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
  • G03C1/015—Apparatus or processes for the preparation of emulsions

Definitions

• This invention relates to photography and particularly to a method of making a photographic emulsion which shows high susceptibility to the Clayden effect.
• Clayden effeet The feature which characterizes the Clayden effeet is that the initial exposure of short duration to relatively high intensity light desensitizes the emulsion so that subsequent exposure to weak intensity light produces less effect than if the pro-exposure had not been given. As usually observed the density resulting from the two superposed exposures is less than that of the single exposure to the low intensity light on making it appear that the effect is a reversal.
• the elfect known as the Clayden effect has a number of practical applications. Yule and Maurer have described in their application Serial No. 291,623, now U. S. Patent No. 2,691,586, use of the Clayden eifect in preparing a pro-screened photographic material with which halftone negatives may be prepared-from a continuous tone positive without the use of the conventional halftone screen.
• the usefulness of such pro-screened materials in the graphic arts for letterpress, lithographic and intaglio printing depends on the degree of desensitization obtainable and hence, on the degree of sensitivity of the material to the Clayden effect.
• the susceptibiilty of the emulsion to the Clayden effect is increased.
• a gelatin solution of an alkali metal chloride and an alkali metal bromide is first prepared, in whichthe solution contains more than about one-half molar proportion of the alkali metal chloride and less than 0.1 molar proportion of the alkali metal bromide.
• the alkali metal halides customarily used are the sodium, potassium or ammonium salts.
• the concentration of alkali metal halide in the gelatin may vary considerably; however, the range from 0.4 gram to 3.0 grams of alkali metal halide per gram of gelatin has been found to give satisfactory results.
• the precipitation of the silver halide should be carried out at a temperature of from 50 to C. in order to obtain the enhanced Clayden effect susceptibility.
• a temperature of approximately 70 C. is preferred.
• the emulsion may be sensitized with an optical sensitizing dye of the merocyanine or hemioxonol class as described in my application Serial No. 440,283, filed concurrently herewith, and this also increases the Clayden efiect susceptibility.
• Example 1 A solution of grams of silver nitrate in 65000. of distilled water at 60 C. was added during 6 /3 minutes to a solution of 50 grams of gelatin, 42 grams of sodium chloride and 1.75 grams of potassium bromide in 1287 cc. of distilled water at 71 C. Four and one-quarter minutes after the commencement of the silver nitrate addition, the additionof a solution of 37 grams of potassium bromide in 127 cc. of distilled waterat 40 C. was begun and continued for the remaining two minutes of the silver run. The resulting emulsion was stirred for '10 minute s at 71 C. before the addition of 25 grams of dry gelatin soaked in water. The emulsion was stirred a further four minutes at 71 C.
• the emulsion was sensitized with a sulfur sensitizer such as disclosed in Sheppard U. S. Patent 1,574,944 to its maximum contrast. A further portion of 86grams of gelatin was then added and stirred until it was dispersed. Before coating there was mixed with the emulsion from 0.1 to 0.2 gram of l'carboxymethyl-5-[(3-ethy1'2-( 1)- benzotxazolylidene)--ethylidene]-3-phenyl-2-thiohydantoin dissolved in 1% alcoholic'tiethylamine solution.
• a sulfur sensitizer such as disclosed in Sheppard U. S. Patent 1,574,944
• Example 3 Three chlorobromide emulsions were made as described in Example 1 exceptthat the second potassium bromide solution was added during the last six minutes, the last four minutes and the last two minutes, respectively, of the silver nitrate run, so that the silver and bromide runs ended at approximately the same time.
• susceptibility to Clayden elfect was found to be increased as "more of the additional potassium bromide was added during the latter part of the run, as shown in the following table:
• What I claim is: 1. The method of making a photographic emulsion having a high susceptibility to, Clayden desensitization,

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Colloid Chemistry (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

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Cited By (9)

Citations (4)

• 0
  • BE BE539322D patent/BE539322A/xx unknown
• 1954
  • 1954-06-29 US US440282A patent/US2756148A/en not_active Expired - Lifetime
• 1955
  • 1955-06-14 GB GB17104/55A patent/GB777181A/en not_active Expired
  • 1955-06-14 DE DEE10861A patent/DE1008570B/de active Pending
  • 1955-06-25 FR FR1126711D patent/FR1126711A/fr not_active Expired

Patent Citations (4)

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