Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2002-03-21
2004-07-06
Ngo, Hoang (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
C399S105000
Reexamination Certificate
active
06760555
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to electrophotographic printing devices and more specifically to the reduction or elimination of toner leakage through seals that are used in printer toner cartridges.
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 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 Electro Photography (EP) process. Laser printing device
100
employs a removable toner cartridge
118
configured to supply toner particles to an integral Organic Photo Conductor (OPC) drum
109
which applies a developed toner image to a receiving media, e.g., a sheet of paper. For monochromatic printing, a single color of toner particles
101
(e.g., black) 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
meters) in size. Agitator (or stirring blade)
103
is typically made of plastic, such as mylar, and ensures that toner particles
101
are uniformly positioned along developer roller
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 roller
104
rotates in a counterclockwise direction about a shaft. Stationary magnet
105
, internal to the developer roller assembly, attracts toner particles
101
to rotating developer roller
104
under influence of magnetic forces produced by stationary magnet
105
. Doctor blade
106
charges the toner and metes out a precise and uniform amount of toner particles
101
onto developer roller
104
as its outer surface rotates external to toner supply hopper
102
. As the outer surface of developer roller
104
rotates back into toner supply hopper
102
developer sealing blade
107
removes any excess toner particles
101
that are affixed to developer roller
104
because they did not transfer to OPC drum
109
.
Primary Charging Roller (PCR)
108
conditions OPC drum
109
using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum
109
in the vicinity of PCR
108
. 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
. In a preferred embodiment, 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 OPC drum
109
is charged to approximately −600 volts by PCR
108
. 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 (i.e., the paper locations that correspond to dark areas of 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 roller
104
. Alternatively, if a nonmagnetic toner is used, developer roller
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 roller
104
. The still negatively charged toner particles held by developer roller
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.
Blank 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 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 hopper
102
. Leakage sometimes occurs at the ends of developer roller
104
. Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer roller
104
. Some printers employ a foam or felt mechanical seal at the ends of developer roller
104
as a physical barrier to prevent toner particles from slipping past the interface between developer roller
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 roller
104
to attract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.
FIGS. 2 and 3
show other embodiments of a prior art developer roller/seal combinations. Support
202
positions seal
201
to ride on the surface portion of developer roller
204
within toner supply hopper
102
to limit toner migration past the seal and out of the hopper. In this arrangement, developer roller
204
interfaces directly with seal
201
in the area of reference point
302
and
303
(FIG.
3
). Toner particles
101
are also present in the area of reference points
302
and
303
, and the toner particles tend to build up in these areas adjacent seal
201
. As developer roller
204
rotates in the direction indicated by arrow
304
(i.e., clockwise as viewed from the left end of developer roller
204
), toner particles become lodged between developer roller
204
and seal
201
. Toner particles
101
are pushed in a direction indicated by arrow
203
. As developer roller
204
continues to rotate and additional toner particles become wedged in this interface, toner particles leak through seal
201
. Seal leakage introduces toner into critical areas of the mechanism, thereby degrading performance, increasing maintenance requirements, and producing undesirable artifacts on the resultant printed paper or other produ
Clifton George Bernhard
Dougherty Patrick S.
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