US2319344A - Process for stabilizing prints obtained by photographic bleaching - Google Patents

Description

by washing,

2. Rendering thedyestufi, or respectively the Patented May18, 1943 PROCESS FOR STABILIZING- PRINTS. 013-" TAIN ED BY PHOTOGRAPHIC BLEACHING Andi- Polgar and Charles Halmos, Paris, France; vested in the Alien Property Custodian No Drawing. Application December 15, 1939, Serial No. 309,482. In France December 15, 1938 1 Claim. (01. 95-7 The present invention has for object various treatments of bleaching layers sensitized by thiocarbamic derivatives, in order to ensure or improve the stability of the prints obtained by photographic bleaching.

It is known that the methods proposed up to now for fixing the bleaching layers against the action of light nearly exclusively belong to the dyeing art, as mordanting by tanin, treatment with copper solutions, etc. The inconveniences of these-methods consisted in the coloration of thelight parts of the proofs printed, in the changing, sometimes fundamental, of the tints obtained and in the necessityof eiiecting. long washings for eliminating the agent in excess.

It has also been proposed, especially for completing the treatments mentioned, to use baths of organic solvents, such as alcohol for elimihating the sensitizers. It has been, proposed, for instance for basic dye-stuffs, to convert them into borofluoric derivatives and to eliminate the sensiti'zer by dissolution in a suitable solvent. It has been proposed to use powerful oxidising agents (nitrous acid) or powerful reducing agents (sulphurous acid) for destroying them. These processes allow of only incompletely attaining the result sought for and are sometimes prejudicial to the organic materials'with which they are placed in contact, and particularly the substratum, the dye-stufis andthe support.

The present invention is based on the idea that an intimate contact is necessary between the dyestuffs and the sensitiz'ers, for imparting to these dye-stufis a good sensitiveness to light, and that 4 the dissociation of the sensitizer and of the dyestufi, considerably diminish the sensitivenessto light of the dye-stuffs.

. According to the invention, thg layers are treated, after exposure to light, by one or more solutions having the property of precipitating the sensitizer. By precipitating the sensitizer a dissociation of the dyestuffs and sensitizers is obtained.

' It need be, respectively 80001111128 to the composition of the layer and according to the dyestuiis it contains, the precipitation of the semi-- tizer will be completed by one or both of the following accessory means:

1. Elimination of the sensitizer from the layer dyestuffs insoluble.

The most simple method of carrying into practice this process consists in the fact that the layer,,,after exposure tolight is introduced in an aqueous solution capable- 0f completely precipitating the sensitizer. Use is made for instance of a, solution of mercuric chloride as solution for precipitating the thiourea derivative. case of a highly soluble thiourea derivative, the elimination of the sensitizer from the layer takes place extremely rapidly, since, among other reascns, the concentration of the sensitizer in the bath is constantly practically null, .owing to the precipitation. Another advantage in this case is that by choosing a suitable concentration of the mercury salt, the precipitate is only formed in the precipitating bath and not-on the layer itself, as it is soluble in an excess of the thiourea derivative.

If the sensitizer is soluble inwater, it will be generally, first of all, eliminated. for the mailer part by washing in water, and alone the last traces of sensitizer, practically extraordinarily diflicult to eliminate, will be precipitated in a suitable manner; The layer will be perfectly desensitized thereby, as an adsorption of the remaining portions of sensitizer on the dyestufi v particles will no longer be possible.

Concerning the rendering of the dyestui! insoluble, this action can be obtained by the use of a suitable bath, if need be, even before eliminating the sensitizer by washing; the sensitizer can also be eliminated by washing in a bath having the faculty of precipitating dyestuffs; the dyestufis can alsobe rendered insoluble beforehand, when manufacturing the sensitized layer;

finally the dyestulI can be rendered insoluble in the very bath intended for precipitating thesensitizer. This latter result is obtained in case it is a question of basic dyestuffs, for instance, by the above mentioned bath, consisting in a solution of mercuric chloride. For instance, the Nile blue dyestufl (Schultz, VII, edition No. 1029) is;

by means of this bath, instantaneously precipitated, fined and maintained in the layer. For increasing the fastness of dyestufis to washin in case basic dyestufls are under consideration,

if acid dyestufls and more especially azoic dyestufls are contemplated, use'can be made, for

7 that purpose, oi organic quaternary ammonium bases, also called cationactive substances, or use can be made for rendering the dyestufl. insoluble, oi soluble derivatives of tin, silicon, tungsten, and

molybdenum. As mentioned use can be made for precipitating the sensitizer and rendering the dyestufis insoluble, of a single solution, if need be, a solution of a plurality of products,

For eliminating the activity by precipitating the thiourea derivatives as sensitizers, the most In the 2' suitable products are actually, mercury salts.

Results are also obtained for instance with certain compound salts of tin and silicon.

These latter salts have the property of forming 4 with an excess of thiocarbamic derivative or by mixture of sulpho-carbamide and mercuric chloride, these substances can also be incorporated beforehand, when manufacturing the sensitive layer.-

A few examples of the process according to the invention will be given hereinafter, it being understood that said examples are not limiting.

Example 1.-'1'he following solution is prepared: 200 grams of water, 30 grams of ammonium chlorostannate, 18 grams of silicotungstic acid. A paper bleaching print prepared with basic dyestufls is treated in a bath of this solution, it is washed with water for 5 minutes,.then it is dried. The stability to light of the print will thus' correspond to the initial stability of the basic dyestuffs incorporated, and the tints to the initial colours.

Example Z.A layer of. the solution according to Example 1 is applied on an exposed bleaching out layer. It is dried. The layer is nearly completely desensitized, without changing the tints.

' Example 3.-On an exposed bleaching out layer containing naphtionic red, oxalic acid and diethanolallylsulpho-urea, is spread a solution of. m diacetylamino phenyl trimethylammonium chloride. it is then washed for a few minutes. Perfect fastness to light is obtained. a

Example 4.After exposure a trichroiiie bleaching out layer is treated. containing as dyestuffs only basic dyestuffs and sulphocarbamic derivatives, as sensitizers, first of all in the following bath: 200 grams of water, 10 grams of mercuric chloride, 1 gram of concentrated hydrochloric acid. Then it is washed in the following bath: 1000 grams of water, 50 grams of sulphourea.

. Example 5.A bleaching out layer is prepared as. follows: in 1000 grams of water are dissolved grams of gelatlne, 5 grams of hydrochloric acid, 4 grams of Nile blue sulphate, 6.5 grams of Flavindulin O, 3.5 grams of sulphopyronine G. 100 grams of acetamide and grams of oxalic acid. Then, the mixture of grams of diethylallylsulpho-urea and 25 grams of mercuric chloride which was previously heated with 50 grams of water, is added. It is spread on paper, exposed to light under a negative and the proof is washed for 15 minutes.

We claim Process for stabilizing prints obtained by photographic bleaching of layers containing bleaching dyestuffs and thiourea derivatives,

consisting in eliminating, after exposure of the ANDRE POLGAR. cmanss HALMOS.