Electrophotography – Image formation – Development
Reexamination Certificate
2001-07-27
2002-10-29
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S279000
Reexamination Certificate
active
06473588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a development roller and a developer unit employing the development roller, designed for electrophotographic image forming apparatus such as copying machines, printers, and facsimile machines.
2. Discussion of Background
There is a tendency to simplify the maintenance of electrophotographic image forming apparatus such as copying machines, printers, and facsimile machines, in particular, small-sized units. For this purpose, a developer unit for developing latent electrostatic images formed on an image-bearing member such as a photo-conductor, sensitized paper, or recording sheet using a mono-component developer is disclosed in Japanese Laid-Open Patent Application 53-3233. In fact, that kind of developer unit has been put to practical use.
FIG. 5
is a schematic view showing one embodiment of such a conventional development unit. In
FIG. 5
, reference numeral
101
indicates a photoconductor drum, which comprises a surface layer portion A and a base member B. The surface layer portion A serves as an image-bearing member. In the base member B, which is provided with a function of supporting the image-bearing member A, an electroconductive rubber layer
103
with relatively large elasticity and a flexible metal foil layer
104
such as an aluminum foil are successively attached to a metallic drum
102
. The surface layer portion A comprises a photoconductive insulator layer
105
, which is formed by, for example, depositing a metal such as selenium on the metal foil layer
104
of the base member B.
A development roller
106
is brought into pressure contact with the surface of the above-mentioned photo-conductor drum
101
. The development roller
106
comprises a metallic core roll
107
and an elastic layer
108
which is provided around the metallic core roll
107
and made of a synthetic rubber or urethane foam, designed to have electroconductivity.
This type of conventional developer unit has the problem that a plasticizer and low-molecular-weight material contained in the elastic layer
108
of the development roller
106
may cause bleeding therefrom and contaminate the surface layer portion A of the photo-conductor drum
101
. Further, toner particles are undesirably attached to the surface of the elastic layer
108
of the development roller
106
as a result of the phenomena of tacking and filming, As a countermeasure against such problems, it is proposed to coat the elastic layer
108
of the development roller
106
with a surface layer (not shown) comprising a resin that is readily releasable from the toner. The above-mentioned proposal is made to prevent the bleeding of the plasticizer or low-molecular-weight material from the elastic layer of the development roller, and at the same time, to prevent the tacking and filming of toner to the development roller.
A bias source
109
is connected across the core roller
107
of the development roller
106
and the base member B of the photoconductor drum
101
. Above the development roller
106
, a hopper
111
containing a mono-component nonmagnetic toner
110
is disposed with an opening at the bottom of the hopper
111
being positioned at a predetermined distance from the surface of the development roller
106
. A triboelectric charging member
112
is attached to the inner wall on the right side of the hopper
111
. A toner layer formed around the development roller
106
is leveled by a leveling member
113
in such a configuration that the surface of the leveling member
113
is brought into pressure contact with the surface of the development roller
106
. The leveling member
113
, which is prepared by successively attaching a rubber layer
115
and a triboelectric charging layer
116
onto a metallic roll
114
, is not rotatably mounted, but fixed.
According to the development process effected by the developer unit of
FIG. 5
, a thin toner layer retained on the surface of the development roller
106
is brought into contact with the photoconductor drum
101
bearing latent electrostatic images thereon. The toner is transferred to the photoconductor drum
101
in accordance with the development field, so that the latent electrostatic images are developed and made into visible toner images. In the case of the development roller
106
of
FIG. 5
, the polarity and the charge quantity of the toner
110
are controlled by triboelectric charging, that is, by the contact of the toner with the triboelectric charging member
112
and the contact of the toner with the triboelectric charging layer
116
of the toner supply layer
113
. The toner
110
is selectively transferred from the development roller
106
to the photoconductor drum
101
depending upon the polarity of the charged toner and the development field on the photoconductor drum
101
. Namely, the toner
110
is selectively deposited on an image portion determined by the latent electrostatic images formed on the photoconductor drum
101
. The development unit as shown in
FIG. 5
has the advantage that color toners are available for achieving color image formation because a magnetic material is not necessary for preparation of the toner composition.
Japanese Patent Publication 64-1022 discloses another developer unit. This development unit employs a mono-component non-magnetic toner and is designed to feed a development roller with the toner by means of a magnetic brush.
FIG. 6
is a schematic cross sectional view showing one embodiment of the above-mentioned conventional developer unit.
In a developer unit
203
shown in
FIG. 6
, as a magnetic roller
208
is driven in rotation in the direction indicated by the arrow, a magnetic carrier is magnetically attracted to the magnetic roller
208
so as to charge non-magnetic toner particles. A magnetic brush
212
is thus formed around the magnetic roller
208
. A development roller
211
stands between the magnetic roller
208
and an electrostatic-image-bearing member
201
. Charged toner particles
207
electrostatically clinging to the magnetic brush
212
are separated therefrom and supported by the development roller
211
in order to develop an electrostatic image formed on the electrostatic-image-bearing member
201
. Namely, the non-magnetic toner particles
207
can be shifted from the magnetic brush
212
to the development roller
211
by the action of an alternating field formed between the magnetic roller
208
and the development roller
211
. In the developer unit
203
, the toner is initially charged by the principle of two-component development, and the charged toner
207
is carried to the development roller
211
by the magnetic brush
212
formed around the magnetic roller
208
. Such a development system requires no member coming in contact with the development roller
211
, thereby reducing the stress applied to the toner particles
207
deposited on the development roller
211
. This makes it possible to secure the developer unit
203
in the image forming apparatus without any replacement.
The conventional developer unit as shown in
FIG. 5
produces various problems, as mentioned above. Namely, toner particles are deposited on the surface of the leveling member for regulating the toner thin layer, in particular when the leveling member is in the form of a blade. The toner filming is caused around the development roller. Further, the surface of the development roller readily exhibits stripe-like scratches with time. Furthermore, the toner is caused to deteriorate because of the application of stress thereto, with a result that the charge quantity of toner and the deposition amount of toner on the development roller change with time. In addition, toner deposition on the background takes place at the time of replenishment of toner. In consideration of occurrence of those problems, the developer unit has been necessarily designed as a detachable cartridge that can be replaced after several tens of thousands of prints have been made. To secure the development unit has been found to be impossible.
To s
Brase Sandra
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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