Interactions between UV curing, hybrid-UV and sheetfed offset inks and coated paper

UV cured offset is a fast growing area of printing which has many diverse applications in printing both paper and other very different substrates such as plastics. However, there is very little published literature which reports the influence of paper properties on the printability and print quality obtained. This study consisted of full scale printing trials and laboratory analysis comparing the printability of UV, hybrid-UV and conventional sheetfed offset ink systems on a variety of coated papers. Four pilot coated papers were prepared using a range of minerals (PCC, GCC, Kaolin and a GCC/Clay blend) and were calendered to the same gloss level. These papers were printed on a commercial sheetfed press using conventional oil-based, UV and hybrid-UV inks. Differences in the print quality, topography and gloss were assessed along with ink rub-off and ink set-off measurements immediately after printing. Imaging reflectometry was used to study differences in the surface topography of the dried ink films and FIB (focused ion beam) depth profiling was used for analysing the depth of penetration of the ink into the coatings. This study has shown that optimisation of coating structure is required for good printability of coated paper surfaces in a similar manner to conventional inks. There is no set-off with UV curable inks, but differences in coating structure do influence ink rub, print gloss, ink hold-out and penetration.