Electrophotography – Image formation – Photoconductive member
Utility Patent
2000-01-27
2001-01-02
Martin, Roland (Department: 1753)
Electrophotography
Image formation
Photoconductive member
C399S284000, C399S285000, C430S096000, C430S102000, C430S110100, C430S111400
Utility Patent
active
06169869
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus and a process cartridge which are used in copying machines, page printers, facsimile units and so forth.
2. Related Background Art
Powdery developers as exemplified by toners are used in image forming apparatus of electrophotographic systems, such as laser beam printers and copying machines.
Toner is kept in a developing container, and is transported onto a toner carrying member (developer carrying member) by a toner transporting means and held on the toner carrying member. Then, the toner is provided with prescribed electric charges by means of a toner-layer-thickness regulation member (e.g., a doctor blade), and is moved to the electrostatic-latent-image forming zone of an image bearing member for bearing electrostatic latent images, where an electrostatic latent image formed on the image bearing member (photosensitive member) is rendered visible. Thereafter, the visible image thus formed is transferred to a transfer material, such as paper, by a transfer means, and then fixed by means of a fixing assembly. Toner remaining on the image bearing member without being transferred to the transfer material is taken off from the surface of the image bearing member by means of a cleaning assembly and sent to a cleaning container. Thus, one image forming process is completed, and users can obtain a desired image.
Now, as one of developing methods, jumping development is known, in which the electrostatic latent image formed on the image bearing member is developed while keeping the developer carrying member of an image forming apparatus in non-contact with the image bearing member. An example of an image forming apparatus employing such jumping development will be described on an image forming apparatus shown in FIG.
1
.
In the image forming apparatus shown in
FIG. 1
, a toner
8
kept in a developing container
3
is carried on a developer carrying member, e.g., a developing sleeve
10
. As the developing sleeve
10
is rotated in the direction of an arrow b shown in the drawing, the toner
8
carried thereon is transported to the developing zone facing a photosensitive member
1
serving as the image bearing member. In the course where the toner
8
is transported there, it is regulated by a doctor blade
9
kept in touch with the developing sleeve
10
, and is coated on the developing sleeve
10
in a thin layer. At the developing zone, the developing sleeve
10
and the photosensitive member
1
face each other, leaving a gap of from 50 to 500 &mgr;m between them. A development bias, formed by superimposing an alternating current on a direct current, is applied to the developing sleeve
10
from a bias power source
12
to cause the toner
8
coated on the developing sleeve
10
in a thin layer to fly and adhere to an electrostatic latent image formed on the photosensitive member
1
, thus the electrostatic latent image is rendered visible as a toner image.
There is a problem of smeared images when images are formed in an environment of high temperature and high humidity. The term “smeared image” refers to the phenomenon that a low-resistance substance adheres to the surface of a photosensitive drum, where electric charges at the part charged electrostatically on the image bearing member photosensitive drum run into latent image areas to spoil images. This smeared image may be caused by moisture condensation on the photosensitive drum surface. In many cases, however, it is caused by talc contained in transfer materials or by surface-active agents contained in OHT (overhead thin film), having adhered to the photosensitive drum surface.
The talc, which is often contained in commonly available transfer materials, reacts with ozone generated from a charging assembly, and an oxide thus formed combines with moisture ascribable to high humidity, so that a low-resistance-substance ozone product is formed on the image bearing member to cause smeared images.
Thus, the problem of smeared images tends to depend on transfer materials. In conventional a image forming apparatus, it has been difficult to solve the problem of smeared images while achieving formation of images with a high resolution and a high minuteness and achieving running stability.
It is proposed to make the photosensitive drum surface abradable with ease so that good images can be formed over a long period of time (Japanese Patent Application Laid-open Nos. 4-78984 and 1-206348). However, the problem of how to prevent smeared images can not well be solved only by designing materials for photosensitive drums.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image forming apparatus that can can avoid the difficulties of smeared images and can form stable and high-grade images.
Another object of the present invention is to provide an image forming apparatus that can avoid the difficulties, such as smeared images and the slip-through of external additives, while improving image density and can form stable and high-grade images.
Still another object of the present invention is to provide a process cartridge that can avoid difficulties, such as smeared images and the slip-through of external additives, can form stable and high-grade images, and also can be maintenance-free.
The above objects can be achieved by the image forming apparatus and process cartridge according to the present invention.
More specifically, the present invention provides an image forming apparatus comprising an image bearing member, a developer carrying member for carrying thereon a developer to transport the developer to a developing zone, and a regulation member provided in touch with the surface of the developer carrying member to regulate the coat weight of the developer carried thereon; the developer carrying member carrying and transporting the developer to the developing zone, and an electrostatic latent image formed on the image bearing member being developed and rendered visible while applying a development bias to the developer carrying member, wherein
the image bearing member comprises a conductive substrate and a photosensitive layer formed thereon, and the photosensitive layer contains at least one polycarbonate resin (I) having a viscosity-average molecular weight not more than 1.5×10
4
and at least one polycarbonate resin (II) having a viscosity-average molecular weight more than 1.5×10
4
; the polycarbonate resin (I) being contained in a proportion of from 30% by weight to 95% by weight based on the total weight of the polycarbonate resins (I) and (II); and
on the developer carrying member, the developer being in a coat weight not more than 1.5 mg/cm
2
at the developing zone after its regulation by the regulation member.
The present invention also provides a process cartridge comprising an image bearing member, a developer carrying member for carrying thereon a developer to transport the developer to a developing zone, and a regulation member provided in touch with the surface of the developer carrying member to regulate the coat weight of the developer carried thereon; the developer carrying member carrying and transporting the developer to the developing zone, and a means for developing and rendering visible an electrostatic latent image on the image bearing member while applying a development bias to the developer carrying member being set as one unit together with the above members so as to be detachably mountable to the main body of an image forming apparatus, wherein
the image bearing member comprises a conductive substrate and a photosensitive layer formed thereon, and the photosensitive layer contains at least one polycarbonate resin (I) having a viscosity-average molecular weight not more than 1.5×10
4
and at least one polycarbonate resin (II) having a viscosity-average molecular weight more than 1.5×10
4
; the polycarbonate resin (I) being contained in a proportion of from 30% by weight to 95% by weight based on the total weight of the polycarbonate resins (I
Inami Satoru
Kato Jun-ichi
Nakazono Yusuke
Shinohara Seiichi
Yoshida Masahiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Martin Roland
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