Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
1999-10-27
2001-12-11
Beatty, Robert (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S314000
Reexamination Certificate
active
06330408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer apparatus having an image carrier for holding thereon an image formed by a developer charged with a prescribed polarity and transfer means disposed opposite the image carrier, wherein a recording medium is fed to an area where the image carrier and the transfer means oppose to each other, and the developer image on the image carrier is transferred the recording medium by using a transfer electric field formed by the transfer means. The invention is applicable to print sections in digital copiers and facsimile machines as well as to digital printers, plotters, and the like.
2. Description of the Related Art
As an image forming apparatus for outputting an image signal onto a recording medium such as paper in the form of a visible image, Japanese Examined Patent Publication JP-B2 2733609, for example, discloses an image forming apparatus that forms an image by transferring a developer image (toner image) on an image carrier (photoconductor drum) to a recording medium using a transfer roller.
In such an image forming apparatus as exemplified by the above prior art, a toner image developed on a photoconductor drum is transferred to a recording medium, i.e., paper surface, by pressing an elastic transfer roller having a medium to high resistance in contacting relationship to the paper. Such contact transfer techniques have the excellent characteristics of being able to produce images of good quality without generating ozone during the process.
In such image forming apparatus, when transferring the toner image developed on the photoconductor drum, a transfer electric field is formed by applying a transfer voltage to the transfer roller. Especially, according to the prior art, a good transfer is achieved by specifying the amounts of charge to be supplied to toner-image areas and non-toner-image areas when transferring the toner image from the photoconductor drum.
With this arrangement, however, it may become difficult to transfer the toner image securely to the paper, depending on the condition of the toner.
For example, when the amount of charge of the toner used is very small and the amount of toner adhering to the photoconductor drum is also very small, reverse transfer may occur and good transfer may not be obtained, thus resulting in a transfer failure. If this happens, various troubles occur, such as an insufficient density or a dropout in a solidly shaded area, the inability to reproduce the desired halftone because of a transfer failure of a screened halftone image, and in the case of a color image forming apparatus, difficulty in reproducing the correct color.
Further, if the transfer is to be performed without neutralizing the charge the toner has, it is required to form a transfer electric field strong enough to overcome the image force being exerted by the charge the toner has, and in this case, an extremely large transfer electric field becomes necessary.
If such a large electric field is formed, since the amount of charge of the toner held to the photoconductor drum is not constant but varies across the surface of the drum, toner particles with smaller charge amounts are easily attracted by the charge and scattered onto the paper on the upstream side of transfer area, causing image degradation.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above-outlined problems, and provides a transfer apparatus comprising an image carrier for holding thereon an image formed by a developer charged with a prescribed polarity and transfer means disposed opposite the image carrier,a recording medium being fed to an area where the image carrier and the transfer means face each other, and a developer image on the image carrier being transferred to the recording medium by using a transfer electric field formed by the transfer means, wherein the transfer apparatus is provided with supply means for supplying a charge to the developer held on the image carrier and thereby substantially neutralizing the charge of the developer while retaining the prescribed polarity.
According to the invention, since the developer held on the image carrier is transferred by substantially neutralizing the charge the developer has while retaining the prescribed polarity, the image force of the developer on the image carrier can be reduced, thus making it easier to transfer the developer to the recording medium by the transfer electric field; as a result, the use of a transfer electric field can be reduced to prevent the scattering of the developer onto the recording medium on the upstream side of the transfer area, and it is possible to reduce the size and the number of components of the power supply unit used to produce the transfer electric field.
The invention also provides a transfer apparatus comprising an image carrier for holding thereon an image formed by developers of a plurality of colors charged with a prescribed polarity and transfer means disposed opposite the image carrier, in which a recording medium is fed to an area of the image carrier which faces the transfer means, to transfer a developer image on the image carrier to the recording medium using a transfer electric field formed by the transfer means, wherein the transfer apparatus is provided with charge supply means for supplying charge appropriate to each color developer held on the image carrier and thereby substantially neutralizing the charge of the developer while retaining the prescribed polarity.
According to the invention, since the developers of the respective colors held on the image carrier are transferred by substantially neutralizing the charge of each color developer while retaining the prescribed polarity, the image force of each color developer on the image carrier can be reduced according to the characteristics of the developer, thus making it easier to transfer each color developer to the recording medium by the transfer electric field; as a result, the use of a transfer electric field can be reduced to prevent the scattering of the developer onto the recording medium on the upstream side of the transfer area, and it is possible to reduce the size and number of components of the power supply unit used to produce the transfer electric field.
In the invention it is preferable that the charge supply means is implemented in common with the transfer means.
Since the charge supply means of the invention is implemented in common with the transfer means, there is no need to provide a separate charge supply means and the number of components can thus be reduced.
In the invention it is preferable that in transfer the charge supply means supply a smaller amount of charge of reverse polarity than the amount of charge held by the developer on the image carrier to substantially neutralize the charge of the developer while maintaining the prescribed polarity of the developer.
REFERENCES:
patent: 5010370 (1991-04-01), Araya et al.
patent: 5189478 (1993-02-01), Hara et al.
patent: 5351113 (1994-09-01), Pietrowski et al.
patent: 5371579 (1994-12-01), Bisaiji
patent: 5450180 (1995-09-01), Ohzeki et al.
patent: 5729810 (1998-03-01), Bergen et al.
patent: 5799225 (1998-08-01), Abe et al.
patent: 5907740 (1999-05-01), Nozawa
patent: 5987292 (1999-11-01), Ohnishi
patent: 6026256 (2000-02-01), Abe et al.
patent: 0367157 (1990-05-01), None
patent: 56-104340 (1981-08-01), None
patent: 6-202429 (1994-07-01), None
patent: 8240937 (1995-09-01), None
patent: 8-240937 (1996-09-01), None
patent: B22733609 (1998-01-01), None
patent: 10-123801 (1998-05-01), None
Doshoda Hiroshi
Kamei Yukikazu
Ohnishi Hideki
Oikawa Tomohiro
Wakahara Shirou
Beatty Robert
Sharp Kabushiki Kaisha
LandOfFree
Transfer apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transfer apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transfer apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582170