CHANGES IN HIDING DURING LATEX FILM FORMATION .5. EFFECT OF OPAQUE POLYMER

In Part V of this continuing series, the Cleveland Society for Coating s Technology Technical Committee investigated how opaque polymer affec ts the changes in hiding of latex paints during the first hour of dryi ng. Hiding was monitored during drying by measuring the reflectance (t ristimulus Y) every 15 sec on paints drawn down over a black substrate . Addition of opaque polymer was found to have three main effects: (1) decreased titanium dioxide efficiency due to extender dilution effect s; (2) increased dry hiding in paints above critical pigment volume co ncentration; and (3) increased hiding by the introduction of air voids which develop within the opaque polymer. Results suggest that void fo rmation within the opaque polymer occurred rapidly; it reduced the ini tial loss in hiding due to film contraction, rather than contributing to the development of dry hiding in the later stages of drying.