Patterning defects in high-speed reverse offset printing: Lessons from contact dynamics

Printing speed limitation is a critical issue for the high-throughput production in printed electronics. In this study, the formation mechanism of severe rash-type defects in a reverse-offset printing system operating at a high speed is discussed. A systematic investigation showed that the size and density of the defects were significantly influenced by the printing speed, indentation and by the material properties, such as thickness and elasticity of the polydimethylsiloxane (PDMS) sheets. The observation via a high-speed camera of the nip formations between a curved PDMS sheet and a flat glass revealed that, at the very initial stage of contact formation, parts of contacts were concurrently and unstably formed then widened; however, during the later stage, the coalescence of these spots led to the generation of air bubbles trapped in the contact regions, which lasted for several seconds. Based on complementary experiments on the extinction behaviours of the trapped air, we propose a new defect formation model for the rash-like transfer defects observed in the printing tests due to the trapped air regions resulting from the contact instability of PDMS.