Influence of cationic photoinitiator type on properties of coating materials based on cycloaliphatic and glycidyl epoxy resins

Epoxy binder based on 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate (EEC) and polytetrahydrofurane diglycidyl ether (PTHDE) was cured using four types of commercial cationic UV-photoinitiators (two iodonium salts and two sulfonium salts) and a medium-pressure mercury lamp. Influence of a type of photoinitiator on thermal, optical, mechanical and barrier features of the varnish coatings was investigated. Moreover, conversion of cycloaliphatic epoxy (CC) and glycidyl (GC) groups was analyzed. Generally, systems containing iodonium or sulfonium hexafluorophosphates exhibited higher GC, gel content, gloss and water-vapor transmission rate as well as lower yellowness and hardness than samples based on SbF6−-type salts. Photoinitiator type did not significantly affect CC parameter, however, application of the iodonium salts mixtures influenced on CC as well as GC, thermal features and gloss of epoxy varnishes and coatings.