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
  • G03C1/0051—Tabular grain emulsions
• • 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
  • G03C1/04—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein with macromolecular additives; with layer-forming 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
  • G03C1/06—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
  • G03C1/06—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein with non-macromolecular additives
  • G03C1/08—Sensitivity-increasing substances
  • G03C1/09—Noble metals or mercury; Salts or compounds thereof; Sulfur, selenium or tellurium, or compounds thereof, e.g. for chemical sensitising
• • 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
  • G03C1/10—Organic 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
  • G03C1/0051—Tabular grain emulsions
  • G03C2001/0055—Aspect ratio of tabular grains in general; High aspect ratio; Intermediate aspect ratio; Low aspect ratio
• • 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
  • G03C1/035—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein characterised by the crystal form or composition, e.g. mixed grain
  • G03C2001/03511—Bromide content
• • 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
  • G03C1/09—Noble metals or mercury; Salts or compounds thereof; Sulfur, selenium or tellurium, or compounds thereof, e.g. for chemical sensitising
  • G03C2001/091—Gold
• • 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
  • G03C1/09—Noble metals or mercury; Salts or compounds thereof; Sulfur, selenium or tellurium, or compounds thereof, e.g. for chemical sensitising
  • G03C2001/096—Sulphur sensitiser
• • 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
  • G03C2200/00—Details
  • G03C2200/03—111 crystal face

Definitions

• the invention is directed to photographic emulsions. More specifically, the invention is directed to high bromide tabular grain emulsions containing selected peptizers.
• Photographic emulsions are comprised of a dispersing medium and silver halide microcrystals, commonly referred to as grains.
• a peptizer usually a hydrophilic colloid
• binder is added to the emulsion and, after coating, the emulsion is dried.
• the peptizer and binder are collectively referred to as the photographic vehicle of an emulsion.
• Gelatin and gelatin derivatives form both the peptizer and the major portion of the remainder of the vehicle in the overwhelming majority of silver halide photographic elements.
• An appreciation of gelatin is provided by this description contained in Mees The Theory of the Photographic Process, Revised Ed., Macmillan, 1951, pp. 48 and 49:
• Gelatin is pre-eminently a substance with a history; its properties and its future behavior are intimately connected with its past. Gelatin is closely akin to glue.
• Pliny wrote "Glue is cooked from the hides of bulls.” It is described equally shortly by a present-day writer as "the dried down soup or consommé of certain animal refuse.”
• the process of glue making is age-old and consists essentially in boiling down hide clippings or bones of cattle and pigs.
• the filtered soup is allowed to cool and set to a jelly which, when cut and dried on nets, yields sheets of glue or gelatin, according to the selection of stock and the process of manufacture.
• Glue is thus distinguished by its adhesive properties; gelatin by its cohesive properties, which favor the formation of strong jellies.
• Photographic gelatin is generally made from selected clippings of calf hide and ears as well as cheek pieces and pates.
• Pigskin is used for the preparation of some gelatin, and larger quantities are made from bone.
• the actual substance in the skin furnishing the gelatin is collagen. It forms about 35 per cent of the coria of fresh cattle hide.
• the corresponding tissue obtained from bone is termed ossein.
• the raw materials are selected not only for good structural quality but for freedom from bacterial decomposition.
• the dirt with loose flesh and blood is eliminated in a preliminary wash.
• the hair, fat, and much of the albuminous materials are removed by soaking the stock in limewater containing suspended lime. The free lime continues to rejuvenate the solution and keeps the bath at suitable alkalinity.
• Gelatin may also be made by an acid treatment of the stock without the use of lime.
• the stock is treated with dilute acid (pH 4.0) for one to two months and then washed thoroughly, and the gelatin is extracted.
• This gelatin differs in properties from gelatin made by treatment with lime.
• collagen generally is the preponderant protein constituent in its tissue of origin, it is always associated with various "ground substances" such as noncollagen protein, mucopolysaccharides, polynucleic acid, and lipids. Their more or less complete removal is desirable in the preparation of photographic gelatin.
• ground substances such as noncollagen protein, mucopolysaccharides, polynucleic acid, and lipids.
• Their more or less complete removal is desirable in the preparation of photographic gelatin.
• Superimposed on the complexity of composition is the variability of composition, attributable to the varied diets of the animals providing the starting materials. The most notorious example of this was provided by the forced suspension of manufacturing by the Eastman Dry Plate Company in 1882, ultimately attributed to a reduction in the sulfur content in a purchased batch of gelatin.
• this invention is directed to a radiation-sensitive emulsion comprised of silver halide grains including tabular grains (a) having ⁇ 111 ⁇ major faces, (b) containing greater than 50 mole percent bromide, based on silver, and (c) accounting for greater than 50 percent of total grain projected area, and a dispersing medium including a peptizer adsorbed to the silver halide grains, characterized in that the peptizer is a water dispersible cationic starch.
• cationic starches are better suited for preparing high bromide ⁇ 111 ⁇ tabular grain emulsions than non-cationic starches and that cationic starches, when present in place of gelatin, facilitate photographic advantages.
• Cationic starches exhibit lower levels of viscosity than have previously been present in preparing tabular grain emulsions. Reduced viscosity facilitates more uniform mixing. Both micromixing, which controls the uniformity of grain composition, mean grain size and dispersity, and bulk mixing, which controls scale up of precipitations to convenient manufacturing scales, are favorably influenced by the reduced viscosities made possible by cationic starch peptizers. Precise control over grain nucleation, including the monodispersity of the grain nuclei, is particularly important to successfully achieving and improving the properties of tabular grain emulsions.
• ECD equivalent circular diameter
• tabularity is defined as ECD/t 2 , where ECD and t are both measured in micrometers ( ⁇ m).
• tabular grain indicates a grain having two parallel crystal faces which are clearly larger than any remaining crystal face and having an aspect ratio of at least 2.
• tabular grain emulsion refers to an emulsion in which tabular grains account for greater than 50 percent of total grain projected area.
• high bromide or “high chloride” in referring to grains and emulsions indicates that bromide or chloride, respectively, are present in concentrations of greater than 50 mole percent, based on total silver.
• the halides are named in order of ascending concentrations.
• ⁇ 111 ⁇ tabular is employed in referring to tabular grains and tabular grain emulsions in which the tabular grains have ⁇ 111 ⁇ major faces.
• gelatino-peptizer is employed to designate gelatin and gelatin-derived peptizers.
• selected cationic starch peptizer and “selected peptizer” are employed to designate a water dispersible cationic starch.
• starch cationic in referring to starch indicates that the starch molecule has a net positive charge at the pH of intended use.
• water dispersible in referring to cationic starches indicates that, after boiling the cationic starch in water for 30 minutes, the water contains, dispersed to at least a colloidal level, at least 1.0 percent by weight of the total cationic starch.
• ddle chalcogen designates sulfur, selenium and/or tellurium.
• the present invention is generally applicable to high bromide ⁇ 111 ⁇ tabular grain emulsions. That is, greater than 50 percent of total grain projected area is accounted for by tabular grains having ⁇ 111 ⁇ major faces, and the tabular grains contain greater than 50 mole percent bromide, based on silver.
• the emulsions of the present invention can be readily distinguished from conventional high bromide ⁇ 111 ⁇ tabular grain emulsions in that a water dispersible cationic starch is adsorbed to the grain surfaces, thereby acting as a peptizer. Any conventional water dispersible cationic starch can be employed as a peptizer.
• starch is employed to include both natural starch and modified derivatives, such as dextrinated, hydrolyzed, alkylated, hydroxyalkylated, acetylated or fractionated starch.
• the starch can be of any origin, such as corn starch, wheat starch, potato starch, tapioca starch, sago starch, rice starch, waxy corn starch or high amylose corn starch.
• Starches are generally comprised of two structurally distinctive polysaccharides, ⁇ -amylose and amylopectin. Both are comprised of ⁇ -D-glucopyranose units. In a-amylose the ⁇ -D-glucopyranose units form a 1,4-straight chain polymer.
• the repeating units take the following form: In amylopectin, in addition to the 1,4-bonding of repeating units, 6-position chain branching (at the site of the -CH 2 OH group above) is also in evidence, resulting in a branched chain polymer.
• the repeating units of starch and cellulose are diasteroisomers that impart different overall geometries to the molecules.
• the ⁇ anomer found in starch and shown in formula I above, results in a polymer that is capable of crystallization and some degree of hydrogen bonding between repeating units in adjacent molecules, but not to the same degree as the ⁇ anomer repeating units of cellulose and cellulose derivatives.
• Polymer molecules formed by the ⁇ anomers show strong hydrogen bonding between adjacent molecules, resulting in clumps of polymer molecules and a much higher propensity for crystallization. Lacking the alignment of substituents that favors strong intermolecular bonding, found in cellulose repeating units, starch and starch derivatives are much more readily dispersed in water.
• the water dispersible starches employed in the practice of the invention are cationic--that is, they contain an overall net positive charge when dispersed in water.
• Starches are conventionally rendered cationic by attaching a cationic substituent to the ⁇ -D-glucopyranose units, usually by esterification or etherification at one or more free hydroxyl sites.
• Reactive cationogenic reagents typically include a primary, secondary or tertiary amino group (which can be subsequently protonated to a cationic form under the intended conditions of use) or a quaternary ammonium, sulfonium or phosphonium group.
• the cationic starch must be water dispersible. Many starches disperse in water upon heating to temperatures up to boiling for a short time (e.g., 5 to 30 minutes). High sheer mixing also facilitates starch dispersion. The presence of cationic substituents increases the polar character of the starch molecule and facilitates dispersion.
• the starch molecules preferably achieve at least a colloidal level of dispersion and ideally are dispersed at a molecular level-i.e., dissolved.
• the water dispersible cationic starch is present during the precipitation (during nucleation and grain growth or during grain growth) of the high bromide ⁇ 111 ⁇ tabular grains.
• precipitation is conducted by substituting the water dispersible cationic starch for all conventional gelatino-peptizers.
• the concentrations of the selected peptizer and the point or points of addition can correspond to those employed using gelatino-peptizers.
• emulsion precipitation can tolerate even higher concentrations of the selected peptizer.
• all of the selected peptizer required for the preparation of an emulsion through the step of chemical sensitization can be present in the reaction vessel prior to grain nucleation.
• This has the advantage that no peptizer additions need be interjected after tabular grain precipitation has commenced. It is generally preferred that from 1 to 500 grams (most preferably from 5 to 100 grams) of the selected peptizer per mole of silver to be precipitated be present in the reaction vessel prior to tabular grain nucleation.
• the high bromide ⁇ 111 ⁇ tabular grain emulsions that are formed preferably contain at least 70 mole percent bromide and optimally at least 90 mole percent bromide, based on silver.
• Silver bromide, silver iodobromide, silver chlorobromide, silver iodochlorobromide, and silver chloroiodobromide tabular grain emulsions are specifically contemplated.
• silver chloride and silver bromide form tabular grains in all proportions, chloride is preferably present in concentrations of 30 mole percent or less. Iodide can be present in the tabular grains up to its solubility limit under the conditions selected for tabular grain precipitation.
• silver iodide can be incorporated into the tabular grains in concentrations ranging up to about 40 mole percent. It is generally preferred that the iodide concentration be less than 20 mole percent. Significant photographic advantages can be realized with iodide concentrations as low as 0.5 mole percent, with an iodide concentration of at least 1 mole percent being preferred.
• the high bromide ⁇ 111 ⁇ tabular grain emulsions can exhibit mean grain ECD's of any conventional value, ranging up to 10 ⁇ m, which is generally accepted as the maximum mean grain size compatible with photographic utility.
• the tabular grain emulsions of the invention typically exhibit a mean ECD in the range of from about 0.2 to 5.0 ⁇ m.
• Tabular grain thicknesses typically range from about 0.03 to 0.3 ⁇ m. For blue recording somewhat thicker grains, up to about 0.5 ⁇ m, can be employed. For minus blue (red and/or green) recording, thin ( ⁇ 0.2 ⁇ m) tabular grains are preferred.
• Ultrathin ( ⁇ 0.07 ⁇ m) tabular grains are specifically preferred for most minus blue recording in photographic elements forming dye images (i.e., color photographic elements).
• An important distinction between ultrathin tabular grains and those having greater ( ⁇ 0.07 ⁇ m) thicknesses resides in the difference in their reflective properties.
• Ultrathin tabular grains exhibit little variation in reflection as a function of the wavelength of visible light to which they are exposed, where as thicker tabular grains exhibit pronounced reflection maxima and minima as a function of the wavelength of light.
• ultrathin tabular grains simplify construction of photographic element intended to form plural color records (i.e., color photographic elements). This property, together with the more efficient utilization of silver attributable to ultrathin grains, provides a strong incentive for their use in color photographic elements.
• tabular grains impart to emulsions generally increases as the average aspect ratio or tabularity of the tabular grain emulsions increases. Both aspect ratio (ECD/t) and tabularity (ECD/t 2 ) increase as average tabular grain thickness decreases. Therefore it is generally sought to minimize the thicknesses of the tabular grains to the extent possible for the photographic application.
• the tabular grains having a thickness of less than 0.3 ⁇ m (preferably less than 0.2 ⁇ m and optimally less than 0.07 ⁇ m) and accounting for greater than 50 percent (preferably at least 70 percent and optimally at least 90 percent) of total grain projected area exhibit an average aspect ratio of greater than 5 and most preferably greater than 8.
• Tabular grain average aspect ratios can range up to 100, 200 or higher, but are typically in the range of from about 12 to 80. Tabularities of >25 are generally preferred.
• silver salts can be epitaxially grown onto the tabular grains during the precipitation process. Epitaxial deposition onto the edges and/or corners of tabular grains is specifically taught by Maskasky U.S. Patent 4,435,501. In a specifically preferred form high chloride silver halide epitaxy is present at the edges or, most preferably, restricted to corner adjacent sites on the tabular grains.
• the emulsions of the invention show unexpected sensitivity enhancements with or without epitaxy when chemically sensitized in the absence of a gelatino-peptizer, employing one or a combination of noble metal, middle chalcogen and reduction chemical sensitization techniques.
• Conventional chemical sensitizations by these techniques are summarized in Research Disclosure , Item 36544, cited above, Section IV. Chemical sensitizations. All of these sensitizations, except those that specifically require the presence of gelatin (e.g., active gelatin sensitization) are applicable to the practice of the invention. It is preferred to employ at least one of noble metal (typically gold) and middle chalcogen (typically sulfur) and, most preferably, a combination of both in preparing the emulsions of the invention for photographic use.
• noble metal typically gold
• middle chalcogen typically sulfur
• emulsion washing can be combined with emulsion precipitation, using ultrafiltration during precipitation as taught by Mignot U.S. Patent 4,334,012.
• emulsion washing by diafiltration after precipitation and before chemical sensitization can be undertaken with a semipermeable membrane as illustrated by Research Disclosure, Vol. 102, October 1972, Item 10208, Hagemaier et al Research Disclosure , Vol.
• a specifically preferred approach to chemical sensitization employs a combination of sulfur containing ripening agents in combination with middle chalcogen (typically sulfur) and noble metal (typically gold) chemical sensitizers.
• Contemplated sulfur containing ripening agents include thioethers, such as the thioethers illustrated by McBride U.S. Patent 3,271,157, Jones U.S. Patent 3,574,628 and Rosencrants et al U.S. Patent 3,737,313.
• Preferred sulfur containing ripening agents are thiocyanates, illustrated by Nietz et al U.S. Patent 2,222,264, Lowe et al U.S. Patent 2,448,534 and Illingsworth U.S. Patent 3,320,069.
• middle chalcogen sensitizers are tetrasubstituted middle chalcogen ureas of the type disclosed by Herz et al U.S. Patents 4,749,646 and 4,810,626.
• Preferred compounds include those represented by the formula: wherein
• X is preferably sulfur and A 1 R 1 to A 4 R 4 are preferably methyl or carboxymethyl, where the carboxy group can be in the acid or salt form.
• a specifically preferred tetrasubstituted thiourea sensitizer is 1,3-dicarboxymethyl-1,3-dimethylthiourea.
• Preferred gold sensitizers are the gold(I) compounds disclosed by Deaton U.S. Patent 5,049,485. These compounds include those represented by the formula: AuL 2 + X - or AuL(L 1 ) + X - (III) wherein
• sulfur sensitizers such as those formula II
• gold sensitizers such as those of formula III
• reduction sensitizers which are the 2-[N-(2-alkynyl)amino]- meta -chalcoazoles disclosed by Lok et al U.S. Patents 4,378,426 and 4,451,557.
• Preferred 2-[N-(2-alkynyl)amino]- meta -chalcoazoles can be represented by the formula: where
• the formula IV compounds are generally effective (with the IVb form giving very large speed gains and exceptional latent image stability) when present during the heating step (finish) that results in chemical sensitization.
• Spectral sensitization of the emulsions of the invention is not required, but is highly preferred, even when photographic use of the emulsion is undertaken in a spectral region in which the tabular grains exhibit significant native sensitivity. While spectral sensitization is most commonly undertaken after chemical sensitization, spectral sensitizing dye can be advantageous introduced earlier, up to and including prior to grain nucleation. Kofron et al discloses advantages for "dye in the finish" sensitizations, which are those that introduce the spectral sensitizing dye into the emulsion prior to the heating step (finish) that results in chemical sensitization. Maskasky U.S.
• Patent 4,435,501 teaches the use of aggregating spectral sensitizing dyes, particularly green and red absorbing cyanine dyes, as site directors for epitaxial deposition. These dyes are present in the emulsion prior to the chemical sensitizing finishing step. When the spectral sensitizing dye present in the finish is not relied upon as a site director for the silver salt epitaxy, a much broader range of spectral sensitizing dyes is available.
• the spectral sensitizing dyes disclosed by Kofron et al particularly the blue spectral sensitizing dyes shown by structure and their longer methine chain analogous that exhibit absorption maxima in the green and red portions of the spectrum, are particularly preferred for incorporation in the tabular grain emulsions of the invention.
• a more general summary of useful spectral sensitizing dyes is provided by Research Disclosure , Item 36544, cited above, Section V. Spectral sensitization and desensitization.
• the spectral sensitizing dye can act also as a site director and/or can be present during the finish, the only required function that a spectral sensitizing dye must perform in the emulsions of the invention is to increase the sensitivity of the emulsion to at least one region of the spectrum.
• the spectral sensitizing dye can, if desired, be added to an emulsion according to the invention after chemical sensitization has been completed.
• the emulsions of this invention and their preparation can take any desired conventional form.
• a novel emulsion satisfying the requirements of the invention has been prepared, it can be blended with one or more other novel emulsions according to this invention or with any other conventional emulsion.
• Conventional emulsion blending is illustrated in Research Disclosure , Item 36544, Section I. Emulsion grains and their preparation, E. Blends, layers and performance categories.
• Other common, but optional features are illustrated by Research Disclosure , Item 36544, Section VII, Antifoggants and stabilizers; Section VIII, Absorbing and scattering materials; Section IX, Coating physical property modifying agents; Section X, Dye image formers and modifiers.
• the features of Sections II and VII-X can alternatively be provided in other photographic element layers.
• Example 1 AgIBr (3 mole % I) Tabular Grain Emulsion Made Using a Cationic Potato Starch
• a starch solution was prepared by boiling for 30 min a stirred mixture of 80 g cationic potato starch (STA-LOK ® 400, obtained from A. E. Staley Manufacturing Co., Decatur, IL.), 27 mmoles of NaBr, and distilled water to 4 L.
• the cationic starch was a mixture of 21% amylose and 79% amylopectin and contained 0.33 wt% nitrogen in the form of a quaternary trimethyl ammonium alkyl starch ether and 0.13 wt% natural phosphorus.
• the cationic starch had an average molecular weight is 2.2 million.
• the resulting solution was cooled to 35°C, readjusted to 4 L with distilled water, and the pH was adjusted to 5.5.
• a 2 M AgNO 3 solution was added at 100 mL per min for 0.2 min.
• a salt solution of 1.94 M NaBr and 0.06 M KI was added initially at 100 mL per min and then at a rate needed to maintain a pBr of 2.21.
• 25 mL of 2 M NaBr solution was added rapidly and the temperature of the contents of the reaction vessel was increased to 60°C at a rate of 5°C per 3 min.
• the AgNO 3 solution was added at 10 mL per min for 1 min then its addition rate was accelerated to 50 mL per min in 30 min until a total of 1.00 L had been added.
• the salt solution was concurrently added at a rate needed to maintain a constant pBr of 1.76.
• the resulting tabular grain emulsion was washed by diafiltration at 40°C to a pBr of 3.38.
• the tabular grain population of the resulting tabular grain emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.2 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 20.
• the tabular grain population made up 92% of the total projected area of the emulsion grains.
• the emulsion grains had a coefficient of variation in diameter of 18%.
• a starch solution was prepared by boiling for 30 min a stirred 400 g aqueous mixture containing 2.7 mmoles of NaBr and 8.0 g of a cationic hybrid corn starch (CATO ® 235, obtained from National Starch and Chemical Company, Bridgewater, NJ.) containing 0.31 wt% nitrogen and 0.00 wt% phosphorus.
• CAO ® 235 a cationic hybrid corn starch
• the resulting solution was cooled to 35°C, readjusted to 400 g with distilled water.
• pH 5.5 was added 2 M AgNO 3 solution at a constant rate of 10 mL per min.
• a salt solution of 1.94 M NaBr and 0.06 M KI was added initially at 10 mL per min and then at a rate needed to maintain a pBr of 2.21.
• the addition of the solutions was stopped, 2.5 mL of 2M NaBr was added rapidly, and the temperature of the contents of the reaction vessel was increased to 60°C at a rate of 5°C per 3 min.
• the AgNO 3 solution was added at 1.0 mL per min for 1 min then its addition rate was accelerated to reach a flow rate of 5 mL per min in 30 min until a total of 100 mL of the AgNO 3 solution had been added.
• the salt solution was concurrently added at a rate needed to maintain a constant pBr of 1.76.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.6 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 27.
• the tabular grain population made up 85% of the total projected area of the emulsion grains.
• Example 3 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Amphoteric Potato Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a cationic amphoteric potato starch (Wespol A ®, obtained from Western Polymer Corporation, Moses Lake, WA.) containing both a quaternary trimethyl ammonium alkyl starch ether, 0.36 wt% nitrogen, and orthophosphate (0.70 wt% phosphorus) substituents.
• a cationic amphoteric potato starch Wespol A ®, obtained from Western Polymer Corporation, Moses Lake, WA.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.7 ⁇ m, an average thickness of 0.05 ⁇ m, and an average aspect ratio of 34.
• the tabular grain population made up 95% of the total projected area of the emulsion grains.
• Example 4 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Amphoteric Potato Starch
• This emulsion was prepared similarly to Example 3, except that the precipitation was stopped after 50 mL of the AgNO 3 solution was added.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.0 ⁇ m, an average thickness of 0.045 ⁇ m, and an average aspect ratio of 25.
• the tabular grain population made up 95% of the total projected area of the emulsion grains.
• Example 5 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Potato Starch and at pH 2.0.
• This emulsion was prepared similarly to Example 2, except that the emulsion was precipitated at pH 2.0 and the starch used was cationic potato starch (STA-LOK ® 400).
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.5 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 22.
• the tabular grain population made up 80% of the total projected area of the emulsion grains.
• This emulsion was prepared similarly to Example 2, except that the emulsion was precipitated at pH 6.0, and the starch used was a cationic waxy corn starch (STA-LOK ® 180, obtained from A. E. Staley Manufacturing Co.) made up of 100% amylopectin derivatized to contain 0.36 wt% nitrogen in the form of a quaternary trimethyl ammonium alkyl starch ether and 0.06 wt% phosphorus, average molecular weight 324,000.
• STA-LOK ® 180 cationic waxy corn starch
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.6 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 27.
• the tabular grain population made up 91% of the total projected area of the emulsion grains.
• Example 7 AgBr Tabular Grain Emulsion Made by Adding 94% of a Cationic Potato Starch After Grain Nucleation
• a starch solution was prepared by boiling for 30 min a stirred 200 g aqueous mixture containing 3.75 mmoles of NaBr and 8.0 g of the cationic potato starch STA-LOK ® 400.
• the starch solution (7.5 g starch) was added, the pH was adjusted to 6.0 and maintained at this value throughout the remainder of the precipitation, and the AgNO 3 solution was added at 1.0 mL per min for 3 min and the NaBr solution was concurrently added at a rate needed to maintain a pBr of 1.76. Then the addition of the NaBr solution was stopped but the addition of the AgNO 3 solution was continued at 1.0 mL per min until a pBr of 2.00 was obtained. Then the addition of the AgNO 3 was accelerated at 0.05 mL per min squared and the NaBr solution was added as needed to maintain a pBr of 2.00 until a total of 0.20 mole of silver had been added.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.0 ⁇ m, an average thickness of 0.055 ⁇ m, and an average aspect ratio of 18.
• the tabular grain population made up 90% of the total projected area of the emulsion grains.
• Example 8 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Amphoteric Corn Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a cationic amphoteric corn starch (STA-LOK ® 356, obtained from A. E. Staley Manufacturing Co.) containing both a quaternary trimethyl ammonium alkyl starch ether (0.34 wt% nitrogen) and orthophosphate (1.15 wt% phosphorus) substituents.
• the cationic amphoteric starch was a mixture of 28% amylose and 72% amylopectin, with an average molecular weight of 486,000.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.6 ⁇ m, an average thickness of 0.07 ⁇ m, and an average aspect ratio of 23.
• the tabular grain population made up 80% of the total projected area of the emulsion grains.
• Example 9 AgBr Tabular Grain Emulsion Made Using a Cationic Potato Starch
• the AgNO 3 solution was added at 1.0 mL per min for 1 min then its addition rate was accelerated to 5 mL per min in 30 min then held at this rate until a total of 200 mL of the AgNO 3 solution had been added.
• the salt solution was concurrently added at a rate needed to maintain a constant pBr of 1.76.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 2.2 ⁇ m, an average thickness of 0.08 ⁇ m, and an average aspect ratio of 28.
• the tabular grain population made up 85% of the total projected area of the emulsion grains.
• Example 10 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Protonated Tertiary Aminoalkyl (Cationic) Corn Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a corn starch (CATO-SIZE ® 69, obtained from National Starch and Chemical Co.) that, as obtained, was derivatized to contain tertiary aminoalkyl starch ethers, 0.25 wt% nitrogen, 0.06 wt% phosphorus. At a pH of 5.5, the tertiary amino groups were protonated to render the starch cationic.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.2 ⁇ m, an average thickness of 0.08 ⁇ m, and an average aspect ratio of 15.
• the tabular grain population made up 55% of the total projected area of the emulsion grains.
• Example 11 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Potato Starch and at pH 5.5 and 80°C.
• This emulsion was prepared similarly to Example 2, except that the starch used was cationic potato starch (STA-LOK ® 400) and the temperature was increased to 80°C (instead of 60°C).
• STA-LOK ® 400 cationic potato starch
• the tabular grain population of the emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.7 ⁇ m, an average thickness of 0.07 ⁇ m, and an average aspect ratio of 24.
• the tabular grain population made up 80% of the total projected area of the emulsion grains.
• Example 12 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Corn Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a cationic corn starch (CATO ® 25, obtained from National Starch and Chemical Company) containing 0.26 wt% nitrogen and 0.00 wt% phosphorus.
• CAO ® 25 obtained from National Starch and Chemical Company
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.2 ⁇ m, an average thickness of 0.07 ⁇ m, and an average aspect ratio of 17.
• the tabular grain population made up 65% of the total projected area of the emulsion grains.
• Example 13 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Corn Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a cationic corn starch (Clinton 788 ®, obtained from ADM Corn Processing, Clinton, IA) containing 0.15 wt% nitrogen and 0.00 wt% phosphorus.
• a cationic corn starch (Clinton 788 ®, obtained from ADM Corn Processing, Clinton, IA) containing 0.15 wt% nitrogen and 0.00 wt% phosphorus.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.0 ⁇ m, an average thickness of 0.08 ⁇ m, and an average aspect ratio of 13.
• the tabular grain population made up 60% of the total projected area of the emulsion grains.
• Example 14 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Wheat Starch
• This emulsion was prepared similarly to Example 2, except that the starch used was a cationic wheat starch (K-MEGA® 53S, obtained from ADM/Ogilvie, Montreal, Quebec, Canada), which, as received was derivatized with a quaternary amine. The degree of substitution is 0.050 corresponding to 0.41 wt% nitrogen. The phosphorus was determined spectrophotometrically to be 0.07 wt%.
• K-MEGA® 53S cationic wheat starch
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.5 ⁇ m, an average thickness of 0.08 ⁇ m, and an average aspect ratio of 19.
• the tabular grain population made up 85% of the total projected area of the emulsion grains.
• Example 15 AgBr Tabular Grain Emulsion Made Using a Cationic Potato Starch
• a starch solution was prepared by boiling for 30 min a stirred 400 g aqueous mixture containing 2.7 mmoles of NaBr and 8.0 g of the cationic potato starch STA-LOK ® 400.
• the resulting solution was cooled to 35°C, readjusted to 400 g with distilled water.
• pH 6.0 pH 6.0 was added 2 M AgNO 3 solution at a constant rate of 10 mL per min.
• a 2 M NaBr solution was added initially at 10 mL per min and then at a rate needed to maintain a pBr of 2.21.
• the addition of the solutions was stopped, 2.5 mL of 2M NaBr was added rapidly, and the temperature of the contents of the reaction vessel was increased to 50°C at a rate of 5°C per 3 min.
• the pH was adjusted to 6.0 and the AgNO 3 solution was added at 1.0 mL per min for 1 min, then its addition rate was accelerated to reach a flow rate of 5 mL per min in 30 min and held at this rate until a total of 200 mL of the AgNO 3 solution had been added.
• the salt solution was concurrently added at a rate needed to maintain a constant pBr of 1.76.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.2 ⁇ m, an average thickness of 0.10 ⁇ m, and an average aspect ratio of 12.
• the tabular grain population made up 70% of the total projected area of the emulsion grains.
• Example 16 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using a Cationic Potato Starch of High Nitrogen Content
• a cationic potato starch solution containing a high nitrogen content was supplied by Western Polymer Corporation.
• the starch was 1.10 wt% in nitrogen and 0.25 wt% in natural phosphorus.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 1.2 ⁇ m, an average thickness of 0.09 ⁇ m, and an average aspect ratio of 13.
• the tabular grain population made up 80% of the total projected area of the emulsion grains.
• Example 17 AgBr Tabular Grain Emulsion Made Using a Cationic Potato Starch
• a starch solution was prepared by boiling for 30 min a stirred 400 g aqueous mixture containing 2.7 mmoles of NaBr and 8.0 g of the cationic potato starch STA-LOK ® 400.
• the resulting solution was cooled to 35°C, readjusted to 400 g with distilled water.
• pH 6.0 pH 6.0 was added 2 M AgNO 3 solution at a constant rate of 10 mL per min.
• a salt solution of 2.5 M NaBr was added initially at 10 mL per min and then at a rate needed to maintain a pBr of 2.21.
• the addition of the solutions was stopped, 2.5 mL of 2M NaBr was added rapidly, and the temperature of the contents of the reaction vessel was increased to 60°C at a rate of 5°C per 3 min.
• the pH was adjusted to 6.0 and the AgNO 3 solution was added at 1.0 mL per min for 1 min then its addition rate was accelerated to reach a flow rate of 5 mL per min in 30 min and held at this rate until a total of 200 mL of the AgNO 3 solution had been added.
• the salt solution was concurrently added at a rate needed to maintain a constant pBr of 1.76. Then the addition of the NaBr solution was stopped and the flow rate of the AgNO 3 solution was dropped to 1 mL per min. When the pBr reached 2.28, the NaBr solution flow was resumed to maintain this pBr. After 60 min of growth at this pBr, the pBr was adjusted to 3.04 and maintained at this value until a total of 0.53 moles of silver had been added.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 2.0 ⁇ m, an average thickness of 0.14 ⁇ m, and an average aspect ratio of 14.
• the tabular grain population made up 85% of the total projected area of the emulsion grains.
• This emulsion was prepared similarly to Example 2, except that the starch used was a corn starch (FILMKOTE ® 54, obtained from National Starch and Chemical Co.), which, as supplied, was derivatized to contain carboxylate groups. The nitrogen content was natural, 0.06 wt%.
• This emulsion was prepared similarly to Example 2, except that the starch used was an orthophosphate derivatized potato starch 0.03 wt% nitrogen (natural), and orthophosphate substituents, 0.66 wt% phosphorus.
• the sample was obtained from Western Polymer Corporation.
• This emulsion was prepared similarly to Example 2, except that the starch (STARPOL ® 530, was obtained from A. E. Staley Manufacturing Co.) used was a hydroxypropyl-substituted corn starch, 0.06 wt% nitrogen (natural) and 0.12 wt% phosphorus.
• starch (STARPOL ® 530, was obtained from A. E. Staley Manufacturing Co.) used was a hydroxypropyl-substituted corn starch, 0.06 wt% nitrogen (natural) and 0.12 wt% phosphorus.
• This emulsion was prepared similarly to Example 2, except that the starch (Soluble Potato Starch obtained from Sigma Chemical Company, St. Louis, MO.) used was a treated and purified water soluble potato starch, 0.04 wt% nitrogen and 0.06 wt% phosphorus.
• starch Soluble Potato Starch obtained from Sigma Chemical Company, St. Louis, MO.
• This emulsion was prepared similarly to Example 2, except that the starch (Supergel ® 1400, obtained from ADM/Ogilvie, Montreal, Quebec, Canada) used was a water soluble noncationic wheat starch.
• the starch Supergel ® 1400, obtained from ADM/Ogilvie, Montreal, Quebec, Canada
• This example demonstrates to the failure of the grain protein zein to act as a peptizer.
• This emulsion was prepared similarly to Example 2, except that the polysaccharide dextran (obtained from Sigma Chemical Co., St. Louis, MO.), having a molecular weight of approximately 500,000, was employed.
• polysaccharide dextran obtained from Sigma Chemical Co., St. Louis, MO.
• This emulsion was prepared similarly to Example 2 except that the polysaccharide used was agar (purified, ash content ⁇ 2%), obtained from Sigma Chemical Co.
• Agar was a poor peptizer for silver halide grains.
• This emulsion was prepared similarly to Example 2, except that the polysaccharide used was pectin from citrus fruit (obtained from Sigma Chemical Co).
• This emulsion was prepared similarly to Example 2, except that the polysaccharide used was gum arabic (obtained from Sigma Chemical Co.), having a molecular weight of about 250,000.
• This emulsion was prepared similarly to Example 2, except that oxidized bone gelatin was substituted for the starch.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 2.2 ⁇ m, an average thickness of 0.07 ⁇ m, and an average aspect ratio of 31.
• the tabular grain population made up 60% of the total projected area of the emulsion grains, down from 85% in Example 2.
• This emulsion was prepared similarly to Control Example 28, except that precipitation was terminated after the addition of 0.1 mole of silver nitrate.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 2.0 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 33.
• the tabular grain population made up only 30% of the total projected area of the emulsion grains.
• This emulsion was prepared similarly to Example 2, except that oxidized bone gelatin was substituted for the starch and the precipitation growth temperature was 60°C, instead of 50°C.
• the tabular grain population of the resulting emulsion was comprised of tabular grains with an average equivalent circular diameter of 3.2 ⁇ m, an average thickness of 0.07 ⁇ m, and an average aspect ratio of 46.
• the tabular grain population made up only 30% of the total projected area of the emulsion grains.
• This emulsion was prepared in bone gelatin using conventional techniques favorable for the formation of tabular grain emulsions for the purpose of providing an emulsion with tabular grain thicknesses equal to or less than and tabular grain projected areas equal to or greater than those of the tabular grain emulsion precipitated in cationic starch reported in Example 1.
• the emulsion was diafiltered-washed to a pBr of 3.38 at 40°C.
• the tabular grains had an average equivalent circular diameter of 2.45 ⁇ m, an average thickness of 0.06 ⁇ m, and an average aspect ratio of 41.
• the tabular grain population made up 95% of the total projected area of the emulsion grains.
• Example 1 STA The tabular grain emulsion of Example 1, precipitated in the presence of cationic starch, was divided into three portions to form three samples. Two portions received no further treatment until sensitization, "Example 1 STA” and “Example 1 STA-Spectral”. The samples were identical, but the latter sample received only spectral sensitization, instead of chemical and spectral sensitization, as in the case of the remaining emulsion samples.
• Example 1 GEL 20 g of bone gelatin in 100 mL distilled water were added.
• the purpose of adding gelatin was to demonstrate the effect of gelatin added as a vehicle after precipitation and before chemical sensitization, as is conventional practice.
• a fourth emulsion sample was taken from a conventional silver iodobromide (2.7 mole % I) tabular grain precipitated in bone gelatin, Control Example 31.
• the purpose of providing this sample was to compare the properties of an emulsion precipitated in gelatin to the emulsions precipitated in the absence of gelatin and sensitized either in the presence or absence of gelatin.
• the resulting sensitized emulsions were mixed with gelatin, yellow dye-forming coupler dispersion, surfactants, and hardener and coated onto clear support at 0.84 g/m 2 silver, 1.7 g/m 2 yellow dye-forming coupler, and 3.5 g/m 2 bone gelatin.
• the coatings were exposed to blue light for 0.02 sec through a 0 to 4.0 log density graduated step tablet, processed in the Kodak Flexicolor C-41TM color negative process using a development time of 3 min 15 sec.
• Example 1 GEL which was precipitated in cationic starch, but had gelatin added before chemical sensitization, exhibited a speed that was 15 relative speed units Easter than the speed of Control Example 31.
• Example STA Quite surprising was the large speed advantage demonstrated by Example STA.
• This emulsion which precipitated and sensitized in the absence of gelatin, was 1.04 log E faster than Control Example 31. In other words, it was more than 10 times faster than the conventional Control Example 31 emulsion.
• Example 1 STA-Spectral was included to demonstrate that the cationic starch itself, apart from the chemical sensitizers, was not imparting the speed observed.
• Example 1 STA-Spectral was 111 relative speed units (1.11 log E) slower than Control Example 31. From this it was concluded that the cationic starch was in some way permitting better interaction of the chemical sensitizer with the grain surface than is conventionally realized by employing gelatin as a peptizer.
• Example 1 STA prepared as described in Example 32 was treated with a 0.2 wt% solution of active proteolytic enzyme (H.T.-Proteolytic 200 from Miles Labs, Inc., Elkhart, IN) for 30 min at 35°C to degrade the gelatin.
• active proteolytic enzyme H.T.-Proteolytic 200 from Miles Labs, Inc., Elkhart, IN
• the emulsion grains were washed twice in distilled water and examined by infra-red spectroscopy. The infra-red absorption spectrum of the starch was clearly observed, demonstrating that the starch remained a permanent part of the emulsion and was not removed by washing.
• a 2 percent by weight cationic starch solution, CS was prepared by boiling for 30 min a stirred mixture of 8 g STA-LOK ® 400, 2.7 mmoles of NaBr and distilled water to 400 mL. The solution was sonicated for 3 min. The resulting solution was cooled to 40°C, readjusted to 400 mL with distilled water, sonicated for 3 min, and the pH adjusted to 6.0.
• GEL gealtin solution
• the viscosity data show that cationic starch has low viscosity at low temperatures while the gelatin solution solidified. This makes cationic starch particularly useful for silver halide grain nucleation and/or growth at temperatures below 25°C.

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