Use of an anhydrous solvent to swell the core of a particle consisting of a core and a shell and use of the resulting particles as an opacifying agent

摘要

An aqueous dispersion of water-insoluble core-shell particles is prepared by emulsion polymerization for use as an opacifying agent in coatings. The particles have interior cores which are swollen with nonaqueous solvent. The polymeric exterior shells have a glass transition temperature greater than about 50 DEG C in the presence of the nonaqueous solvent. The partition coefficient for the nonaqueous solvent between the interior core polymer phase and the exterior shell polymer phase is at least about 1.25. Coatings compositions formulated using the core-shell particles show increased opacity, as single light scattering microvoids are formed in individual particles when the solvent evaporates and the core collapses inside the rigid exterior shell. Opacity develops even when aqueous coatings containing the particles are dried under high humidity conditions.