Importance

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Abstract

A photoreactive binder that may be used to enhance photospeed in either conventional plates or on-press developable lithographic printing plates. Briefly, a polymer of m-isopropenyl-.alpha.,.alpha.-dimethylbenzyl isocyanate is derivatized for vinyl group reactivity by reacting the isocyanate groups thereof with hydroxyalkyl acrylate. The resulting photopolymeric binder provides significantly higher photospeed than the non-reactive binder currently utilized in the production of conventional printing plates. The resulting lithographic printing plate also shows better durability (as manifested by longer run-length) and is more easily developed by the microencapsulated developers utilized in the present invention. As to the preparation of the photoreactive binders, the application discloses a method of copolymerizing m-isopropenyl-.alpha.,.alpha.-dimethylbenzyl isocyanate (m-TMI) through complexation with an electron-deficient monomer such as maleic anhydride to accelerate free radical copolymerization with other monomers, and thus, provides greater monomer-to-polymer conversion. Use of the resulting product in the photoresist of a lithographic printing plate improves its adhesion to an underlying substrate.

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First Claim