Patent ID: 6030762
Filing Date: 2000-02-29
Classification: G03C

Abstract:
Method of preparing a silver halide emulsion comprising silver chlorobromoiodide or silver chloroiodide tabular grains with at least 75 mole % of chloride and from 0.1 up to 3 mole % of iodide, based on silver, further having {111} crystal faces, an average aspect ratio of at least 2:1, with at least 75% of the total projected area of all grains being provided by said tabular grains and with a variation coefficient on sphere equivalent diameter (SED) of all grains being lower than 0.30, said method comprising the steps ofpreparing a dispersion medium and a crystal habit growth modifier in a reaction vessel;precipitating silver chlor(oiod)ide or silver chlorobrom(oiod)ide nuclei in a crystal nucleation step by mixing silver salt and halide salt solutions in the said dispersion medium,growing the said nuclei during one or more growth and/or physical ripening steps;characterized bymaintaining the said dispersion medium at an initial pH value between 6.0 and 9.0 during the said crystal nucleation step;setting pH to a value of not more than 4.0 for at least 30 seconds, between ending the said nucleation step and ending the said growing step; followed byresetting pH to the said initial pH value.