Silver halide photographic emulsion containing 2 sensitizing dyes having heterocyclic quaternary nitrogen

Abstract From the Canadian patent

A silver halide photographic emulsion is provided which contains in combination at least one sensitizing dye of formula (I) and at least one sensitizing dye of formula (II): (I), wherein Z1 represents a methyl or ethyl group R1 and R2 each, represent an alkyl or sulfoalkyl group X1? represents acid, anions, and n represents an integer of 1 or 2 but n is 1 when, the sensitizing dye forms an intramolecular salt (II), wherein Z2 represents a lower alkyl group W1 and W2 each represent, a hydrogen or halogen atom or an alkyl group W3 and W4 each, represent a hydrogen or halogen atom or an alkyl alkoxy, hydroxy, or phenyl group, where W3 and W4 may be joined to form a benzene ring, but at least …