Parameters influencing the spray behavior of waterborne coatings

The influence of liquid pressures and orifice diameters on the sprayability of non-Newtonian, waterborne latex coatings, that vary in latex particle s ize and thickener composition are examined in this study. It is observed th at the higher the dynamic uniaxial extensional viscosities (DUEVs, eta(e)) of the coatings, the larger the Sauter mean diameters (SMDs) of the spray d roplets and the broader the droplet size distributions. The shear viscositi es at high shear rates and the parameter reflecting shear elasticity, the s torage moduli, at low deformation rates do not correlate with the droplet s izes and the distributions observed. In addition to these observations, the Sauter mean diameters of spray droplets decrease with increasing spray pre ssures and with decreasing orifice diameters; however, with increasing pres sures, pulsations in the fluid due to turbulence create areas of high and l ow droplet density. The relationship of the SMD to orifice diameters using fan nozzles is defin ed by the relationship: SMD/d(h) = 5.5 [sigma eta(e)(4)/(rho(A)d(h)(3)Delta P-L(2))](0.25) + 2 [sig ma rho(L)/(rho(A)d(h)Delta P-L)](0.25). The experimental results associated with each of these parameters are discu ssed in the text.