Patented Jan. 18, 1944 2,339,309 UNITED STATES PATENT OFFICE 2,339,309 PHOTOGRAPHIC REDUCING COMPOST ON AND PROCESS John Raul Weber, South River, N.J., and Lynn Barratt Morris, Washington, D. C., assignors, by mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del, a cor poration of Delaware No Drawing. Application September 25, 1941, Serial No. 412,340 21 Claims. (C. 95-88) This invention relates to photographic compo forms set forth above, which may undergo re sitions and more particularly to photographic arrangement depending upon whether the COm processing solutions and to photographic proc pound is in acid or alkaline medium, or upon esses for utilizing such compositions. In one of physical characteristics such as temperature and its more specific aspects it relates to photographic pressure. reducing solutions for treating silver salts and photographic processes utilizing such solutions. Furthermore, it is conceivable, considering the In some of its further aspects it relates to new Second formula, that it forms a salt when in alka chemical compositions for photographic develop line Solution e. g. the sodium sulfinate when in ment and toning. Sodium hydroxide solution. It is further con O ceivable that in acid solution it forms salts on the This invention has for an object to provide new imino group, for instance, a hydrochloride. and useful reducing compositions for silver salts. Since the utility of the compound in accord A further object is to provide a reducing agent ance with this invention does not depend upon which can be used for the reduction of photo the exact structure of the oxygenated reaction graphic images in alkaline, neutral or acid media. 5 product of thiourea or hydrocarbon substituted A still further object is to provide more effective thiourea with hydrogen peroxide, and for conven and more economical reducing agents which can ience, the names imino-amino-methane sulfinic be used in acid media. A still further object is to acid or formamidine sulfinic acid will be used. provide new and useful developer solutions. An The expression an imino-amino-methane sulfinic other object is to provide developer solutions for 20 acid will be used to cover formamidine sulfinic reversal processes. Yet another object is to pro acid and its derivatives which are capable of re vide a practical and economical means for toning ducing silver salts. a silver image to produce warm and pleasing To be more specific, it has been found that an brown to sepia toned images. Still other objects imino-amino-methane sulfinic acid in aqueous will be apparent from the following description 25 Solution and especially formamidine sulfinic acid of the invention. is capable of preferential reduction of exposed It has been found that the oxygenated reaction silver halide grains in the presence of unexposed products of hydrogen peroxide with thiourea and silver halides to give a photographic image so certain of its hydrocarbon substitution products long as the solution is definitely acid. However, have considerable utility in photographic proc 30 if the pH of the solution is increased toward neu essing baths especially for reducing silver salts to tral, the reduction potential of the compound in metallic silver in photographic elements. creases, tending to give an overall blackening ef The exact structure of oxygenated reaction fect which is relatively weak at a pH of 6 but products of thiourea, with hydrogen peroxide pre quite powerful at pH values in excess of 6.8. pared from these reactants in neutral solution is 35 The last mentioned effect is advantageously not known with certainty. It has been called used in accordance with one aspect of the inven thiourea dioxide by some investigators which is tion in reversal processes. The Ordinary proc indicative of a formula such as that set forth in esses of preparing positive images by removal of (A) below. Others, however, have advanced the a negative image, followed by reduction of the name imino-amino-methane-sulfinic acid and 40 remaining silver halides in a reducing solution formamidine sulfinic acid which implies a struc containing an imino-amino-methane sulfinic ture having formula (B): acid, can be carried out with or without a sec O Ond exposure to light. The most convenient methods employ no second exposure, but merely C 45 consist of immersing the film, after the original NH O image has been removed and the emulsion cleared NE OBI / and Washed in a solution containing sufficient (B) C-S formamidine sulfinic acid to reduce the silver N. NE O Salts to metallic silver. While acid solutions are It is possible that both formulae may be equally 50 useful, especially if re-exposure is resorted to, correct, because the compound may exist in sev it has been found that alkaline solutions of an eral desmotropic forms. It is possible that the imino-amino-methane sulfinic acid have a power compound exists in a desmotropic form wherein ful reducing action on exposed or unexposed it. an equilibrium normally obtains between the two USidinehalide sulfinic grains. acid. This is especially true of formam 2 2,339,309 In a further aspect of the invention an imino EXAMPLE WI amino-methane sulfinic acid is used in acid solu Formamidine sulflinic acid------grams-- 4.5 tion as the ordinary developer. Such solutions Potassium bromide------do---- 3 are capable of reducing the silver halide grains Potassium metabisulfite------do---- 4.5 of an exposed photographic emulsion to form a Water ------milliliters-- 1000 metallic silver image. A silver halide emulsion containing latent images as formed by exposure Alkaline developer solutions suitable for the to an original scene or by printing from a de second developer in producing images by re veloped photographic element, is treated in an versal methods can be made by admixing the aqueous acid solution containing Sufficient of an 0 ingredients set forth in the following examples imino-amino-methane sulflinic acid to develop in any desired order. the exposed silver salts. Formanidine sulfinic EXAMPLE v1.1 acid developers, however, are preferred. Formamidine sulfinic acid.------a.S.- 25 In still another aspect of the invention, Potassium sulfite------do---- 50 aqueous acidic solutions containing Small 5 Potassium bromide------do---- 30 amounts of an imino-amino-methane sulfinic Sodium hydroxide------do---- 20 acid are used to redevelop a bleached silver 1000 image. A photographic element containing a Water ------milliliters.-- bleached silver image is immersed in an aqueous ExAMPLE VIII acidic solution of the type described in sufficient 20 Formanidine sulfinic acid------gaS. 5 amount to reduce the silver salts. The resulting Hydroquinone------do---- 10 image is characterized by various tones depend Potassium carbonate------do---- 30 ing upon the particular pH value of the devel Potassium sulfite------do---- 50 oper formula. Water ------milliliters.-- 1000 The treating solutions used in the processes 25 outlined above may contain in addition to the EXAMPLE IX imino-amino-methane sulfinic acid various modi Formamidine sulfinic acid.------granS.-- 30 fying agents which are useful in developer Solu Sodium sulfite------do---- 55 tions such as restrainers, preservatives, agents Potassium bromide------do---- 38 for controlling image tone, wetting agents, hard 30 Sodium hydroxide------do---- 25 eners, materials whose presence retards the rate Water ------milliliters-- 000 of diffusion of the solution in emulsion layers etc. The invention, however, is not limited to EXAMPLE X solutions, on the contrary, dry reducing composi Formamidine sulfinic acid ------gaS.-- 36 tions containing the specified ingredients with 3 Sodium carbonate------do---- 50 the exception of water are comprehended. Sodium sulfite------do---- 40 The invention will be further illustrated, but Water ------milliliterS.-- 1000 is not intended to be limited by the following examples. The first group consists of developer EXAMPLE X solutions useful for Ordinary development of 40 Formamidine sulfinic acid.------3.a.S. 8 silver images or sepia toning by redevelopment. Potassium bromide------do---- 15 They can be made by admixing the ingredients Sodium hydroxide------do---- 15 in any desired order with water. Dry composi Water ------milliliters-- 1000 tions can be made in a similar manner by ad The amount of formanidine sulflinic acid is mixing the components in dry forms. 45 not limited to that set forth in the above ex EXAMPLE I amples but may be varied over a wide range. Formamidine sulfinic acid------grams-- 18 The amount to be used varies somewhat in ac Sodium bisulfite------do---- 36 cordance with the material treated. Potassium bromide------do---- 6 50 Acid development Water ------milliliters-- 1000 In the acid reduction or development pro cedures a range of concentrations from about ExAMPLE II 0.5% to 2.0% by Weight of formamidine sulfinic Formamidine sulfinic acid------grams-- 15 acid in respect to the final weight of the solution Sodium bisulfite------do---- 20 55 represents a practical range. N-hydrocarbon Potassium bromide------do---- 5 substituted formamidine sulfinic acids. can be Potassium metabisulfite------do---- 6 used in like amounts. Water ------milliliters. 1000 The compositions of the acid baths should be ExAMPLE II balanced so that the pH value of the developing 60 bath is from pH 3 to pH 6. Values higher or Formamidine sulfinic acid.------grams-- 24 lower than those given will usually produce poor Sodium bisulfite------do---- 52 results, a higher pH tending to produce a fog and Potassium bromide------do---- 8 too low a pH slowing down the reducing action to Water ------milliiters. 1000 an unworkable extent. By proper adjustment ExAMPLE IV 85 both negative and positive plates, films and pa Formamidine sulflinic acid------grams-- 20 pers can be satisfactorily developed. The pH Sodium bisulfite------do---- 45 concentrations can be adjusted by the addition Potassium bromide------do---- 5 of various acidic or alkaline materials or com Water ------milliiters 1000 pounds Such as lactic acid, glycollic acid, sodium 70 acetate, Sodium amino acetate, sodium citrate, ExAMPLE W boric acid, etc. Formamidine sulfinic acid------grams-- 10 Toning development Potassium bromide------do---- 3 Potassium metabisulfite------do---- 9 Redevelopment of a bleached silver image as Water ------milliliters-- 1000 Ts above described in an imino-amino-sulfinic acid 2,389,809 3 developer of the acidic type especially aqueous e. g. phenyl, chlorphenyl, etc. Suitable substi formamidine sulflinic acid developers, has a sur tuted compounds include N-methyl formanidine prising and unexpected effect on the color of the sulflinic acid, N-ethyl formamidine sulfinic acid, image produced. Instead of the normal image N-alkyl formanidine sulflinic acid, N-phenyl tones obtained by the development of an original . formamidine sulfinic acid and N-chlorophenyl exposed but undeveloped emulsion, the bleached formamidine sulfinic acid which can be made image reappears in brownish to sepia tone values. from the corresponding N-hydrocarbon substi Any one of the common bleaching baths known tuted thiourea and hydrogen peroxide. to the art may be used, such as ferricyanide In place of all or a part of the specific pre bromide or copper sulfate-chloride bleaches. A O servatives, set forth in the above examples, can developed film, plate or paper print which has be substituted one or more other sulfites, bisul been fixed and thoroughly washed is simply in fites, etc. Suitable additional compounds of this mersed in a bleaching bath until the image is type include lithium, ammonium, substituted am. thoroughly bleached and is then washed and monium and amine salts of sulfurous acid, e. g. transferred to a bath containing a developing 5 bath of formamidine sulfinic acid. After a short triethanolamine-, morpholine-, tetramethylam time the image reappears in brownish to Sepia monium-, and trimethylbenzylammonium sul tones which may be varied by changes in the de fites. A portion of the bisulfites can be replaced veloping bath. A more convenient method of by lithium sodium, potassium and ammonium varying the tone values, however, can be used bisulfites and meta bisulfites. Other compounds in which the original image is first bleached, 20 include acetone bisulfites, formaldehyde sodium then washed, then developed in a dilute metol sulfoxylate, hexahydric alcohols and lactic and hydroquinone developer, neutralized in an acid glycollic acids. stop bath after partial redevelopment and then Similarly in place of the specific restrainers transferred to a formamidihe Sulfinic acid de of the above examples which can be inter veloper to complete the redeveloper. The first 5 changed in any desired manner, can be substi part of the development in an ordinary alkaline tuted one or more other compounds of this type. developing bath converts parts of the latent Suitable other compounds include, sodium and image to metallic silver and the rest is con lithium bromides, chlorides, and iodides potas verted to brown silver salt by the formamidine 30 siumetc. chloride and iodide, ammonium bromide, sulfinic acid bath. By varying the length of Agents for controlling the image tones can be time the emulsion is in each bath, many different incorporated with the novel reducing agents intermediate tones between brown and black may hereof. Among the useful agents are quinone be produced. The amount of imino-amino hydrochloride, quinoline, 5-nitrobenziminazole, methane sulfinic acid has some effect on the triazole, benztriazole, iminazole, pseudo thiohy image color. In general, the higher the concen dantoin, indophenyl iodonium chloride, etc. tration the darker the image. Amounts from Compounds which retard the rate of diffusion 0.5% to 2.0% by weight of the sulfinic acid in of solutions through emulsion layers, e. g. sugar, respect to the final weight of the solution gives etc., may be added to the reducing compositions. satisfactory results. However, lesser amounts 40 Similarly wetting agents such as the sodium salts and amounts in excess of 2.0% may be used. of alkyl sulfates and alkyl Sulfonic acids of 8 Various other developing agents can be used to 18 carbon atoms; C- and N- alkyl betaines in place of the metol-hydroquinone developer. wherein the alkyl groups contain 8 to 18 carbon Suitable agents include chlorohydroquinone, atoms, etc. can be used in the compositions and 2:4-diaminophenol hydrochloride and p-hy procedures. Also emulsion hardeners such as droxyphenyl amino acetic acid. potassium aluminum sulfate and chrome alum Reversal development have a useful hardening action in solutions of low pH. Aldehyde hardeners are useful in alka Various procedures can be used in this phase line or neutral Solution. of the invention. In general, however, an ex 50 The developer or reducing solutions of this posed film, plate or paper print is developed ac invention are useful in developing various types cording to the usual procedure known to the art of photographic elements such as camera, cin and then bleached in an acid Solution of pota S ema, portrait, lithographic and X-ray, films and sium bichromate which removes the silver image. plates and photographic papers, etc. They are After washing and clearing in a Sodium bisul 5 5 useful with various types of film base materials fite solution, the photographic element is then and do not have a deleterious effect thereon. transferred to an alkaline Solution of formami Thus cellulose derivative film bases, e. g. cellulose dine sulfinic acid such as those described in Ex nitrate, methyl cellulose, ethyl cellulose acetate, amples I and VI. This bath rapidly reduces all cellulose acetate-propionate and cellulose ester the silver halide which was not originally af O and ether film bases, in general; synthetic res fected by the light and bleached out after de ins, e. g. polyvinyl acetals, etc.; and Super poly velopment. Consequently a reversed image is mers, e. g. nylon, may form part of the elements produced which may be fixed, hardened and treated. washed to give a positive image of the original Warious types of silver halide emulsion layers subject. An alkaline formamidine sulfinic acid 65 may be treated as Will be apparent from the solution to be used in such a process should pref above. For instance, simple and mixed silver erably contain from about 0.5% to 3% by weight chloride, silver bromide, silver iodide, silver chlo of formamidine sulfinic acid. For best results ride-bromide, and silver chloride-bromide-iodide, the pH of such solution should be above 9.5. gelatin emulsion layers, may be satisfactorily Other N-hydrocarbon substituted imino-ami processed by the novel solutions and procedures no-methane sulfinic acids which are capable of hereof. reducing silver salts, can be used in the above The reducing solutions can be used with var described procedures and compositions in similar ious types of colloid binding media. They do amounts. Suitable substituents include lower al not have harmful effects on gelatin, agar agar, kyl groups, e. g. methyl and ethyl; aryl radicals, 75 albumins, synthetic resins, e. g. polyvinyl acetals 4 2,889,809 layer in an aqueous solution containing form used as the binding agents for the silver salts. amidine sulfinic acid. The baths can be used over a fairly wide range il. In a photographic reversal process involv of temperature with complete safety. In add ing a first development and bleaching of de tion, they have a fairly long useful life through veloped images, the step which comprises de out practical processing temperatures. veloping the reversed image in an aqueous solu One of the most important advantages of the tion containing an imino-amino-methane-sul invention is that formamidine sulfinic acid is a finic acid. - much more energetic photographic reducing 12. A photographic process for obtaining direct agent in both acid and alkaline solutions than 0 positives which comprises effecting a first de are the compounds already employed in the art. velopment, removing the silver image formed and Overall blackening by alkaline solutions in re effecting a final reduction of the remaining silver versal processes is likewise more easily and quick salt in an aqueous solution containing an imino ly obtained by the compound of the invention amino-methane-sulfinic acid. than by equivalent quantities of hydrosulfites or 13. A photographic process for obtaining direct sulfoxylates. Another advantage of the inven 5 positives which comprises effecting a first de tion is that it permits the formation of brownish velopment, removing the silver image formed and to sepia toned images having wide gradation of effecting a final reduction of the remaining silver color from reddish brown to brownish black by salt in an aqueous Solution containing formami partial redevelopment of a bleached silver image dine Sulfinic acid. in an ordinary developer and Completing the re 20 14. A photographic process for obtaining direct development in a formamidine sulfinic acid de positives which comprises effecting a first de veloper. V velopment, removing the silver image formed and As many apparently widely different embodi effecting a final reductilon of the remaining form ments of this invention may be made, without 25 salt in an alkaline solution containing form departing from the spirit and scope thereof, it amidine sulfinic acid. is to be understood that we do not limit ourselves 15. A photographic process for obtaining direct to the specific embodiments hereof except as de positives which comprises effecting a first de fined by the appended claims. velopment, removing the silver image formed and We cairn: effecting a final reduction of the remaining silver 1. A photographic reducing solution contain 30 salt in an alkaline solution containing an imino ing a water soluble sulfite and an imino-amino amino-methane sulfinic acid. methane-sulfinic acid. 16. A photographic process for obtaining direct 2. A dry photographic reducing composition positives which comprises effecting a first de containing a water soluble sulfite and an imino Velopment, removing the silver image formed and amino-methane-sulfinic acid. 35 effecting a final reduction of the remaining silver 3. An aqueous acidic photographic reducing Salt in an alkaline solution containing formami solution containing a water soluble sulfite and an dine Sulfinic acid having a pH in excess of 6.8. imino-amino-methane-sulfinic acid. 17. The process of producing reddish brown to 4. An alkaline photographic reducing composi sepia tones in a photographic silver image which tion containing an alkaline compound, a water 40 Comprises redeveloping a bleached silver image soluble sulfite and an imino-amino-methane-sul in an aqueous Solution containing an imino finic acid. amino-methane-sulfinic acid having a pH less 5. A dry photographic reducing composition than 6.0. containing an alkaline compound, a water Solu 18. The process of producing reddish brown ble sulfite and an imino-amino-methane-sulfinic 45 to sepia tones in a photographic silver image acid. which comprises redeveloping a bleached silver 6. An aqueous photographic reducing solution salt image in an aqueous solution containing containing a Water soluble sulfite and formami formamidine sulfinic acid having a pH less than 6. dine sulfinic acid. 19. The process of toning which comprises par 7. An aqueous acidic photographic reducing SO 50 tially developing a bleached image with an ordi lution containing a water Soluble sulfite and nary developing agent and completing the de formamidine sulfinic acid. velopment in an aqueous solution containing an 8. An alkaline photographic reducing solution imino-amino-methane-Sulfinic acid. containing an alkaline compound, a water soluble 55 20. An alkaline photographic reducing compo sulfite and formamidine sulfinic acid. sition Containing an alkaline compound, a Water 9. The process which comprises reducing a soluble sulfite, and formamidine sulfinic acid. light sensitive photographic element in an aque 21. An alkaline photographic reducing Compo ous solution containing an imino-amino-meth sition containing sodium hydroxide, an alkali ane-sulfinic acid. metal sulfite and formamidine Sulfinic acid. 10. The process which comprises developing a 60 JOHN RAU WEBER, photographic element containing a silver salt LYNN BARRAT MORRIS.