Importance

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Abstract

Method for producing large size, low density, elongated thermoplastic cellular bodies comprising the steps of forming a mixture of a thermoplastic polymer and a blowing agent dissolved therein under pressure and at a temperature at which the viscosity of the mixture is sufficient to retain the blowing agent when the mixture is allowed to expand, extruding said mixture into a holding zone under conditions that prevent said mixture from foaming, the holding zone having an outlet die orifice opening into a zone of lower pressure and temperature at which said mixture foams and an openable gate closing the die orifice; periodically opening said gate and substantially concurrently applying mechanical pressure by a movable ram on the mixture, preferably while scraping the sides of the holding zone with said ram, to eject the mixture from the holding zone through the die orifice at a rate in excess of that at which substantial foaming in the die orifice occurs and less than that at which substantial irregularities in the cross-sectional area or shape of the cellular body occurs; and permitting the ejected mixture to expand unrestrained in at least one dimension to produce the elongated thermoplastic cellular body. Apparatus for producing elongated thermoplastic cellular bodies comprising an extruder for feeding a mixture of thermoplastic polymer and plasticizing blowing agent at a temperature suitable for producing a cellular body when the mixture is subjected to lower pressure; an expandable holding chamber receiving said mixture from the extruder and maintaining the mixture in a molten state at a pressure above the foaming pressure thereof, ram means for ejecting the mixture out of the chamber; a die having an orifice, preferably in line with the ram means, through which the mixture is ejected by operation of the ram means, and gate means contacting the exterior surface of the die for closing and sealing the die orifice while the holding chamber is being filled.

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First Claim