Heat sensitive recording element and a thermographic method

Abstract From the Canadian patent

A thermal imaging method for forming color images is provided which employs as the color imageforming material, a colorless precursor of a preformed image dye possessing at least one thermal protecting group that undergoes fragmentation upon heating and at least one leaving group that undergoes irreversible elimination upon heating, said protecting and leaving groups maintaining the precursor in its colorless form until heat is applied to effect removal of these groups whereby the precursor is converted to an image dye.