Photochemical Characteristics and Design of Synergistic Photoinitiator Combinations for UV Curable Inks and Coatings

This doctoral thesis investigates the photochemical characteristics, curing behaviour and design of photoinitiator systems for UV-curable printing inks and coatings. The work examines the relationships between resin and reactive-diluent structure, rheological behaviour, photopolymerisation kinetics, mechanical properties and curing performance.

A broad range of commercial Type I and Type II photoinitiators is studied using UV absorption spectroscopy, phosphorescence spectroscopy, microsecond flash photolysis, real-time infrared spectroscopy (RTIR), colorimetry, rheological measurements and hardness testing. Particular attention is given to photoinitiator reactivity, excited-state behaviour, radical formation, oxygen inhibition, photoyellowing and curing performance in both clear and pigmented UV systems.

The thesis also applies Design of Experiments and Mixture Design methodologies to the development of synergistic near-eutectic photoinitiator blends combining high curing reactivity with bulk stability. Optimised liquid photoinitiator systems were developed for UV offset lithographic and UV flexographic printing inks, including formulations designed for both dark- and light-coloured pigmented systems.

The doctoral research was undertaken within an industrial-academic framework between Swale Process, Manchester, UK, and the Department of Chemistry and Materials, Faculty of Science and Engineering, Manchester Metropolitan University. Juan Segurola was employed by Swale Process as an R&D researcher before commencing the PhD and carried out the doctoral research while working as a salaried industrial researcher. The thesis was submitted to Manchester Metropolitan University for the degree of Doctor of Philosophy in March 1999.