FTIR spectroscopy studies of photochemical and thermal processes on offset lithographic printing plates

摘要

Fourier Transform Infrared (FTIR) spectroscopy was used to study photochemical and thermal processes that take place during and after irradiation, and post-treatment, of lithographic printing plates. This technique was used both in Transmission as well as in Specular Reflectance mode. The processes studied included: a) Monitoring free radical photopolymerization of acrylate loigomers and monomers; b) Post-cure of the plates by baking at temperatures between 300 deg F (149 deg C ) and 500 deg F (260 deg C ); c) Following the photo-decomposition of diazo molecules on commercial plate substraes. It has been possible to determine the induction period before polymerization when radical scavengers are present in the formulation. The implication of the results on the microstructure of the network is also discussed. Attempts were made to correlate some of these observations, Such as the degree of polymerization (D.P.) and the mole-cular structure and physical properties of the monomer-oligomers used, with the performance of the plates, in particular with the resolution and the length of run on a commercial printing press.