JP2013195559A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device and an image forming apparatus capable of securely preventing residual toner from attaching to a sheet even when the residual toner having escaped a cleaning device is left on an image carrier.SOLUTION: A transfer device of the present invention is characterized in comprising: transfer means which transfers a toner image formed on an outer peripheral surface of a rotating transfer body by toner charged with a predetermined polarity to a transferred medium by rotationally contacting with the transfer body; cleaning means which includes a plurality of cleaning parts on which voltages of the predetermined polarity and the polarity opposite thereto are applied so as to remove toner transferred to the transfer means; and charging means which is provided downstream the cleaning means in the rotation direction of the transfer means, and charges toner left on the transfer means with the predetermined polarity.

Description

  The present invention relates to a transfer device and an image forming apparatus.

  In an electrophotographic image forming apparatus, the surface of a photosensitive drum is charged, and an electrostatic latent image is formed by irradiating the photosensitive drum with a light beam corresponding to a desired image. A toner image is formed by attaching charged toner to the electrostatic latent image. The toner image is transferred from the surface of the photosensitive drum onto a transfer member such as a transfer belt, and the toner image on the transfer member is further transferred onto the sheet to form an image on the sheet.

  Such an image forming apparatus is provided with a cleaning device for removing residual toner on the surface of an image carrier including a photosensitive drum and a transfer member. The cleaning device includes a roller-like brush, and removes residual toner on the surface of the image carrier by rotating the brush in contact with the image carrier.

  As a technique using such a cleaning device, there is one that applies a bias voltage to a cleaning brush (for example, Patent Document 1). According to this technique, a bias voltage having a single polarity is applied to the cleaning brush, while a bias voltage having a reverse polarity is applied from the cleaning brush to the cleaning brush or roller on the upstream side in the rotation direction of the image carrier. In this way, the charged residual toner that has not been removed by the upstream cleaning brush is collected by the cleaning brush to which the reverse polarity voltage is applied by the electrostatic force.

JP 2009-210933 A

  However, when a large amount of toner is supplied to the photoconductive drum for image stabilization control or the like, the residual toner may not be completely removed by the cleaning device. In such a case, the technique described in Patent Document 1 is not considered at all for the residual toner that could not be removed by the cleaning device. Therefore, in the technique described in Patent Document 1, if residual toner that has passed through the cleaning device and has not been removed remains on the image carrier, it adheres to the back surface of the paper during the subsequent image forming process, resulting in poor cleaning contamination. Will appear on the paper.

  The present invention has been made based on the above problems, and a transfer device capable of preventing the residual toner from adhering to the sheet even when the residual toner that has passed through the cleaning device remains on the image carrier. An image forming apparatus is provided.

  The above object of the present invention is achieved by the following means.

  (1) A transfer means for transferring a toner image formed on an outer peripheral surface of a transfer body rotated by toner charged to a predetermined polarity to a transfer medium by rotating contact with the transfer body, and transferring to the transfer means A cleaning unit having a plurality of cleaning portions to which a voltage having the predetermined polarity and a polarity opposite to the predetermined polarity is applied in order to remove the toner, and a downstream side in the rotation direction of the transfer unit from the cleaning unit And a charging unit that charges the toner remaining in the transfer unit to the predetermined polarity.

  (2) The transfer unit includes a plurality of roller members and a belt member held by the plurality of roller members, and transfers a toner image at a nip portion where the transfer body and the belt member are in contact with each other. The transfer apparatus according to (1), characterized in that it is characterized in that

  (3) The image forming apparatus includes a transfer voltage applying unit configured to apply a voltage having a polarity opposite to the predetermined polarity to a roller member in contact with the transfer body via the belt member among the plurality of roller members. The transfer device according to (2).

  (4) The transfer device according to any one of (1) to (3), wherein the charging unit is disposed in a non-contact manner with respect to the transfer unit.

  (5) An image comprising: an image forming unit; and the transfer device according to any one of (1) to (4), which transfers the toner image formed by the image forming unit. Forming equipment.

  According to the present invention, since the residual toner can be prevented from adhering to the paper, it is possible to reliably prevent the back surface of the paper from being stained by the residual toner.

1 is a cross-sectional view schematically showing a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view illustrating configurations of a secondary transfer device, a cleaning device, and a cleaning charging device according to the present embodiment. 6 is a graph showing the distribution polarity of residual toner that has passed through the cleaning device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the following description does not limit the technical scope and terminology described in the claims.

  FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus according to the present embodiment.

  The image forming apparatus A shown in FIG. 1 is also referred to as a tandem color image forming apparatus, and four sets of image forming units form image data on paper using an electrophotographic image forming process. .

  The image reading device SC reads an image on a document. Specifically, the image reading device SC scans and exposes the document placed on the slit SL by the scanning optical system. Reflected light from the document image is read by a line image sensor via a mirror. The read reflected light is photoelectrically converted into image signals of respective colors. The image signal is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like by an image processing unit (not shown), and then input to the optical writing device 3 of the corresponding color image forming unit 10. Is done.

  The four image forming units include an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image forming unit that forms a cyan (C) color image. The unit 10C is an image forming unit 10K that forms a black (K) color image.

  The image forming unit 10Y includes a photosensitive drum 1Y, and a charging device 2Y, an optical writing device 3Y, a developing device 4Y, and a drum cleaning device 5Y disposed around the photosensitive drum 1Y. Similarly, the image forming unit 10M includes a photosensitive drum 1M, and a charging device 2M, an optical writing device 3M, a developing device 4M, and a drum cleaning device 5M disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charging device 2C, an optical writing device 3C, a developing device 4C, and a drum cleaning device 5C arranged around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, and a charging device 2K, an optical writing device 3K, a developing device 4K, and a drum cleaning device 5K disposed around the photosensitive drum 1K. The photosensitive drums 1Y, 1M, 1C and 1K of the image forming units 10Y, 10M, 10C and 10K, charging devices 2Y, 2M, 2C and 2K, optical writing devices 3Y, 3M, 3C and 3K, and developing devices The 4Y, 4M, 4C, and 4K and the drum cleaning devices 5Y, 5M, 5C, and 5K have the same functions. Therefore, in the following description, symbols Y, M, C, or K are not used unless otherwise specified.

  The photosensitive drum 1 is exposed by a light beam such as a laser beam, and forms a latent image on the exposed portion. Specifically, the photosensitive drum 1 has a photosensitive material on the surface, and the surface uniformly charged by the charging device 2 is exposed by the light beam of the optical writing device 3 so that the exposed portion is static. It becomes an electric latent image.

  The charging device 2 uniformly charges the surface of the photosensitive drum 1. The charging device 2 has a corona discharge electrode of a scorotron type or the like, and the surface of the photosensitive drum 1 is charged negatively by ions generated by the electrode.

  The optical writing device 3 scans and exposes the photosensitive drum 1 with a light beam based on the image signal. The exposed portion of the charged photosensitive drum 1 has a reduced potential, and an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1.

  The developing device 4 supplies toner to the latent image. Specifically, a charged toner adheres to a portion where the potential of the electrostatic latent image on the photosensitive drum 1 is lowered, whereby a toner image is formed. The toner images are formed by the developing devices 4Y, 4M, 4C, and 4K supplying toner onto the photosensitive drums 1Y, 1M, 1C, and 1K corresponding to the respective colors. In this embodiment, it is assumed that the toner is charged to the negative electrode as in the photosensitive drum 1.

  The intermediate transfer belt 6 is an endless belt, is constructed by a plurality of support rollers, and is supported so as to be able to run. The toner images of the respective colors formed on the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the outer peripheral surface of the intermediate transfer belt 6 by the primary transfer units 7Y, 7M, 7C, and 7K. A color toner image is formed on the outer peripheral surface of the intermediate transfer belt 6 by superimposing layers of each color (Y, M, C, K).

  The paper transport unit 20 transports the paper S. The paper S is stored in the paper feed trays 291, 292 and 293 and is fed by the first paper feed unit 21. Alternatively, the paper S may be fed from the manual feed tray. The paper transport unit 20 transports the paper S to the secondary transfer unit 7A via the loop forming roller pair 22 and the registration roller pair 23.

  The double-sided conveyance unit 24 includes a paper conveyance path for forming images on both sides of the paper S and a plurality of conveyance roller pairs. The sheet S on which the color toner image is fixed on one surface (front surface) of the sheet S by the fixing device 50 is conveyed from the fixing device 50 to the lower duplex conveying path, switched back, and then conveyed again to the registration roller 23. Further, an image is formed on the other surface (back surface).

  The secondary transfer device 30 secondarily transfers the color toner image on the intermediate transfer belt 6 onto the paper S. Specifically, the secondary transfer device 30 as a secondary transfer unit is disposed in contact with the intermediate transfer belt 6 in the secondary transfer portion 7A, and the sheet S is the secondary transfer device 30. It passes through a nip portion (secondary transfer portion 7A) between the transfer belt 31 and the intermediate transfer belt 6. At the nip portion, the secondary transfer device 30 presses the sheet S against the intermediate transfer belt 6 and applies a voltage having a polarity opposite to that of the toner to the rotating roller 32, whereby the color toner image is secondarily transferred onto the sheet S. The Further, the secondary transfer device 30 includes a plurality of support rollers for constructing and driving the secondary transfer belt. At this time, the toner adhered to the portion other than the portion to be transferred to the sheet S on the intermediate transfer belt 6 and the toner formed on the intermediate transfer belt 6 for image stabilization control are transferred to the secondary transfer belt 31. Is done.

  The cleaning device 40 removes residual toner on the secondary transfer belt 6 using electrostatic force. Specifically, the cleaning device 40 as a cleaning unit includes two cleaning brushes, and removes charged residual toner on the secondary transfer belt by applying voltages of different polarities to the cleaning brushes. In the present embodiment, as described above, the secondary transfer belt of the secondary transfer device 30 is disposed in contact with the intermediate transfer belt 6. Therefore, as described above, the toner remaining on the intermediate transfer belt 6 is transferred to the secondary transfer belt. However, by arranging the cleaning device 40 on the secondary transfer belt, the residual toner on the secondary transfer belt is transferred. Can be removed. Details of the secondary transfer device 30 and the cleaning device 40 will be described later with reference to FIGS.

  The cleaning charging device 45 charges the residual toner that has passed through without being removed by the cleaning brush of the cleaning device 40. Specifically, the cleaning charging device 45 as a charging unit includes a corona discharge electrode of, for example, a scorotron type, and charges residual toner with ions generated by applying a predetermined voltage to the electrode. Further, by disposing the cleaning charging device 45 in a non-contact manner with respect to the secondary transfer belt 31, it is possible to avoid peeling discharge and efficiently charge the residual toner. The amount of charging voltage applied to the cleaning charging device 45 for charging the residual toner will be described later.

  Each unit of the image forming apparatus A is connected to the control unit 90 and is appropriately controlled by the control unit 90. A storage unit (not shown) configured as a part of the control unit 90 stores programs corresponding to various processes of the image forming apparatus A, and a CPU (not illustrated) configured as a part of the control unit 90. Each function of the image forming apparatus A is exhibited by executing programs corresponding to various processes.

  Next, the secondary transfer device 30, the cleaning device 40, and the cleaning charging device 45 according to the present embodiment will be described in detail.

  FIG. 2 is a cross-sectional view showing configurations of the secondary transfer device, the cleaning device, and the cleaning charging device according to the present embodiment, and FIG. 3 is a graph showing the distribution polarity of residual toner that has passed through the cleaning device.

  As shown in FIG. 2, the secondary transfer belt 31 of the secondary transfer device 30 is constructed by a plurality of support rollers including a rotation roller 32. The secondary transfer belt 31 is driven around by these support rollers. Among these support rollers, a positive voltage (for example, 500 V) is applied to the rotating roller 32 by voltage applying means (not shown). In this way, the negative residual toner on the secondary transfer belt 31 is attracted to the secondary transfer belt 31 by the potential due to the positive voltage via the secondary transfer belt 31. As will be described later, in this embodiment, the residual toner is attracted to the secondary transfer belt 31 by charging the residual toner to a negative polarity, and the residual toner can be prevented from adhering to the paper S.

  The cleaning device 40 includes cleaning brushes 41 and 42, collection rollers 43 and 44, and a cleaning charging device 45.

  The cleaning brushes 41 and 42 rotate in contact with the secondary transfer belt 31 to remove residues such as residual toner and paper dust attached on the secondary transfer belt 31. In the metal cores of the cleaning brushes 41 and 42, an electric-resistant brush fiber made of acrylic carbon or the like is planted around at a desired pile density, pile diameter and pile length. Or you may wind and paste the sheet | seat which planted the said brush fiber around a metal core. The cleaning brushes 41 and 42 are rotationally driven, for example, in the reverse direction with respect to the rotational direction of the secondary transfer belt 31.

  The collection rollers 43 and 44 collect the residue in the cleaning brushes 41 and 42 from the cleaning brushes 41 and 42 by rotating in contact with the cleaning brushes 41 and 42, respectively. The cleaning brushes 41 and 42 are connected to voltage application devices 46 and 47, respectively, and a positive or negative voltage is applied with a bias voltage amount of a predetermined potential. For example, a positive voltage of 1 k to 2 kV is applied to the collection roller 43, and a negative voltage of 1 k to 2 kV is applied to the collection roller 44.

  Since the voltage applied to the collection rollers 43 and 44 charges the cleaning brushes 41 and 42, residual toner having a polarity can be guided to the cleaning brushes 41 and 42 by electrostatic force and removed. In this embodiment, since the toner image is formed using toner charged on the negative electrode, most of the residual toner is also charged on the negative electrode. Therefore, by applying a positive voltage to the collecting roller 43 upstream of the rotation direction of the secondary transfer belt 31 among the two cleaning brushes 41 and 42, the cleaning brush 41 removes the toner charged on the negative electrode by electrostatic force. it can.

  Further, the residual toner that has passed through without being removed by the cleaning brush 41 is charged to the positive electrode by the positive voltage applied to the collection roller 43 via the cleaning brush 41. Therefore, as shown in FIG. 2, the subsequent cleaning brush 42 positioned on the downstream side is charged to the negative electrode by the collection roller 44, whereby the residual toner charged to the positive electrode can be removed by electrostatic force.

  Even when the cleaning device 40 having such a configuration is used, residual toner may remain on the secondary transfer belt 31 depending on conditions. At this time, the amount of residual toner remaining on the secondary transfer belt 31 after cleaning by the cleaning device 40 and its polarity distribution are as shown by the dotted distribution curve in the graph of FIG. As shown by the dotted lines in FIG. 3, it can be seen that almost half of the residual toner is charged to the positive electrode and the negative electrode by passing through the cleaning brushes 41 and 42 charged to the positive electrode and the negative electrode. Further, since the residual toner has passed through the cleaning brush 42 that has finally been charged to the negative electrode, the amount of residual toner charged to the negative electrode is slightly larger than the residual toner charged to the positive electrode.

  Returning to FIG. 2, the cleaning charging device 45 charges the residual toner on the secondary transfer belt 31 that has passed through the cleaning brushes 41 and 42 of the cleaning device 30. The cleaning charging device 45 charges the residual toner with the same polarity as the toner on which the toner image is formed. In this embodiment, since the toner held in the developing device 4 is charged to the negative electrode, the cleaning charging device 45 charges the residual toner to the negative electrode. The residual toner charged to the negative electrode is attracted to the secondary transfer belt 31 by the rotating roller 32 charged to the positive electrode on the downstream side in the rotation direction of the secondary transfer belt 31, so that the residual toner adheres to the paper S. Can be prevented.

  The amount of residual toner charged by the cleaning charging device 45 after passing through the cleaning device 40 and its polarity distribution are as shown by the solid distribution curve in FIG. As shown by the solid line in FIG. 3, it can be seen that the residual toner is charged by the cleaning charging device 45, so that the polarity of most of the residual toner is charged to the negative electrode. Therefore, as described above, the residual toner is attracted to the rotating roller 32 to which a positive voltage is applied via the secondary transfer belt 31, and can be prevented from adhering to the paper S when passing through the transfer nip. Further, according to the above-described embodiment, even when image stabilization control for adhering a large amount of toner to the photosensitive drum 1 is performed, for example, when the image forming apparatus A is turned on or periodically when a predetermined number of images are formed. It is possible to prevent the residual toner from adhering to the paper S during the image formation.

(Example)
Next, the result of an experiment in which the residual toner on the secondary transfer belt 31 is charged using the cleaning charging device 45 according to the present embodiment and then the paper is passed through the transfer belt will be described.

  “Charging potential” in Table 1 below indicates a voltage applied to the cleaning charging device 45. The “blackening area ratio” is the black color when black toner charged to the negative electrode is supplied to the photosensitive drum 1 and the paper is passed through the secondary transfer belt 31 to digitize the paper to which the residual toner is adhered. The ratio of the number of pixels to the number of pixels of the entire paper is shown. “Performance” indicates performance judgment, and the blackened area ratio of 0.02% is such that the toner adhering to the paper cannot be visually confirmed, and the blackened area ratio or less was set as an acceptance criterion (◯). Further, the blackened area ratio of 0.09% is such that toner adhesion to the paper is slightly observed, but there is no problem in practical use, and the blackened area ratio or less is set as an acceptable standard (Δ). The blackening area ratio standard (x) larger than the allowable standard is such that the residual toner adhering to the paper can be visually confirmed as dirt, and is not suitable for practical use.

  As shown in Table 1 above, if the cleaning charging device 45 is not used (charging potential = 0V), the blackening area ratio does not reach the acceptance standard much (0.2%). On the other hand, it can be seen that the use of the cleaning charging device 45 significantly reduces the blackened area ratio. In particular, when a negative voltage of − (minus) 750 V or higher was applied to the cleaning charging device 45, the blackening area ratio was 0.02% or less, which satisfied the performance criteria.

  As described above, according to the present embodiment and the example, even when the residual toner is not completely removed by the cleaning device 40, the residual toner is attached to the sheet by charging the residual toner with the cleaning charging device. Can be prevented. In addition, according to the present embodiment, the cleaning charging device 45 is arranged in a non-contact manner, thereby avoiding the peeling discharge when charging by contacting and efficiently charging the residual toner to a desired polarity. Can do.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.

  For example, the number of cleaning brushes is not limited to two. Any number may be configured. Further, instead of or in addition to the cleaning brush, a cleaning blade for removing residual toner may be configured in the cleaning device, and a voltage may be applied to the cleaning blade.

  In the above embodiment, the cleaning device 40 is disposed on the secondary transfer belt 31 of the secondary transfer device 30. However, it is not limited to this. The cleaning device 40 may be disposed with respect to the intermediate transfer body 6 after the secondary transfer. In this case, the cleaning device 40 can remove the residual toner on the intermediate transfer belt 6.

  In the above embodiment, the cleaning charging device 45 is constituted by a discharge electrode and is disposed in a non-contact manner with respect to the secondary transfer belt 31, but is not limited thereto. For example, it may be configured to contact the transfer belt like a charging roller.

A image forming apparatus,
S paper,
SC image reader,
SL slit,
1Y, 1M, 1C, 1K photosensitive drum,
2Y, 2M, 2C, 2K charging unit,
3Y, 3M, 3C, 3K optical writing unit,
4Y, 4M, 4C, 4K developing device (developing means),
5Y, 5M, 5C, 5K drum cleaning device,
6 Intermediate transfer belt,
7A Secondary transfer part,
7Y, 7M, 7C, 7K primary transfer part,
10Y, 10M, 10C, 10K image forming unit,
20 Paper transport section,
21 First paper feeding unit,
22 Loop forming roller pair,
23 Registration roller pair,
24 Double-sided conveyance path,
25 Paper discharge roller,
291, 292, 293 paper feed trays,
30 Secondary transfer device,
31 Secondary transfer belt,
32 rotating rollers,
40 Cleaning device (cleaning means),
41, 42 Cleaning brush,
43, 44 Collection roller,
45 Charging device for cleaning (charging means),
46, 47 Voltage application device (voltage application means),
50 fixing device,
80 operation display section,
90 Control unit.

Claims (5)

A transfer means for transferring a toner image formed on the outer peripheral surface of a transfer member rotated by toner charged to a predetermined polarity to a transfer medium by rotating and contacting the transfer member;
A cleaning unit having a plurality of cleaning units to which a voltage of the predetermined polarity and a polarity opposite to the predetermined polarity is applied in order to remove the toner transferred to the transfer unit;
A charging unit disposed on the downstream side in the rotation direction of the transfer unit from the cleaning unit and charging the toner remaining on the transfer unit to the predetermined polarity;
A transfer apparatus comprising:   The transfer unit includes a plurality of roller members and a belt member held by the plurality of roller members, and performs transfer of a toner image at a nip portion where the transfer body and the belt member are in contact with each other. The transfer device according to claim 1.   3. The transfer voltage applying means for applying a voltage having a polarity opposite to the predetermined polarity to a roller member in contact with the transfer body via the belt member among the plurality of roller members. The transfer apparatus described.   The transfer apparatus according to claim 1, wherein the charging unit is disposed in a non-contact manner with respect to the transfer unit. Image forming means;
The transfer device according to claim 1, which transfers the toner image formed by the image forming unit;
An image forming apparatus comprising: