JP2017198928A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: in an image forming apparatus that causes a current to flow to image carriers from contact members connected to a voltage maintaining device to primarily transfer toner images, when the electrical resistance of an intermediate transfer belt changes, good primary transferability is difficult to be ensured.SOLUTION: An opposing roller 13 that is an opposing member to a secondary transfer roller 20 as a current supply member is electrically connected to metal rollers 14 as contact members in contact with an inner peripheral surface of an intermediate transfer belt 10. The metal rollers 14 is connected to a Zener diode 15 as a voltage maintaining device in which a predetermined voltage is maintained by a current from the secondary transfer roller 20 being supplied thereto, through a resistance member 17 in which electrical resistance is changed in the same tendency as that of the intermediate transfer belt 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.

  In an electrophotographic color image forming apparatus, in order to print at high speed, each color image forming unit is independently provided, and a toner image is sequentially transferred from each color image forming unit to an intermediate transfer member. A configuration is known in which toner images are transferred to a transfer material all at once.

  In such an image forming apparatus, each color image forming unit has a photosensitive drum as an image carrier. The toner image formed on the photosensitive drum of each image forming unit applies a voltage from a primary transfer power source to a primary transfer member provided opposite to the photosensitive drum via an intermediate transfer member such as an intermediate transfer belt. Thus, primary transfer is performed on the intermediate transfer member. The toner image of each color primarily transferred from the image forming unit of each color to the intermediate transfer member is applied to the paper or OHT from the intermediate transfer member by applying a voltage from the secondary transfer power source to the secondary transfer member in the secondary transfer unit. Secondary transfer is performed collectively on a transfer material such as. The toner images of the respective colors transferred to the transfer material are then fixed on the transfer material by fixing means.

  Japanese Patent Application Laid-Open No. 2004-228688 provides a configuration in which a contact member that contacts the inner peripheral surface of the intermediate transfer belt is provided in the vicinity of the photosensitive drum, and a voltage maintaining element that is maintained at a predetermined voltage when supplied with current is connected to the contact member. Is disclosed. In this configuration, a voltage is applied from a secondary transfer power source to a secondary transfer roller as a current supply member, and a current is passed from the secondary transfer roller to a plurality of photosensitive drums via a conductive intermediate transfer belt, Primary transfer is performed. The voltage maintaining element maintains a predetermined voltage when current is supplied from the current supply member. In this configuration, a toner image can be primarily transferred from each photosensitive drum to the intermediate transfer belt by causing a current to flow from the contact member maintained at a predetermined voltage to the photosensitive drum via the intermediate transfer belt. By using such a configuration, an appropriate primary transfer current can be supplied to each photosensitive drum without providing a power supply dedicated to primary transfer, and primary transferability can be stabilized. .

JP2013-231942A

  However, in the configuration of Patent Document 1, there is a concern that it is difficult to ensure good primary transferability when the electrical resistance of the intermediate transfer belt fluctuates. For example, when using an intermediate transfer belt having ionic conductivity, the electrical resistance of the intermediate transfer belt is low in a high temperature and high humidity environment, and the electrical resistance of the intermediate transfer belt is high in a low temperature and low humidity environment. The difference in electrical resistance of the intermediate transfer belt due to fluctuation is large. In the configuration of Patent Document 1, since the contact member connected to the voltage maintaining element is always maintained at a predetermined voltage, a primary transfer failure may occur if the electric resistance of the intermediate transfer belt varies. .

  For example, it is assumed that the contact member connected to the voltage maintaining element is maintained at a voltage suitable for primary transfer of the toner image from the photosensitive drum to the intermediate transfer belt in a standard temperature and humidity environment. In this case, in a low-temperature and low-humidity environment where the electric resistance of the intermediate transfer belt is high, the current flowing from the contact member maintained at a predetermined voltage to the photosensitive drum via the intermediate transfer belt is relative to the desired primary transfer current. Insufficient primary transfer may occur. Also, in a high temperature and high humidity environment where the electrical resistance of the intermediate transfer belt is low, the current flowing from the contact member maintained at a predetermined voltage to the photosensitive drum via the intermediate transfer belt is excessive with respect to the desired primary transfer current. As a result, a primary transfer failure may occur.

  An object of the present invention is an image forming apparatus that primarily transfers a toner image by causing a current to flow from a contact member connected to a voltage maintaining element to an image carrier, even when the electrical resistance of an intermediate transfer belt varies. And ensuring good primary transferability.

  In order to solve the above-described problems, the present invention provides an image carrier that carries a toner image, and an endless and rotatable intermediate member that is electrically conductive and to which a toner image from the image carrier is primarily transferred. A transfer belt, a current supply member that contacts the outer peripheral surface of the intermediate transfer belt and supplies a current to the intermediate transfer belt, and a predetermined voltage is supplied by supplying current from the current supply member via the intermediate transfer belt. And a contact member that contacts the inner peripheral surface of the intermediate transfer belt, and current flows from the contact member to the image carrier through the intermediate transfer belt. Accordingly, in the image forming apparatus that primarily transfers the toner image from the image carrier to the intermediate transfer belt, the image forming apparatus includes a resistance member whose electric resistance varies in the same tendency as the intermediate transfer belt, Side is electrically connected to the ground, the other end of the voltage maintenance element is characterized by being connected to the contact member via the resistor member.

  According to the present invention, even when the electrical resistance of the intermediate transfer belt fluctuates in an image forming apparatus that primarily transfers a toner image by flowing a current from a contact member connected to a voltage maintaining element to an image carrier. Good primary transferability can be ensured.

1 is a schematic cross-sectional view illustrating an image forming apparatus according to a first exemplary embodiment. FIG. 3A is an enlarged schematic diagram of an image forming unit according to the first exemplary embodiment. (B) is a schematic diagram explaining the arrangement configuration of each member in Example 1. FIG. (A) is a schematic diagram for explaining a measuring device for measuring the electrical resistance in the circumferential direction of the intermediate transfer belt in Example 1. FIG. FIG. 6B is a schematic diagram illustrating a method for measuring the electrical resistance in the circumferential direction of the intermediate transfer belt according to the first exemplary embodiment. 6 is a table for explaining that the electric resistance of the intermediate transfer belt in Example 1 varies depending on the environment. It is a table | surface explaining that the electrical resistance of the resistance member in Example 1 is fluctuate | varied with the surrounding environment. FIG. 3 is a schematic diagram illustrating a primary transfer voltage in each measurement environment in Example 1. It is a schematic sectional drawing explaining the other structure in an image forming apparatus. 6 is a schematic diagram illustrating a configuration of an image forming unit in Embodiment 2. FIG. 6 is a schematic diagram illustrating a primary transfer voltage in each measurement environment in Example 2. FIG.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following examples should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited.

Example 1
FIG. 1 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus according to the present exemplary embodiment. The image forming apparatus according to the present exemplary embodiment is a so-called tandem type image forming apparatus provided with a plurality of image forming units a to d. The first image forming unit a is yellow (Y), the second image forming unit b is magenta (M), the third image forming unit c is cyan (C), and the fourth image forming unit d is black (Bk). ) To form an image with each color toner. These four image forming units are arranged in a line at regular intervals, and the configuration of each image forming unit has many portions that are substantially common except for the color of the toner to be accommodated. Therefore, hereinafter, the image forming apparatus of this embodiment will be described using the first image forming unit a.

  The first image forming unit a includes a photosensitive drum 1a that is a drum-shaped photosensitive member, a charging roller 2a that is a charging member, a developing unit 4a, and a drum cleaning unit 5a.

  The photosensitive drum 1a is an image carrier that carries a toner image, and is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow R1 (counterclockwise) in the drawing. The developing unit 4a stores yellow toner and develops yellow toner on the photosensitive drum 1a. The drum cleaning unit 5a is a unit for collecting the toner adhering to the photosensitive drum 1a. The drum cleaning unit 5a includes a cleaning blade that contacts the photosensitive drum 1a and a waste toner box that stores toner and the like removed from the photosensitive drum 1a by the cleaning blade.

  When a control means (not shown) such as a controller receives an image signal, an image forming operation is started, and the photosensitive drum 1a is rotationally driven. In the rotating process, the photosensitive drum 1a is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by the charging roller 2a, and is subjected to exposure according to the image signal by the exposure means 3a. As a result, an electrostatic latent image corresponding to the yellow component image of the target color image is formed on the photosensitive drum 1a. Next, the electrostatic latent image is developed by the developing means 4a at the development position and visualized as a yellow toner image on the photosensitive drum 1a. Here, the normal charging polarity of the toner accommodated in the developing means 4a is negative, and the electrostatic latent image is reversely developed with toner charged to the same polarity as the charging polarity of the photosensitive drum 1a by the charging roller 2a. Yes. However, the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus that positively develops an electrostatic latent image with toner charged to a polarity opposite to the charged polarity of the photosensitive drum 1a.

  The endless and rotatable intermediate transfer belt 10 is electrically conductive and is stretched by a counter roller 13 as a counter member, a driving roller 11 and a tension roller 12, and is in contact with the photosensitive drum 1a. A next transfer portion is formed and is driven to rotate at substantially the same peripheral speed as that of the photosensitive drum 1a. The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 in the process of passing through the primary transfer portion where the photosensitive drum 1a and the intermediate transfer belt 10 are in contact with each other. The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the drum cleaning unit 5a, and then subjected to an image forming process below charging.

  In this embodiment, at the time of primary transfer, a toner image is primarily transferred to the intermediate transfer belt 10 by a current supplied from a secondary transfer roller 20 as a current supply member that contacts the outer peripheral surface of the intermediate transfer belt 10. Therefore, a primary transfer voltage is formed on the metal roller 14a. A method for forming the primary transfer voltage in this embodiment will be described later.

  Similarly, the second, third, and fourth image forming portions b, c, and d form a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image. Primary transfer is performed by sequentially overlapping the transfer belt 10. As a result, four color toner images corresponding to the target color image are formed on the intermediate transfer belt 10. Thereafter, the four color toner images carried on the intermediate transfer belt 10 are fed by the paper feeding means 50 in the process of passing through the secondary transfer portion formed by the contact between the secondary transfer roller 20 and the intermediate transfer belt 10. Secondary transfer is performed at once on the surface of the transfer material P such as paper or OHT.

The secondary transfer roller 20 has an outer diameter of 18 mm covered with a nickel-plated steel rod having an outer diameter of 6 mm and a foamed sponge body mainly composed of NBR and epichlorohydrin rubber having a volume resistivity of 10 ⁸ Ω · cm and a thickness of 6 mm. Something is used. The rubber hardness of the foamed sponge body is 30 ° (Asker hardness meter C type). The secondary transfer roller 20 is in contact with the outer peripheral surface of the intermediate transfer belt 10, and is pressed against the opposing roller 13 as an opposing member via the intermediate transfer belt 10 with a pressing force of about 50 N to form a secondary transfer portion. doing.

  The secondary transfer roller 20 as a current supply member is driven to rotate with respect to the intermediate transfer belt 10, and a voltage is applied from the transfer power supply 21 to the counter roller 13 as a counter member from the secondary transfer roller 20. A current flows toward it. As a result, the toner image carried on the intermediate transfer belt 10 is secondarily transferred to the transfer material P in the secondary transfer portion. When the toner image on the intermediate transfer belt 10 is secondarily transferred to the transfer material P, the current flowing from the secondary transfer roller 20 toward the counter roller 13 via the intermediate transfer belt 10 is constant. The voltage applied from the transfer power source 21 to the secondary transfer roller 20 is controlled. Further, the current for performing the secondary transfer is determined in advance according to the ambient environment in which the image forming apparatus is installed and the type of the transfer material P. The transfer power source 21 is connected to the secondary transfer roller 20 and applies a transfer voltage to the secondary transfer roller 20. Further, the transfer power source 21 can output in the range of 100 [V] to 4000 [V].

  The transfer material P onto which the four-color toner image carried on the intermediate transfer belt 10 in the secondary transfer portion has been transferred is then introduced into the fixing means 30, where the four-color toner is heated and pressed. It is melted and mixed and fixed to the transfer material P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the belt cleaning means 16. The belt cleaning unit 16 is provided to face the counter roller 13 with the intermediate transfer belt 10 interposed therebetween. The belt cleaning unit 16 includes a cleaning blade that contacts the outer peripheral surface of the intermediate transfer belt 10 and a waste toner container that stores toner and the like removed from the intermediate transfer belt 10 by the cleaning blade.

  In the image forming apparatus of this embodiment, a full-color print image is formed by the above operation.

  Next, the intermediate transfer belt 10, the opposing roller 13 as the opposing member, the driving roller 11 as the stretching member, the stretching roller 12, and the metal roller 14 as the contact member will be described. In the present embodiment, the facing roller 13, the driving roller 11, the stretching roller 12, and the metal rollers 14a to 14d are electrically connected.

  The intermediate transfer belt 10 is an endless belt obtained by adding a conductive agent to a resin material and imparting conductivity. The intermediate transfer belt 10 is stretched around three axes of a driving roller 11, a stretching roller 12, and a counter roller 13. Is stretched with a total pressure of 60N. As shown in FIG. 1, the intermediate transfer belt 10 receives a driving force from a driving source (not shown) and rotates in the direction of the arrow R2 in the drawing to substantially the same peripheral speed as the photosensitive drums 1a to 1d. Is driven to rotate.

  Further, metal rollers 14a to 14d as contact members are arranged at positions corresponding to the plurality of photosensitive drums 1a to 1d provided in the moving direction of the intermediate transfer belt 10, respectively. Each of the metal rollers 14a to 14d is in contact with the inner peripheral surface of the intermediate transfer belt 10 in the vicinity of the corresponding photosensitive drums 1a to 1d. The metal rollers 14a to 14d are arranged on the downstream side of the corresponding photosensitive drums 1a to 1d with respect to the moving direction of the intermediate transfer belt 10.

  The photosensitive drums 1a to 1d are arranged at regular intervals, and the metal rollers 14a to 14d are arranged at the same intervals with respect to the corresponding photosensitive drums 1a to 1d. Each of the metal rollers 14a to 14d is formed of a straight nickel-plated SUS round bar having an outer diameter of 6 mm, and is in contact with the intermediate transfer belt 10 over a predetermined region in the longitudinal direction perpendicular to the moving direction of the intermediate transfer belt 10. As the intermediate transfer belt 10 rotates, it is driven to rotate. Further, the toner images are primarily transferred from the photosensitive drums 1 a to 1 d to the intermediate transfer belt 10 by the voltages formed on the metal rollers 14 a to 14 d.

  FIG. 2A is a schematic diagram enlarging the space between the image forming unit a and the image forming unit b in the present embodiment. As shown in FIG. 2A, the metal roller 14a is disposed downstream of the primary transfer portion formed by contact between the photosensitive drum 1a and the intermediate transfer belt 10 with respect to the moving direction of the intermediate transfer belt 10. Yes. Further, the metal roller 14a is disposed closer to the corresponding photosensitive drum 1a than the adjacent photosensitive drum 1b on the downstream side of the metal roller 14a in the moving direction of the intermediate transfer belt 10. Further, the metal roller 14a is disposed so as to ensure the amount of winding of the intermediate transfer belt 10 around the photosensitive drum 1a. When a line connecting the positions where the photosensitive drum 1a and the photosensitive drum 1b are in contact with the intermediate transfer belt 10 is defined as a virtual line TL, the metal roller 14a is disposed at a position where the metal roller 14a enters the photosensitive drum 1a side with respect to the virtual line TL. .

  Here, the distance from the axial center of the photosensitive drum 1a to the axial center of the photosensitive drum 1b is defined as W, and the distance from the axial center of the photosensitive drum 1a to the axial center of the metal roller 14a is defined as T. Further, the height of lifting of the metal roller 14a with respect to a virtual line TL connecting the position where the photosensitive drum 1a and the intermediate transfer belt 10 are in contact with the position where the photosensitive drum 1b and the intermediate transfer belt 10 are in contact is defined as H1. In this embodiment, W = 50 mm, T = 10 mm, and H1 = 2 mm.

  As described above, the image forming unit a is described. However, also in the image forming units b to d, the distance W between the photosensitive drums 1, the distance T between the photosensitive drums 1 and the metal rollers 14, and the metal rollers. The lifting height H1 of 14 is set to the same value as that in the image forming unit a. That is, the photosensitive drums 1a to 1d are arranged at equal intervals at a distance W, and the metal rollers 14a to 14d are all arranged at the same distance T with respect to the corresponding photosensitive drums 1a to 1d. Similarly, each of the metal rollers 14a to 14d is disposed at a lifting height H1 with respect to a virtual line TL connecting positions where the photosensitive drums 1a to 1d and the intermediate transfer belt 10 are in contact with each other.

  FIG. 2B is a schematic diagram illustrating the arrangement configuration of each member of the image forming apparatus according to the present exemplary embodiment. As shown in FIG. 2B, the distance from the axial center of the opposing roller 13 to the axial center of the photosensitive drum 1a is defined as D1, and the distance from the axial center of the photosensitive drum 1d to the axial center of the driving roller 11 is defined as D2. . Furthermore, the lifting height of the opposing roller 13 with respect to the virtual line TL connecting the positions where the photosensitive drums 1a to 1d and the intermediate transfer belt 10 are in contact is defined as H2. At this time, D1 = 40 mm, D2 = 30 mm, H2 = 2 mm, and the lifting height of the driving roller 11 with respect to the virtual line TL is 0 mm.

  The intermediate transfer belt 10 has a circumferential length of 700 mm and a thickness of 90 μm, and uses endless polyvinylidene fluoride (PVdF) mixed with an ionic conductive agent as a conductive agent. In this embodiment, polyvinylidene fluoride (PVdF) is used as the material of the intermediate transfer belt 10, but other materials may be used as long as they are thermoplastic resins. For example, materials such as polyester, acrylonitrile-butadiene-styrene copolymer (ABS), and mixed resins thereof may be used.

The volume resistivity of the intermediate transfer belt 10 in this embodiment is 1.5 × 10 ⁹ Ω · cm. The volume resistivity was measured using a ring probe type UR (model MCP-HTP12) on a Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation. The measurement conditions were set to a temperature of 23 ° C., a humidity of 50%, an applied voltage of 100 [V], and a measurement time of 10 sec. In the configuration of this embodiment, the intermediate transfer belt 10 having a volume resistivity in the range of 1 × 10 ⁷ to 10 ¹⁰ Ω · cm can be used.

  Here, the volume resistivity is a measure of conductivity as a material of the intermediate transfer belt. Therefore, the volume resistivity is a measure of a belt (hereinafter referred to as a conductive belt) that can form a desired voltage by actually passing a current in the circumferential direction. The electrical resistance in the circumferential direction of the intermediate transfer belt will be described. In this embodiment, an endless conductive belt capable of flowing a current in the circumferential direction is used as the intermediate transfer belt 10.

  FIGS. 3A and 3B are schematic views for explaining a method of measuring the electrical resistance in the circumferential direction of the intermediate transfer belt 10 in this embodiment. The circumferential electrical resistance of the intermediate transfer belt 10 was measured using a circumferential resistance measuring device 100 (hereinafter referred to as a measuring device 100) shown in FIG. First, the configuration of the measuring apparatus 100 will be described. The intermediate transfer belt 10 to be measured is stretched with a tension of 60 N so that there is no slack between the inner roller 101 and the driving roller 102. The inner roller 101 made of metal is connected to a high voltage power source (TREK company high voltage power source: Model — 610E) 103, and the drive roller 102 is electrically connected to the ground. The surface of the drive roller 102 is covered with a conductive rubber having a sufficiently low resistance with respect to the intermediate transfer belt 10, and the intermediate transfer belt 10 is rotationally driven by the drive roller 102 at a surface speed of 100 mm / sec in the illustrated arrow R3 direction. The The longitudinal width of the intermediate transfer belt 10 is 270 mm, and the longitudinal widths of the inner roller 101 and the driving roller 102 are 260 mm.

  Next, a method for measuring the electrical resistance in the circumferential direction of the intermediate transfer belt 10 using the measuring apparatus 100 will be described. A constant current IL is applied to the inner roller 101 while the intermediate transfer belt 10 is rotated at 100 mm / sec by the driving roller 102, and the voltage [V] L is monitored by the high-voltage power source 103 connected to the inner roller 101. The intermediate transfer belt 10 of this example was measured with a constant current of IL = 5 μA.

The measurement system shown in FIG. 3A is regarded as an equivalent circuit shown in FIG. In this case, the electrical resistance RL in the circumferential direction of the intermediate transfer belt 10 at the distance L (300 mm in this embodiment) between the inner roller 101 and the drive roller 102 is calculated by RL = 2 × [V] L / IL. I can do it. By converting this RL into an intermediate transfer belt circumferential length equivalent to 100 mm of the intermediate transfer belt 10, the electrical resistance in the circumferential direction of the intermediate transfer belt 10 is obtained. In this embodiment, since the current flows from the secondary transfer roller 20 to each of the photosensitive drums 1a to 1d through the intermediate transfer belt 10, the electrical resistance in the circumferential direction of the intermediate transfer belt 10 is preferably 2 × 10 ⁹ Ω or less.

In the configuration of this embodiment, the intermediate transfer belt 10 having an electrical resistance value in the circumferential direction of 1.5 × 10 ⁸ Ω measured in the measurement environment at a temperature of 23 ° C. and a humidity of 50% using the measurement method described above is used. . The intermediate transfer belt 10 was measured with a constant current of IL = 5 μA, and the monitor voltage [VL] at that time was 1125 [V]. The monitor voltage [VL] is measured in one section of the intermediate transfer belt 10 and is obtained from the average value of the section measurement values. Further, regarding RL, since RL = 2 × [VL] / IL, RL = 2 × 1125 / (5 × 10 ⁻⁶ ) = 4.5 × 10 ⁸ Ω, and this is converted to 100 mm equivalent. The electrical resistance value in the circumferential direction of the intermediate transfer belt 10 in this embodiment is 1.5 × 10 ⁸ Ω.

The intermediate transfer belt 10 is mixed with an ionic conductive agent as a conductive agent, and has ionic conductivity as its electrical characteristics. The electrical resistance of the ion conductive intermediate transfer belt 10 varies depending on the surrounding environment. FIG. 4 shows an intermediate transfer measured in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%), a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), and a low temperature low humidity environment (temperature 15 ° C., humidity 10%). It is a table | surface which shows the volume resistivity of the belt 10, and the electrical resistance of the circumferential direction. As shown in FIG. 4, the intermediate transfer belt 10 has an electrical resistance value of 5.1 × 10 ⁸ Ω in the circumferential direction even in a low-temperature and low-humidity environment where the electrical resistance increases, and the above-described preferable intermediate transfer belt The electrical resistance value in the circumferential direction of the belt 10 is in the range of 2 × 10 ⁹ Ω or less.

  Next, a configuration necessary for forming the primary transfer voltage in each of the metal rollers 14a to 14d will be described with reference to FIG.

  In this embodiment, a driving roller 11 as a stretching member that stretches the intermediate transfer belt 10 in contact with the intermediate transfer belt 10, a stretching roller 12, and a counter roller 13 as a counter member include a plurality of contact members. The metal rollers 14a to 14d are electrically connected. These members (the driving roller 11, the stretching roller 12, the opposing roller 13, and the metal rollers 14a to 14d) that are in contact with the inner peripheral surface of the intermediate transfer belt 10 are electrically connected to a Zener diode 15 as a voltage maintaining element. Connected. A resistance member 17 is electrically connected between each of these members in contact with the inner peripheral surface of the intermediate transfer belt 10 and the Zener diode 15, and a terminal on one end side of the Zener diode 15 is connected to the resistance member 17. The terminal on the other end side is electrically connected to the ground.

  The Zener diode 15 generates a predetermined voltage (hereinafter referred to as a Zener voltage) on the cathode side when a certain current or more flows. In this embodiment, the Zener voltage is set to 200 [V]. The anode side of the Zener diode 15 is electrically connected to the ground, and the cathode side is connected to the resistance member 17. The Zener diode 15 maintains a contact point between the secondary transfer roller 20 and the resistance member 17 connected to the cathode side at a Zener voltage when current flows from the secondary transfer roller 20 to the Zener diode 15 via the intermediate transfer belt 10 and the resistance member 17. ing.

  In the present embodiment, the secondary transfer roller 20 is used as the current supply member. However, the present invention is not limited to this, and any current can be used as long as it can supply a current that can maintain the Zener diode 15 at the Zener voltage. A member other than the next transfer roller 20 may be used as a current supply member.

  In this embodiment, each member (the driving roller 11, the stretching roller 12, the opposing roller 13, and each of the metal rollers 14 a to 14 d) that comes into contact with the inner peripheral surface of the intermediate transfer belt 10 is connected to the Zener diode 15 via the resistance member 17. And are electrically connected. Therefore, the voltage formed on each of these members at the time of image formation is a voltage obtained by adding the voltage dropped due to the current flowing through the resistance member 17 to the Zener voltage of the Zener diode 15. In other words, the primary transfer voltage in this embodiment is a voltage obtained by adding the voltage dropped due to the current flowing through the resistance member 17 to the Zener voltage of the Zener diode 15. A current is supplied to the Zener diode 15 from the secondary transfer roller 20 as a current supply member via the intermediate transfer belt 10, so that the primary rollers of the metal rollers 14 a to 14 d in contact with the inner peripheral surface of the intermediate transfer belt 10 are primary. A transfer voltage is formed. Due to the primary transfer voltage formed on the metal rollers 14a to 14d, current flows from the metal rollers 14a to 14d to the photosensitive drums 1a to 1d via the intermediate transfer belt 10, and the intermediate transfer is performed from the photosensitive drums 1a to 1d. The toner image is primarily transferred to the belt 10.

  Next, the resistance member 17 of the present embodiment will be described.

  The resistance member 17 connected between each member (the driving roller 11, the stretching roller 12, the opposing roller 13, each metal roller 14 a to 14 d) in contact with the inner peripheral surface of the intermediate transfer belt 10 and the Zener diode 15 is an ion. It is a resistance member having conductivity. Specifically, the resistance member 17 uses a polyester sheet mixed with an ionic conductive agent as a conductive agent. Therefore, the resistance member 17 has ionic conductivity, and the electric resistance varies in the same tendency as the intermediate transfer belt 10 in which the electric resistance varies depending on the surrounding environment in which the image forming apparatus is installed.

  In this embodiment, polyester is used as the resistance member 17, but the present invention is not limited to this. For example, a material such as polyvinylidene fluoride (PVdF) or acrylonitrile-butadiene-styrene copolymer (ABS) mixed with an ionic conductive agent and a mixed resin thereof may be used.

  The resistance member 17 is in contact with the inner peripheral surface of the intermediate transfer belt 10 while being sandwiched between two metal plates bonded on both sides (the driving roller 11, the stretching roller 12, the opposing roller 13, The metal rollers 14a to 14d) and the Zener diode 15 are connected. The metal plate which is an electrode for the resistance member 17 has a square shape with a length of 10 mm and a width of 10 mm. The resistance member 17 has a square sheet shape with a length of 20 mm, a width of 20 mm, and a thickness of 200 μm. The metal plate is bonded to both surfaces of the resistance member 17 so that the center of the resistance member 17 and the center of the metal plate coincide. Has been. The resistance member 17 is supplied from each member (the driving roller 11, the stretching roller 12, the opposing roller 13, and each of the metal rollers 14a to 14d) that contacts the current supplied from the secondary transfer roller with the inner peripheral surface of the intermediate transfer belt 10. It flows toward the Zener diode 15.

  FIG. 5 shows the resistance member 17 used in this example in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%), a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), and a low temperature and low humidity environment (temperature 15). It is a table | surface of the electrical resistance value measured by (degreeC humidity 10%). As shown in FIG. 5, the resistance member 17 has a lower electrical resistance in a high temperature and high humidity environment (temperature 30 ° C. and humidity 80%) than in a standard temperature and humidity environment (temperature 23 ° C., humidity 50%). In a low-temperature and low-humidity environment (temperature of 15 ° C. and humidity of 10%), the electrical resistance increases. As shown in FIG. 4, the intermediate transfer belt 10 in this embodiment also has an electric resistance in a high temperature and high humidity environment (temperature 30 ° C. and humidity 80%) as compared to a standard temperature and humidity environment (temperature 23 ° C. and humidity 50%). The electrical resistance increases in a low-temperature, low-humidity environment (temperature: 15 ° C., humidity: 10%). Thus, compared with the standard temperature and humidity environment (temperature 23 degreeC humidity 50%), the tendency of the electrical resistance rise and fall in each surrounding environment is the same between each member. The electric resistance fluctuates at "." That is, the resistance of the resistance member 17 varies in the same tendency as that of the intermediate transfer belt 10 depending on the surrounding environment in which the resistance member 17 is installed.

The electrical resistance value between the metal plates sandwiching the resistance member 17 from the front and back was 2.5 × 10 ⁷ Ω when a current of 5 μA was passed in a standard temperature and humidity environment at a temperature of 23 ° C. and a humidity of 50%. .

  Hereinafter, the operation and effect of the resistance member 17 will be described. When the intermediate transfer belt 10 having ionic conductivity is used, the electric resistance of the intermediate transfer belt 10 varies depending on the surrounding environment. Therefore, depending on the surrounding environment where the image forming apparatus is installed, the primary transfer property may be stabilized. There were cases where it was difficult. In this embodiment, by connecting the resistance member 17 between the Zener diode 15 and each of the metal rollers 14a to 14d, even when the electric resistance of the intermediate transfer belt 10 fluctuates, the primary transfer property is stabilized. It becomes possible to make it.

  As a comparative example, the operation and effect of the present embodiment will be described in detail using a configuration in which the resistance member 17 is not provided between the Zener diode 15 and the metal rollers 14a to 14d. One end side (anode side) of the Zener diode of the comparative example is electrically connected to the ground, and the other end side (cathode side) is directly connected to each member in contact with the inner peripheral surface of the intermediate transfer belt 10. . Note that the Zener voltage in the comparative example is 400 [V], and the other set values and configurations are the same as in this embodiment except for the configuration of the Zener voltage and the configuration in which the resistance member 17 is not provided.

  FIG. 6 shows a high temperature and high humidity environment (temperature 30 ° C., humidity 80%), a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), and a low temperature and low humidity environment (temperature 15 ° C. humidity). 10%) is a diagram illustrating a relationship between primary transfer voltage and primary transfer property in three environments. In this embodiment and the comparative example, all the metal rollers 14a to 14d are electrically connected to the Zener diode 15 via the resistance member 17, and the voltages of the metal rollers 14a to 14d have the same value. Further, since the distances between the photosensitive drums 1a to 1d and the corresponding metal rollers 14a to 14d are the same in the image forming units a to d, the primary transfer property in the image forming units a to d is used. Are almost identical. Therefore, hereinafter, each of the photosensitive drums 1a to 1d will be referred to as a photosensitive drum 1, and each of the metal rollers 14a to 14d will be referred to as a metal roller 14 for description.

  The squares in FIG. 6 indicate that an image defect occurs due to excessive current flowing through the photosensitive drum 1 because the primary transfer voltage formed on the metal roller 14 is high. In FIG. 6, Δ indicates that the primary transfer voltage formed on the metal roller 14 is low, so that a toner image cannot be sufficiently transferred from the photosensitive drum 1 to the intermediate transfer belt 10, thereby causing an image defect. . The circles in FIG. 6 indicate that no image defect occurred.

  As shown in FIG. 6, the primary transfer voltage regions where no image defect occurs are different in the three surrounding environments where printing is performed. This is because the electrical resistance of the intermediate transfer belt 10 varies depending on the surrounding environment. Due to that. When the primary transfer voltage is set to the same value regardless of the surrounding environment, if the electric resistance of the intermediate transfer belt 10 fluctuates, the value of the current flowing from the metal roller 14 to the photosensitive drum 1 changes. Therefore, in the configuration using the intermediate transfer belt 10 whose electric resistance varies depending on the surrounding environment, in order to maintain good primary transfer performance regardless of the surrounding environment, it is matched with the fluctuation of the electric resistance of the intermediate transfer belt 10. It is necessary to adjust the primary transfer voltage.

  The solid line in FIG. 6 indicates the primary transfer voltage measured using the configuration of this example in each of the three measurement environments. In addition, dotted lines in FIG. 6 indicate primary transfer voltages measured using the configuration of the comparative example in each of the three measurement environments.

In order to verify the primary transferability shown in FIG. 6, the transfer material P was a letter size (width 216 mm) Xerox Business 4200 (basis weight: 75 g / m ² ) stored in each measurement environment. It was used. The print mode was a single-sided print mode, and an image having an average density of 10% of yellow (Y), magenta (M), cyan (C), and black (Bk) was printed.

  In the configuration of the present embodiment, the metal roller 14 is electrically connected to the Zener diode 15 via the resistance member 17. Therefore, the primary transfer voltage in each measurement environment in the image forming apparatus of the present embodiment is 200 [V] which is the Zener voltage of the Zener diode 15 and a voltage obtained by adding the voltage dropped due to the current flowing through the resistance member 17. It becomes.

  The resistance of the resistance member 17 varies depending on the surrounding environment where the image forming apparatus is installed. That is, the electrical resistance of the resistance member 17 is low in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%), and the electrical resistance of the resistance member 17 is high in a low temperature low humidity environment (temperature 15 ° C., humidity 10%). As a result, the voltage drops due to the current flowing through the resistance member 17 in a low-temperature and low-humidity environment (temperature of 15 ° C. and humidity of 10%) where the electrical resistance is higher than in a high-temperature and high-humidity environment (temperature of 30 ° C. and humidity of 80%). Becomes larger. Therefore, the respective primary transfer voltages in the three measurement environments are as shown by the solid lines in FIG.

  In the present embodiment, the primary transfer voltage formed on the metal roller 14 can be varied in each ambient environment because the electrical resistance of the resistance member 17 varies depending on the ambient environment. That is, even in a high temperature and high humidity environment where the electrical resistance of the intermediate transfer belt 10 is low (temperature 30 ° C. and humidity 80%), in a low temperature and low humidity environment where the electrical resistance of the intermediate transfer belt 10 is high (temperature 15 ° C. and humidity 10%). However, an appropriate primary transfer voltage can be applied to the metal roller 14. As a result, as shown in FIG. 6, no image defect occurred in any of the three measurement environments.

  In this embodiment, the Zener voltage of the Zener diode 15 is set to 200 [V] so that the primary transfer voltage in each measurement environment is in the range of ◯ in FIG.

  More specifically, the primary transfer voltage in this embodiment is the lowest in a high-temperature and high-humidity environment (temperature 30 ° C. and humidity 80%), and in a low-temperature and low-humidity environment (temperature 15 ° C. and humidity 10). %) Is the highest. This is because the electric resistance of the intermediate transfer belt 10 varies depending on the surrounding environment. In addition, the resistance of the resistance member 17 varies in the same tendency as the intermediate transfer belt 10 depending on the surrounding environment, and the voltage dropped due to the current flowing through the resistance member 17 is in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%). The smallest and largest in a low-temperature and low-humidity environment (temperature 15 ° C., humidity 10%). In this embodiment, at least the lowest primary transfer voltage and the zener voltage among the primary transfer voltages that can obtain good primary transfer properties in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%) should be the same. For example, a desired primary transfer voltage can be obtained in each measurement environment. As described above, in this embodiment, the Zener voltage of the Zener diode 15 is set to the lowest primary transfer voltage among the primary transfer voltages that can obtain a good primary transfer property in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%). The transfer voltage is set to 200 [V].

  In each measurement environment shown in FIG. 6, the secondary transfer current for forming the primary transfer voltage is set so as to satisfy the secondary transfer property in the secondary transfer portion. In this embodiment, the temperature is about 35 μA in a high temperature and high humidity environment (temperature 30 ° C., 80% humidity), about 30 μA in a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), and a low temperature, low humidity environment (temperature 15 ° C., humidity). 10%) is about 25 μA. The current flowing through the Zener diode 15 during image formation is about 15 μA in a high temperature and high humidity environment (temperature 30 ° C. and humidity 80%), about 10 μA in a standard temperature and humidity environment (temperature 23 ° C. and humidity 50%), and low temperature and low humidity. Under the environment (temperature 15 ° C., humidity 10%), it was about 5 μA.

  On the other hand, since the metal roller of the comparative example is connected to the Zener diode without passing through the resistance member, the voltage is always 400 [V] which is a Zener voltage regardless of the measurement environment, and the electric resistance of the intermediate transfer belt. Even if fluctuated, the primary transfer voltage was always constant. As a result, as shown by the dotted line in FIG. 6, although no image defect occurred in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%) and a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), An image defect occurred in a low humidity environment (temperature 15 ° C., humidity 10%).

  As described above, in the configuration of the image forming apparatus of this embodiment, the resistance member 17 whose electric resistance varies depending on the surrounding environment is provided between the metal roller 14 and the Zener diode 15. As a result, when the electrical resistance of the intermediate transfer belt 10 varies in the surrounding environment, the primary transfer voltage can be varied according to the surrounding environment, and a good 1 is obtained in the primary transfer portion without being influenced by the surrounding environment. It becomes possible to ensure the next transferability.

  In this embodiment, the stretching roller 12 that is the stretching member of the intermediate transfer belt 10 is electrically connected to the counter roller 13, but may be in an electrically floating state.

  Further, in this embodiment, the metal roller 14 as a contact member arranged in the vicinity of the photosensitive drum 1 is arranged offset to the downstream side of the photosensitive drum 1 with respect to the moving direction of the intermediate transfer belt 10. However, the present invention is not limited to this, and a configuration in which the intermediate transfer belt 10 is offset and arranged upstream of the photosensitive drum 1 or a configuration in which the intermediate transfer belt 10 is opposed to the photosensitive drum 1 via the intermediate transfer belt 10. It may be. More specifically, a member that contacts the intermediate transfer belt 10 and is electrically connected to the Zener diode 15 via the resistance member 17 is at the same distance as the photosensitive drums 1a to 1d of the image forming units a to d. As long as the arrangement is arranged, the effect of the present embodiment can be obtained.

  For example, as shown in FIG. 7, the effect of the present invention can be obtained even in a configuration in which one metal roller 14 is provided between the photosensitive drum 1b and the photosensitive drum 1c as an image carrier. In the configuration of FIG. 7, one end side (anode side) of the Zener diode 15 is electrically connected to the ground, and the other end side (cathode side) is connected to the resistance member 17. The resistance member 17 is connected to the metal roller 14, the facing roller 13, and the driving roller 11.

  In the configuration of FIG. 7, the counter roller 13 is disposed at a position closest to the photosensitive drum 1 a in contact with the inner peripheral surface of the intermediate transfer belt 10, and is disposed at a position closest to the photosensitive drum 1 d. Is the drive roller 11. Further, the metal roller 14 is disposed at a position in contact with the inner peripheral surface of the intermediate transfer belt 10 and closest to the photosensitive drum 1b and the photosensitive drum 1c. At this time, the distance from the axial center of the metal roller 14 to the axial center of the photosensitive drum 1b is T1, and the distance from the axial center of the metallic roller 14 to the axial center of the photosensitive drum 1c is T2. Further, the distance from the axial center of the opposing roller 13 to the axial center of the photosensitive drum 1a is D3, and the distance from the axial center of the driving roller 11 to the axial center of the photosensitive drum 1d is D4.

  In the configuration of FIG. 7, T1 = T2 = D3 = D4, and the same voltage is applied to the metal roller 14, the opposing roller 13, and the driving roller 11 that are electrically connected to the Zener diode 15 through the resistance member 17. Has been. Therefore, in the configuration of FIG. 7, a current flows from the metal roller 14, the opposing roller 13, and the driving roller 11 to each of the photosensitive drums 1 a to 1 d, so that a toner image is transferred to the intermediate transfer belt 10 at each primary transfer portion. The next transfer can be performed. In this configuration, the primary transfer voltage for primary transfer of the toner image to the intermediate transfer belt 10 is a voltage formed on the metal roller 14, the opposing roller 13, and the drive roller 11.

  Also in the configuration of FIG. 7, when the electrical resistance of the intermediate transfer belt 10 varies, the primary transfer voltages of the metal roller 14, the opposing roller 13, and the driving roller 11 can be varied according to the surrounding environment. As a result, as in the first embodiment, it is possible to ensure good primary transferability in the primary transfer portion without being influenced by the surrounding environment.

  In this embodiment, the metal roller 14 is used as the contact member. However, the present invention is not limited to this, and a roller member having a conductive elastic layer, a conductive sheet member, a conductive brush member, or the like may be used.

  In this embodiment, the Zener diode 15 is used as the voltage maintaining element. However, the present invention is not limited to this, and a constant voltage element can be used as long as it can be maintained at a predetermined voltage or higher by supplying a current. Some varistors can also be used.

  In this embodiment, the resistance member 17 made of a material different from that of the intermediate transfer belt 10 is used as the resistance member 17 whose electric resistance varies in the same tendency as the intermediate transfer belt 10 depending on the surrounding environment. However, it is more desirable that the fluctuation amount of the electric resistance of the resistance member 17 due to the surrounding environment is approximately the same as the fluctuation amount of the electric resistance of the intermediate transfer belt 10 due to the surrounding environment. From this point of view, if the material constituting the resistance member 17 is the same as the material constituting the intermediate transfer belt 10, a more effective effect can be obtained.

  The resistance member 17 in the present embodiment has a configuration in which the electrical resistance varies depending on the electrical characteristics of the resistance member 17 itself according to the surrounding environment. That is, the resistance member 17 of the present embodiment detects the surrounding environment by a detection means provided separately from the resistance member 17, and varies the electric resistance by a control means for controlling the electric resistance according to the detection result. It is not a simple configuration. Therefore, the configuration of the present embodiment is a simple configuration because it is not necessary to provide a control unit that performs control to vary the electric resistance of the resistance member 17 according to the detection result of the detection unit that detects the surrounding environment.

(Example 2)
In the first exemplary embodiment, the members (the driving roller 11, the stretching roller 12, the opposing roller 13, and the metal rollers 14 a to 14 d) that are in contact with the inner peripheral surface of the intermediate transfer belt 10 are electrically connected to each other and the resistance member 17. The configuration of connecting to the Zener diode 15 via the above has been described. On the other hand, as shown in FIG. 8, in the second embodiment, the offset amount of the stretching roller 212 is adjusted, and a part of the intermediate transfer belt 210 is used as a resistance member whose electric resistance varies depending on the surrounding environment. explain. The configuration of the image forming apparatus according to the present exemplary embodiment is the same as that of the first exemplary embodiment except that a part of the intermediate transfer belt 210 is used as the resistance member 217 instead of the resistance member 17. The members to be attached are denoted by the same reference numerals as those in the first embodiment, and the description thereof is omitted.

  FIG. 8 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus in this embodiment. As shown in FIG. 7, in the configuration of this embodiment, the stretching roller 212 as a stretching member is arranged upstream of the facing roller 213 as a facing member with respect to the moving direction of the intermediate transfer belt 210. . If the distance from the axial center of the tension roller 212 to the axial center of the opposing roller 213 is D5, D5 = 25 mm. Hereinafter, in the present exemplary embodiment, a portion of the intermediate transfer belt 210 at the distance D5 at a position corresponding to between the facing roller 213 and the stretching roller 212 is referred to as a resistance member 217.

  Each metal roller 214a to 214d as a contact member is electrically connected to a counter roller 213 as a counter member. Each of the metal rollers 214a to 214d is disposed in the vicinity of each of the photosensitive drums 201a to 201d provided in a plurality with respect to the moving direction of the intermediate transfer belt 210. The respective metal rollers 214a to 214d are respectively arranged on the downstream side of the primary transfer portion formed by the contact between the corresponding photosensitive drums 201a to 201d and the intermediate transfer belt 210 with respect to the moving direction of the intermediate transfer belt 210. Yes. Further, the respective metal rollers 214 a to 214 d are arranged on the upstream side of the adjacent photosensitive drums 201 b to 201 d and the driving roller 211 on the downstream side of the respective metal rollers 214 a to 214 d with respect to the moving direction of the intermediate transfer belt 210. . More specifically, the metal rollers 214a to 214d are arranged closer to the corresponding photosensitive drums 201a to 201d than the adjacent photosensitive drums 201b to 201d and the driving roller 211.

  As shown in FIG. 8, each of the metal rollers 214a to 214d is disposed on the downstream side by a distance D6 with respect to the photosensitive drums 201a to 201d as the corresponding image carriers. Hereinafter, each of the photosensitive drums 201a to 201d is referred to as a photosensitive drum 201, and each of the metal rollers 214a to 214d is referred to as a metal roller 214. The distance D6 is a distance from the axis center of the photosensitive drum 201 to the axis center of the metal roller 214, and D6 = 25 mm. In this embodiment, each member is set such that the distance D6 from the axial center of the photosensitive drum 201 to the axial center of the metal roller 214 is equal to the distance D5 from the axial center of the stretching roller 212 to the axial center of the opposing roller 213. Is arranged.

  As shown in FIG. 8, one end side (anode side) of a Zener diode 215 as a voltage maintaining element is electrically connected to the ground, and the other end side (cathode side) is a stretching roller 212 as a stretching member. It is connected to the. Unlike the first embodiment, the Zener diode 215 is not directly connected to the opposing roller 213 as the opposing member and the metal roller 214 as the contact member.

  The power supply 221 applies a voltage output from a transformer (not shown) to the secondary transfer roller 220 as a current supply member, so that current is supplied from the secondary transfer roller 220 to each member. The current supplied from the secondary transfer roller 220 as the current supply member flows toward the stretching roller 212 via the resistance member 217 and then is supplied to the Zener diode 215, whereby the Zener diode 215 has a predetermined voltage. (Zener voltage). That is, the voltage formed on the tension roller 212 and the voltage formed on the counter roller 213 are different, and the voltage formed on the counter roller 213 is the sum of the voltage dropped by the current flowing through the resistance member 217 and the zener voltage. Voltage. Therefore, the voltage formed on the counter roller 213 is larger than the voltage formed on the stretching roller 212.

  In this embodiment, a part of the intermediate transfer belt 210 is used as the resistance member 217, and the material constituting the resistance member 217 is the same as the material constituting the intermediate transfer belt 210. That is, since the intermediate transfer belt 210 in this embodiment is also an ion conductive member whose electric resistance varies depending on the surrounding environment, as in the first embodiment, the electric resistance of the resistance member 217 also varies depending on the surrounding environment. It is a member. Accordingly, the opposing roller 213 electrically connected to the metal roller 214 is electrically connected to the Zener diode 215 via the resistance member 217 whose electric resistance varies in the same tendency as the intermediate transfer belt 210 depending on the surrounding environment. . As a result, the primary transfer voltage formed on the metal roller 214 electrically connected to the counter roller 213 is the sum of the Zener voltage of the Zener diode 215 and the voltage dropped due to the current flowing through the resistance member 217.

  Next, the operation and effect of this embodiment will be described with reference to FIG. FIG. 9 shows three measurement environments: a high temperature and high humidity environment (temperature 30 ° C., humidity 80%), a standard temperature and humidity environment (temperature 23 ° C., humidity 50%), and a low temperature low humidity environment (temperature 15 ° C., humidity 10%). FIG. 6 is a diagram showing the relationship between the voltage of the metal roller 214 and the primary transfer property. The meanings of the symbols □, Δ, and ○ in FIG. 9 are the same as those described in the first embodiment.

  The voltage region of the metal roller 214 where no image defect occurs differs depending on the surrounding environment where printing is performed. In this embodiment, since the offset amount (distance D6) of the metal roller 214 is set larger than that in the first embodiment, the primary transfer voltage necessary for obtaining good primary transfer performance is high. If the offset amount (distance D6) of the metal roller 214 is increased, the winding angle of the intermediate transfer belt 210 around the photosensitive drum 201 can be reduced while stabilizing the contact between the intermediate transfer belt 210 and the metal roller 214. It becomes. As a result, image defects that may occur due to creep of the intermediate transfer belt 210 can be reduced. In this embodiment, the offset amount (distance D6) of the metal roller 214 is set to a value larger than that in the first embodiment.

  In this embodiment, as shown in FIG. 8, a part of the intermediate transfer belt 210 whose electric resistance varies depending on the surrounding environment is used as the resistance member 217, so that the metal roller according to the electric resistance of the intermediate transfer belt 210 itself. The primary transfer voltage 214 can be varied. As a result, as shown in FIG. 9, as in Example 1, no image defect occurred due to excess or deficiency of the primary transfer voltage of the metal roller 214 in any of the measurement environments described above.

  In the configuration of this embodiment, the metal roller 214 electrically connected to the counter roller 213 is connected to the Zener diode 215 via the intermediate transfer belt 210 itself. As a result, not only the fluctuation of the electric resistance of the intermediate transfer belt 210 due to the surrounding environment of the image forming apparatus but also the fluctuation of the electric resistance of the intermediate transfer belt 210 due to the use of the image forming apparatus, the primary of the metal roller 214. The transfer voltage can be varied.

  As described above, according to the configuration of the present embodiment, the metal roller 214 that is electrically connected so as to have the same voltage as the opposing roller 213 is passed through the resistance member 217 that is a part of the intermediate transfer belt 210. Are connected to the Zener diode 215. As a result, even when the electrical resistance of the intermediate transfer belt 210 varies in the surrounding environment, the primary transfer voltage of the metal roller 214 can be varied in accordance with the surrounding environment, and the same effect as in the first embodiment is obtained. be able to.

  In this embodiment, the metal roller 214 as the contact member is disposed on the downstream side of the photosensitive drum 201 with respect to the moving direction of the intermediate transfer belt 210. However, the present invention is not limited to this. The structure to arrange | position may be sufficient. Further, the contact member is not limited to the metal roller 214, and may be a roller member having a conductive elastic layer, a conductive sheet member, a conductive brush member, or the like.

1 Photosensitive drum (image carrier)
10 Intermediate transfer belt 11 Drive roller (stretching member)
12 Tension roller (Tension member)
13 Opposing roller (opposing member)
14 Metal roller (contact member)
15 Zener diode (voltage maintaining element)
17 Resistance member 20 Secondary transfer roller (current supply member)
21 Transfer power supply

Claims (13)

An image carrier for carrying a toner image;
An endless and rotatable intermediate transfer belt that is electrically conductive and to which a toner image from the image carrier is primarily transferred, and contacts the outer peripheral surface of the intermediate transfer belt to supply current to the intermediate transfer belt A current supply member, a voltage maintaining element capable of maintaining a predetermined voltage by being supplied with current from the current supply member via the intermediate transfer belt, and an inner peripheral surface of the intermediate transfer belt An image forming apparatus that primarily transfers a toner image from the image carrier to the intermediate transfer belt when a current flows from the contact member to the image carrier through the intermediate transfer belt. ,
Comprising a resistance member whose electric resistance varies in the same tendency as the intermediate transfer belt,
One end side of the voltage maintaining element is electrically connected to ground, and the other end side of the voltage maintaining element is connected to the contact member via the resistance member.   When a current is supplied from the current supply member to the voltage maintaining element via the intermediate transfer belt, a primary transfer voltage for primary transfer of a toner image from the image carrier to the intermediate transfer belt is generated. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed on a contact member.   A current flows from the current supply member to the resistance member via the intermediate transfer belt, and the primary transfer voltage is a voltage obtained by adding the voltage that has dropped due to the current flowing to the resistance member and the predetermined voltage. The image forming apparatus according to claim 2.   A plurality of stretching members that stretch the intermediate transfer belt are provided, and the plurality of stretching members are connected to the contact member and connected to the voltage maintaining element via the resistance member. The image forming apparatus according to any one of claims 1 to 3.   A plurality of the image carriers and the contact members are provided with respect to the moving direction of the intermediate transfer belt, and the plurality of contact members are provided corresponding to the plurality of image carriers, respectively. The image forming apparatus according to claim 4.   Each of the plurality of contact members is disposed on the downstream side of a position where the image carrier and the intermediate transfer belt corresponding to the contact member are in contact with each other with respect to the moving direction of the intermediate transfer belt. The image forming apparatus according to claim 5.   The distance from the axial center of each said image carrier to the axial center of each said contact member is equal in the said several image carrier and the said several contact member of Claim 5 or 6 characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the contact member is a metal roller.   The image forming apparatus according to claim 1, wherein the voltage maintaining element is a Zener diode.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt has ionic conductivity.   The image forming apparatus according to claim 1, wherein the resistance member has ionic conductivity.   The image forming apparatus according to claim 1, wherein a material constituting the resistance member is the same as a material constituting the intermediate transfer belt. A power source for applying a voltage to the current supply member, and a current supplied from the power source to the intermediate transfer belt via the current supply member, whereby the toner image carried on the intermediate transfer belt is transferred to the transfer material; The image forming apparatus according to claim 1, wherein the image is secondarily transferred to the image forming apparatus.

Images