Pigmented Formulations Containing Biobased Nanoparticle Binders for Curtain Coating Applications; Part 2: Curtain Stability Study, PaperCon 2016

This paper continues to characterize pigmented curtain coatings, including controls containing a styrene-butadiene-acrylonitrile (XSB) latex binder and a petro-based extensional viscosity
modifier, and experimental coatings in which the XSB latex binder was partially replaced with a biobased latex binder and the petro-based extensional viscosity modifier was completely
replaced with one of two inorganic rheology modifiers. The unique effects of the various rheology modifiers on coating properties is presented and discussed. The degree of correlation
between surface tension and CaBER filament lifetime for control and experimental coatings is reported.

The curtain stability of these coatings at flow rates of 20 to 65 mL/s was studied using a slot-fed die set-up equipped with a controlled coating recirculation loop. It was found that the curtain
stability was significantly enhanced by the addition of the petro-based extensional viscosity modifier, as well as by inorganic rheology modifier when biobased latex was present. By
impinging the curtain exiting the slot-fed die set-up and determining the Mach angle at the point of impingement, which angle relates to the dynamic surface tension of the coating, the
corresponding Weber numbers were calculated as a known and accepted measure of curtain stability. Amongst the coatings, the ones containing 35% and 45% (wt. %) biobased latex plus
an inorganic rheology modifier resulted in the most stable curtains, while the stability of the other coating formulations was lower but still comparable to the all-synthetic latex control
coating. The findings showed the relative importance of coating surface tension, shear rate dependence of viscosity, viscoelasticity as well as extensional viscosity to the curtain stability at
different flow rates. A coating with relatively low surface tension (< 40 mN/m) and shear viscosity required a more elastic structure and/or higher extensional viscosity to form a stable
curtain, especially at higher flow rates.

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