Patent attributes
A method for providing a foamed, opacifying element includes providing a foamable aqueous composition, aerating it to a foam density of 0.1-0.5 g/cm3, applying the foamed aqueous composition to a porous substrate, drying, and densifying the dried layer. Such foamable aqueous compositions have 0.05-15 weight % of porous particles; at least 20 weight % of a binder; at least 0.0001 weight % of additives (including a surfactant); water; and at least 0.001 weight % of an opacifying colorant. Each porous particle includes a continuous polymeric phase and discrete pores; a mode particle size of 2-50 μm; and a porosity of 20-70 volume %. The continuous polymeric phase Tg is >80° C. and has a polymer viscosity of 80-500 centipoises at an ethyl acetate shear rate of 100 sec−1 at a concentration of 20 weight % at 25° C.
