Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2002-03-21
2004-02-24
Royer, William J. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
Reexamination Certificate
active
06697585
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to electrophotographic printing devices and more specifically to the reduction of toner leakage through seals in these devices.
BACKGROUND
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form the desired image on the a print medium, which is usually some type of paper. While the toner particles are solid, their small size (on the order of 3-15 microns) results in highly fluid properties. Once the toner particles are is applied to the paper, the paper is advanced along the a paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner particles are is fused to the paper through a process of heat and pressure.
FIG. 1
is a diagram of typical laser printing device
100
employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles
101
are held in toner supply hopper
102
. Toner particles
101
are typically small plastic (e.g. styrene) particles on the order of 5 microns (10-6) meter in size. Agitator, or stirring blade,
103
is typically made of plastic or mylar and ensures toner particles
101
are uniformly positioned along developer sleeve
104
while inducing a negative charge onto the toner particles
101
in the range of −30 to −40 micro coulomb per gram (&mgr;C/g). Developer sleeve
104
rotates in a counterclockwise direction about an internal stationary magnet
105
which acts as a shaft. Toner particles
101
are attracted to the rotating developer sleeve
104
by the magnetic forces of stationary magnet
105
. Doctor blade
106
helps in charging toner particles
101
and metes out a precise and uniform amount of toner particles
101
onto developer sleeve
104
as its outer surface rotates external to toner supply hopper
102
. Developer sealing blade
107
removes excess toner particles
101
affixed to developer sleeve
104
as its outer surface rotates back into toner supply hopper
102
.
Primary Charging Roller (PRC)
108
conditions Organic Photo Conductor (OPC) drum
109
using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum
109
. Production of the uniform charge also has the effect of erasing residual charges left from the previous cycle.
A central component of the EP process is OPC drum
109
. OPC drum
109
is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PRC
108
. Initially, the unexposed surface of the OPC drum
109
is charged to a potential of approximately −600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC drum
109
. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the aluminum substrate.
Laser beam
110
exposes OPC drum
109
one scan line at a time at the precise locations that will receive toner particles
101
(paper locations which correspond to the image being printed). OPC drum
109
is discharged from −600 V to approximately −100 V at points of exposure to laser beam
110
, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles
101
are magnetically attracted to rotating developer sleeve
104
. Alternatively, if nonmagnetic toner is used, developer sleeve
104
may comprise a foam roller to mechanically capture toner particles
101
. In this case, an open cell foam roller may be included to apply toner particles
101
to developer sleeve
104
. The still negatively charged toner particles
101
held by developer sleeve
104
is are attracted to the relatively positively charged (i.e., less negatively charged) areas of the surface of OPC drum
109
and “jumps” across a small gap to the relatively positively charged latent image on OPC drum
109
creating a developed image.
Paper to receive the developed image from OPC drum
109
is transported along paper path
111
between OPC drum
109
and transfer roller
112
, with the toner particles
101
forming the developed image are transferred from the surface of OPC drum
109
to the paper. The transfer occurs by action of transfer roller
112
which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles
101
to move to the paper. Wiper blade
113
cleans the surface of the OPC drum
109
by scraping off the waste (untransferred) toner particles
101
into waste hopper
115
, while recovery blade
114
prevents the waste toner particles from falling back onto the paper. Fusing occurs as the paper, including transferred toner particles
101
is passed through a nip region between heated roller
116
and pressure roller
117
where the toner particles
101
is are melted and fused (or “bonded”) to the paper. Heated roller
116
and pressure roller
117
as a unit are referred to as the fuser assembly.
One design consideration with electrophotographic imaging devices such as laser printers and copying systems is the need to minimize the leakage of toner or toner particles
101
from toner supply hopper
102
. As shown in
FIG. 2
, in its normal position, developer sleeve
104
has an enclosed toner supply on one side of the seal
201
and is open to the internal structure of the toner cartridge on the other side of the seal
201
. Seals
201
in this area are incorporated in an attempt to reduce or eliminate toner leakage from toner supply hopper
102
.
In addition to leakage along the a roller, leakage sometimes occurs at the ends of developer sleeve
104
(FIG.
1
). Several methodologies have been used to reduce or eliminate such leakage. For example, i.e., some printers employ a foam or felt mechanical seal at the ends of developer sleeve
104
as a physical barrier to prevent toner particles
101
from leaking past the end of developer sleeve
104
and out of toner supply hopper
102
. Alternatively, when the toner includes magnetic particles, such as in some black and white toners, magnetic seals may be provided at the ends of developer sleeve
104
to attract and capture toner particles
101
and create a physical barrier, consisting of the toner particles
101
, to prevent additional toner particles
101
from leaking.
FIG. 2
shows another view of the configuration of developer sleeve
104
, toner buildup
203
and seal
201
. As shown, seal
201
is positioned between support
202
and developer sleeve
104
. Support
203
may be semicircular regions formed in the sidewalls of toner supply hopper
102
allowing a rear portion of developer sleeve
104
to intrude into the toner supply hopper
102
to receive toner particles
101
while an exposed frontal portion of the developer sleeve
104
provides toner particles
101
to the OPC drum
109
as previously described. Because of the fluidity of the toner particles
101
, as developer sleeve
104
rotates, toner particles
101
are forced into the region whereat seal
201
contacts developer sleeve
104
. This action causes toner buildup
202
and corresponding increased toner fluid pressure in the contact region causing the toner particles
101
to leak under, around and through seal
201
.
Accordingly, a need exists for a system and a method for reducing toner leakage in a toner cartridge.
SUMMARY OF THE INVENTION
The present invention is directed to a sealing mechanism for use in a toner c
Dougherty Patrick S.
Phillips Quintin T.
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