Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2002-11-14
2004-05-04
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S299000, C399S315000
Reexamination Certificate
active
06731890
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electrostatographic method and apparatus or electrostatic transfer of toner particles from a toner-image-donor roller to a receiver sheet in a transfer station, and more particularly to a time-varying transfer station current while the receiver sheet is in the transfer station.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 6,184,911 includes exemplary disclosure of a modular printer in which a respective secondary transfer station, included in a respective module of a plurality of tandem imaging modules, has a current regulated power supply for providing transfer station current in the respective secondary transfer station.
The Rodenberg et al. patent (U.S. Pat. No. 5,040,029) discloses a paper receiver member inserted between a photoconductive (PC) web and a transfer drum included in a multicolor electrostatographic printer, the paper receiver to be picked up by the drum. The transfer electric field is turned off for the leading edge of the receiver to aid separation from the PC web. After the last image is transferred, the transfer field is applied to the lead edge to help attach the paper receiver member to the web.
FIG. 1A
illustrates an exemplary configuration of rollers in a transfer station, designated by the numeral
100
. The transfer station is for electrostatic transfer and includes a toner-image-donor roller
110
including a deformable or compliant blanket
111
around a rigid core
112
. Roller
110
can be for example an intermediate transfer type of roller, a photoconductor type of roller, or an electrographic imaging type of roller. Outer layers around blanket
111
which characterize the particular type of roller
110
are not shown, e.g., for usage as an intermediate transfer roller. A receiver sheet
130
is shown being transported on a transport web
135
towards a nip
140
formed between a transfer member
120
(roller or other suitable transfer member such as an electrified ski or brush for example) and roller
110
, in which nip a toner image
115
carried by toner-image-donor roller is to be transferred to receiver sheet
130
. Another receiver sheet
131
including a transferred image
116
is the previous in a series of N receiver sheets moved through nip
140
, with receiver sheet
130
being identified as sheet (N+1). Transfer member includes a rigid core
122
and preferably a compliant layer
121
around the core. Electrostatic transfer is accomplished by providing an electric field between rollers
110
and
120
so as to urge toner particles to move from roller
110
to
120
within nip
140
.
FIG. 1B
illustrates the exemplary problem of unwanted wrap. Sometimes, a receiver sheet will detach from a transport web and stick to a toner-image-donor roller as the receiver sheet comes out of a transfer nip, causing a paper jam. A wrap is exemplified in the configuration
150
showing a toner-image-donor roller
155
, a transfer member
165
, a transport web
170
and a receiver sheet
160
partially wrapped around roller
155
. The receiver sheet
160
is electrostatically adhered or tacked down to web
170
. Receiver sheet
160
, prior to being tacked down to web
170
, tended to curl upwards, i.e., away from the web. After being adhered as depicted in
FIG. 1A
, such curl is largely flattened by the electrostatic tack force, yet a propensity to curl still exists near the leading edge
161
of receiver sheet
160
, where the tack force can be opposed by a relatively strong curl stress
When even a small air gap forms between a receiver sheet and a transport web at the leading edge of the sheet as the sheet emerges from the transfer nip, the high electric field in the post-nip region can cause ionization of the air in this air gap. Due to the electric field, charge of one polarity will be deposited on the receiver sheet and the charge of the other polarity will be deposited on the transport web. The same electric field will cause the charge deposited on the receiver sheet to be attracted to the toner-image-donor roller, thereby attracting the receiver sheet to the intermediate roller.
In addition to curl, several other factors can contribute to producing an air gap between a receiver sheet and a transport web at the lead edge of the sheet, as the sheet emerges from the transfer nip. These other factors include paper cockle, burrs on the lead edge from cutting the sheets, receiver surface roughness, and transport web surface roughness or kinks.
A way to reduce the occurrence of wraps is to make roller
155
very small, say 50 mm diameter or less. However, this is generally disadvantageous or impractical, and a transfer member typically has a diameter of at least 150 mm so as to provide sufficient space for necessary process elements. For example, a photoconductive primary imaging roller (not illustrated in
FIG. 1B
) is generally used in conjunction with an intermediate transfer roller
155
, with bulky process elements such as for example chargers, a toning station, a writer, and cleaners situated at various locations around the photoconductor drum and the intermediate roller, which situation demands a large diameter intermediate transfer roller.
Moreover, a typical transfer station current required for transferring a toner image to a receiver sheet is about 25 microamps, for a typical nip length (e.g., perpendicular to direction of arrow b of
FIG. 1B
) of about 360 mm and a transport web speed of about 300 (millimeters)(sec
−1
). Tests have shown that reducing transfer station current to 15 microamps or less reduces the tendency of receiver sheets to wrap on an intermediate transfer roller. However, it was found that a transfer station current this low does not produce good transfer. Therefore, simply reducing the transfer station current is not an option for avoidance of wrapping.
There remains a need to overcome the problem of unwanted wraps occurring in electrostatic transfer stations, which problem is ameliorated by the invention described below.
SUMMARY OF THE INVENTION
The invention provides apparatus and method for preventing or greatly reducing the frequency of paper jams, which can occur in a transfer station for electrostatic transfer of toner particles to a receiver sheet moving through the transfer station. As described above, such paper jams can for example result from a curl of a receiver sheet. This curl can cause a receiver sheet to wrap, thereby causing a paper jam in the transfer station.
More specifically, the invention provides an electrostatographic machine inclusive of a transfer station for electrostatic transfer of a toner image from a toner image carrier, such as a toner-image-donor roller (TIDR), to a toner-image area on a receiver sheet, the transfer station including a programmable, current regulated, power supply for purposes of producing a time variation of transfer station current for transferring the toner image. In particular, by controlling the magnitude of the transfer station current in a leading edge portion area of a receiver sheet, wrapping of receiver sheets can be reduced or eliminated.
In embodiments of an electrostatographic machine according to the invention, the receiver sheet is included in a plurality of receiver sheets successively moved through the transfer station, with toner transfer taking place in a nip formed between the TIDR and a transfer member (TR). The transfer station further includes a transport web for transporting the receiver sheet through the transfer station, the transport web being included in the nip, with the receiver sheet electrostatically adhered to the front face of the transport web, the back face of the transport web being in contact with the transfer member. The receiver sheet has a leading edge included in a leading edge margin area and a trailing edge included in a trailing edge margin area. Toner is transferred to the toner-image area hut not to a margin area. The electrostatographic machine includes a programmable power supply for supplying a transfer station current in the transfer station. During a time period
Rakov David McLaughlin
Shuster Frank Alexander
Kessler Lawrence P.
NexPress Solutions LLC
Pendegrass Joan
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