Characterizing the Efficiency of UV LED Curing

This paper examines the effects of some key operating parameters of UV sources on the curing of various UV inks, coatings and adhesives. The effects of peak UV wavelength and peak intensity are quantitatively evaluated using FT-IR. The data are helpful in guiding both formulators, raw material suppliers and end users to better understand the impact of the UV sources, especially UV LED sources, on the speed and degree of cure for various systems. Introduction The objective of the testing for this paper was to gain a better understanding of the effect of delivery of dose (peak intensity) and of wavelength on cure rates especially as these relate to UV LED sources. The data reported suggests that for the range of UV materials selected that the cure rate reaction dynamics are similar whether curing with a traditional mercury vapor lamp with a broad UV spectral emission or a narrow spectral emission UV source with UV emissions at 365nm (345 to 385nm) or 395nm (380 to 420nm). Equipment and Materials For this paper, materials that were formulated or were known to work in the UV-A region were chosen. Practically all of these materials cure with UV-A wavelength UV LED sources but will also typically cure well with a traditional mercury vapor lamp system with sufficient UV-A energy (typically centered at 365nm).Of course, not all UV curable materials will cure in this region, but photoinitators have a broad absorption range and even if a material is marketed as being optimized for a specific lower wavelength peak, it doesn’t mean the material won’t cure with other wavelengths. The UV curable materials selected were: Inks: Piezo inkjet ink from vendor 1 formulated for UV-A Piezo inkjet ink from vendor 2 formulated for UV-A Adhesives: General purpose adhesive typically used in medical applications Custom formulated adhesive for speaker application Coating: Custom formulated top coat for wood panels