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
  • G03C5/29—Development processes or agents therefor
  • G03C5/305—Additives other than developers

Definitions

• This invention relates in general to photographic developers, and more particularly to developers used to develop latent images present in those photosensitive silver halide photographic films employed in the graphic arts for making line or half-tone images and other films used for producing photographic reproductions having very high contrast and image sharpness. These developers are frequently referred to as lith type developers.
• the preferred photographic developer for producing high contrast and image sharpness for the graphic arts is a solution of a p-dihydroxybenzene developing agent.
• Normally hydroquinone is utilized as the developing agent for photographic silver halide emulsions.
• Working solutions containing such developing agents are very susceptible to aerial oxidation and consequently possess a very short tray life. After a few hours of exposure to ordinary atmospheric conditions, even without actual use, the response of the developer is greatly impaired and the solutions become generally ineffective. This loss of elfectiveness results in loss of density range and dot quality, and contrast is reduced or lost in the images being produced.
• this loss of effectiveness of developing solutions is extremely costly whenever large volumes of developer are being utilized as in automatic processing machines.
• One technique for reducing costs of developer in automatic processing machines is to utilize developer replenishers, these being commonly stored in large quantities within the processing machine, however, these replenishers are similarly subject to aerial oxidation and will accordingly become ineffective after limited periods of exposure.
• an improved photographic developer which employs a combination of a p-dihydroxybenzene together with a combination of a water soluble sulfite and ascorbic acid.
• the p-dihydroxybenzene component is normally hydroquinone, the Water soluble sulfite normally being sodium sulfite, the ascorbic acid normally being either ascorbic acid or the sodium or other alkali salts of ascorbic acid as well 3,512,981 Patented May 19, 1970 as certain stereioisornetric forms of ascorbic acid.
• the ascorbic acids have the following general structure:
• R represents a hydroxy group when n represents a positive integer from 1 to 4 and R represents a hydrogen atom when n represents a positive integer of from 2 to 4.
• ascorbic acid including sodium or potassium ascorbate, 1 erythroascorbic acid, and d glucoascorbic acid have been found effective in this combination.
• the developing solutions employing a p-dihydroxybenzene such as hydroquinone a synergistic effect is experienced when both sulfite and ascorbic acid are present, this synergistic effect being manifested in the preparation of a highly stable solution capable of preparing reproductions having sharp contrast with sharpness of image.
• 'It is a further object of the present invention to provide a photographic developer replenisher that has an extended tray and shelf life.
• an exposed photographic silver halide emulsion is processed or developed in a solution of a p-dihydroxybenzene developing agent, preferably hydroquinone, the solution containing ascorbic acid or its derivatives in an amount preferably in the range of about .5 to 10 grams to liter of solution (depending upon the degree of extended tray life desired) and between about V2 gram and 5 grams of a dissociated sulfite per liter of solution.
• the term dissociated is employed herein in a comprehensive sense, and accordingly is intended to include ionized, as well. It has been found that the synergestic effect as pointed out hereina'bove is diminished when less than about A.
• This phenomenon defined as peppering may be described as the formation of one or more randomly arranged generally round high or low density spots occurring in areas of reciprocal developed density. While the phenomenon is not entirely understood, it appears to be the result of an accelerated development of certain areas of the photosensitive silver halide emulsion film which areas have received only a minimal or marginal amount of exposure, and which exposure is below that lower threshold limit necessary to obtain a maximum or high density. This phenomena occurs more frequently with those photosensitive silver halide emulsions which are normally regarded as having the highest ability to render high contrast over prolonged developing time ranges.
• the developer of the present invention is capable of providing rapid developing of latent images present in photosensitive silver halide emulsion films, this rapid development being possible without the introduction of areas of peppering in the product.
• the sulfite is kept at a level concentration of between about /2 and grams per liter determined as sodium sulfite, and formaldehyde bisulfite complexes are utilized as sulfite buffers to provide a solution having a constant and controllable low sulfite concentration within the desired range.
• This range provides a working solution having a sulfite concentration of from between about 0.004 molar and 0.04 molar. Solutions with a sulfite concentration of 0.002 molar may be useful in some systems.
• the formaldehyde bisulfite complexes control the sulfite concentration through replenishing of the sulfite consumed during the developing reactions,
• Photographic emulsions designed for producing high contrast images including lith type emulsions are commercially available.
• One such type is available under the designation Kodalith films from Eastman Kodak Company of Rochester, N.Y., various similar types being available commercially from the E. I. du Pont de Nemours Company of Wilmington, Del., as well as others. While these various photographic emulsions have the desired high contrast and dot quality when developed in known high contrast developers, it is of course desirable to increase the useful life of the developer solution by increasing the resistance of the developing solution to aerial oxidation upon exposure to ordinary atmospheric conditions.
• the developing solutions of the present invention contain a p-dihydroxybenzene developing agent such as hydroquinone, although toluhydroquinone, 2,5-dimethylhydroquinone and the like have been found useful.
• p-dihydroxybenzene is intended to include materials such as 1,2,4-trihydroxybenzene and the like.
• aminobenzene developing agents such as for example p-aminophenol, n-methyl-p-aminophenol, p-phenylenediamine, etc. It will be appreciated, of course, that trace quantities in the range of, for example, less, th n 0.05 gram per liter of these developing agents may be present in some solutions, greater quantities having been found to reduce contrast.
• the ascorbic acids and the isomers and their derivatives, which are used in the developer solution are acids of the structural formula set forth hereinabove. Ascorbic acids are commonly referred to as Vitamin C and their preparation, sources and derivatives are described in the Encyclopedia of Chemical Technology, vol. 2, pages 150 to 163, published by the Interscience Encyclopedia, Inc. These ascorbic acids and the isomers and their derivatives are most readily obtained in pharmaceutical grade, however, pharmaceutical grade is not necessary. Good results are achieved Whenever developer solutions generally free of impurities are employed which provide extended tray life and shelf life of the working solutions of the present invention. The inclusion of ascorbic acid in the sulfite containing solution has been found to result in very little, if any, loss in speed of developing, and no loss in contrast (gamma) even after extended times of exposure of the developer solution to atmospheric air.
• the second and third strips of the same exposed film were processed under identical conditions in the same developer solution, the second strip being processed after 4 hours and the third strip being processed after 6 hours.
• the degradation of the relative speed and contrast range is shown in the sensitometric results of the second and third strips which were processed after 4 and 6 hours, respectively.
• This composition utilized a multi-functional hydroxybenzene as a substituted hydroquinone, this being 1,2,4-trihydroxybenzene. Good results were achieved with this composition.
• EXAMPLE E A developing solution was prepared having a composition similar to that in Example A, with the exception of toluhydroquinone being substituted for hydroquinone, the quantity remaining at 12 grams per liter. This solution was not as readily balanced as the solution in Example A, however developer activity level was considered satisfactory.
• a stable photographic developer solution consisting of an aqueous solution of:
• an ascorbic acid analogue selected from the group 6 consisting of those certain substances having the structural formula wherein R represents a hydroxy group when n represents a positive integer from 1 to 4 and R represents a hydrogen atom when n represents a positive integer of from 2 to 4, and the alkali salts of said certain substances;
• the photographic developer solution as set forth in claim 2 being particularly characterized in that said l-ascorbic acid is present in said solution in an amount ranging from between about 0.5 gram per liter and 10 grams per liter.
• the photographic developer solution as set forth in claim 1 being particularly characterized in that said dissociated sulfite is derived from the combined presence of an alkali sulfite and formaldehyde bisulfite in said solution.
• the photographic developer solution as set forth in claim 1 being particularly characterized in that said p-dihydroxybenzene developing agent is selected from the group consisting of hydroquinone, toluhydroquinone, 2,5-dimethylhydroquinone, 2,5-diethylhydroquinone, and 1,2,4-trihydroxybenzene.
• a stable photographic developer solution consisting of an aqueous solution of:
• an ascorbic acid analogue selected from the group consisting of those certain substances having the structural formula wherein R represents a hydroxy group when n represents a positive integer from 1 to 4 and R represents a hydrogen atom when n represents a positive integer of from 2 to 4, and the alkali salts of said certain substances;

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

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Cited By (8)

Citations (3)

• 1968
  • 1968-02-05 US US702797A patent/US3512981A/en not_active Expired - Lifetime
  • 1968-07-05 DE DE19681772801 patent/DE1772801A1/de active Pending
• 1969
  • 1969-02-04 BE BE727894D patent/BE727894A/xx unknown

Patent Citations (3)

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