Surface Elastic Effects in Premetered Coating Techniques

The effect of the dilational surface elasticity ε on coating was investigated in two-layer slide coatings and single-layer slot and curtain coating experiments, respectively, up to 2 m/s. In the slide experiments both the surfactant concentration and ε were varied in the lower layer. While the position of the static contact line (SCL) is a function of the elasticity modulus ε, the dynamic contact line (DCL) position is insensitive to this variable. Also, the vacuum range increases with increasing the modulus ε. Best correlations were obtained when ε was measured at 1−2 Hz with a longitudinal wave generator. In curtain coating, the curtain edges can be stabilized and the wet thickness decreased by increasing the elasticity ε. Also, in slot coating experiments the minimum wet thickness correlates with ε as well. The modulus that best characterizes these coating techniques was determined at 0.1−0.2 Hz by means of a Langmuir trough.