Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-12-28
2001-06-05
Braun, Fred L (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000, C399S308000
Reexamination Certificate
active
06243555
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electrostatography and more particularly to a reproduction method and apparatus that employs transfer of toner images to receiver members.
BACKGROUND OF THE INVENTION
In a multicolor electrophotographic (EP) reproduction apparatus comprising two or more image forming stations and an insulating paper transport web, the transfer of a toner image from an image carrier or toner image-bearing member (TIBM), i.e., a photoconductor (PC) or an intermediate transfer member (ITM), to a receiver, electrostatically or mechanically held to the paper transport web, is achieved by use of a constant current supplying device, i.e., a corona charger, brush or roller charger, which sprays or otherwise deposits a constant amount of charge, of opposite polarity from the toner, to the backside of the paper transport web, an example of such an apparatus is described in International published application W098/04961. As the receiver tacked to the paper transport web separates from the image carrier, in addition to the transfer charge located on the backside of the paper transport web, post-nip ionization charge of the same polarity as the toner is sprayed on the toned side of the receiver. For the case of positive wrap, i.e., wrap of the receiver about the image carrier, the magnitude of the post-nip ionization charge sprayed on the front side of the paper transport web defines the polar charge in the area of the receiver. The difference in the magnitudes of front-side and back-side charges defines the net charge in the area of the receiver. Polar charge due to post-nip ionization occurring during transfer at an upstream image forming station adversely impacts subsequent image transfers.
FIG. 1
shows the reduction in the efficiency of toner transfer with increasing polar charge, since polar charge reduces the transfer field. As may be seen from
FIG. 1
, transfer efficiency decreases with increase in polar charge for images at maximum density, or halftones at 141 lines per inch with 40% coverage and even more dramatically for a halftone at 20% coverage. Net charge can cause image disruption during non-controlled air breakdown of the electric field produced by the net charge as the toned image on the receiver comes near a grounded plane.
To circumvent problems due to polar charge and net charge in a known prior art EP color machine wherein a receiver is transported by a paper transport web through the machine there are provided numerous corona chargers to condition the image and the receiver after transfer. Two conditioning chargers apply charge, opposite in polarity from the toner charge, to the front side of the toned receiver. Two conditioning chargers apply charge, opposite in polarity from the transfer charge, to the backside of the receiver. These chargers reduce both the polar charge and the net charge, insuring improved subsequent transfers. However, this image conditioning strategy is costly and produces excessive ozone.
SUMMARY OF THE INVENTION
The invention is directed to providing an inexpensive and easy approach to image conditioning in a multi-color electrostatographic apparatus which utilizes sequential, image forming stations and a paper transport web, the web partially wrapped around a portion of a TIBM in an electrostatic transfer station. In the claims and summary of the invention, reference to first and second toner image-bearing members (TIBMs) implies a relative sequential relationship between these two TIBMs and not that the first and second TIBMs can only be the first and second TIBMs in a series of three or more TIBMs. Thus, the first and second TIBMs could refer to any adjacent pair in a sequence of TIBMs which operate upon a receiver.
In accordance with the invention, there is provided a reproduction method comprising moving each of a first and second toner image bearing members (TIBMs), each of the TIBMs having a respective toner image formed thereon, through a respective transfer nip with a web that has or supports a toner image receiving surface; moving the web through each nip with each TIBM, the web having or supporting on a first surface thereof the toner image receiving surface as the receiving surface is moved through the transfer nip with the first TIBM to the transfer nip with the second TIBM; providing on each TIBM in each nip a predetermined amount of pre-nip wrap by the web and a predetermined amount of post-nip wrap by the web; electrostatically transferring a toner image at each transfer nip to the receiving surface so that a toner image transferred by the second TIBM is deposited on the receiving surface so as to form a composite image with the toner image transferred to the receiving surface by the first TIBM; and between the nip with the first TIBM and the nip with the second TIBM discharging a second surface of the web opposite the first surface with a discharge member at a fixed predetermined potential to reduce charge on the web to condition the web for receipt by the receiving surface of a second toner image from the second TIBM.
In accordance with a second aspect of the invention, there is provided a reproduction apparatus comprising first and second toner image bearing members (TIBMs), each of the TIBMs having a respective toner image formed thereon and each of the TIBMs being in nip relationship with a respective transfer backing member to form a respective transfer nip through which a web that has or supports a toner image receiving surface passes; each TIBM having electrical bias potential between a portion thereof and the respective transfer backing member to urge electrostatic transfer of the toner image at each transfer nip to the receiving surface; and between the nip with the first TIBM and the nip with the second TIBM there is provided near or engaged with a second surface of the web, opposite the first surface, a discharge member at a fixed predetermined potential to reduce charge on the web to condition the web for receipt by the receiving surface of a second toner image by the second TIBM.
In accordance with a third aspect of the invention, there is provided a reproduction method comprising forming on each of first and second primary image-forming members (PIFMs), a respective toner image; transferring the respective toner images respectively to respective first and second intermediate transfer members (ITMs) at respective primary nips; moving each of the first and second ITMs with the respective toner images formed thereon through a respective secondary transfer nip with a web that has or supports a toner image receiving surface; moving the web through each secondary transfer nip with each ITM, the web having or supporting on a first surface thereof the toner image receiving surface as the receiving surface is moved through the secondary transfer nip with the first ITM to the secondary transfer nip with the second ITM; providing on each ITM in each secondary nip a predetermined amount of post-nip wrap by the web; and electrostatically transferring in a constant current transfer mode a toner image at each secondary transfer nip to the receiving surface so that a toner image transferred by the second ITM is deposited on the receiving surface so as to form a composite image with the toner image transferred to the receiving surface by the first ITM.
REFERENCES:
patent: 5172172 (1992-12-01), Amemiya et al.
patent: 5189479 (1993-02-01), Matsuda et al.
patent: 5612772 (1997-03-01), Enomoto et al.
patent: 5897247 (1999-04-01), Tombs et al.
patent: 5923937 (1999-07-01), Thompson et al.
patent: 6016415 (2000-01-01), Herrick et al.
patent: 6075965 (2000-06-01), Tombs et al.
patent: 6081678 (2000-06-01), Kato
patent: WO 98/04961 (1998-02-01), None
Herrick Diane M.
Tombs Thomas N.
Wright Graham S.
Braun Fred L
Leimbach James D.
Nexpress Solutions LLC
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