| 摘要 |
1,250,717. Monodisperse photographic silver halide emulsions. EASTMAN KODAK CO. Jan.28, 1969 [Jan.29, 1968], No.4561/69. Heading G2C. A monodisperse photographic silver halide emulsion (i. e. one in which at least 95% by weight and/or by number of the grains have a diameter which is within 40% of the mean grain diameter) comprises silver halide grains for in the presence of an organic thioether silver halide solvent (i.e. an organic thioether compound which in 0À02 molar aqueous solution at 60‹ C. can dissolve more than twice the weight of silver chloride that will dissolve in the same amount of water at 60‹ C.). The silver halide preferably comprises at least 50 mole per cent silver bromide, and preferably at least 80% by weight or number of the grains are regular. The mean grain diameter is preferably at least 0À25 micron. The grains may be cubic-regular and have a mean diameter of not more than 2 microns. The emulsion may be a negative or direct-positive emulsion. The thioether solvent preferably contains at least one moiety of the formula -OCH 2 CH 2 S-. The thioether solvent is added before the grains have attained their ultimate size and shape. The grains are preferably formed in an aqueous medium of which the pH is maintained at less than 7 and of which the pAg is maintained between 7À1 and 9À6 throughout the grain formation. Direct-positive emulsions prepared using this process may have a photographic speed or sensitivity greater than that of direct-positive silver halide emulsions prepared by known methods. |
