JP5697703B2 - Image forming apparatus and method for neutralizing image carrier - Google Patents

Description

  Embodiments described herein relate generally to an image forming apparatus such as a printer or a multifunction peripheral, and more particularly, to an image forming apparatus that removes a transfer memory remaining on a photoconductor and a method for removing electricity from the image carrier.

  2. Description of the Related Art In electrophotographic image forming apparatuses such as copying machines and printers, there are apparatuses that include a plurality of static eliminators to neutralize a transfer memory remaining on a photoreceptor after a toner image is transferred to a sheet. Further, there is a device that removes the transfer memory remaining on the photoconductor by rotating the photoconductor in reverse when the power is turned on and charging the photoconductor with a charger and then removing the charge on the photoconductor. However, there is a need for an apparatus that can remove the transfer memory remaining on the photosensitive member during image formation with higher accuracy and speed.

JP-A-2005-31111 Japanese Patent Application Laid-Open No. 11-258953

  An object to be solved by the present invention is to provide an image forming apparatus and an image carrier neutralizing method for removing a transfer memory remaining on a photoconductor during image formation, improving image unevenness due to the transfer memory, and obtaining high image quality. Is to provide.

To achieve the above object above, the image forming apparatus of the embodiment, an image bearing member, a charging unit for charging the image bearing member at a said image bearing member and the gap, which has been charged before Symbol charging unit An image forming unit that forms an image on an image carrier, a transfer unit that transfers the image formed on the image carrier to a recording medium, and a space between the transfer unit and the charging unit, The optical axis is inclined in the direction of the charging start area of the image carrier by the unit, and a part of the charging area of the image carrier including the charging start area by the charging unit overlaps with the charging by the charging unit. It is arranged between the second LED lamp to be exposed and the second LED lamp from the transfer portion, and the angle of the optical axis with respect to the surface of the image carrier is set so that the optical axis of the second LED lamp is greater than the angle to the surface of the image carrier, before Exposing the image bearing member before the charging by the charging unit, and a first LED lamp.

FIG. 2 is a schematic configuration diagram illustrating an image forming unit according to the first embodiment. FIG. 3 is a schematic explanatory diagram illustrating a surface potential of the photosensitive drum according to the first embodiment. Schematic explanatory drawing which shows the charge area | region of the charger of 1st Embodiment, and the static elimination area | region of a static elimination device. The graph which shows the static elimination result by 1st Embodiment and a comparative example. Schematic explanatory drawing which shows the charge area | region of the charger of 2nd Embodiment, and the static elimination area | region of a static elimination device.

  Embodiments will be described below.

(First embodiment)
An image forming apparatus according to a first embodiment will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram illustrating a process unit 10 as an example of the image forming apparatus according to the first embodiment. The process unit 10 includes a charger 12 that is a charging unit, an exposure unit 13, a developing unit 14, a transfer unit 16, a cleaner 17, and a static eliminator 18 that is a static elimination unit around a photosensitive drum 11 that is an image carrier. However, the size or arrangement position and arrangement angle of the process unit 10 are not limited.

  The photosensitive drum 11 has, for example, a negative charging characteristic, and the charger 12 uniformly applies a negative charge to the photosensitive drum 11. When the diameter of the photosensitive drum is φ30, the charging width of the charger 12 is set to 14 mm. The exposure device 13 is a laser exposure device, for example, and irradiates the photosensitive drum 11 with laser light based on image data or the like to form an electrostatic latent image on the photosensitive drum 11.

  The developing device 14 applies a negatively charged toner to the exposed portion (image forming portion (β)) of the photoconductive drum 11 with a negative polarity developing bias, and generates an electrostatic latent image on the photoconductive drum 11. Visualize. The toner may be either a non-erasable toner or a decolorable toner that can be erased by heating at a predetermined temperature, for example. The exposure device 13 and the developing device 14 constitute an image forming unit.

  The transfer device 16 applies a positive polarity transfer bias to the photosensitive drum 11 to transfer the toner image on the photosensitive drum 11 to a recording medium such as a sheet P. The cleaner 17 removes the toner remaining on the photosensitive drum 11 after the transfer is completed, for example, with a cleaning blade. The static eliminator 18 irradiates the photosensitive drum 11 with wavelength light having sensitivity using, for example, an LED lamp, and neutralizes the charge remaining on the photosensitive drum 11. The static eliminator 18 tilts the optical axis so that the charging start area (ε) shown in FIG. 3 (area where charging and neutralization overlap) is, for example, about 10% of the entire charging area. In the first embodiment, the optical axis of the static eliminator 18 is inclined toward the charger 12 by 15 degrees from a predetermined position, for example.

  With these configurations, the process unit 10 develops the electrostatic latent image formed on the photosensitive drum 11 with toner, and transfers the toner image onto the sheet P. After transferring the toner image to the sheet P, the process unit 10 removes the residual toner on the photosensitive drum 11 with the cleaner 17 and removes the residual charge on the photosensitive drum 10 with the static eliminator 18. The process unit 10 performs the next image forming process after removing the residual charge of the photosensitive drum 11 caused by the preceding image forming process.

  The charge eliminating process for removing the charge remaining on the photosensitive drum 11 after the transfer is completed will be described in detail. The surface potential of the photosensitive drum 11 at the time when the process unit 10 has completed the transfer process through charging, exposure, and development is, for example, a solid line (A) in FIG. In order to transfer the negatively charged toner on the photosensitive drum 11 to the sheet P in the transfer process, the transfer unit 16 applies a positive transfer bias to the photosensitive drum 11. The surface potential −v2 of the unexposed portion (α) where the image of the photosensitive drum 11 subjected to the transfer bias is not formed is lower than the surface potential −v1 at the time of charging. The surface potential of the image forming portion (β) to which the toner on the photosensitive drum 11 subjected to the transfer bias adheres becomes, for example, + v3, and is slightly positively charged.

  During the charge removal process after the transfer is completed, the charge removal light 18 a from the charge remover 18 removes negative charges remaining on the photosensitive drum 11. However, when the positive charge remains on the photosensitive drum 11 having the negative charging characteristic, the static elimination light 18a cannot remove the remaining positive charge.

  For example, the positive charge on the photosensitive drum 11 is not removed only by irradiating the static elimination light 18a in the static elimination region (δ) adjacent to the charging start position f of the photosensitive drum 11. The surface potential of the photosensitive drum 11 after neutralization is as indicated by, for example, the solid line (B) in FIG. 2 only by irradiating the neutralization light in the neutralization region (δ). Negative charges are removed from the unexposed portion (α) of the photosensitive drum 11 and the surface potential becomes ± 0 or a residual potential (minus potential) that cannot be removed any more, but in the image forming portion (β). A positive charge remains, resulting in a surface potential of + v3. The positive charge remaining in the image forming portion (β) appears as a transfer memory on the toner image in the next image forming process, causing image quality defects.

  As shown in FIG. 3, the static eliminator 18 according to the first embodiment irradiates the static elimination light (18a) on the static elimination region (δ) adjacent to the charging start position f of the photosensitive drum 11 by the charger 12. Further, the static eliminator 18 irradiates the charge start area (ε) of the charging area (γ) by the charger 12 with the static elimination light 18a. The static eliminator 18 neutralizes the static elimination region (δ) and the charging start region (ε).

  In the charging start region (ε), the static eliminator 18 irradiates the static elimination light 18 a overlapping the charging process of the charger 12 to remove the charge on the photosensitive drum 11. In the charging start area (ε), the image forming portion (β) of the photosensitive drum 11 that has been positively charged is charged to a negative potential by the charger 12, and then the negative charge is removed by the static eliminator 18.

  The upstream end portion 12a of the charger 12 includes a gap G of 5 mm, for example, with the photosensitive drum 11. The static elimination light 18 a from the static eliminator 18 enters the charging start region (ε) of the photosensitive drum 11 through the gap G between the charger 12 and the photosensitive drum 11. The charging start region (ε) is, for example, negatively charged by the charger 12, so that the potential on the surface of the photosensitive drum 11 is reduced within a range that does not affect image formation compared to before the start of charging. It is an area.

  In the static elimination region (δ), the static eliminator 18 irradiates the photosensitive drum 11 that has undergone the cleaning with the static elimination light 18 a to remove negative charges on the photosensitive drum 11. In the charging start region (ε), the negative charging by the charger 12 and the irradiation of the neutralizing light 18a by the static eliminator 18 are overlapped to remove the negative charged charges of the unexposed portion (α) and the image forming portion (β). .

  The surface potential of the photosensitive drum 11 at the static elimination end position j that has passed through the charging start region (ε) is, for example, as shown by the solid line (C) in FIG. The photosensitive drum 11 has the surface potential difference between the unexposed portion (α) and the image forming portion (β) removed from the charges of both the unexposed portion (α) and the image forming portion (β) by the preceding image forming process. It becomes almost ± 0.

  The process unit 10 continues to charge the photosensitive drum 11 that has passed the static elimination end position j to the charging start area (ε) in the continuous charging area (θ) that follows the static elimination end position j of the charger 12. The process unit 10 charges the photosensitive drum 11 in the charging start area (ε) and the continuous charging area (θ), and then performs each process of exposure, development, and transfer to form a toner on the sheet P by the next image forming process. Form an image.

  For example, if the transfer bias due to the transfer process is strong, even if the charging process and the charge eliminating process overlap in the charging start region (ε), some positive charge may remain in the image forming portion (β) of the photosensitive drum 11. . Even if a slight amount of positive charge remains on the photosensitive drum 11 at the neutralization end position j, the potential difference between the unexposed portion (α) and the image forming portion (β) is small. Since the potential difference between the unexposed portion (α) and the image forming portion (β) is small, the influence of the transfer memory on the toner image is reduced.

  A solid line D in FIG. 4 shows a transfer memory on the photosensitive drum 11 when the effect of the static elimination by the static eliminator 18 of the first embodiment is verified by changing the strength of the transfer bias of the transfer unit 16. In the first embodiment using the static eliminator 18 that irradiates the static elimination region (δ) and the charging start region (ε), if the strength of the transfer bias of the transfer unit 16 is medium (normal use range), the transfer memory Is almost zero. Therefore, the transfer memory does not appear on the toner image by the next image forming process, and image defects due to the transfer memory are prevented.

  On the other hand, the transfer memory of the photosensitive drum in the case where the static elimination effect by the comparative example in which static elimination is not performed in the charging start region (ε) is verified in the same manner is as shown by the broken line E in FIG. In the comparative example, a transfer memory is generated even when the transfer bias is weak, and the potential of the transfer memory increases as the transfer bias is increased. In the comparative example, there is a possibility that the transfer memory appears on the toner image by the next image forming process and an image defect is caused.

  In the first embodiment, the charging characteristic of the image carrier is negative polarity. However, the image carrier may be one having positive charging characteristics. In the case of an image bearing member having a positive polarity in charging characteristics, the charge removing unit irradiates the charge removing light at the charging start region, overlapping with the charging unit plus charging the image bearing member.

  According to the first embodiment, the static eliminator 18 irradiates the photosensitive drum 11 with the static elimination light 18a in the static elimination area (δ) after the transfer is completed. Further, the charge remover 18 irradiates the charge start region (ε) from the gap G to the charge start region (ε), overlapping with charging the charge start region (ε) of the photosensitive drum 11 by the charger 12. In the charging start area (ε) of the photosensitive drum 11, the image forming portion (β) of the photosensitive drum 11 is changed from positive charging to negative charging. Irradiation with the neutralizing light 18a overlaps with the negative charging of the image forming portion (β), the surface potential difference between the unexposed portion (α) and the image forming portion (β) is set to approximately ± 0, and the next image formation Start the process. A transfer memory does not appear on the toner image by the next image forming process, and a high-quality toner image is obtained.

(Second Embodiment)
An image forming apparatus according to the second embodiment will be described with reference to FIG. The second embodiment is different from the first embodiment in the charge removal unit. In the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 5, the second embodiment includes a first static eliminator 20 that is a first static eliminator and a second static eliminator 21 that is a second static eliminator. The first static eliminator 20 and the second static eliminator 21 irradiate the photosensitive drum 11 with wavelength light having sensitivity using, for example, an LED lamp, and neutralize charges remaining on the photosensitive drum 11.

  The first static eliminator 20 irradiates the first static elimination light 20a substantially perpendicularly to the first static elimination region (δ1) upstream of the charging start position f of the photosensitive drum 11 mainly. The second static eliminator 21 irradiates the second static elimination light 21 a mainly from the gap G toward the charging start area (ε) of the photosensitive drum 11.

  The first charge removal light 20a more efficiently removes negative charges on the photosensitive drum 11 in the first charge removal region (δ1). The second charge removal light 21a removes negative charges on the photosensitive drum 11 in the second charge removal region (δ2). Further, the second static elimination light 21a overlaps the charging process of the charger 12 in the charging start region (ε), and more efficiently removes the charges of the unexposed portion (α) and the image forming portion (β). .

  The surface potential difference between the unexposed portion (α) and the image forming portion (β) of the photosensitive drum 11 after passing through the charging start region (ε) is approximately ± 0. Therefore, the transfer memory does not appear on the toner image by the next image forming process, and image defects due to the transfer memory are prevented.

  In the second embodiment, the first static eliminator 20 and the second static eliminator 21 are arranged separately, but the static eliminator is not limited to this. The first static elimination light 20a perpendicular to the photosensitive drum 11 and the second static elimination light 21a directed toward the charging start region (ε) may be accommodated in the same case.

  According to the second embodiment, the negative charge remaining on the photosensitive drum 11 is efficiently removed by the first static eliminator 20 in the first static elimination region (δ1). Further, the charge elimination light 21a is irradiated in the charge start region (ε) so as to overlap with the negative charge, so that the surface potential difference between the unexposed portion (α) and the image forming portion (β) is approximately ± 0. A transfer memory does not appear on the toner image by the next image forming process, and a high-quality toner image is obtained.

  According to at least one embodiment described above, the image carrier is neutralized in overlap with the start of charging in the next image forming process. After the charge having the opposite polarity to the charging characteristics of the image carrier remaining on the image carrier is removed, the next image forming process is performed. The transfer memory does not appear on the toner image in the next image forming process, and a high-quality toner image is obtained to prevent image defects caused by the transfer memory.

  Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Process unit 11 ... Photosensitive drum 12 ... Charger 16 ... Transfer device 18 ... Static eliminator

Claims (2)

An image carrier;
A charging unit for charging the image bearing member at a said image bearing member and the gap,
An image forming unit for forming an image on said image bearing member charged before Symbol charging unit,
A transfer portion for transferring the image formed on the image carrier to a recording medium;
The image carrier that is disposed between the transfer unit and the charging unit and includes the charging start region by the charging unit with an optical axis inclined toward the charging start region direction of the image carrier by the charging unit. A second LED lamp that exposes a part of the charging area overlapping with charging by the charging unit ;
The optical axis is disposed between the transfer unit and the second LED lamp, and the angle of the optical axis with respect to the surface of the image carrier is greater than the angle of the optical axis of the second LED lamp with respect to the surface of the image carrier. An image forming apparatus comprising: a first LED lamp that exposes the image carrier before the charging by the charging unit. A charging step for charging the image bearing member by a charging unit that separates the image bearing member and the gap,
An image forming step of forming an image on said image bearing member charged by the pre-Symbol charging step,
A transfer step of transferring the image to a recording medium;
The second LED lamp having an optical axis directed toward the charging start area of the image carrier in the charging step causes a part of the charging area including the charging start area of the image carrier in the charging step to An overlapping exposure process for overlapping exposure with the charging process ;
Before the overlap exposure step by the first LED lamp, the angle of the optical axis with respect to the surface of the image carrier is larger than the angle of the optical axis of the second LED lamp with respect to the surface of the image carrier . And an exposure step of exposing the image carrier.

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