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Powder coating cured by ultraviolet light (UV powders) is a technology that combines the advantages of thermosetting powder coatings with those of liquid ultraviolet cure coating technology.The difference from standard powder coatings is that melting and curing are separated into two distinct processes : upon exposure to heat, UV curable powder coating particles melt and flow into a homogeneous film that is crosslinked only when it is exposed to UV light. The most popular crosslinking mechanism used for this technology is the free radical process : activation of photoinitiators in the molten film by UV light results in the formation of free radicals that initiate a polymerisation reaction involving resin double bonds. Final coating aspect and performance depends on the selection of resin systems, photoinitiators, pigments, fillers, additives , powder coating process conditions and curing parameters .The crosslinking efficiency of specific formulations and cure conditions can be assessed by using differential photocalorimetry. Recent optimization of UV powder coatings has resulted in extremely good flow out , making smooth finishes achievable at temperatures as low as 100°C
Technological and economic benefits explain the growing interest in the UV powder technology.An illustration of this interest is given in figure 1 with the number of patents found over the last thirty years.