SUMMARY OF THE INVENTION
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present application, it has been discovered that wetting microspheres of phase change materials with water and maintaining a uniform dispersion of the microcapsules in a wet coating minimizes or eliminates the tendency of such microspheres to destabilize the binder polymer in which the microspheres are dispersed.
A coating composition which includes microspheres containing a phase change material is prepared by mixing dry microspheres with an excess of water to induce the microspheres to swell with water until swelling is complete. Preferably, a surfactant and a dispersant are added to the water prior to mixing with the microspheres. The surfactant decreases surface tension of the layers of the microspheres and thereby promotes wetting of the microspheres. An antifoam agent is added to and mixed slowly with the microsphere/water mixture to remove air trapped as dispersed bubbles in the mixture. A thickener is added to adjust the viscosity of the mixture to prevent the microspheres from floating or sinking in the mixture. A viscosity of at least 500 cps is preferred. Adjusting the pH of the mixture to 8.5 or greater promotes swelling of the microspheres. Swelling is typically complete in from 6 to 24 hours, at which time the microspheres will have reached an equilibrium with the aqueous phase in which they are dispersed. Thereafter, the microsphere dispersion is added to a mixture of a polymer dispersion, surfactant and dispersant having a pH approximately the same as the pH of the microsphere dispersion. The viscosity and rheology of the resulting coating compound is adjusted to meet the requirements of the coating method employed.