JP2012211931A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which, when a transfer material is wound on an intermediate transfer body, the transfer material can be forcibly separated without restriction by a layout.SOLUTION: An image forming apparatus 1 includes an image carrier 102, developing means 104, an intermediate transfer belt 201 that accepts a primarily transferred toner image and can freely travel, secondary transfer means 309 that secondarily transfers the toner image formed on the intermediate transfer belt 201 onto a recording medium, and belt cleaning means 409 that is disposed downstream the secondary transfer means 309 along the traveling direction of the intermediate transfer belt 201 and cleans the intermediate transfer belt 201, and also includes a backup roller 304 and a secondary transfer member 308 as the secondary transfer means 309. A suspension roller 204 for imparting tension to the intermediate transfer belt 201 is disposed between the backup roller 304 and the belt cleaning means 409.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer that forms an image using an intermediate transfer member.

  Conventionally, toner images of different colors formed on a plurality of photoconductors are superimposed and transferred (primary transfer) onto a belt-shaped intermediate transfer member, and then each color toner image on the intermediate transfer belt is collectively transferred onto a transfer sheet. 2. Description of the Related Art An image forming apparatus that fixes a color toner image transferred onto a transfer sheet by a fixing unit after (secondary transfer) is known. The secondary transfer portion of such an image forming apparatus is provided with a backup roller that also functions as a suspension roller for the intermediate transfer belt, and a roller-shaped secondary transfer member that is in pressure contact with the backup roller via the intermediate transfer belt. These function as secondary transfer means. In such a secondary transfer means, the outer diameter and hardness of the backup roller, the tension of the intermediate transfer belt, the resistance, etc. are set so that the transfer paper can be easily and automatically separated after the secondary transfer. Yes.

  However, these settings are naturally limited, and it is difficult to always obtain a stable separation performance according to the environment in the apparatus and the change in the state of the transfer paper. It is difficult to obtain a stable separation performance with a weak and thin coated paper or the like, and there is a possibility that the transfer paper is wound around the intermediate transfer belt due to insufficient separation. In such a state, the wound transfer paper enters the toner cleaning means on the intermediate transfer belt, and the user cannot remove the wound transfer paper, or is attached to the transfer paper even if it is removed. There has been a problem in that hands and clothes are stained by unfixed toner.

  In order to alleviate such a problem, for example, “Patent Document 1” discloses a technique in which a separation claw is provided on the backup roller and a means for sucking the intermediate transfer belt is provided at a position near the downstream side of the position of the separation claw. ing. In addition, a recording material detection sensor for detecting a transfer paper traveling on the conveyance path after the secondary transfer and a recording material detection sensor for detecting the transfer paper on the separated intermediate transfer belt are arranged in front of the belt cleaning unit to perform transfer. A technique for stopping the driving of the intermediate transfer belt before the paper enters the cleaning unit is disclosed in, for example, “Patent Document 2”.

  However, in the technique disclosed in “Patent Document 1”, it is possible to slightly prevent damage to the belt surface due to the separation claw by restricting flapping of the intermediate transfer belt, but the intermediate transfer belt and the separation claw are always in contact with each other. As a result, the intermediate transfer belt is damaged. Further, with the technique disclosed in “Patent Document 2”, it is possible to prevent transfer paper that could not be separated at the secondary transfer portion from entering the belt cleaning unit, but from the secondary transfer position to the belt cleaning unit. If the distance is short, the recording material detection sensor cannot be arranged, and there is a problem that restrictions on the layout occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forcibly separating a transfer material without being restricted by a layout when the transfer material is wound around an intermediate transfer member. To do.

  According to the first aspect of the present invention, an image carrier on which an electrostatic latent image is formed, a developing unit that visualizes the electrostatic latent image, and a toner image that is visualized by the developing unit is subjected to primary transfer. A freely movable intermediate transfer belt, secondary transfer means for secondary transfer of a toner image formed on the intermediate transfer belt to a recording medium, and downstream of the secondary transfer means in the running direction of the intermediate transfer belt. A belt cleaning unit arranged on the side for cleaning the intermediate transfer belt, and a backup roller for stretching the intermediate transfer belt as the secondary transfer unit, and a second roller disposed opposite to the intermediate roller via the intermediate transfer belt In the image forming apparatus having a secondary transfer member, a suspension roller is provided between the backup roller and the belt cleaning unit and applies tension to the intermediate transfer belt. Characterized in that it.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus further includes a separating member that is disposed between the suspension roller and the belt cleaning unit and separates the recording medium from the intermediate transfer belt. The separating member is not in contact with the intermediate transfer belt, and its tip is located inside a region extending from the linear portion of the intermediate transfer belt stretched between the backup roller and the suspension roller. It is characterized by that.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the separation member is a casing of the belt cleaning unit.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the suspension roller further includes a concave portion on a surface thereof.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, at least one of the concave portions is provided at a position inside the minimum width size of the recording medium.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the suspension roller further has a convex portion on a surface thereof.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the convex portion is further provided at one or more locations inside the minimum width size of the recording medium.

  According to an eighth aspect of the invention, in the image forming apparatus according to any one of the first to seventh aspects, the intermediate transfer belt is a resin belt.

  According to the present invention, even if the recording medium is wound around the intermediate transfer belt in the secondary transfer portion, the intermediate transfer belt is disposed between the backup roller and the belt cleaning means constituting the secondary transfer portion. The suspension roller for applying tension can increase the curvature of the intermediate transfer belt, and the recording medium can be separated from the intermediate transfer belt by the waist of the recording medium, so that the belt remains with the recording medium wrapped around the intermediate transfer belt. It can be prevented from being carried to the cleaning means, and a good image forming operation can be continuously performed.

1 is a schematic front view of an image forming apparatus employing a first embodiment of the present invention. FIG. 2 is a schematic diagram of an image forming unit used in the first embodiment of the present invention. It is the schematic explaining the secondary transfer part and belt cleaning means which are used for the 1st Embodiment of this invention. It is the schematic of the suspension roller used for the 2nd Embodiment of this invention. It is the schematic of the secondary transfer part vicinity in the 2nd Embodiment of this invention. It is the schematic of the suspension roller used for the 3rd Embodiment of this invention. It is the schematic of the secondary transfer part vicinity in the 3rd Embodiment of this invention.

  FIG. 1 shows an image forming apparatus to which an embodiment of the present invention can be applied. In the figure, the image forming apparatus 1 employs a tandem indirect transfer system in which a plurality of image forming units 101Y, 101M, 101C, and 101Bk are arranged along the intermediate transfer belt 201. A transfer device including an endless belt-like intermediate transfer belt 201 is provided at the center of the image forming apparatus 1, and the intermediate transfer belt 201 stretched around the support rollers 202 and 203, the backup roller 304, and the tension roller 206. Is driven to run clockwise in FIG.

  In the intermediate transfer belt 201 described above, belt cleaning means 409 for cleaning the intermediate transfer belt 201 is disposed at a position between the support position by the backup roller 304 and the support position by the tension roller 206. , 203 are arranged in parallel along the traveling direction with yellow (Y), magenta (M), cyan (C), and black (Bk) image forming units 101Y, 101M, 101C, and 101Bk. Has been. Each image forming unit 101 has the same configuration, for example, the configuration shown in FIG.

  FIG. 2 shows an image forming unit 101Bk for black (Bk). The image forming unit 101Bk is provided with a drum-shaped photosensitive member 102Bk as an image carrier, a charging device 103Bk for forming a toner image on the photosensitive member 102Bk, an exposure device 110Bk, a developing device 104Bk as a developing unit, and the like. ing. The charging device 103Bk uniformly charges the photoconductor 102Bk using, for example, a charging brush to which a DC voltage is applied, and a charging roller, a charging charger, or the like may be used instead of the charging brush.

  The exposure device 110Bk is an LED writing type exposure device comprising a light emitting diode (LED) array and a lens array arranged in the main scanning direction, which is the axial direction of the photosensitive member 102Bk, and causes the LED to emit light in accordance with an image signal. An electrostatic latent image is formed on the photoreceptor 102Bk. As an exposure apparatus, a laser scanning system that includes a laser light source, an optical polarizer (polygon mirror, etc.), and an imaging scanning optical system may be used instead.

  The developing device 104Bk has a developing roller (or developing sleeve) that carries and rotates the developer, an agitating and conveying member that agitates and conveys the developer and supplies the developer to the developing roller, and the like. The formed electrostatic latent image is developed with a developer toner to form a visible image. As the developer, a one-component developer composed only of toner or a two-component developer composed of toner and a magnetic carrier is used. The image forming unit 101Bk shown in FIG. 2 uses black toner, the image forming unit 101Y uses yellow toner, the image forming unit 101M uses magenta toner, and the image forming unit 101C uses cyan toner.

  The toner image formed on the photoreceptor 102Bk by the above-described charging, exposure, and development is primarily transferred to the intermediate transfer belt 201 in the primary transfer portion. In this primary transfer portion, a transfer brush 105Bk, which is a primary transfer unit and to which a transfer bias is applied from a DC power source, is disposed at a position facing the photoconductor 102Bk via the intermediate transfer belt 201. A photosensitive member cleaning device 106Bk for removing residual toner on the photosensitive member 102Bk is disposed at a position facing the developing device 104Bk through the photosensitive member 102Bk.

  The black (Bk) image forming unit 101Bk has been described above, but the other yellow (Y), magenta (M), and cyan (C) color image forming units 101Y, 101M, and 101C are similarly configured. . In FIG. 1, the same number is given to the same component, and the symbols Y, M, C, and Bk are attached after the number to be written to distinguish each color. In this image forming apparatus 1, at the time of color image formation, toner images of the respective colors are formed on the photoreceptors 102Y, 102M, 102C, and 102Bk in the respective color image forming portions 101Y, 101M, 101C, and 101Bk of yellow, magenta, cyan, and black. Later, a color image is formed by superimposing transfer onto the intermediate transfer belt 201. Further, at the time of monochrome image formation, the image forming operation is performed only by the image forming unit 101Bk, and the formed monochrome toner image is primarily transferred to the intermediate transfer belt 201.

  On the other hand, a secondary transfer as a secondary transfer means having a secondary transfer roller 308 as a secondary transfer member, a cleaning blade 305, a static elimination needle 307, etc. at a position facing each image forming unit 101 via the transfer device. A portion 309 is provided. The secondary transfer roller 308 is disposed in pressure contact with the backup roller 304 via the intermediate transfer belt 201, and secondarily transfers the toner image on the intermediate transfer belt 201 to a recording medium such as paper.

  Below the image forming apparatus 1, a paper feed unit having a paper feed cassette 151 and a paper feed roller 152, a paper feed path 155 having a transport roller pair 153, a resist roller pair 154, and the like are disposed. Further, on the downstream side of the secondary transfer unit 309 in the transfer paper conveyance direction, a conveyance unit 156 that conveys a recording medium on which an image has been transferred, a fixing device 107 that fixes an unfixed toner image on the recording medium, and recording after fixing. A paper discharge roller 108 for discharging the medium to a paper discharge tray is disposed.

  Next, the operation of the image forming apparatus 1 described above will be described. When a start switch of an operation unit (not shown) is pressed, one of the support rollers 202 and 203 and the backup roller 304 is rotationally driven by a driving means (not shown), and the other two rollers are driven to rotate and intermediate. The transfer belt 201 is driven to run in the clockwise direction in FIG. At the same time, each photoconductor 102 starts rotating in each image forming unit 101, and yellow, magenta, cyan, and black single color toner images are formed on each photoconductor 102. As the intermediate transfer belt 201 travels, each single color toner image is superimposed and transferred onto the intermediate transfer belt 201 in the primary transfer portion, and a composite color toner image is formed on the intermediate transfer belt 201.

  When the start switch is pressed, the paper feed roller 152 rotates, and a sheet-like recording medium such as paper is fed out from the paper feed cassette 151 and guided to the paper feed path 155, and then abuts against the registration roller pair 154. And paused. Thereafter, the registration roller pair 154 is rotated in synchronization with the composite color toner image on the intermediate transfer belt 201, and the recording medium is sent between the intermediate transfer belt 201 and the secondary transfer roller 308 in the secondary transfer unit 309. . Then, a color image is transferred onto the recording medium by transfer in the secondary transfer unit 309.

  In this embodiment, as shown in FIG. 3, a bias having the same polarity as the toner is applied from the DC power source to the backup roller 304 (in this embodiment, a negative bias is applied because the toner is negatively charged) By ejecting the toner from the intermediate transfer belt 201, the toner is transferred to the recording medium, and the transfer margin in the low-resistance recording medium is increased. The secondary transfer roller 308 is grounded.

  The recording medium after the image transfer is transported by the transport unit 156 and sent to the fixing device 107, and heat and pressure are applied to the fixing device 107 to fix the transferred image, and then the paper is discharged by the paper discharge roller 108. Are stacked on a paper discharge tray (not shown). On the other hand, the intermediate transfer belt 201 after image transfer is obtained by a belt cleaning unit 409 that includes a cleaning blade 410 that contacts the intermediate transfer belt 201 and a housing 411 that houses the cleaning blade 410 and removes foreign matter removed from the intermediate transfer belt 201. Residual toner is removed and it is ready for the next image forming operation. At a position facing the cleaning blade 410 with the intermediate transfer belt 201 interposed therebetween, a cleaning roller 205 constituting the belt cleaning unit 409 is disposed.

  The resistance of the intermediate transfer belt 201 is set to a logarithm of volume resistivity (LogR) of 10.0 or less so that a stable transfer image can be obtained without a residual image problem due to a residual potential. Further, since the secondary transfer roller 308 is in contact with the intermediate transfer belt 201, the background stain toner on the intermediate transfer belt 201 and the pattern for process control are provided between portions where the recording medium such as transfer paper is not placed or between the sheets. Since the toner is transferred and contaminates the secondary transfer roller 308, the cleaning blade 305 removes foreign matters such as toner on the secondary transfer roller 308. Here, the secondary transfer roller 308 has a two-layer structure, and the rubber layer 308a is coated with a surface layer 308b made of a fluorine-based resin having good releasability, so that the cleaning performance by the cleaning blade 305 is improved. Yes.

  Further, in the present embodiment, a charge eliminating needle 307 is provided on the downstream side of the secondary transfer unit 309 in the recording medium conveyance direction. The recording medium after the secondary transfer is in close contact with the intermediate transfer belt 201 and is difficult to be peeled off. However, a sine wave having a peak-to-peak voltage of 10 kV from a high-voltage power source (not shown) is applied to the charge removal needle 307 from the back side of the recording medium. The AC voltage is applied so that the recording medium after the secondary transfer is not wound around the intermediate transfer belt 201 by neutralizing (discharging) the accumulated charge of the recording medium.

  As described above, the normal image forming apparatus is configured to make it difficult for the recording medium to be wound around the intermediate transfer belt 201. However, in recent years, electrophotographic copying machines and printers have been colorized, speeded up, and the like. Higher image quality is advancing, especially in the field of on-demand publications, and it is possible to handle a small number of copies. The movement created by a color printer has become remarkable, and when a coated paper for offset printing with good surface smoothness, thinness and weakness is used as a recording medium in such an image forming apparatus, the recording medium is intermediate. There is a possibility that the winding is caused by tightly contacting the transfer belt 201 and the recording medium enters the belt cleaning unit 409.

  The above-described problems are prevented by disposing a sheet detection sensor between the secondary transfer unit 309 and the belt cleaning unit 409 and stopping the running of the intermediate transfer belt 201 when a recording medium is detected by the sensor. In this image forming apparatus 1, the distance from the secondary transfer unit 309 to the belt cleaning unit 409 is close, and a sheet detection sensor is disposed between the secondary transfer unit 309 and the belt cleaning unit 409. However, the time from when the sensor is turned on until the recording medium reaches the belt cleaning means 409 is short, and it is difficult to prevent problems. Therefore, in the present invention, as shown in FIGS. 1, 3, and 4, a suspension roller 204 that applies tension to the intermediate transfer belt 201 is provided at a position between the backup roller 304 and the cleaning roller 205. .

  The suspension roller 204 is composed of a small-diameter roller so that the recording medium wound around the intermediate transfer belt 201 is forcibly separated from the intermediate transfer belt 201 before entering the belt cleaning unit 409, and the intermediate transfer belt 201 has a large curvature. It is arranged to be. In this embodiment, a metal roller having a diameter of 12 mm is used. As the suspension roller 204, the smaller the diameter, the larger the curvature and the separation can be made by the waist of the recording medium. However, if the diameter is too small, the suspension roller 204 is stopped when the intermediate transfer belt 201 is stopped for a long time. A deformation of the intermediate transfer belt 201 called a curl ridge occurs at a contact portion with the 204, and a horizontal band image or the like is generated at the deformed portion. Therefore, the suspension roller 204 is preferably about 10 to 16 mm in diameter.

  With this configuration, even when the recording medium is wound around the intermediate transfer belt 201 in the secondary transfer unit 309, the intermediate transfer is provided between the backup roller 304 and the belt cleaning unit 409 constituting the secondary transfer unit 309. The suspension roller 204 for applying tension to the belt 201 can increase the curvature of the intermediate transfer belt 201, and the recording medium can be separated from the intermediate transfer belt 201 by the waist of the recording medium. It can be prevented from being conveyed to the belt cleaning unit 409 while being wound around the transfer belt 201, and a good image forming operation can be continuously performed.

  However, as described above, the coated paper having high surface smoothness has high adhesion because the recording medium is in contact with the intermediate transfer belt 201 without any fine gap, and separation is difficult. Therefore, in the second embodiment of the present invention, a recess 204a is formed on the surface of the suspension roller 204 as shown in FIG. At least one concave portion 204a is disposed at an inner position of the minimum width size of the recording medium to be used. At the contact portion with the concave portion 204a, the intermediate transfer belt 201 has an inward direction as shown in FIG. A minute dent is formed, and a function is formed in which a gap is formed between the intermediate transfer belt 201 and the recording medium wound around the intermediate transfer belt 201 to weaken the adhesion force. When the leading end of the recording medium enters the suspension roller 204, the force is forced Separation can be performed.

  In the recess 204a formed in the suspension roller 204, the deeper the depth a, the larger the indentation toward the inner side of the intermediate transfer belt 201. If the width b is too narrow, the recess does not occur due to the waist of the intermediate transfer belt 201. If the recording medium is too wide, the inclination of the recording medium becomes gradual, and the recording medium follows the intermediate transfer belt 201, so that no gap is formed between the recording medium and the intermediate transfer belt 201, and the function cannot be achieved. The optimum values of the depth a and the width b of the recess 204a vary depending on the material (Young's modulus, hardness, etc.), thickness, and belt tension of the intermediate transfer belt 201. When the intermediate transfer belt 201 is an elastic belt, it is difficult to form a recess to follow the recess 204a. Therefore, it is necessary to set the depth a deep, but when the intermediate transfer belt 201 is a resin belt, Even if the depth a is shallow, a minute dent can be formed. In this embodiment, polyimide having a thickness of 50 μm is used as the intermediate transfer belt 201. When the belt tension is 1.5 N / cm, the depth a of the recess 204a is 0.1 mm or more, and the width b is 3 to 20 mm. With this setting, minute recesses are formed in the intermediate transfer belt 201, and the recording medium wound around the intermediate transfer belt 201 can be reliably separated.

  In the above-described embodiment, the three recesses 204a are formed, but the separation performance is improved by providing the recesses 204a at a plurality of locations. Furthermore, in this embodiment, even if the leading end of the recording medium is separated from the intermediate transfer belt 201 at the position of the suspension roller 204, the recording medium is again attracted to the intermediate transfer belt 201 by the electrostatic attraction force with the intermediate transfer belt 201. In order to prevent this, as shown in FIG. 3, when tension is applied to the intermediate transfer belt 201 by the suspension roller 204, the linear portion of the intermediate transfer belt 201 stretched by the backup roller 304 and the suspension roller 204 is removed. By disposing the front end portion of the housing 411 in the extended area A, the recording medium separated from the intermediate transfer belt 201 by its own waist can be reliably separated from the intermediate transfer belt 201 by the front end portion of the housing 411. it can. At this time, the housing 411 functions as a separation member. Note that the front end of the housing 411 is disposed in a non-contact manner with respect to the intermediate transfer belt 201, so that the intermediate transfer belt 201 is not damaged.

  FIG. 6 shows a suspension roller 204 used in the third embodiment of the present invention. In this third embodiment, a convex portion 204 b is formed on the surface of the suspension roller 204. At least one convex portion 204b is disposed at a position inside the minimum width size of the recording medium to be used. At the contact portion with the convex portion 204b, the intermediate transfer belt 201 has an outer side as shown in FIG. A minute convex portion is formed in the direction, and a function is formed in which a gap is formed between the intermediate transfer belt 201 and the recording medium wound around the intermediate transfer belt 201 to weaken the adhesion, and the leading end of the recording medium enters the suspension roller 204. Then, separation can be performed forcibly. Also in the third embodiment, the separation performance can be improved by providing the convex portions 204b at a plurality of locations.

  In the above embodiment, an example in which a color copying machine having a plurality of photoconductors 102 is used as the image forming apparatus 1 is shown. However, an image forming apparatus to which the present invention is applicable is not limited to this, and a printer, plotter, facsimile, The present invention can be applied to other image forming apparatuses such as these multifunction peripherals and monochrome copying machines having only one photosensitive member 102.

1 Image forming device (copier)
102 Image carrier (photosensitive member)
104 Developing means (developing device)
201 Intermediate transfer belt 204 Suspension roller 204a Concave portion 204b Convex portion 304 Backup roller 308 Secondary transfer member (secondary transfer roller)
309 Secondary transfer unit (secondary transfer unit)
409 Belt cleaning means 411 Separating member (housing)

JP 2003-241531 A Japanese Patent No. 4122780

Claims (8)

An image bearing member on which an electrostatic latent image is formed, a developing unit that visualizes the electrostatic latent image, and a freely movable intermediate transfer belt on which a toner image visualized by the developing unit is primarily transferred A secondary transfer unit that secondary-transfers the toner image formed on the intermediate transfer belt to a recording medium; and the intermediate transfer belt disposed downstream of the secondary transfer unit in the running direction of the intermediate transfer belt. An image forming apparatus including a backup roller that stretches the intermediate transfer belt as the secondary transfer unit, and a secondary transfer member that is disposed to face the intermediate transfer belt via the intermediate transfer belt. In the device
An image forming apparatus comprising: a suspension roller that is disposed between the backup roller and the belt cleaning unit and applies tension to the intermediate transfer belt. The image forming apparatus according to claim 1.
A separation member disposed between the suspension roller and the belt cleaning means for separating the recording medium from the intermediate transfer belt, the separation member being in non-contact with the intermediate transfer belt; and An image forming apparatus, wherein a leading end is located inside a region where a linear portion of the intermediate transfer belt stretched between the backup roller and the suspension roller is extended. The image forming apparatus according to claim 2.
The image forming apparatus, wherein the separation member is a casing of the belt cleaning unit. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the suspension roller has a recess on a surface thereof. The image forming apparatus according to claim 4.
The image forming apparatus according to claim 1, wherein the concave portion is provided at one or more positions inside the minimum width size of the recording medium. The image forming apparatus according to any one of claims 1 to 3,
The suspension roller has a convex portion on the surface thereof. The image forming apparatus according to claim 6.
The image forming apparatus according to claim 1, wherein the convex portion is provided at one or more positions inside the minimum width size of the recording medium. The image forming apparatus according to any one of claims 1 to 7,
The image forming apparatus, wherein the intermediate transfer belt is a resin belt.

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