Design of eutectic photoinitiator blends for UV/visible curable acrylated printing inks and coatings

The optimisation of photoinitiator systems used in UV printing inks and coa tings has been carried out by means of Design of Experiments (Mixture desig ns). Mixture designs have been used to improve the reactivity of photoiniti ator blends in order to design cost effective, synergistic, near eutectic p hotoinitiator blends for curing UV printing inks. Both the reactivity and b ulk stability of photoinitiator blends have been studied. The photoinitiato r blends consisted of three commercial photoinitiators, benzophenone (BP), isopropyl thioxanthone (ITX), which are Type II photoinitiators and benzil dimethyl ketal (BDK) a Type I photoinitiator. Ethyldimethylamino benzoate ( EPD), a commercial aromatic tertiary amine, which is an efficient electron/ proton donor was used to enhance the reactivity of the Type II photoinitiat ors. The results highlighted that the EPD content plays a crucial role in t he final reactivity of the photoinitiator blends. Relatively high proportio ns of EPD with respect to the overall centroid (25% each component) were re quired to design photoinitiator blends of enhanced reactivity. These result s agreed with mechanistic studies published in the literature where it was observed that with Type II photoinitiators, such as BP and ITX, the tertiar y amine synergist acted as the main initiating radicals of the polymerisati on process. On the other hand, from the stability point of view, high proportions of EP D decreased the stability (eutectic properties) of the photoinitiator blend s. BP showed good solvating properties in the photoinitiator blends and had the highest influence on stability of the photoinitiators studied. Relativ ely high proportions of BP enhanced the stability of photoinitiator blends. Multiple response optimisation for stability and reactivity resulted in ph otoinitiator blends that exhibited both enhanced reactivity and stability. (C) 1999 Elsevier Science S.A. All rights reserved.