Method of on-press developing lithographic plates utilizing microencapsulated developers

A method of lithographically printing images on a receiving medium utilizing a lithographic printing plate, the printing plate having provided thereon a polymeric photoresist capable of being imagewise degraded or hardened upon imagewise exposure to actinic radiation, said method comprising the steps of:

• imagewise exposing the polymeric photoresist to actinic radiation for a sufficient duration and at a sufficient intensity to imagewise degrade or harden the exposed areas;
• bringing a developer sheet into substantially face-to-face contact with the polymeric photoresist layer, wherein the developer sheet comprises a sheet support, and a microcapsule layer deposited on the sheet support, the microcapsule layer comprising a plurality of microcapsules, each microcapsule comprising an external shell phase and an internal encapsulant phase, the internal encapsulant phase comprising a developer component capable of promoting the imagewise removal of either exposed or unexposed areas of the polymeric resist layer when the internal encapsulant phase is released by the blanketwise rupturing of the microcapsules;
• blanketwise rupturing the microcapsules of the developer sheet to blanketwise release the internal encapsulant phase thereby rendering either exposed or unexposed areas of the polymeric photoresist susceptible to removal by press fountain and ink solutions;
• and
• treating the polymeric photoresist with press fountain and ink solutions in a printing press to remove either exposed or unexposed areas of the polymeric photoresist and correspondingly bare the underlying substrate, whereby ink becomes imagewise localized in either unremoved polymeric photoresist or bared substrate to form an image transferable to a receiving medium.