Thermal diazotype sheets

A heat reactive diazotype sheet having at least two layers, with one layer coated upon the other, one of said layers comprising a heat-softenable binder material and an acid-stabilized light sensitive diazonium salt capable of reacting with an azo-coupler compound to form a dye, and the other of said layers comprising a heat-softenable binder material and an acid-neutralizer component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt so as to provide a weakly basic environment for the diazonium salt in the sheet and to render said acid-stabilized diazonium salt reactive with said azo-coupler compound, and at least one of said layers containing an azo-coupler, said diazotype sheet being characterized by said acid-neutralizer component being comprised of at least 25% by weight imidazoline acid-neutralizer compound selected from the group consisting of 2-phenyl-2-imidazoline, 1,5-tetramethylene-2-o-tolylimidazoline, 2-benzyl-2-imidazoline, trifuryl-2-imidazoline, and 1,2-diphenyl-4,4-dimethyl-2-imidazoline.