Electrophotography – Image formation – Development
Reexamination Certificate
1999-06-17
2001-03-20
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Development
C399S178000, C399S296000
Reexamination Certificate
active
06205311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for the electrophotographic printing of a print image having a plurality of colors on a carrier, whereby the print image contains at least first image element with the color of the carrier, at least one second image element with a second color and at least one third image element with a third color. The first image element is allocated to a first surface element of a photo conductor layer. The photo conductor layer and an electrode layer carrying a predetermined reference potential are contained in a light-sensitive layer system. The reference potential is usually the zero potential. The second image element is allocated to a second surface element and the third image element is allocated to a third surface element of the photo conductor layer.
2. Description of the Related Art
A method for color printing is disclosed, for example, by U.S. Pat. No. 4,078,929. The method disclosed therein bears the name “Tri-Level Method”. What is disadvantageous in this method is that only toner particles of two colors can be applied in a printing process. Moreover, the developer stations for applying the toner particles are operated with electrical polarities that are opposite one another. This requires additional structural measures at the developer stations, so that the developer stations are not identically constructed. The individual developer stations or, respectively, their component parts as well as the toners as well are thus not interchangeable, and the manufacturing outlay and servicing outlay is higher than given identical developer stations and identical toners.
Japanese Patent Application JP-63265255 discloses a printing method wherein toner particles of only one polarity are employed for the application of three colors. Before developing the second and the third color, the potential of the surfaces of the photoconductor that are not yet covered is respectively lowered by a total illumination. At the same time, the potential of the most recently developed surfaces is boosted.
U.S. Pat. No. 5,155,541 discloses a method wherein techniques of color photography and of the tri-level method are combined. A lowering of the potential by a total illumination with a lamp ensues between two developing steps with the same toner polarity.
German Published Application DE 44 08 978 A1 discloses methods for image generation wherein a total illumination and, potentially, an increase of the potential as well is implemented between developing steps with the same toner polarity. Various methods are explained wherein the total illumination is implemented either before or after the boosting of the potential.
Japanese Patent Application JP 08 044140 A discloses a printing method for a multi-color printing wherein a total illumination is implemented between two developing steps in order to lower the potential on areas of the photoconductor that have not yet been developed.
SUMMARY OF THE INVENTION
An object of the invention is to provide a simple method and an improved, simply constructed printer for printing at least three colors with high printing quality.
Given a method of the species initially cited, this object is achieved in a method for the electrophotographic printing of a print image with a plurality of colors on a carrier, whereby the print image contains at least a first picture element having the color of the carrier, at least one second image element having a second color and at least one third image element having a third color and at least one further picture element having a further color, a first surface element of a photo conductor layer is allocated to the first picture element, a second surface element is allocated to the second image element, a third surface element is allocated to the third picture element, and a further surface element is allocated to the further picture element, the photo conductor layer and an electrode layer carrying a predetermined reference potential are contained in a layer system; and in that the following steps are successively implemented in the indicated sequence:
S1) the surface elements are charged to a starting potential of a first polarity;
S2) the surface elements are differently illuminated such that, following the illumination, the third surface element has a third potential, the second surface element has a second potential that is higher in amount compared to the third potential, the further surface element has a further potential higher in amount compared to the second potential, and the first surface element has a first potential that is higher in terms of amount compared to the further potential;
S3) the surface elements are developed with color particles of the third color,
whereby color particles of the first polarity and of the third color are deposited on the third surface element upon employment of a first auxiliary electrode that has a first auxiliary potential that is higher in terms of amount than the momentary potential on the third surface element and lower in terms of amount than the momentary potential on the second surface element;
S4) the surface elements are arranged close to a means for increasing potential, whereby the potential on the third surface element is increased in terms of amount after the application of the color particles of the third color,
S5) the surface elements are arranged close to a light source having an approximately uniform light distribution, the third surface element covered with color particles is illuminated substantially less than the non-covered first surface element, the non-covered further surface element and the non-covered second surface element, and the momentary potential on the second surface element is reduced in terms of amount to a potential that is lower in terms of amount than the momentary potential on the third surface element;
S6) the surface elements are developed with color particles of the second color, charged color particles of the first polarity and of the second color are deposited on the second surface element upon employment of a second auxiliary electrode that has a second auxiliary potential that is higher in terms of amount than the momentary potential on the second surface element and lower in terms of amount than the momentary potential on the third surface element and the momentary potential on the first surface element;
S7) the surface elements are arranged close to a further means for increasing potential, the potential on the second surface element is increased in terms of amount after the application of the color particles of the second color;
S8) the surface elements are arranged close to a further light source, the non-covered further surface element is respectively considerably more illuminated that surface elements covered with color particles, and the potential on the further surface element is reduced in terms of amount to a potential that is lower in amount than the momentary potential on the second surface element;
S9) the surface elements are developed with color particles of the further color, color particles of the first polarity of the further color are deposited on the further surface element upon employment of a further auxiliary electrode that has a further auxiliary potential that is higher in amount than the momentary potential on the further surface element and lower in amount than the momentary potentials on the other surface elements. Compared to the known “tri-level method”, the color particles of the first color and of the second color have the same polarity during developing in the invention. What this measure achieves is that the developer stations for applying the color particles of the first color and of the second color can be constructed essentially identically. The polarity of different assemblies and components in the printer is reduced by the invention compared to known printers having differently constructed developer stations. A simply constructed printer derives due to the invention.
In the present invention, the surface elemen
Maess Volkhard
Schleusener Martin
Lee Susan S. Y.
Oce Printing Systems GmbH
Sciff Hardin & Waite
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