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The use of cationic UV curing systems based on cycloaliphatic diepoxides continues to grow
in several applications, mainly within the rigid and flexible packaging sectors. Today's
development consists primarily in optimizing cationic formulations in order to meet more stringent
end use requirements. The kinetic of photoinitiated cationic polymerization is largely influenced by
the nature of the components of the formulation; in particular, it is well established that:
cycloaliphatic epoxies react faster than glycidylether's; vinylether's are among the fastest
cationically curing monomers; hydroxyl-containing compounds lead to chain transfer reactions
which may enhance or slow down the curing process, depending on the nature and concentration
of these compounds. But, beside the formulation, the curing performance of a given UV curing
system can also be significantly influenced by the characteristics of the source of UV light. The
latter include, in particular: the UV dose ), i.e. the total photon quantity arriving at a
surface per unit area, and the UV irradiance ), i.e. the photon flux arriving at a surface
per unit area.
Along these lines, we have studied the influence of high UV irradiance on the performance
of cationic UV curing systems. Properties reported in present report were cure rate and solvent
resistance shortly after UV exposure. This study also includes preliminary data from the
evaluation of a new type of cationically curing monomer that has recently been introduced on the
market, namely a low viscosity oxetane derivative. The influence of this reactive diluent on the
curing performance of cycloaliphatic diepoxide based systems is reported in this paper.
