Film formation, reproducibility of production and curing with respect to release stability of functional coatings from aqueous polymer dispersions.

The formation of film coatings from aqueous polymer dispersions is a complex process, highly dependent on additives and process parameters. Release instability of modified release coatings from aqueous polymer dispersions is a frequently described problem that hinders the general application of such dispersions. However, if some important prerequisites are fulfilled, storage stability should be achievable. Most important are: (a) The appropriate plasticizing time has to be considered, incorporating sparingly soluble plasticizers in the dispersion. (b) Necessary pore formers increase the permeability of the coating to a desired and constant extent only if they are compatible with the polymer. (c) Coating in the fluidized bed at or slightly above the minimum film forming temperature may lead to only incomplete film formation. Curing at higher temperatures improves the polymer particles coalescence to a physically stable state. Other stability aspects such as physical and chemical aging, migration of plasticizers and drugs and incompatibilities are also discussed.