Electrophotography – Image formation – Transfer
Patent
1996-06-03
1998-06-09
Smith, Matthew S.
Electrophotography
Image formation
Transfer
399233, 399308, 399310, G03G 1501
Patent
active
057650845
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a printing apparatus and a printing method for electrically transferring toner images developed on a latent image bearing member onto an intermediate transfer member, for recording on a recording medium.
BACKGROUND ART
Known printing apparatuses, for example, electrophotographic printers include a color electrophotographic apparatus disclosed in Japanese Laid-open Patent Application (Kokai) No.1-282571(1989), in which electrostatic latent images formed on a photosensitive element are developed and electrically transferred for lamination onto an intermediate transfer member one after another, and the laminated toner images are fixed and recorded onto a recording medium such as recording paper all at once.
In the conventional printing apparatus, when the toner images developed on a photosensitive element are transferred for lamination onto an intermediate transfer member, the following two conditions must be satisfied.
Firstly, a sufficient electric field must be secured for electrically transferring the toner images from the photosensitive element onto the intermediate transfer member. Usually, the electric field is obtained by applying a bias voltage between the photosensitive element and the intermediate transfer member.
Secondly, any toner image transferred onto the intermediate transfer member must not return to the photosensitive element when the toner image of the next color is transferred, that is, reverse transfer must not occur.
In the conventional printing apparatus, when a toner image is transferred for lamination onto the intermediate transfer member, discharging treatment for compensating the polarity of the previous toner image is effected to allow better transfer of the subsequent toner image.
This is because it is considered that the previous toner image already transferred on the intermediate transfer member is charged in the same polarity as the subsequent toner image, and that the electric charges possessed by the previous toner image change the potential of the surface of the intermediate transfer member toward the same polarity as the charges of the toner image, acting in the direction to prevent the transfer of the subsequent toner image.
The above discharging treatment also removes the charges owned by the insulation layer on the surface of the intermediate transfer member, to satisfy the above first condition.
However, the discharging treatment decreases the charges owned by the toner image or reverses the polarity, to lower the electrostatic attractive force between the toner image and the intermediate transfer member. For this reason, the toner image is liable to leave from the intermediate transfer member, and when the next toner image is transferred from the photosensitive element to the intermediate transfer member, the previous toner image is transferred back to the photosensitive element as a problem of this technique.
The present invention has been completed in view of the above problem. A purpose of the present invention is to present a printing apparatus and a printing method which can prevent the reverse transfer of the previous toner image when the subsequent toner image is transferred for lamination onto the intermediate transfer member, without the need for any new device.
On the other hand, for a printing apparatus in which electrostatic latent images formed on a photosensitive drum are developed by developer liquid and the developed toner image are transferred and fixed on a recording medium such as recording paper, for example, an electrophotographic printer, it is known that a bias voltage is forcibly applied to an excess developer liquid removing roller used for removing excess developer liquid from the latent image bearing member (Japanese Patent Publication (Kokoku) No.1-43307(1989)), and that excess developer liquid on the photosensitive drum with toner images developed is removed by a self bias method (Japanese Patent Publication (Kokoku) No.57-48789(1982)) for the purpose to improve the image quality by prev
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Asada Hiroyoshi
Inagaki Jun
Nakao Yuichi
Smith Matthew S.
Toray Industries Inc.
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