Millisecond fluid pattern formation in the nip of a gravure printing machine

摘要

Rapid fluid splitting in a gravure printing press is studied using high-speed video imaging. The fluid flow and dynamics of the liquid-air meniscus in the wedge between a rigid printing cylinder and a planar substrate plate is singular at the contact point, and the capillary pressure behind the meniscus appears to diverge here. In case of lamella splitting conditions (in contrast to point splitting) a continuous meniscus is forming over the complete width of the contact zone. Spontaneous pattern formation, i.e. viscous fingering, is observed. We study the effect of a periodic gravure pattern on the movement of the liquid meniscus close to the nip. Differently from earlier observations on smooth surfaces we find that finger frequency does not algebraically scale with printing velocity, but exhibts a lock-in phenomenon. Pattern size scales with integer multiples of the raster width of the gravure pattern. We elaborate a tentative explanation for the rapid emptying of gravure cells in the moment of lift-off of the printing form and substrate, indicating that finger instability and cell emptying flows are mutually coupled by the local pressure gradients on the 10-mu m scale.