| abstract |
Foamed polyurethanes substantially free from non-uniform density distribution are obtained by dispersing an inert gas with mechanical stirring into a foamed polyurethane-forming composition containing substantially no blowing agent and comprising (1) an organic polyisocyanate component, (2) a polyol component comprising a high molecular weight polyol (A1) and a low molecular weight polyol (A2), (3) a dehydrating agent (B) and optionally organic microballoons, and curing the resulting composition containing therein the inert gas substantially homogeneously distributed. Foamed polyurethanes thus obtained are light-weight and of reduced warpage after processing and are suitable for model materials. Polyol (A1) may be selected from polyether polyols, polyester polyols, castor oil polyols, polybutadiene polyols, vinyl polymers containing hydroxyl groups and polymer/polyols, and is preferably castor oil. The dehydrating agent is preferably a zeolite, calcium oxide, calcium sulphate, calcium chloride, barium oxide or barium sulphate. The inert gas may be air, carbon dioxide or nitrogen. |