Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2002-03-21
2004-01-20
Royer, William J. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
Reexamination Certificate
active
06681087
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to imaging devices and specifically to the reduction or elimination of toner leakage past toner seals in imaging devices through the use of capacitive or static charge.
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 a desired image on a print medium, which is usually some type of paper. Once the toner particles are 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 particles are 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 such as mylar and ensures toner particles
701
are uniformly positioned along developer sleeve
705
while inducing a negative charge onto the toner particles
701
in the range of −30 to −80 micro coulomb per gram (&mgr;c/g). Developer sleeve
705
rotates in a counterclockwise direction about an internal stationary magnet
704
acting as a shaft. Toner particles
701
are attracted to the rotating developer sleeve
705
by the magnetic forces of stationary magnet
704
. Doctor blade
706
charges the toner particles
701
and metes out a precise and uniform amount of toner particles
701
onto developer sleeve
705
as its outer surface rotates external to toner supply hopper
702
. Developer sealing blade
707
removes excess toner particles
701
affixed to developer sleeve
705
as its outer surface rotates back into toner supply hopper
702
and prevents toner particles
701
from falling out of toner supply hopper
702
onto paper, along the length of developer sleeve
705
.
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 any previous printing or transfer cycle.
A critical 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 PCR
708
. Initially, the unexposed surface potential of the OPC drum
709
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 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 underlying aluminum substrate.
Scanning laser beam
710
exposes OPC drum
709
one line at a time at the precise locations that are to receive toner particles
701
(paper locations which correspond to dark areas of 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
705
. Alternatively, if a nonmagnetic toner is used, developer sleeve
705
may comprise a developer roller to mechanically capture and transport toner particles
701
. In this case, an open cell foam roller may be included to apply toner particles
701
to developer sleeve
705
. The still negatively charged toner particles
701
held by developer sleeve
705
are attracted to the relatively positively charged areas of the surface of OPC drum
709
and “jump” across a small gap to the relatively positively charged latent image on OPC drum
709
creating a “developed” image on the OPC drum
709
.
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
701
and causing them to move onto the paper. Wiper blade
713
cleans the surface of the OPC drum
709
by scraping off the waste (untransferred) toner into waste hopper
715
, while recovery blade
714
prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles
701
, are 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.
Referring to
FIG. 8
, color printing follows a slightly different procedure in that a foam roller
801
(1 of 4) is used to deposit particular color toner particles (e.g., CMYK: cyan, magenta, yellow and black) onto developer roller
802
for the corresponding color. Foam roller
801
is made of an open cell foam with bias, while developer roller
802
has a coated exterior charged with a bias of between −350 to −450 VDC.
One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner particles
701
from a toner supply hopper
702
. Leakage sometimes occurs at the ends of developer sleeve
705
(FIG.
7
). Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer sleeve
705
. Some printers employ a foam or felt mechanical seal at the ends of developer sleeve
705
as a physical barrier to prevent toner particles from slipping past the interface between developer sleeve
705
and toner supply hopper
702
. Alternatively, when the toner exhibits magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer sleeve
705
to attract 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.
Accordingly, a need exists for a structure and method for reducing toner leakage in a toner cartridge.
SUMMARY OF THE INVENTION
The present invention includes a method of sealing a toner supply to a developer sleeve, the method including the steps of introducing a static-electric charge on toner particles to create charged toner particles and inducing an attractive charge onto each end of the developer sleeve. The static-electric charge and the attractive charge result in toner particles being attracted to the ends of the developer sleeve which create a barrier of charged toner particles to prevent leakage of the charged toner particles.
Another embodiment of the present invention is directed at a sealing apparatus for sealing an interface between a toner supply and a developer sleeve. In this embodiment the invention includes electrostatically charged toner particles and a charged seal on each end of the developer sleeve.
REF
Meyer Brent L.
Whitehead Dennis D.
Hewlett--Packard Development Company, L.P.
Royer William J.
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