Optimal Performance of UV Powder Coatings
Powder coating cured by ultraviolet light (UV powder coating) is a technology that combines the advantages of thermosetting powder coating with those of liquid ultraviolet-cure coating technology. The difference from standard powder coating 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 polymerization 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 UV powder technology.
The combination of polyester and epoxy chemistries developed for UV powders allows the challenging requirements of the market segments such as wood, wood composite, plastic and metal to be fully met. Although “hybrid powders” combining polyester and epoxy resins have been known for more than 20 years in thermosetting powders, the degree of cure achieved at low temperatures (e.g., 120 °C) becomes “just good enough” only after long curing times. In contrast, UV-cured powder coating films fulfill the most stringent specifications after “a couple of minutes” under heat and UV light.