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
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/06—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein with non-macromolecular additives
  • G03C1/08—Sensitivity-increasing substances
• • 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
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/485—Direct positive emulsions

Definitions

• Silver halide emulsions are usually sensitized before coating onto a support. Under certain adverse storage conditions such as radiation, however, such photographic elements become fogged and the element is of no use. It would be desirable to have a photographic element which could be stored in a comparatively insensitive form and then sensitized just prior to or during use.
• an object of this invention to provide a method for sensitizing a substantially unsensitized silver halide emulsion layer. Another object is to provide a method for sensitizing an internal image unsensitized silver halide emulsion layer. Another object is to provide unsensitized silver halide emulsions containing compounds which will sensitize the emulsions after an appropriate treatment. Still another object is to provide direct positive photographic elements having an internal image emulsion which has been sensitized according to the invention. Another object is to provide methods for using the direct positive elements of the invention. Yet still'another object is to provide unsensitized photographic elements which can be stored in a comparatively insensitive form and then sensitized just prior to or during use. Other objects will become apparent hereinafter.
• a silver halide emulsion is prepared but not sensitized. Instead a selected sulfur sensitizing compound is merely added to the emulsion under conditions so that substantially no sensitization takes place, and the emulsion is thne coated onto a support.
• the photographic element can then be stored in this form and adverse storage conditions, e.g., radiation, will not cause fogging.
• an alkaline medium such as ammonia vapors or alkaline solutions.
• Any alkaline solution can be used which is effective for the intended purpose. For example a 5% (by weight) sodium carbonate solution can :be used and it will cause sensitization in about ten seconds.
• the time of contacting the photographic element with the alkaline solution will, of course, depend upon the particular alkaline solution used. Between about ten seconds and five minutes has been found to be effective for most alkalnie solutions.
• the sulfur compounds which can be added -to the silver halide emulsions of the invention are generally labile sulfur compounds such as the thioureas including s-diphenylthiourea, phenylthiourea, thiourea, allylthiourea, sdiethylthiourea, etc. which thioureas are preferred.
• Certain noble metal compounds, such as certain gold compounds, may also be employed with the sulfur compound as an auxiliary sensitizer.
• the concentrations of the sulfur compound can be any concentration which is effective for the purpose intended. Generally, a concentration of from about 1.0 mg. to about 50 mg. per mole of silver has been found to be elfective.
• the noble metal compound can also be used in any concentration effective for the intended purpose. For example, concentrations of from about 0.1 gram to about 10.0 grams of noble metal compound per sliver mole were found to be quite satisfactory.
• the sulfur compound is added in such a manner so that little of it reacts with the silver halide grains.
• a preferred way is to dissolve the compound in an aqueous gelatin solvent, set the solution obtained and then add it to the silver halide emulsion. It is also desirable to coat the emulsion as soon as it is prepared before any sensitization has taken place.
• An internal image emulsion is defined in US. Pat. 3,178,282 as one which, when measured according to normal photographic techniques by coating a test portion of the emulsion on a transparent support, exposing to a light intensity scale having a fixed time between 0.01 and 1 second, bleaching 5 minutes in a 0.3% potassium ferricyanide solution at F. and developing for about 5 minutes at 65 F.
• Developer B has a sensitivity, measured at a density of 0.1 above fog, appreciably greater (e.g., at least 1.4 log E greater) than the sensitivity of an identical test portion which has been exposed in the same way and developed for 6 minutes at 68 F. in Developer A.
• a sensitivity measured at a density of 0.1 above fog, appreciably greater (e.g., at least 1.4 log E greater) than the sensitivity of an identical test portion which has been exposed in the same way and developed for 6 minutes at 68 F. in Developer A.
• Several suitable emulsions of this type are described in Davey and Knott US. Pat. 2,592,250, issued Apr. 8, 1952.
• Silver chloride, silver bromide and silver chlorobromide emulsions of the internal latent image type can be used.
• Internal image emulsions can be used to produce direct positive or reversal photographic elements.
• the process described in British Pat. 581,773 can be employed by imagewise exposing an internal image emulsion, flashing and then developing in a surface image developer. If desired, the emulsion may be contacted with the developer before flashing.
• the silver halide grains containing an internal latent image are apparently desensitized so that a uniform second exposure gives a positive latent image of the first exposure.
• the instant invention may be employed in such a process before the flashing and developing steps to produce an emulsion with a higher reversal speed. In addition, the maximum density and minimum density are greatly improved.
• the instant invention may also be employed to produce a direct positive by use of an organic photo-reaction.
• An unsensitized emulsion is coated in the presence of a thiourea compound and a dye under conditions in which the thiourea does not react with the silver halide. It is then exposed imagewise.
• the thiourea is effectively removed by a photo-reaction which is catalyzed by certain dyes, including members of the triphenylmethane, cyanine 7 and azo dye classes, leaving an imagewise distribution of the thiourea.
• the emulsion is then either sensitized or fogged (depending on the amount of thiourea present) in the unexposed areas by bathing in a sodium carbonate solution.
• Oxidizing agents such as potassium persulfate, hydrogen peroxide or benzoyl peroxide may also be incorporated into the emulsion to increase contrast and maximum density, and reduce minimum density.
• the silver halide emulsions of the instant invention may also contain conventional addenda such as speed increasing addenda, e.g., quaternary ammonium salts, polyethylene glycols, thioethers, etc., gelatin plasticizers, coating aids, anti-foggants and hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde bis(sodium bisulfite), maleic dialdehyde, aziridines, clio-xane derivatives and polysaccarides.
• speed increasing addenda e.g., quaternary ammonium salts, polyethylene glycols, thioethers, etc., gelatin plasticizers, coating aids, anti-foggants and hardeners
• aldehyde hardeners e.g., formaldehyde, mucochloric acid, glutaraldehyde bis(sodium
• emulsions may be useful in X-ray and other non-optically sensitized emulsions, and may also be used in orthochromatic, panchromatic and infrared sensitive emulsions.
• the addenda may be added to the emulsion before or after sensitizing dyes, if any, are used. Sensitizing dyes useful in sensitizing such emulsions are described, for example,
• Spectral sensitizers which can be used are the cyanines, merocyanines, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styryls and hemicyanines.
• Developing agents can also be incorporated into the silver halide emulsions if desired or be contained in a separate underlayer.
• Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide.
• the silver halides used can be those which form latent images predominantly on the surface of the silver halide grains or those which form latent images inside the silver halide crystals as exemplified by Davey and Knott US. Pat. 2,592,250. 1
• the silver halide emulsions of the instant invention can contain any of the hydrophilic water-permeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers, etc. Mixtures of these binding agents can also be used.
• the binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in US. Pats. 3,142,568; 3,193,386; 3,062,674 and 3,220,844, and include the water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.
• the silver halide emulsions of the instant invention may be coated on a wide variety of supports.
• Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, poly(ethylene terephthalate) film and related films or resinous materials as well as glass, paper, metal and the like.
• Supports such as paper which are coated with a-olefins polymers, particularly polymers of a-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene-butene copolymers and the like can also be employed.
• EXAMPLE 1 A silver chlorobromide developing-out emulsion containing 2% gelatin was prepared and was added to an equal volume of 20% gelatin solution giving an emulsion of 23 grams equivalent silver nitrate per kilogram of emulsion. The emulsion was melted and brought to 40 C. when the pH was approximately 7.0. Successive additions of a set 10% solution of an inert gelatin containing 0.1% thiourea were added at four minute intervals, each addition representing approximately 5 mg. of thiourea per mole of silver halide. A sample of emulsion was removed and coated three minutes after each addition of sensitizer. Portions of the coatings were exposed to tungsten light for one minute and then processed; they had very low photographic sensitivity.
• EXAMPLE 2 An emulsion of the type in British Pat. 581,773 in which the internal sensitivity was much higher than the surface sensitivity was melted and brought to 40 C., the pH being 6.5 and pAg being 8.0. Thiourea was added at various concentrations as described above. Optimum sensitivity was reached with a thiourea concentration of about 10 mg. per mole of silver halide.
• the emulsion was coated on film base and a sample of the coating was imagewise exposed. The exposed sample was sensitized by bathing for ten seconds in sodium carbonate solution (this effected a very large increase in speed), and then exposed uniformly to tungsten light. Development in a surface image developer, (e.g., Formula 1 of British Pat. 581,773) at room temperature for five minutes produced a direct positive image of good quality.
• a comparison test was carried out using a material prepared from a portion of the emulsion to which no thiourea had been added. After the imagewise exposure, the material was treated with a carbonate solution. The quality of that image was markedly inferior to that of the image obtained with the material of the present invention, the maximum density being lower and the minimum density being higher than that of the present invention. Furthermore, the sensitivity of the sensitized material of this invention was much greater than that of the comparison material after treatment with the carbonate solution.
• a method for obtaining a positive image comprising:
• a method according to claim 1 wherein said compound containing a labile sulfur atom is a thiourea compound.
• a method according to claim 1 wherein said photographic element comprises from about 1.0 mg. to about 50 mg., per mole of silver, of said compound containing labile sulfur atoms and conditions are maintained in said element whereby substantial reaction of said compound containing labile sulfur atoms with the silver halide grains will not occur before the imagewise-exposure step.
• a method for obtaining a positive image in a photographic element comprising:
• N-methyl-p-aminophenol sulfate 0.31 sodium sulfite, desiccated 39.6 hydroquinone 6.0 sodium carbonate, desiccated 18.7 citric acid 0.68 potassium metabisulfite 1.5

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)
• Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (5)

Cited By (4)

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• 1965
  • 1965-12-16 GB GB53382/65A patent/GB1178683A/en not_active Expired
• 1966
  • 1966-12-14 US US601534A patent/US3586505A/en not_active Expired - Lifetime
  • 1966-12-15 DE DE1547762A patent/DE1547762C3/de not_active Expired
  • 1966-12-15 BE BE691280D patent/BE691280A/xx unknown
  • 1966-12-16 FR FR87801A patent/FR1513428A/fr not_active Expired

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