UV-curable epoxy varnishes modified with polyvinyl resins

Epoxy varnishes based on 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate (EEC) and polyvinyl components, i.e., two polyvinyl butyral resins (PVB) and one polyvinyl butyral-stat-acetal resin (PVBA) were prepared and cured using a commercial cationic iodonium photoinitiator and medium-pressure mercury lamp. An influence of a type and content of polyvinyl resin (5, 10, and 20 wt.%) on thermal, optical, mechanical, and barrier features of varnish coatings was investigated. Coats containing the highest amount of PVB resins exhibited higher epoxy group conversion, higher gloss, and smoother surface in comparison with EEC/PVBA samples. Moreover, cured coats and films with PVB reached markedly higher barrier features, i.e., limited distilled water absorption and low water vapor transmission rate. An influence of reactivity and UV transmittance value of the photocurable varnishes on coat wrinkling process was presented and discussed.