Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2002-06-17
2004-01-20
Royer, William J. (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S114000
Reexamination Certificate
active
06681089
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to toner cartridges in imaging devices and specifically to the reduction or elimination of electrostatic charge buildup on toner cartridges during transit.
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, the toner particles are fused to the paper through a process of heat and pressure.
FIG. 4
is a diagram of a typical laser printing device
400
employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles
401
(e.g., black) are held in a toner supply hopper
402
. The toner particles
401
are typically small plastic (e.g., styrene) particles on the order of 5 microns (10
−6
) meter in size. An agitator, or stirring blade,
403
is provided in the toner supply hopper
402
and is typically made of plastic or mylar and ensures toner particles
401
are uniformly positioned along a developer sleeve
404
while inducing a negative charge onto the toner particles
401
in the range of −30 to −40 micro coulomb per grami (&mgr;c/g). The developer sleeve
404
rotates in a counterclockwise direction about an internal stationary magnet
405
which acts as a shaft. The toner particles
401
are attracted to the rotating developer sleeve
404
by the magnetic forces of the stationary magnet
405
. A doctor blade
406
helps in charging toner particles
401
and meters out a precise and uniform amount of toner particles
401
onto developer sleeve
404
as its outer surface rotates external to toner supply hopper
402
. A developer sealing blade
407
removes excess toner particles
401
affixed to developer sleeve
404
as its outer surface rotates back into toner supply hopper
402
.
A primary charging roller (PCR)
408
conditions an organic photoconductor (OPC) drum
409
using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum
409
. Production of the uniform charge by PCR
408
also creates the effect of erasing residual charges left from a previous cycle.
A major component of the EP process is OPC drum
409
. OPC drum
409
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
408
. Initially, the unexposed surface potential of the OPC drum
409
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 cylinder or 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
409
. 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.
A laser beam
410
exposes OPC drum
409
one line at a time at the precise locations that will receive toner particles
401
(paper locations which correspond to the image being printed). OPC drum
409
is discharged from −600V to approximately −100V at points of exposure to laser beam
410
, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles
401
are magnetically attracted to rotating developer sleeve
404
. Alternatively, if nonmagnetic toner is used, developer sleeve
404
may comprise a foam roller to mechanically capture toner particles
401
. In this case, an open cell foam roller may be included to apply toner to developer sleeve
404
. The still negatively charged toner particles
401
held by developer sleeve
404
are attracted to the relatively positively charged areas of the surface of OPC drum
409
and “jump” across a small gap to the relatively positively charged latent image on OPC drum
409
creating a developed image.
Paper to receive toner particles
401
from OPC drum
409
is transported along paper path
411
between OPC drum
409
and transfer roller
412
, with the developed image transferred from the surface of OPC drum
409
to the paper. The transfer occurs by action of transfer roller
412
which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles
401
to move to the paper. A wiper blade
413
cleans the surface of the OPC drum
409
by scraping off the waste (untransferred) toner into waste hopper
415
, while recovery blade
414
prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles
401
, is passed through a nip region between heated roller
416
and pressure roller
417
where the is toner particles
401
are melted and fused (or “bonded”) to the paper. Heated roller
416
and pressure roller
417
are together referred to as a fuser assembly.
During shipping of a toner cartridge, internal parts such as OPC drum
409
, PCR
408
, transfer roller
412
, and developer roller sleeve
404
, may rub relative to each other thereby creating static charges. Large static charges may become trapped in the organic photoconductor (OPC) on OPC drum
409
and cause a defect in printer operations when the toner cartridge is positioned in an imaging device such as a printer or copier. This effect is called “plus charge memory” or “rubbed memory.” Rubbed memory may be negative or positive. A negative charge trapped inside of the organic photoconductor (OPC) will create a repelling action leaving a portion of OPC drum
409
uncharged. Uncharged portions of OPC drum
409
may result in non-printed areas on a printed page.
During normal operation PCR
408
is arranged to uniformly charge the surface of OPC drum
409
. However, the charge trapped during transit in the organic material of OPC drum
409
disrupts the constant charge field transferred from PCR
408
. This causes a non-uniform charge across the surface of OPC drum
409
resulting in uneven print density and other defects on a printed page. Thus, to eliminate these printing defects it is necessary that a constant charge be applied to OPC drum
409
prior to modulation of the charge by a laser or projected image.
SUMMARY OF THE INVENTION
The present invention is directed to a system which uses a removable cover to isolate an organic photoconductor from at least one other component of a toner cartridge. The present invention also includes a method of reducing electrostatic charge on a photoconductor including the steps of isolating the photoconductor from other components in a toner cartridge with a removable cover, removing the removable cover prior to insertion of the toner cartridge into an electrophotographic printing device and inserting the toner cartridge into the device.
REFERENCES:
patent: 4860898 (1989-08-01), Hiro et al.
patent: 5499486 (1996-03-01), Kimoto et al.
patent: 5974287 (1999-10-01), Kurz et al.
patent: 6317573 (2001-11-01), Baker et al.
patent: 6336017 (2002-01-01), Miyamoto et al.
Hewlett-Packard Development Company LP.
Royer William J.
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