 401 for displaying the adjustment value (offset value) of the secondary transfer bias and an adjustment value input section ((+) button, (-) button) 402 for inputting (changing) the adjustment value. In this embodiment, each of the adjustment value display section 401 and the adjustment value input section 402 is provided for the front side (the image surface in single-sided printing, the first surface in double-sided printing) and the back side (the second surface in double-sided printing). In addition, in the secondary transfer bias adjustment screen 400, there is an OK (confirmation) button 403 for confirming the change of the setting and then storing the change in the storage section 35 and a cancel button 404 for canceling the change of the setting. The user operates the adjustment value input section 402 so that the secondary transfer bias (specifically, the recording material partial pressure) can be changed from the default value corresponding to the adjustment value 0 by a predetermined change width (for example, +50V to +500V (or -50V to -500V) for each adjustment value +1 (or -1). The adjustment changed by the adjustment value input section 402 is displayed at the adjustment value display section 401. Then, the user can determine the change of setting by operating the determination button 403, and then the change can be stored in the storage section 35, and the change of setting can be canceled by operating the cancel button 404. The user inputs the adjustment value (S203) and repeats the output of the image and the check of the output image (S204), so that the optimal value of the secondary transfer bias can be set (S205). At this time, it is preferable whether the secondary color can be mainly properly transferred.

[0116] Incidentally, as an image output for adjusting (checking) the secondary transfer bias, the user can use an image that the user actually expects to obtain as a product, or can also use a predetermined image for adjustment. In the case of adjusting the secondary transfer bias when the image on the two surfaces (faces) of the recording material S is formed, it is only necessary to output the image for adjusting the secondary transfer bias by using the two-sided printing of the above-mentioned two-sided mechanism 60. In the case of the image actually obtained by the user as a product, the user repeats the input of the adjustment value and the output of the image as described above, so that the optimal value of the secondary transfer bias can be set. In the case where the voltage value of the secondary transfer bias is insufficient, the colorant cannot be fully transferred, so that the image concentration is reduced. In the case where the voltage value of the secondary transfer bias is too large, an image defect occurs in which the colorant (image) is not partially transferred due to abnormal discharge, etc. In addition, in the case of using a predetermined image for adjustment, the user can output an adjustment chart with a plurality of representative color blocks (test images, test toner images) transferred while switching the voltage value of the secondary transfer bias for each color block.

[0117] In this case, the user can Fig.12The image forming apparatus 1 can output the adjustment map by clicking the map output button 405 displayed in the secondary transfer bias adjustment screen 400 shown in part (b) of the drawing. Fig.13 is a schematic diagram showing an example of an adjustment map. Fig.13 In the adjustment diagram of the secondary transfer bias adjustment screen 400, a plurality of secondary color (e.g., blue) solid color images and a plurality of black solid color images are transferred while switching the voltage values ​​of the secondary transfer bias voltages, respectively. For example, the user inputs the adjustment values ​​printed in association with the color patches for obtaining the optimal transfer property (density) into the adjustment value display unit 401 in the secondary transfer bias adjustment screen 400.

[0118] Next, the user checks whether the value of the potential limit bias voltage set in advance for the recording material S is appropriate, and then adjusts the value of the potential limit bias voltage (S206 to S208).

[0119] At this time, first, the user can check whether the potential limit bias value is appropriate by checking the image output last in the adjustment of the secondary transfer bias, or can also check whether the potential limit bias value is appropriate by rechecking the output image.

[0120] As described above, the user sets the recording material setting screen 300 ( Fig.11 In part (b) of FIG. 1 , the adjustment button 301 is operated so that Fig.14 The potential limiting bias adjustment screen 500 shown in FIG. 1 is displayed on the operation section 70 (display section 70 a ). Fig.14In the potential limit bias adjustment screen 500, an adjustment value display section 501 for displaying an adjustment value (offset value) of the potential limit bias and an adjustment value input section ((+) button, (-) button) 502 for inputting (changing) the adjustment value are displayed. In this embodiment, for each of the image forming units 10 of yellow, magenta, cyan, and black, each of the adjustment value display section 501 and the adjustment value input section 502 is provided for the front side (image surface for single-sided printing, first surface for double-sided printing) and the back side (second surface for double-sided printing). In addition, in the potential limit bias adjustment screen 500, an OK (confirmation) button 503 for determining a change in setting and storing the change in setting in the storage section 35 and a cancel button 504 for canceling the change in setting are displayed. The user can change the potential limit bias from the default value corresponding to the adjustment value 0 in a change width (for example, +50V to +500V (or -50V to -500V)) for each adjustment value +1 (or -1) by operating the adjustment value input section 502. The adjustment value changed by the adjustment value input section 502 is displayed at the adjustment value display section 501. Then, the user determines the change of setting by operating the determination button 503, and then can cause the storage section 35 to store the change of setting, and can cancel the change of setting by operating the cancel button 504. The user inputs the adjustment value (offset value) (S206) and repeats the output of the image and the check of the output image (S207), so that the optimum value of the potential limit bias can be set (S208).

[0121] Incidentally, as an image output for adjusting (checking) the potential limiting bias, an image that the user actually expects to obtain as a product may be used, or a predetermined adjustment image may be used. In the case where the potential limiting bias in the formation of images on both surfaces of the recording material S is adjusted, by using double-sided printing of the above-mentioned two-sided mechanism 60, it is only necessary to output an image for adjusting the potential limiting bias. For example, a halftone image (for example, a halftone image with an image ratio of 50% for the image portion) of a single color (each of yellow, magenta, cyan, and black) is output on the entire surface of the recording material S (which may include page margins). Then, in a manner such as Fig. 9 In the case where dispersion occurs at the front end and the rear end as shown in part (a) of Fig.12In the case where the image interference shown in part (b) appears as a whole (or partially appears on the front end side), the potential limiting bias is adjusted. That is, in the case where such dispersion and image interference occur, the absolute value of the potential limiting bias changes in the decreasing direction. In addition, in the case where dispersion and image interference do not occur, the absolute value of the potential limiting bias changes in the increasing direction, so that in addition to the adjustment of the above-mentioned secondary transfer bias, the secondary transfer properties can also be improved. Then, after confirming the user input adjustment value and repeating the image output and the inspection of the output image as described above, the user can end the adjustment of the potential limiting bias. Fig.15 is a schematic diagram showing another example of an adjustment image that can be used to adjust the potential limit bias. Fig.15 In the adjustment image, a band-shaped halftone image (for example, a halftone image with an image ratio of 50% for the image portion) is formed for each color of yellow, magenta, cyan, and black. Based on such an adjustment image, a plurality of colors ( Fig.15 All colors in the example of FIG. 1 ) can reduce dispersion and image disturbance, making it possible to achieve a reduction in the amount of recording material S required for adjusting the potential adjustment bias and a reduction in the labor required for adjusting the potential adjustment bias.

[0122] Furthermore, in the case where the user adjusts the potential limiting bias by using an image that is actually expected to be obtained as a product, in some cases, it is difficult to obtain the desired effect by adjusting the potential limiting bias for each color of yellow, magenta, cyan, and black. Therefore, for example, the potential limiting bias can be adjusted collectively for all colors of yellow, magenta, cyan, and black. At this time, the change widths per predetermined adjustment value for all colors can be made the same or different from each other. For example, in the case of toner transferred to the intermediate transfer belt 6 at the primary transfer portion N1 on the more upstream side, the number of primary transfer portions N1 is larger and more subjected to discharge, so that the charge amount is likely to become larger. For this reason, in the case where the absolute value of the potential limiting bias changes in the decreasing direction, the change width per predetermined adjustment value of the potential limiting bias can be made smaller as the image forming unit 10 is on the more upstream side. In addition, in the case where the absolute value of the potential limiting bias changes in the increasing direction, the change width per predetermined adjustment value of the potential limiting bias can be made larger as the image forming unit 10 is on the more upstream side. The change width per predetermined adjustment value of the potential limit bias may be set by preliminary experiments or the like based on the degree of increase in the charge amount of toner of each color or the like. Fig.16 An example of the potential limit bias adjustment screen 500 in this case is shown. Fig.16 The potential limit bias adjustment screen 500 is Fig.14The potential limit bias adjustment screen 500 is different in that a single adjustment value display unit 501 and a single adjustment value input unit 502 are provided for each of the front and back sides. The user operates the adjustment value input unit 502, so that the potential adjustment bias can be changed collectively from the default value corresponding to the adjustment value 0 for all colors among yellow, magenta, cyan, and black. At this time, as described above, for the colors among yellow, magenta, cyan, and black, the change width of each adjustment value +1 (or -1) of the potential adjustment bias can be made the same or different from each other. In addition, for example, the change width of at least two colors can be made the same, or the change width of at least one color can be made different from the change width of another color, so that the change width of yellow and magenta is made different from the change width of cyan and black, etc.

[0123] In addition, if Fig.17 As shown in FIG. 1 , the image forming apparatus 1 can output Fig.15 A graph output button 505 for the adjustment image (adjustment graph) of the potential limit bias shown in FIG. 50 can be provided in the potential limit bias adjustment screen 500. Thus, the user does not need to prepare the adjustment graph as shown in FIG. Fig.15 The adjustment diagram shown in Figure 1 allows the user to more easily adjust the potential limiting bias.

[0124] Here, as a method of suppressing dispersion and image interference, it will be considered to make the absolute value of the secondary transfer bias voltage small. However, in this case, it becomes difficult to ensure the secondary transfer latitude between the single color and the secondary color, making it difficult to easily form a setting that obtains the result desired by the user. For this reason, as a method of suppressing dispersion and image interference, a method of adjusting the potential limiting bias voltage is effective. By adjusting the potential limiting bias voltage, dispersion and image interference can be suppressed while ensuring the secondary transfer latitude.

[0125] Therefore, in this embodiment, the image forming device 1 includes: a photosensitive member 11 that can be charged to a predetermined polarity and carries a toner image; an intermediate transfer belt 6 that contacts the photosensitive member 11 to form a primary transfer section N1, conveys the toner image primarily transferred from the photosensitive member 11 in the primary transfer section N1 for secondary transfer to a recording material S in a secondary transfer section N2, and is capable of moving circumferentially; a primary transfer member 15 that contacts the inner peripheral surface of the intermediate transfer belt 6 and is used to primarily transfer the toner image from the photosensitive member 11 to the intermediate transfer belt 6 under the application of a first bias voltage (primary transfer bias voltage); and a first applying section 75 for applying a bias voltage having a polarity that is the same as the predetermined polarity. The image forming apparatus 1 includes a first bias voltage having a polarity opposite to that of the first transfer portion N1; an electrode member (potential limiting member) in contact with the inner peripheral surface of the intermediate transfer belt 6 at the downstream side of the primary transfer portion N1 in the moving direction of the intermediate transfer belt 6; a second applying portion 80 for applying a second bias voltage (potential limiting bias voltage) having the same polarity as a predetermined polarity; a storage portion 35 in which a setting value of the second bias voltage is stored in association with the type of the recording material S; and a controller 3 for controlling the second applying portion 80 so that during image formation on the predetermined type of recording material S, the second bias voltage is applied to the electrode member 8 based on the setting value of the second bias voltage stored in the storage portion 35 in association with the predetermined type of the recording material S. In this embodiment, the image forming apparatus 1 includes a changing means (operating portion 70, potential limiting bias voltage adjustment screen 500, CPU 31) capable of changing the setting value of the second bias voltage stored in the storage portion 35 in association with the predetermined type of the recording material S.

[0126] Furthermore, in this embodiment, the image forming apparatus 1 includes at least two photosensitive members 11, at least two primary transfer members 15 provided corresponding to the at least two photosensitive members 11, and at least two electrode members 8 provided corresponding to the at least two photosensitive members 11, and the above-mentioned changing means can independently change the setting value of the second bias voltage stored in the storage section 35 in association with the predetermined kind of the recording material A and applied to the at least two electrode members 8 by a single changing instruction. Furthermore, the changing means can collectively change the setting value of the second bias voltage stored in the storage section 35 in association with the predetermined kind of the recording material S and applied to the at least two electrode members 8 by a single changing instruction. In this embodiment, the changing means is constituted by an adjustment value input section 502 including a potential limit bias adjustment screen 500 as an input section for receiving a change instruction of the setting value of the second bias voltage by an operation of an operator. Incidentally, the image forming apparatus 1 may be configured such that an operator provides an instruction to change the setting value of the second bias voltage in an external device, and in this case, the above-mentioned changing component may also be configured by including an output / input circuit (input / output unit) as an input unit for receiving the change instruction from the external device.

[0127] As described above, according to this embodiment, in a configuration capable of suppressing an increase in the charge amount of the colorant on the intermediate transfer member by applying a bias voltage to an electrode member disposed downstream of the primary transfer portion, it becomes possible to suppress image defects such as scattering that can occur depending on the type of recording material.

[0128] [Example 2]

[0129] Next, another embodiment of the present invention will be described. The basic structure and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or structures as those of the image forming apparatus of Embodiment 1 are represented by the same reference numerals or symbols as those of Embodiment 1, and their detailed description will be omitted.

[0130] 1. Overview of this embodiment

[0131] This embodiment is different from Embodiment 1 in that, in the case where the value of the potential limiting bias is changed, primary transfer ATVC is always performed before subsequent image formation.

[0132] The potential limiting member 8 is disposed in contact with the back surface of the intermediate transfer belt 6 so as to be close to the downstream side of the primary transfer portion N1. For this reason, when the value of the potential limiting bias applied to the potential limiting member 8 is changed, in some cases, the changed value of the potential limiting bias has an influence on the value of the primary transfer bias.

[0133] Fig.18 : is a graph showing an example of the relationship between the voltage value of the primary transfer bias (the output voltage value of the primary transfer power supply 75) and the current value (the value of the current flowing through the primary transfer power supply 75). Fig.18 In FIG. 1 , the dotted line indicates a case where a potential limiting bias of −1500 V is applied to the potential limiting member 8, the chain line indicates a case where a potential limiting bias of −3000 V is applied to the potential limiting member 8, and the solid line indicates a case where no potential limiting bias is applied to the potential limiting member 8 (the potential limiting member 8 is in an electrically floating state). Fig.18 A state in which a charging bias (DC voltage) of -600 V is applied is shown, and a current value when a primary transfer bias (DC voltage) is applied is shown.

[0134] like Fig.18As shown in , when the potential limiting bias is applied to the potential limiting member 8, compared with the case where the potential limiting member is not applied to the potential limiting member 8, even when the primary transfer bias applied to the primary transfer roller 15 is the same, in some cases, the current flowing through the primary transfer roller 15 becomes larger. This is due to the following reasons. When the primary transfer bias is applied to the primary transfer roller 15, in addition to the current (primary transfer current) flowing into the photosensitive drum 11 side, the current also flows into the potential limiting member 8 side. Then, the current flowing into the potential limiting member 8 side changes according to whether the potential limiting bias is applied to the potential limiting member 8 or not, or according to the change in the value of the potential limiting bias applied to the potential limiting member 8. In the case where the primary transfer bias is subjected to constant voltage control, the output voltage of the primary transfer power supply 75 is controlled to become substantially constant, and therefore, when the current flowing into the potential limiting member 8 side becomes larger, the current flowing through the primary transfer power supply 75 becomes larger. In other words, when the primary transfer bias is controlled so that the same target current flows through the primary transfer power source 75, the current (primary transfer current) actually flows to the photosensitive drum 11 side. For this reason, in the case where the value of the potential limiting bias is adjusted, when image formation is performed while the primary transfer ATVC is not performed, image defects due to improper primary transfer occur in some cases. For example, when the absolute value of the primary transfer bias applied to the potential limiting member 8 becomes large or when the impedance of the primary transfer portion N1 is low, the amount of output flowing into the potential limiting member 8 becomes large, and the primary transfer efficiency is likely to decrease.

[0135] Fig.19 : is a flowchart showing an example of a process for adjusting the potential limit bias in this embodiment. Fig.19 The contents of the processes S301 to S307 and S309 are similar to Fig.10 . As shown in S307, in the case where the user changes the adjustment value (offset value) of the potential limiting bias, the primary transfer ATVC is performed before the subsequent image formation. Specifically, in the case where the adjustment value of the potential limiting bias is changed, before the subsequent image formation (the image that the user actually expects to obtain or the adjusted image), the controller 3 controls to perform the primary transfer ATVC.

[0136] 2. Correction control of primary transfer bias

[0137] Next, a method for more accurately adjusting the primary transfer bias in the case where a predetermined bias value is changed will be further described. As described above, in this embodiment, regarding the target voltage of the potential limiting bias, a default value according to the environment (temperature, humidity) is pre-set for each type of recording material S. Then, during image formation or during the primary transfer ATVC, the potential limiting bias is subjected to constant voltage control at the target voltage. Due to the influence of individual differences in the resistance value of each of the intermediate transfer belt 6, the primary transfer roller 15, and the potential limiting member 8, etc., in some cases, for each individual of the image forming device 1 or for each use state of the image forming device 1, the value of the current flowing toward the potential limiting member 8 side as described above changes due to changes in the environment (such as, a temperature rise inside the image forming device 1) or changes in the potential limiting bias.

[0138] Fig. 20 : is a schematic diagram showing the current around the primary transfer section N1. For example, when the target current Ia is supplied from the primary transfer power supply to the primary transfer roller 15, in the case where the potential limiting member 8 is not provided, the target current Ia and the effective transfer current I1 flowing in the direction of the photosensitive drum 11 are substantially consistent with each other. However, by disposing the potential limiting member 8 downstream of the primary transfer section N1, the current path from the primary transfer roller 15 is branched to the effective transfer current and the advection current I2 flowing in the direction of the potential limiting member 8. In the primary transfer ATVC, a target voltage of the execution bias voltage Vtr for causing the target current according to the total resistance value of the primary transfer section N1 to flow is determined. At this time, the advection current I2 toward the potential limiting member 8 fluctuates due to the influence of the above-mentioned resistance fluctuation and the like. For this reason, in the case of performing the primary transfer ATVC without considering the advection current I2 toward the potential limiting member 8, the actual effective transfer current I1 is reduced, so that the primary transfer properties are impaired in some cases. Therefore, by correcting the primary transfer bias in consideration of the current flowing from the primary transfer portion N1 toward the potential restricting member 8 , the primary transfer current flowing in the direction of the photosensitive drum 11 can be maintained at an appropriate value more accurately.

[0139] Fig.21 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 in this case. Fig.21 The structure shown in FIG. 1 is schematically similar to Figure 2 However, in Fig.21 In the configuration shown in , a voltage detection sensor 80a as a voltage detection component (voltage detection unit) for detecting its output voltage and a current detection sensor 80b as a current detection component (current detection unit) for detecting its output current are connected to the potential limiting power supply 80.

[0140] also, Fig. 22 2 is a timing chart showing the progression of the voltage value and the current value of the primary transfer bias and the potential limiting bias for illustrating the primary transfer bias correction control in this case. When the primary transfer ATVC is executed, the controller 3 performs correction of the primary transfer bias.

[0141] In a state where the potential limiting bias is applied to the potential limiting member 8, the controller 3 detects current values ​​of the current flowing through the potential limiting member 8 (potential limiting power source 80) when the test bias is not applied to the primary transfer roller 15 and when the test bias is applied to the primary transfer roller 15. Then, the controller 3 performs correction of the primary transfer bias based on these detected current values.

[0142] That is, the driving of the intermediate transfer belt 6 is started, so that the pre-rotation step (T1) is started. Thereafter, the potential limiting bias is started to be applied from the potential limiting power supply 80 to the potential limiting member 8 under constant voltage control (T2). Then, before the test bias is applied to the primary transfer roller 15, the current value Ib1 flowing through the potential limiting member 8 is detected by the current detection sensor 80b. Thereafter, the primary transfer ATVC is started, and a test bias is applied from the primary transfer power supply 75 to the primary transfer roller 15 under constant current control so as to achieve the target current I1 (T3). The target current I1 at this time corresponds to the target current of the primary transfer bias according to the environment during image formation. Then, as described above, the execution bias Vtr is determined. Incidentally, as described above, in the primary transfer ATVC, three levels of test bias are applied to the primary transfer roller 15, but in Fig. 22 In the figure, for the sake of simplicity, only the test bias voltage targeting the target current under constant current control is shown. The execution bias voltage Vtr determined in this case is affected by the fluctuation of the current Ib1 flowing through the potential limiting member 8 as described above. As a result, there may be a deviation between the target current Ia and the actual effective transfer current I1.

[0143] Therefore, the current value Ib2 of the current flowing through the potential limiting member 8 when the test bias is applied to the primary transfer roller 15 is detected by the current detection sensor 80b. In addition, the difference A1 (=|Ib1-Ib2|) between the current value Ib1 detected when the test bias is not applied to the primary transfer roller 15 and the current value Ib2 detected when the test bias is applied to the primary transfer roller 15 is obtained. Then, the difference ΔI is regarded as the convection current I2, and the difference ΔI is added to the target current I1 of the test bias, so that the target current Ia is determined. In addition, based on the voltage-current characteristics obtained by ATVC, the execution bias Vtr' corrected corresponding to the target current Ia is determined. During image formation, the execution bias Vtr' determined after correction is applied to the primary transfer roller 15 under constant voltage control (T4 to T5).

[0144] Incidentally, the primary transfer bias is subjected to constant voltage control, and thus a voltage value corresponding to the target current Ia is determined, but the present invention is not limited thereto. For example, in the case where the primary transfer bias is subjected to constant current control, it is only necessary to determine the target current Ia as described above, and during image formation, the primary transfer bias is subjected to constant current control under the determined target current Ia. In addition, as the current flowing through the potential limiting member 8 when the test bias is applied, the current when the test bias corresponding to the target current and predetermined is applied is detected, but the present invention is not limited thereto. For example, an execution bias Vtr determined based on the voltage-current characteristics obtained when applying multiple levels of test bias and corresponding to the target current is applied again as a test bias, and the current flowing through the potential limiting member 8 at this time can be detected. In addition, in this embodiment, the potential limiting bias applied to the potential limiting member 8 during image formation is subjected to constant voltage control, but the potential limiting bias may be subjected to constant current control. In this case, the primary transfer bias may only need to be determined based on the detection voltages when the test bias is applied to the primary transfer roller 15 in the primary transfer ATVC and when the test bias is not applied to the primary transfer roller 15 in the primary transfer ATVC.

[0145] Therefore, in this embodiment, the controller 3 can control so that when a predetermined condition is satisfied, the setting operation (primary transfer ATVC) for setting the first bias applied by the first applying section 75 to the primary transfer member 15 during the non-image formation period in the case where the test bias is applied by the first applying section 75 to the primary transfer member 15 is performed. Furthermore, in this embodiment, when the change of the setting value of the second bias (primary transfer) by the changing section is not performed after the first image formation and before the second image formation after the first image formation, even in the case where the above-mentioned setting operation is not performed during the non-image formation period before the second image formation, when the change of the setting value of the second bias by the changing section is performed after the first image formation and before the second image formation, the controller 3 controls to perform the above-mentioned setting operation during the non-image formation period before the second image formation.

[0146] As described above, according to this embodiment, effects similar to those of Embodiment 1 are obtained, and in addition, changes in primary transfer properties due to adjustment of the potential limiting bias can be suppressed.

[0147] [Other embodiments]

[0148] As described above, the invention has been described based on the specific embodiments, but the present invention is not limited to the above-described embodiments.

[0149] In the above-described embodiment, the predetermined charge polarity of the photosensitive member is negative polarity, but is not limited thereto. The predetermined charge polarity of the photosensitive member may also be positive polarity. Similarly, in the above-described embodiment, the normal charge polarity of the toner is negative polarity, but may also be positive polarity. Various applied voltages in the case where the predetermined charge polarity of the photosensitive member and the normal charge polarity of the toner are positive polarity may only need to be appropriately changed according to the above-described embodiment so that these polarities are changed to polarities opposite to those in the above-described embodiment.

[0150] Furthermore, the photosensitive member is not limited to a drum-shaped photosensitive member (photosensitive drum), but may be an endless belt-shaped photosensitive member (photosensitive belt) or the like.

[0151] Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming a full-color image, but may be an image forming apparatus capable of forming only a monochrome (white / black or monochrome) image.

[0152] Furthermore, in the above-described embodiments, the display and operation described as being performed by the operation section of the image forming apparatus may also be performed by an external device.

[0153] Furthermore, in the above-described embodiment, description is made such that when the adjustment of the potential limiting bias is performed, the adjustment of the secondary transfer bias is also performed, but the adjustment of the potential limiting bias may also be performed.

[0154] Furthermore, in the above-described embodiment, the case where the secondary transfer bias and the potential limit bias are adjusted from the default values ​​is described as an example, but when these biases have been adjusted from the default values, they may be adjusted from the current settings.

[0155] Furthermore, in the above-described embodiment, each of the primary transfer bias and the secondary transfer bias is subjected to constant voltage control, but at least one of these biases may be subjected to constant current control.

[0156] In addition, when describing the above-mentioned embodiments, as a halftone image, a halftone image in which the area ratio of the image portion is 50% is used as an example, but the halftone image may be any halftone image having an area ratio (ratio of the amount of applied colorant to the solid color image) of, for example, about 30% to about 80% of the image portion.

[0157] Furthermore, in the above-described embodiments, the voltage applied to the potential limiting member (electrode member) during image formation is subjected to constant voltage control, but the voltage applied to the potential limiting member (electrode member) may also be subjected to constant current control.

[0158] Furthermore, in the image forming apparatus, the information about the environment (installation environment of the image forming apparatus) used for various controls may be information about at least one of temperature and humidity of at least one of the inside and the outside of the image forming apparatus.

[0159] According to the present invention, in a configuration capable of suppressing an increase in the amount of charge of the toner on the intermediate transfer member by applying to the electrode member disposed downstream of the primary transfer portion, it becomes possible to suppress image defects such as scattering that can occur depending on the type of recording material or the like.

[0160] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming device, comprising: a photosensitive member charged to a predetermined polarity and configured to carry a toner image; an intermediate transfer belt onto which the toner image is transferred from the photosensitive member in the primary transfer section; a primary transfer member forming the primary transfer section in which the photosensitive member and the intermediate transfer belt are in contact with each other, the primary transfer member being in contact with an inner peripheral surface of the intermediate transfer belt, and configured to transfer a toner image from the photosensitive member to the intermediate transfer belt under application of a transfer bias; an electrode member that contacts an inner peripheral surface of the intermediate transfer belt at a downstream side of the primary transfer portion with respect to a moving direction of the intermediate transfer belt; a first applying portion configured to apply a bias voltage having a polarity opposite to the predetermined polarity to the primary transfer member; a second applying portion configured to apply a bias voltage having a polarity identical to the predetermined polarity to the electrode member; as well as A controller is configured to control the second applying portion so as to change the bias voltage applied to the electrode member based on the kind of recording material.

2. The image forming apparatus according to claim 1, further comprising: a storage section configured to store a setting value of a bias voltage applied to the electrode member in association with a kind of a recording material; as well as An operation portion to which an instruction for changing a setting value of a bias voltage applied to the electrode member stored in the storage portion in association with a predetermined kind of recording material can be manually input.

3. The image forming apparatus according to claim 2, comprising: at least two photosensitive members; at least two primary transfer members, the at least two primary transfer members being respectively arranged corresponding to the at least two photosensitive members; as well as At least two electrode members are provided corresponding to the at least two photosensitive members, respectively.

4. The image forming apparatus according to claim 3, wherein: The operation section is capable of independently changing, by a separate change instruction, the setting values ​​of the bias voltages applied to the at least two electrode members stored in the storage section in association with the kind of the predetermined recording material.

5. The image forming apparatus according to claim 3, wherein: The operating section is capable of collectively changing, by a single change instruction, the setting values ​​of the bias voltages applied to the at least two electrode members stored in the storage section in association with the kind of the predetermined recording material.

6. The image forming apparatus according to claim 2, wherein: The controller is capable of performing control so as to perform a setting operation for setting a bias voltage having a polarity opposite to the predetermined polarity applied by the first applying portion to the first primary transfer member during image formation when a test bias voltage is applied by the first applying portion to the first primary transfer member during image formation, when a predetermined condition is satisfied, during non-image formation. Here, in the case where a change in a setting value of a bias voltage applied to the electrode member is performed by the operating portion, the controller controls so that the setting operation is performed after the setting value is changed and before subsequent image formation is performed.

7. An image forming device, comprising: a photosensitive member charged to a predetermined polarity and configured to carry a toner image; an intermediate transfer belt onto which the toner image is transferred from the photosensitive member in the primary transfer section; a primary transfer member forming the primary transfer section in which the photosensitive member and the intermediate transfer belt are in contact with each other, the primary transfer member being in contact with an inner peripheral surface of the intermediate transfer belt, and configured to transfer a toner image from the photosensitive member to the intermediate transfer belt under application of a transfer bias; an electrode member that contacts an inner peripheral surface of the intermediate transfer belt at a downstream side of the primary transfer portion with respect to a moving direction of the intermediate transfer belt; a first applying portion configured to apply a bias voltage having a polarity opposite to the predetermined polarity to the primary transfer member; a second applying portion configured to apply a bias voltage having a polarity identical to the predetermined polarity to the electrode member; as well as An operation portion to which an instruction for changing a setting value of a bias voltage applied to the electrode member during formation of an image on a predetermined recording material can be manually input.

8. The image forming apparatus according to claim 7, comprising: at least two photosensitive members; at least two primary transfer members, the at least two primary transfer members being respectively arranged corresponding to the at least two photosensitive members; as well as At least two electrode members are provided corresponding to the at least two photosensitive members, respectively.

9. The image forming apparatus according to claim 8, wherein: The operation section is capable of independently changing, by a separate change instruction, the setting values ​​of the bias voltages applied to the at least two electrode members stored in the storage section in association with the kind of the predetermined recording material.

10. The image forming apparatus according to claim 8, wherein: The operating section is capable of collectively changing, by a single change instruction, the setting values ​​of the bias voltages applied to the at least two electrode members stored in the storage section in association with the kind of the predetermined recording material.

11. The image forming apparatus according to claim 8, wherein: The controller is capable of performing control so as to perform a setting operation for setting a bias voltage having a polarity opposite to the predetermined polarity applied by the first applying portion to the first primary transfer member during image formation when a test bias voltage is applied by the first applying portion to the first primary transfer member during image formation, when a predetermined condition is satisfied, during non-image formation. Here, in the case where a change in a setting value of a bias voltage applied to the electrode member is performed by the operating portion, the controller controls so that the setting operation is performed after the setting value is changed and before subsequent image formation is performed.

Images