Photodevelopable photographic silver halide emulsions - made in the presence of substd. thiourea cpds., have improved sensitivity

摘要

Photodevelopable photographic Ag halide emulsions are made by reacting (A) a water soluble Ag salt with (B) 0.1 to 40% molar (w.r.t. (A)) of a water soluble chloride and with (C) a water soluble bromide or a mixt. of a water soluble bromide and a water soluble iodide, to make up the remaining halide, in a soln. of a hydrophilic protective colloid, in the presence of a thiourea cpd. of formula R1R2N-C(=S)-SR2R4 (I) in which R1-4 are each represent opt. substd. alkyl gps., or in which the molar fraction (II) is imidazolidine-thione, 1,3-diazacyclohexane-2-thione or 1,3-diazacyclohexane-2-thione-4,6-dione; and R2 and R4 are as above, or in which R1R2N- and/or -NR3R4 form a heterocyclic ring, to form silver chlorobromide or silver chloroiodobromide particles. Emulsions have improved sensitivity to image formation to exposure to high energy light radiation, then the image intensifies considerably on global exposure to light of lower intensity, without the use of processing solns. and without fogging.