US2336380A - Process for the production of color separation pictures of correct tone value - Google Patents

Description

Dec. 7, '1943'.

G. WILMANNs 2,336,380 PROCESS FOR THE PRODUCTION OF COLOR SEPARATION PICTURES OF CORRECT TONE VALUE Filed April 5, 1940 EXPOSURE WITH VELLW YE BASE' v oel/EL 0.050 /A/ Awww/:nc 4MM/0 @Evan/25e.

Patented. ec. 7, 1943 PROCESS FOR THE PRODUCTION OF COLOR SEPARATION PICTURES OF CORRECT TONE VALUE vGustav Wilmanns, Wolfen, Kreis Bitterfeld. Germany, assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware Application April 5, 1940. Serial No. 328,099 In Germany April 5, 1939 7 Claims. (Cl. 95-2) This invention relates to the production of photographic color separation pictures of correct tone values.

In the production of color sensations from colored originals there is a well known diiculty. that the densities of the negative, especially behind blue and green filters, do not correspond with the tone values of the color. If they are printed without retouching, completely incorrect coloring is obtained,'for instance the blue colors behind the blue lter are reproduced in the negative often much lighter than the yellow colors. The densities therefore are just the opposite from what they should be.

To overcome these diiculties diiferent methods have been proposed. The most important one is to cover over the'color separation negative with a mask of a thin positive, produced behind a complementary colored filter. In order to obtain a yellow printing plate, a negative exposed behind a` blue filter and covered with a thin positive of a yellow-lter-exposure is needed. In this way vmost of the faulty color reproduction may be corrected. For the reproduction of a blue-green printing plate the red filter negative is to be covered correspondingly with a diapositive mask of a green-iilter-exposure and for the production of a purple printing plate a negative, exposed behind a green iilter, must be covered with a diapositive mask of a red-filterexposure.

. Variousprocesses have been developed, in order to arrange these different masks, i. e. negative and positive masks above one another. Generally it is somewhat complicated to work with these masks. Methods have been found, however, to work in a more simple way with the two superimposed layers of emulsion. For instance two emulsion layers are cast on top of one another, of which one layer is a direct duplicate emulsion, the other an ordinary negative emulsion. In this way the positive and the negative are obtained correctly superimposed in a single developing process one on top of the other; U. S. patent applications Ser. No. 258,461, filed February 25, 1939, and Ser. No. 282,740, filed July 3, 1939. These methods, however, are limited on account of the relatively low sensitivity of the direct duplicate emulsion.

Ourl invention has therefore for an object to provide the production of a corrected color separation picture by using a lm carrying two silver halide emulsion layers which may be arranged one on each side or both on the same side of the support, of which one layer consists of a positive separation picture obtained by a bleaching out of dyes by'means of the silver image and the other layer of a negative separation picture obtained by color-forming development" with dyestui components fast to diffusion.

Another object is the provision of a corrected color separation picture by using for the two separation pictures dyestuifs which are of the same spectral quality.

Still another object is the provision of a corrected color separation picture by using for the two separation pictures dyestuis which are of different spectral quality, thereby yielding a so called elastic negative.

These and other objects will appear from the detailed specification following hereinafter.

It has been found that the possibility of an increase in sensitivity exists, if for the production of the positive and negative color separation pictures in the two layer material, a layer for bleaching out of dyes by means of the silver image is combined with a layer forming the color by development and consisting of dyestuif components fast to diifusion.

In the process of bleaching-out of dyes by means of the silver image certain dyestus being already in the emulsion or caused to diffuse afterwards into it, are bleached out at those places, wherever silver is developed. After the negative-processing of the silver, the bleachingout of the dyestuifs and the dissolving of the remaining silver halide, a positive dyestuff image is obtained. In the process of color-forming development simultaneously with the negativesilver a dyestuil' image is produced. After dissolving of the silver there remains therefore a negative dyestuff image. In this way it is possible to build up in a simple procedure in two superimposed layers a positive and a negative dyestu' image. Between the two layers a lter layer is to be arranged, which is dyed complementary with regard to the sensitization of the negative emulsion layer. Instead of this special filter layer it is also sufcent to dye the uppermost layer in the same way. 'The dyestuifs obtained in both layers may be the same with regard to their spectral quality. However, it is A silver halide emulsion layer sensitized for yellow and containing a dyestui for instance Sirius R Extra or Chrysophenin G is cast onto a film or a plate for the production of a yellow printing plate. 'I'hereon is cast a thin yellow filter consisting of a dyestui which either in the photographic baths or in the washing baths is easily decolorized. The uppermost unsensitized silver halide emulsion layer contains a dyestuff component known by the Agfa color process which is fast to diffusion and which develops into the same or a different color as possessed by the positive picture produced by the silver-dye bleaching method. After exposure of the separation picture one develops first of all in a solution which produces in the lower emulsion layer a black silver image only. In the uppermost layer, however, there is produced during the development of the latent silver halide image a dyestuff-picture originating from the dyestuif components present in the emulsion layer. A developer suitable for the purpose is for instance dimethyl-p-phenylenediamine. Silver negatives in both emulsion layers and, besides that, a negative dyestui image in the uppermost layer are thus obtained. Then the yellow dyestui of the lower emulsion layer is destroyed by a bath of thiourea in acid solution at those places which contain silver, whereby a yellow dyestu positive is obtained. In this bath also the dyestuff of the uppermost emulsion layer may be reduced under certain conditions. If these dyestuffs, however, are fast to diffusion according to U. S. Patent 2,179,238; the reduction product remains at its original place in the gelatin of the uppermost layer and may be reconverted by oxidation agents into the dyestui. A suitable oxidation agent for this purpose is potassium ferricyanide. Finally the silver and silver halide is dissolved by a Farmer reducer, so that in both emulsion layers only dyestuff images remain i. e. a positive in the lower and a negative in the uppermost emulsion layer.

The production of the blue-green-printing assasso t plate and of the purple printing plate may be accomplished in a similar. manner.

I claim:

1. Process for the production of color separation pictures of correct tone value which includes the steps of exposing to a colored object a film having two emulsion layers on a single support, one emulsion being sensitive to light oi' a given spectral range and containing a dyestuii component for color development which, though soluble in aqueous liquids is fast to diffusion with respect to the binding agent of the emulsion, and the second emulsion being sensitive to light of a dierent spectral range and containing a uniformly distributed dye which is selectively removable by bleaching in dependence on a silver image, developing said 'lm in a, single developer to form simultaneously a negative silver and dye image of one color sensation of said object in said first layer by color-forming development and a negative silver image of another color sensation of said object in said second layer, and removing the silver negative images from said layers by a treating bath which selectively bleaches the dye of said second layer at the portions where silver was present, thereby forming a negative separation image of said first color sensation and a superimposed positive correcting mask corresponding to said second color sensation.

2. The process as defined in claim 1, wherein the dye images in the negative separation image and in the positive correcting mask are of similar spectral quality.

3. The process as defined in claim 1, wherein the dye images in said negative separation image and said positive correcting mask are of different spectral quality.

4. The process as defined in claim 1 wherein the removal of the silver negative images and the selective bleaching of the dyes of the second layer at the portions where silver is present is effected by means of thiourea.

5. The process as defined in claim 1 wherein said second emulsion is sensitized for yellow.

6. The process as dened in claim 1 wherein said second emulsion is sensitized for yellow and is dyed with Sirius R Extra.

7. The process as dened in claim l wherein the emulsion layer containing the dyestuf! component is subjected to an oxidation treatment after the selective bleaching of the dye in the second emulsion layer.

GUSTAV WILMANNS.

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