We experimentally study the occurrence of pattern formation during the slot-die coating of lowviscosity 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.

We experimentally study the occurrence of pattern formation during the slot-die coating of partially wetting liquids onto polyethylenterephthalat-substrates outside the coating window. The experimental investigation is supported by numerical simulations of a dynamical model. Our results demonstrate that beyond a critical coating speed, the deposition of homogeneous coating layers undergoes an instability resulting in the self-organized emergence of patterned coatings, i.e., stripes of different orientation and droplet patterns. We investigate the transitions between the different patterns as triggered by changes in the control parameters inherent to slot-die coating, e.g., the liquid viscosity and the coating gap height. The relatively simple theoretical approach is based on lubrication theory. It is already able to reproduce most of the patterns observed experimentally and reveals a wettability-driven instability mechanism.