Method and apparatus for the continuous production of a uniform slab or sheet from heat expandable thermoplastic particles

In a method for producing a continuously molded sheet, said method being of the type wherein a hot gas selected from the group consisting of hot air and steam is introduced to thermoplastic granules containing a heat expanding agent in at least one heated zone associated with a molding channel, said molding channel having inner and outer concentric arcuate surfaces, which inner and outer concentric arcuate surfaces have perforations therethrough, said hot gas being introduced through said perforations in said outer concentric arcuate surface, the improvement comprising:

• a. introducing an amount of water throughout said granules in said molding channel, through said perforations in said outer concentric arcuate surface to cause said granules to adhere to one another;
• and,
• b. evacuating said water from said molding channel subsequent to expanding said granules, through said perforations in said inner concentric arcuate surface.

In combination with an apparatus for producing a continuously molded sheet, said apparatus including means for delivering granules of a thermoplastic material containing a heat expanding agent to an open ended molding channel, said molding channel having at least one heated zone associated therewith wherein said granules are subjected to a hot gas introduced into said heated zone for continuously expanding and molding said granules within said molding channel, the improvement comprising:

• (a) metering means for introducing a predetermined amount of a water into said molding channel in conjunction with said introduction of said hot gas;
• and
• (b) draining means for evacuating said water from said molding channel subsequent to the expansion of said granules.

In combination with an apparatus for producing a continuously molded sheet, said apparatus including means for delivering granules of a thermoplastic material containing a heat expanding agent to an open ended molding channel, said molding channel having inner and outer concentric arcuate surfaces having perforations therethrough and further having at least one heated zone associated therewith wherein said granules are subjected to a hot gas selected from the group consisting of hot air and steam introduced into said molding channel through said perforations of said outer concentric arcuate surface for continuously expanding and molding said granules within said molding channel, the improvement comprising:

• (a) pump means for introducing an amount of water through said perforations of said outer concentric arcuate surface into said molding channel in conjunction with said introduction of said hot gas;
• and,
• (b) draining means for evacuating said water from said molding channel through said perforations in said inner concentric arcuate surface upon the expansion of said granules.