Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
• • 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 more particularly ,0 the process of regenerating exhausted silver bleaching solutions.
• the most commonly employed silver bleaching solution consists essentially of an aqueous solution of an alkali ferricyanide and an alkali bromide, and if desired, small amounts of a buffer or a bleaching accelerator, such as the phenoxyethanol described in United States Patent 2,419,900.
• exhausted bleach solutions comprising an alkali ferricy- Application December 30, 1949, Serial No. 136,145
• anide and an alkali bromide are regenerated or rejuvenated by the action of'a reagent or mixture of reagents capable of releasing elementary bromine in aqueous solutions.
• the action of bromine on an exhausted bleach solution appears It has been to perform a dual function (1) by oxidizing the ferrocyanide ions to ferricyanide ions, and (2) by supplying additional bromide ions.
• Bromine, itself or its solution in water commonly known as bromine water performs a similar function but tends to destroy some of theferricyanide.
• bromine gives off highly objectionable toxic vapors and must be handled with extreme care in order to avoid serious burns. In addition, if accidentally spilled, it may seriously affect not only the film but also tanks, spools, and similar equipment utilized in the film processing.
• Reagents of this type are the alkali metal hypobromides, i. e., sodium, potassium or lithium hypobromide, a mixture of an alkali metal bromate and hydrobromic acid in the molar ratio of 1:6, and a mixture of an alkali metal bromate and alkali metal bromide in a molar ratio of 1:5, and containing in addition approximately 6 to 7 mols of either sulfamic acid or an anhydrous alkali bisulfate.
• the anhydrous alkali biculfate may be replaced by 3 to approximately 3.5 mols of sulfuric acid diluted with a sufiicient amount of water to make approximately a 20% solution. 4
• the amount of the alkali metal hypobromide or mixture of alkali metal bromate and hydrobromic acid, and the like, is such as will release one molar equivalent of bromine for each molar equivalent of ferrocyanide present in the exhausted bleach.
• the actual, or approximate amount can, therefore, be determined stoichiometrically after the determination of the ferrocyanide content by colorimetric, potentiometric, or other suitable titration means.
• Amounts of the reagent or molar equivalent mixture thereof smaller than the molar equivalent of ferrocyanide present in the exhausted bleach bath give incomplete regeneration, whereas any appreciable excess tends todestroy some of the ferricyanide. A small excess can, however, be tolerated in most instances without impairing the eificiency of the regenerated bleach solution.
• photographic bleach solutions contain an alkali metal ferricyanide, such as lithium, potassium or sodium ferricyanide as an oxidizing agent dissolved in a suitable solvent, such as, for example, water with or without thepresence of other adjuva'nts.
• a suitable solvent such as, for example, water with or without thepresence of other adjuva'nts.
• a typical bleach solution consists of about 100 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, potassium I and sodium bromide grams (converting agent) Dialkali metal hosphate 40 grams (buffering agent) Alkali metal 1), sulfate or organic acid, such as citric acid 5 grams (buffering salt) Alkali metal tetraphosphate grams (COIIOSIOD preventative) Water to make 1 liter (solvent)
• an oxidizing agent I mean any alkali metal ferricyamde that will oxidize axmetallic silver image to form a silver salt.
• "Most commonly used oxidizing agents are alkali metal -'ferricy-' anide, such as lithium, potassium,.and sodium ferricyanides or mixtures of these salts.
• I mean a compound such as an alkali metal bromide which by reason of a difference in solubility will replace the silver ferricyanide formed in. the bleaching reaction to form silverbromide and .thus impel the le ch. Converting a nts a sometimes called halogenizingagentsreaction to completion.
• I means. substance that is added to bring theferricyanide bleach solution .to a specified pH and to maintain this-pH even though small amounts-20f acids oraa ka may be carried intozthle bleach of the him.
• alkali metal phosphate such as disodium phosphate sodium tetraphosphate, and the like have been found to prevent corrosion effectively.
• the ferrocyanide ion concentration of the exhausted bleach solutionr was determined, according to the method of Brunner. Means and-Zappert, described inlthe Journal of the Society'of Motion Picture Engineers, vol. 53, page 3O, and
• Photographic tests showed that the bleaching j actionof the rejuvenated bleach was equal to that of .a fresh solution.
• Example II One 'liter of a fresh bleach solution prepared as in Example I was used for the bleaching of 50 feet of color developed 35 mm. film. After bleaching, the solution showed signs .of exhaustion andnpon colorimetric analysis indicated .a
• Example III One liter of an exhausted bleach solution, of he same composition as in; Example I, was analyzed by iodometric titrationand-found to contain 10. grams of .ferrooyanideion per liter.
• the bleach solution was regenerated by adding,
• Example -I-V Example III was repeated with the exception that 5.66 grams of anhydrous sodium bisulfate were replaced by 9. 9 mls. of a 20% aqueous solution of sulfuric acid. The exhausted bleach solution was completely rejuvenated and did not re-- quire any further adjustment of its pH.
• 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'b'yfthe bleached film.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Inorganic Chemistry (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22471510

Family Applications (1)

Country Status (5)

Cited By (9)

Citations (3)

• 0
  • BE BE500332D patent/BE500332A/xx unknown
• 1949
  • 1949-12-30 US US136145A patent/US2611699A/en not_active Expired - Lifetime
• 1950
  • 1950-12-27 GB GB31393/50A patent/GB673058A/en not_active Expired
  • 1950-12-29 FR FR1030282D patent/FR1030282A/fr not_active Expired
  • 1950-12-31 DE DEG4932A patent/DE866909C/de not_active Expired

Patent Citations (3)

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