Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-08-31
2003-11-11
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C430S058050
Reexamination Certificate
active
06647230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image-forming apparatus employing an electrophotographic recording system having an exposure unit which radiates light modulated in accordance with image signals and a contact developing unit for developing electrostatic latent images formed by this exposure unit. More particularly, this invention relates to an image-forming apparatus which can prevent mismatching in the expression of density gradation and spots around line images from being caused by the shortage of charge quantity due to reversely charged toner. This invention also relates to a process cartridge used in the image-forming apparatus.
2. Related Background Art
In general, image-forming apparatus employing an electrophotographic recording system have a photosensitive member which is rotatively driven, a charging assembly which electrostatically charges the surface of the photosensitive member uniformly, an exposure means by which the surface of the photosensitive member is exposed to form an electrostatic latent image corresponding to image signals, a developing means by which the electrostatic latent image is developed with a toner to form a visible image, a transfer means by which the visible image is transferred onto recording paper, and a fixing means by which the visible image transferred onto the recording paper is fixed.
In this case, as the developing means, two types are known in which a developing roller comes into contact with the photosensitive member to perform development (hereinafter called a contact developing system) and the developing roller performs development in a state of noncontact with the photosensitive member (hereinafter called a noncontact developing system). The contact developing system includes a type in which, as disclosed in Japanese Patent Applications Laid-Open No. 62-223711 and No. 1-239566, the developing roller is elastically brought into contact with the surface of the photosensitive member and a type in which, as disclosed in Japanese Patent Applications Laid-Open No. 4-247478, as the developing roller a roller comprised of an elastic member is provided with a resin thin-sheet sleeve on its surface.
FIG. 4
is a diagrammatic cross-sectional view showing the construction of an example of a known image-forming apparatus employing as the developing means the contact developing system (hereinafter this apparatus is called a conventional apparatus).
In
FIG. 4
, reference numeral
101
denotes a drum-shaped photosensitive member (photosensitive drum);
102
, a contact developing roller;
103
, a developing unit;
104
, a transfer roller;
105
, a charging roller;
106
, an exposure means;
108
, a toner feed roller;
109
, a developing blade; and
110
, a toner.
The photosensitive drum
101
is constituted of a drum-shaped metallic crude pipe and a photosensitive material applied to its surface. When operated, it is rotatively driven around a rotating shaft in the direction of an arrow shown in the drawing, by means of a drive unit (not shown). The developing roller
102
and the developing unit
103
constitute the developing means. The developing roller
102
is so constructed and disposed as to be always in contact with the surface of the photosensitive drum
101
and rotatable with the rotation of the photosensitive drum
101
. The developing unit
103
has a developing blade
109
so constructed as to come into touch with the developing roller
102
. The toner
110
is made to pass the part of the developing blade
109
touching the developing roller
102
, and the quantity of the toner
110
carried on the developing roller
102
is regulated to form a thin layer of the toner
110
on the developing roller
102
. At the same time, the friction caused at the touching part imparts a sufficient triboelectric charges (triboelectricity) to the toner
110
. Also, in the developing unit
103
, the toner feed roller
108
, coming into contact with the developing roller
102
, is provided at a position which is on the upstream side of the developing blade
109
in the direction of the rotation of the developing roller
102
, to feed the toner
110
to the developing roller
102
so as to be carried thereon.
The transfer roller
104
constitutes the transfer means, and is so constructed that it is rotated in contact with the photosensitive drum
101
and the recording paper (not shown) passes the contact zone formed between the photosensitive drum
101
and the transfer roller
104
at the time of transfer.
The charging roller
105
electrostatically charges the surface of the photosensitive drum
101
uniformly at a constant potential by means of a charge voltage generation power source (not shown). It is kept in pressure contact with the surface of the photosensitive drum
101
at a stated pressure to electrostatically charges the surface of the photosensitive drum
101
while being rotated with the rotation of the photosensitive drum
101
.
The exposure means
106
feeds light signals modulated in accordance with image signals sent from an image signal source (not shown). It provides the surface of the photosensitive drum
101
with the light signals to form thereon an electrostatic latent image corresponding to the image signals.
How the conventional apparatus is operated is described below. To describe the whole operation of the conventional apparatus, the photosensitive drum
101
rotated in the direction of an arrow a shown in
FIG. 4
is first uniformly charged on its surface by means of the charging roller
105
, and then an electrostatic latent image corresponding to image signals is formed on its surface by means of the exposure means
106
. Subsequently, the electrostatic latent image is developed by making the toner
110
adhere thereto by means of the developing roller
102
to which development voltage has been applied from the charge voltage generation power source (not shown), so that a visible image corresponding to this electrostatic latent image is formed on the surface of the photosensitive drum
101
. This visible image formed on the surface of the photosensitive drum
101
is transferred onto the recording paper by means of the transfer roller
104
. The visible image thus transferred is fixed onto the recording paper and thereafter taken out as a recorded image together with the recording paper. Meanwhile, the surface part of the photosensitive drum
101
having passed the part of the transfer roller
104
is cleaned to remove the toner through a cleaning means (not shown). Then, the process described above is again carried out repeatedly.
The construction of a photosensitive layer of the photosensitive drum
101
is roughly grouped into a single layer type containing both a charge-generating material and a charge-transporting material in the same layer and a multilayer type having a charge generation layer containing a charge-generating material and a charge transport layer containing a charge-transporting material.
An electrophotographic photosensitive member having the photosensitive layer of a multilayer type includes a photosensitive member comprising a substrate and superposed thereon the charge generation layer and the charge transport layer in this order. The charge transport layer is formed by applying a solution prepared by dissolving in a resin having film-forming properties a charge-transporting material including polycyclic aromatic compounds having a structure such as a biphenylene, anthracene, pyrene or phenanthrene structure in the main chain or side chain; nitrogen-containing ring compounds such as indole, carbazole, oxazole and pyrazoline; hydrazone compounds and styryl compounds; followed by drying. The resin having film-forming properties may include polyester, polycarbonate, polystyrene, polymethacrylate and polyarylate. The charge generation layer is formed by coating the substrate with a dispersion prepared by dispersing in a resin such as polyvinyl butyral, polystyrene, polyvinyl acetate or acrylic resin a charge-generating material including azo pigme
Ishii Yasuyuki
Kobayashi Tetsuya
Nakagawa Tsuyoshi
Uehara Shinji
Braun Fred L.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Image-forming apparatus for use with negatively-charged... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image-forming apparatus for use with negatively-charged..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image-forming apparatus for use with negatively-charged... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3161695