Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2000-12-01
2002-07-16
Chen, Sophia S. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
C399S297000, C399S357000
Reexamination Certificate
active
06421511
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transfer device and an image formation apparatus such as a copier, a facsimile, or a printer each equipped with the transfer device. More particularly, this invention relates to the transfer device which has a transfer belt supported by a plurality of rotors and carries and conveys a transfer material, and a cleaning member that cleans the surface of the transfer belt, and which transfers a toner image formed on the image carrier onto a transfer material on the transfer belt. This transfer device also has a dielectric layer on the surface of the cleaning member. This invention also relates to the image formation apparatus with the transfer device.
BACKGROUND OF THE INVENTION
Conventionally, a transfer device for transferring a toner image formed on an image carrier onto a transfer material has been provided in an image formation apparatus such as a copier or a printer.
As this type of transfer device, there has been known one that carries transfer paper as a transfer material on the transfer belt and conveys it to a transfer area where a photosensitive body as an image carrier and a transfer belt supported by a support roller as a rotor are provided opposite to each other and contact each other. This transfer device then generates a transfer electric field at the transfer area when the transfer paper passes through the transfer area, and transfers the toner image formed on the photosensitive body onto the transfer paper by this transfer electric field.
In the transfer device configured as explained above, because the transfer belt and the photosensitive body contact each other via transfer paper, toner dirt stuck on the photosensitive body or splashed toner at the time of transfer maybe deposited on the transfer belt, which causes inconvenience such as soil on the back of the transfer paper or defective transfer. Therefore, it is necessary to additionally provide a cleaning unit to remove the toner deposited on the transfer belt in the transfer device.
As a cleaning unit for a transfer belt, there has been conventionally known a cleaning unit in an electric-field cleaning method in which the toner on the transfer belt is electrostatically moved to the side if a cleaning member by rubbing the surface of the transfer belt with a conductive member as a cleaning member to which a cleaning bias of the opposite polarity to an electric charge polarity of the toner is applied (e.g., JP, HEI 07-64444 A, JP, HEI 09-152788 A). In this electric-field cleaning method, an electric field which has electrostatic force (hereafter referred to as bias electric field) to allow the toner on the transfer belt to move toward the conductive member is produced between the conductive member and the transfer belt. The toner on the transfer belt is moved to the cleaning member side by this bias electric field to clean the toner off the transfer belt.
In the electric-field cleaning method, however, sufficient cleaning performance could not be obtained, and imperfect cleaning sometimes occurred. This imperfect cleaning easily occurs especially when a transfer belt with high resistance such that volume resistivity is 10
12
to 10
13
ohm-cm or more is used or when the amount of charge on toner is large.
When the high-resistance transfer belt is used, force with which toner is electrostatically absorbed to the transfer belt is increased because dielectric polarization is easily generated as compared to a belt with low resistance, and transfer charge applied to the belt at the time of transfer, that is, electric charge of the opposite polarity to an electric charge polarity of toner is easily held on the charge-applied surface. When the amount of charge on the toner is large, the force with which the toner is electrostatically absorbed to the transfer belt is also increased based on Coulomb force or image force. The toner on the transfer belt is layered, therefore, when electrostatic absorption force between the toner and the transfer belt is such strong, there is sometimes a case where even the toner on the top layer can not be moved to the conductive member side by the cleaning electric field. Therefore, it is conceivable that, when the electrostatic absorption force between the toner and the transfer belt is strong, a cleaning bias to be applied to the conductive member is increased in order to obtain excellent cleaning performance according to the electric-field cleaning method.
However, when the cleaning bias is too large, dielectric breakdown may be produced at a contact section between the cleaning member and the transfer belt in the thickness direction of the transfer belt, which may cause a current to leak. When the current leaks, the bias electric field is not formed, thus, sufficient cleaning performance in the electric-field cleaning method can not be attained.
Further, when the cleaning bias is too large, electric charge of the opposite polarity to that of toner is injected to the toner on the transfer belt, so that the electric charge polarity of the toner may be reversed. Such toner whose electric charge polarity has been reversed (hereafter referred to as reversed-polarity toner) can not be cleaned off in the electric-field cleaning method. Therefore, the reversed-polarity toner becomes a cause of reduction in cleaning performance.
Not only is there a case where the reversed-polarity toner is generated by injection of charge, but also there is a case where the reversed-polarity toner may be deposited on the transfer belt when the reversed-polarity toner existing on the surface of the photosensitive body contacts the transfer belt. Such reversed-polarity toner then becomes a cause of reduction in cleaning performance as well.
The applicant of this invention has proposed (Patent Application No. HEI 11-301773) a transfer device which can clean the surface of a transfer belt more sufficiently than the conventional electric-field cleaning method and also can clean reversed-polarity toner off the belt even when a high-resistance transfer belt is used or when the amount of charge on toner is large, and also has proposed an image formation apparatus with the transfer device. In this transfer device, when the dielectric layer provided on the surface of the cleaning member and the toner on the transfer belt contact each other, electric charge of the opposite polarity to an electric charge polarity of the toner is induced on the surface of the dielectric layer by dielectric polarization, and electrostatic absorption force is generated between the dielectric layer and the toner. Accordingly, electrostatic absorption force between the toner and the dielectric layer (hereafter referred to as dielectric absorption force) and electrostatic absorption force between the transfer belt and the toner (hereafter referred to as belt absorption force) act on the layered toner between the transfer belt and the dielectric layer. Each magnitude of the respective electrostatic absorption force acting on the toner varies inversely with the square of the distance to the toner. Therefore, the dielectric absorption force is stronger than the belt absorption force with respect to the toner on the top layer of the surface of the transfer belt, which allows the toner to be moved to the side of the dielectric layer and the toner to be cleaned off the transfer belt. Accordingly, even when a high-resistance transfer belt is used or when the amount of charge on toner is large, the surface of the transfer belt can be more sufficiently cleaned as compared to that of the conventional electric-field cleaning method. Further, electric charge of the opposite polarity to an electric charge polarity of toner is always induced on the surface of the dielectric layer, therefore, the toner whose electric charge polarity has been reversed can also be moved to the surface of the dielectric layer. Resultantly, soil on the back of a transfer material due to imperfect cleaning of a transfer belt or defective transfer do not possibly occur.
It has also been proposed in the specification acco
Ishii Hiroshi
Miyashita Atsuko
Saitoh Hiroshi
Sugiyama Toshihiro
Chen Sophia S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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