US2054390A - Photographic bleachjng-out layers - Google Patents

Description

Patented Sept. l5, 1936 PATENT OFFICE 2,054,390 Pno'roGRArmc BLEAcmNG-OUT Lammev Ernst Rst, Zurich, Switzerland, and Andr Pulgar, Paris, France Apputauon August 29, 1934, serial No. '141,000v

l In Switzerland September 7, 1933 16 Claims.

This invention relates to the production of improved photographic bleaching out layers, that is to say, layers for the production of permanent images by the bleaching out process of color photography.

The great difliculty in the manufacture of bleaching out layers consisted hitherto in that:-

(1) From a large number of dyestuffs there must be selected certain ones having parallel (simultaneous) bleaching capacity, requiring the same length of time to bleach out to the same desired extent;

(2) A bleach-out sensitizer must be found, or rather a mixture of sensitizers, which accelerates the bleaching out of the ycomponents equally or vto the same'extent, i. e., according to nearly the same characteristic curves of degree of bleach attained with time. other conditions being constant, and

(3) In addition to those requirements the mixture, before the exposure, must have a neutral shade so that the uncolored portion of the original does not assume a color in the reproduction.

The fulfilment of the first two requirements alone was hitherto impossible; the fulfilment of the third requirement even after the fulfilment of the first two is improbable since the dyestuils f have different dyeing power.

It is the object of the present invention to provide a bleaching out layer which is much more satisfactory than those hitherto known.

In the bleaching-out process of color photography, the fugitive dyes of different colors (as yellow, red, blue) which are incorporated in the sensitive bleach-out layer in a greyish mixture, bleach out under the action of light of the same wave length which they respectively absorb, to leave the color to which the layer is exposed.

In this bleach-out process, there is often added one or more additional substances as bleach-out sensitizers (also called acceptors), whose function is to increase (or diminish) the bleachingout reaction or sensitivity to bleaching-out of the several fugitive dyes applied to the material under exposure in the bleaching-out layer under the action of the light of the wave lengths which they respectively absorb. These "bleach-out sensitizers themselves are generally substantially colorless, such as allylthiourea, and in general are not themselves dyes. l

One feature of this invention is based on the discovery that on plotting graphically the time characteristics of bleaching out as the half value times of the dyestuffs concerned as a function of the concentration of the bleach-out sensitizer,

it is possible to select suitable dyestufls for inclusion in a bleaching out layer, the curves of all of which approach each other very closely or include only a small area. The half value time is the time in which half of the quantity present 5 of a given dye is bleached out. Thus three curves of red. yellow and blue dyestuifs, or fourcurves of yellow, orange, violet and green dyestuffs, or more curves corresponding to the number of dyestuffs used, may intersect at one point.

There is thus a bleach-out sensitizer concentration at which different dyestuis bleach out to practically the same extent. At this concentration the bleaching out will have practically the same time characteristic even for the different exposure times and light intensities after a certain minimum exposure. On this account it is also possible to employ such dyestufl's as hitherto did not receive consideration. although they possess -very valuable properties. In addition in 20 most cases it is possible to use only one bleachout sensitizer.

Thus in accordance with one feature of this invention the dyestuffs for inclusion in a bleaching out layer are selected in the manner set out 25 above and the bleach-out sensitizer is employed in the particular concentration required.

As one example for the production of a bleaching out layer according to this feature of theinvention, an emulsion is produced which is capable 30 of being applied to paper and contains a deep violet mixture of the dyestuffs erythrosin, fluorescein and Victoria'blue in a total concentration of about 1%, the emulsion being sensitized as to bleaching out with 1.5% total concentration of 35 allyl-thiourea (also called thiosinamine and allylthiocarbamide) as a bleach-out sensitizer. After a time of exposure in which a perceptible alteration in the dyestuffs can be ascertained, there are obtained simultaneous similar bleaching out char- 40 acteristics plotted against the time of exposure for this particular sensitizer concentration of the three diierent colored dyes.

- In another example a mixture of erythrosin, auramin and methylene blue is sensitized with about 3% of anethol. The importance of this particular selected value of concentration will be realized in this case when it is mentioned that on increasing the bleach-out sensitizer concentration by 1% the bleaching out value for erythrosin varies by about 30% although the values for the other two dyestuffs remain practically the same.

In practice the theoretical value of the bleach- 55 are thus produced over the unexposed portionsl by means of the unchanged FeCla.

In addition to this action the additional substance may accelerate the bleaching of the dyestuft. In the above example the bleaching of dyestulls is accelerated which bleach out by oxidation. On the other hand by the bleaching the formation of FeClz is also accelerated.

The process is particularly suited to the manufacture of color photo-printing papers. In this case the dyestuffs can also be employed very dilute since for technical printing merely an indication of the color shade is suilicient and the deep shades (for example black lines) are produced by the additional substance.

It has also been found that to produce black layers there can be employed very advantageously diazo layers which can be developed dry, wet, or in a stream of gas.

In the manufacture, for example, of color vphoto-printing papers with a diazo compound as additional substance care must be taken that the rays of those wave lengths to which the diazo compound is sensitive penetrate the entire surface apart from entirely dark places. Unless the individual fieldsof the surface act as very sharp color filters this is the case. In this case the dyestuis of the photo-printing paper must be sufficiently dilute and W'ell sensitized so that the gamma of the layer is sufliciently large, the graduation is thus sharp and the colors accordingly are sufficiently accurately reproduced.

The following example illustrates this feature of the invention:-

VNWith 20 grams of a diazo mixture hitherto customary for photo-printing papers is admixed the following mixture:-

0.05 gram safranine GG 0.50 gram avinduline 0.08 gram of the compound of the indodicarbocyanine type. CH3 CH: CH3 CH3 C cin Br CH3 1.5 grams allylthiourea, i. e., thiosinamin 30.0 grams 1% gelatin solution.

After complete solution, furthermore, 0.2 gram dimethylallyl-thiourea is added. (With small variations of the concentration of this latter substance, adjustment can be made of the asynchronism of the characteristic of the dyestuff mixture, i. e., the non-parallelism of the characteristics of the different dyes, along the lines outlined above.) Finally the whole is diluted with a further 50 grams of hot water.

The compound of the indodicarbocyanine type just mentioned is: 10-bromo-lz1z3z3z3'z3 hexamethylindodicarbocyanine bromide, and its preparation is described by Beattie et'al., Journal`of the Chemical Society (London), 1932, page 262.

The allylthiourea, as stated, is mixed with the dyestufs as a rst bleach-out sensitizer which -Will qualitatively. considerably increase the sensitivity of the dyestuffs' to bleaching out, but without any quantitative adjustments of the bleaching-out reactions of the different dyes to close coincidence. The dimethylallylthiourea is subsequently added as the adjusting sensitizer to facilitate adjusting to close correspondence for the different dyes the bleaching-out times required to attain a determined degree of bleach,

by modifying the characteristic curves of bleachout times against sensitizer concentration required to obtain a determined degree of bleach. In the above example also, the allylthiourea is less effective as a. sensitizer than the dimethylallylthiourea. Also, the allylthiourea facilitates the suspension and partial solution in water of the dimethylallylthiourea which by itself is practically insoluble in water.l

The application can also take place without binding agent, the substances being wholly or partly dissolved. in organic solvents. After application they dry or crystallize out. The process can be carried out in such a. manner that only on moistening with water, or with the fixing agent or with the developer, is the fibre colored, l

that is to say it is not till this point that the colors are produced.

The same effect is attained when the dyestuffs are not dissolved but the whole solid mass (dyestuffs and sensitizers) nely pulverized and rubbed into the paper nbre.

The bleaching out layer rendered sufciently sensitive can very advantageously be employed for the copying of color films, in which case in some circumstances they can be employed for the same purpose without the black auxiliary layer.

Having now particularly described and ascertained the naturel of our said invention and in what manner the same is to be performed, we declare that what We claim is:-

1. A bleach-out layer for color photography comprising a sensitive layer carrying a plurality of different dyes, said layer having incorporated therein a bleach-out sensitizer substantially in the concentration determined as the value of sensitizer concentration for which the half-value bleaching-out times for the respective dyes most closely approach coincidence.

2. A bleach-out layer for color photography comprising a sensitive layer carrying a plurality of different dyes and having incorporated therein a bleach-out sensitizer to which each of said dyes is sensitive, said dyes and said sensitizer being so Selected that the curves of half-'value bleaching out times of the respective dyes plotted as a function of th-e sensitizer concentration approach Very closely to meeting in a common point, and said sensitizer being incorporated in said layer substantially in the value of concentration for which said curves of half-Value times most closely approach meeting in a common point.

3. A bleach-out layer for color photography comprising a sensitive layer carrying a plurality of different fugitive dyes respectively in lthe amounts which are optimum for the photographic subject to be reproduced Without the employment of a bleach-out sensitizer, said bleach-out layer V wherein the dyes incorporated are thiazolinocarbocyanine salts.

7. A bleach-out layer according to claim 2,

in'g a plurality of diierent fugitive dyes and having incorporated therein a bleach-out sensitizer to which each of said dyes is sensitive substantially in the concentration for which the halfvalue bleaching-out times for the respective dyes most closely approach coincidence, and further comprising a separate control layer superposed on said first named layer and having incorporated therein a light-sensitive substance which will be rendered black over the unexposed portions of said control layer in the finished reproduction.

11. A'bleach-out layer according to claim 2, Whereinqthere is incorporated as an additional control agent a light-sensitive substance which under the process of developing will be rendered black over the unexposed portions of the layer.

12. In the manufacture of bleaching-out layers for color photography from a base'sensitive layer, the process which consists in incorporating in said sensitive layer a plurality of diierent fugitive dyes, adding to different test specimens of said layer a bleach-out sensitizer t which each-of said dyes is responsive as to bleaching successive- 1y in varying amounts, determining for which value of sensitizer concentration the half-value bleaching-out times for the respective dyes most closely approach coincidence, and incorporating in the production specimens of said bleachingout layers said sensitizer in the concentration so determined. l

13. In the manufacture of bleaching-out layers for color photography from a base sensitive layer, the process which consists in incorporating in said sensitive layer a plurality of diierent fugitive dyes, adding to different test specimens of said layer a bleach-out sensitizer to which each'of said ldyes is responsive as to bleaching out suc.-

cessively in varying amounts, determining fory which value of sensitizer concentration the halfvalue bleaching-out times for the respective dyes most closely approach coincidence, incorporating in the production specimens of said bleaching-out layers said sensitizer in the concentration so determined, and applying to said layer a light-sensitive compound which will be rendered black over the unexposed portions ofthe tive dyes, adding to diierent test specimens of said layer a bleach-out sensitizer to which each of said dyes is responsive as to bleaching out successively in varying amounts, determining for which value of sensitizer concentration the halfvalue bleaching-out times for the respective dyes most closely approach coincidence, incorporating in the production specimens of said bleachingout layers said sensitizer in the concentration so determined, and applying ierric chloride to said layer. v

15. In the manufacture of bleaching-out layers for color photography from a base sensitive layer, the process which consists in incorporating .in said sensitive layer a plurality of different fugitive dyes, adding to diierent test specimens of said layer a bleach-out sensitizer to which each of said dyes is responsive as to bleaching out successively in varying amounts, determining for which value of sensitizer concentration the halfvalue bleaching-out times for the respective dyes most closely approach coincidence, incorporating in the production specimens of said bleachingout layers said sensitizer in the concentration so determined, and applying an organic diazo compound to said layer. Y

16. In the manufacture of bleaching-out layers for color photography from a base sensitive layer, the process which consists in incorporating in said sensitive layer a plurality of different fugitive dyes, adding to diierent test specimens of said layer a bleach-out sensitizer to which each of said dyes is responsive as to bleaching successively in varying amounts, determining for which value o f sensitizer concentration the bleachingout times for the respective dyes required to lbleach out a determined substantial percentage of the quantity of dyes present most closely approach coincidence, and incorporating in the production specimens of said bleaching-out layers said sensitizer in the concentration so determined.

EaNs'r Rs'r. ANDR FOLGAR.

Sept. 15, 1936. SCHMIDT 2,054,391

MULTIPLE CYLINDERWEB DRIER Filed July 25, 1955

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