However, as the ratio of the traditional acrylic is increased (1:3:3 formulation) the spray pattern exhibits thicker ligaments and a greater number of larger drop sizes are evident, similar to the spray patterns seen in latex paints with moderate DUEVs. (4) The highest traditional acrylic level (1:2:4 formulation) was not sprayable from a fan nozzle.
The particle velocity patterns of the four formulations that provided spray patterns also follow the velocities profiles noted in latex paints with increasing DUEVs. The lower viscosity fluids (3:3:1 and 1:4:2), exit the nozzle at high velocities, dissipate into finer drops, and as discussed in the previous article (4) in this series, the fine droplet sizes decrease in velocity as they distance from the nozzle, due to the greater aerodynamic drag on their greater surface area.
Soules, DA, Fernando, RH, Glass, JE, "Dynamic Uniaxial Extensional Viscosity (DUEV) Effects in Roll Application: I.
Further studies in this area, (7) however, proved that the misting behavior of roll-applied coatings (spatter) was more appropriately related to dynamic uniaxial extensional viscosities (DUEVs).
DUEVs are difficult to measure in low viscosity fluids, and there may always be a preference to indicate that poor sprayability is related to the formulation's viscosity at high shear rates.
By blending these two types of W-SPs at low concentrations it was possible to produce shear thinning fluids that possessed constant shear viscosities at a given shear rate with changing compositions, but with different DUEVs. These fluids defined the influence of DUEVs on the number of ribs formed as a function of roll velocities and the gap setting between rolls, and they are used here to differentiate the relative role of HSVs and DUEVs in spray applications.
The blends used in this study consist of variable component ratios among individual sets (Table 1), and each set is formulated to produce the same viscosity/shear rate profile, storage modulus (G'), and surface tension, but with different DUEVs, allowing for separate control of the shear and extensional responses.
The comb has a significantly higher molecular weight than the telechelic HEURs and it has a determinable (37) DUEV at a 1.5 wt% (approaching 7 Pa.s at 100 [s.sup.-1]).
With the highest molecular weight HEUR used at the highest HEUR concentration, the [C.sub.14][H.sub.29]-comb-HEUR coating would have the highest projected coating DUEV of the associative thickener coatings studied.
The high-[M.sub.v] HEC thickened large particle (477 nm) size latex coating is shear-thinning, like the large hydrophobe telechelic HEUR formulation; however, the HEC formulation has a significant DUEV, which alone can account for the spray profile.
Earlier seminal studies in the spatter behavior of roll applied waterborne coatings demonstrated that misting behavior was more appropriately related to DUEVs (16) than any shear deformation related function.
Previously, DUEVs for a 1.0 wt% of [C.sub.6][H.sub.13][H.sub.12]MDI-HEUR coating with the same latex used in this study were less (14) than 0.4 Pa.s at extension rates beyond 500; with 0.125 wt% HEC the values are similar.