JP2018173671A - 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 in a circumferential direction of an intermediate transfer belt, when the thickest layer of layers constituting the intermediate transfer belt has ion conductivity, good primary transferability may not be obtained.SOLUTION: An image forming apparatus comprises an intermediate transfer belt 10 including, with respect to a thickness direction of the intermediate transfer belt, a base layer 10a that has ion conductivity and is the thickest layer of a plurality of layers constituting the intermediate transfer belt 10, and an internal layer 10b that has electronic conductivity and has a lower electric resistance than that of the base layer 10a.SELECTED DRAWING: Figure 3

Description

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

  Conventionally, an electrophotographic color image forming apparatus has a configuration in which a toner image is sequentially transferred from an image forming portion of each color to an intermediate transfer member, and further, the toner image is collectively transferred from the intermediate transfer member to a transfer material. It has been.

  In such an image forming apparatus, each color image forming section has a drum-shaped photosensitive member (hereinafter referred to as 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.

  In Patent Document 1, a conductive intermediate transfer belt is used as an intermediate transfer member, and a current supplied from a current supply member is caused to flow in the circumferential direction of the intermediate transfer belt, whereby a plurality of photosensitive drums are transferred to the intermediate transfer belt. A configuration for primary transfer of a toner image is disclosed.

JP 2012-098709 A

  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. In the configuration in which primary transfer is performed by flowing current from the current supply member in the circumferential direction of the intermediate transfer belt, if the distance from the current supply member to the photosensitive drum is large, the current for primary transfer is transferred to the intermediate transfer belt. The distance that flows through becomes longer. In this case, the voltage at the primary transfer portion where the photosensitive drum and the intermediate transfer belt are in contact with each other (hereinafter referred to as the primary transfer voltage) drops by the amount of current flowing in the circumferential direction of the intermediate transfer belt. The voltage is easily affected by fluctuations in the electrical resistance of the intermediate transfer belt.

  For example, with respect to the thickness direction of the intermediate transfer belt, the intermediate transfer belt in which the thickest layer of the intermediate transfer belt is an ion conductive layer has a tendency that the electric resistance of the intermediate transfer belt varies depending on the surrounding environment. It is in. More specifically, the electrical resistance of the intermediate transfer belt tends to be low in a high temperature and high humidity environment, and the electrical resistance of the intermediate transfer belt tends to be high in a low temperature and low humidity environment. Consider a case in which such an intermediate transfer belt is used to apply a voltage to the current supply member so that the primary transfer voltage is a voltage suitable for primary transfer in a standard environment. In this case, the primary transfer voltage drop amount in the low temperature and low humidity environment is larger than the primary transfer voltage drop amount in the standard environment. Therefore, it is necessary for primary transfer of the toner image on the photosensitive drum onto the intermediate transfer belt. The primary transfer voltage is insufficient, and image defects may occur. In addition, the primary transfer voltage drop amount in the high temperature and high humidity environment is smaller than the primary transfer voltage drop amount in the standard environment. Therefore, it is necessary for primary transfer of the toner image on the photosensitive drum onto the intermediate transfer belt. The primary transfer voltage becomes excessive, and image defects may occur.

  Therefore, the present invention provides an image forming apparatus that performs primary transfer by passing an electric current in the circumferential direction of the intermediate transfer belt, even when the thickest layer of the intermediate transfer belt has ionic conductivity. The purpose is to ensure primary transferability.

  The present invention relates to an image carrier that carries a toner image, an intermediate transfer belt that is conductive and includes a plurality of layers, a current supply member that contacts the intermediate transfer belt, and a voltage applied to the current supply member. And applying a voltage from the power source to the current supply member, thereby causing a current to flow in the circumferential direction of the intermediate transfer belt to transfer a toner image from the image carrier to the intermediate transfer belt. In the image forming apparatus that performs the next transfer, the intermediate transfer belt is a first layer that has ionic conductivity and is the thickest layer among the plurality of layers that constitute the intermediate transfer belt in the thickness direction of the intermediate transfer belt. And a second layer having electronic conductivity and lower electrical resistance than the first layer.

  According to the present invention, in an image forming apparatus that performs primary transfer by passing an electric current in the circumferential direction of the intermediate transfer belt, it is good even when the thickest layer of the intermediate transfer belt has ionic conductivity. It is possible to ensure the primary transferability.

1 is a schematic cross-sectional view illustrating an image forming apparatus in Embodiment 1. FIG. FIG. 3A is a schematic diagram in which an image forming unit in Example 1 is enlarged. (B) It is a schematic sectional drawing explaining the arrangement configuration of each member in Example 1. FIG. 3 is a schematic diagram illustrating a cross section of an intermediate transfer belt in Embodiment 1. FIG. It is a schematic diagram explaining the secondary transfer property of an independent patch pattern. 6 is a table for explaining fluctuations in electrical resistance due to the surrounding environment of the intermediate transfer belts in Example 1 and Comparative Example. It is a table | surface explaining the presence or absence of generation | occurrence | production of the image defect in each measurement environment in Example 1 and a comparative example. It is a schematic diagram for explaining a negative ghost as an image defect that occurs when verifying primary transferability. FIG. 3 is a schematic diagram for explaining a current flowing in an image carrier via an intermediate transfer belt in Embodiment 1. FIG. 10 is a schematic diagram illustrating a cross section of an intermediate transfer belt in a modified example. 2 is a schematic cross-sectional view illustrating an image forming apparatus as another configuration of Embodiment 1. FIG. FIG. 6 is a schematic cross-sectional view illustrating an image forming apparatus in Embodiment 2. (A) It is a schematic sectional drawing explaining the image forming apparatus in Example 3. FIG. (B) It is a schematic diagram explaining arrangement | positioning of each member in Example 3. FIG. FIG. 3A is a schematic cross-sectional view illustrating an arrangement relationship between an intermediate transfer belt and a protection member when viewed from the moving direction of the intermediate transfer belt in Embodiment 1. (B) It is a schematic diagram explaining the structure of the intermediate transfer belt and protection member in Example 1. FIG. FIG. 6 is a schematic diagram for explaining edge scraping of the image carrier due to electric discharge generated between the charging roller and the image carrier. 6 is a schematic diagram illustrating a relative positional relationship between each member and an image area in the width direction of the intermediate transfer belt in Embodiment 1. FIG. FIG. 4A is a schematic diagram illustrating a cross section of an intermediate transfer belt when viewed from a moving direction of the intermediate transfer belt in Example 2. (B) is a schematic diagram illustrating a configuration of an intermediate transfer belt in Example 2. FIG. FIG. 10 is a schematic diagram illustrating a relative positional relationship between each member and an image region in the width direction of the intermediate transfer belt in Embodiment 2.

  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 otherwise specified, the scope of the present invention is not intended to be limited.

Example 1
[Configuration of Image Forming Apparatus]
FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus of this 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 an arrow R1 in the figure. 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.

  An image forming operation is started when a control means (not shown) such as a controller receives an image signal, and the photosensitive drum 1a is rotationally driven. In the course of rotation, the photosensitive drum 1a is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this embodiment) by the charging roller 2a, and is exposed according to an image signal by the exposure means 3a. The 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 stored 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. . 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 has conductivity, forms a primary transfer portion in contact with the photosensitive drum 1a, and is driven to rotate at substantially the same peripheral speed as the photosensitive drum 1a. The intermediate transfer belt 10 is stretched by a counter roller 13 as a counter member, and a driving roller 11 and a tension roller 12 as tension members. 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. 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.

  At the time of primary transfer, current is supplied to the conductive intermediate transfer belt 10 from the secondary transfer roller 20 as a secondary transfer member (current supply member) that contacts the outer peripheral surface of the intermediate transfer belt 10. When the current supplied from the secondary transfer roller 20 flows in the circumferential direction of the intermediate transfer belt 10, the toner image is primarily transferred from the photosensitive drum 1 a to the intermediate transfer belt 10. The primary transfer of the toner image in each primary transfer portion of this embodiment will be described in detail later.

  Thereafter, similarly, a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image are formed and sequentially transferred onto the intermediate 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 collectively on the surface of a transfer material P such as paper or an OHP sheet.

The secondary transfer roller 20 is a nickel-plated steel rod having an outer diameter of 6 mm, an outer diameter of 18 mm covered with 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. Is used. The rubber hardness of the foamed sponge body was measured using an Asker hardness meter C type, and the hardness was 30 ° when loaded with 500 g. 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 50 N so that the secondary transfer portion is moved. Forming.

  The secondary transfer roller 20 is driven to rotate with respect to the intermediate transfer belt 10, and when a voltage is applied from the transfer power supply 21, a current flows from the secondary transfer roller 20 toward the counter roller 13 as a counter member. . 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. The magnitude of the current for performing the secondary transfer is determined in advance according to the surrounding 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 images have been transferred by the secondary transfer is then heated and pressed by the fixing means 30, whereby the four-color toners are 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 a belt cleaning unit 16 provided to face the opposing roller 13 via the intermediate transfer belt 10. 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 driving roller 11, the stretching roller 12, the counter roller 13 as a counter member of the secondary transfer roller 20, and a contact member that contacts the inner peripheral surface of the intermediate transfer belt 10. The metal roller 14 will be described.

  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.

  The counter roller 13 is connected to the ground via a Zener diode 15 as a voltage maintaining element. The secondary transfer roller 20 to which a voltage is applied from the transfer power supply 21 supplies a current to the counter roller 13, whereby a current flows through the zener diode 15 via the counter roller 13. The Zener diode 15 as a voltage maintaining element is an element that maintains a predetermined voltage (hereinafter referred to as a Zener voltage) when a current flows, and generates a Zener voltage on the cathode side when a current exceeding a certain level flows. . That is, one end side (anode side) of the Zener diode 15 is connected to the ground, the other end side (cathode side) is connected to the counter roller 13, and a voltage is applied from the transfer power supply 21 to the secondary transfer roller 20. The counter roller 13 is maintained at a Zener voltage.

  In this embodiment, a current flows from the opposing roller 13 maintained at a Zener voltage to the photosensitive drums 1 a to 1 d via the intermediate transfer belt 10, whereby toner images are transferred from the photosensitive drums 1 a to 1 d to the intermediate transfer belt 10. Primary transfer is performed. At this time, in order to obtain a desired primary transfer efficiency, in this embodiment, the Zener voltage is set to 300 [V].

  As shown in FIG. 1, the intermediate transfer belt 10 is substantially identical to the photosensitive drums 1a, 1b, 1c, and 1d by a driving roller 11 that rotates in a direction indicated by an arrow R2 in response to a driving force from a driving source (not shown). It is rotationally driven at a peripheral speed of. As shown in FIG. 1, a metal roller 14 that is a contact member that contacts the inner peripheral surface of the intermediate transfer belt 10 is disposed between the photosensitive drum 1 b and the photosensitive drum 1 c.

  FIG. 2A is an enlarged schematic view between the photosensitive drum 1b and the photosensitive drum 1c. As shown in FIG. 2A, the metal roller 14 is disposed at an intermediate position between the photosensitive drum 1b and the photosensitive drum 1c. Further, the metal roller 14 is an imaginary line TL that connects the positions where the photosensitive drum 1b and the photosensitive drum 1c are in contact with the intermediate transfer belt 10 so that the amount of winding of the intermediate transfer belt 10 around the photosensitive drums 1b and 1c can be secured. Is disposed at a position where it enters the photosensitive drum side.

  The metal roller 14 is formed of a straight nickel-plated SUS round bar having an outer diameter of 6 mm, and is rotated following the rotation of the intermediate transfer belt 10. The metal roller 14 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 and is disposed in an electrically floating state.

  Here, the distance from the axial center of the photosensitive drum 1b to the axial center of the photosensitive drum 1c is defined as W, and the lifting height of the metal roller 14 with respect to the virtual line TL is defined as H1. In this embodiment, W = 50 mm and H1 = 2 mm. The distances between the photosensitive drums 1a, 1b, 1c, and 1d are all equal, and the distance W is set to 50 mm.

  FIG. 2B is a schematic cross-sectional view showing the configuration of the primary transfer portion of this embodiment. In this embodiment, the driving roller 11 and the counter roller 13 are arranged as shown in FIG. 2B in order to secure the amount of winding of the intermediate transfer belt 10 around the photosensitive drum 1a and the photosensitive drum 1d. The driving roller 11 and the counter roller 13 are disposed at positions that enter the photosensitive drum side with respect to the virtual line TL that connects the positions where the photosensitive drums 1 a, 1 b, 1 c, and 1 d contact the intermediate transfer belt 10. At this time, 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 driving roller 11 to the axial center of the photosensitive drum 1d is defined as D2. Further, the lifting height of the opposing roller 13 with respect to the virtual line TL is defined as H2, and the lifting height of the driving roller 11 is defined as H3. In this embodiment, D1 = D2 = 50 mm and H2 = H3 = 2 mm.

[Configuration of intermediate transfer belt]
FIG. 3 is a schematic diagram showing a cross section of the intermediate transfer belt 10 in this embodiment when viewed from the axial direction of the metal roller 14. The intermediate transfer belt 10 has a circumferential length of 700 mm and a thickness of 90 μm, and is formed by a base layer 10a (first layer) and an inner surface layer 10b (second layer). The base layer 10a is made of endless polyvinylidene fluoride (PVdF) mixed with an ionic conductive agent such as a polyvalent metal salt or a quaternary ammonium salt as a conductive agent, and the inner layer 10b is mixed with carbon as a conductive agent. Acrylic resin was used.

  Here, the base layer is defined as the thickest layer among the layers constituting the intermediate transfer belt 10 in the thickness direction of the intermediate transfer belt 10. In this embodiment, the inner surface layer 10 b is a layer formed on the inner peripheral surface side of the intermediate transfer belt 10, and the base layer 10 a is related to the thickness direction that is a direction intersecting the moving direction of the intermediate transfer belt 10. It is formed at a position closer to each of the photosensitive drums 1a to 1d than the inner surface layer 10b. In this embodiment, the inner surface layer 10b of the intermediate transfer belt 10 was formed by performing spray coating on the base layer 10a. When the thickness of the base layer 10a is defined as t1 and the thickness of the inner surface layer 10b is defined as t2, t1 = 87 μm and t2 = 3 μm.

  In this embodiment, polyvinylidene fluoride (PVdF) is used as the material of the base layer 10a. However, the material is not limited to this. May be used. In this embodiment, acrylic resin is used as the material of the inner surface layer 10b. However, other materials may be used, for example, materials such as polyester may be used.

  Moreover, as an ionic conductive agent added to the base layer 10a, a high molecular type and a low molecular type conductive agent can be used. For example, in the polymer type, it is possible to use polyether ester amide, polyethylene oxide-epichlorohydrin or polyether ester as nonionic type, quaternary ammonium group-containing acrylate polymer as cationic type, polystyrene sulfonic acid as anionic type. is there. In addition, in the low molecular weight type, a derivative containing an ether group or a derivative containing an ether ester as a nonionic type, a primary to tertiary ammonium salt or a quaternary ammonium salt and their derivatives as a cationic type, a carboxylate as an anionic type, It is possible to use sulfate ester salts, sulfonate salts, phosphate ester salts and their derivatives. These polymer-type or low-molecular-type ionic conductive agents can be used alone or in combination of two or more. Among them, from the viewpoint of heat resistance and conductivity, quaternary ammonium salts, sulfonates, Ether ester amide and the like are preferably used.

  The base layer 10a of the intermediate transfer belt 10 has ionic conductivity. The intermediate transfer belt having ionic conductivity has a feature that the secondary transfer property for an isolated patch-like toner image (hereinafter referred to as an independent patch pattern) is better than the intermediate transfer belt made of an electronic conductive material. is there. FIGS. 4A and 4B are schematic diagrams for explaining the secondary transfer property of the independent patch pattern.

  For example, an independent patch pattern as shown in FIG. 4A is likely to cause a transfer failure when transferred from the intermediate transfer belt to the transfer material P. As shown in FIG. 4B, in the independent patch pattern, since the resistance of the non-toner image area S is lower than the electric resistance of the toner image area T, the current for performing the secondary transfer is non-toner image area. There is a possibility of selectively flowing to S. As a result, the independent patch pattern cannot be secondarily transferred to the transfer material, and transfer failure may occur.

  Due to the electrical characteristics of the electronic conductive intermediate transfer belt, the electric resistance value decreases when a large amount of current flows, so that the current i2 flowing into the non-toner image area S at both ends of the independent patch pattern increases. On the other hand, compared to an electronic conductive intermediate transfer belt, an ion conductive intermediate transfer belt tends to have less change in electrical resistance due to the amount of flowing current. As a result, the current i2 can be prevented from flowing excessively in the non-toner image area S, and the current i1 can be allowed to flow in the toner image area T. Therefore, transfer failure is unlikely to occur during secondary transfer. Even when the intermediate transfer belt is composed of a plurality of layers, the effect of reducing secondary transfer defects can be obtained by providing an ion conductive layer in the vicinity of the surface layer of the intermediate transfer belt. Even in an intermediate transfer belt having an electronic conductive layer in the vicinity of the surface layer, secondary transfer defects can be reduced depending on the electric resistance of the electronic conductive layer.

  In this embodiment, the intermediate transfer belt 10 having different electric resistances of the base layer 10a and the inner surface layer 10b is used, and the electric resistance of the inner surface layer 10b is set lower than that of the base layer 10a. Here, regarding the intermediate transfer belt 10, the surface resistivity measured from the outer peripheral surface side (base layer 10a side) is defined as the electric resistance of the base layer 10a, and the surface resistivity measured from the inner peripheral surface side (inner surface layer 10b side) is defined as the inner surface layer. It is defined as an electric resistance of 10b. That is, the intermediate transfer belt 10 of this embodiment has different surface resistivity measured from the outer peripheral surface side and surface resistivity measured from the inner peripheral surface side, and the surface resistivity measured from the inner peripheral surface side is different. Is smaller than the surface resistivity measured from the outer peripheral surface side.

Further, in the intermediate transfer belt 10 in this embodiment, the volume resistivity of the intermediate transfer belt 10 reflects the electric resistance of the base layer 10a because of the relationship between the electric resistance and thickness of the base layer 10a and the inner surface layer 10b. In a standard environment (temperature 23 ° C., humidity 50%), the surface resistivity measured from the outer peripheral surface side of the intermediate transfer belt 10 is 3.2 × 10 ⁹ Ω / □ and measured from the inner peripheral surface side of the intermediate transfer belt 10. The surface resistivity was 1.0 × 10 ⁶ Ω / □, and the volume resistivity was 5 × 10 ⁹ Ω · cm.

  The volume resistivity and surface resistivity of the intermediate transfer belt 10 were measured using a Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation under a measurement environment at a temperature of 23 ° C. and a humidity of 50%. The volume resistivity is measured by using a ring probe type UR (model MCP-HTP12), applying the probe from the outer peripheral surface side of the intermediate transfer belt 10 and applying voltage 100 [V] and measuring time 10 seconds. It was. The surface resistivity was measured using a ring probe type UR100 (model MCP-HTP16) under the conditions of an applied voltage of 10 [V] and a measurement time of 10 seconds. The surface resistivity on the inner peripheral surface side of the intermediate transfer belt 10 is measured by applying a probe to the inner surface layer 10b side, and the surface resistivity on the outer peripheral surface side of the intermediate transfer belt 10 is measured by applying a probe to the base layer 10a side. did.

  Below, the effect of a present Example is demonstrated in detail using the comparative example 1 and the comparative example 2. FIG. As Comparative Example 1, an intermediate transfer belt having the same material and shape as those of the base layer 10a of this example and having no inner surface layer 10b was used. In Comparative Example 1, the Zener voltage of the Zener diode is set to 300 [V], and other than the configuration of the intermediate transfer belt 10, the configuration of the other image forming apparatuses and various set values are the same as in this embodiment. In Comparative Example 2, the same intermediate transfer belt as in Comparative Example 1 was used, and the Zener voltage of the Zener diode was set to 500 [V]. In Comparative Example 2, except for the configuration of the intermediate transfer belt 10 and the Zener voltage, other configurations of the image forming apparatus and various set values are the same as those of the present embodiment.

  FIG. 5 is a table for explaining the volume resistivity and the surface resistivity in each measurement environment of the intermediate transfer belt 10 of this embodiment and the intermediate transfer belts of Comparative Examples 1 and 2. As shown in FIG. 5, the volume resistivity of the intermediate transfer belt 10 of this embodiment and the intermediate transfer belts of Comparative Examples 1 and 2 are substantially the same in each measurement environment. This is because the electric resistance of the inner surface layer 10b of the intermediate transfer belt 10 of this embodiment is sufficiently lower than the electric resistance of the base layer 10a, and the volume resistivity of the intermediate transfer belt 10 of this embodiment reduces the electric resistance of the base layer 10a. It is to reflect.

  On the other hand, by providing the inner surface layer 10b, the surface resistivity on the inner peripheral surface side of the intermediate transfer belt 10 of this embodiment is the same as the surface resistivity on the inner peripheral surface side of the intermediate transfer belts of Comparative Example 1 and Comparative Example 2. (Hereinafter simply referred to as surface resistivity). As described above, in this embodiment, the intermediate transfer belt 10 having different electric resistances of the base layer 10a and the inner surface layer 10b is used, and the electric resistance of the inner surface layer 10b is set lower than that of the base layer 10a.

  Further, since the inner surface layer 10b of the intermediate transfer belt 10 of this embodiment has electronic conductivity, the surface resistivity on the inner peripheral surface side of the intermediate transfer belt 10 is not affected by the surrounding environment, and is almost equal in each measurement environment. Does not fluctuate. On the other hand, since the intermediate transfer belts of Comparative Example 1 and Comparative Example 2 do not have the inner surface layer 10b and are composed only of the base layer having ionic conductivity, the high temperature and high humidity environment (temperature 30 ° C., humidity 80%). ) The lower the surface resistivity.

FIG. 6 is a table for explaining primary transferability in each image forming unit when image formation is performed in each measurement environment using the configurations of the present embodiment and Comparative Examples 1 and 2. For the verification of the primary transferability shown in FIG. 6, a letter size (width 216 mm) Xerox Business 4200 (basis weight: 75 g / m ² ) stored in each measurement environment was used as the transfer material P. The print mode was verified in the single-sided print mode. As an image for verifying the primary transferability, for each of the photosensitive drums 1a to 1d, a secondary image in which a solid image is formed on a part thereof and then a halftone image is formed and a solid image of two colors of toner are superimposed. A color image (hereinafter referred to as a secondary color image) was used. Here, the secondary color image is an image having an average density of 200% of red (R), green (G), and blue (B).

  A circle in FIG. 6 indicates that no image defect occurred. In FIG. 6, □ indicates that the current formed in the primary transfer portion (hereinafter referred to as the primary transfer voltage) is high, so that an excessive current flows through the photosensitive drum. It is a schematic diagram explaining the image defect observed at this time. In FIG. 6, Δ indicates that the current flowing through the photosensitive drum is insufficient because the primary transfer voltage at the primary transfer portion is low.

  When an excessive current flows into the photosensitive drum 1, more current flows into a portion (non-image portion) that does not carry a toner image than a portion (image portion) that carries a toner image, and the surface potential of the photosensitive drum is increased. A potential difference occurs. Even after the photosensitive drum is charged by the charging roller, the potential difference formed on the photosensitive drum remains when passing through the primary transfer portion, and this potential difference causes a density difference when developing the toner image on the photosensitive drum. That is, due to the potential difference formed by excessive current flowing into the photosensitive drum when passing through the primary transfer portion, the image portion in the previous cycle becomes white in the next cycle of the photosensitive drum as shown in FIG. An image defect called “negative ghost” appears.

  On the other hand, when the current flowing through the photosensitive drum is insufficient, the transfer rate of the toner image that is primarily transferred from the photosensitive drum to the intermediate transfer belt decreases. In this case, transfer failure occurs in the image forming portion where the transfer rate is reduced, and image defects occur due to insufficient primary transfer of secondary images of red (R), green (G), and blue (B). To do.

  As shown in FIG. 6, in the configuration of Comparative Example 1, image defects were observed in images formed by all image forming units. This is because the current flows in the circumferential direction of the intermediate transfer belt of Comparative Example 1 so that the primary transfer voltage of each of the image forming units a to d is lower than the Zener voltage (300 [V]) at the counter roller 13. This is because the current flowing through the photosensitive drum 1 is insufficient.

  In the configuration of Comparative Example 2, although no image defect was observed in the images formed by the image forming unit a and the image forming unit b in the standard environment (temperature 23 ° C., humidity 50%), the image forming unit c and the image An image defect was observed in the image formed by the forming portion d. This is because, as in Comparative Example 1, a current flows in the circumferential direction of the intermediate transfer belt, so that the primary transfer voltages of the image forming unit c and the image forming unit d that are separated from the counter roller 13 are changed by the counter roller 13. This is because the voltage drops below the zener voltage (500 [V]). In particular, in a low-temperature and low-humidity environment (temperature of 15 ° C. and humidity of 10%) in which the electric resistance of the intermediate transfer belt is high, the voltage that drops due to the current flowing in the circumferential direction of the intermediate transfer belt becomes large, as shown in FIG. Image defects were observed in all the image forming units.

  Further, in the configuration of Comparative Example 2, in the high temperature and high humidity environment (temperature 30 ° C. and humidity 80%) where the electrical resistance of the intermediate transfer belt is low, the image forming unit c and the image forming unit d that are separated from the opposing roller 13 are used. There was no image defect in the formed image. On the other hand, in the image forming unit a and the image forming unit b that are close to the opposing roller 13, the electric resistance of the intermediate transfer belt is low with respect to the Zener voltage, and the current is excessive in the image forming unit a and the image forming unit b. The image defect by flowing was seen.

  As described above, in the configurations of Comparative Example 1 and Comparative Example 2, the electrical resistance of the ion conductive intermediate transfer belt varies depending on the surrounding environment, and it is difficult to obtain an appropriate primary transfer voltage in each image forming unit. There was a case.

  On the other hand, as shown in FIG. 6, in the configuration of the present embodiment, image defects due to changes in the surrounding environment did not occur. This is due to the fact that the intermediate transfer belt 10 of this embodiment has an inner surface layer 10b having an electronic resistance lower than that of the base layer 10a on the inner peripheral surface side. Hereinafter, the path of the current flowing toward each of the photosensitive drums 1a to 1d via the intermediate transfer belt 10 will be described in detail using mainly the current flowing toward the photosensitive drum 1a. FIG. 8 is a schematic diagram for explaining the current flowing through the photosensitive drum 1a via the intermediate transfer belt 10 in this embodiment.

  As shown in FIG. 8, the current flowing through the intermediate transfer belt 10 from the counter roller 13 maintained at the Zener voltage is applied to the inner surface layer 10b having a lower electrical resistance than the base layer 10a in the direction indicated by the arrow Cd (the circumferential direction of the intermediate transfer belt 10). ). In the primary transfer portion where the photosensitive drum 1a and the intermediate transfer belt 10 are in contact, the thickness direction of the base layer 10a extends from the inner surface layer 10b toward the photosensitive drum 1a charged at a lower potential than the intermediate transfer belt 10. A current flows in the direction indicated by the arrow Td. As a result, the toner image is primarily transferred from the photosensitive drum 1 a to the intermediate transfer belt 10.

  The inner surface layer 10b has electronic conductivity electrical characteristics, and its electrical resistance hardly varies regardless of the surrounding environment. Further, since the base layer 10a has ionic conductivity, its electric resistance changes depending on the surrounding environment. In this embodiment, the current path flowing through the base layer 10a is only the thickness of the base layer 10a, and the inner layer 10b is shown by an arrow in the figure. It is shorter than the distance of the current flowing in the Cb direction. Therefore, the intermediate transfer belt 10 of this embodiment can suppress the fluctuation of the primary transfer voltage due to the fluctuation of the electric resistance of the base layer 10a having ionic conductivity, as compared with the intermediate transfer belt of the comparative example 2. As a result, in the configuration of this embodiment in which primary transfer is performed by passing a current in the circumferential direction of the intermediate transfer belt 10, an appropriate primary transfer voltage can be obtained in each image forming unit, and occurrence of image defects is suppressed. it can.

In this example, the volume resistivity is in the range of 1 × 10 ⁹ to 1 × 10 ¹⁰ Ω · cm, the surface resistivity on the inner peripheral surface side is smaller than the surface resistivity on the outer peripheral surface side, The intermediate transfer belt 10 having a surface resistivity on the peripheral surface side of 4.0 × 10 ⁶ Ω / □ or less was used. The greater the thickness of the inner surface layer 10b, the lower the surface resistivity on the inner peripheral surface side. However, if the thickness of the inner surface layer 10b is too large, the intermediate transfer belt 10 may be cracked or the base layer of the inner surface layer 10b. Separation from 10a occurs. Considering these, in this embodiment, the thickness of the inner surface layer 10b is set to 3 μm.

  In this embodiment, the intermediate transfer belt 10 including two layers of the ion conductive base layer 10a and the electronic conductive inner surface layer 10b is used. However, the intermediate transfer belt 10 is not limited to the two-layer configuration. For example, FIG. 9 shows an example of a three-layer intermediate transfer belt 110 as a modification of the present embodiment. As shown in FIG. 9, a modified intermediate transfer belt 110 has a surface layer 110c (third layer) in addition to a base layer 110a and an inner surface layer 110b. Further, the surface layer 110c is formed at a position closer to the photosensitive drums 1a to 1d than the base layer 110a in the thickness direction of the intermediate transfer belt 110.

  For the surface layer 110c, an acrylic resin or a polyester resin mixed with a metal oxide or the like as a conductive agent can be used. In the example of FIG. 9, an acrylic resin is used as the surface layer 110c. Further, if the thickness of the surface layer 110c is defined as t3, t3 = 2 μm in the example of FIG.

In the intermediate transfer belt 110, the surface resistivity measured from the outer peripheral surface side reflects the electric resistance of the surface layer 110c, and in the modification, the surface resistivity measured from the outer peripheral surface side is 2.6 × 10 ¹¹ Ω / □. Met. Moreover, the surface resistivity measured from the inner peripheral surface side (the inner surface layer 110b side) was 4.7 × 10 ⁶ Ω / □. As in the example of FIG. 9, even if the surface layer 110c is electronically conductive, if the electrical resistance is high, transfer defects in the secondary transfer portion of the independent patch pattern as described above are unlikely to occur. In addition, since the surface layer 110c is electronically conductive, it is possible to reduce the influence of fluctuations in the electrical resistance of the ion conductive base layer 110a caused by the surrounding environment. In the case of measuring the surface resistivity of the base layer 110a in the three-layer intermediate transfer belt 110, the intermediate transfer belt 10 of Example 1 is removed after the surface layer 110c is removed or the surface layer 110c is peeled off from the base layer 110a. The same measurement as that of the base layer 10a may be performed.

  In addition, the material having ion conductivity such as the base layer 110a in this embodiment exhibits electric conductivity by movement of ions in the material. For this reason, there is a possibility that the ionic conductive agent is biased by long-term use and the ionic conductive agent oozes out. However, as in the example of FIG. 9, the ion conductive base layer 110a is sandwiched from the front and back surfaces by the electronic conductive surface layer 110c and the inner surface layer 110b, thereby obtaining an effect of suppressing the leaching of the ionic conductive agent. I can do it.

  In this embodiment, the secondary transfer roller 20 is used as the current supply member. However, the present invention is not limited to this, and as long as the current can flow in the circumferential direction of the intermediate transfer belt 10, a circumscribed roller 23 different from the secondary transfer roller 20 is used as a current supply member as shown in FIG. May be. FIG. 10 is a schematic cross-sectional view illustrating an image forming apparatus as another configuration of the present embodiment. As shown in FIG. 10, a voltage is applied from the power source 22 to the circumscribing roller 23, and a current flows to the Zener diode 15 through the driving roller 11 as an opposing member of the circumscribing roller 23. Zener voltage is generated. As a result, the driving roller 11 connected to the cathode side of the Zener diode 15 is maintained at a Zener voltage, and a current flows to each of the photosensitive drums 1a to 1d via the intermediate transfer belt 10, and the intermediate transfer is performed from each of the photosensitive drums 1a to 1d. The toner image is primarily transferred to the belt 10.

  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 resistance element or a varistor that is a constant voltage element can also be used. It is also possible to supply current to each of the photosensitive drums 1 a to 1 d via the intermediate transfer belt 10 from the secondary transfer roller 20 to which a voltage is applied from the transfer power source 21 without using the Zener diode 15. In this case, the current flowing from the secondary transfer roller 20 flows in the thickness direction of the base layer 10a toward the inner surface layer 10b and then in the circumferential direction of the inner surface layer 10b. It flows in the thickness direction of the base layer 10a toward the drums 1a to 1d.

  Furthermore, 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 can be used. is there.

(Example 2)
In the first exemplary embodiment, the configuration in which a current is supplied from the opposing roller 13 maintained at the Zener voltage in the circumferential direction of the intermediate transfer belt 10 and the toner images are primarily transferred from the photosensitive drums 1a to 1d to the intermediate transfer belt 10 has been described. . On the other hand, as shown in FIG. 11, in the second embodiment, each member (the driving roller 211, the stretching roller 212, the opposing roller 213, and the metal roller 214) that is in contact with the inner peripheral surface of the intermediate transfer belt 210 is Zener A configuration for connecting the diode 215 will be described.

The intermediate transfer belt 210 includes an ion conductive base layer 210a (first layer) and an electronic conductive inner surface layer 210b (second layer) as in the intermediate transfer belt 10 of the first embodiment. . The configuration of the intermediate transfer belt 210 is the same as that of the first embodiment except that the surface resistivity on the inner peripheral surface side of the intermediate transfer belt 210 is 1.0 × 10 ⁷ Ω / □.

  Hereinafter, in the configuration of the image forming apparatus according to the present exemplary embodiment, the same components as those in the first exemplary embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 11 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus in the present embodiment. As shown in FIG. 11, in the configuration of this embodiment, one end side (anode side) of the Zener diode 215 is connected to the ground. The other end side (cathode side) of the Zener diode 215 is connected to a driving roller 211 and a stretching roller 212 as a stretching member, a facing roller 213 as a facing member, and a metal roller 214 as a contact member, respectively. ing. In this configuration, it is possible to maintain the voltage formed on the driving roller 211 and the metal roller 214 arranged at positions close to the photosensitive drums 201b to 201d at a Zener voltage.

  Accordingly, the current path in the inner surface layer 210b of the current flowing through the photosensitive drums 201b to 201d via the intermediate transfer belt 210 can be made shorter than that in the first embodiment. That is, a current can be supplied from the driving roller 211 and the metal roller 214 maintained at the Zener voltage to the downstream image forming unit that is far from the opposing roller 213, and each image forming unit a to d is good. It is possible to obtain primary transferability. According to the configuration of this embodiment, even in the case where the intermediate transfer belt 210 having a surface resistivity higher than the surface resistivity on the inner surface layer side of the intermediate transfer belt 10 of Embodiment 1 is used, the image forming portions a to d are good. It is possible to ensure the primary transferability.

(Example 3)
In the first exemplary embodiment, a metal roller 14 as a contact member is disposed between the image forming unit b and the image forming unit c, and a current flows from the counter roller 13 maintained at a Zener voltage in the circumferential direction of the intermediate transfer belt 10. Explained. On the other hand, as shown in FIGS. 12A to 12B, in the third embodiment, a plurality of metal rollers 314a to 314d electrically connected to the Zener diode 315 are connected to the respective photosensitive drums 301a to 301d. The arrangement of each will be described. The configuration of the image forming apparatus of the present embodiment is the same as that of the embodiment except that a plurality of metal rollers 314a to 314d that are electrically connected to the Zener diode 315 are arranged for the respective photosensitive drums 301a to 301d. Same as 1. Therefore, the same members as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted.

  FIG. 12A is a schematic cross-sectional view illustrating the configuration of the image forming apparatus in this embodiment. As shown in FIG. 12A, in the configuration of this embodiment, one end side (anode side) of the Zener diode 315 is connected to the ground. The other end side (cathode side) of the Zener diode 315 is connected to a counter roller 313 as a counter member and metal rollers 314a to 314d as contact members. In this configuration, when a voltage is applied from the transfer power supply 21 to the secondary transfer roller 20, the voltage formed on the opposing roller 313 and each of the metal rollers 314a to 314d can be maintained at a Zener voltage.

  FIG. 12B is a schematic diagram for explaining the arrangement of the photosensitive drums 301a to 301d and the metal rollers 314a to 314d in the present embodiment. As shown in FIG. 12B, with respect to the moving direction of the intermediate transfer belt 10, each of the metal rollers 314a to 314d is disposed downstream from the corresponding photosensitive drum 301a to 301d by a distance D3. Here, the distance D3 is a distance from the axial center of each of the metal rollers 314a to 314d to the axial center of each of the corresponding photosensitive drums 301a to 301d. In this embodiment, current flows from the respective metal rollers 314a to 314d arranged in the vicinity of the respective photosensitive drums 301a to 301d and maintained at the Zener voltage to the respective photosensitive drums 301a to 301d via the intermediate transfer belt 10. As a result, the toner images are primarily transferred from the photosensitive drums 301a to 301d to the intermediate transfer belt 10.

  Thus, also in this embodiment, the same effect as that of Embodiment 1 can be obtained. Further, by setting the distances from the respective metal rollers 314a to 314d to the respective photosensitive drums 301a to 301d to be equal distances, currents having substantially the same magnitude can be supplied to the respective photosensitive drums 301a to 301d. Thereby, it is possible to obtain a good primary transfer property for each of the image forming portions a to d.

Example 4
In the first embodiment, the configuration of the intermediate transfer belt 10 having the base layer 10a and the inner surface layer 10b has been described. On the other hand, as shown in FIGS. 13A to 13B, in the fourth embodiment, a configuration in which the protective member 8 is provided on the outer peripheral surface side in the width direction of the intermediate transfer belt 10 will be described. The intermediate transfer belt 10 is the same as that of the first embodiment except that the protective member 8 is provided at the end on the base layer 10a side, and the parts common to the first embodiment are the same as those of the first embodiment. The description is abbreviate | omitted and attached | subjected.

[Generation of the surface of the photosensitive drum]
FIG. 14 is a schematic diagram for explaining the scraping of the surface of the photosensitive drum 1 due to the electric discharge generated between the charging roller 2 and the photosensitive drum 1. At this time, the current flowing from the intermediate transfer belt 10 to the photosensitive drum 1 also flows into a non-image area outside the area F1 where the charging roller 2 and the photosensitive drum 1 are in contact, as indicated by an arrow i in the figure. As a result, in the region F2 where the photosensitive drum 1 and the intermediate transfer belt 10 are in contact with each other, not only the image region in which the photosensitive drum 1 can carry the toner image but also the drum potentials at both ends of the region F2.

  Thereafter, the photosensitive drum 1 is charged by receiving a discharge from the charging roller 2 at a position in contact with the charging roller 2. However, at this time, since the drum potentials at both ends of the region F2 are lowered, at the positions where both ends of the charging roller 2 and the photosensitive drum 1 are in contact, that is, at both ends of the region F1, the photosensitive drum 1 The surface is also discharged from the end surface Ef of the charging roller 2. As a result, at both ends of the region F1, the surface of the photosensitive drum 1 is deteriorated and scraped because excessive discharge is received from the charging roller 2. An insulating layer is formed on the surface of the photosensitive drum 1, and when the surface is scraped, current may leak from the charging roller 2 toward the position where the surface of the photosensitive drum 1 is scraped. . As a result, the charging voltage of the charging roller 2 is lowered, which may cause a charging failure when the surface of the photosensitive drum 1 is charged.

[Protective member]
Therefore, in this embodiment, by providing the protective member 8 on the outer peripheral surface side of the intermediate transfer belt 10, the surface of the photosensitive drum 1 at the both ends of the region F1 is prevented from being scraped. FIG. 13A is a schematic cross-sectional view illustrating the positional relationship between the intermediate transfer belt 10 and the protection member 8 when viewed from the moving direction of the intermediate transfer belt 10 in this embodiment. As shown in FIG. 13A, protective members 8 are provided on both ends of the base layer 10 a of the intermediate transfer belt 10 in the width direction as a direction intersecting the moving direction of the intermediate transfer belt 10. FIG. 13B is a schematic diagram illustrating the configuration of the intermediate transfer belt 10 and the protection member 8 in this embodiment. As shown in FIG. 13B, the protection member 8 is an endless intermediate transfer. The belt 10 is provided around the outer peripheral surface of the belt 10 and on both ends of the intermediate transfer belt 10.

  As the protective member 8, a polyester base adhesive tape for electrical insulation composed of a polyester film and an acrylic adhesive is used, and the film thickness in the thickness direction of the intermediate transfer belt 10 is 53 μm and the width is 8 mm. In the present embodiment, the protective members 8 are doubled on both ends of the outer peripheral surface of the intermediate transfer belt 10.

  FIG. 15 shows the photosensitive drum 1, the charging roller 2, the protective member 8, the intermediate transfer belt 10, and the image related to the width direction of the intermediate transfer belt 10 in this embodiment when the end of one side of the photosensitive drum 1 is used as a reference. It is a schematic diagram explaining the length of an area | region and relative positional relationship. As shown in FIG. 15, the lengths in the width direction of the photosensitive drum 1, the charging roller 2, and the intermediate transfer belt 10 are 250 mm, 228 mm, and 236 mm, respectively. The length of the protective member 8 in the width direction is 8 mm, and is provided on each end of the intermediate transfer belt 10.

  Moreover, the edge part of the charging roller 2 exists in the position of 11 mm and 239 mm shown by FIG. 15, and the protection member 8 is provided in 7-15 mm and 235 mm-243 mm. The area where the photosensitive drum 1 and the intermediate transfer belt 10 are in direct contact is between 15 and 235 mm including the image area. As shown in FIG. 15, the area of the photosensitive drum 1 in contact with both ends of the charging roller 2 overlaps with the area of the photosensitive drum 1 in contact with the protective member 8.

  Since the protective member 8 has an insulating property, the flow of current from the inner surface layer 10b of the intermediate transfer belt 10 to the photosensitive drum 1 is suppressed in the region where the protective member 8 and the photosensitive drum 1 are in contact with each other. This is because the volume resistivity of the protection member 8 is higher than the volume resistivity of the intermediate transfer belt 10, and it is difficult for current to flow through the portion where the protection member 8 and the photosensitive drum 1 are in contact. As a result, a decrease in drum potential at both ends of the region where the photosensitive drum 1 is in contact with the charging roller 2 can be suppressed, generation of excessive discharge from the charging roller 2 can be suppressed, and the promotion of scraping can be suppressed. .

  As described above, according to the configuration of the present embodiment, not only the same effects as those of the first embodiment can be obtained, but also the surface of the photosensitive drum 1 can be prevented from being scraped and the charging failure of the photosensitive drum 1 can be generated. Can be suppressed. In this embodiment, the configuration in which the protective member 8 is provided on the intermediate transfer belt 10 having the base layer 10a and the inner surface layer 10b has been described. However, the present invention is not limited to this, and three or more layers shown in the modification of the first embodiment are used. The protective member 8 may be provided on the intermediate transfer belt 110 having these layers.

(Example 5)
In the fourth embodiment, the configuration in which the insulating protective members 8 are provided on both ends of the intermediate transfer belt 10 that has the inner surface layer 10b and contacts the photosensitive drum 1 has been described. In contrast, as shown in FIGS. 16A to 16B, in the fifth embodiment, a configuration in which the inner surface layer 510b is not formed on both end sides of the intermediate transfer belt 510 will be described. The configuration of this embodiment is the same as that of Embodiment 4 except that the inner surface layer 510b is not formed on both ends of the intermediate transfer belt 510 and the protective member 8 is not used. Therefore, the same members as those of the fourth embodiment are denoted by the same reference numerals as those of the fourth embodiment, and the description thereof is omitted.

  FIG. 16A is a schematic diagram illustrating a cross section of the intermediate transfer belt 510 when viewed from the moving direction of the intermediate transfer belt 510 in the present embodiment. As shown in FIG. 16A, the inner surface layer 510b is not formed on both end sides of the intermediate transfer belt 510 in the width direction as a direction intersecting the moving direction of the intermediate transfer belt 510. In this embodiment, when the inner layer 510b (second layer) is formed on the base layer 510a (first layer) by spray coating, masking is performed on both ends of the base layer 510a, so that the inner layer 510b is formed on both ends. Thus, an intermediate transfer belt 510 that does not form is obtained.

  In this embodiment, in the width direction of the intermediate transfer belt 510, the inner surface layer 510b is not formed in a width range of 8 mm from both ends of the intermediate transfer belt 510 toward the center of the intermediate transfer belt 510. . FIG. 16B is a schematic diagram for explaining the configuration of the intermediate transfer belt 510 in this embodiment. As shown in FIG. 16B, the both ends of the intermediate transfer belt 510 with respect to one rotation of the intermediate transfer belt 510 are illustrated. The inner surface layer 510b is not formed.

  FIG. 17 illustrates the lengths of the photosensitive drum 1, the charging roller 2, the intermediate transfer belt 510, and the image area with respect to the width direction of the intermediate transfer belt 510 in this embodiment, with reference to the end portion on one side of the photosensitive drum 1. It is a schematic diagram explaining relative positional relationship. As shown in FIG. 17, the lengths in the width direction of the photosensitive drum 1, the charging roller 2, and the base layer 510a and the inner surface layer 510b of the intermediate transfer belt 510 are 250 mm, 228 mm, 236 mm, and 220 mm, respectively.

  The ends of the charging roller 2 are disposed at positions of 11 mm and 239 mm shown in FIG. Moreover, the inner surface layer 510b is not formed in 7-15 mm and 235 mm-243 mm, but is formed between 15 mm-235 mm with respect to the base layer 510a. In other words, the area where the intermediate transfer belt 510 and the photosensitive drum 1 in direct contact with the portion where the inner surface layer 510b is formed is between 15 and 235 mm including the image area. As shown in FIG. 17, the region of the photosensitive drum 1 that contacts both ends of the charging roller 2 overlaps the region of the intermediate transfer belt 510 that does not form the inner surface layer 510b.

  Similar to the intermediate transfer belt 10 of the first embodiment, the intermediate transfer belt 510 in the present embodiment has an inner surface layer 510b having a lower electrical resistance than the base layer 510a. Therefore, the current that flows from the intermediate transfer belt 510 to the photosensitive drum 1 flows in the circumferential direction of the inner surface layer 510b, and then the base layer from the inner surface layer 510b toward the photosensitive drum 1 at a position where the intermediate transfer belt 510 and the photosensitive drum 1 are in contact. It flows in the thickness direction of 510a. In other words, in the configuration of the present embodiment, the flow of current to the positions on both ends of the intermediate transfer belt 510 where the inner surface layer 510b is not formed is suppressed. This suppresses a decrease in drum potential at both ends of the region where the charging roller 2 and the photosensitive drum 1 are in contact. As a result, the occurrence of excessive discharge from the charging roller 2 can be suppressed, and the promotion of the abrasion of the surface of the photosensitive drum 1 can be suppressed.

  As described above, also in the configuration of the present embodiment, the same effect as that of the fourth embodiment can be obtained. In this embodiment, the inner surface layer 510b is not formed in the range of 8 mm from both ends of the intermediate transfer belt 510 in the width direction of the intermediate transfer belt 510. However, the present invention is not limited to this, and if the intermediate transfer belt 510 does not form the inner surface layer 510b in a region where excessive discharge from the charging roller 2 may occur, the same effects as in this embodiment can be obtained. That is, it is sufficient that the inner surface layer 510b is not formed at least at positions corresponding to both ends of the region where the charging roller 2 and the photosensitive drum 1 are in contact with each other.

1 Photosensitive drum (image carrier)
10 Intermediate transfer belt 10a Base layer (first layer)
10b Inner surface layer (second layer)
13 Opposing roller (opposing member)
14 Metal roller (contact member)
20 Secondary transfer roller (current supply member)
21 Transfer power supply

Claims (20)

An image carrier that carries a toner image, an intermediate transfer belt having a plurality of conductive layers, a current supply member that contacts the intermediate transfer belt, and a power source that applies a voltage to the current supply member And applying a voltage from the power source to the current supply member to cause a current to flow in the circumferential direction of the intermediate transfer belt to primarily transfer a toner image from the image carrier to the intermediate transfer belt. In the forming device,
The intermediate transfer belt has an ionic conductivity in the thickness direction of the intermediate transfer belt and a first layer which is the thickest layer among the plurality of layers constituting the intermediate transfer belt, and has an electronic conductivity. And a second layer having a lower electrical resistance than the first layer.   The image forming apparatus according to claim 1, wherein the first layer is in contact with the image carrier.   2. The intermediate transfer belt according to claim 1, wherein the intermediate transfer belt includes a third layer having an electric resistance higher than that of the first layer, and the third layer is in contact with the image carrier. Image forming apparatus.   The image forming apparatus according to claim 3, wherein the third layer has electronic conductivity.   The current supply member is a secondary transfer member that secondary-transfers a toner image from the intermediate transfer belt to a transfer material when a voltage is applied from the power source, and the secondary transfer member passes through the intermediate transfer belt. The second layer is formed at a position farther from the image carrier than the first layer with respect to the thickness direction, and is in contact with the counter member. The image forming apparatus according to any one of claims 1 to 4.   By supplying a current from the secondary transfer member to the opposing member, a toner image is primarily transferred from the image carrier to the intermediate transfer belt, and the toner image primarily transferred to the intermediate transfer belt is transferred. The image forming apparatus according to claim 5, wherein the image is secondarily transferred to the material.   The current flowing in the circumferential direction of the intermediate transfer belt from the facing member toward the image carrier flows through the second layer and then flows through the first layer to the image carrier. The image forming apparatus according to claim 6.   A voltage maintaining element capable of maintaining a predetermined voltage by supplying a current from the opposing member; one end of the voltage maintaining element is connected to ground; the other end of the voltage maintaining element is The image forming apparatus according to claim 5, wherein the image forming apparatus is connected to a facing member.   When a current flows from the secondary transfer member to the voltage maintaining element through the counter member, the counter member maintained at the predetermined voltage faces the image carrier in the circumferential direction of the intermediate transfer belt. The image forming apparatus according to claim 8, wherein a current flows.   A contact member in contact with the second layer of the intermediate transfer belt is provided in the vicinity of the image carrier, and the other end of the voltage maintaining element is connected to the opposing member and the contact member. The image forming apparatus according to claim 8, wherein the image forming apparatus is an image forming apparatus.   11. A tension member that stretches the intermediate transfer belt is provided, and the other end side of the voltage maintaining element is connected to the tension member, the opposing member, and the contact member. The image forming apparatus described in 1.   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 10 or 11.   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 12.   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, The Claim 12 or 13 characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 10, wherein the contact member is a metal roller.   The image forming apparatus according to claim 8, wherein the voltage maintaining element is a Zener diode. A length in the width direction that intersects the moving direction of the intermediate transfer belt is shorter than the length of the image carrier, and a charging member that contacts the image carrier and charges the image carrier, and in the thickness direction A protective member disposed between the image carrier and the intermediate transfer belt and having a higher electrical resistance than the first layer;
17. The protective member according to claim 1, wherein the protective member is disposed at a position corresponding to at least both ends of a region where the charging member and the image carrier are in contact with each other in the width direction. The image forming apparatus described in the item.   With respect to the width direction, the protection member is outside the image area where the image carrier can carry a toner image, at least from both ends of the area where the charging member and the image carrier are in contact with each other. The image forming apparatus according to claim 17, wherein the image forming apparatus is provided up to both ends of the intermediate transfer belt. A length in the width direction intersecting the moving direction of the intermediate transfer belt is shorter than the length of the image carrier, and includes a charging member that contacts the image carrier and charges the image carrier.
17. The second layer according to claim 1, wherein the second layer is not formed at positions corresponding to both end portions of a region where the charging member and the image carrier are in contact with each other with respect to the width direction. 2. The image forming apparatus according to item 1. With respect to the width direction, outside of the image area where the image carrier can carry a toner image, at least from both ends of the area where the charging member and the image carrier are in contact with each other, the intermediate transfer belt The image forming apparatus according to claim 19, wherein the second layer is not formed up to both ends.

Images