Parameters Influencing the Spray Behavior of Waterborne Coatings

By Lin-lin Xing, J. Edward Glass, Raymond H. Fernando

The influence of liquid pressures and orifice diameters on the sprayability of non-Newtonian, waterborne latex coatings, that vary in latex particle size and thickener composition are examined in this study. It is observed that the higher the dynamic uniaxial extensional viscosities (DUEVs, ηe) of the coatings, the larger the Sauter mean diameters (SMDs) of the spray droplets and the broader the droplet size distributions.

The shear viscosities at high shear rates and the parameter reflecting shear elasticity, the storage moduli, at low deformation rates do not correlate with the droplet sizes and the distributions observed. In addition to these observations, the Sauter mean diameters of spray droplets decrease with increasing spray pressures and with decreasing orifice diameters; however, with increasing pressures, pulsations in the fluid due to turbulence create areas of high and low droplet density.

The relationship of the SMD to orifice diameters using fan nozzles is defined by the relation-ship: SMD/d_h = 5.5 [ση_e4/(ρ_Ad_h³∆P_L²)]^0.25 + 2 [σρ_L/(ρ_Ad_h∆P_L)]^0.25 The experimental results associated with each of these parameters are discussed in the text.