Digital Imaging of Lithographic Materials by Radical Photopolymerization and Photonic Baking with NIR Diode Lasers

Abstract

Abstract Photo‐initiated cross‐linking of multifunctional acrylic esters in polymeric binders was investigated based on digital imaging using the Computer‐to‐Plate (CtP) technology applying laser exposure in the near‐infrared (NIR). Generation of initiating radicals occurs by electron transfer from the excited state of the NIR‐sensitizer to the radical generator, an onium salt. Iodonium salts derived from several borates and those with the bis(trifluoromethylsulfonyl)imide anion resulted in lithographic materials with high sensitivity. Photo‐induced electron transfer plays a major function to generate initiating radicals by a sensitized mechanism but thermal events also influence sensitivity of the coating. Internal conversion was the major deactivation pathway while a certain fraction of NIR‐dye fluorescence was also available. A line shape focused laser system with emission in the NIR was successfully used to bake the materials.