US3598588A - Processing solution for silver halide photographic material after fixation process - Google Patents

Abstract

HARMFUL EFFECT OF RESIDUAL THIOSULFATE IN PROCESSED PHOTOGRAPHS IS REDUCED BY A FINAL RINSE IN AQUEOUS SOLUTION OF COMPOUND HAVING MONOCHLORO- OR MONOBROMO-SUBSTITUTED CARBON AND ALSO HAVING AN ALDEHYDE, CARBOXYL OR SULFO GROUP, THE CHLORINE OR BROMINE OF WHICH REACTS WITH THE THIOSULFATE. SOLUTION CAN HAVE PH OR 4 TO 8.

Description

United States Patent Int. Cl. G03c5/26, 5/38 US. Cl. 96-50 5 Claims ABSTRACT OF THE DISCLOSURE Harmful effect of residual thiosulfate in processed photographs is reduced by a final rinse in aqueous solution of compound having monochloroor monobromo-substituted carbon and also having an aldehyde, carboxyl or sulfo group, the chlorine or bromine of which reacts with the thiosulfate. Solution can have pH of 4 to 8.

The invention relates to a method of processing exposed photographic material, characterized by a final bath which leads to photographic images with improved keeping qualities.

Conventional photographic processing includes the fixing of the unexposed silver halide, whereby the silver halide is converted to a complex compound with alkali metal or ammonium thiosulfates and, in the subsequent rinsing, is washed out to a greater or lesser extent, depending on the rinsing period and water temperature. Practically complete removal of the silver thiosulfate complex requires rinsing for at least half an hour at about 25 C. Residual thiosulfate is highly disadvantageous, since particularly in a weakly acidic photographic layer the density of the silver image is reduced during storage because of the formation of silver sulfide. Moreover, yellowish or brownish stains are formed in the black silver, particularly under tropical conditions. If the residual thiosulfate is uniformly distributed in the layer and in the support, a uniform decrease in density occurs, and this is particularly noticeable in the brighter image portions by a color change towards yellow.

Since, with machine processing, long rinsing times re quire very large machines and a. high consumption of water, a number of measures have been described by means of which the harmful effect of the residual thiosulfate is alleviated by a separate subsequent bath. Three types of subsequent baths have been employed. One type comprises oxidizing baths containing such compounds as chlorite or hypochlorite. The disadvantage of these baths is that developer residues carried over with the silver image itself are also oxidized. Furthermore, baths having a high concentration of sulfites or phosphates have been described, in order to facilitate rinsing. Finally, the harmful influence of residual thiosulfate can also be suppressed by an alkaline bath, since thiosulfate decomposition occurs more slowly in alkaline media than in acidic. The disadvantage of the last two types of baths is that the harmful influence of the thiosulfate is not eliminated, but is only reduced. Furthermore, with the conventional processing a substantially longer rinsing time is required for pictures on supports having the thickness .of cardboard than for pictures on supports having the thickness of paper. An additional disadvantage is that with the continuously running paper web in continuous printing processors, small quantities of thiosulfate are constantly carried along and these are concentrated in the drying cloth of the drying drum. Because of this, the pictures are once again contaminated with thiosulfate, and this can only be overcome by frequently changing the drying cloth.

It is among the objects of the present invention to modify the known processing methods in such a way that the thiosulfate remaining in the photographic layer after rinsing is converted into a harmless compound.

We now have found that photographic images with excellent keeping qualities are obtained if, after the conventional processing steps, the fixed photographic material is treated with an aqueous solution of a watersoluble organic compound having a monochlorine-substituted or monobromine-substituted carbon, the halogen of which is capable of reacting with thiosulfate.

Water-soluble, aliphatic monochlorine-substituted or monobromine-substituted compounds which further contain at least one aldehyde, carboxyl or sulfo group and which have up to 5 carbon atoms, are preferred. The following are examples of particularly suitable compounds.

monochloroacetic acid monochloroacetaldehyde monochloropropionic acid 2-chloroethane sulfonic acid 2,3-dibromosuccinic acid.

Instead of the free acids, it is obvious that the watersoluble derivatives thereof, such as salts and amides, can also be used.

Particular utility is exhibited by monochloroacetic acid or monochloroacetaldehyde.

The eflicacy of the compounds used in the manner according to the invention is extremely surprising and is limited to monohalogen compounds. Compounds with more than one halogen atom attached to the same carbon atom, for example dichloroacetic or trichloroacetic acids, do not have any noticeable effect.

The aqueous baths used in the processing step according to the invention advantageously contain 0.1 to g. of the monohalogen compounds per liter of bath. Saturated solutions of the compounds can also optionally be used. The optimum concentration can be determined by a few simple routine tests. It depends on the nature of the photographic material and the required treatment time. In most instances, a concentration of 3 to 30 g. per liter is sufficient.

The treatment times can also fluctuate within Wide limits but it is generally sufficient to treat the photographic materials with the bath according to the invention for about 2 minutes. Sometimes the destruction of the residual thiosulfate is not completed in the bath, but since the monohalogen compounds of the inventive invention bath remains in the layer, any remaining thiosulfate that did not react in the bath is completely destroyed during the subsequent hot drying and also during storage of the picture, particularly under tropical conditions.

The usual decomposition reaction of the thiosulfate, which proceeds with formation of hydrogen sulfide and thus conversion of the image silver into silver sulfide, is completely avoided by using the bath according to the invention.

More especially with the mechanical processing of photographic materials, the rinsing time and thus the consumption of water are greatly reduced thereby. Contamination of the drying cloth of the drying drum with thiosulfate and thus a subsequent soiling of the pictures does no longer occur. Thiosulfate on the drying cloth immediately reacts under heat with the monohalogen compound which is likewise on the cloth. Completel durable pictures can thus be obtained on supports independently of the thickness of the support. The high-gloss ca- EXAMPLE A conventional photographic black-and-white positive paper, which comprises a gelatino-silver chlorobromide emulsion layer on a baryta-coated paper support, is exposed to form an image and is developed in a developer having the following composition:

G. Sodium hexametaphosphate 2 Anhydrous sodium sulfite 3O Hydroquinone 4 1-phenylpyrazolidone-3 0.2 Potassium bromide 1 Anhydrous sodium carbonate dissolved in 1 liter of water 30 The developed material is treated for 1 minute in 2% by weight aqueous acetic acid and thereafter is fixed for 3 minutes in a fixing bath of the following composition:

20 g. of potassium metabisulfite 150 g. of anhydrous sodium thiosulfate, dissolved in 1 liter of water A strip of the fixed material is now rinsed for 3 minutes and thereafter subjected to high-glaze drying. Using the ASA method, considerable quantities of residual thiosulfate can be detected in the specimens processed in this way. On being stored in tropical climatic conditions at 40 C. and 98% relative humidity, the silver image, particularly at the areas of low and medium density, is converted, because of thiosulfate decomposition, into silver sulfide and is thus destroyed.

Another strip of the fixed material is rinsed for 1 minute and treated for 2 minutes in a bath having the following composition: 30 g. of sodium chloroacetate dissolved in 1 liter of water.

The high-glaze drying is immediately carried out. Using the ASA method, thiosulfate can no longer be detected or can be detected only in a negligible amount. The keeping qualities of the silver image in tropical climatic conditions are excellent.

The favourable effect of the processing according to the invention is also experienced, to the same degree, when using other types of photographic materials, such as multilayer photographic materials or color photographic materials.

What is claimed is:

1. 'In the process for the production of photographic images by exposure of a photographic material containing at least one light-sensitive silver halide emulsion layer and developing and fixing the exposed material, the improvement according to which the fixed material is treated with an aqueous solution of a water-soluble aliphatic compound having a monochlorine substituted or monobromine substituted carbon and at least one aldehyde, carboxyl or sulfo group having up to 5 carbon atoms, the chlorine or bromine being capable of reacting with thiosulfate.

2. A process as defined by claim 1, in which the compound is monochloroacetic acid or a salt thereof.

3. A process as defined by claim 1, in which the aqueous solution contains the aliphatic monochlorine or mo nobromine substituted compound in a quantity of 0.1 to 100 g. per liter. 7

4. A process as defined by claim 1, in which the aqueous solution has a pH of from 4 to 8.

5. A process as defined by claim 1 in which the compound is monochloroacetic acid, monochloroacetaldehyde, 2-chloroethane sulfonic acid, 2,3-dibromosuccinic acid, monochloropropionic acid or salts or amides of said acids.

References Cited UNITED STATES PATENTS 2,387,000 10/ 1945 Alburger 88 2,343,696 3/1944 Muehler et a1. 9588 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R. 96--61