Direct observation of microcontact behaviours in pattern-generation step of reverse offset printing

In this study, we investigate the static and dynamic aspects of the nip formed during roll-to-sheet-type reverse offset printing. First, we show that several modes of roof collapses (bottom contact defects) could be formed depending on the poly(dimethylsiloxane) (PDMS) blanket thickness and pattern size. We regulate the manifestation of the defect modes driven by the local pile-up of the incompressible PDMS, as modelled by the contact mechanics formulation, together with a complementary numerical simulation. In dynamics, we first differentiate between the static nip and dynamic nip during printing, where the width is extended by the kinetically controlled adhesion of the blanket PDMS. Further, we observe that depending on the pattern structure, there was spatial deviation of the microscopic contact and subsequent separation behaviours of the cliché from a macroscopically recognizable nip, and consequently, local detachment rates were heterogeneous in the pattern-generation process of the reverse offset printing, even with a constant machine speed. In addition, we found that the parts of a pattern where the ink transfer fails in a high-speed patterning condition corresponded to the region of the locally enhanced detachment rates found during direct observation. (paper)