METHOD OF PREPARING SILVER BROMIDE OR SILVER BROMIDE/IODIDE PHOTOGRAPHIC EMULSION Russian patent published in 1997 - IPC

FIELD: light-sensitive emulsions. SUBSTANCE: invention in particular relates to preparing silver bromide or silver bromide/iodide emulsions with flat microcrystals and can be used for manufacturing negative and positive photographic materials in chemical-photographic industry. Drift of silver in photographic material is reduced due to the following improvements: (i) controlled two-jet emulsifying at heating by way of introducing silver nitrate aqueous solution and aqueous solution of silver bromide or silver bromide/iodide water-gelatin solution containing potassium bromide; (ii) isolation of solid phase and washing; (iii) spectral sensibilizing; and (iv) chemical ripening in presence of sodium thiosulfate and gold salt. Emulsifying stage is carried out at 40-80 C and pBr = 1 ± 0.15, potassium halide and silver nitrate solutions being fed with equal acceleration within acceleration range 1.5 10^-6- 2.2 10^-2 mol/min from initial volume velocity 4.41 10^-7-1.1 10^-5 to final volume velocity 1.88 10^-6-8.07 10^-5, and introducing additional amount of gelatin to gelatin/silver ratio 0.6-2.87. EFFECT: reduced drift of silver from 6 to 3 molar %. 1 tbl