Electrophotography – Cleaning of imaging surface – Blade
Reexamination Certificate
2002-10-10
2004-03-09
Brase, Sandra (Department: 2852)
Electrophotography
Cleaning of imaging surface
Blade
Reexamination Certificate
active
06704539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image-forming apparatus having a cleaning blade kept in contact with an image-carrying member such as an amorphous-silicon photosensitive member, and also relates to the cleaning blade.
2. Related Background Art
Nowadays, as image-forming apparatus of an electrophotographic system, complex machines having all output terminals such as a copying machine, a printer and a facsimile machine together have come to be accepted in the market. This means that electrophotographic systems have widely been accepted as output terminals adaptable to such a network. However, as one of great problems, the “duty cycle” has become a subject of discussion. The duty cycle herein refers to the limit number of sheets for which the main body continues being normally operated without any serviceman maintenance. One of the most important factors which determine the duty cycle is considered to be the lifetime of photosensitive drums.
From the viewpoint of ecology, it has also become absolute subjects for manufacturers to lessen any waste, i.e., to lessen any articles for consumption, make such articles for consumption have a longer lifetime and improve their reliability.
Moreover, with progression from conventional analog apparatus to digitized ones, it has also become absolute subjects to make the main-body cost equivalent to, or lower than, that of analog ones.
Furthermore, in recent years, in copying machines and printers, which have hitherto chiefly been held by black-and-white machines, originals or output files are rapidly increasingly being made full-color also in offices. Not only digital machines equivalent to analog machines but also full-color printers equivalent to black-and-white machines in respect of main-body cost and running cost have become absolute subjects. In order to settle such subjects, techniques which can dramatically lower TCO (total cost of ownership; total necessary cost viewed from users) are desired.
Under such circumstances, amorphous-silicon photosensitive members have become more and more widely used because of their high hardness (9,800 N/m
2
or more in Vickers hardness) and superior durability (running performance), heat resistance and environmental stability, and have become indispensable for high-speed machines which are required to have especially high reliability. The amorphous-silicon photosensitive members have replacement lifetime in a number of sheets which is at least one digit larger than OPC (organic photoconductor) photosensitive members commonly used in recent years. In other words, they have a lifetime equivalent to the main-body lifetime, and also have the effect on waste reduction. In addition, they do not take time and labor for, e.g., collection and regeneration of process cartridges making use of the OPC photosensitive members.
If the techniques making use of such amorphous-silicon photosensitive members mounted on high-speed machines come mountable on full-color printers, it is considered achievable to provide apparatus which can achieve the duty cycle and low running cost of the high-speed machine in respect of black-and-white printing and also can perform color printing. In particular, in order to achieve the duty cycle and low running cost of high-speed machines on the part of users who use black-and-white printing in a high percentage, it is considered essential to mount the amorphous-silicon photosensitive member on a one-drum type full-color printer making use of a rotary developing assembly.
However, in the apparatus of this type, the stuff adhering to the photosensitive-member (image-bearing member) surface to affect image quality are not only the toner. Any foreign matter having adhered to the photosensitive-member surface, such as fine paper dust coming from paper used as transfer materials in almost all cases, organic components depositing therefrom and corona products produced because of the presence of a high-pressure member in the apparatus, may cause low-resistance especially in a high-humidity environment to obstruct the formation of sharp electrostatic latent images. This is considered to be the factor which causes deterioration in image quality. Such a phenomenon of the deterioration in image quality is known to tend to occur in the case of the amorphous-silicon photosensitive member, which is constructed by forming films by glow discharge decomposition of silanes.
In order to avoid such a disadvantage, especially when one-component magnetic toners are used, a cleaning assembly is proposed in which a magnet roller is provided on the upstream side of a cleaning blade as viewed in the travel direction of the photosensitive member, to form a magnetic brush with part of the toner collected into the cleaning assembly, and this magnetic brush is brought into contact with the photosensitive-member surface to re-supply the magnetic toner thereto so that the foreign matter like the above can be removed by rubbing by the abrasive action attributable to toner particles at the blade portion.
In the means making use of such a magnetic brush, the abrasive action may hardly be localized non-uniformly on the photosensitive-member surface and may cause less deterioration of the photosensitive member, than the manner in which the photosensitive-member surface is rubbed with an abrasive member prepared separately such as a web or a rubber roller. In combination with such a method, an additional means may be used in which, e.g., the photosensitive member is provided with a heater so that its surrounding humidity can be kept low during night and stand-by to prevent the photosensitive-member surface from becoming low-resistance. This has achieved a certain effect to hold back image deterioration to be caused as stated above.
In image-forming apparatus which repeats the step of transferring transferable toner images formed on the photosensitive-member surface, to transfer materials chiefly comprised of paper, it is essential that residual toner remaining on the photosensitive member without being transferred to the transfer material at the timer of transfer is well removed each time.
Accordingly, as cleaning means, many proposals have been made up to now. Those in which the residual toner is scraped off by a cleaning blade comprised of an elastic materials such as urethane rubber are widely put into practical use because they are simple in construction, compact and low-cost and yet have good toner removal function. As a rubber material for the cleaning blade, urethane rubber is commonly used, as having a high hardness and yet being rich in elasticity, and excelling in wear resistance, mechanical strength, oil resistance and ozone resistance.
However, such a cleaning blade may cause filming on the photosensitive-member surface. The cause thereof is considered as follows: The photosensitive member has surface resistance which tends to become low-resistance. As factors which cause the photosensitive-member surface to have low resistance, fine paper dust coming from paper used as transfer materials in almost all cases, organic components depositing therefrom and various metal oxides and oxygen compounds produced at the time of high-energy corona discharge from a high-pressure member in the apparatus, together with any components becoming nitrate ions upon oxidation of nitrogen in air, may adhere to the photosensitive-member surface, so that a thin film (hereinafter “filming layer”) is formed on the photosensitive-member surface as a result of long-term use.
Where a magnetic toner is used as a toner to perform magnetic brush development, the filming layer may readily be removed by the abrasive action of the toner particles at the cleaning blade. However, in the case of non-magnetic toners such as color toners, the toner particles have less abrasive action to tend to cause the filming layer. The filming layer may absorb moisture in a high-humidity environment to become low-resistance to obstruct the formation of sharp electrostatic latent images, and this may cause deteriorat
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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