Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2002-03-21
2004-02-10
Royer, William J. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
Reexamination Certificate
active
06690900
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 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 is applied to the paper, the paper is advanced along 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 is fused to the paper through a process of heat and pressure.
FIG. 7
is a diagram of typical laser printing device
700
employing an ElectroPhotography (EP) process. For monochromatic printing, a single color of toner particles
701
are held in toner supply hopper
702
. Toner particles
701
are typically small plastic (e.g. styrene) particles on the order of 5 microns (10
−6
) meter in size. Agitator, or stirring blade,
703
is typically made of plastic or mylar and ensures toner particles
701
are uniformly positioned along developer sleeve
704
while inducing a negative charge onto the toner particles
701
in the range of −30 to −40 microcoulomb per gram (&mgr;c/g). Developer sleeve
704
rotates in a counterclockwise direction about an internal stationary magnet
705
which acts as a shaft. Toner particles
701
are attracted to the rotating developer sleeve
704
by the magnetic forces of stationary magnet
705
. Doctor blade
706
helps in charging toner particles
701
and metes out a precise and uniform amount of toner particles
701
onto developer sleeve
704
as its outer surface rotates external to toner supply hopper
702
. Developer sealing blade
707
allows excess toner particles
701
affixed to developer sleeve
704
to be returned to toner supply hopper
702
without leakage.
Primary Charging Roller (PCR)
708
conditions Organic PhotoConductor (OPC) drum
709
using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum
709
. Production of the uniform charge by PCR
708
also has the effect of erasing residual charges left from the previous cycle.
A major component of the EP process is OPC drum
709
. OPC drum
709
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
708
. Initially, the unexposed surface potential of the OPC drum
709
is 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
709
. 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
710
exposes OPC drum
709
one line at a time at the precise locations that will receive toner particles
701
(paper locations which correspond to the image being printed). OPC drum
709
is discharged from −600V to approximately −100V at points of exposure to laser beam
710
, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles
701
are magnetically attracted to rotating developer sleeve
704
. Alternatively, if nonmagnetic toner particles
701
are used, developer sleeve
704
may comprise a foam roller to mechanically capture toner particles
701
. In this case, an open cell foam roller may be included to apply toner particles
701
to developer sleeve
704
. The still negatively charged toner held by developer sleeve
704
is attracted to the relatively positively charged areas of the surface of OPC drum
709
and “jumps” across a small gap to the positively charged latent image on OPC drum
709
creating a developed image.
Paper to receive toner from OPC drum
709
is transported along paper path
711
between OPC drum
709
and transfer roller
712
, with the developed image transferred from the surface of OPC drum
709
to the paper. The transfer occurs by action of transfer roller
712
which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles to move to the paper. Wiper blade
713
cleans the surface of the OPC drum
709
by scraping off the (untransferred or waste) toner particles
701
into waste hopper
715
, while recovery blade
714
prevents the waste toner particles from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller
716
and pressure roller
717
where the toner particles
701
are melted and fused (or “bonded”) to the paper. Heated roller
716
and pressure roller
717
are together referred to as the fuser assembly.
One design consideration with imaging devices such as laser printers and copying systems is to minimize the leakage of toner or toner particles
701
from the toner supply hopper
702
. As shown in
FIG. 8
, in its normal position, developer sleeve
704
has a toner supply on one side of seal
801
and the atmosphere on the other side of seal
801
. Seals in this area are incorporated in an attempt to reduce or eliminate toner leakage.
Leakage sometimes occurs along a roller and at the ends of developer sleeve
704
. Several methodologies have been used to reduce or eliminate such leakage. For example, some printers employ a foam or felt mechanical seal at the ends of developer sleeve
704
as a physical barrier to prevent toner particles
701
from leaking past the end of developer sleeve
704
and out of toner supply hopper
702
. Alternatively, when the toner includes magnetic particles, such as in some black and white printers, magnetic seals may be provided at the ends of developer sleeve
704
to attract and capture toner particles
701
and to create a physical barrier, consisting of the toner particles
701
, to prevent additional particles from leaking.
FIG. 8
shows the configuration of developer sleeve
704
, toner particles
701
and seal
801
. As shown, seal
801
is positioned between support
802
and developer sleeve
704
. As developer sleeve
704
rotates, toner particles
701
are forced into junction
803
of seal
801
and developer sleeve
704
. This action causes a buildup of toner and corresponding fluid pressure at junction
803
causing toner particles
701
to leak under, around and through seal
801
.
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 system and method which comprises a toner cartridge including a developer roller having a cylindrical exterior surface with one or more peripheral tapering channels formed in the surface at one end of the developer roller. The channel has a narrow proximal end nearest the nearest end of the developer roller and a wide distal end toward the middle of the developer roller. The narrow proximal end of the channel extends deeper into the surface of the developer roller than does the wide distal end.
REFERENCES:
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: 6487383 (2002-11-01), Buchanan et al.
“Oasis-Tech's Tool Box-Laser Printing Process” [on-line][Retrieved on Nov. 26, 2001]Retrieved from: http://www.oasis-imaging.
Dougherty Patrick S.
Phillips Quintin T.
Hewlett--Packard Development Company, L.P.
Royer William J.
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