Color photographic materials with improved blue sensitization

A color silver halide photographic element comprising a support having thereon:

• a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler,
• a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and
• a yellow dye image-forming unit comprising at least one blue-sensitive silver iodobromide emulsion layer having associated therewith at least one yellow dye-forming coupler,
• wherein the at least one blue-sensitive silver iodobromide emulsion layer comprises silver iodobromide grains having an aspect ratio of from about 2 to about 40 and comprising at least 1 and up to and including 15 mol % iodide, which silver iodobromide grains have associated therewith at least two blue spectral sensitizing dye layers comprising:
• (a) an inner dye layer adjacent the silver iodobromide grains comprising at least one anionic blue spectral sensitizing Dye 1, and
• (b) an outer dye layer adjacent to the inner dye layer comprising at least one cationic blue spectral sensitizing Dye 2,
• wherein Dye 1 and Dye 2 are held together by substantially only a non-covalent force, Dye 2 absorbs light at equal or higher energy than Dye 1, and the maximum energy emission wavelength of Dye 2 overlaps but is not exactly corresponding to the maximum energy absorption wavelength of Dye 1,
• wherein the silver iodobromide grains also have initially associated therewith an amine borane compound in an amount of from about 0.03 to about 0.5 μmol per mol of silver iodobromide, and
• wherein the silver iodobromide grains also have initially associated therewith from about 0.8 to about 4 μmol per mol of silver iodobromide of a thiosulfonate compound having the structure:
• R1—SO2S-M1
• wherein R1 represents an aliphatic, carbocyclic, or heterocylic group and M1 represents a mono-, di-, or tri-valent cation.

A method of preparing a blue-sensitive silver iodobromide emulsion by mixing silver iodobromide grains having an aspect ratio of from about 2 to about 40 and comprising at least 1 and up to and including 15 mol % iodide, individually with:

• (a) an anionic blue spectral sensitizing Dye 1 to provide an inner dye layer adjacent the silver iodobromide grains,
• (b) a cationic blue spectral sensitizing Dye 2 to provide an outer dye layer adjacent to the inner dye layer,
• wherein Dye 1 and Dye 2 are held together by substantially only a non-covalent force, Dye 2 absorbs light at equal or higher energy than Dye 1, and the maximum energy emission wavelength of Dye 2 overlaps but is not exactly corresponding to the maximum energy absorption wavelength of Dye 1,
• (c) an amine borane compound in an amount of from about 0.03 to about 0.5 μmol per mol of silver iodobromide, and
• (d) from about 0.8 to about 4 μmol per mol of silver iodobromide of a thiosulfonate compound having the structure:
• R1—SO2S-M1
• wherein R1 represents an aliphatic, carbocyclic, or heterocylic group and M1 represents a mono-, di-, or tri-valent cation,
• wherein the blue-sensitive silver iodobromide emulsion is prepared using the following sequence of steps:
• (a′) mixing the silver iodobromide grains with the amine borane compound,
• (b′) mixing the silver iodobromide grains with a first portion of a thiosulfonate compound,
• (c′) mixing the silver iodobromide grains with the Dye 1,
• (d′) mixing the silver iodobromide grains with a second portion of a thiosulfonate compound,
• (e′) chemically sensitizing the silver iodobromide grains with sulfur, gold, or both sulfur and gold,
• (f′) treating the silver iodobromide grains by:
• heating them to a temperature of from about 50 to about 70° C., holding the silver iodobromide grains at the temperature for at least 3 and up to and including 60 minutes, and cooling the silver iodobromide grains to a temperature of from about 35 to about 45° C., and
• (g′) mixing the silver iodobromide grains with the Dye 2.