Surface elastic effects in premetered coating techniques

The effect of the dilational surface elasticity ∈ 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 ∈ were varied in the lower layer. While the position of the static contact line (SCL) is a function of the elasticity modulus ∈, the dynamic contact line (DCL) position is insensitive to this variable. Also, the vacuum range increases with increasing the modulus ∈. Best correlations were obtained when ∈ 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 ∈. Also, in slot coating experiments the minimum wet thickness correlates with ∈ as well. The modulus that best characterizes these coating techniques was determined at 0.1-0.2 Hz by means of a Langmuir trough.