Method and apparatus for microcellular polymer extrusion
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.
1 . A system comprising:
an extruder designed to convey a first stream of a fluid, polymeric material in a downstream direction and having a blowing agent port constructed and arranged to inject a blowing agent into the stream, the extruder adapted to admix the stream with the blowing agent to form a single-phase solution of polymeric material and blowing agent;
a nucleator constructed and arranged to divide the single-phase solution of polymeric material into separate portions and to continuously nucleate each of the separate portions at a rate sufficient to form a microcellular polymeric material.
2 . A method comprising:
establishing a stream of polymeric material flowing at a rate of at least about 5 lbs per hour within a polymer processing space between a rotating screw and an extruder barrel;
introducing, into the stream of polymeric material, a blowing agent through a plurality of orifices of the extruder barrel while passing the orifices with a flight of the rotating screw; and
admixing the polymeric material and the blowing agent to form a single-phase solution of polymeric material and blowing agent.
3 - 10 . (canceled)
11 . A method comprising continuously extruding microcellular polymeric material having cells of essentially uniform size of less than about 50 microns average size from a single-phase solution of polymeric material and blowing agent contained in extrusion apparatus including a nucleating pathway, the blowing agent present in the solution in an amount less than about 80 percent saturation concentration as determined at the lowest pressure in the system after the point of blowing agent injection prior to the nucleating pathway.
12 - 13 . (canceled)