JP2020003579A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of reducing a FPOT in a structure using an ion conductive intermediate transfer body.SOLUTION: In an image forming apparatus 100, a primary transfer voltage value supplied to a primary transfer member 13 by voltage supply means 51 is constant without depending on use environment, and the direction of change in electrical resistance to change in temperature and humidity is different between the primary transfer member 13 and an intermediate transfer body 30. When the electrical resistances of the intermediate transfer body and primary transfer member are RbNN and Rt1NN, respectively, in the normal temperature and humid environment, are RbHH and Rt1HH, respectively, in high temperature and high humidity environment and are RbLL and Rt1LL, respectively, in low humidity and temperature environment, and when the electrical resistance ratios thereof are ΔRbH=RbHH/RbNN, ΔRt1 H=Rt1HH/Rt1NN, ΔRbL=RbLL/RbNN and ΔRt1L=Rt1LL/Rt1 NN, and primary transfer currents having two levels are I1 and I2 (I1<I2), the following formula Rt1NN/RbNN>(ΔRbH×I2-ΔRbL×I1)/(ΔRt1L×I1-ΔRt1H×I2) is satisfied.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic method or an electrostatic recording method, and more particularly to an image forming apparatus having an intermediate transfer member.

  2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic method or the like, a primary transfer of a plurality of color toner images from an image carrier to an intermediate transfer member is sequentially performed, and a plurality of color toner images superimposed on the intermediate transfer member are collectively collected. There is an image forming apparatus of an intermediate transfer type that performs secondary transfer to a recording material by using a secondary transfer method.

  In such an image forming apparatus, a member obtained by adding an ionic substance as a conductive agent to a transfer member or an intermediate transfer member may be used. Generally, an ion-conductive member (that is, an ion-conductive member) tends to change its electrical resistance value under the influence of the temperature and humidity of the surrounding environment. As a control to cope with such environmental fluctuation of the electric resistance value, there is an ATVC control method (Active Transfer Voltage Control: hereinafter, referred to as "ATVC") (Patent Document 1). That is, at the time of non-image formation, the transfer voltage is controlled at a constant current with a preset current value, and the change in the generated voltage value at that time detects the change in the electrical resistance of the transfer section (transfer member, intermediate transfer body). At the time of image formation, constant voltage control of the transfer voltage is performed based on the result of the arithmetic processing of the generated voltage value.

JP 2000-75694 A

  However, the conventional ATVC requires a time for detecting the electric resistance of the transfer portion, typically immediately before image formation, in order to determine a transfer voltage at the time of image formation. Therefore, it is necessary to start image formation after waiting for this time. As a result, the time from the start of printing to the time when an image is formed on the first recording material and output (First Print Out Time: hereinafter, referred to as “FPOT”) becomes longer by the time. I will.

  In recent years, the value of FPOT has become a very important index as an index indicating the performance of an image forming apparatus from the viewpoint of usability, and it is desired to shorten the FPOT.

  Therefore, an object of the present invention is to provide an image forming apparatus that can shorten FPOT in a configuration using an ion-conductive intermediate transfer member.

  The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention relates to an image bearing member that carries a toner image, an ion-conductive intermediate transfer member, and a primary contact member that comes into contact with the intermediate transfer member and that makes contact with the image bearing member. An image forming apparatus comprising: a primary transfer member configured to transfer a toner image from the image carrier to the intermediate transfer member at a transfer unit; and a voltage supply unit configured to supply a primary transfer voltage to the primary transfer member. The primary transfer voltage value supplied to the primary transfer member by the voltage supply means is constant irrespective of the usage environment, and the direction of increase and decrease of the electric resistance between the primary transfer member and the intermediate transfer body with respect to the increase and decrease of temperature and humidity. The electrical resistances of the intermediate transfer member and the primary transfer member in a normal temperature and normal humidity environment are RbNN and Rt1NN, respectively, and the electrical resistance values of the intermediate transfer member and the primary transfer member in a high temperature and high humidity environment are respectively Rb H, Rt1HH, the electrical resistance values of the intermediate transfer member and the primary transfer member in a low-temperature and low-humidity environment are RbLL and Rt1LL, respectively. The electrical resistance ratio of each transfer member is ΔRbH = RbHH / RbNN, ΔRt1H = Rt1HH / Rt1NN, and the electrical resistance of the intermediate transfer member between the low-temperature and low-humidity environment and the normal temperature and normal humidity environment, respectively. When the ratios are ΔRbL = RbLL / RbNN, ΔRt1L = Rt1LL / Rt1NN, and the two-level primary transfer currents are I1 and I2 (I1 <I2), respectively, the following equation is used. ) / (ΔRt1L · I1−ΔRt1H · I2).

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to shorten FPOT in the structure using an ion-conductive intermediate transfer body.

FIG. 2 is a schematic sectional view of the image forming apparatus. FIG. 3 is a schematic sectional view near a primary transfer portion. FIG. 3 is a graph for explaining primary transfer performance. FIG. 4 is a graph illustrating a relationship between an electric resistance of a primary transfer member and a primary transfer voltage. FIG. 9 is a schematic sectional view of another example of an image forming apparatus.

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

[Example 1]
1. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 of the present embodiment is a tandem-type printer that employs an intermediate transfer method and can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes a plurality of image forming units (stations) that form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. It has fourth image forming units 1Y, 1M, 1C and 1K. Elements having the same or corresponding functions or configurations in each of the image forming units 1Y, 1M, 1C, and 1K are omitted from the reference characters Y, M, C, and K indicating that they are elements for any color. It may be explained comprehensively. In the present embodiment, the image forming unit 1 includes a photosensitive drum 9, a charging roller 10, an exposing device 11, a developing device 12, a primary transfer member 13, a drum cleaning device 14, and the like, which will be described later.

  When image formation is started, rotation of a photosensitive drum 9 which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image carrier, an intermediate transfer belt 30 described later, and the like are started. . The photosensitive drum 9 rotates in the direction of arrow R1 in the figure. The intermediate transfer belt 30 rotates in the direction of arrow R2 in the figure while contacting the photosensitive drum 9. The surface of the rotating photosensitive drum 9 is charged to a predetermined charging potential of a predetermined polarity (negative in this embodiment) by a charging roller 10 which is a roller-shaped charging member as charging means. During the charging step, a charging voltage including a negative DC component is applied to the charging roller 2. The charged surface of the photosensitive drum 9 is scanned and exposed on the basis of image information by an exposure device 11 as an exposure unit, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 9. The electrostatic image formed on the photosensitive drum 9 is developed (visualized) by supplying toner as a developer by a developing device 12 as a developing unit, and a toner image is formed on the photosensitive drum 9. In the present embodiment, the exposed portion (image portion) on the photosensitive drum 9 where the absolute value of the potential is reduced by being exposed based on the image information after the charging process is applied to the exposed portion (image portion) having the same polarity as the charged polarity of the photosensitive drum 9 ( In this embodiment, the negatively charged toner adheres. In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative.

  An intermediate transfer belt 30 composed of a movable (rotatable) endless belt as an intermediate transfer member is disposed so as to face each photosensitive drum 9. The intermediate transfer belt 30 is stretched around a tension roller 31 as a plurality of stretching rollers (supporting rollers), a secondary transfer facing roller 32, and a driving roller 33, and is stretched with a predetermined tension. A brush-like primary transfer member (brush member, primary transfer brush) 13 as primary transfer means is arranged on the inner peripheral surface side of the intermediate transfer belt 30 so as to correspond to each photosensitive drum 9. The primary transfer member 13 is pressed toward the photosensitive drum 9 via the intermediate transfer belt 30 to form a primary transfer portion N1 where the photosensitive drum 9 and the intermediate transfer belt 30 come into contact. The toner image formed on the photosensitive drum 9 as described above is primary-electrostatically transferred onto the rotating intermediate transfer belt 30 by the operation of the primary transfer member 13 in the primary transfer portion N1. You. In the primary transfer step, the primary transfer power supply 51 supplies the primary transfer member 13 with a primary transfer voltage (1) which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive in this embodiment). Next transfer bias) is applied. For example, at the time of forming a full-color image, the yellow, magenta, cyan, and black toner images formed on the respective photosensitive drums 9 are superimposed on the intermediate transfer belt 30 at the respective primary transfer portions N1. The primary transfer is performed sequentially.

  A secondary transfer roller 34 which is a roller-shaped secondary transfer member as secondary transfer means is disposed at a position facing the secondary transfer opposing roller 32 on the outer peripheral surface side of the intermediate transfer belt 30. The secondary transfer roller 34 is pressed toward the secondary transfer opposing roller 32 via the intermediate transfer belt 30 to form a secondary transfer portion N2 where the intermediate transfer belt 30 and the secondary transfer roller 34 come into contact. The toner image formed on the intermediate transfer belt 30 as described above is conveyed while being sandwiched between the intermediate transfer belt 30 and the secondary transfer roller 34 by the action of the secondary transfer roller 34 in the secondary transfer portion N2. Is secondarily electrostatically transferred onto a recording material (sheet) P such as paper (paper). At the time of the secondary transfer step, the secondary transfer power supply 35 supplies the secondary transfer roller 34 with a secondary transfer voltage (2) which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive in this embodiment). Next transfer bias) is applied. The recording material P is supplied to the secondary transfer portion N2 by a feeding device (not shown) at the same timing as the toner image on the intermediate transfer belt 30.

  The recording material P to which the toner image has been transferred is conveyed to a fixing device 15 as fixing means. The fixing device 15 fixes (melts and fixes) the toner image on the recording material P by heating and pressing the recording material P carrying the unfixed toner image. The recording material P on which the toner image is fixed is discharged (output) outside the apparatus main body of the image forming apparatus 100.

  Toner remaining on the surface of the photosensitive drum 9 without being transferred to the intermediate transfer belt 30 during the primary transfer process (primary transfer residual toner) is removed from the surface of the photosensitive drum 9 by a drum cleaning device 14 as a photosensitive member cleaning unit. And collected in a waste toner container. Further, on the outer peripheral surface side of the intermediate transfer belt 30, at a position facing the drive roller 33, a cleaning roller 17 as a toner charging member is arranged so as to contact the intermediate transfer belt 30. A cleaning voltage (cleaning bias), which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive in this embodiment), is applied to the cleaning roller 17 by a toner charging power supply 18. The toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 30 without being transferred to the recording material P during the secondary transfer process is charged to a positive polarity when passing through the cleaning roller 17, and is subjected to primary transfer. The image is reverse-transferred to the photosensitive drum 9 in the portion N1. Thereafter, the toner is removed from the surface of the photosensitive drum 9 by the drum cleaning device 14 and collected in a waste toner container.

  In this embodiment, in each image forming section 1, the photosensitive drum 9, and the charging roller 10, the developing device 12, and the drum cleaning device 14 as process means acting on the photosensitive drum 9, constitute a cartridge 8 integrally. ing. The cartridge 8 is configured to be detachable from an apparatus main body of the image forming apparatus 100. Then, for example, when the photosensitive drum 9 reaches the end of its life, the cartridge 8 is removed from the apparatus main body of the image forming apparatus 100 and is replaced with a new one.

2. Intermediate Transfer Belt In the present embodiment, an ionic conductive belt member obtained by adding an ionic conductive agent to polyethylene naphthalate as a resin material was used as the intermediate transfer belt 30. In this example, an aliphatic sulfonic acid salt was used as the ion conductive agent. In this embodiment, the thickness of the intermediate transfer belt 30 is 70 μm. In this embodiment, the volume resistivity of the intermediate transfer belt 30 in a normal temperature and normal humidity environment (23 ° C./50% RH; hereinafter, referred to as “NN environment”) is 10 ^10.4 Ωcm.

  The volume resistivity of the intermediate transfer belt 30 was measured using a high resistivity meter Hiresta-UP (MCP-HT450) (manufactured by Mitsubishi Chemical Corporation). A metal UR100 probe (MCP-HTP16) as a measurement probe was pressed against the surface of the intermediate transfer belt 30, and a metal surface (ground surface) was used as the opposing plate. Under the conditions of an applied voltage of 500 V, a measurement time of 10 s, and a volume resistivity measurement mode, the volume resistivity (unit: Ω · cm) of the intermediate transfer belt 30 was measured with a metal probe.

In the intermediate transfer belt 30 of the present embodiment, conductivity is exhibited by the ionized ions moving as carriers. Since the movement of ions is activated in a high-temperature and high-humidity environment, the volume resistivity of the intermediate transfer belt 30 of the present embodiment is lower in a high-temperature and high-humidity environment. The volume resistivity of the intermediate transfer belt 30 of the present embodiment is set to a low-temperature and low-humidity environment (15 ° C./10% RH: hereinafter referred to as “LL environment”) and a high-temperature and high-humidity environment (30 ° C./80% RH: hereinafter). HH environment "). As a result, the volume resistivity in the LL environment was 10 ^10.8 Ωcm, and the volume resistivity in the HH environment was 10 ^9.8 Ωcm.

  FIG. 2 is a schematic cross-sectional view near the primary transfer portion N1 (cross-section substantially orthogonal to the rotation axis direction of the photosensitive drum 9). In the present embodiment, the width (short width) of the contact portion between the photosensitive drum 9 and the intermediate transfer belt 30 in the moving direction of the intermediate transfer belt 30 is 2 mm, and the width in the direction substantially orthogonal to the moving direction of the intermediate transfer belt 30 ( The longitudinal width is 220 mm. In this case, from the volume resistivity of the intermediate transfer belt 30 described above, the electrical resistance value RbNN in the thickness direction of the intermediate transfer belt 30 in the NN environment (hereinafter, also simply referred to as “electrical resistance”) RbNN is 40 MΩ. Further, the environmental fluctuation width of the electric resistance value in the thickness direction of the intermediate transfer belt 30 between the HH environment and the LL environment is about one digit (10 to 100 MΩ). Note that these settings are substantially the same in all the primary transfer units N1 of the first, second, third, and fourth image forming units 1Y, 1M, 1C, and 1K. Note that the electric resistance value of the intermediate transfer belt 30 in the thickness direction is the electric resistance value of the intermediate transfer belt 30 in the direction in which the primary transfer current flows in the primary transfer portion N1.

  In this embodiment, the intermediate transfer belt 30 is driven and rotated by the driving roller 33 at a peripheral speed of 140 mm / sec (corresponding to the process speed).

3. Primary Transfer Member In this embodiment, as the primary transfer member 13, a brush member provided with brush fibers formed of conductive nylon fibers in which carbon powder is uniformly dispersed was used. Each of the conductive nylon fibers is densely arranged on a base cloth and bonded to a substrate, which is a substrate made of a metal plate-like member (sheet metal), using a conductive adhesive or the like. By doing so, a brush member is configured. In this embodiment, as the conductive nylon fiber, fineness of 170dtex / 30F, volume resistivity was used in ¹⁰ 7.8 ^{to 10 8.3} [Omega] cm in NN environments. In this embodiment, the fiber density of the brush member is 200 kF / inch ² . Further, in the present embodiment, as shown in FIG. 2, the width (longitudinal width) of the raised portion of the brush member in a direction substantially perpendicular to the moving direction of the intermediate transfer belt 30 is 220 mm, and the width in the moving direction of the intermediate transfer belt 30. (Short width) is 4 mm. Further, in this embodiment, the length of the brush fiber is 5 mm, the brush fiber is raised in a direction perpendicular to the substrate, and the brush member is brushed against the surface (inner peripheral surface) of the intermediate transfer belt 30. The fiber is fixed so as to penetrate 1 mm.

The nylon fiber of the brush member has high water absorption, and expands in size by absorbing water in a high-temperature and high-humidity environment. When the size expands, the distance between the carbon particles as the conductive agent increases and the electrical resistance increases. The volume resistivity of the conductive nylon fiber having a volume resistivity of ^108.1 Ωcm in the NN environment was measured in the LL environment and the HH environment. As a result, the volume resistivity in the LL environment was ^107.8 Ωcm, the volume resistivity in the HH environment was ^108.4 Ωcm, and the environmental fluctuation was about 0.6 digits.

  In the present embodiment, the electric resistance value (hereinafter, also simply referred to as “electric resistance”) Rt1NN of the brush member in the NN environment was about 40 MΩ. In this embodiment, a brush member having an electrical resistance Rt1NN in the NN environment of 22 to 71 MΩ is used, with the manufacturing variation of the electrical resistance of the brush member being 0.5 digits. In this embodiment, the environmental fluctuation of the electric resistance value of the brush member was about 0.6 digits. The electric resistance value of the primary transfer member 13 is an electric resistance applied to the primary transfer member 13 when a primary transfer current flows in the primary transfer portion N1.

  The electric resistance value of the brush member was measured using an insulation resistance meter IR4055 (HIOKI). The counter electrode was pressed in such a manner as to penetrate the brush member by 1 mm, and the measuring terminal was used by connecting to the substrate of the brush member and the counter electrode. The electric resistance (unit: MΩ) of the brush member was measured under the conditions of an applied voltage of 500 V and a measurement time of 10 s.

  In this embodiment, the fibers having the above-described volume resistivity and the brush member having the brush size are used, but the present invention is not limited to this. For example, the electrical resistance value of the brush member may be adjusted by increasing the volume resistivity of the conductive nylon fiber, shortening the brush length or decreasing the fiber density.

4. Conditions for Primary Transfer Current Next, conditions for the primary transfer current necessary for the primary transfer performance will be described. The image defects related to the primary transfer described here are a transfer defect of a multi-color and a decrease in image density due to re-transfer of a single color. Note that upstream and downstream with respect to the primary transfer mean upstream and downstream in the moving direction (rotation direction) of the intermediate transfer belt 30 even if not particularly mentioned.

  Multi-color transfer failure means that the photosensitive drum 9 of the downstream image forming unit 1 is placed on the toner image on the intermediate transfer belt 30 that has been primarily transferred by the primary transfer unit N1 of the upstream image forming unit 1. When primary transfer of the upper toner image is performed, it indicates a transfer failure in which primary transfer residual toner remains on the photosensitive drum 9. In the primary transfer section N1, a negatively charged toner on the intermediate transfer belt 30 is interposed between a positive voltage applied to the primary transfer member 13 and a negatively charged toner on the photosensitive drum 9. When the current becomes difficult to flow, the transfer efficiency is reduced. The transfer failure of the multicolor occurs particularly when the primary transfer current is low. When the toner of the second and subsequent colors becomes thinner than an allowable range, the transfer failure becomes apparent as an image failure.

  On the other hand, the re-transfer of a single color means that the toner on the intermediate transfer belt 30 that has been primarily transferred by the primary transfer unit N1 of the image forming unit 1 on the upstream side is transferred to the primary transfer unit N1 on the image forming unit 1 on the downstream side. Indicates that a part of the toner on the intermediate transfer belt 30 is transferred onto the photosensitive drum 9 of the image forming unit 1 on the downstream side when passing through the portion of the photosensitive drum 9 facing the non-image portion. . When the potential difference between the primary transfer voltage and the non-image portion potential on the photosensitive drum 9 exceeds the discharge threshold of the toner, the toner on the intermediate transfer belt 30 whose polarity has been inverted from minus to plus due to the discharge becomes minus. The image is retransferred to a non-image area on the photosensitive drum 9 which is charged to a negative polarity. Monochromatic retransfer occurs especially when the primary transfer current is high, and when the primary transfer voltage is too high beyond an allowable range, the density is remarkably reduced and the image becomes apparent as an image defect.

  FIG. 3 shows the relationship between transfer failure of a secondary color and retransfer of a single color in the present embodiment. The horizontal axis indicates the primary transfer current value per single image forming unit 1 with respect to the non-image portion potential of the photosensitive drum 9 (−500 V in this embodiment). The vertical axis indicates an optical density value which is an index value correlated with the weight of the primary transfer residual toner and the weight of the retransferred toner. This optical density value was obtained as follows. That is, the primary transfer residual toner or the retransferred toner on the photosensitive drum 9 was collected with a tape, attached to paper, and measured with an optical densitometer. Then, the measured value of the optical densitometer when only the tape was stuck on the paper was subtracted from the measured value to obtain an optical density value. The optical density value measured by this method shows a substantially proportional relationship with the weight of the primary transfer residual toner and the weight of the retransferred toner. The smaller the optical density value, the better the primary transfer is, or the more retransfer is suppressed.

  In this embodiment, the optical density values of 0.1, 0.2, and 0.3 are respectively 5%, 10%, and 15% of the weight of the primary transfer residual toner or the weight of the retransferred toner relative to the weight of the toner on the photosensitive drum 9. Is equivalent to In this embodiment, if the optical density value is 0.2 or less, the level of poor transfer of the secondary color and the level of retransfer of the single color are visually good, and the primary transfer current at that time depends on the use environment. 3 to 10 μA.

  In this embodiment, in order to shorten FPOT, the primary transfer voltage value is controlled at a constant voltage value regardless of the use environment. That is, in this embodiment, it is necessary to control the primary transfer current within the above-described range of the primary transfer current (3 to 10 μA) at a constant primary transfer voltage value regardless of the use environment.

5. Comparative Example In order to facilitate understanding of the present invention, problems in the configuration of the comparative example (Comparative Examples 1 and 2) will be clarified. Here, the intermediate transfer belt in the comparative example is substantially the same as the intermediate transfer belt in the present embodiment. Unless otherwise specified, other configurations of the comparative example are substantially the same as the configuration of the present embodiment.

<Comparative Example 1>
In Comparative Example 1, a roller member is used as a primary transfer member. As the roller member of Comparative Example 1, the outer circumference of a core metal having an outer diameter of 5 mm was covered with an elastic layer formed of a foamed sponge body of NBR (nitrile butadiene rubber) adjusted to a thickness of 4.5 mm. An elastic roller was used. An ionic conductive agent is added to the foamed sponge body in order to impart conductivity. The volume resistivity of the foamed sponge body, ^{10 5.5} [Omega] cm in NN environment 10 ⁵ [Omega] cm at HH environment are 10 ⁶ [Omega] cm in LL environment, environmental variation in the electrical resistance of the roller member is about one order of magnitude .

  In Comparative Example 1, the width (short width) of the contact portion between the roller member and the intermediate transfer belt in the moving direction of the intermediate transfer belt was 2 mm, and the width (longitudinal width) in a direction substantially perpendicular to the moving direction of the intermediate transfer belt was 220 mm. In this case, from the above-mentioned volume resistivity, the electric resistance value in the thickness direction of the elastic layer of the roller member (hereinafter, also simply referred to as “electric resistance”) is 0.1 MΩ in the HH environment and 0.3 MΩ in the NN environment. , 1MΩ in the LL environment. Table 1 shows the electrical resistance value of the intermediate transfer belt, the electrical resistance value of the roller member, and the total resistance obtained by adding both values in Comparative Example 1 in each environment.

  From Table 1, it can be seen that in Comparative Example 1, the LL environment makes it difficult for the primary transfer current to flow, and the HH environment makes it easy to flow. The primary transfer voltage VLL required to make the primary transfer current 3 μA or more in the LL environment is 303 V or more (VLL ≧ 303 V). Further, the primary transfer voltage VHH required to reduce the primary transfer current to 10 μA or less in the HH environment is 101 V or less (VHH ≦ 101 V). Therefore, in Comparative Example 1, a constant primary transfer voltage value that satisfies the primary transfer performance in the LL environment and the HH environment cannot be set.

  In Comparative Example 1, as the one transfer member, an ion-conductive roller member in which the direction of increase and decrease in electric resistance with respect to increase and decrease in temperature and humidity was the same as that of the intermediate transfer belt was used. A constant primary transfer voltage that satisfies the primary transfer performance even when a metal roller composed of, for example, a nickel-plated SUS round bar or the like is used as the primary transfer member, in which environmental changes in electrical resistance can be almost ignored. The result is similar to the above in that the value cannot be set.

<Comparative Example 2>
In Comparative Example 2, a brush member is used as a primary transfer member. Comparative Example 2 differs from Comparative Example 1 in that the primary transfer member and the intermediate transfer belt differ in the direction in which the electric resistance increases or decreases with respect to the temperature and humidity. In Comparative Example 2, the electric resistance value of the brush member is different from that of the present embodiment.

Conventionally, a brush member used for a primary transfer member is used as an electrode of a primary transfer power source, and thus has an electrical resistance value that is two orders of magnitude lower than that of the intermediate transfer belt of this embodiment, for example. In Comparative Example 2, such a conventional brush member is used. In Comparative Example 2, a conductive nylon fiber having a volume resistivity of 10 ⁶ Ωcm in an NN environment was used as a brush member, and a brush member having an electric resistance of 0.3 MΩ was used. The environmental variation of the electric resistance value of the brush member of Comparative Example 1 is about 0.6 digits as in the present embodiment. Table 2 shows the electrical resistance of the intermediate transfer belt, the electrical resistance of the brush member, and the total resistance obtained by summing the electrical resistance of the intermediate transfer belt in each environment.

  Table 2 shows that, in Comparative Example 2, the LL environment makes it difficult for the primary transfer current to flow, and the HH environment makes it easy for the primary transfer current to flow. The primary transfer voltage VLL required to make the primary transfer current 3 μA or more in the LL environment is 300.6 V or more (VLL ≧ 300.6 V). In addition, the primary transfer voltage VHH required to reduce the primary transfer current to 10 μA or less in an HH environment is 108 V or less (VHH ≦ 108 V). Therefore, in Comparative Example 2, a constant primary transfer voltage value that satisfies the primary transfer performance in the LL environment and the HH environment cannot be set.

6. Details of the configuration of the present embodiment <Setting of primary transfer voltage>
Next, the setting of the primary transfer voltage in this embodiment will be described. Table 3 shows the electrical resistance value of the intermediate transfer belt, the electrical resistance value of the brush member, and the total resistance obtained by summing the electrical resistance values of the intermediate transfer belt in each environment.

  First, the case where the electric resistance value of the brush member is the center of the manufacturing variation will be described. Table 3 shows that the LL environment makes it difficult for the primary transfer current to flow and the NN environment makes it easy to flow. The primary transfer voltage VLL required to make the primary transfer current 3 μA or more in the LL environment is 360 V or more (VLL ≧ 360 V). Further, the primary transfer voltage VNN required to reduce the primary transfer current to 10 μA or less in the NN environment is 800 V or less (VNN ≦ 800 V). Therefore, in this case, in order to satisfy the primary transfer performance irrespective of the use environment, the primary transfer voltage may be set between 360 and 800V.

  Next, the case where the electric resistance value of the brush member is at the lower limit of the manufacturing variation will be described. From Table 3, it can be seen that the primary transfer current hardly flows in the LL environment, and the primary transfer current easily flows in the HH environment. The primary transfer voltage VLL required to make the primary transfer current 3 μA or more in the LL environment is 333 V or more (VLL ≧ 333 V). Further, the primary transfer voltage VHH required to reduce the primary transfer current to 10 μA or less in the HH environment is 540 V or less (VHH ≦ 540 V). Therefore, in this case, in order to satisfy the primary transfer performance irrespective of the use environment, the primary transfer voltage may be set between 333 and 540V.

  Next, the case where the electric resistance value of the brush member is the upper limit of the variation in manufacturing will be described. Table 3 shows that the primary transfer current hardly flows in the HH environment, and the primary transfer current easily flows in the NN environment. The primary transfer voltage VHH required to make the primary transfer current 3 μA or more in the HH environment becomes 456 V or more (VHH ≧ 456 V). Further, the primary transfer voltage VNN required to reduce the primary transfer current to 10 μA or less in the NN environment is 1110 V or less (VNN ≦ 1110 V). Therefore, in this case, in order to satisfy the primary transfer performance irrespective of the use environment, the primary transfer voltage may be set between 456 and 1110V.

  As described above, in the present embodiment, in order to satisfy the primary transfer property regardless of the use environment, including the manufacturing variation of the electrical resistance value of the brush member and the environmental fluctuation, the primary transfer voltage May be set between 456 and 540 V, for example, 500 V.

<Conditions for Maintaining Primary Transfer Voltage Value>
Next, the conditions under which the primary transfer voltage value can be kept constant as in this embodiment will be described.

  FIG. 4 shows the ratio (Rt1NN / RbNN) between the electric resistance value RbNN of the intermediate transfer belt and the electric resistance value Rt1NN of the brush member in the NN environment shown in Table 3 on the horizontal axis, and shows “3 μA voltage” and “10 μA” in the ratio. FIG. 5 is a graph plotting “voltage”. Here, the “3 μA voltage” is a voltage necessary to supply a primary transfer current of 3 μA in an environment in which the primary transfer current hardly flows among the LL environment, the NN environment, and the HH environment. The “10 μA voltage” is a voltage at which a primary transfer current of 10 μA flows in a usage environment where the primary transfer current flows most easily among the LL environment, the NN environment, and the HH environment.

  The “intersection A” between the line connecting the plots for the 3 μA voltage and the line connecting the plots for the 10 μA voltage in FIG. 4 exists in the following cases. That is, as in the present embodiment, the direction of increase or decrease in the electrical resistance with respect to the increase or decrease in temperature and humidity is different between the intermediate transfer belt and the primary transfer member (that is, the environmental resistance change between the intermediate transfer belt and the primary transfer member is different). Present in the case of a conflicting configuration. In the case of the configuration as in Comparative Example 2 in which the electrical resistance of the brush member as the primary transfer member is low (that is, the case on the left side of the intersection A in FIG. 4), the voltage of 3 μA> 10 μA, and the primary voltage is independent of the usage environment. A fixed primary transfer voltage value that satisfies transfer performance cannot be set. On the other hand, in the case of a configuration in which the brush member as the primary transfer member has a high electrical resistance as in the present embodiment (that is, the case where the brush member is on the right side of the intersection A in FIG. 4), the voltage is 3 μA <10 μA, regardless of the usage environment. A constant primary transfer voltage value that satisfies the primary transfer performance can be set.

  That is, the environmental fluctuation of the electric resistance of the primary transfer portion is caused by the electric resistance value of the intermediate transfer belt in the case of Comparative Example 2 in which the electric resistance value of the brush member is lower than the electric resistance value of the intermediate transfer belt. Environmental change is dominant. On the other hand, in the case of the configuration according to the present embodiment in which the electric resistance of the intermediate transfer belt and the electric resistance of the brush member are substantially the same, environmental fluctuation of the electric resistance of the brush The effect of offsetting environmental change starts to appear.

<Intersection A>
Next, a method for determining the intersection A will be described.

  The straight line with the slope (1) in FIG. 4 is the 3 μA voltage in the LL environment, and the straight line with the slope (2) is the 10 μA voltage in the HH environment.

First, let Vmin be 3 μA voltage and Imin = 3 μA. Further, Rt1LL is the electric resistance of the brush member in the LL environment, and RbLL is the electric resistance of the intermediate transfer belt in the LL environment. Further, Rt1NN is the electrical resistance of the brush member in the NN environment, and RbNN is the electrical resistance of the intermediate transfer belt in the NN environment. Further, the environmental change (electric resistance ratio) ΔRbL of the electric resistance of the intermediate transfer belt between the LL environment and the NN environment is represented by ΔRbL = RbLL / RbNN, and the electric resistance of the brush member between the NN environment and the LL environment is calculated. Environmental fluctuation (electric resistance ratio) ΔRt1L is defined as ΔRt1L = Rt1LL / Rt1NN. Further, the ratio X between the electric resistance value RbNN of the intermediate transfer belt and the electric resistance value Rt1NN of the primary transfer member in the NN environment is defined as X = Rt1NN / RbNN. At this time, Vmin is represented by the following equation.
Vmin = (Rt1LL + RbLL) · Imin
= RbNN · (ΔRt1L · X + ΔRbL) · Imin

Next, Vmax is set to a voltage of 10 μA, and Imax is set to 10 μA. Also, Rt1HH is the electric resistance of the brush member in the HH environment, and RbHH is the electric resistance of the intermediate transfer belt in the HH environment. Further, the environmental change (electrical resistance ratio) ΔRbH of the electric resistance of the intermediate transfer belt between the HH environment and the NN environment is represented by ΔRbH = RbHH / RbNN, and the electric resistance of the brush member between the HH environment and the NN environment. The environmental fluctuation (electric resistance ratio) ΔRt1H is defined as ΔRt1H = Rt1HH / Rt1NN. At this time, Vmax is expressed by the following equation.
Vmax = (Rt1HH + RbHH) · Imax
= RbNN · (ΔRt1H · X + ΔRbH) · Imax

From the above two equations, Vmin = Vmax at the intersection A, so that X at the intersection A is XA, and XA is expressed by the following equation.
XA = (ΔRbH · Imax−ΔRbL · Imin) / (ΔRt1L · Imin−ΔRt1H · Imax)

here,
Imin = 3 μA,
Imax = 10 μA,
ΔRbH = 10 ^−0.6 ,
ΔRbL ^{= 10 +0.4,}
ΔRt1L = 10 ^−0.3 ,
ΔRt1H = 10 ^{+ 0.3}
Than,
XA = Rt1NN / RbNN = 0.272
Becomes

  That is, in order to set the primary transfer current to 3 to 10 μA at a constant primary transfer voltage value regardless of the use environment, it is necessary to satisfy X> XA = 0.272.

<Comparison between Example and Comparative Example>
In Comparative Example 2, from Table 2, X = 0.3 / 40 = 0.0075 <0.272, and the primary transfer performance cannot be satisfied at a constant primary transfer voltage regardless of the use environment. Therefore, in Comparative Example 2, it is necessary to perform the ATVC and change the primary transfer voltage value according to the use environment. Therefore, in the case of the image forming apparatus using the conventional ion-conductive intermediate transfer belt as in the configuration of Comparative Example 2, it is necessary to perform the following ATVC. That is, during non-image formation before image formation, constant current control is performed at a preset primary transfer current value using a primary transfer power supply and a primary transfer current detection circuit connected to the brush member. Then, the fluctuation of the electric resistance of the primary transfer portion is detected based on the fluctuation of the generated voltage value at this time, and the constant voltage control is performed based on the result of the arithmetic processing of the generated voltage value at the time of image formation. Therefore, in such an image forming apparatus, the FPOT becomes longer by the time required for detecting the electric resistance of the primary transfer portion.

  On the other hand, in the present embodiment, X = 22/40 = 0.55> 0.272 according to Table 3, which means that the primary transfer performance can be satisfied at a constant primary transfer voltage value regardless of the use environment. it can. Therefore, there is no need to perform ATVC as in the case of Comparative Example 2, and FPOT can be shortened accordingly. Further, in this embodiment, there is no need to detect the primary transfer current, so that a current detection circuit is not required. Further, in the present embodiment, a variation in the electrical resistance value of the brush member in manufacturing is also taken into consideration. (3) (the width between the line connecting the plots of the 10 μA voltage and the line connecting the plots of the 3 μA voltage) in FIG. 4 indicates the width of the manufacturing variation of the electrical resistance value of the brush member. That is, in the present embodiment, even when the electric resistance value of the brush member is not uniquely determined and varies, the primary transfer performance can be satisfied with a constant primary transfer voltage value regardless of the use environment.

  As described above, the image forming apparatus 100 of the present embodiment includes the image carrier 9 that carries the toner image and the ion-conductive intermediate transfer body 30. Further, the image forming apparatus 100 according to the present embodiment is configured such that the toner is transferred from the image carrier 9 to the intermediate transfer body 30 at the primary transfer portion N1 where the image carrier 9 and the intermediate transfer body 30 come into contact with each other. It has a primary transfer member 13 for transferring an image. Further, the image forming apparatus 100 of this embodiment has a voltage supply unit (primary transfer power supply) 51 for supplying a primary transfer voltage to the primary transfer member 13. In the image forming apparatus 100 according to the present embodiment, the primary transfer voltage value supplied to the primary transfer member 13 by the voltage supply unit 51 is constant regardless of the use environment. Here, that the primary transfer voltage value is constant means that the setting of the primary transfer voltage value is constant irrespective of the use environment (that is, the setting of the primary transfer voltage value is not intentionally changed according to the use environment). Configuration), and there may be a variation within an allowable error range. Further, in the image forming apparatus 100 according to the present embodiment, the primary transfer member 13 and the intermediate transfer body 30 differ in the direction in which the electrical resistance increases or decreases with respect to the increase or decrease in temperature and humidity. Here, the electrical resistances of the intermediate transfer member 30 and the primary transfer member 13 in a normal temperature and normal humidity environment are RbNN and Rt1NN, respectively. The electrical resistances of the intermediate transfer member 30 and the primary transfer member 13 in a high-temperature and high-humidity environment are RbHH and Rt1HH, respectively. The electrical resistances of the intermediate transfer member 30 and the primary transfer member 13 in a low-temperature and low-humidity environment are RbLL and Rt1LL, respectively. Further, the respective electrical resistance ratios of the intermediate transfer member 30 and the primary transfer member 13 between the high-temperature and high-humidity environment and the normal temperature and normal humidity environment are represented by ΔRbH = RbHH / RbNN and ΔRt1H = Rt1HH / Rt1NN, respectively. The electrical resistance ratios of the intermediate transfer member 30 and the primary transfer member 13 between the low-temperature and low-humidity environment and the normal temperature and normal humidity environment are ΔRbL = RbLL / RbNN and ΔRt1L = Rt1LL / Rt1NN, respectively. Further, two-level primary transfer currents are defined as I1 and I2 (I1 <I2). At this time, the image forming apparatus 100 of the present embodiment satisfies the following equation: Rt1NN / RbNN> (ΔRbH · I2-ΔRbL · I1) / (ΔRt1L · I1-ΔRt1H · I2). Here, the two-level primary transfer currents I1 and I2 (I1 <I2) are typically I1 = Imin and I2 = Imax. Imin and Imax are typically the lower limit and upper limit of the primary transfer current value, respectively, determined in advance so that image defects such as multicolor transfer defects and single-color retransfer can be sufficiently suppressed. . In this embodiment, Imin = 3 μA and Imax = 10 μA. In the present embodiment, the primary transfer member 13 is a brush member having brush fibers formed of conductive nylon fibers. In this embodiment, the intermediate transfer body 30 is formed by an endless belt.

  As described above, according to the present embodiment, by defining the relationship between the electric resistance of the ion-conductive intermediate transfer belt 30 and the electric resistance of the primary transfer member 13, the ATVC of the primary transfer portion N1 is defined. FPOT can be shortened without maintaining the image quality.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description is omitted. .

  FIG. 5 is a schematic sectional view of the image forming apparatus 100 of the present embodiment. In this embodiment, the secondary transfer facing roller 32 and the driving roller 33 are electrically grounded (connected to ground) via the voltage maintaining element 52. Further, in this embodiment, each primary transfer member 13 disposed between the drive roller 33 and the secondary transfer opposing roller 32 is also grounded via the voltage maintaining element 52. The voltage maintaining element 52 is a member to be connected (secondary transfer opposing roller 32, drive roller 33, each primary transfer member 13) when a current flows from the current supply member to the voltage maintaining element 52 via the intermediate transfer belt 30. Is an element for maintaining the potential of the pixel at a predetermined potential.

  In this embodiment, the predetermined potential maintained by the voltage maintaining element 52 is a potential set so as to maintain a primary transfer potential at which a desired transfer efficiency can be obtained in each primary transfer unit N1. In this embodiment, a Zener diode, which is a constant voltage element, is used as the voltage maintaining element 52. The voltage maintained on the cathode side when a certain amount of current or more flows through the Zener diode is defined as Zener voltage.

  When a Zener diode is used as the voltage maintaining element 52, the Zener voltage may be set so that the Zener diode can maintain the predetermined potential as described above. In this embodiment, the Zener voltage is set to 500 V so that the same desired transfer efficiency as in the first embodiment can be obtained.

  In this embodiment, a voltage is applied to the secondary transfer roller 34 and the cleaning roller 17 from the secondary transfer power supply 35 and the toner charging power supply 18, respectively. As a result, current flows from the secondary transfer roller 34 and the cleaning roller 17 as current supply members to the grounded Zener diode 52 via the secondary transfer opposing roller 32 and the drive roller 33, respectively. When the Zener diode 52 maintains the Zener potential, the potentials of the secondary transfer roller 34 and the drive roller 33 connected to the cathode side of the Zener diode 52 are maintained at the Zener potential of 500V. Further, since each primary transfer member 13 is also connected to the Zener diode 52, the potential of each primary transfer member 13 is also maintained at the Zener potential of 500 V, similarly to the secondary transfer facing roller 32 and the driving roller 33. You.

  In the present embodiment, since X> Xa is satisfied as in the first embodiment, a constant primary transfer voltage value (potential of the primary transfer member 13) maintained by the Zener diode 52 is used. The primary transfer performance can be satisfied regardless of the use environment.

  As described above, in the present embodiment, the voltage supply unit includes the current supply members (the secondary transfer roller 34 and the cleaning roller 17) that contact the intermediate transfer body 30 and supply the current to the intermediate transfer body 30. Further, in this embodiment, the voltage supply means has a voltage maintaining element 52 connected to the primary transfer member 13 and maintaining the primary transfer member 13 at a predetermined potential. In the present embodiment, the voltage maintaining element 52 includes at least one tension member facing at least one current supply member among a plurality of tension members that stretch the intermediate transfer body 30 formed by an endless belt. Is also connected. Then, the voltage maintaining element 52 maintains the tension member at the predetermined potential. In this embodiment, the at least one current supply member is the secondary transfer roller 34 and the cleaning roller 17, and the at least one stretching member is the secondary transfer opposing roller 32 and the drive roller 33.

  As described above, according to the present embodiment, the relationship between the electric resistance of the ion-conductive intermediate transfer belt 30 and the electric resistance of the primary transfer member 13 is defined in the same manner as in the first embodiment. The same effects as in Example 1 can be obtained. Further, in the present embodiment, the primary transfer voltage value is maintained by connecting the primary transfer member 13 to the voltage maintaining element 52, so that it is not necessary to use a power supply dedicated to the primary transfer, and The configuration can be simplified, reduced in size, and reduced in cost.

[Others]
As described above, the present invention has been described with reference to the specific embodiments, but the present invention is not limited to the above embodiments.

  For example, the primary transfer member is not limited to a brush-like member, but may be a roller-like, pad-like, sheet-like (film-like) member, or the like.

  Further, the intermediate transfer member is not limited to being formed by an endless belt, but may be a drum-shaped member formed by stretching a sheet on a frame, for example.

  Further, the current supply member is not limited to a roller-shaped member, and may be, for example, a brush-shaped, pad-shaped, sheet-shaped (film-shaped) member, or the like.

  Further, the voltage maintaining element is not limited to a Zener diode which is a constant voltage element, and any other element such as a varistor can be used.

9 Photosensitive drum 13 Primary transfer member 30 Intermediate transfer belt 51 Primary transfer power supply 52 Zener diode

Claims (4)

An image carrier for carrying a toner image;
An ion-conductive intermediate transfer member,
A primary transfer member that contacts the intermediate transfer member and transfers a toner image from the image carrier to the intermediate transfer member at a primary transfer portion where the image carrier and the intermediate transfer member are in contact with each other;
Voltage supply means for supplying a primary transfer voltage to the primary transfer member;
In the image forming apparatus having
A primary transfer voltage value supplied to the primary transfer member by the voltage supply unit is constant regardless of a use environment;
The primary transfer member and the intermediate transfer body have different directions of increase and decrease in electrical resistance with respect to increase and decrease in temperature and humidity,
The electrical resistances of the intermediate transfer member and the primary transfer member in a normal temperature and normal humidity environment are RbNN and Rt1NN, respectively, and the electrical resistance values of the intermediate transfer member and the primary transfer member in a high temperature and high humidity environment are RbHH and Rt1HH, respectively. The electrical resistance values of the intermediate transfer body and the primary transfer member in a low humidity environment are respectively RbLL and Rt1LL, and the electrical resistance values of the intermediate transfer body and the primary transfer member between a high temperature and high humidity environment and a normal temperature and normal humidity environment, respectively. The electric resistance ratios are ΔRbH = RbHH / RbNN, ΔRt1H = Rt1HH / Rt1NN, and the electric resistance ratios of the intermediate transfer member and the primary transfer member between a low-temperature low-humidity environment and a normal temperature normal humidity environment are ΔRbL = RbLL / RbNN, ΔRt1L = Rt1LL / Rt1NN, and let the primary transfer currents of two levels be I1 and I2 (I1 <I2). When, the following equation,
Rt1NN / RbNN> (ΔRbH · I2-ΔRbL · I1) / (ΔRt1L · I1-ΔRt1H · I2)
An image forming apparatus characterized by satisfying the following.   The image forming apparatus according to claim 1, wherein the primary transfer member is a brush member including brush fibers formed of conductive nylon fibers.   A voltage supply unit configured to contact the intermediate transfer member and supply a current to the intermediate transfer member; a voltage maintaining element connected to the primary transfer member to maintain the primary transfer member at a predetermined potential; The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, wherein the intermediate transfer member is formed by an endless belt.

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