LATEX PARTICLE-SIZE AND CPVC

Monodisperse vinyl acetate/butyl acrylate (85/15) latexes were prepare d with particle sizes between 200 and 1200 nm. These were used in a si mple paint formulation with TiO2 as the only pigment. Two optical meth ods were used for determination of the critical pigment volume concent ration (CPVC) of these paints. These are specular gloss at an incidenc e angle of 85 degrees and CIE Z (lightness) values of a blue tinted fo rmulation. Both methods gave coincident results for the CPVC as a func tion of latex particle size. Our data fit the expression X = 1.44Y(2.6 5) where X = number of latex particles/number of pigment particles, at CPVC and Y = diameter of pigment particles/diameter of latex particle s. Earlier, Bowell reported the same exponential relation, with a diff erent pre-exponential factor, for acrylic latexes. The common exponent is explained with a model in which the latex and pigment particles as sume a condition close to minimum porosity during packing. CPVC reflec ts the packing of particles during the initial stages of dryness of th e latex. The 'universal' relation reported here permits facile predict ion of the effects of latex particle size on the CPVC and binding capa city in water-based paints.