In radical UV curing, photoinitiators generate reactive radicals which trigger the polymerisation of the coating. However, directly at the surface, these radicals compete with oxygen from the ambient air. This so-called oxygen inhibition can result in the surface curing less effectively than the underlying layers. The potential consequences range from reduced chemical and mechanical resistance to lower production speeds. It is precisely at this point that the wavelength of the UV light used becomes significant.

As promising as the technology is, UVC LEDs are still at a much earlier stage of development than UVA LEDs. The manufacture of very short-wavelength UV LEDs is technically challenging in terms of materials. Whilst UVA LEDs now achieve high efficiency and long service lives, the efficiency and available power of UVC systems remain significantly lower. The costs are also currently still significantly higher.

However, development is progressing – driven, amongst other things, by a second major market: the UVC disinfection of air, water and surfaces. The same short UV wavelengths that are of interest for certain photoinitiators can also photochemically affect the DNA and RNA of microorganisms and have therefore long been used for disinfection applications. In this context, LEDs offer the potential to tailor the emitted wavelength much more precisely to the specific application.

For industrial UV curing, the combination of several wavelengths could therefore prove particularly interesting. UVA can provide deep curing, whilst shorter UV wavelengths specifically target the surface. Rather than simply replacing the broad spectrum of a conventional UV lamp, LED technology could thus provide a spectrum precisely tailored to the coating, photoinitiator and process in future. However, which wavelengths are actually suitable depends heavily on the specific coating or paint formulation. This is precisely why testing is crucial.