Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-03-13
2003-03-04
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S252000
Reexamination Certificate
active
06529699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine, and an electrophotographic printer and the like, and a process cartridge.
2. Related Background Art
Conventionally, as electrophotography, there has been proposed a method in which an electrical latent image is formed on a photosensitive body having a photo-conductive surface in many ways, the latent image is developed with toner as a visualized image or toner image, the toner image is transferred onto a transfer material such as paper on demand, and, then, the toner image is fixed to the transfer material by heat and pressure, thereby obtaining a copy.
Nowadays, since improvement in resolving power and sharpness of an image have been requested, formation of a thin toner layer and associated devices must be developed more and more, and various methods for achieving this have been proposed.
For example, recently, there has been proposed a developing method of a non-magnetic one-component DC contacting type in which a semi-conductive developing roller or a developing roller having a dielectric surface layer is used and development is effected by contacting such a developing roller with a surface of a photosensitive body.
FIG. 10
shows such a developing method of a non magnetic one-component DC contacting type. In this method, a photosensitive drum
21
and a developing roller
81
contact each other and are rotated in the directions shown by the arrows A, B, respectively. The photosensitive drum
21
is charged by a charging roller
2
, and a latent image is formed on the photosensitive drum
21
by a laser beam from an exposing unit
5
. The latent image is visualized by a developing apparatus
80
. Thereafter, toner
84
on the photosensitive drum
21
that is developed is transferred onto a transfer material
9
by a transfer roller
6
and then the toner image is fixed to the transfer material by a fixing apparatus
7
. On the other hand, residual toner
84
remaining on the photosensitive drum
21
that was not transferred is removed by a cleaning blade
3
and then is collected into a cleaning container
4
.
In the developing apparatus
80
, there is provided an elastic roller
82
disposed within a developing container
85
containing toner
84
as one-component developer and urged against the developing roller
81
at an upstream side of an elastic blade
83
in a rotational direction of the developing roller
81
, and, by rotating tho elastic roller in a direction shown by the arrow D, the toner
84
is supplied onto the developing roller
81
. The toner
84
supplied to the developing roller
81
is carried as the developing roller
81
is rotated, and then the toner is charged by friction in an abut area between the elastic blade
83
and the developing roller
81
, thereby forming a thin layer. The thin toner layer
84
is shifted by the developing roller
81
and is supplied to the electrostatic latent image in a nip between the developing roller and the photosensitive drum
21
. Thereafter, the toner
84
remaining on the photosensitive drum (which was not applied to development in the nip between the photosensitive drum
21
and the developing roller
81
) is removed by the elastic roller
82
, and at the same time, as mentioned above, new toner
84
is supplied onto the developing roller
81
. Such operations are repeated.
However, the above-mentioned conventional developing method of a non-magnetic one-component DC contacting type has the following problem.
FIG. 11
shows an image gradient of 64 gradations in 600 dpi in the above-mentioned method. The conventional photosensitive drum
21
is an organic photosensitive body of a laminated type and includes a charge transport layer having a thickness of 25 ,um. As can be seen from
FIG. 11
, in this method in which the development is effected by using DC voltage, density can quickly rise, but, image density quickly enters a saturated condition, and, thus, even when the gradient is improved, an image having a substantially high gradient may not be obtained.
To avoid this, if the charging amount of toner is increased, although the image density can moderately be increased, in the conventional example shown in
FIG. 11
, an optimum range in which the saturation of density and the desired gradient become compatible is only −30 &mgr;C/g, which is vers narrow.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image forming apparatus and a process cartridge in which an optimum range of the toner charging amount is wide and an excellent gradient can be obtained.
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“Persistant Internal Polarization (Photoelectrets),” Berg, Focal Press Limited, Zurich Switerzland, pp. 94-116.
Ishii Yasuyuki
Kobayashi Tetsuya
Nakagawa Tsuyoshi
Uehara Shinji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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