Electrophotography – Cleaning of imaging surface
Reexamination Certificate
1999-11-11
2002-03-26
Grainger, Quana M. (Department: 2852)
Electrophotography
Cleaning of imaging surface
C399S346000
Reexamination Certificate
active
06363237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a unit for imparting lubricity to the surface of an electrophotographic photographic photoconductor for use in an image formation apparatus such as facsimile apparatus, printers, electrophotographic copying machines or the like, which is hereinafter referred to as a lubricity-imparting unit. The present invention also relates to an image formation apparatus using the lubricity-imparting unit and also to an image formation method using the image formation apparatus.
2. Discussion of Background
In the image formation apparatus such as printers, electrophotographic copying machines and facsimile apparatus, using electrophotography, there are disposed various units such as a charging unit, an exposure unit, a development unit, an image fixing unit, a cleaning unit, a charge quenching unit around a photoconductor, representative examples of which are a selenium photoconductor, a silicone photoconductor and an organic photoconductor, and image formation is carried out with successive operation of the above-mentioned units.
In the course of image formation steps, contaminating materials such as ozone and nitrogen oxides are produced in a charging step (hereinafter referred to as corona charge products) and deposited on the surface of the photoconductor, and residual toner components remain on the surface of the photoconductor after a development step. Furthermore, paper dust formed from image transfer sheets in an image transfer step, shavings of a photoconductive layer of the photoconductor, and gas components generated from the image fixing unit are also deposited on the surface of the photoconductor.
When the photoconductor is used for image formation repeatedly for an extended period of time, the above-mentioned contaminating materials build up on the surface of the photoconductor, and the surface of the photoconductor conductor becomes difficult to clean so that the cleaning performance of the photoconductor is reduced, and the abrasion of the surface of the photoconductor is promoted, with an increase in the coefficient of friction of the surface of the photoconductor. Eventually it may occur that a portion of the photoconductor with which a cleaning blade comes into contact is deformed or distorted.
The result is that improper image transfer locally takes place, the quality of images is lowered with considerable insufficiency in resolution and sharpness and the life of the photoconductor is shortened.
A corona charging method and a contact charging method are currently used in practice to charge the photoconductor. The corona charging method in fact produces a much larger quantity of corona charge products than the contact charging method does. Regardless of the quantity of the corona charge products produced, the above-mentioned problems are equally caused once the produced corona charge products build up.
Furthermore, when the coefficient of friction of the surface of the photoconductor is increased by the presence of the contaminating materials and accordingly the frictional resistance of the surface of the photoconductor is increased, the frictional pressure of the cleaning blade applied to the surface of the photoconductor is also increased. The result is that the photoconductor is caused to vibrate and makes discontinuous sharp noise called “blade's weeping”. When this inappropriate state continues and develops, the blade is caught by the photoconductor during its rotation, and eventually the photoconductor is locked and the rotation thereof is stopped, so that the photoconductive layer of the photoconductor is further abraded.
However, the formation of such contaminating materials is unavoidable when the electrophotographic image formation process is carried out.
Generally, photoconductors for use in an electrophotographic image formation apparatus originally have a high coefficient of friction, in particular, when they have not been used yet and brand-new. Therefore, if image formation is repeated without taking any step for reducing the coefficient of friction of such a brand-new photoconductor, the above-mentioned contaminating materials further increase the coefficient of friction of the surface of the photoconductor and inevitably bring about the above-mentioned problems.
Therefore it is desired that there come out a technique that makes it possible to change the surface of the photoconductor to such a surface that the above-mentioned contaminating materials can be easily eliminated therefrom, and are difficult to be deposited thereon.
As one of such techniques, there has been proposed a method of coating a lubricant on the surface of the photoconductor to reduce the coefficient of friction of the surface of the photoconductor and also to improve the abrasive resistance of the surface of the photoconductor.
For instance, in Japanese Laid-Open Patent Application 56-113183, there is proposed a method of continuously applying a lubricant to the surface of the photoconductor by rotating a pouch made of a porous cloth in which a powder-like lubricant is contained or on an external surface for which the powder-like lubricant is deposited, in contact with the surface of the photoconductor, whereby the frictional resistance between the blade and the surface of the photoconductor is reduced.
When the powder-like lubricant is applied from such a rotating member as mentioned above, it is very likely that the powder-like lubricant is scattered to pollute the neighboring place of the photoconductor. Furthermore, it is very difficult to control the amount of the powder-like like lubricant to coat. It is also difficult to reduce the coefficient of friction of the surface of the photoconductor by merely coating the powder-like lubricant thereon, so that it is necessary to form a thin layer of the lubricant on the surface of the photo-conductor. However, when the coated amount varies, the coefficient of friction of the surface of the photoconductor also varies from place to place, so that the desired effect is difficult to obtain.
In Japanese Laid-Open Patent Application 3-269478, there is proposed a method of coating a lubricant which can be formed into a thin layer, such as magnesium silicate or zinc stearate, in the form of a thin layer on a top portion of the cleaning blade in order to prevent the blade from chattering or being turned over or torn up.
This method is effective. However, if the lubricant is not supplied to the coated layer for a long period of time while in use, the lubricating effect of the coated layer will not last. Once the frictional resistance between the cleaning blade and the surface of the photoconductor is increased, a noise with high frequency is generated, and eventually it becomes highly possible that the desired operation cannot be continued any longer. In particular, when a photoconductor composed of a resin for which coefficient of friction increases is used, the above-mentioned noise with high frequency is apt to be generated, so that it may occur the rotation of the photoconductor is stopped and the image formation apparatus is damaged.
In Japanese Laid-Open Patent Application 8-202226, there is proposed an image formation apparatus provided with a cleaning section in which there is disposed a device for applying a lubricant to a brush and then applying a controlled amount of the lubricant from the brush to the surface of the photoconductor.
In Japanese Laid-Open Patent Application No. 8-3052233, there is proposed an image formation apparatus provided with a control unit for detecting a toner image formed on an image bearing member and for coating a lubricant on the surface of the image bearing member in accordance with a reference value for the detection.
Furthermore, in Japanese Laid-Open Patent Application No. 6-342236, there is proposed an image formation apparatus provided with a unit for applying a lubricant to a charging roller for which line speed is made different from the rotation speed of the photoconductor, and for applying the lubricant to t
Kojima Narihito
Nagame Hiroshi
Nakajima Akiyo
Sakon Yohta
Takeichi Ryuta
Cooper & Dunham LLP
Grainger Quana M.
Ricoh & Company, Ltd.
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