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Due to environmental and legislation constraints the coating industry is moving
through a major evolution. Low solids, solvent containing paints are decreasing in
importance. As a result of this increasing pressure to reduce VOC's, UV curable
coatings are experiencing an important growth in the marketplace. In some application
fields like for instance the wood coating industry, coating techniques are used requiring
low viscosity. This is rather difficult to obtain with 100% systems. Waterbased UV
curable coatings offer an interesting solution for this problem. The advantages of UV
curable waterbased systems for many industrial applications have been discussed
previously in the literature (1-4).
Recent improvements in dispersion technology such as the surfactant selection, the
optimization of various parameters in the dispersion process and the enhancement of
dispersion stability have made it possible to disperse a wide variety of radiation curable
oligomers in water. These oligomers include epoxy-, urethane- and polyester acrylates.
In this paper, properties of dispersion based formulations, before and after cure will be
discussed.
One of the limiting factors for the use of radiation curable waterbased systems was the
poor performance. This poor performance is mainly due to the use of water as a
solvent. Wetting, levelling and coalescence problems are observed, due to the high
surface tension of water and its poor solvency. Much work has been done to overcome
these problems and very encouraging results were obtained. In this paper, the
performance of some of these dispersions will be presented. Products were applied on
wood, glass or metal depending on the properties evaluated. Comparisons were made
with corresponding undispersed resins. Two types of dispersions will be presented. The
first category gives tacky films after the evaporation of the water. The second gives
tack - free films after water evaporation but before the UV cure. This type of dispersion
can be handled and sanded before the UV curing step. Tack - free before cure systems
are interesting because they are less sensitive to dust collection and because they allow
the repair of coating imperfections before the UV curing step. This leads to reduced
waste in the production process.
