Photosensitive negative-working tonable element

Claim 1

A photosensitive element comprising a support bearing a layer of a negative-working tonable photoimaging composition which consists essentially of (a) at least one organic polymeric binder taken from the group consisting of polyvinylformal, polyvinylpyrrolidone, polyacrylate, cellulose acetate, polymethacrylate, and polyvinyl acetate; (b) a photosensitizer which upon absorption of actinic radiation is capable of generating an acid; and (c) at least one acetal compound of the formula ##STR4## wherein R 2 is alkyl of 1 to 18 carbon atoms, furyl, substituted furyl, phenyl, substituted phenyl, naphthyl, and substituted naphthyl, R 3 is alkyl of 1 to 18 carbon atoms, and OR 3 when taken together form a 5, 6 or 7 membered ring, (d) a plasticizer in an amount of up to 20% by weight based on the total dry weight of the photoimaging composition; and (e) a polymeric anhydride in an amount up to 10% by weight based on the total weight of solids the polymeric binder (a) being plasticized by the decomposition product of the acetal compound.