Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C5/00—Photographic processes or agents therefor; Regeneration of such processing agents
  • G03C5/26—Processes using silver-salt-containing photosensitive materials or agents therefor
  • G03C5/395—Regeneration of photographic processing agents other than developers; Replenishers therefor
  • G03C5/3952—Chemical, mechanical or thermal methods, e.g. oxidation, precipitation, centrifugation

Definitions

• This invention relates to a photographic process and particularly to the process of regenerating exhausted silver bleaching "solutions.
• the most commonly employed silver bleaching solution consists essentially of an aqueous solution of an alkali ferricy'anide and :an alkali bromide, and if desired, small amounts of a buffer, such as an alkali metal phosphate and bisulfate to maintain the hydrogen ion concentration constant.
• the bleach solutions although reasonably stable during storage, lose their 'efiiciency as soon as they have been used for the treatment of relatively small areas of film.
• the metallic silver image on the film is oxidized to silver ions by the ferricyanide ions which are in turn reduced to ferro'cyanide ions.
• the silver ions are precipitated by the bromide ions as silver bromide and removed by subsequent treatment of the film in a fixing bath. Since the silver bromide is removed, the net efiect in the bleaching solution is a conversion of ferricyanide ions to ferro'cyani-de ions and a loss of bromide ions.
• exhausted bleach solutions comprising an alkali ferricyanide and an alkali bromide are regenerated or rejuvenated by the action of any organic N- bromo derivatives of a compound containing the groups --CHzNHz, -CONH2, or --(C"O)dNI-I, and derivative of an aromatic compound containing the group, SO2NH2, in which at least one of the hydrogen atoms is substituted by a bromine atom, and including N-bromomelamine and the di-, tri-, and hexa-bromo derivatives of the amides of cyanuric acid, which are capable of releasing elementary bromine in aqueous solutions.
• aforestated compounds are immaterial so long as they are aliphatic or aromatic in nature or are the mono and polybromo derivatives of the amides of cyanuric acid.
• N-tribromomelamine N -hexa.bromomelamine The use of liquid bromine for rejuvenation of alkali ferrocyanide bleach baths theoretically requires one atom of bromine per molecule of ferrocyanide. When using any one of the aforestated N-bromo compounds, one mol offerrocyanlde requires only one mol divided by twice the number of N-bromo atoms in the compound. By way of example, one mol of ferrocyanide theoretically requires grams of bromine, where as only 69 grams of N -bromo acetamide are theoretically required.
• the advantage of utilizin the N-bromo compounds is that they are solids which are reasonably stable for long periods of time, are nonirritating, and produce no toxic vapors.
• the N- bromo compounds may be added directly to the bleach solution thus avoiding the dilution which occurs with the use of a solvent. Since the reaction involved consumes one equivalent of hydrogen ions, the ions must be replaced by the addition of a small amount of an acid or of an acid salt to the bleach solution, such as sulfuricacid, citric acid, hydrobromic acid, sulfamic acid, or an alkali bisulfate, e. g., sodium bisulfate.
• a sufiicient amount of the acid or acid salt is added to the exhausted bleach bath so'as to restore the pH to its original value. Solid acids or acid salts may be added directly, but it is advisable to dilute the sulfuric acid with water.
• bromide ions are consumed in the bleaching process, only half of which are replaced by the N-bromocompound, additional bromide ions may be added'if it is desired to restore the bromide to its original concentration. This can be accomplished by the use of a bromide salt. If hydrobromic acid is used as the acidifying agent, the bromide concentration is automatically restored.
• the actual or approximate amount of the N- bromo compound to be added is determined stoiohiometrioally after the determination of the ferrocyanide content by colorimetric, potentiometric, or other suitable titration means. Amounts'of the N-bromo compounds smaller than that the oretically required to oxidize the ierrocyanide ions present in the exhausted bleach bath give somewhat incomplete rejuvenation, whereas any appreciable excess tends to destroy some of the ferrioyanide. A small excess, 1. e., above the theoretical amount, can, however, be tolerated in most instances without impairing the efiiciency of the regenerated bleach solution.
• a typical bleach solution consists of about grams of an oxidizing agent per liter of solution and may contain one or more of the following ingredients: Alkali metal bromide, such as lithium,
• an oxidizing agent we mean any I alkali metal ferricyanide that will oxidize a metallic silver image to form a silver salt. Most commonly'used oxidizing agents are alkali metal ferricyanide, such as lithium, potassium, and sodium ferricyanide or mixture of these salts.
• a converting agent we mean acompound, such as an alkali metal bromide, which by reason of a diiference in solubility will replace the silver ferrocyanide formed in the bleaching reaction to form silver bromide and thus impel thebleach reaction to completion.
• Converting agents are sometimes called halogenizing agents.
• buffering agents we mean a substance that is added to bring the ferricyanide bleach solution to a specified pH and to maintain .thispI-I even though small amounts of acids or alkali may be carried into the bleach by the film.
• the pH of the solutions used in bleaching films are maintained between 3 and 9, although apH between 5 and '7 is generally preferred. 1
• alkali metal phosphate such as disodium phosphate, sodium tetraphosphate, sodium hexametaphosphate, and the like, have been found to prevent corrosion effectively.
• solvent we refer to such liquid in which the above materials are dissolved and which is usually water.
• Photographic tests on sensitometric strips showed that the bleaching rate of the used or exhausted bleach solution dropped below the practical limit and that even extended bleaching of a small length of color developed 35 mm. reversal film failed to remove the residual silver stain.
• the ferrocyanide ion concentration of the exhausted bleach solution was determined, according to the method of Brunner, Means and Zappert, described in the Journal of the Society of Motion Picture Engineers, vol. 53, page 30, and found to be 13.3 grams per liter.
• Example II To 1800 mls. of used bleach of Example I and containing 2.12 grams of ferrocyanide ion per liter, 1.5. grams of N -dibromobenzenesulfonamide, 1.15 grams of potassium bromide and 1.15 grams of sodium bisulfate were added with stirring. After standing for 10 minutes, the solution had been completely regenerated, and showed excellent bleaching properties.
• Example I'II To 2000 mls.. of used bleach, of Example I, and containing 5.27 grams of ferrocyanide ion per liter, 2.85 grams of N-bromoacetamide, and 8.4 grams vof 20% hydrobromic acid were added. Photographic tests showed that the performance of this regenerated bleach was equal to that of afresh bleach solution.
• Example IV To 1500 mls.. of used bleach of Example I, and containing 5.27 grams of ferricyanide ion per liter, 2.52 grams of N-bromosuccinimide, 1.5 grams of sodium bromide and 1.4 grains of sulfamic acid. After stirring for several minutes, the solution was regenerated and showed excellent bleaching properties.
• Example V To 1000 mls. of used bleach of Example I, and containing 6.35 grams of ferrocyanide ion per liter, 3 rams of N-bromobenzamide and 3.75
• the concentration of the various constituents of the bleach solution decreases gradually. Some water is brought into the bleaching tank by the wetted film and. small quantities of the ferricyanide salts are carried away by the bleached film. This dilution in most cases does not materially affect the bleaching rate, If desired, the. solution can, however, be kept at full strength by adding small amounts of the same constituents or chemicals originally used for the preparation of the bleach solution.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)

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Citations (1)

• 0
  • BE BE500365D patent/BE500365A/xx unknown
• 1949
  • 1949-12-30 US US136146A patent/US2611700A/en not_active Expired - Lifetime
• 1950
  • 1950-12-27 GB GB31394/50A patent/GB687311A/en not_active Expired
  • 1950-12-30 FR FR1034731D patent/FR1034731A/fr not_active Expired
  • 1950-12-31 DE DEG4931A patent/DE873654C/de not_active Expired

Patent Citations (1)

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