US2860978A - Photographic washing accelerators - Google Patents

Description

Unite 4 2,860,978 PHOTOGRAPHIC WASHING ACCELERATORS No Drawing. Application April 1, 1954 Serial No. 420,454

1 Claim. (Cl. 96-61) This invention relates to photography and more particularly to a process for accelerating the removal of sodium thiosulfate and silver salts from fixed photographic materials by the use of aqueous soluble sulfite washing solutions. 7

A common method of washing the fixed photographic image to remove the fixing chemicals is to employ running water from one-half hour to an hour. This removal of the fixing chemicals and the soluble by-products of the fixing operation is required in order to prevent deterioration of the print, film or plate.

Heretofore numerous hypo eliminators and washing accelerators have been described in the literature which are designed to lessen the washing time. Many of these have been tabulated by Crabtree, Eaton and Muehler in a paper printed in PSA J. 6:6-14, 1940, and they include oxidizing agents, alkalies and common salt. The latter substance, sodium chloride was presumed by Eaton and Crabtree, J. Soc. Mot. Pict. Eng, June 1, 1943, 380-391, to be the active ingredient in the accelerated washing obtained with sea water.

The washing accelerators described in the above literature while operable have a number of disadvantages. The oxidizing agents are inconvenient to use, unstable, and often cause excessive softening of the emulsion, as do the alkalies. Further, they tend to remove the soluble sodium thiosulfates but not the less soluble silver thiosulfates. In fact, the action of such Washing accelerators is not as intense as desired particularly with photographic papers.

It is the principal object of the present invention to pro vide an improved method of accelerating the removal of hypo and silver salts from fixed. photographic materials.

Another object is to remove these thiosulfates more rapidly and with less inconvenience than occasioned by previous methods.

Still another object is to remove the residual hypo concentration and to stabilize the hypo compounds which are not removed so that the tendency toward fading and staining is greatly reduced.

A further object of the invention is to improve the stability of the treated photographic material.

Another object is to provide an improved washing solution for washing fixed photographic images.

Other objects will appear hereinafter.

In accordance with the present invention these and other objects are attained by employing as a Washing medium for washing fixed photographic images an aqueous solution containing one or more soluble sulfites. The sulfite ion employed may be the sodium salt as well as soluble sulfites of alkali metals and amines. Acid sulfites and neutral sulfites may be employed and the pH adjusted if desired by the addition of appropriate alkalies or alkaline or acidic substances. The preferable pH range for such a preparation is between pH values of 4 and 10, and a neutral solution, of substantially pH=7, has proved particularly useful. The sulfite may be pre- States Patent 2,860,978 Patented Nov. 18 1958 Following fixation in a fixing bath which contains silver from previous use, Kodak Velox F-3 single weight paper was bathed for 5 minutes in (a) water, (b) a 2% solution of sodium bisulfite, and (c) a 2% solution of sodium sulfite. utes in cold water. Measurementof silver residual in sample prints after each washing showed that both the sulfite and bisulfite were effective in aiding its removal, the concentration being reduced from 0.017 mg. per square inch to 0.002 mg. per square inch. The residual hypo concentrations were 0.22 mg. per square inch (water only), 0.12 mg. per square inch (bisulfite treated), and 0.03Jmg. persquare inch (sulfite treated).

Example 2 Kodak Microcard paper, which is difiicult to free from hypo in short washing periods, was fixed in a fresh fixing bath of standard composition, washed 3 minutes, and bathed for 1 minute in (a) a 2% solution of sodium sulfite, and (b) a mixture containing 10% sodium sulfite and 2% sodium bicarbonate. The Washing was then continued for 2 more minutes. The hypo content of paper washed only for 6 minutes Was found to be 0.19 mg. per square inch, and these prints faded rapidly on moist incubatiOnat F., PSA I. 238:8l7, 1948, Method for Example 3 A bath containing sodium sulfite (2%) and sodium bicarbonate (1%) was employed with a series of fixed photographic papers, of fixing baths (both fresh and exhausted), and of washing cycles. This solution was compared with the prior art employed in removing hypo including the use of (1) an alkali (sodium metaborate),

(2) a neutral salt (sodium sulfate), and (3) the powerful peroxide-ammonia hypo eliminator, PSA J. 6:6-14, 1940. The papers. employed included single weight, double weight, and extra thin bases, with and without baryta coatings, and in one case, a Water resistant base was employed. The hypo content obtained in these tests was in every case comparable to the lowest hypo content achieved by prior art methods (usually obtained with the HE-2, peroxide-ammonia eliminator), while the stability of the resultant image was in general superior to that obtained by any other method. The silver content of the treated prints was particularly low and less than that obtained with alkali treatment or with peroxide-ammonia.

Example 4 Mixtures of sodium bisulfite with tetra sodium pyro- The prints Were then washed for 15 min- Bathing in the sodium 3 phosphate, sodium bisulfite'with disodium hydrogen phosphate, and sodium sulfite with sodium bisulfite were all found effective in removing hypo from Kodak Opal G paper andinstabilizing the image.

Example. 5 c

A 2% solution of sodium sulfite containing, in addition, an antiplumming agent was found'to assist in'the removal" Example 6 In place of the sodium sulfite employed in Examples 1 to 5, we have repeated these examples employinglithium,

potassium and ammonium sulfites and have found all,

of them are fully as effective as the sodium sulfite for hypo elimination from fixed photographic materials.v

Amine sulfites, such as triethanolamine sulfite, andthe sulfite salts of ethylene diamine would also be entirely;

suitable.

Example 7 We have found that the following washingsolution is' particularly suited for washing fixed photographic materials.

Grams per'liter Sodium sulfite 20,0 Sodium bisulfit 5.0

Sequestrene Na-4 (tetrasodium salt of ethylene di amine tetracetic acid) 0.5

This solution has been found to be highly effective I for both films and papers and has been particularly beneficial in obtaining archival levels when washingmicro-t films. It has been found-possible to greatly dilute this formula and still obtain efiective hypo elimination'when film is immersed in the bath for a long period and in one application the bath has been beneficially employed at of the above concentration.

It appears that the effectiveness of the-sulfite'solutions may be due to the following mechanisms: (a) Upon immersion in the sodium sulfite solution the thiosulfate ions absorbed to the gelatin, are displaced by sulfite ions from the solution until equilibrium is reached; (b) if alkaline,

the solution also tends to displace the alum, which has a marked mordanting action for thiosulfate ions, and (c) the sulfite ions, left in the print, stabilize any residual hypo by causing the reaction to shift to the right.

It has also been proposed to employ as a washing'aid a solution containing both a soluble salt of a polyvalent anion and an alkaline substance. Suitable anions in;- clude sulfate, phosphate, pyrophosphate, tetraphosphate and citrate, which may be employed as sodium, potassium ammonium, lithium and magnesium salts. These salts may be employed in concentrations of 0.5 to 10% but the preferred range is l to 2%. Suitable alkalies include sodium mctaborate, sodium tetraborate, sodium bicarbonate, sodium sesquicarbonate, sodium carbonate, ammonium hydroxide, sodium hydroxide, dibasic and tribasic phosphates, and organic amines. Potassium, ammonium, and lithium salts may, of course, be substituted for the sodium salts provided the alkalinity is suitable. These alkalies may be,used in concentrations of from 0.25% to 10% depending on the specific alkali and the eifect desired.

The following is an example of the use of these washing aids.

Example 8 Kodak Velox F-3 (single weight) and Platino G-3 (double weight) papers were developed, rinsed and 4 fixed in a bath of Kodak F-S containing silver to simulate use. The F-5 acid hardening fixing bath is for general use with films and plates as disclosed on page 15 in the Book of Formulas published by Eastman Kodak Company, 1936. The bath contains sodium thiosulfate 960.0 grams, sodium sulfite grams,.acetic acid 190 cc., boric acid crystals 30 grams, potassium alum 60 grams and water. 6.5 liters. They were then immersed in one of the following solutions for 5 minutes and washed for 20 minutes. The hypo and silver concentrations were estimated with the KodakHT-Z solution. The HT-Z solution contains water 1750 cc., acetic acid 125.0 cc., silver nitrate 7.5 grams. In addition, strips were given moist incubation for 2 weeks at 110 F. While the sodium thiosulfate alone produced a significant reduction in silver and hypo, particularly on the single weight paper, the further addition of the alkali caused a more complete elimination of hypo and silver, and further, greatly improved the stability towardsmoist incubation. For example,jwhereas prints treated only in water faded severely in 2 days, and those in sodium sulfate faded in 7 days, those bathed in solutions containing sodium sulfite and an alkali faded only slightly in 14 days.

i The above solutions efiiciently cause the elimination of hypo and greatly reduce the danger of fading from this source. However, another cause of impermanence is the reaction of the image with gaseous vapors, particularly paint vapors and other sources of peroxide. We have foundthat we can protect against this type of fading, as well'as that due to residual thiosulfate, by adding a reactive selenium compound to the sulfite washing accelerator. Another benefit of-the addition of this type of selenium compound is that the image is also protected against the change of image tone on hot drying known as plumming. In accomplishing this protection the image is very lightly reacted with the selenium compoundbut to a smallenough' extent that it need not necessarily be visibly affected.

Compounds containing a labile selenium atom suitable for this purpose are the selenosulfates, selenocyanates and the selenides. Of these the selenosulfates are par, ticularly' effective. The selenosulfates may be readily formed by dissolving metallic selenium in a solution of an alkali metal sulfite.

The following examples illustrate the preparation of such a selenosulfate and its incorporation in a washing aid.

Example 9 Ten grams of metallic selenium and grams of potassium sulfite were mixed and 200 cc. of warm water were added slowly with stirring. Stirring was continued for 5 minutes and the solution then filtered leaving a residue of 0.05 gram of unreacted selenium or impurity. The solutionwas evaporated to dryness and yielded approximately grams of a pure white powder comprising a mixture of potassium selenosulfate with excess potassium sulfite. The above preparation containing 10% selenium by weight was blended with various sulfite and bisulfite mixtures. It was found to be completely stable when blended with sodium sulfite, potassium sulfite or potassium metabisulfite but visible discoloration occurred when sodium bisulfite was present in the mixture. The preferred mixture contained 10 grams of the above potassium selenosulfate-potassium sulfite mixture, 200 grams of sodium sulfite and 5 grams of tetra-sodium salt of ethylene diamine tetracetic acid. A solution of 21 grams of this powder in 1000 cc. water was used to treat processed prints after fixing and found effective in preventing peroxide fading.

Example 10 To a sulfite washing accelerator containing, per liter of working strength bath, 20 grams of sodium sulfite and '5 grams of sodium bisulfite, quantities of selenium varying-from 1.0to 0.02 gram per liter were added by heating in a more concentrated form and then diluting for use. Kodak Platino paper was processed normally, bathed in this solution for 3 minutes, and washed for 20 minutes. The hypo content was low (about 0.05 mg. per square inch) but when the prints were exposed to an atmosphere of vapors from a hydrogen peroxide solution the control prints (bathed in the unmodified sulfite solution or washed only) became very brown in hue and lost density, while those treated with the solutions containing the selenium, even at the lowest concentration employed, were almost completely unaffected. Some change in image tone was produced by the highest concentration of selenium, but not by the lower concentrations.

Example 11 print, on strong exposure to paint vapors faded in a similar manner, while that slightly selenided proved entirely stable.

Example 12 Yet another type of image instability is the shift in hue and density which may occur on the hot drying of a print. The prints of Example 11 were subjected to a standard plumming test by immersing a portion in water at 190 F. for 30 seconds. The Athena print which had been treated in the solution containing selenium showed little plumming tendency whereas the control print strongly showed the development of a strong plum color. The same qualitative difference was noted for the Medalist print, although the plumming of the control was here less evident.

We claim:

In the method of exposing, developing, fixing, water washing and drying a gelatin-silver halide emulsion layer, the improvement residing in the step which consists in rinsing said emulsion layer intermediate the said fixing and water washing steps with a solution consisting of about 20.0 grams sodium sulfite, 5.0 grams sodium bisulfite and 0.5 gram tetrasodium salt of ethylene diamine tetraacetic acid per liter of solution, whereby the time of the duration of said water washing step is materially reduced.

References Cited in the file of this patent UNITED STATES PATENTS 1,064,379 Rehlander June 10, 1913 1,286,890 Bullock Dec. 3, 1918 1,499,749 Rehlander July 21, 1924 2,024,644 Hickman et a1. Dec. 17, 1935 2,172,216 Miller Sept. 5, 1939 2,382,683 Wadman Aug. 14, 1945 2,475,134 Harsh July 5, 1949 2,607,686 Current Aug. 19, 1952 2,656,273 Henn et a1. Oct. 20, 1953 OTHER REFERENCES Photographische Korrespondenz (January 1918), No. 688, pages 9-17.

La R. F. P. C. (Nov. 1, 1930), pages 332, 334.