  We experimentally study the occurrence of pattern formation during the
slot-die coating of low-viscosity nearly Newtonian liquids onto
Polyethylenterephthalat (PET)-substrates. In particular, it is demonstrated
that with increase of the coating speed a homogeneous coating becomes unstable
with respect to periodic stripe patterns. Thereby, depending on the liquid
viscosity, the stripes can be oriented parallel or perpendicular with respect
to the coating direction. Mixed states do also occur. The spatial period of
perpendicular [parallel] stripes increases [decrease] with the coating speed.
The dependence of the effect on various control parameters of slot-die coating
is investigated. Finally, a simple theoretical model based on the hydrodynamics
of thin films of partially wetting liquids is analysed. Comparing the results
to the experiments, conclusions are drawn regarding the acting instability and
pattern formation mechanisms.
