Effect of concentration of iron-arene photoinitiator on its migration from cured polymer film

Abstract

Nowadays, UV curable systems (inks, varnishes) are frequently used in printing industry. Their unquestionable advantages are the absence of volatile organic compounds, good chemical resistance and short curing times (fractions of second). A disadvantage of a UV-cured system is the possibility of migration of unreacted photoinitiators, monomers and other substances from the cured polymeric film. This parameter is of high importance in food packaging industry. In most cases, migration is an unwanted effect during which the unreacted photoinitiator or binder can be released from the package, contaminate and affect the food. In some cases, slow migration of antioxidants from packages to food is used intentionally. In this case, the antioxidants act positively on the food quality. This paper is aimed at research of curing and migration of substances from a cationically polymerizable system containing iron-arene photoinitiator Irgacure 261 and epoxidic binder Celloxide 2021P. The curing of systems was monitored at different concentrations of photoinitiator via infrared spectroscopy. By UV/VIS spectroscopy, migration of photoinitiators was monitored under different curing conditions and times of extraction. The results show that the greatest effect on the extracted amount of photoinitiator was exhibited by the concentration of the photoinitiator in the curing systems. With increasing curing time, the amount of extracted photoinitiator decreased, but this decrease was not significant. The UV/VIS spectroscopy data analysis is generally suitable for the determination of migration of substances from simple systems (two or three components), but for more complex systems is not appropriate. With larger number of components (commercial inks and varnishes), there will be overlap between the absorption spectra of individual components, and thus it will be impossible to determine their concentration in the extract.