Effect of viscoelasticity on dynamics and stability in roll coatings

Flow behaviors and coating windows of Newtonian and viscoelastic liquids in forward and reverse roll coating processes have been examined. Viscoelastic liquids considered in this study, as a Boger fluid, have different elastic or extensional properties but almost same shear viscosity as Newtonian case. Coating thickness in both flows strongly depends on the viscoelasticity in polymer solutions as well as operating conditions such as capillary number and gap size between two rolls. Also, uniform coating windows are drastically reduced for the viscoelastic liquids. These results evidently support that a small amount of polymer in coating liquids play an indispensable role in altering dynamics and stability of coating processes.