Modification and control of plastic

Claim 1

A METHOD OF MODIFYING A SOLID FOAM OF A THERMOPLASTIC RESIN, WHICH FOAM POSSESS INDIVIDUALLY CLOSED CELLS AND IS OF IRREGULAR DENSITY, THROUGHOUT A CONSIDERABLE PORTION OF THE BODY OF THE SAME TO INCREASE THE DENSITY OF PORTIONS OF THE BODY OF FOAM TO A PREDETERMINED EXTENT, WHICH METHOD COMPRISES DETERMINING THE DENSITY VARIATIONS THROUGH THE THICKNESS OF THE BODY OF FOAM FROM ONE SIDE OF THE LATTER TO THE OTHER AND THEREBY DETERMINING THE EXTENT TO WHICH THE VARIOUS PORTIONS OF THE FOAM MUST BE REDUCED IN THICKNESS BY COMPRESSION BY PRESSING SAID SIDES OF THE FOAM BODY TOWARD ONE ANOTHER IN ORDER TO ELIMINATE SAID VARIATIONS IN AVERAGE DENSITY, COMPRESSING THE PLASTIC FOAM OF IRREGULAR DENSITY WITHIN A MOLD TO REDUCE THE THICKNESS OF THE VARIOUS PORTIONS OF THE FOAM BODY BY AMOUNTS SUCH AS TO BRING ALL PORTIONS OF THE BODY OF FOAM TO DESIRED AND PREDETERMINED DENSITY VALUES BETWEEN THOSE INITIALLY POSSESSED BY THE RESPECTIVE PORTIONS OF THE FOAM BODY AND THE ABSOLUTE DENSITY OF THE RESIN IN THE CELL WALLS THEREOF, HEATING THE COMPRESSED FOAM IN THE MOLD TO A TEMPERATURE BETWEEN THE SECOND ORDER TRANSITION TEMPERATURE OF THE CELL WALLS THEREOF AND 30* C. THEREABOVE, AND THEN COOLING THE FOAM TO BELOW SAID SECOND ORDER TRANSITION TEMPERATURE WHILE IT IS CONFINED WITHIN THE MOLD.