Method for preparation of a photothermographic material with increased photosensitivity

A photothermographic material with increased photosensitivity obtained by a process for preparing a photothermographic material with increased photosensitivity, said photothermographic material comprising a support and a photo-addressable thermally developable element, exclusive of a compound R—S(M)n wherein R is an aliphatic hydrocarbon, aryl or heterocyclic group, M is a hydrogen atom, or cation, and letter n is a number determined so as to render the molecule neutral and also exclusive of a compound capable of releasing a mobile dye corresponding to or inversely corresponding to the reduction of silver halide to silver at elevated temperatures, said photo-addressable thermally developable element containing a light-insensitive organic silver salt, a photosensitive agent in catalytic association with said light-insensitive organic silver salt, a reducing agent for said light-insensitive organic silver salt in thermal working relationship therewith, a silver salt having a water-solubility greater than 0.1 g in 1 L water at 20° C. and a binder, comprising the steps of:

• (i) increasing the photosensitivity of a photosensitive silver halide by chemical sensitisation with a chemical sensitising merocyanine dye containing a thione group in a non-oxidative aqueous medium, optionally in the presence of said light-insensitive organic silver salt and/or in the presence of said silver salt having a water-solubility greater than 0.1 g in 1 L water at 20° C., thereby preparing said photosensitive agent;
• (ii) coating said support with one or more aqueous solutions or dispersions together containing said light-insensitive organic silver salt, said photosensitive agent, said reducing agent, said silver salt having a water-solubility greater than 0.1 g in 1 L water at 20° C. and said binder;
• and
• (iii) drying said coating or coatings thereby producing said photo-addressable thermally developable element.