Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-02-03
2001-03-06
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S312000
Reexamination Certificate
active
06198900
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image forming apparatuses including transfer means for transferring a toner image formed on a photosensitive body onto a recording medium, and/or charging means for charging the photosensitive body, for use in the printing section of digital copying machines and facsimile machines, digital printers, plotters, etc., and also relates to charge supply devices suitable for use as, for example, the transfer means and the charging means.
BACKGROUND OF THE INVENTION
Various types of image forming apparatuses for forming an image on a recording medium on the basis of an electrostatic latent image (charge pattern) formed on a photosensitive body, have been conventionally proposed. Among the proposed apparatuses, for example, an image forming apparatus disclosed in Japanese Laid-open Patent Application (Tokukaisho) No. 49-24139/1974 adopts a so-called electrostatic transfer system of developing an electrostatic latent image after transferring the electrostatic latent image formed on a photosensitive body to a recording medium by transfer means. The following description will explain this image forming apparatus.
As illustrated in
FIG. 13
, the image forming apparatus of this document includes a photosensitive body
101
for carrying an electrostatic latent image thereon. The photosensitive body
101
is formed by three layers, namely, a high insulating layer
101
a
, photoconductive layer
101
b
, and electrode layer
101
c
, arranged in this order from the outer side.
Disposed around the photosensitive body
101
is a primary corona discharger
102
for charging the surface of the photosensitive body
101
by applying a voltage of a predetermined polarity to the surface of the photosensitive body
101
by corona discharge, a secondary corona discharger
103
for charging the surface of the photosensitive body
101
by applying a voltage of the opposite polarity to that of the voltage applied by the primary corona discharger
102
, to the surface of the photosensitive body
101
by corona discharge, and an entire-surface exposing light source
104
.
With the use of the first corona discharger
102
and secondary corona discharger
103
which are not in contact with the photosensitive body
101
as means for charging the photosensitive body
101
, it is possible to prevent movement of charges on the surface of the photosensitive body
101
and lowering of the strength of an electrostatic latent image due to the movement of charges, which occur in a structure where the surface of the photosensitive body
101
is charged by bringing the electrode into contact with the photosensitive body
101
.
A transfer section
105
is provided on the downstream side of the entire-surface exposing light source
104
, in a rotating direction (clockwise direction in
FIG. 13
) of the photosensitive body
101
. The transfer section
105
includes a transfer belt
106
pressed against the photosensitive body
101
via a transfer sheet
110
, and two transfer rollers
107
a
,
107
b
for stretching the transfer belt
106
therebetween. Provided on the sheet feeding side of the transfer section
105
are feed rollers
108
a
,
108
b
for transporting the transfer sheet
110
to the transfer section
105
while sandwiching the transfer sheet
110
therebetween. On the other hand, provided on the sheet output side of the transfer section
105
are feed rollers
109
a
,
109
b
for outputting the transfer sheet
110
having an electrostatic latent image transferred thereto from the transfer section
105
and transporting the output transfer sheet
110
to a developing section (not shown) while sandwiching the transfer sheet
110
therebetween.
In this structure, when the surface of the photosensitive body
101
is uniformly charged in a predetermined polarity by the primary corona discharger
102
, a light image is projected onto the photosensitive body
101
while applying a voltage of the opposite polarity by the secondary corona discharger
103
, thereby forming on the highly insulating layer
101
a
of the photosensitive body
101
an electrostatic latent image corresponding to the light image. Subsequently, the surface of the highly insulating layer
101
a
is illuminated with a light beam from the entire-surface exposing light source
104
so as to release permanent internal polarization in the photoconductive layer
101
b
. As a result, the variation of charge in the photosensitive body
101
is stabilized immediately, and the electrostatic latent image formed according to the light image is stabilized.
Thereafter, the electrostatic latent image is transported to a transfer region between the photosensitive body
101
and the transfer belt
106
by a rotation of the photosensitive body
101
, and transferred to the transfer sheet
110
transported to the transfer region by the transport rollers
108
a
,
108
b
, and the transfer belt
106
. After separating the transfer sheet
110
from the photosensitive body
101
, the transfer sheet
110
is output from the transfer section
105
by the transport rollers
109
a
,
109
b
, and transported to a developing section.
By the way, in such an image forming apparatus adopting the electrostatic transfer system, it is likely that distorted electrostatic latent image is transferred to the transfer sheet
110
due to non-uniformity of the contract pressure between the transfer belt
106
and photosensitive body
101
, etc. As a result, variations in the strength of the transferred image on the transfer sheet
110
occur. Moreover, in the above-mentioned structure, since development is performed after the transfer of the electrostatic latent image to the transfer sheet
110
, the transfer sheet
110
is likely to get dirty.
In resent years, therefore, development of image forming apparatuses adopting a development transfer system, in which an electrostatic latent image formed on a photosensitive body is developed into a visible image in advance on the photosensitive body with a developer such as toner and then the visible image is transferred to a recording medium, has been actively carried out.
However, in an image forming apparatus of typical structure employing the development transfer system, as illustrated in
FIG. 14
, for example, when a high electric potential is applied to a transfer roller
201
as transfer means so as to perform image formation at a high speed, toner
204
on a photosensitive body
203
flies toward a sheet
202
, i.e., so-called scattering of toner
204
occurs, before the sheet
202
is transported to a transfer position between the transfer roller
201
and the photosensitive body
203
and comes into contact with the photosensitive body
203
. As a result, the outline of the transferred toner image is blurred, and thus the image quality deteriorates. The following description will explain the theory of occurrence of the scattering of toner.
Here, it is assumed that a straight line OQ′ connecting a center O of the rotation axis of the transport roller
201
and a point Q′ at which scattering of the toner
204
occurs, the point Q′ being located on the upstream side of a nip region of the surface of the photosensitive body
203
along a rotating direction (clockwise direction in
FIG. 14
) of the photosensitive body
203
, is divided into two straight lines OP′ and P′Q′ by a point P′ on the surface of the transfer roller
201
, and regions including the straight lines OP′ and P′Q′ are denoted as region P and region Q, respectively.
Moreover, suppose that the lengths of the straight lines OP′ and P′Q′ are d
p
and d
Q
, the electric potentials applied to the regions P and Q are V
P
and V
Q
. and electric fields formed in the regions P and Q are considered to be formed along the straight lines OP′ and P′Q′ as shown in FIG.
14
and denoted by E
p
and E
Q
, respectively, for simplification purposes, the electric fields E
P
and E
Q
are given by the lengths d
p
and d
Q
and the electri
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Grainger Quana M.
Sharp Kabushiki Kaisha
Tucker David A.
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