Characterization of curtain coating colors

Curtain coating is an important paper coating technology relevant for the applications that have an increasing demand for optimization of coating functionality and minimization of costly components. In this study we have highlighted the characteristics of some simple low solids curtain coating colors which may help to formulate and optimize curtain coating flows in order to prevent operational defects, such as irregular heel formation, air-entrainment and other curtain instabilities. Furthermore the characteristics of these simple colors are used for simulation modeling to verify the model and predict color behavior in a curtain coater slide without necessarily running a pilot trial for every combination of color components. In this work a good correlation between the film thinning rate predicted by the model and the dynamic surface tension at 1 second bubble life time was found. High viscosity stabilizes the curtain and less surface tension deviation from its static value at a relevant time scale is also beneficial to curtain stability. The model could be used to predict slide curtain minimum flow rate (MFR) from coating color rheology and dynamic surface tension measurement. Our results suggest that extensional viscosity is of limited importance in curtain coating for coating colors exhibiting low viscoelasticity.