Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-06-28
2001-11-06
Braun, Fred L (Department: 2852)
Electrophotography
Image formation
Transfer
C399S311000
Reexamination Certificate
active
06314265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a transfer printing station with an electrostatic transfer printing means for transferring a toner image generated on an electrographic intermediate carrier onto at least one recording medium in a transfer printing area of the transfer printing station, with guide elements arranged in the transfer printing area for guiding the recording medium close to the intermediate carrier during the transfer printing event, and with a contact pressure element arranged between the guide elements that presses the recording medium against the intermediate carrier during the transfer printing event.
2. Description of the Related Art
Such a transfer printing station is disclosed by U.S. Pat. No. 5,400,125. It employs a leaf-shaped blade as a contact pressure element, the edge thereof pressing the web-shaped recording medium against the electrographic intermediate carrier, a photoconductor drum. Although relatively good practical results have been capable of being achieved with this solution, a few disadvantages nonetheless derive. Thus, the blade-shaped contact pressure element is a wear part whose service life is relatively short and that requires frequent replacement. Since the blade edge of the contact pressure element rubs against the recording medium, considerable contamination due to toner abrasion and paper abrasion derives in the transfer printing area. When different web widths of the recording medium are employed, then a contact pressure element matched to this web width must be utilized. Due to the blade-shaped contact pressure element, moreover, irregularities in the electrostatic field derive in the transfer printing area; these irregularities can produce stripes in the print image.
Japanese Patent document discloses a transfer printing station with a contact pressure element in the transfer printing area. The contact pressure element is fashioned at a guide element, whereby the transfer printing station contains only a single guide element. The contact pressure element is fashioned a as contact pressure roller and has lateral supporting wheels that are supported on edge regions of an intermediate carrier that have no image-generating function. The recording medium is supplied with an edge close to a supporting wheel. The other supporting wheel has a larger diameter than the first-cited supporting wheel, as a result whereof a wedge-shaped gap forms between the surface of the contact pressure roller and the surface of the intermediate carrier. What is thereby achieved is that the contact pressure roller is not charged with toner material in the area of the enlarged gap.
German Patent document discloses an electrographic printer wherein two webs of a recording medium lying side-by-side are simultaneously printed. One of the webs can have already undergone a fixing process.
SUMMARY OF THE INVENTION
An object of the present invention is to fashion a transfer printing station of the species initially cited such that, on the one hand, non-uniformly shaped recording media of different thickness or width can also be uniformly placed against the recording medium during transfer printing in order to produce a print image with high quality via the contact pressure element, and such that, on the other hand, it is assured in all operating conditions that the contact pressure element does not enter into contact with the intermediate carrier.
This object and others are achieved by a transfer printing station for an electrographic printer or copier device having: an electrostatic transfer printing means for transferring a toner image generated on an electrographic intermediate carrier onto at least one recording medium in a transfer printing area of the transfer printing station, guide elements arranged in the transfer printing area for guiding the recording medium close to the intermediate carrier during the transfer printing event, at least one contact pressure element that is resistant to bending, arranged between the guide elements displaceable relative to the intermediate carrier opposite a spring power, and that presses the at least one recording medium against the intermediate carrier during the transfer printing event, and with at least one spacer element allocated to the contact pressure element and supported on the intermediate carrier for maintaining a defined minimum spacing between contact pressure element and intermediate carrier, whereby the contact pressure element is fashioned as contact pressure rail.
The contact pressure element, which is fashioned as a contact pressure roller or as a contact pressure rail and essentially extends over the entire width of the electrographic intermediate carrier, for example a photoconductor drum, is fashioned resistant to bending and comprises a spacer element, preferably in the form of a supporting roller, supported on the intermediate carrier for maintaining a defined minimum spacing between the contact pressure element and the intermediate carrier.
The force of the contact pressure can be increased due to the resistance to bending in combination with the distance-securing function of the spacer element, so that a rippled recording medium can also be pressed smoothly against the electrographic intermediate carrier. What the increased pressing power also effects is that no air cushion can form between the recording medium and the intermediate carrier, as has often occurred in the Prior Art devices.
When the contact pressure element is fashioned as a contact pressure roller, it rolls over the recording medium and only rolling friction arises between the recording medium and the contact pressure roller. Accordingly, the abrasion at the recording medium is reduced and the risk of contamination is low.
According to a development of the invention, the surface of the contact pressure element is electrically conductive and has a predetermined electrical potential, preferably ground potential. In this way, electrical charges that arc generated on the surface of the recording medium by electrostatic charging arc collected and eliminated to ground. A disturbance of the electrical field in the transfer printing area is thus avoided.
A preferred exemplary embodiment of the invention is characterized in that the contact pressure element has two supporting rollers whose diameters are dimensioned such that a minimum spacing between the contact pressure element and the intermediate carrier is not downwardly transgressed. The rolling of the supporting rollers on defined sections of the intermediate carrier outside the actual writing area assures that the contact pressure element is always held in a defined position relative to the recording medium even given a lack of roundness and ripple of the intermediate carrier. Deviations in shape of a photoconductor drum such as, for example, lack of roundness and ripple do not, given the present invention, lead to the pressing position of the recording medium against the photo-sensitive surface of the intermediate carrier changing.
A preferred employment of the transfer printing station is characterized in that the web has already undergone a transfer printing procedure, i.e. is provided with a toner image, and has been conveyed over a longer conveying path and been potentially subjected to a thermal fixing. Ripples and grooves can form on the recording medium due to the renewed thermal fixing, these potentially leading to a deteriorated print image. By employing the invention, these ripples and grooves are smoothed in the transfer printing area, so that the recording medium lies flush against the intermediate carrier for the transfer of toner.
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patent: 42 13 236 C2 (1992-
Brecht Stefan
Kreiter Alexander
Kuermeier Christian
Meschenmoser Friedrich
Stuerzer Anton
Braun Fred L
Oce Printing Systems GmbH
Schiff & Hardin & Waite
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