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The main components of a UV-curable coating are mono- and polyfunctional
acrylic monomers, prepolymerized resins, pigments, extenders,inhibitors,
stabilizers, and photoinitiators. Radicals can essentially be formed by two
mechanisms: photofragmentation or excitation of a photosensitizer followed by
hydrogen abstraction. Both mechanismshav been thoroughly discussed in the
literature.
In cationically induced photopolymerization the mechanisms of formation of
protons or carbocations are extensively examined by a numbèr:of research
groups
The curing rate and the overall performance of the film are critically dependent
on:
(1) The functionality of the monomers, the miscibility of the components, and the
viscosity, which depends on the prepolymerized resin;
(2) The overlap' between the emission spectrum of the UV radiation source and
the UV absorption spectrum of the photoinitiator, the binders, and the pigments.
Oxygen inhibition is a very well known phenomenon in the free radical induced
photopolymerization of acrylates. Once the initiator radical pair has been formed,
terminating reactions with oxygen wit! easily predominate Over propagation
reactions with acrylic double bonds due to the biradical nature of oxygen in its
ground state.
