Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-03-14
2004-01-13
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06678494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus employing an electrophotographic system as an image forming method, and more particularly to an image forming apparatus furnished with a transfer device for transferring a developer image formed on an image carrier onto a transfer material.
2. Description of the Related Art
In an image forming apparatus employing an electrophotographic photoconductor (hereafter abbreviated as “photoconductor”) as an image carrier, image formation is achieved as follows. Firstly, the surface of the photoconductor is uniformly charged by a charging device and is thereafter exposed to light by an optical recording device so as to form an electrostatic latent image. Subsequently, the resultant electrostatic latent image is developed in a development device using a developer, and a developer image carried on the photoconductor is transferred onto a conveyed recording material by a transfer device. Lastly, the transferred developer image is fixed onto the recording material by a fixing device. The recording material onto which the developer image is fixed is available to users, for example, as an item representing an image.
Recently, in an image transfer process for transferring a developer image onto a recording material, there has been widely used a transfer system for performing transfer by bringing a transfer body, such as a transfer roller, transfer brush, or transfer block, into proximity to or abutment with a surface of an image carrier. This is because, this transfer system generates less ozone than a conventional electrostatic transfer system which exploits a discharge triggered by a corona discharge wire, and is therefore one of environmentally-friendly transfer systems.
However, in the above-stated transfer system for performing transfer by bringing a transfer body, such as a transfer roller, transfer brush, or transfer block, into proximity to or abutment with a surface of an image carrier, allowance of space for conveyance of a transfer material is less than in the conventional electrostatic transfer system employing a corona discharge wire. Thus, high conveyance accuracy is required.
That is, if the conveyance accuracy is low, the following problems arise. The transfer material tends to be deviated from a conveying path and may possibly be brought into contact with members arranged nearby, resulting in a bending or paper jam. Moreover, if the transfer material makes contact with the nearby members, a developer image having been already transferred is disturbed, or residual toner remaining on the surface of the image carrier, as well as toner scattered around the image carrier, inconveniently adhere to the surface of the transfer body, which has an adverse effect on the transfer process. Further, for example, environmental factors such as humidity surrounding the apparatus and the firmness of the transfer material are expected to vary widely. This makes it difficult to convey the transfer material in a wider range.
Specifically, there exist the following problems. During image formation is being conducted on a plurality of transfer materials, between the instant when image formation on a preceding transfer material is completed and the instant when a front-end portion of a subsequent transfer material enters opposed portions of the image carrier and the transfer body, namely, in a state where the transfer material is not present between the image carrier and the transfer body, the transfer body is inconveniently brought into direct contact with the surface of the image carrier. Consequently, toner stuck to the image carrier adheres to the surface of the transfer body. As a rear-end portion of the subsequent transfer material comes out of the opposed portions of the image carrier and the transfer body, the rear-end portion of the transfer material rubs against the surface of the transfer body with toner, and the toner undesirably stuck to the transfer body adheres to the rear-end portion of the transfer material, which results in the rear-end portion being stained. As a result, if the transfer material kept in a stained state is subjected to fixing process, the toner stuck to the rear-end portion is inconveniently fixed to the transfer material, and thus it is inevitable that the rear-end portion of the transfer material is stained.
SUMMARY OF THE INVENTION
An object of the invention is to provide an image forming apparatus which is capable of, despite having a simple structure, conveying a transfer material properly and securely even in a case where allowance of space is limited, for example, where an image carrier and a transfer body are arranged in proximate or abutting relation.
Another object of the invention is to provide an image forming apparatus which is capable of conveying a transfer material at a spaced interval with a transfer body so that a rear-end portion of the transfer material is kept out of abutment or contact with a surface of the transfer body.
The invention provides an image forming apparatus comprising:
an image carrier for carrying a developer image;
transfer means having a transfer body for electrostatically transferring the developer image carried on the image carrier onto a transfer material; and
transfer material guiding means disposed at a downstream side of opposed portions of the image carrier and the transfer body along a direction in which the transfer material is conveyed, for guiding the transfer material in conveyance by acting upon a reverse surface of the transfer material in such a manner that, when a rear-end portion of the transfer material passes through the opposed portions, the rear-end portion is kept away from the transfer body.
According to the invention, the transfer material guiding means, which is disposed at a downstream side of the opposed portions of the image carrier and the transfer body along a transfer material conveying direction, guides the transfer material in conveyance by acting upon the reverse surface of the transfer material in such a manner that, when the rear-end portion of the transfer material passes through the opposed portions, the rear-end portion is kept away from the transfer body. Thus, even in a case where sufficient space allowance cannot be ensured in the vicinity of the opposed portions of the image carrier and the transfer body, conveyance of a transfer material can be achieved properly and securely in a relatively simple structure. Particularly, since the rear-end portion of the transfer material having undergone a transfer process is unlikely brought into contact with the surface of the transfer body, the rear-end portion of the transfer material is free from toner stains.
In the invention, it is preferable that the transfer material guiding means includes a rotary body which is supported so as to be rotatable about an axis arranged parallel to a width direction of the transfer material that is perpendicular to the transfer material conveying direction.
According to the invention, as the transfer material is conveyed (transported) downstream along the transfer material conveying direction, the rotary body abutting on the reverse surface of the transfer material is rotated. This helps reduce friction with respect to the transfer material and thus allows the transfer material to be guidedly supported on a fixing side smoothly.
In the invention, it is preferable that the transfer material guiding means includes a disc-shaped first guiding member and a second guiding member having a star-shaped axially perpendicular section, the first and second guiding members being integrally supported so as to be rotatable about the axis arranged parallel to a width direction of the transfer material that is perpendicular to the transfer material conveying direction.
According to the invention, the transfer material guiding means includes the disc-shaped first guiding member and the second guiding member having a star-shaped axially perpendicular se
Kida Hiroshi
Masuda Yoshiaki
Yamauchi Hirokazu
Brase Sandra
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
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