UV ‐Curable Inkjet Inks and Their Applications in Industrial Inkjet Printing, Including Low‐Migration Inks for Food Packaging

Using novel DirectCure lamps exhibiting an enhanced emission at wavelengths between 200 and 220 nm, acrylate chain start radicals are directly generated via acrylate double-bond excitation. Thus, the acrylate molecule is effective as “internal” photoinitiator. Migration product concentrations measured after DirectCure or EB final curing of radiation curable printing inks and varnishes show comparable values. Photons with a wavelength of 172 nm, as produced by a xenon excimer source, are able to directly generate radical pairs in acrylate coatings. The radicals formed initiate the curing process. However, curing is restricted to the coating surface because the penetration depth of 172-nm photons in acrylates is limited to about 500 nm. As result of a surface area increase after excimer curing, the excimer-cured layer is folding up. Structures with a typical roughness of micrometers are obtained which are characteristic for excimer matting.