Rheology parameters controlling spray atomization and roll misting behavior of waterborne coatings

Formation of small coating droplets is a phenomenon common to spray and rol l application of coatings. Generation of small droplets, referred to as ato mization, is the mechanism of controlling the quality and thickness of the applied coating layer in spray technology. Ln roll coating application, sma ll coating droplets are formed at the nip-exit region under certain conditi ons. Because of the high-shear rates at roll nips and spray nozzles, it is common to relate high-sheer viscosity with atomization and roll misting beh avior of coatings. This paper will review the relative importance of shear and extensional flaws, and the response of coatings to such flows, in affec ting misting and atomization behavior. Experimental efforts to quantify the effect of shear and extensional rheological parameters have clearly establ ished a lack of correlation of high-shear viscosities with both spray atomi zation and roll misting behavior of coatings. However, extensional viscosit y is shown to have a strong correlation. Finally, how rheology modifiers ca n be selected to circumvent misting problems in roll coating applications a nd atomization problems in spray applications is discussed. (C) 2000 Publis hed by Elsevier Science S.A.