Electrophotography – Image formation – Charging
Reexamination Certificate
2001-07-05
2003-05-13
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Charging
C399S285000
Reexamination Certificate
active
06564027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and the like, utilizing an electrophotographic or electrostatic recording system.
2. Description of the Related Art
In conventional image forming apparatuses, such as copying machines, printers and the like, a latent image formed on an image bearing member comprised of an electrophotographic photosensitive body or an electrostatic recording dielectric body is visualized by using toner as developer, which is powder. Recently, in order to cope with compactness, simplification, energy reduction and environmental problems, an image forming apparatus in which a cleaning container or a waste toner container is omitted or in which generation of ozone due to discharging is reduced has been noticed.
Now, as an example, a cleanerless image forming apparatus of a reversal developing system with nonmagnetic negatively electrified toner using noncontact developing and noncontact electrifying type will be described with reference to FIG.
6
.
FIG. 6
is a sectional view showing a schematic construction of a conventional image forming apparatus using dry type one-component developing apparatus.
As shown in
FIG. 6
, such an image forming apparatus comprises a photosensitive drum
101
as a latent image bearing member rotated in a direction shown by the arrow p, an electrifier
102
, an exposing device
103
for supplying image information, a developing device
104
, a transferring device
105
as transferring means and a fixing device
106
.
The developing device
104
includes a developing roller
110
as a developer carrying member rotated in a direction shown by the arrow q to carry toner as developer to an opposed area between the photosensitive drum
101
and the developing roller. The developing roller
110
is a rigid body having conductivity, and a gap between the developing roller and the photosensitive drum
101
is selected to be about 300 &mgr;m. Further, around the developing roller
110
, there are provided a peeling roller
111
rotated in a direction shown by the arrow r and serving to supply nonmagnetic one-component toner onto the developing roller
110
and to peel the toner from the developing roller
110
, a regulating blade
112
for applying desired electrifying amount to the toner on the developing roller
110
and for regulating a toner amount, and a developing bias voltage power source
113
for applying developing bias obtained by overlapping an AC voltage and a DC voltage to the developing roller
110
. In this example, a DC voltage of −350 V and rectangular waveform AC voltage having a frequency of 1800 Hz and peak-to-peak voltage of 1600 V are applied to the developing roller
110
from the developing bias voltage power source
113
. Further, the peeling roller
111
is constituted by forming a foam sponge around a metallic core support shaft.
The electrifier
102
includes an electrifying roller
120
as electrifying means rotated in a direction shown by the arrow s and having a conductive metal core (not shown) and a conductive elastic layer (not shown) covering the metal core, and an electrifying bias voltage power source
121
for applying a DC developing bias voltage to the electrifying roller
120
. In this example, a DC voltage of −600 V is applied to the electrifying roller
120
from the electrifying bias voltage power source
121
. The electrifying roller
120
is contacted with the photosensitive drum
101
and is rotated with peripheral speed difference with respect to the photosensitive drum. In this example, by using the photosensitive drum having a charge injecting layer on the surface thereof and the electrifying roller having low resistance, the photosensitive drum can be electrified with potential substantially the same as the electrifying bias voltage without discharging.
As shown in
FIG. 6
, the photosensitive drum
101
is rotated in the direction p and is uniformly charged to −600 V on the surface thereof by the electrifying roller
120
, and, thereafter, an electrostatic latent image is formed on the photosensitive drum
101
by the exposing device
103
. The electrostatic latent image is visualized as a toner image by the toner carried by the developing roller
110
opposed to and contacted with the photosensitive drum
101
from the developing device
104
. Thereafter, the toner image on the photosensitive drum
101
is transferred onto a transfer material
107
as a recording medium such as paper or OHP sheet by the transferring device
105
. Then, by the fixing device
106
, the toner image is dissolved and ultimately fixed onto the transfer material
107
.
On the other hand, after the transferring, residual toner (referred to as “transfer-residual toner” hereinafter) remaining on the photosensitive drum
101
is often electrified with weak positive polarity because it is subjected to the transferring bias voltage. When the transfer-residual toner reaches an abut area (referred to as “electrostatic charge nip” or “electrifying nip” hereinafter) between the electrifying roller
120
and the photosensitive drum
101
, the transfer-residual toner is returned to negative polarity while being subjected to friction and agitating and is carried to a developing station by the rotation of the photosensitive drum
101
. The toner carried to the developing station is collected on the developing roller simultaneously with the developing and is used again for visualizing a new electrostatic latent image.
However, in the above-mentioned conventional image forming apparatus, there may arise the following problem during image formation.
In such an image forming apparatus, at the developing station, an electric field for biasing the toner from the photosensitive drum to the developing roller with respect to an image portion and a nonimage portion on the photosensitive drum and an electric field for biasing the toner from the developing roller to the photosensitive drum with respect to the image portion and the nonimage portion on the photosensitive drum are in generated alternately. When the electric field for biasing the toner from the developing roller to the photosensitive drum is being applied to the developing roller, after the electrostatic latent image on the photosensitive drum passes the developing area, the toner will also be adhered to the nonimage portion. Consequently, during the transferring, a portion of the transfer material corresponding to the nonimage portion is contaminated by the toner, with the result that a high quality image output cannot be attained.
Further, when the negatively electrified toner passed through the electrifying nip is collected at the developing station, since the electric field for biasing the toner from the developing roller to the photosensitive drum is generated, the toner cannot be collected completely.
To solve the above problem, it is considered that a developing method is improved as a contact developing system in which an elastic developing roller to which only DC voltage is applied is contacted with the photosensitive drum. In this case, DC voltage of −350 V is applied to the developing roller.
As a result, since the electric field for biasing the toner from the developing roller to the photosensitive drum is always generated with respect to the image portion on the photosensitive drum and the electric field for biasing the toner from the photosensitive drum to the developing roller is always generated with respect to the nonimage portion on the photosensitive drum, the toner is not adhered to the nonimage portion, thereby achieving a high quality image output.
Further, when the toner passed through the electrifying nip is collected at the developing station, since the electric field for biasing the toner from the photosensitive drum to the developing roller is always generated, the toner can be collected completely.
However, at a contact area (referred to as “developing nip” hereinafter) between the developing roller and the p
Haraguchi Manami
Sakaizawa Katsuhiro
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Image forming apparatus 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, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3009434