METHOD OF PREPARING SILVER IODOBROMIDE PHOTOGRAPHIC EMULSIONS CONTAINING DISCOID MICROCRYSTALS Russian patent published in 2004 - IPC

FIELD: light-sensitive materials.

SUBSTANCE: silver iodobromide emulsions containing discoid microcrystals intended for manufacturing high-sensitivity black-and-white technical films with high resolution capability and required latitude. Method of invention comprises performing two-step emulsification, wherein silver iodide suspension is first prepared using water-gelatin solution no.1 and equimolar amounts of aqueous solution of potassium or ammonium iodide no.2 and aqueous solution of silver nitrate no.3, after which equimolar amounts of solution no.3 and aqueous solution of potassium or ammonium bromide no.4 are introduced with constant rate, concentrations of solutions no.2, no.3, and no.4 being 2.0-2.5 mole/l. Subsequent operations are: Ostwald ripening in presence of ammonia, separation of solid phase, washing, dispersing, chemical sensitizing, consecutive addition of sodium thiosulfate and gold compound to emulsion. According to invention, first emulsification step is accomplished by adding to solution no.1 solution n.2 to achieve pI 1.5-2.2, ammonia, and then, at constant rate, solutions no.2 and no.3 at pI 1.5-2.2, whereas, in the second emulsification step, constant pBr value 1.8-2.2 is maintained using, in the first step, 2-5% of the total volume of solution no.3 and, in the chemical sensitizing operation, addition of sodium thiosulfate is followed by additional introduction of compound of formula I: , where Y is S or O and R and R¹ are lower alkyls, or formula II: ,

where R² and R³ are lower alkyls and X^- is halide ion or CH₃C₆H₄SO-3

, each in amounts (50-200)·10^-6 mole per 1 mole AgHal. Method allows increasing altitude by 25-30% and light sensitivity level by 30-50%, while simultaneously fog density level is lowered by 1.3-1.8 times and application of silver is preserved as well as main characteristics such as resolution capacity and contrast factor.

EFFECT: improved performance characteristics of emulsion and simplified emulsion preparation technology.

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