Electrophotography – Image formation – Development
Reexamination Certificate
1998-10-07
2001-05-08
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C399S284000
Reexamination Certificate
active
06229979
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a developing device for developing an electrostatic image on an image bearing member, for an image forming apparatus such as a copying machine or a printer of an electrophotographic type or electrostatic recording type.
In an electrophotographic type image forming apparatus, an electrostatic latent image formed on the image bearing member is visualized into a toner image by a developing device.
One of such a developing device is a dry type one component developing device of various type. In any of them, it is difficult to form a thin layer of toner which is a one-component developer, on a developer carrying member.
On the other hand, improvement of resolution of an image and a sharpness or the like are recently desired, and further improvement in the thin layer formation method is desired.
For example, as disclosed in Japanese Laid-open Patent Application No. SHO 54-43038, an elastic blade, functioning as a regulating member, of a material such as metal and rubber is contacted to a developing sleeve which is a developer carrying member, and the toner is passed through the contact portion between the elastic blade and the developing sleeve, by which a thin layer of the toner having a regulated thickness is formed, and sufficient triboelectric charge is applied to the toner by the friction in the contact portion.
In this case, when the non-magnetic toner is regulated by the elastic blade, a toner supply member for supplying the toner onto the developing sleeve is additionally required. In the case of magnetic toner, the toner can be supplied onto the developing sleeve by the magnetic force of the magnet in the developing sleeve, but in the case of non-magnetic toner, the supply of the toner is not possible by magnetic force.
Then, a developing device
50
as shown in
FIG. 15
has been proposed. In this developing device
50
, an elastic roller
55
of a foam member or a fur brush of polyurethane foam, sponge or the like is contacted to the developing sleeve
52
at a position upstream of an elastic blade
51
with respect to a rotational direction of the developing sleeve
52
, in a developing container
54
accommodating non-magnetic toner
53
as an one-component developer, and is rotated in a direction indicated by an arrow D, by which the toner
53
is supplied to the developing sleeve
52
.
The toner
53
supplied to the developing sleeve
52
is fed to the contact portion between the elastic blade
51
and the developing sleeve
52
with the rotation of the developing sleeve
52
, and is formed into a thin layer, and fed for development of an electrostatic latent image on a photosensitive member
1
which is an image bearing member. The toner
53
remaining on the developing sleeve
52
without being consumed for development, is removed by the elastic roller
55
, and a fresh toner
53
is supplied to the developing sleeve
52
by the elastic roller
55
, and this is repeated. When the material of the developing sleeve
52
is metal, it is not preferable to use a thin plate for an elastic blade
51
in view of wearing effect thereof, and it is desired to use a rubber material such as urethane or silicon to provide a thin toner layer.
With such a structure, a thin layer formation of non-magnetic toner on the developing sleeve is made possible.
FIG. 16
is a view of a developing device
50
of
FIG. 15
as seen from the photosensitive member
1
, wherein the developing sleeve
52
is omitted for better understanding, and the contact nip between the elastic blade
51
and the developing sleeve
52
is indicated by hatching lines.
As shown in
FIG. 16
, an end seal member
57
is provided in a gap between the opening of the developing container
54
and each of the opposite ends of the developing sleeve
52
, the end seal member
57
being of fiber material such as a wool felt or Teflon pile, or of polyurethane foam, sponge rubber or the like to prevent leakage of the toner through the gap between the developing container
54
and the opposite longitudinal end portions of the developing sleeve
52
; and in addition, as shown in
FIG. 16
, the elastic blade
51
is nipped between the developing sleeve
52
and the end seal member
57
at the opposite ends (in other words, by urging the back side of the elastic blade
51
by the end seal member
57
) to prevent the leakage of the toner at the opposite ends of the elastic blade
51
.
However, with such a structure, it is necessary to press-contact the end seal member
57
to the developing sleeve
52
with a quite high pressure to assure the sealing property, with the result that elastic blade
51
nipped between the developing sleeve
52
and the end seal member
57
is deformed as if it follows the peripheral surface of the developing sleeve
52
from the nip of the developing sleeve
52
at the opposite ends to the edge portion.
As a result, the longitudinally inside end portion of the elastic blade
51
tends to separate, and therefore, the developer layer formed on the developing sleeve
52
at these portions are thicker than the other portion, and the charging of the toner
53
becomes low. Thus, the charging is non-uniform in the longitudinal direction of the developing sleeve
52
, and therefore, when a voltage (developing bias) is applied to the developing sleeve
52
during the developing operation, and the toner
53
may transfer from the opposite ends of the developing sleeve
52
to the photosensitive member
1
, resulting in a foggy image, and/or in non-uniformity in the image density due to the non-uniformity of the amount of the charge of the toner on the developing sleeve
52
.
As a solution to this problem, it would be considered to provide an inclined cut portion at each of the opposite ends of the elastic blade. As shown in
FIG. 17
, a distance from a most downstream point, with respect to a rotational direction of the developing sleeve, of a nip between an elastic blade
58
and the developing sleeve
52
to the free end of the elastic blade
58
, is continuously reduced toward the end adjacent each of the opposite longitudinal ends of the elastic blade
58
, and at least the free end portion at the end portion is in the contact nip. Therefore, even if the longitudinally inside end portion of the elastic blade
51
separates, and therefore, the developer layer formed on the developing sleeve
52
at these portions are thicker than the other portion, as mentioned above, the toner leakage is prevented at the opposite ends of the elastic blade
58
and the developing sleeve
52
since the contact nip is small, and an edge contact tends to occur. In addition, the thin layer of the non-magnetic toner can be satisfactorily formed on the developing sleeve
52
, and the electrostatic latent image can be developed satisfactorily on the photosensitive member
1
(image bearing member).
However, when the developing operation is repeated may times with the developing device, the toner
53
tends to be packed at the opposite ends of the elastic blade
58
as compared with the central portion, since the pressure (force per unit area) is large in the end portions. By the packing, the elastic blade
58
is raised at the opposite ends of the nip with the result that the toner layer becomes gradually thick on lines. The electrical attraction force(mirror force) onto the developing sleeve
52
decreases, with the result of deposition of the toner
53
to the photosensitive member
1
as fog, or the toner
53
falls from the surface to the developing sleeve
52
, thus remarkably contaminating the inside of the image forming apparatus (toner leakage).
On the inclined cut portions of the elastic blade
58
at the opposite ends, the toner
53
fed by the rotation of the developing sleeve
52
is accumulated, and the toner
53
moves toward the ends with many developing operations repeated. Such toner
53
enters through the small gaps, formed by the end seal member
57
, each of the opposite ends of the elastic blade
58
and the developing sleeve
52
. As
Hashimoto Kouji
Hoshi Nobuharu
Ishii Yasuyuki
Oguma Toru
Sasaki Shin-ichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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