Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2002-03-21
2003-11-25
Braun, Fred L (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
Reexamination Certificate
active
06654576
ABSTRACT:
TECHNICAL FIELD
The present invention is related generally to toner cartridges for imaging devices and, more particularly, to the reduction or elimination of toner leakage from such 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 print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller that is engaged by a mating pressure roller. As the paper passes between the rollers, toner 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
is 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 such as mylar and ensures toner particles
101
are uniformly positioned along developer sleeve
104
while inducing a negative charge onto the toner particles in the range of −30 to −80 micro coulomb per gram (&mgr;c/g). Developer sleeve
104
rotates in a counterclockwise direction about an internal stationary magnet
105
acting 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
charges the toner 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
. 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
and prevents toner particles
101
from falling out of toner supply hopper
102
onto paper, along the length of developer sleeve
104
.
Primary Charging Roller (PCR)
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 by PCR
108
also has the effect of erasing residual charges left from any previous printing or transfer cycle.
A critical 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 PCR
108
. Initially, the unexposed surface potential of the OPC is charged to 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. 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 underlying aluminum substrate.
Scanning laser beam
110
exposes OPC drum
109
one line at a time at the precise locations that are to receive toner (paper locations which correspond to dark areas of the image being printed). OPC drum
109
is discharged from −600V to approximately −100V 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 a nonmagnetic toner is used, developer sleeve
104
may comprise a developer roller to mechanically capture and transport toner particles
101
. In this case, an open cell foam roller may be included to apply toner to developer sleeve
104
. The still negatively charged toner particles held by developer sleeve
104
are attracted to the relatively positively charged areas of the surface of OPC drum
109
and “jump” across a small gap to the relatively positively charged latent image on OPC drum
109
creating a “developed” image on the drum.
Paper to receive toner from OPC drum
109
is transported along paper path
111
between OPC drum
109
and transfer roller
112
, with the developed image 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 and causing them to move onto the paper. Wiper blade
113
cleans the surface of the OPC drum
109
by scraping off the waste (untransferred) toner into waste hopper
115
, while recovery blade
114
prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller
116
and pressure roller
117
where the toner is melted and fused (or “bonded”) to the paper. Heated roller
116
and pressure roller
117
are together referred to as the fuser assembly.
One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner from the hopper. Leakage sometimes occurs at the ends of developer sleeve
104
. Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer sleeve
104
. Some printers employ a foam or felt mechanical seal at the ends of developer sleeve
104
as a physical barrier to prevent toner particles from slipping past the interface between developer sleeve
104
and toner supply hopper
102
. Alternatively, when the toner includes magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer sleeve
104
to tract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Unfortunately such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.
FIG. 2
shows developer roller
201
with conventional prior art seal
202
in place to reduce toner leakage. Seal
202
rides along an outer surface of developer roller
201
. However, toner fluid pressure may be sufficient to cause toner particles to seep under seal
202
and out the end of the roller assembly.
Accordingly, a need exists for a structure and method for reducing toner leakage in a torner cartridge.
SUMMARY OF THE INVENTION
The present invention is directed to a sealing mechanism for use in a toner cartridge comprising a developer roller with an annular groove. In one embodiment of the invention, the annular groove intrudes into the surface, a bottom of the groove having a diameter smaller than a diameter of the outer roller. A flexible end seal has a stepped profile, a central portion extending into and engaging the annular groove and peripheral outer portion in contact with an outer surface of the roller.
REFERENCES:
patent: 4992767 (1991-02-01), Hozumi et al.
patent: 5369477 (1994-11-01), Foote et al.
patent: 5757395 (1998-05-01), Chew et al.
patent: 5760817 (1998-06-01), Foote et al.
patent: 5854961 (1998-12-01), Wibbels et al.
patent: 5983053 (1999-11-01), Mordenga et al.
patent: 6185393 (2001-02-01), Karakama et al.
patent: 62-208073 (1987-09-01), None
patent: 63-106766 (1988-05-01), None
“Oasis- Tech's Tool Box- Laser Printing Process” [on-line][R
Braun Fred L
Hewlett--Packard Development Company, L.P.
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