METHOD FOR PREPARING OF BROMINE-IODINE-SILVER PHOTOGRAPHIC EMULSION WITH MICROCRYSTALS OF NUCLEUS-ENVELOPE TYPE Russian patent published in 1995 - IPC

FIELD: method for production of photographic emulsion. SUBSTANCE: method involves controlled double-stream crystallization The process is carried out by adding solution 2 containing AgNO₃ and water together with solution 3 containing KBr, KJ and water into solution 1 which contains gelatin, ammonia, KBr and water. Solution 3 is added by 4-10 portions, concentration of iodide in the former portion being 0-0.03 M/M of Ag in solution 2. Concentration of iodide in next portions is gradually increased by 0.01-0.25 M/M of Ag in solution 2 up to concentration 0.06-0.40 M/M of Ag in solution 2. Then said concentration is decreased by 0.01-0.25 M/M of Ag in solution 2 till its value in the last portion is 0.-0.20 M/M of Ag in solution 2. Summary content of iodide in all the portions of solution 3 is 0.04-0.20 M/M of Ag in solution 2, volume of each portion being 5-50 of total volume of solution 3. pH is maintained within 7.4-11.2, pBr being maintained within 1.4-3.4. Then envelope is plated on thus prepared nucleus, the process is carried out by adding solution 4 which contains AgNO₃ and water together with solution 5 which contains KBr, KJ and water. Concentration of iodide in solution 5 is 0-0.05 M/M of Ag in solution 4. Method enables to increase photosensitivity by 10-40 and to increase resolving power by 16-25 EFFECT: increases photosensitivity and resolving power. 2 tbl