Natural sandwich of filled polyurethane foam

A process of preparing a molded, integral-skin, filled foam product comprising the steps of:

• providing a mold presenting an enclosed molding cavity;
• charging said cavity with a foamable molding composition which comprises
• a polyurethane composition designed to yield rigid and products and which comprises an isocyanate, a polyol, and a blowing agent;
• an inorgantic, particulate filler material which is substantially chemically unreactive with said isocyanate and polyol, the major proportion by weight of said filler material having a diameter of at least about 10 microns;
• and
• a density distribution control agent which is liquid at room temperature, substantially chemically unreactive with said isocyanate and polyol and soluble in said foamable composition, does not significantly accelerate or decelerate the reaction between the components of said foamable composition, and serves to reduce the viscosity of said foamable composition with said filler material therein,
• said density distribution control agent being selected from the group consisting of carbon tetrachloride, trichloroethylene, chloroform, methylchloroform, perchloroethylene and ethyl acetate,
• said foamable composition including from about 20 to 75 parts by weight of said polyurethane composition, from about 25 to 80 parts by weight of said filler, and from about 3 to 12 parts by weight of said density distribution control agent,
• the ratio by weight of filler material to polyurethane molding composition being in the range of approximately 1:3 to 4:1;
• causing said foamable composition to react within said mold to create a hardened product,
• said filler and density distribution control agent serving, during said reaction, to cooperatively reduce the temperature of reaction to a level for preventing an excessive increase in the pressure within said mold over that provided by the blowing agent,
• the reduced viscosity of said foamable composition derived from the use of said density distribution control agent therein serving, during said reaction, to reduce the thickness of cell walls formed just prior to gelation, in order to cause a greater expansion in the central area of the mold cavity and a corresonding concentration of material in the regions of said cavity adjacent the mold walls,
• said reaction being carried out such that said product has
• a rigid, closed cellular core, a rigid, closed cellular outer portion, at least a pair of opposed outer layers, and a very thin, rigid, essentially void-free outer surface,
• said core having a first density, a first average cell size, and respective first concentrations of polyurethane material and filler material,
• said outer portion having a second density which is at least about three to ten times as great as said first density, a second average cell size less than said first average cell size, and respective second concentrations of polyurethane material and filler material which are substantially greater than the corresponding first concentrations,
• the percent by weight of said filler material in said product being substantially the same in both said core and outer portion,
• the ratio of the thickness of said core to the combined thicknesses of said opposed layers being in the range of approximately 10:1 to 1:2,
• said outer surface having a durometer hardness value of at least approximately 50 throughout its area.