JP6480764B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a color copying machine or a printer including an intermediate transfer belt.

  A quadruple tandem / intermediate transfer belt type color image forming apparatus including a transfer belt as an intermediate transfer member corresponds to at least four colors of yellow (Y), magenta (M), cyan (C), and black (K). Each color developing device is provided, and a developer image (toner image) formed by each color developing device is sequentially transferred (primary transfer) to the intermediate transfer belt. At this time, a multi-color or full-color developer image composed of developer images of the respective colors is formed on the intermediate transfer belt. In the following, description will be given by taking full color as an example. Next, the color developer image formed on the intermediate transfer belt is transferred from the intermediate transfer belt onto a transfer material such as paper (secondary transfer), and the transferred color developer image is transferred by a fixing device. It is configured to be fixed on a transfer material.

  An example of the four-tandem / intermediate transfer belt-type color image forming apparatus is an image forming apparatus described in Patent Document 1. The image forming apparatus described in Patent Document 1 is configured such that a two-layer intermediate transfer belt is stretched around a secondary transfer counter roller, a drive roller, and a tension roller. In the image forming apparatus described in Patent Document 1, the secondary transfer counter roller on the upstream side in the circumferential direction of the intermediate transfer belt is disposed to face the secondary transfer roller, and is connected to the secondary transfer roller. The secondary voltage can be transferred by the transfer voltage supplied from the printer. In addition, the current is supplied from the secondary transfer power source to the intermediate transfer belt, and the voltage generated by the current supplied to the intermediate transfer belt is used as the primary transfer voltage to transfer the developer from the image carrier to the intermediate transfer belt. It has a configuration. At this time, in the developing device described in Patent Document 1, each of the secondary transfer counter roller, the driving roller, and the tension roller is electrically connected and connected to the ground via a Zener diode.

  As another form of the image forming apparatus described in Patent Document 1, as shown in FIG. 3, 350 V, 400 V, and 450 V are sequentially supplied from DC power supplies 13 to 16 connected to the primary transfer rollers 9 to 12, respectively. , An image forming apparatus configured to be supplied with a primary transfer voltage of 500V. With this configuration, each of the image carriers 5 to 8 is changed by the different primary transfer voltages supplied to the primary transfer rollers 9 to 12 in accordance with the movement of the intermediate transfer belt 4 in the direction indicated by the white arrow in FIG. The developer images, that is, the developers 31 y, 31 m, 31 c, and 31 k of the image carriers 5 to 8 are respectively transferred (primary transfer) to the intermediate transfer belt 4, and a color developer image 32 is formed on the outer peripheral surface of the intermediate transfer belt 4. It is the structure formed. The color developer image 32 formed on the outer peripheral surface of the intermediate transfer belt 4 is transferred onto a transfer material 19 such as paper by a secondary transfer voltage supplied from the DC power supply 18 to the secondary transfer roller 17. It has become. Two guide rollers 20 and 21 are disposed in the vicinity of the secondary transfer roller 17, and a cleaning blade 22 is disposed at a position facing the guide roller 21 via the intermediate transfer belt 4.

JP 2013-231960 A

  However, in the image forming apparatus in which the image carriers 5 to 8 and the primary transfer rollers 9 to 12 are arranged to face each other via the intermediate transfer belt 4, the image carriers 5 to 8 and the developers 31y, 31m, 31c, and 31k are negative electrodes. The primary transfer rollers 9 to 12 are configured to be applied with voltages having different positive polarities. At this time, in order to transfer the developer images on the outer peripheral surfaces of the image carriers 5 to 8 to the intermediate transfer belt 4, the developers 31y, 31m, 31c, and 31k adhere to the outer peripheral surfaces of the image carriers 5 to 8. It is necessary to make the Coulomb force between the primary transfer rollers 9 to 12 and the developers 31y, 31m, 31c, and 31k larger than the adhering force.

  On the other hand, when the electric field (transfer electric field) formed by the potential difference between the charging potential of the image carriers 5 to 8 and the voltage of the primary transfer rollers 9 to 12 is E, and the charge of the developer is q, the developers 31y and 31m. , 31c, 31k, the Coulomb force F is F = qE. Accordingly, the developer 31y, 31m from the image carrier 5-8 to the intermediate transfer belt 4 is increased by increasing the voltage applied to the primary transfer rollers 9-12 and increasing the strength of the transfer electric field E (electric field strength). , 31c and 31k increase linearly. However, when the transfer electric field E is further increased beyond the predetermined transfer electric field E ′, a so-called retransfer phenomenon occurs in which the developer transferred to the intermediate transfer belt 4 is transferred again to the image carrier, and the transfer is performed. It is known that efficiency is reduced. There are two causes for the decrease in the transfer efficiency, and the first cause is that a void discharge occurs in the transfer gap and the transfer electric field changes. The second cause of the decrease is that the charged charge of the developer changes due to the void discharge, and in the extreme, the developer has a reverse polarity due to the void discharge and cannot follow the transfer electric field. It is.

  3 is an enlarged view of M (magenta), C (cyan), and K (black) image carriers 6 to 8 and the primary transfer rollers 10 to 12 in the image forming apparatus shown in FIG. In the case of printing the solid image, the influence of the developer transferred to the intermediate transfer belt 4 upstream is affected downstream. However, in the following description, in each transfer step (process) of Y, M, C, and K, the charging potential of the image carriers 5 to 8 is −500 V, and the potential of the latent image forming portion is −20 V. The background potential of the Y, C, and K image carriers 5, 7, and 8 is -500V, and the latent image potential of the M image carrier 6 is -20V. Further, the Y primary transfer roller 9 is supplied with + 350V from the power source 13, the M primary transfer roller 10 is supplied with + 400V from the power source 14, the C primary transfer roller 11 is supplied with power from 15 to + 450V, and the K primary transfer roller 12 is supplied with power. 16 to + 500V is supplied as the primary transfer voltage. The voltages of the power supplies 13 to 16 supplied to the primary transfer rollers 9 to 12 are such that the primary transfer current that flows when the potential of the image carriers 5 to 8 is the background potential of −500 V is a solid image (solid latent image potential of −20 V). ) Is controlled so that the current value corresponds to the toner movement current (about 20 μA) when printing.

  As shown in FIG. 4, the M image carrier 6 has a latent image forming portion of −20 V, and the M-only developer 31 m is placed on the outer peripheral surface of the image carrier 6. To be attached. The developer 31m is transferred from the image carrier 6 to the intermediate transfer belt by a transfer electric field formed by a potential difference between the latent image formation potential of -20V of the image carrier 6 and the voltage from the power supply 14 supplied to the primary transfer roller 10. 4 is transferred. At this time, peeling discharge may occur between a part of the developer 31m transferred to the intermediate transfer belt 4 (denoted by the developer 33 in FIG. 4) and the image carrier. In this case, as shown in FIG. 4, the developer 33 is charged closer to the positive polarity than the negative polarity charge that should originally be due to the peeling discharge. The image carrier 6 of M has a latent image forming potential of −20V, whereas the image carrier 7 of C in the next step has a background potential of −500V. While the potential difference between the image transfer body and the image carrier is higher than the predetermined transfer electric field E ′, the potential difference between the C developer in the next step and the image carrier further exceeds the predetermined transfer electric field E ′. The electric field E is increased by 480 V (potential difference between the M image carrier 6 and the C image carrier 7). As a result, the charged developer 33 moves (re-transfers) to the C image carrier 7 charged to −500 V, which is an image carrier in the next step. Similarly, when a peeling discharge occurs in a part of the developer 31m (denoted by the developer 34 in FIG. 4) of the developer 31m transferred to the C image carrier 7 and the intermediate transfer belt 4, the developer 34 Is retransferred to the K image carrier 8 charged to −500 V, which is the image carrier in the next step, with a higher probability than the developer 33 in the C step. In particular, FIG. 4 illustrates the influence of the developer transferred to the intermediate transfer belt 4 upstream on the downstream side only when printing a solid image of only M. The developer 31m of each color is added to the outer peripheral surface and transferred so as to overlap each step. At this time, the developer 31m on the side close to the intermediate transfer belt 4 (lower layer side) is not in direct contact with the image carrier, so that retransfer is difficult to occur, but the developer 31m on the side farther from the intermediate transfer belt 4 (upper layer side) Since it is in direct contact with the image carrier, it is easy to re-transfer.

  Further, when a peeling discharge occurs in a part of the developer 31m transferred to the K image carrier 8 and the intermediate transfer belt 4 (indicated by the developer 35 in FIG. 4), the intermediate transfer belt 4 In this case, a color developer image 32 is formed in which a developer 31m having a charge transferred from the image carrier 6 to the intermediate transfer belt 4 and a developer 35 charged to a positive polarity rather than a negative charge which should be originally formed are mixed. Will be. However, the color developer image 32 is a developer image in which the developers 33 and 34 retransferred to the image carriers 7 and 8 are missing. In particular, in the image forming apparatus shown in FIGS. 3 and 4, the primary transfer rollers 9 to 12 are supplied with a voltage having a larger absolute value on the downstream process side. The potential difference with the image carrier exceeds the predetermined transfer electric field E ′, and the transfer electric field E ′ further increases. The developers 31y, 31m, and 31c transferred to the intermediate transfer belt 4 in each of the Y, M, and C processes move (re-transfer) to the image carriers 7 and 8 of the downstream M, C, and K processes. The amount that is lost cannot be ignored.

The color developer image 32 transferred to the intermediate transfer belt 4 is transferred onto the transfer material 9 by the secondary transfer voltage supplied from the DC power supply 18 to the secondary transfer roller 17. At this time, since the secondary transfer voltage supplied to the secondary transfer roller 17 is positive +1300 V, the developer charged closer to the positive polarity than the original negative charge is hardly transferred. Further, the developer 35 reversed to the positive polarity is not transferred. That is, of the developer 31m transferred from the image carrier 6 to the intermediate transfer belt 4, the developer transferred onto the transfer material 9 is a developer excluding the developers 33, 34, and 35. As a result, streaks, polka dots, and the like are generated in the developer image transferred to the transfer material 9. The occurrence of streaks, polka dots, or the like in the developer image accompanying the retransfer of the developer, that is, the decrease in transfer efficiency, is particularly caused by the volume resistivity of the intermediate transfer belt 4 being 1E + 10 (1 × 10 ¹⁰ ) Ω · cm It becomes remarkable in the range exceeding 10V). Therefore, the volume resistivity of the intermediate transfer belt 4 needs to be 1E + 10 (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied) or less.

In the image forming apparatus shown in FIG. 3, the voltages of the power supplies 13 to 16 supplied to the primary transfer rollers 9 to 12 are the primary transfer current that flows when the potential of the image carriers 5 to 8 is the background potential of −500 V. The voltage is controlled so that the primary transfer current that flows when the toner movement current when printing is −500 V becomes a current value corresponding to the toner movement current (about 20 μA) when printing a solid image. On the other hand, when the volume resistivity of the intermediate transfer belt 4 is reduced, a predetermined current due to a potential difference between the image carrier 5 to 8 and the primary transfer rollers 9 to 12 for each color process is generated by the image carrier 5 of that color. In addition to 8, the current leaking to other processes adjacent to the intermediate transfer belt 4 and to the driving roller 2 and the tension roller 3 becomes large. Therefore, the primary transfer current flowing from the primary transfer rollers 9 to 12 to the image carriers 5 to 8 for each color process, that is, the electric field strength between the image carriers 5 to 8 and the primary transfer rollers 9 to 12 is increased. Insufficient transfer results in poor transfer. Therefore, the volume resistivity of the intermediate transfer belt 4 needs to be 1E + 9 (1 × 10 ⁹ ) Ω · cm (when 10 V is applied) or more.

In particular, in an image forming apparatus that can use paper of A2 size or larger, the belt width of the intermediate transfer belt 4 needs to be a size corresponding to the paper size. However, while maintaining the uniformity of the volume resistivity within the intermediate transfer belt 4 (deviation within one), the volume resistivity ranges from 1E + 9 (1 × 10 ⁹ ) Ω · cm to 1E + 10 (1 × 10 ¹⁰ ) Ω · cm. Further, the variation (individual difference) in the volume resistivity of the intermediate transfer belt 4 used in many image forming apparatuses is also in the range of 1E + 9 (1 × 10 ⁹ ) Ω · cm to 1E + 10. Since it is necessary to be within the range of (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied), there is a problem that the productivity, environmental performance, and durability of the image forming apparatus are lowered.

  Patent Document 1 also describes a configuration in which a secondary transfer counter roller, a drive roller, and a tension roller, which are electrically connected, are connected to ground via a Zener diode. An intermediate transfer belt is an insulating material. Is a two-layer structure consisting of a conductive material and a structure in which a primary transfer voltage is generated by actively passing a current in the extending direction (circumferential direction) of the intermediate transfer belt to reduce leakage current generated in the intermediate transfer belt No consideration has been given to the technology to be performed, and there has been the same problem as described above.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique capable of improving the productivity, environmental performance, and durability of an image forming apparatus.

(1) The present invention for solving the above problems includes a plurality of image carriers on which a negative developer image is carried, an annular semiconductive intermediate transfer belt to which the developer image is transferred, A plurality of stretching rollers that stretch the intermediate transfer belt, a plurality of primary transfer rollers that are arranged to face each other through the intermediate transfer belt for each of the image carriers, and each of the plurality of primary transfer rollers, An image forming apparatus comprising a plurality of primary transfer voltage power supplies that are higher in voltage than the developer image carrying portion and that supply different voltages to the primary transfer roller for each primary transfer roller;
The tension roller is connected to a tension roller adjacent to a transfer region where the image carrier and the primary transfer roller are disposed, and the absolute value of the potential of the tension roller is 0 V or more and a limit voltage or less. comprising a voltage limiting circuit for holding the,
At least one of the plurality of stretching rollers is opposed to a secondary transfer roller that secondarily transfers the developer image transferred to the intermediate transfer belt onto a transfer material via the intermediate transfer belt. A counter roller arranged, the counter roller being connected to any voltage supply means including 0V,
At least one of the plurality of stretching rollers is a guide roller adjacent to the opposing roller, and the guide roller is electrically connected directly to the ground. It is.

(2) The present invention for solving the above problems includes a plurality of image carriers on which a positive developer image is carried, an annular semiconductive intermediate transfer belt on which the developer image is transferred, A plurality of stretching rollers that stretch the intermediate transfer belt, a plurality of primary transfer rollers that are arranged to face each other through the intermediate transfer belt for each of the image carriers, and each of the plurality of primary transfer rollers, An image forming apparatus comprising a plurality of primary transfer voltage power supplies that are lower in voltage than the developer image carrying portion and that supply different voltages to the primary transfer roller for each primary transfer roller,
The tension roller is connected to a tension roller adjacent to a transfer region where the image carrier and the primary transfer roller are disposed, and the absolute value of the potential of the tension roller is 0 V or more and a limit voltage or less. comprising a voltage limiting circuit for holding the,
At least one of the plurality of stretching rollers is opposed to a secondary transfer roller that secondarily transfers the developer image transferred to the intermediate transfer belt onto a transfer material via the intermediate transfer belt. A counter roller arranged, the counter roller being connected to any voltage supply means including 0V,
At least one of the plurality of stretching rollers is a guide roller adjacent to the opposing roller, and the guide roller is electrically connected directly to the ground. It is.

( 3 ) The present invention for solving the above-mentioned problems is characterized in that the intermediate transfer belt is semiconductive having a volume resistivity of 1 × 10 ⁸ Ω · cm or more (1) or (2) The image forming apparatus described in the above.

( 4 ) An image forming apparatus according to any one of (1) to ( 3 ), wherein the voltage limiting circuit is a varistor.

( 5 ) The present invention for solving the above-mentioned problems is that the absolute value of the limiting voltage of the voltage limiting circuit is equal to or higher than the transfer voltage supplied to the closest transfer roller among the primary transfer rollers. The image forming apparatus according to any one of (1) to ( 4 ).

According to the present invention of (1) and (2) described above, the tension roller is connected to the tension roller adjacent to the transfer region in which the image carrier and the primary transfer roller are arranged, and the tension roller. The guide roller adjacent to the opposing roller arranged in the secondary transfer area is electrically connected directly to the ground. because are configured to be, Ru negligible influence secondary transfer voltage is applied to the primary transfer. As a result, the lower limit of the allowable range of variation in volume resistivity of the intermediate transfer belt 4 is 1E + 8 (1 × 10 ⁸ ), which is one digit smaller than the conventional 1E + 9 (1 × 10 ⁹ ) Ω · cm (when 10 V is applied). ) Ω · cm (when 10 V is applied), and the variation range of the volume resistivity of the intermediate transfer belt 4 is 1E + 8 (1 × 10 ⁸ ) Ω · cm (when 10 V is applied) to 1E + 10 (1 × 10 ¹⁰ ). It can be in the range of Ω · cm (when 10 V is applied), and the effect that the productivity, environmental performance, and durability of the image forming apparatus can be greatly improved can be obtained.

According to the present invention described in (4), (5), and (6), the absolute value of the voltage limiter of the voltage limiting circuit is the transfer that is supplied to the closest transfer roller among the primary transfer rollers. Since the voltage is higher than the voltage, leakage current flowing from the primary transfer roller to the ground via the intermediate transfer belt and the stretching roller can be efficiently prevented. As a result, the range of variation in the volume resistivity of the intermediate transfer belt 4 is in the range of 1E + 8 (1 × 10 ⁸ ) Ω · cm (when 10 V is applied) to 1E + 10 (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied). Therefore, the productivity, environmental performance, and durability of the image forming apparatus can be greatly improved.
Other effects of the present invention will become apparent from the description of the entire specification.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure for demonstrating the measuring method of the volume resistivity of the intermediate transfer belt of this embodiment. It is a figure for demonstrating schematic structure of the conventional image forming apparatus. It is a figure for demonstrating the principle of the retransfer in the conventional image forming apparatus.

  Embodiments to which the present invention is applied will be described below with reference to the drawings. However, in the following description, the same components are denoted by the same reference numerals, and repeated description is omitted.

  FIG. 1 is a diagram for explaining a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a method for measuring a volume resistivity of an intermediate transfer belt according to the present embodiment. The image forming apparatus of this embodiment will be described in detail with reference to FIGS. However, the white arrow shown in FIG. 1 indicates the moving direction of the intermediate transfer belt. In FIG. 1, for the sake of simplicity, the detailed configurations of the Y, M, C, and K developing devices are omitted, and only the image carriers 5 to 8 included in the developing devices are described. Further, a feeding mechanism for the transfer material 19 such as paper and a known fixing mechanism for fixing the color developer image 32 composed of the developers 31y, 31m, 31c, and 31k on the transfer material 19 are omitted.

  As shown in FIG. 1, in the image forming apparatus of the present embodiment, image carriers (photosensitive members) 5 to 8 included in Y, M, C, and K developing devices have an endless shape (annular shape) in this order. 4 is a quadruple tandem / intermediate transfer belt type color image forming apparatus disposed along the outer circumferential surface side of the intermediate transfer belt 4 along the moving (circulating) direction. In the image forming apparatus of the present embodiment, a negatively charged photoreceptor is used as the image carrier and reversal development is performed. The intermediate transfer belt 4 is stretched around a counter roller (secondary transfer counter roller) 1, a driving roller 2 and a tension roller 3. Further, primary transfer rollers 9 to 12 are respectively arranged at positions facing the respective image carriers 5 to 8 via the intermediate transfer belt 4, and each primary transfer roller 9 to 12 has a DC power source (primary transfer voltage power source). ) 13 to 16 are connected to each other. That is, a primary transfer region (transfer region), which is a region where the image carriers 5 to 8 and the primary transfer rollers 9 to 12 are disposed, is formed between the drive roller 2 and the tension roller 3. .

At this time, the DC power supply 13 is sequentially applied from the primary transfer roller 9 disposed opposite to the most upstream Y image carrier 5 to the primary transfer roller 12 disposed opposite to the most downstream K image carrier 8. A DC voltage of ˜16 to 350V, 400V, 450V, and 500V is supplied as a primary transfer voltage. That is, in each of the Y, M, C, and K processes, the downstream primary transfer voltage is higher than the upstream primary transfer voltage. The DC voltage for primary transfer supplied from the DC power sources 13 to 16 to the primary transfer rollers 9 to 12 is not limited to 350 V, 400 V, 450 V, and 500 V, including the order, and other voltage values. It may be. However, when the DC voltage for primary transfer is set to another voltage value, the varistor voltage V _{ZD of} varistors 23 and 24, which will be described later, may also be a varistor voltage V _ZD corresponding to the other DC voltage for primary transfer. preferable.

In the image forming apparatus of this embodiment, the driving roller 2 and the tension roller 3 adjacent to the primary transfer rollers 9 to 12 are connected to the ground via varistors 23 and 24 that are voltage limiting circuits. It has become. That is, as compared with the conventional image forming apparatus shown in FIG. 3, when the ground is used as a reference, the potentials of the driving roller 2 and the tension roller 3 are higher than the ground by the varistor voltage V _ZD of the varistors 23 and 24. In particular, the absolute values of the potentials of the drive roller 2 and the tension roller 3 are maintained at 0 V or more and the limit voltage (varistor voltage V _ZD ) or less. At this time, the varistor voltage V _ZD of the varistors 23 and 24 of this embodiment is set to 1000 V in consideration of the spark (spark discharge) to the adjacent member. However, the varistor voltage V _ZD is not limited to 1000 V and can be selected as appropriate. However, it is preferable that the varistor voltage V _ZD is equal to or higher than the primary transfer voltage supplied to the adjacent primary transfer rollers 9 and 12. For example, in a configuration in which the varistor voltages V _ZD of the varistors 23 and 24 are the same, it is preferable that the primary transfer voltage of the primary transfer roller 12 on the higher primary transfer voltage side is 500 V or higher. On the other hand, a configuration using varistors having different varistor voltages V _ZD1 and V _ZD2 corresponding to primary transfer voltages of the primary transfer rollers 9 and 12 in which the driving roller 2 and the tension roller 3 are close to each other may be used. In this case, the varistor voltage V _ZD1 of the varistor 23 is preferably 500 V or higher, which is the primary transfer voltage of the primary transfer roller 12, and the varistor voltage V _ZD2 of the varistor 24 is preferably 350 V or higher, which is the primary transfer voltage of the primary transfer roller 9. . The voltage limiting circuit is not limited to a configuration using a varistor as a voltage limiting element, and is formed using a Zener diode, an avalanche diode, a TVS (Transient Voltage Suppressor) diode, or the like as another voltage limiting element. It may be a configuration. The voltage limiting circuit is preferably a nonpolar voltage limiting circuit. Furthermore, the voltage limiting circuit for the driving roller 2 may be shared with the primary transfer voltage power supply of the primary transfer roller 12, and the voltage limiting circuit for the tension roller 3 may be shared with the primary transfer voltage power supply of the primary transfer roller 9. Preferably, a primary transfer voltage power source and a high resistance are connected to the primary transfer roller 12 as a voltage limiting circuit for the driving roller 2 via a high resistance, and a primary transfer voltage power source and a high resistance are connected to the tension roller 3 as a voltage limiting circuit. Good to connect through.

  The intermediate transfer belt 4 is made of polyimide, which is a semiconductive resin material, and has a thickness of 100 μm. Furthermore, the intermediate transfer belt 4 has a width equal to or greater than A2. The resin material forming the intermediate transfer belt 4 is not limited to polyimide, and other resin materials may be used. Further, the width of the intermediate transfer belt 4 is not limited to A2 or more, and the thickness thereof is not limited to 100 μm.

  Further, a secondary transfer roller 17 is arranged at a position facing the opposing roller 1 via the intermediate transfer belt 4. The secondary transfer roller 17 is supplied with a secondary voltage of, for example, +1200 V from a DC power source 18. The next transfer voltage is supplied, and the counter roller 1 is supplied with an arbitrary voltage including 0 V by the voltage supply means 36. In addition, two guide rollers 20 and 21 connected to the ground are arranged in the vicinity of the secondary transfer roller 17, and the intermediate transfer belt 4 is stretched around the guide rollers 20 and 21. The peripheral surface is in contact with the guide rollers 20 and 21. Further, a cleaning blade (cleaner) 22 is disposed at a position substantially opposite to the guide roller 21 via the intermediate transfer belt 4, and the developers 31 y, 31 m, 31 c, remaining on the outer peripheral surface of the intermediate transfer belt 4 are disposed. 31k is scraped off by the cleaner 22 and collected. However, the secondary transfer voltage is not limited to 1200 V. Furthermore, at the timing when the transfer material is not in the secondary transfer roller 17 site, the bipolar voltage is alternately switched to avoid contamination of the secondary transfer roller 17. It is preferable to apply to. The voltage supply means 36 may be a direct current power source or the like for supplying a predetermined voltage. For example, a configuration in which the surface of the opposed roller 1 is coated with a known resistive paint or the like and connected to the ground, or a known The structure etc. which are connected to earth | ground via the resistive element of this may be sufficient. That is, as long as a transfer voltage for secondary transfer is generated between the opposing roller 1 and the secondary transfer roller 17, the configuration of the voltage supply means 36 is not limited.

  With this configuration, each image carrier 5 to 8 is developed by the primary transfer voltage supplied to each primary transfer roller 9 to 12 as the intermediate transfer belt 4 moves in the direction indicated by the white arrow in FIG. The developer images, that is, the developers 31y, 31m, 31c, and 31k of the image carriers 5 to 8 are respectively transferred (primary transfer) to the intermediate transfer belt 4, and a color developer image (monochrome) is formed on the outer peripheral surface of the intermediate transfer belt 4. 32 including the developer image) is formed. The color developer image 32 formed on the outer peripheral surface of the intermediate transfer belt 4 is printed on paper or the like by a difference in voltage supplied to the secondary transfer roller 17 (secondary transfer voltage) and voltage supplied to the counter roller 1. After being transferred onto the transfer material 19 and fixed on the transfer material 19 by a fixing mechanism (not shown), it is discharged to the outside.

In the image forming apparatus according to the present embodiment, the driving roller 2 and the tension roller 3 that are arranged close to the primary transfer rollers 9 to 12 are connected to the ground via varistors 23 and 24 that are voltage limiting circuits. ing. Accordingly, the potential of the intermediate transfer belt 4 in the primary transfer region where the image carriers 5 to 8 and the primary transfer rollers 9 to 12 are arranged, that is, the potential of the intermediate transfer belt 4 between the driving roller 2 and the tension roller 3 is the varistor 23. , 24 does not exceed the varistor voltage V _ZD , the leakage current from the primary transfer rollers 9, 12 to the drive roller 2 and the tension roller 3 does not occur. Therefore, the potential of the intermediate transfer belt 4 in at least the primary transfer region between the driving roller 2 and the tension roller 3 is the conventional configuration (the driving roller 2 and the tension) due to the primary transfer voltage supplied to the primary transfer rollers 9 to 12. As compared with the configuration in which the roller 3 is directly connected to the ground)

On the other hand, also in the configuration of the present embodiment, the guide rollers 20 and 21 arranged in the secondary transfer region of the intermediate transfer belt 4 are directly connected to the ground. Therefore, a leakage current from the primary transfer rollers 9 and 12 to the ground via the intermediate transfer belt 4 and the guide rollers 20 and 21 may occur. However, the extension length of the intermediate transfer belt 4 from the primary transfer rollers 9 and 12 to the guide rollers 20 and 21 is the extension length of the intermediate transfer belt 4 from the primary transfer rollers 9 and 12 to the drive roller 2 or the tension roller 3. The extension length is much larger than the length. Therefore, it is considered that a leakage current from the primary transfer rollers 9 and 12 to the ground via the intermediate transfer belt 4 and the guide rollers 20 and 21 is generated. However, the leakage current in this case is negligible (10% or less). Current. Therefore, in the configuration of this embodiment, the potential of the intermediate transfer belt 4 in the primary transfer region is such that the potential difference between the tension roller 3 and the primary transfer roller 9 and the potential difference between the drive roller 2 and the primary transfer roller 12 are reduced. It is thought to contribute. At this time, it is considered that the possibility that the potential of the intermediate transfer belt 4 in the primary transfer region reaches the varistor voltage V _ZD of the varistors 23 and 24 is very small.

  Hereinafter, based on FIG. 1, the intermediate transfer belt 4 to the drive roller in the primary transfer region are caused by the potential difference between the primary transfer roller 9 and the tension roller 3 of Y and the potential difference between the primary transfer roller 12 and the drive roller 2 of K. 2 and the leakage current to the tension roller 3 will be examined in detail.

  +350 V is supplied to the primary transfer roller 9 of Y, and the tension roller 3 adjacent to the primary transfer roller 9 is connected to the ground via a varistor 24. On the other hand, as described above, the leakage current from the primary transfer roller 9 to the ground via the intermediate transfer belt 4 and the guide rollers 20 and 21 can be ignored. Therefore, when the ground is used as a reference, the potential of the intermediate transfer belt 4 in the region between the primary transfer roller 9 and the tension roller 3 is about +350 V that is the primary transfer voltage supplied to the primary transfer roller 9. As a result, the leakage current from the primary transfer roller 9 to the ground via the intermediate transfer belt 4 and the tension roller 3 that has occurred in the conventional configuration can be prevented in the configuration of the image forming apparatus of this embodiment.

  Similarly, the leakage current from the K primary transfer roller 12 to the ground via the intermediate transfer belt 4 and the drive roller 2 that occurs in the conventional configuration can be prevented by the configuration of the image forming apparatus of the present embodiment. .

As a result, in the image forming apparatus of the present embodiment, when the volume resistivity of the intermediate transfer belt 4 is 1E + 8 (1 × 10 ⁸ ) Ω · cm (when 10 V is applied) or more, the image carrier for each color process. Thus, it is possible to prevent a current that should flow only between 5 and 8 and the primary transfer rollers 9 to 12 from flowing to the ground via the driving roller 2 and the tension roller 3. That is, 1E + 8 (1 ×), where the lower limit of the allowable range of variation in the volume resistivity of the intermediate transfer belt between individual individuals is one digit smaller than the conventional 1E + 9 (1 × 10 ⁹ ) Ω · cm (when 10 V is applied). 10 ⁸ ) Ω · cm (when 10 V is applied).

Such a volume resistivity of the intermediate transfer belt 4 is measured by the measuring method shown in FIG. As shown in FIG. 2A, a conductive electrode plate 26, a part of the intermediate transfer belt 4, an electrode 27 at the tip of the convex resin material, and a 1 kg weight 28 are provided on the upper surface of the insulating plate 25 made of resin material. In this order, they were overlapped and measured. At this time, the volume resistivity is calculated by applying a DC voltage of 10 V from the DC power source 30 between the electrode plate 26 and the electrode 27 at the tip of the convex resin material and measuring the current with an ammeter 29. . In particular, as shown in FIG. 2B, a convex electrode having an area of 5 cm ² is in contact with one surface of a part of the intermediate transfer belt 4, and the voltage application time is 10 seconds. Volume resistivity was calculated.

  As described above, in the image forming apparatus of the present embodiment, among the rollers in contact with the intermediate transfer belt 4, the two guide rollers 20 and 21 are directly connected to the ground and the primary transfer rollers 9 to 12 are connected. The driving roller 2 and the tension roller 3 arranged close to each other are connected to the ground via varistors 23 and 24 which are voltage limiting circuits. As a result, the generation of leakage current from the primary transfer rollers 9 to 12 to the driving roller 2 or the tension roller 3 can be significantly suppressed, and the transferability can be stabilized.

Accordingly, the variation range of the volume resistivity of the intermediate transfer belt 4 is set to a range of 1E + 8 (1 × 10 ⁸ ) Ω · cm (when 10 V is applied) to 1E + 10 (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied). Can do. That is, the allowable range of variation in volume resistivity within the same intermediate transfer belt 4 and the allowable range of variation in volume resistivity among intermediate transfer belts 4 used in a large number of image forming apparatuses are the conventional 1E + 9 (1 × Compared with 10 ⁹ ) Ω · cm (when 10 V is applied) to 1E + 10 (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied), it is possible to enlarge by one digit. As a result, the productivity, environmental performance, and durability of the image forming apparatus can be greatly improved. Further, the volume resistivity variation range in the same intermediate transfer belt 4 is 1E + 8 (1 × 10 ⁸ ) Ω · cm (when 10 V is applied) to 1E + 10 (1 × 10 ¹⁰ ) Ω · cm (when 10 V is applied). As a result, it is possible to improve the output image quality of the image forming apparatus.

  In this embodiment, the case where the present invention is applied to an image forming apparatus configured to apply different voltages to the primary transfer rollers of Y, M, C, and K has been described. The present invention is also applicable to an image forming apparatus in which substantially the same voltage is applied as a primary transfer voltage.

  In the image forming apparatus of the present embodiment, different varistors 23 and 24 are connected to the driving roller 2 and the tension roller 3, but the driving roller 2 and the tension roller 3 are electrically connected to each other. It may be configured to be connected to ground via a varistor. At this time, the varistor 23 may be provided only on the driving roller 2 adjacent to the primary transfer roller 12 having the highest primary transfer voltage.

  Furthermore, in the image forming apparatus of the present embodiment, the intermediate transfer belt 4 is configured to use a single-layer polyimide that is a semiconductive resin material, but may be configured to be laminated in two or more layers. The configuration is not limited.

  Furthermore, the arrangement order of the developing devices (image carriers 5 to 8) of the present embodiment is not limited to Y, M, C, and K, and may be other arrangement orders such as K, C, M, and Y. There may be.

  Furthermore, in the image forming apparatus of the present embodiment, reversal development is performed using a negatively charged photoreceptor as an image carrier, but the present invention is not limited to this, and a positively charged photoreceptor is used. Or regular development may be performed. In this case, the DC power supplies (primary transfer voltage power supplies) 13 to 16 and 18 supply the primary transfer rollers 9 to 12 with a voltage lower than the developer image carrying portion.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment of the invention. However, the invention is not limited to the embodiment of the invention, and various modifications can be made without departing from the scope of the invention. It can be changed.

DESCRIPTION OF SYMBOLS 1 Opposite roller 2 Driving roller 3 Tension roller 4 Intermediate transfer belt 5-8 Image carrier 9-12 Primary transfer rollers 13-16, 18 DC power supply 17 Secondary transfer roller 19 Transfer material 20, 21 Guide roller 22 Blades 23, 24 Varistor 25 Insulating plate 26 Conductive electrode plate 27 Convex electrode 28 Weight 29 Ammeter 30 DC power supply 31y, 31m, 31c, 31k Developer 32 Color developer image 36 Voltage supply means

Claims (5)

A plurality of image carriers on which a negative developer image is carried; an annular semiconductive intermediate transfer belt to which the developer image is transferred; and a plurality of stretching rollers that stretch the intermediate transfer belt; A plurality of primary transfer rollers arranged to face each other through the intermediate transfer belt for each of the image carriers and a voltage higher than at least a portion where the developer image is carried, arranged for each of the plurality of primary transfer rollers. An image forming apparatus comprising: a plurality of primary transfer voltage power supplies that supply different voltages to the primary transfer roller for each primary transfer roller;
The tension roller is connected to a tension roller adjacent to a transfer region where the image carrier and the primary transfer roller are disposed, and the absolute value of the potential of the tension roller is 0 V or more and a limit voltage or less. comprising a voltage limiting circuit for holding the,
At least one of the plurality of stretching rollers is opposed to a secondary transfer roller that secondarily transfers the developer image transferred to the intermediate transfer belt onto a transfer material via the intermediate transfer belt. A counter roller arranged, the counter roller being connected to any voltage supply means including 0V,
At least one of the plurality of stretching rollers is a guide roller adjacent to the opposing roller, and the guide roller is electrically connected directly to the ground. . A plurality of image carriers on which a positive developer image is carried; an annular semiconductive intermediate transfer belt to which the developer image is transferred; and a plurality of stretching rollers that stretch the intermediate transfer belt; A plurality of primary transfer rollers arranged to face each other through the intermediate transfer belt for each of the image carriers and a voltage lower than at least a portion where the developer image is carried, arranged for each of the plurality of primary transfer rollers. An image forming apparatus comprising: a plurality of primary transfer voltage power supplies that supply different voltages to the primary transfer roller for each primary transfer roller;
The tension roller is connected to a tension roller adjacent to a transfer region where the image carrier and the primary transfer roller are disposed, and the absolute value of the potential of the tension roller is 0 V or more and a limit voltage or less. comprising a voltage limiting circuit for holding the,
At least one of the plurality of stretching rollers is opposed to a secondary transfer roller that secondarily transfers the developer image transferred to the intermediate transfer belt onto a transfer material via the intermediate transfer belt. A counter roller arranged, the counter roller being connected to any voltage supply means including 0V,
At least one of the plurality of stretching rollers is a guide roller adjacent to the opposing roller, and the guide roller is electrically connected directly to the ground. . The image forming apparatus according to claim 1 , wherein the intermediate transfer belt is semiconductive having a volume resistivity of 1 × 10 ⁸ Ω · cm or more . The image forming apparatus according to claim 1, wherein the voltage limiting circuit is a varistor . Absolute value of the limiting voltage of the voltage limit circuit, among the primary transfer roller, one of claims 1 to 4, characterized in that a transfer voltage than that supplied to the transfer roller closest The image forming apparatus described in 1.

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