JP2006259080A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the life of a transfer belt by maintaining throughput and transfer performance even when an image forming apparatus shifts from a full color mode to a monochrome mode and by preventing slide friction. <P>SOLUTION: A plurality of stretch members (a tension roller 9, a drive roller 10, and support rollers 16 and 18) for stretching an intermediate transfer belt 8 are fixed in position. The image forming apparatus has: the full color mode in which a primary transfer roller 4c and a photoreceptor drum 2c holds the intermediate transfer belt 8; and the monochrome mode in which the photoreceptor drum 2c and the intermediate transfer belt 8 are separated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, and in particular, an image for forming a full color image in which a plurality of image forming units or cartridges including an image carrier, an image carrier charging member, a developing device and the like are stacked The present invention relates to a forming apparatus.

  There is an image forming apparatus capable of switching between a mono color mode for forming a single color image and a full color mode for forming a multi-color image. Here, in order to prevent sliding between the photosensitive member and the intermediate transfer belt, an image forming apparatus that separates the photosensitive members 102a, 102b, and 102c other than the black photosensitive member 102d from the intermediate transfer belt 108 when the mode is switched. Yes (see, for example, Patent Document 1).

  An image forming apparatus disclosed in Patent Document 1 is shown in FIG. In this image forming apparatus, a tension roller 116 as a swing shaft is provided on the upstream side of the intermediate transfer belt 108 with respect to the black photosensitive member 102d, and the tension roller 109 and the primary transfer roller 104 are connected to the tension roller 116. The swing shaft can be displaced.

  As described above, since the stretching roller 116 is located upstream of the photosensitive member 102d, the photosensitive member and the intermediate transfer belt can be used in the black primary transfer portion for image formation in both the mono color mode and the full color mode. Therefore, the intermediate transfer belt can be driven with high accuracy.

JP 2001-242680 A

  However, the tension roller 109 is disposed at the end of the intermediate transfer unit. Further, the tension roller 109 has a large amount of winding around the belt. For this reason, there were the following two problems.

  The first problem is caused by moving the tension roller 109 disposed at the end of the intermediate transfer unit. That is, in order to secure a sufficient retraction amount in all the separated primary transfer rollers 104, there is a problem that the movement amount of the tension roller 109 must be increased, and the size of the apparatus main body is increased.

  In order to increase the throughput of a print job in which full color and mono color are mixed, it is necessary to shorten the switching time between mono color and full color as much as possible. However, because the amount of movement of the tension roller is large, it is necessary to increase the switching speed. There is sex. In this case, there is a problem that the peripheral speed of the intermediate transfer belt becomes unstable immediately after the mode switching due to the impact at the time of contact and separation. For this reason, for example, black transfer failure occurs due to fluctuations in the peripheral speed of the intermediate transfer belt during the formation of a monocolor image immediately after switching from full color to monocolor, and conversely, there is a latent effect when switching from monocolor to full color. Image blurring or transfer failure may occur.

  The second problem is caused by operating and separating the tension roller 109 having a large winding amount around the intermediate transfer belt 108. In other words, a slight misalignment of the tension roller 109 during the separation operation and the contact operation causes a shift in the scanning direction of the intermediate transfer belt 108 and belt running instability, and during image formation immediately after contact and separation. Color misalignment and margin amount in the scanning direction will occur.

  In order to avoid this, it is conceivable to slow down the switching speed and wait for image formation until the peripheral speed of the intermediate transfer belt is stabilized. However, the throughput is lowered as an adverse effect.

  Accordingly, an object of the present invention is to extend the life of a belt by maintaining throughput and transfer performance and preventing rubbing even when shifting from a full color mode to a mono color mode.

  A typical configuration according to the present invention for achieving the above object is to form an electric field between the first and second image carriers carrying toner and the first image carrier. A second transfer unit that forms an electric field between the first transfer unit that transfers toner from the image carrier and the second image carrier and transfers toner from the second image carrier. And an endless shape that is stretched between a plurality of stretching members and moves between the first image carrier and the first transfer unit and between the second image carrier and the second transfer unit. In the image forming apparatus positioned between the first transfer unit and the second transfer unit, the one of the plurality of stretching members is The tension member is fixed, the first mode in which the second transfer means and the second image carrier sandwich the belt, and the second image carrier. And having a second mode in which said the body belt are separated.

  As described above, a plurality of tension members are fixed to the belt, and one tension member is disposed between the first image carrier and the second image carrier. For this reason, the belt before and after the first image carrier is in the first or second mode between the first image carrier and the second image carrier. Keep the belt posture. For this reason, the transfer performance can be kept high. Further, when switching to the first mode, the tension member that stretches the belt is not moved, and the second image carrier is separated from the belt. For this reason, the switching operation can be performed quickly, and the throughput can be kept high. In addition, since the belt can be separated from the second image carrier, sliding between the image carrier and the belt can be prevented, and the life of the belt can be extended.

[First Embodiment]
A first embodiment of the present invention will be described with reference to the drawings. In the description, an outline of the image forming apparatus, a detailed description of each component, a detailed description of the periphery of the primary transfer roller 4, and a detailed description of the support rollers 16 and 18 will be given in this order.

(General description of image forming apparatus)
FIG. 1 is a schematic configuration diagram of a color image forming apparatus using an intermediate transfer system. In the present embodiment, an inline intermediate transfer method, that is, a tandem color image forming apparatus that forms toner images of respective colors in a plurality of image forming units (stations) each provided with an image carrier. The image forming apparatus according to the present embodiment employs an electrophotographic system.

  The image forming apparatus 90 forms an electrostatic latent image on a photoconductor adjacent to the intermediate transfer belt 8 in a plurality of image forming portions of each color provided along the intermediate transfer belt 8 based on the image input data. Then, the monochromatic toner is developed on the electrostatic latent image to form a monochromatic toner image. Then, the single color toner images formed in the respective image forming portions are superimposed on the intermediate transfer body 8 to form a multiple toner image, the multiple toner image is transferred to a transfer material, and the multiple toner image on the transfer material is transferred. The fixing device 21 is used for fixing.

  Here, in each color image forming section, a plurality of drum-shaped photoreceptors (photoreceptor drums) 2 (2a, 2b, 2c, 2d) as image carriers are arranged in a row. The photosensitive drum 2a is Y (yellow), the photosensitive drum 2b is M (magenta), the photosensitive drum 2c is C (cyan), and the photosensitive drum 2d is BK (black). Is formed. The plurality of photosensitive drums 2 are divided into a photosensitive drum 2 d (first image carrier) that is not separated from the intermediate transfer belt 8 and photosensitive drums 2 a, 2 b, and 2 c that are separated from the intermediate transfer belt 8. Of the photosensitive drums 2a, 2b, and 2c that are separated from the intermediate transfer belt 8, the one closest to the photosensitive drum 2d is used as the second image carrier.

  Around each photosensitive drum 2, as a means for forming a toner image, a charging roller 7 (7a, 7b, 7c, 7d) as a primary charging means, an exposure device 1 (1a, 1b, 1c, 1d), development A developing device 3 (3a, 3b, 3c, 3d) and a photosensitive drum cleaning blade 5 (5a, 5b, 5c, 5d) are arranged. Each developing device 3 accommodates toner cartridges 6 (6a, 6b, 6c, 6d) of the respective colors.

  Each color photoconductor drum 2 is an organic photoconductor in this embodiment, has an OPC photosensitive layer on an aluminum drum base (not shown), and is rotated at a predetermined process speed by a driving device (not shown). Driven.

  At the lower part of each color photosensitive drum 2, the surface is covered with an elastic body such as foam rubber via an intermediate transfer belt (endless belt) 8 at each primary transfer nip portion 13 (13a, 13b, 13c, 13d). The primary transfer roller 4 (4a, 4b, 4c, 4d) as a plurality of transfer means is in contact. The primary transfer roller 4d facing the first image carrier (photosensitive drum 2d) is the first transfer means, and the primary transfer roller 4c facing the second image carrier (photosensitive drum 2c) is the second. Transfer means.

  The intermediate transfer belt 8 includes a driving roller 10, a tension roller 9, a support roller 16, and a support roller 18 as stretching members. Further, it is rotated in the direction of the arrow in the figure by driving of the driving roller 10. Each stretching member has a roller shape and is fixedly disposed.

  The transfer material P such as paper conveyed from the feeding cassette 20 is guided to a nip portion formed by the secondary transfer roller 15 and the intermediate transfer belt 8, and the toner image formed on the intermediate transfer belt 8 is transferred to the transfer material. Transferred onto P. Thereafter, the transfer material P is pressed and heated by the fixing device 21 to fix the toner image fixed on the transfer material P.

  On the other hand, the toner image (waste toner) on the intermediate transfer belt 8 that could not be transferred to the transfer material in the secondary transfer portion is scraped off from the intermediate transfer belt 8 by the intermediate transfer body cleaning blade 11, and then the waste toner feeding mechanism. 12 is sent to the waste toner container 14 and stored.

  Such an in-line intermediate transfer type image forming apparatus achieves high speed, and further uses an intermediate transfer member, so that the transfer target in the process of overlaying the developer is always the same object (here, the intermediate transfer member) A stable superimposed image can be obtained.

(Detailed description of each component)
Each component that performs the image forming operation will be described in detail.

  The exposure apparatus 1 includes a near-infrared laser diode (not shown) having a wavelength of 760 nm and a polygon scanner that scans the photosensitive drum 2 with laser light, and lowers the potential of the image portion to −250V. Further, the developing device 3 is a contact developing device using a non-magnetic one-component toner as a developer, and a polymer toner having a core / shell structure with a particle size of about 7 μm and containing wax as a toner is applied to the developing device 3 (not shown). After the toner is applied to the developing sleeve 3 by a roller and the thickness of the toner layer is regulated by an elastic blade (not shown), the toner is developed on the photosensitive drum 2 in contact with the electrostatic latent image.

  In the present embodiment, the primary transfer roller 4 is an NBR / hydrin rubber having a diameter of 16 mm, and the hardness is 30 ° in Asker C hardness under a load of 500 g. The primary transfer roller 4 is driven to rotate by friction with the back surface of the intermediate transfer belt 8, and both ends are supported by bearings. One of the bearings is a conductive bearing, and the transfer bias is applied to the core metal of the primary transfer roller 4 through the conductive bearing. Further, biasing means such as a spring is provided below the bearings at both ends of the primary transfer roller 4, and the primary transfer roller 4 is pressed against the back side of the intermediate transfer belt 8 by this spring. In this embodiment, the total pressure is 10 N so that the photosensitive drum 2 and the primary transfer roller 4 are in contact with each other via the intermediate transfer belt 8 during image formation.

In this embodiment, the secondary transfer roller 15 is configured by covering a core metal having a diameter of 12 mm on the outer periphery thereof with a conductive rubber layer covering a longitudinal direction (image forming width direction) of 310 mm so that the diameter is 22 mm. The resistance value was 10 ⁷ Ω. The measurement method is a result of measurement using an R8340 ultrahigh resistance meter (registered trademark) manufactured by Advantest while the roller to be measured is driven and rotated with respect to an aluminum cylinder having a diameter of 30 mm. The measurement conditions are applied voltage; 2 kV, application time: 30 seconds, contact pressure: 9.8 N, rotational peripheral speed: 190 mm / sec.

  A secondary transfer bias power source (not shown) is connected to the core of the secondary transfer roller 15 via a power supply spring. A secondary transfer bias that can be changed during secondary transfer is applied to the secondary transfer roller 15 from a connected secondary transfer bias power source.

  The driving roller 10 is formed by coating a core metal having a diameter of 30 mm with an EPDM rubber whose resistance is adjusted with carbon black to a thickness of 500 μm. The tension roller 9 is an aluminum hollow tube having a diameter of 30 mm, has springs at both end bearings, and stretches the belt with a total pressure of 40N.

  The support roller 16 and the support roller 18 are SUS metal rollers having a diameter of 12 mm. The driven roller is fixedly disposed so as to be always in contact with the back surface of the intermediate transfer belt 8 and is driven to rotate by friction from the back surface of the intermediate transfer belt 8.

In this embodiment, the intermediate transfer belt 8 is a single-layer endless (seamless) resin belt having a thickness of 75 μm, a circumferential length of 1115 mm, and a longitudinal direction (image forming width direction) length of 310 mm, and resistance adjustment was performed by carbon dispersion. It is made of polyimide. The volume resistivity of the intermediate transfer belt 8 was 10 ⁹ Ωcm, and the surface resistance was 10 ¹² Ω / cm 2 or more. The volume resistivity measurement method is based on JIS-K6911. In order to obtain good contact between the electrode and the surface of the belt 8, conductive rubber is used as an electrode, and the volume resistivity of the intermediate transfer belt 8 is set to 100V. It is the result of measurement using an R8340 ultrahigh resistance meter (registered trademark) manufactured by Advantest under the condition of application for 10 seconds. The measured values on either the front or back side of the intermediate transfer belt 8 were the same.

  Note that the image forming conditions in this embodiment are: process speed: 190 mm / s, primary transfer bias: +300 V, secondary transfer bias: +2.3 kV.

(Detailed description around the primary transfer roller 4)
The image forming apparatus of the present embodiment has a full color mode (first mode) in which image formation is performed using all the photosensitive drums 2a to 2d, and a monocolor mode (in which only the photosensitive drum 2d is formed). The second mode) can be switched. FIG. 2A is a diagram for explaining a state around the intermediate transfer belt 8 in the full color mode, and FIG. 2B is a diagram for explaining a state around the intermediate transfer belt 8 in the mono color mode.

  As shown in FIG. 2, the intermediate transfer belt 8 includes a primary transfer roller moving mechanism 27 for moving the primary transfer rollers 4a to 4c. The moving mechanism 27 includes a link member (connecting member) 26 that connects and integrally arranges the primary transfer rollers 4a to 4c, and the primary transfer roller 4b between the primary transfer rollers 4a and 4b above the link member 26. And 4c, each having a half-moon-shaped rotatable switching cam 25 (25a, 25b).

  With this configuration, when the switching cams 25a and 25b rotate and the half-moon-shaped string part (straight line part) is down, the switching cam 25 does not contact the link member 26, and the link member Do not depress 26. Therefore, the primary transfer rollers 4a to 4c are pressed against the photosensitive drums 2a to 2c by the urging means.

  When the switching cams 25a and 25b rotate and are below the half-moon arc portion (arc-shaped portion), the switching cam 25 abuts on the link member 26 and pushes the link member 26 down. Then, the primary transfer rollers 4a to 4c disposed integrally with the link member 26 are released from being pressed against the photosensitive drums 2a to 2c against the urging force of the urging means, and the photosensitive drum 2a. -2c. At the same time, it is separated from the intermediate transfer belt 8.

  FIG. 3 is a block diagram of a data processing control system of the image forming apparatus. As a data processing control system of the image forming apparatus 90, a decoder 51 that receives image data transmitted from the personal computer PC and decomposes and develops it into image data for each color, and Y (yellow) and M that are decomposed and developed by the decoder 51. A page memory 52 (52Y, 52M, 52C, 52BK) for storing image data for each color (magenta), C (cyan), and BK (black) is provided. In addition, mode discriminating means 53 is provided as mode discriminating means for discriminating between the mono color mode and the full color mode based on the input image data. The mode discrimination means 53 is connected to a CPU 54 for controlling the engine as a control means that functions as a drive control means and controls each part of the image forming apparatus.

  In the configuration described above, when the image data transmitted from the personal computer PC is determined to be the full color mode in the mode determining means 53, the engine control CPU 54 rotates the switching cam 25 in FIG. As shown in FIG. 2 (a), the half-moon-shaped chord portion is turned downward. Thereby, all the photosensitive drums 2 a to 2 d can be kept in contact with the intermediate transfer belt 8. By forming an image in this state, a full color image can be formed.

  When the mode determining means 53 determines that the mode is the mono color mode, the engine control CPU 54 rotates the switching cam 25 in FIG. 2B, and the phase of the switching cam 25 is illustrated in FIG. Lower the half-moon arc. Thus, the photosensitive drums 2a to 2c that are not used in the mono color mode are separated from the intermediate transfer belt 8. Here, the photosensitive drums 2a to 2c are stopped by an instruction from the engine control CPU 54. By performing monocolor image formation using only the photosensitive drum 2d in this state, it is possible to form an image while the Y, M, and C photosensitive drums 2a to 2c that are not used in the monocolor mode are stopped. It becomes. As a result, the photoconductive drums 2a to 2c do not rub against the photoconductive drum cleaning blades 5a to 5c, so that the lifetime can be extended.

  As described above, in this embodiment, the contact and separation between the intermediate transfer belt 8 and the photosensitive drum 2 are performed by moving the primary transfer rollers 4a to 4c disposed on the back surface of the intermediate transfer belt 8. For this reason, the time until the intermediate transfer belt 8 immediately after separation and contact is stably conveyed is short, and it is possible to prevent problems such as transferability and color misregistration. The reason will be described below.

  The importance of the separation operation and contact operation between the intermediate transfer belt 8 and the photosensitive drum 2 is that the operation time is short and the running of the intermediate transfer belt 8 and the photosensitive drum 2 after the operation is stable. In the contact and separation method in the conventional image forming apparatus as shown in FIG. 7, contact and separation are performed by driving a tension roller 109 with a large winding amount of the intermediate transfer belt 8. For this reason, if the alignment of the tension roller 109 is deviated during the operation, the intermediate transfer belt 8 may become unstable or run.

  If image formation is started in a state in which the running performance of the intermediate transfer belt 8 is not stable, the photosensitive drum 2 and the intermediate transfer belt 8 are located at a portion (primary transfer portion) where the photosensitive drum 2 faces the primary transfer roller 4. Relative speed will fluctuate. For this reason, there is a problem that transfer unevenness occurs due to deterioration of color misregistration and fluctuation of shear stress between the toner and the intermediate transfer belt 8 in the transfer nip.

  In this embodiment, the intermediate transfer belt 8 and the photosensitive drum 2 are brought into contact with and separated from each other by moving the primary transfer roller 4 with a small winding amount of the intermediate transfer belt 8. For this reason, since the running of the intermediate transfer belt 8 is stabilized immediately after the operation, even if image formation is started immediately after the mode switching, there is little influence on transferability and color misregistration hardly occurs.

(Detailed description of support rollers 16 and 18)
In the present embodiment, the support rollers 16 and 18 whose positions are fixed are in contact with and supported by the back surface of the intermediate transfer belt 8 in both the full color mode and the mono color mode. The support roller 16 is disposed on the upstream side in the belt conveyance direction of the intermediate transfer belt 8 with respect to the photosensitive drum 2d, and on the downstream side of the belt transfer of the intermediate transfer belt 8 with respect to the photosensitive drum 2c. Further, the support roller (post-transfer support member) 18 is disposed on the downstream side of the intermediate transfer belt 8 in the belt conveyance direction with respect to the photosensitive drum 2d.

  If the tension angle between the photosensitive drum 2 and the intermediate transfer belt 8 in the primary transfer portion of the BK is different between the full color mode and the mono color mode as in the conventional image forming apparatus, transfer efficiency such as transfer efficiency and scattering However, there is a problem that it changes in the full color mode and the mono color mode.

  A description will be given of how transferability differs when the tension angle between the photosensitive drum 2 and the intermediate transfer belt 8 in the primary transfer portion of BK is different, with reference to FIG. FIG. 4 is a diagram showing a stretched state of the intermediate transfer belt 8 having the same configuration as that of the present embodiment except that the support roller 16 and the support roller 18 are not provided. The solid line shows the stretched state of the intermediate transfer belt 8 in the mono color mode, and the dotted line shows the stretched state of the intermediate transfer belt 8 in the full color mode. A portion indicated by an arrow is a width in which the photosensitive drum 2 and the primary transfer roller 4 are in contact with each other via the intermediate transfer belt 8 in the mono color mode (hereinafter referred to as transfer nip width), and a portion B is a full color mode. The nip width is shown.

  As shown in FIG. 4, when the tension angle of the intermediate transfer belt 8 changes according to the mode, the shape of the gap 19 upstream of the primary transfer nip changes. For this reason, when the electric field strength of the gap portion 19 changes and the electric field strength of the gap portion 19 is large, the toner image on the photosensitive drum 2 is affected by the electric field before reaching the primary transfer nip. Fly to the 8th side. When an image composed of fine dots and lines is printed, the shape of the dots and lines may be lost due to the influence of the flying toner. Therefore, in order to improve transferability, the position of the primary transfer roller 2 and the tension angle of the intermediate transfer belt 8 are determined so that the electric field strength of the gap 19 upstream of the primary transfer nip does not affect the image. There is a need.

  Further, when the tension state of the intermediate transfer belt 8 changes, there is a problem that the transfer nip width changes like the nip width A and the nip width B. If the nip width changes according to the mode, there is a problem that the impedance of the primary transfer portion changes. In particular, in a system in which the primary transfer bias is performed at a constant voltage, there is a problem that when the impedance of the primary transfer portion changes, the transfer current fluctuates and transfer efficiency decreases.

  Therefore, in the configuration without the support rollers 16 and 18 as shown in FIG. 4, if the configuration of the primary transfer portion is determined so that the transfer property in the full color mode is optimal, the transfer in the mono color mode is performed. There is a problem that the sex will deteriorate.

  In the present embodiment, since there are the support roller 16 and the support roller 18 that are fixedly arranged, the angles supported on the back surface of the intermediate transfer belt 8 are always the same, and the shape of the intermediate transfer belt 8 is constant. . For this reason, the tension angle and the nip width of the intermediate transfer belt 8 in the primary transfer portion of BK (the width in the transport direction of the intermediate transfer belt 8) are constant regardless of the mode. As a result, the same good transferability can be obtained in both the full color mode and the mono color mode.

  Since the length of contact with the photosensitive drum 2 in the direction orthogonal to the conveying direction of the intermediate transfer belt 8 is constant and the nip width is constant regardless of the mode, the intermediate transfer belt 8 is fixed to the photosensitive drum. The area of the belt sandwiched between 2d and the primary transfer roller 4d is also constant. For this reason, since the toner image can be transferred with the same area, the image quality can be kept constant.

  As described above, in this embodiment, the primary transfer rollers 4a to 4c are operated to separate and contact the surface of the intermediate transfer belt 8, and the support roller 16 and the support roller 18 are disposed. Switch between full-color and mono-color modes in a short time. For this reason, it is possible to extend the life of the consumables without deteriorating transferability and color misregistration.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to the drawings. Configurations similar to those in the above-described embodiment (for example, basic operations of the image forming apparatus) are denoted by the same reference numerals and description thereof is omitted. FIG. 5 is a diagram showing a state of stretching of the intermediate transfer belt 8 in the second embodiment. In the drawing, the solid line represents the stretch state in the full color mode, and the dotted line represents the stretch state in the mono color mode.

  As shown in FIG. 5, the supporting member for stretching the intermediate transfer belt 8 is stretched by four rollers: a driving roller 10, a supporting roller 16, a tension roller 9, and a supporting roller 17 except for the primary transfer roller 4. ing. All the supporting members are fixedly arranged.

  As in the first embodiment, the driving roller 10 is formed by coating a core metal having a diameter of 30 mm with EPDM rubber whose resistance is adjusted with carbon black to a thickness of 500 μm. The support roller 16 is a core metal having a diameter of 12 mm covered with a solid rubber of EPDM having a thickness of 2 mm, and the hardness is 45 ° in Asker C hardness under a load of 500 g.

  The support roller 17 is an aluminum hollow tube having a diameter of 30 mm, and both end shafts thereof are fixed. The support roller 17 is a driven roller that is rotated by being driven by friction from the back surface of the intermediate transfer belt 8. The tension roller 9 is made of a hollow aluminum tube having a diameter of 25 mm. The tension roller 9 is disposed on the lower surface of the intermediate transfer belt 8 and is configured to apply a load of 40 N to the intermediate transfer belt 8 with a spring.

  As shown in FIG. 5, the tension angle of the intermediate transfer belt 8 in the primary transfer portion of the BK station is determined by the support roller 16 and the support roller 17 that are fixedly arranged. For this reason, the tension angle is substantially constant regardless of the mode.

  In the present embodiment, the surface of the support roller 16 is covered with solid rubber to form an elastic layer. The reason is used below.

  The support roller 16 is driven to rotate by friction from the back surface of the intermediate transfer belt 8. For this reason, if the frictional resistance on the surface of the support roller 16 is low, slip may occur between the intermediate transfer belt 8 and scratches may occur on the back surface of the belt. As a countermeasure, it is conceivable to increase the amount of the support roller 16 entering the intermediate transfer belt 8 so that the support roller 16 receives a larger driving force. However, if left unattended for a long time as a negative effect, permanent deformation (hereinafter referred to as winding) of the winding portion of the intermediate transfer belt 8 occurs. For this reason, the winding amount of the intermediate transfer belt 8 around the support roller 16 needs to be made as small as possible from the viewpoint of winding. Therefore, in this embodiment, the surface of the support roller 16 is covered with solid rubber to increase the coefficient of friction so that stable rotation can be obtained even when the amount of the intermediate transfer belt 8 wound around the support roller 16 is small. And a configuration in which no curling occurs.

  In the case where the support roller 16 is covered with an elastic layer, if the hardness of the elastic layer is low, the collapse amount of the roller itself cannot be ignored in the monocolor mode. If the amount of crushing is large, the difference in the tension angle of the intermediate transfer belt 8 between the full color mode and the mono color mode becomes large.

  According to the experiments of the present inventor, in the configuration shown in the present embodiment, the Asker C hardness of the support roller 16 is set to 35 ° or more, so that there is a difference in transferability and color shift between the full color mode and the mono color mode. Was not recognized. With such hardness, there is no effect of the crushing amount of the roller surface on the image quality, and a good frictional force can be obtained even with a configuration with a small amount of wrapping. Thereby, the quality of an image can be kept high.

  In the present embodiment, the surface material as the elastic layer of the support roller 16 is solid rubber, but is not limited thereto. For example, a surface coated with urethane resin or ceramic, or a roller surface blasted or surface modified may be used.

  As described above, in the present embodiment, the support roller 16 and the support roller 17 are fixedly disposed before and after the primary transfer portion of the photosensitive drum 2d and the primary transfer roller 4d, so that transferability and color can be improved. It is possible to extend the life of the consumables without deteriorating the deviation. Further, the support roller 16 is configured to have an elastic layer made of a material having a high friction coefficient. Accordingly, it is possible to obtain a stable rotation of the intermediate transfer belt 8 on the support roller 16 while preventing the intermediate transfer belt 8 from winding.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to the drawings. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 6 is a diagram showing a state of stretching of the transfer material transport belt 23 in the third embodiment. In the drawing, the solid line represents the stretch state in the full color mode, and the dotted line represents the stretch state in the mono color mode.

  In the present embodiment, as shown in FIG. 6, an endless belt is a transfer material transport belt 23 that transports a transfer material to a transfer unit. In addition, a plurality of facing members that face the transfer material conveyance belt are the photosensitive drums of the respective colors. The same applies to this case.

  The image forming apparatus according to the present embodiment has four independent color stations each having yellow, magenta, cyan, and black photoconductors, a developing device, and a cleaning device arranged in a vertical row, and these are adsorbed to a transfer material conveyance belt. A full-color image is obtained by transferring the transferred paper and transferring it. The following description will focus on differences from the image forming apparatus described in the first embodiment.

  The transfer material P fed from a feed cassette 20 (not shown) contacts the transfer material transport belt 23 via a transfer inlet guide (not shown). A suction roller 22 to which a bias is applied is provided in the vicinity of the contact point between the transfer material P and the transfer material transport belt 23. During image formation, a voltage of +1 KV is applied to apply an electric charge to the transfer material P to perform suction transport. Generating power.

The suction roller 22 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed in EPDM rubber for resistance adjustment. The core of the suction roller 22 is configured to be able to apply a high pressure bias for suction. The resistance value of the suction roller is adjusted to 1 × 10 ⁶ Ω when a metal foil having a width of 1 cm is wound around the outer periphery of the roller and a voltage of 500 V is applied between the core and the metal core.

  The transfer material P that has passed through the suction roller 22 and gained the suction force with the transfer material transport belt 23 enters the first color transfer station. The transfer material P that is nipped and transported together with the transfer material transport belt 23 is transferred to the first color photosensitive drum by a transfer roller (transfer means) 24a provided on the back surface of the transfer material transport belt 23 at the transfer portion facing the photoreceptor drum 2a. The toner image from 2 is transferred.

  As the bias applied to the transfer roller 24, a voltage calculated from the impedance of the transfer material conveying belt 23 and the transfer material calculated from the current flowing through the suction roller 22 while passing through the transfer material P is applied. In single-sided printing in a normal environment, a DC bias of about +1.5 kV is applied from a high voltage power source at each station. Note that the image formation on the photosensitive drum 2 is the same as that described in the first embodiment, and a description thereof will be omitted.

  The transfer material transport belt 23 is a tension member, which is the drive roller 10, the transfer roller 24, the support roller 16, the support roller 17, and the tension roller 9, as in the second embodiment. All the tension members are roller-shaped and fixedly arranged. The support rollers 16 and 17 are driven rollers that are driven and rotated by friction from the back surface of the transfer material conveyance belt 23.

  The transfer material transport belt 23 is driven by the driving roller 10 and is driven to rotate at a peripheral speed of 190 mm / sec in the direction of the arrow. The transfer material transport belt 23 is made of polyimide as in the first embodiment, and the thickness and resistance value are the same.

The transfer roller 24 is epichlorohydrin rubber capable of applying a high pressure adjusted to a volume resistivity of 1 × 10 ⁷ Ωcm, and is in contact with the nip portion of the OPC from the back surface of the transfer material transport belt 23 with a transfer pressure of 2.94 N in total pressure.

  Thereafter, each time passing through each color station, a different color toner image is transferred from the photosensitive drum 2 to create a full color image.

  After the transfer of all colors is completed, the transfer material P separated by the curvature from the rear end of the transfer material conveyance belt is fixed by the fixing device 21 and discharged to the outside through the conveyance unit to obtain a final print. .

  Also in the configuration of the present embodiment, there are mode detection means for the full color mode and the mono color mode, and when the mono color mode is determined, the photosensitive drum 2 and the transfer material transport belt 23 are connected to each other in the transfer portion where image formation is not performed. The service life of the consumables is extended by separating them and stopping the rotation of the photosensitive member 2.

  Also in the embodiment described above, the support roller 16 and the support roller 17 that are fixedly arranged make the tension angle of the transfer material conveyance belt 23 in the black transfer portion constant, and from the full color mode to the mono color mode. When the mode is switched to the hour, it is possible to form an image without impairing color misregistration or transferability.

Other Embodiment
In the above-described embodiment, the mono color mode forms a black image, but is not limited thereto. That is, any configuration may be used as long as transfer rollers other than the frequently used color are separated.

1 is a schematic configuration diagram of a color image forming apparatus using an intermediate transfer method. FIG. 3 is a diagram showing a state of stretching of the intermediate transfer belt 8 in the first embodiment. 1 is a block diagram of a data processing control system of an image forming apparatus. FIG. 6 is an explanatory diagram of a comparative example showing a stretched state of the intermediate transfer belt 8 when the support roller 16 and the support roller 18 are not provided. FIG. 6 is a diagram illustrating a state of stretching of an intermediate transfer belt 8 according to a second embodiment. The figure which shows the mode of tension of the transfer material conveyance belt 23 in 3rd Embodiment. FIG. 6 is an explanatory diagram of a conventional image forming apparatus.

Explanation of symbols

P: transfer material 2 ... photosensitive drum (image carrier)
4 ... Primary transfer roller (transfer means)
8 ... Intermediate transfer belt (endless belt)
9 ... Tension roller (stretching member)
10 ... Drive roller (stretching member)
16 ... Support roller (stretching member)
17 ... Support roller (stretching member)
18 ... Support roller (stretching member)
23 ... Transfer material transport belt (endless belt)
24 ... Transfer roller (transfer means)
90. Image forming apparatus

Claims (8)

A first transfer means for forming an electric field between the first and second image carriers carrying the toner and the first image carrier and transferring the toner from the first image carrier; A second transfer means for forming an electric field with the second image carrier and transferring toner from the second image carrier; and a plurality of tension members, and the first image An endless belt that moves between the carrier and the first transfer means, and between the second image carrier and the second transfer means, In the image forming apparatus, the one stretching member is positioned between the first transfer unit and the second transfer unit.
The plurality of stretching members are fixed, the first mode in which the second transfer unit and the second image carrier sandwich the belt, and the second image carrier and the belt are separated from each other. An image forming apparatus having the second mode.   The image forming apparatus according to claim 1, wherein in the first mode, an image is formed by superimposing the toner on the first image carrier and the toner on the second image carrier.   The image forming apparatus according to claim 1, wherein the belt is in contact with the plurality of stretching members in the first mode and the second mode.   The area of the belt sandwiched between the first image carrier and the first transfer means is the same in the first mode and the second mode. The image forming apparatus according to claim 1.   The shape of the belt immediately before and immediately after being sandwiched between the first image carrier and the first transfer means in the moving direction of the belt is the same in the first mode and the second mode. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   The image forming apparatus according to claim 1, wherein the plurality of stretching members have a roller shape.   The image forming apparatus according to claim 1, wherein the toner on the first image carrier and the toner on the second image carrier are transferred to the belt.   The belt carries a transfer material, and the toner on the first image carrier and the toner on the second image carrier are transferred to a transfer material carried on the belt. Item 7. The image forming apparatus according to any one of Items 1 to 6.

Images