Development of In-Line Printing Press Calendering Station

Abstract

Metallic conductive inks used for printed electronics have a tendency to create low conductivity layers unless they are fully dried. Yet, even after the drying, conductivity can be further improved by a post-heat-cure process. A hot soft nip calender was modified to be able to place it in line with a flexographic printing press and to study the effect of calendering on electrical performance of printed conductive layers. Two print trials were performed on the Comco Commander Flexographic Press at the Western Michigan University (WMU) Printing Pilot Plant with the calender placed in line with the moving web of the press. Three substrates were employed, a commercial label paper, a folding carton boxboard and a polyethylene-terephthalate (PET) polymer film. Two inks, one containing silver flakes and the other silver nanoparticles, were employed to print conductive layers during the print trials. Traces (lines) were printed using a three-banded anilox roll, with different cell volumes, to study the effects of ink transfer. The results were analyzed to evaluate the effects of the design variables, calender nip temperature and pressure, anilox cell volume, ink and substrate on electrical performance of printed silver inks.The results showed that, for all inks and substrates, the electrical resistance is reduced at higher nip temperature and pressure, relative to that without calendering. Furthermore, the same resistance can be obtained with a lower anilox cell volume and calendering than with higher cell volume but without calendering. This translates to a higher ink mileage (lower ink usage) for the same electrical performance if the calendering is used. The economic benefits of this are large, because of the high cost of the silver inks.