Abstract: The present invention provides blowing agent introduction systems and methods for introducing blowing agent into polymeric foam processing systems. The methods may involve introducing one or more doses of blowing agent into polymeric material in an extruder during a plastication period of a molding cycle. Prior to introduction, a dose is confined in an accumulator which, for example, has a volume defined between an inlet valve and an outlet valve. A control system may receive inputs related to system parameters (e.g., pressure of polymeric material in extruder, axial position of screw in barrel, whether screw is rotating, and the like) and based on the inputs coordinates operation of the valves to confine and introduce the blowing agent dose(s). The introduction systems may be used in discontinuous plasticating processes, such as injection molding and blow molding, and can be particularly useful in processes that use precise quantities of blowing agent.

Abstract: Continuous polymeric extrusion nucleation systems and methods useful for making polymeric microcellular foamed materials, including crystalline and semi-crystalline polymeric microcellular materials, are provided. Pressure drop rate is an important feature in some embodiments, and the invention provides systems for controlling these and other parameters. One aspect involves a multiple-pathway nucleator that is separated from a shaping die by a residence chamber. Another aspect involves a die for making advantageously thick articles, including a multiple-pathway nucleation section. Microcellular material can be continuously extruded onto wire, resulting in a very thin, essentially closed-cell microcellular insulating coating secured to a wire. Other very thin microcellular products can be fabricated as well.

Abstract: The invention provides a counter-rotating extrusion system for processing foam material. The system is designed to introduce a physical blowing agent into the extruder, thoroughly disperse the blowing agent within the polymer melt and, preferably, to maintain relatively high pressures downstream from the point of blowing agent introduction. High quality polymeric foams, including microcellular foams, can be produced using the extrusion system. The system is particularly suitable for the production of foams using shear sensitive and degradable materials, such as PVC.