Electrophotography – Image formation – Development
Reexamination Certificate
2002-07-30
2004-05-18
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C399S283000, C399S284000
Reexamination Certificate
active
06738593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a developing device for use in an image forming apparatus such as a copying machine or a printer using a recording method of the electrophotographic type or the electrostatic recording type.
2. Description of Related Art
FIG. 9
of the accompanying drawings is a schematic cross-sectional view of a printer of the electrophotographic type.
A usually drum-shaped electrophotographic photosensitive member
150
(hereinafter referred to as the photosensitive drum
150
) as a latent image bearing member is uniformly charged by a primary charger
151
. Next, light is applied from an exposing device
152
onto the photosensitive drum
150
correspondingly to image information inputted from an external device to thereby form a latent image. This electrostatic latent image on the photosensitive drum
150
is made into a visible image, i.e., a toner image, by a developing device
160
by a developer T (hereinafter referred to as the toner) having the same triboelectrification polarity as the voltage applied from the primary charger
151
. The toner image is transferred to a transferring material P by a transferring charger
153
. The transferring material P is separated from the photosensitive drum
150
and subsequently is conveyed to a fixing device
155
, and the toner image thereon is fixed thereby and thereafter becomes a permanent image. Also, any toner T not transferred by the transferring charger
153
but remaining on the photosensitive drum
150
is removed by a cleaning device
154
, and the photosensitive drum
150
is used for the next image forming process.
The nonmagnetic monocomponent developing device
160
will be described here in detail with reference to
FIGS. 10A and 10B
of the accompanying drawings. The construction of the nonmagnetic monocomponent developing device
160
will first be shown.
In the nonmagnetic monocomponent developing device
160
, generally gravity is utilized (
FIG. 10A
) or an agitating member is used (
FIG. 10B
) to carry a sufficient toner T to a developing portion having a developing roller
161
as a developer bearing member and a roller
162
(hereinafter referred to as the RS (remove and supply) roller) for supplying and removing the toner T onto and from the developing roller
161
. Accordingly, the positional relationship between the developing portion and a toner containing portion becomes such that the developing portion is disposed downwardly of the toner containing portion or at a horizontal position with respect to the direction of gravity.
The toner containing portion has the toner T which is an insulative monocomponent developer and an agitating member
164
. In this example, the toner T is of a negatively chargeable property and is a negatively chargeable nonmagnetic toner containing a pigment of one of yellow, magenta, cyan and black colors. As regards the agitating member
164
(FIG.
10
B), a first toner agitating member
164
and a second toner agitating member
165
each comprising a plate worked into one of various shapes or a screw or the like are rotated to thereby carry the toner T in the toner containing portion to the developing roller
161
. The number of the agitating members need not be two, but may be any number if they can carry the toner T from the end portion of a developing container to the vicinity of the developer bearing member
161
in accordance with one of the various constructions of the developing device
166
.
In
FIG. 10B
, a developing container partition plate
166
is formed with a proper height so that a constant amount of toner may always be supplied onto the RS roller
162
near the developing roller
161
.
In the nonmagnetic monocomponent developing method, the supply of the toner T by a magnetic force becomes impossible and therefore, the RS roller
162
made of urethane sponge is brought into contact with the developing roller
161
. The RS roller
162
is rotated in a counter direction at the nip portion with the developing roller
161
to thereby supply the toner T onto the developing roller
161
and at the same time, removes the toner T on the developing roller
161
which has not been used for development even if it has passed the position opposed to the photosensitive drum
150
.
A regulating blade
163
made of an elastic material such as urethane rubber as a toner amount regulating member (layer thickness regulating member) abuts against the developing roller
161
to thereby regulate the toner T on the developing roller
161
and form a thin toner layer, and prescribes the amount of toner T to be carried to a developing area (the position opposed to the photosensitive drum
150
). The amount of toner T carried to the developing area is determined by the abutment pressure, the abutment length of the regulating blade
163
contacting with the developing roller
161
.
The regulating blade
163
is adhesively secured or welded onto a thin metal plate of phosphor bronze, stainless!steel or the like having a thickness of several hundreds of &mgr;m, and the regulating blade
163
is a chip blade made to uniformly abut against the developing roller
161
by the resiliency of the thin metal plate. At this time, the abutment condition of the regulating blade
163
is determined by the material, thickness, amount of entry and set angle of the thin metal plate.
The toner T carried to the developing area, as in the aforedescribed magnetic monocomponent developing method, adheres to the latent image on the photosensitive drum
150
to thereby visualize the latent image as a toner image.
According to the above-described monocomponent developing method, it becomes possible to form a thin toner layer suited for development by a simple construction and therefore, the downsizing and simplified maintenance of the electrophotographic apparatus are possible.
The above-described monocomponent developing device
160
, however, has suffered from the problem that as image outputting is repeated for a long period of time, image density lowers and the dot reproducibility of halftone image portions lowers.
A main factor which gives rise to the above-noted problem is the deterioration of the toner T. The deterioration of the toner T refers to the aggravation of the developing characteristic such as a reduction in the chargeability of the toner T and an increase in the agglutinability of the toner T caused by an extraneous additive present on the surface of the toner T being embedded in a toner T binder.
The cause of the above-described deterioration of the toner T will be described below.
In the monocomponent developing device
160
, the main cause of the deterioration of the toner T is what is called frictional contact deterioration. As described in the conventional art, in the monocomponent developing method, the photosensitive drum
150
and the developing roller
161
, the developing roller
161
and the regulating blade
163
, and the developing roller
161
and the RS roller
162
are brought into contact with each other with predetermined pressure with a view to output images of high quality. When the toner T passes between these, the values of physical properties including chargeability are changed by stress and frictional heat. Here, it is said that the temperature to which the toner T rises by frictional heat when it passes the developer regulating blade
163
reaches several tens of centigrade degrees or higher regarding a microscopic area called the surface of the toner T.
Also, when the circulation of the toner T in the developing device
160
is bad, the deterioration of the toner T is promoted. When the toner T once passed between the photosensitive drum
150
and the developing roller
161
and removed by the RS roller
162
is immediately supplied again to the developing roller
161
by the RS roller
162
, the surface temperature of the toner T rises further by the influence of continuous stress and frictional heat and at last, it locally fuses the surface of the toner T to thereby promote the deterioration of
Kanari Kenji
Kawamura Takeshi
Moriya Shuji
Nakagawa Ken
Osada Hikaru
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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