Electrophotography – Cleaning of imaging surface – Plural diverse
Reexamination Certificate
2002-08-30
2004-03-02
Tran, Hoan (Department: 2852)
Electrophotography
Cleaning of imaging surface
Plural diverse
C399S350000, C399S357000
Reexamination Certificate
active
06701122
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a cleaning device for removing an untransferred toner remaining on the circumferential surface of a photoconductor drum, and more specifically, to a cleaning device disposed above the photoconductor drum, and an image forming apparatus equipped with the cleaning device.
DESCRIPTION OF THE PRIOR ART
In recent years, there have been increases in electrostatic copiers of an in-body paper delivery type in which a paper stack space is provided in a region between image forming means, including a photoconductor drum, and document exposure/image reading means disposed above the image forming means in the body of an image forming apparatus to achieve compactness of the entire apparatus. In such a copier, paper is transported vertically upwardly from a paper feed cassette or a manual paper feed tray disposed below the image forming means. While the paper transported vertically upwardly is passing through a transfer zone disposed beside the photoconductor drum, a toner is transferred to the paper by transfer means. The paper having the toner transferred thereto is transported, unchanged, vertically upwardly, and then passed beside a fixing device. During this passage, the toner transferred to the paper is fixed onto the paper. The paper bearing the fixed toner is transported vertically upwardly, then changed in the direction of transport, and transported in a horizontal direction. Finally, the paper is delivered to a paper receiving tray in the paper stack space. The untransferred toner, which has not been transferred onto the paper, but has remained on the circumferential surface of the photoconductor drum, is removed by a cleaning device provided downstream from the transfer zone in the direction of rotation of the photoconductor drum. In such a copier of the in-body paper delivery type, the paper is transported vertically upwardly beside the photoconductor drum. Thus, there is no choice but to provide the cleaning device above the photoconductor drum. As a result, the cleaning device is configured to have a lower end portion downwardly opening toward the circumferential surface of the photoconductor drum.
Of the copiers of the in-body paper delivery type, those operating at a low speed have been predominant conventionally, but have recently been replaced by high speed ones gradually. With this technical background, the copiers in the above-mentioned configuration are increasing the use of a low temperature fixing toner, an a-Si(amorphous silicon)-based photoconductor drum, or a high sensitivity OPC (Organic Photoconductor) photoconductor drum.
When the toner remaining on the circumferential surface of the photoconductor drum is removed using a cleaning blade, additives detached from the toner may deposit on the circumferential surface of the photoconductor drum, and may be unremovable by cleaning. If the additives remain on the circumferential surface of the photoconductor drum, the remaining additives form cores, around which the poorly cleanable toner grows, forming masses. Every time the resulting masses slip beside the cleaning blade, they fuse, leaving streaky toner deposits on the circumferential surface of the photoconductor drum. Since a fresh toner is developed on the toner deposits, copy smudges resembling black spots corresponding to the toner deposits appear on the surface of the paper which is a copy. Particularly when the low temperature fixing toner is used, this tendency is marked. With the speeding of the in-body paper delivery type copier, a demand is becoming intense for a solution to this problem. Furthermore, when a magnetic toner is used, the following facts are presented: First, a magnetic powder contained in the magnetic toner, such as magnetite, becomes a causative substance, like the aforementioned detached additives, for the toner deposits on the circumferential surface of the photoconductor drum. Secondly, if a high copying speed is intended, a binder resin needs to have the property of fixing at an even lower temperature, in order to obtain fixing performance comparable to that of a nonmagnetic toner with the use of the magnetic toner. For these reasons, black spot-like copy smudges may occur noticeably. Even in light of the difference in weight between the magnetic toner and the nonmagnetic toner, if the copying speed of the in-body paper delivery type copier is increased, black spot-like smudges of the copy due to the deposition of the toner is even more marked, posing a problem to be solved.
Furthermore, the photoconductor drum itself poses the following problem: When an a-Si-based photoconductor drum is used, products of electric discharge, such as NO
x
and SO
x
, are generated by a main charger, a transfer charger, and a static eliminator disposed around the photoconductor drum. When these discharge products are exposed to a high humidity environment while depositing on the circumferential surface of the photoconductor drum, they adsorb moisture in the air to disturb an electrostatic latent image on the circumferential surface of the photoconductor drum, thereby causing image distortion. In addition, ozone which develops from the chargers and the static eliminator oxidizes and deteriorates the circumferential surface of the photoconductor drum, causing a tendency toward aggravation of image distortion. If a photoconductor drum other than the a-Si-based photoconductor drum, for example, the OPC photoconductor drum, is used, on the other hand, the toner undergoes filming on the circumferential surface of the photoconductor drum. As a result, photosensitivity and chargeability decline, so that fog in non-image areas or a decrease in image density tends to occur. Filming of the toner refers to the phenomenon that during repeated image formation and cleaning for long periods of time, the toner particles pressed against, slid over and rubbed against the circumferential surface of the photoconductor drum by the cleaning blade are deformed plastically and fused in a film form onto the circumferential surface.
To deal with the foregoing problems, it is necessary to polish the circumferential surface of the photoconductor drum aggressively, and always maintain the circumferential surface of the photoconductor drum in a clean state. For this purpose, a cleaning roller composed of an elastic material such as urethane rubber is provided upstream from the cleaning blade. This cleaning roller is driven so as to be rotationally moved in the same direction as the photoconductor drum at a peripheral speed higher than that of the photoconductor drum at the site of its pressurized contact with the photoconductor drum. Alternatively, the cleaning roller is rotated in a manner following the photoconductor drum. By so doing, the cleaning roller is slid over and rubbed against the circumferential surface of the photoconductor drum to polish it. More concretely, the cleaning roller shows its own action of cleaning, and in addition, polishes the circumferential surface of the photoconductor drum by sliding on and rubbing against it via the toner and the toner additives remaining on the circumferential surface of the photoconductor drum, thereby keeping the circumferential surface of the photoconductor drum always clean. Consequently, image distortion, toner filming, or toner deposition on the circumferential surface of the photoconductor drum is prevented.
As described above, it is desirable in the in-body paper delivery type copier to provide the cleaning roller in the cleaning device. However, the provision of the cleaning roller in addition to the cleaning blade and the toner outletting spiral means requires a considerable proportion of the space around the photoconductor drum, inducing upsizing of the entire copier. An alternative measure would be to thrust the cleaning blade in the axial direction of the photoconductor drum, thereby minimizing the slipping escape of the deposited toner from the cleaning blade. Even if this measure is taken, however, image distortion and toner filming cannot be prevented effectively, and
Maeshima Masanobu
Ninomiya Hiromichi
Yamane Naoki
Kyocera Mita Corporation
Smith , Gambrell & Russell, LLP
Tran Hoan
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