Foamed resin process

Claim 1

A PROCESS FOR PREPARING A FOAMED THERMOPLASTIC RESIN STRUCTURE WHICH COMPRISES DEPOSITING A THIN FILM OF AN AQUEOUS DISPERSION OF A FINELY-DIVIDED THERMOPLASTIC RESIN UPON A SUPPORT, REMOVING SUBSTANTIALLY ALL OF THE WATER THEREFROM TO PROVIDE A NON-CONTINUOUS FILM OF SAID THERMOPLASTIC RESIN PARTICLES UPON THE SUPPORT, CONTACTING SAID THERMOPLASTIC RESIN PARTICELS WITH A VAPORIZABLE FOAMING AGENT FOR A PERIOD OF TIME OF UP TO ABOUT 10 MINUTES AND SUBSTANTIALLY IMMEDIATELY THEREAFTER HEATING AND FILM OF THERMOPLASTIC RESIN PARTICLES TO A TEMPERATURE ABOVE THE SOFTENING TEMPERATURE OF THE THERMOPLASTIC RESIN; SAID THERMOPLASTIC RESIN PARTICLES HAVIN A GLASS TRANSITION TEMPERATURE OF AT LEAST ABOUT 50*C. AND AN AVERAGE PARTICLE SIZE OF LESS THAN 100 MICRONS; SAID VAPORIZABLE FOAMING AGENT BEING SELECTED FROM THE GROUP CONSISTING OF (A) A NON-REACTIVE ORGANIC COMPOUND WHICH HAS AT MOST A SLIGHT SOLVENT ACTION ON THE THERMOPLASTIC RESIN AND HAS AN ATMOSPHERIC BOILING POINT IN THE RANGE OF FROM ABOUT -10 TO ABOUT 80*C. AND (B) MIXTURES CONSISTING PREDOMINANTLY OF (A) WITH MINOR AMOUNTS OF AN ORGANIC COMPOUND HAVING A SOLVENT ACTION ON THE THERMOPLASTIC RESIN.