Photocopying – Including fiber optics
Patent
1983-08-11
1985-09-24
Grimley, A. T.
Photocopying
Including fiber optics
430 43, 430 44, 430 45, G03G 1501, G02B 2717, G03G 1322
Patent
active
045429790
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to xerography and more particularly, to a method and apparatus for forming a multicolor proof print from at least two light transmitting color separations.
2. Description of the prior art
It is known in multi-color printing to make use of color separations, i.e. partial images in each of the three basic colors (yellow, magenta, cyanogen) usually supplemented with a partial image in black. Different techniques are known for obtaining such color separations from the original to be reproduced. Before commencing the final production printing run of such separations, a check must be made to ensure that a satisfactory final result is obtained with the color separations formed. For this purpose, a proof print normally is made on a proof printing press. This is a time-consuming process. Furthermore, the proof printing press required for such procedure is expensive.
The general state of the art with which the present invention is concerned is described in U.S. Pat. Nos. 3,999,987 and 3,836,244. Additionally, U.S. Pat. No. 4,120,577 describes the problems which occur when making color reproductions as a result of the charge which remains on the electrophotographic material after exposure and supply of toner. Said U.S. Pat. No. 4,120,577 teaches removal of the residual charge by use of a special corona-electrode. In the present invention, such residual charge is removed by an extra exposure step.
The present invention provides a method and apparatus for forming a multi-color print in a quick and inexpensive manner and in which the print corresponds so much with the print formed on a printing press that it is possible to make a very accurate assessment of the color separations.
SUMMARY OF THE INVENTION
The method of the invention is characterized by the formation of a charge pattern from each color separation by exposure of a photoconductive coating which has been charged in advance to a certain charge level. The charge pattern is developed a predetermined period of time after the charge state has been achieved. Toner is used having a color which corresponds with the color separation concerned. The toner image thus obtained is transferred onto a receptor surface such that the second and subsequent toner images are in registration with the preceding ones. The photoconductive coating for each of the partial images is charged up to an identical final charge state; the development with toner starts after the coating has achieved the final charge state, which is identical for all partial images.
The present invention is based on the knowledge that fully reproducible and comparable results are obtained if development of the respective partial images starts at an identical point on the darkness decay curve of the corresponding coating. This point is essentially the commencement of development after a period which is identical for all partial images after the final charge state has been achieved. In actual practice, it has been observed that results are obtained which closely match those obtained with a proof print. It is less expensive to construct a device for performing the method of the invention than a proof printing machine.
In the present invention, charging and development of the coating preferaby is undertaken during a period which is identical for all of the respective toner partial images. Preferably, several coatings having mutually identical characteristics are used for the formation of the respective partial images. Charging of a photoconductive coating is undertaken during the period of development of the coating which has been charged up and exposed with a partial image of a different color immediately prior thereto.
DESCRIPTION OF THE DRAWING
FIG. 1 shows a schematic frontal view of the mutual position of the different constituent parts of the arrangement in accordance with the invention;
FIG. 2 provides a view in the direction of the arrow 2;
FIG. 3 provides a view in the direction of the arrow 3;
FIGS. 4a to 4e sho
REFERENCES:
patent: 3836244 (1974-09-01), Lehman
patent: 3836363 (1974-09-01), Plutchak
patent: 3998539 (1976-12-01), Kidd
patent: 3999987 (1976-12-01), Davis et al.
patent: 4120577 (1978-10-01), Watanabe et al.
patent: 4204728 (1980-05-01), Goshima et al.
patent: 4230405 (1980-10-01), Kurtz
patent: 4234350 (1980-11-01), Mailloux et al.
Coulter Stork Patents B.V.
Flower Terry
Grimley A. T.
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