Patented Apr. 20, 1948 2,440,206 UNITED STATES PATENT office retary2,440,206 to General Aniline & Film Corporation, Ne York, N.Y., a corporation of Delaware . No Drawing. Application September 16, 1944, serial No. 554,539 6 Claims. (C. 95-7) 1. 2 This invention relates to the improvement of thionates, preferably those containing a total of photographic emulsions and more particularly to three or more sulfur atoms and thioanhydrides the incorporation of antifogging or stabilizing of Sulfonic acids containing a total of three or agents into silver halide emulsions. more sulfur atoms will improve the stabilization A large number of substances have been de characteristic of photographic emulsions con Scribed as being effective in preventing an in taining a sulfinate or seleninate to an extent un crease in fog and thus stabilizing or controlling obtainable With the Sulfinate. Or seleniinate treat the keeping quality of photographic emulsions. ment. The remarkably improved result is mani Many of these stabilizers have definitelimitations fested in a reduction of the fog density to approx in their ability to produce desirable effects with O imately 50% of that obtained when using sulfinate out producing unfavorable side reactions. Thus, or Seleniinate alone. ... Thus, films having a fog Some stabilizers desensitize or produce fog, when density of 25 to 30 density units after having added during the mixing or ripening, but exert added sulfinate are reduced to a fog density of 12 favorable effects when added to the melted emul to 15 density units by adding small amounts of Sion before coating. It is one object of this in 5 a polythionate or thioanhydride. vention, therefore, to produce a stabilized emul This reduction in fog density produces a better Sion of improved photographic quality while in clearness, better keeping quality and an unusual corporating the stabilizing agents over a wider brilliance which is especially desirable in medical range of application during the manufacture of and industrial radiographs. Concentrations of photographic emulsions. 0.025-0.500% by mol of the polythionate or thio In U. S. Patent 2,057,764 there is described a anhydride compounds to the Sufinates or selenin process of stabilizing photographic silver halide ates are sufficient to produce this reduction in fog emulsions by incorporating sulfinic or seleninic density. Suitable polythionates and thioanhy acids Or their salts into the emulsion in the form drides which will produce this desirable effect of a solution in a suitable solvent during the prep When used in combination. With a Sulfinate or aration of the emulsion or by incorporating the Seleniinate include Such compounds as sodium Stabilizer into the finished emulsion by bathing trithionate, Sodium tetrathionate, potassium pen : the emulsion layer with a weak solution of the tathionate, potassium, hexathionate, dibenzene ! stabilizer. It is stated that the fogging influence sulfonyl mono-, di-, tri-, and tetrasulfide. of Supports, preparation layers, backing layers, 30 Polythionates have been used in silver halide ; intermediate layers, sublayers, protective layers, emulsions without Sufinates or Seleniinates for the or baryta layers could be prevented by incorpor production of photographic effects wherein the atting these stabilizers into Such layers. As com polythionate is employed as a ripening substance, pared with films which were not provided with that is, a substance capable of enhancing the the Sulfinic acid or seleninic acid stabilizers, it is 35 photographic speed. Such a process is described stated that the films containing the stabilizer in U.S. Patent 1673,522. It is interesting to note showed a fog density unit of approximately one that this use of polythionates for enchancing the half. It has now been discovered that the stabi sensitivity of the emulsion is usually accom lizing effect of the sulfinic or Seleninic acids or panied by a definiteloSS of clearness. It is, there their salts, as described in U. S. Patent 2,057,764, 40 fore, Surprising that polythionates exert a fog can be considerably improved and the range of preventing or anti-ripening or stabilizing action application greatly extended if small amounts of when used in combination with sulfinates or sel polythionic acids or their alkalimetal salts of the eninates. formula, The polythionates or thioanhydrides, which MOSO2-Sn-SO2OM 45 produce this increased stabilization, can be formed in the solution of the Sulfinate or selenin wherein M is an alkali metal or hydrogen and n. ate by reaction between Some of the Sulfinate or is a positive integer, or of the thioanhydrides of seleninate and colloidal sulfur added to the sul sulfonic acids of the formula finate or seleninate solution, or nascent sulfur or 50 Selenium produced by catalytic decomposition of RSO2-S-SO2R, a suitable labile sulfur compound such as sodium wherein R is an organic radical and n is a positive thiosulfate which has been added to the sulfinate integer, are present in the emulsions containing or seleninate solution. This invention, therefore, the sulfinates or seleninates. It has been ob contemplates and includes such formation of the served that extremely small quantitles of poly- 55 polythionates or thioanhydrides in the sulfinate 2,440,206 3 4. - - - or seleninate solution. In carrying out this phase amples will serve to further illustrate the inven of the invention, the colloidal sulfur or selenium, tion, it being understood that the invention is not or labile sulfur compound and its decomposition limited thereto. catalyst such as Sodium arsenite, is added to the Eacample I Sulfinate or Seleniinate Solution and allowed to To One kilogram of melted gelatino-silver stand for several days at room temperature or halide emulsion containing from 6 to 7% of sil heated for a short time at a raised temperature wer halide and approximately 8% gelatin, there of approximately 40° C. The polythionates and were added during ripening: thionanhydrides are then formed in the Sulfinate . or seleniinate solution in accordance with the fol. 15 cc. of a 20% Solution of the Sodium Salt of 10 benzene Sulfinic acid in water and lowing mechanism: s 5 cc. of potassium pentathionate of a concentra I. RSO Na -- S - RSO.S.Na . tion of one gram per liter in water. II. 4RSO2SNa -- nS --> ------- - - - - After ripening, the emulsion was cast on a film RSosn.so, R + RSSR + Nasso. + Nags 15 base and cut into test film lengths. Similar test III. 4RSSR - 2Na2S - 6NaOH - - . 8RSNa -- Na2S2O3 +3HO - ; films were made with the same silver halide emull Sion but without the addition of either the So IV. Na2S2O3 eatO Na2SnO6 or NaOSO-S-SOONa . - - dium Salt of benzene Sulfinic acid or the potas C8 sium pentathionate. Additional Similar test films 20 were made with the same silver halide emulsion to wherein R is an organic radical, n is a positive which had been added during ripening the same integer, and the suifur may be replaced by se quantity of the sodium salt of benzene sulfinic lenium. - ... acid as above, but omitting the potassium penta Thus as a specific example, sodium benzene thionate. sulfinate plus sulfur yields sodium benzene thio The fog density of each of these types of test sulfonate (Equation #I). This sodium benzene film was determined for the freshly prepared thiosulfonate further reacts with sulfur to form film and test pieces of each type were then in the thioanhydrides, dibenzene sulfonyl polysul cubated for six days at 50° C. It was observed fides (Equation #II). The by-products are di that the fog density of the films treated with phenyl disulfides and sodium sulfide. The di 30 benzene sodium sulfinate solution to which had phenyl disulfide further reacts to form thiophenol been added potassium pentathionate was de and sodium thiosulfate (Equation III) which lat creased by 50%, in the case of the freshly pre ter can be easily oxidized to sodium polythionate pared film, and about 45%, in the case of the (Equation IV). The sodium thiosulfate may, of incubated film, of the fog density of the films course, be added as such to the sulfinate or sele 35 ninate solution and be directly oxidized to so which had been treated only with sodium ben dium polythionate. In either case, any suitable Zene Sulfinate. oxidizing catalyst may be employed, such as salts Eacample II of arsenic, tin and antimony. I have observed To one kilogram of melted gelatino-silver that such catalysts may also accelerate the oxi 40 halide emulsion containing from 6 to 7% silver dation to polythionates of thiosulfuric acid ester halide and approximately 8% gelatin, there were saltsin alkaline solutions, Suchthiosulfuric acid added during ripening: - ester salts as, for instance, phenylthiosulfuric 5 cc. of a 20% solution of a sodium salt of ben acid ester sodium salt or small amounts of thio Zene seleninic acid in water and sulfates or compounds of similar structures may 45 5 cc. of sodium tetrathionate of a concentration often be present in technical grades of sulfinates of one gram per liter in water. regardless of how the sulfinate has been pre pared. In order to improve such technical grades After ripening the emulsion was cast on a film of sulfinates or seleniinates for the purpose of fog base and cut into test film lengths. Similar test 50 films were made of the silver halide-emulsion but prevention in photographic emulsions and at without the addition of either of the sodium salt the same time to eliminate the time consuming of benzene seleninic acid or the sodium tetra and expensive procedure of chemical purification thionate. Additional similar test films were also and recrystallization one of the above mentioned made with the same silver halide emulsion to catalysts, such as sodium ars e or a mixture of which was added the same quantity of the so arsenic and tin salts, may be a dium salt of benzene seleninic acid as above, but finates during the manufactu omitting the sodium tetrathionate.