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Radiation curing technology is increasing due to its unique advantages over conventional
thermal cured methods. The increasing utility of curable materials, such as
lacquers, inks and coatings provides an incentive for the development of new varieties
of photopolymers (1-3).
Materials development has played and will continue to play an important role in the
commercial development of radiation cure technology. The first commercial application
of radiation curing of unsaturated polyesters I styrene was developed in the
late 60's and early 70's (4). Styrene reduces the viscosity of the polyester and reacts by
crosslinking the unsaturated polyester chains under UV exposure. Styrene has
been used widely because it is miscible with the polyester, shows a low degree of
homopolymerization and is inexpensive. However, the volatility and the skin penetration
are potential health hazards during have an inherently faster cure speed but a
very high viscosity. In order to obtain a suitable application viscosity, epoxy resins
need to be diluted before curing which affects the cure speed and properties. The
unavailability of suitable diluents for radiation curing systems led chemical suppliers
to approach polyfunctional acrylate monomers based on various polyols. This
resulted in the so-called first generation of monomers in the early 70's, which include
TMPTA, PETA, HDDA, TEGDA, etc. These monomers show good diluency in
combination with good cure and low volatility but they are an irritant to the skin.
These monomers are still used in industry, however there has been an ongoing trend
towards development and use of less irritating materials. Primarily based on alkoxyl
polyols, numerous acrylate monomers have been invented and put into use (5). In
the late 80's, vinyl ether monomers were introduced as alternatives to acrylate
monomers. Cationically curable vinylethers show good diluency and fast cure speed
and none oxygen inhibition.
