| Abstract: | Phase-separation behaviors of latex dispersions, using commercial latices of three different median sizes, and pigmented coatings are examined. Both the dispersions and pigmented coatings at a 0.32 volume fraction of total dispersed phase were thickened with water-soluble polymers, with and without surfactant hydrophobes. Latex dispersions thickened with water-soluble polymers without hydrophobe modification follow the phase-separation behavior described by the volume restriction flocculation (VRF) concept (i.e., molecular weight of the thickener or particle size of the latex). This is surprising since commercial latices contain a variety of surface-stabilizing moieties, in addition to surfactant. Latex dispersions thickened with commercial and model hydrophobically modified ethoxylated urethane (HEUR) polymers do not follow the phase-separation behavior predicted by the VRF concept. The lack of correlation of phase behavior with latex median size in HEUR-thickened formulations led to an examination of four secondary thickeners, noted for providing high viscosities at low shear rates. With an all-acrylic, large median-size latex, the combinations of commercial HEURs with secondary thickeners are effective in eliminating phase separation; only partial reduction in phase separation is observed with a vinyl acetateacrylic large-particle latex. The influence of HEUR/secondary thickener blends on the film properties also is discussed. © 1993 John Wiley & Sons, Inc. |
