High aspect ratio silver bromoiodide emulsions and processes for their preparation
AssigneeEastman Kodak Company
InventorsHerbert S. Wilgus, John A. Haefner
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Abstract
A tabular grain silver halide emulsion is disclosed comprised of a dispersing medium and silver bromoiodide grains. Tabular silver bromoiodide grains having a thickness less than 0.3 micron and a diameter of at least 0.6 micron have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of the silver bromoiodide grains. The high aspect ratio silver bromoiodide grains are prepared by concurrently running silver, bromide, and iodide salts into a reaction vessel while controlling pBr. Prior to the concurrent addition of silver and iodide salts the reaction vessel is substantially free of iodide.
Claims22
A high aspect ratio tabular grain silver halide emulsion comprised of a dispersing medium and silver bromoiodide grains, wherein tabular silver bromoiodide grains having a thickness of less than 0.3 micron and a diameter of at least 0.6 micron have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of said silver bromoiodide grains.
A high aspect ratio tabular grain silver halide emulsion comprised of gelatin or a gelatin derivative peptizer and silver bromoiodide grains comprised of from 0.1 to 20 mole percent iodide, wherein tabular silver bromoiodide grains having a thickness of less than 0.3 micron and a diameter of at least 0.6 micron have an average aspect ratio of at least 12:1 and account for at least 70 percent of the the total projected area of said silver bromoiodide grains.
A high aspect ratio tabular grain silver halide emulsion comprised of gelatin or a gelatin derivative peptizer and silver bromoiodide grains comprised of up to 15 mole percent iodide, wherein said silver bromoiodide grains having a thickness of less than 0.3 micron and a diameter of at least 0.6 micron have an average aspect ratio in the range of from 20:1 to 50:1 and account for at least 90 percent of the total projected area of said silver bromoiodide grains.
In a process of preparing a radiation-sensitive silver bromoiodide emulsion comprised of a dispersing medium and silver bromoiodide grains by introducing silver, bromide, and iodide salts into a reaction vessel containing at least a portion of the dispersing medium,
- the improvement comprising
- adjusting the pBr of the dispersing medium within the reaction vessel prior to introduction of the iodide salt to a level of from 1.1 to 1.6,
- maintaining the reaction vessel substantially free of iodide prior to introduction of the silver and bromide salts, and
- maintaining the pBr within the reaction vessel at a level of at least 0.6 during introduction of the iodide salt,
- thereby producing within the dispersing medium contained within the reaction vessel silver bromoiodide grains, said silver bromoiodide grains having a thickness of less than 0.3 micron and a diameter of at least 0.6 micron exhibiting an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of said silver bromoiodide grains.
Dependencies are inferred from the claim text.