Patent ID: 6010840
Filing Date: 2000-01-04
Classification: G03C

Abstract:
Method for preparing a gelatinous emulsion having grains rich in silver choride, wherein at least 70%, of total projected area of all grains is provided by {111} tabular grains having an average aspect ratio of more than 2:1, an average equivalent circular diameter of at least 0.3 .mu.m and an average thickness of from 0.05 to 0.25 .mu.m wherein a percent variation on average equivalent circular diameter of said tabular grains is 30% or less and wherein a percent variation on average thickness of said tabular grains is 20% or less and wherein said tabular grains are present in percent numerical amounts of at least 90%, said method comprising following steps:preparing in a reaction vessel a dispersion medium comprising an initial amount of a crystal habit modifying agent;precipitating therein silver halide crystal nuclei by double-jet precipitation of an aqueous silver nitrate and an aqueous solution comprising halide ions, wherein less than 10% by weight of a total amount of silver nitrate used is consumed;growing said silver halide crystal nuclei by further precipitation of silver halide by means of double-jet precipitation of an aqueous silver nitrate solution and an aqueous solution comprising halide ions, wherein more than 90% by weight of a total amount of silver nitrate is consumed, characterized in that during at least one of the said steps at least one compound is added to the said reaction vessel, said compound being a hydrophilic amphoteric block copolymer containing(i) a non-ionic acrylic block comprising a sequence of units having pendant nitrile groups according to formula I and(ii) a acrylamid(in)ic block comprising a sequence of units according to formula II, said hydrophilic amphoteric block copolymer further comprising within said acrylamid(in)ic block(s) units having pendant acidic groups or salts thereof as well as units having pendant basic groups or salts thereof,wherein said formulae I and II correspond to following structures: ##STR8## wherein R.sup.1 represents hydrogen or alkyl; and ##STR9## wherein R.sup.2 represents hydrogen or alkyl, R.sup.3 is hydrogen, alkyl or aryl andwherein X represents O or NH.