Negative-working dry peel apart photopolymer element with polyvinylformal binder

A negative-working dry peel apart photopolymerizable element consisting essentially of a support, a cover sheet and therebetween a layer of photopolymerizable composition having a dry thickness of at least 0.0005 mm and an optical density in the actinic region of not more than 0.7, the photopolymerizable composition consisting essentially of (1) at least two halogen-free polymeric organic binders, (2) a free radical generating, addition polymerization initiator or initiator system activatable by actinic radiation, and (3) at least one ethylenically unsaturated monomer having a boiling point above 100.degree. C. at normal atmospheric pressure and at least one terminal ethylenic group capable of forming a high polymer by free radical initiated, chain-propagated, addition polymerization, the monomer being present in a quantity in excess of the absorptive capacity of the binders for the monomer so that a thin layer of substantially free monomer is present at least on the surface of the photopolymerizable layer at the interface between the layer and the cover sheet, the adhesion of the photopolymerizable layer to the cover sheet being greater before polymerization than it is to the support whereas after polymerization the adhesion of said layer to the support is greater than it is to the cover sheet, at least one of the support or cover sheet being transparent to actinic radiation, the improvement being that the ratio of binder components to monomeric component is 0.5 to 1.0 to 3.0 to 1.0, at least one of the polymeric organic binders contains 0.5 to 40.0 percent by weight of polyvinylformal based on the total weight of polymeric binder present and is incompatible so as to be present as a dispersed phase in the layer to provide an appreciable reduction in cohesive strength of the photopolymerizable layer as compared to when the incompatible binder is not present in the layer.