Polymer foaming using metal oxide particles
Systems and methods for forming foamed thermoplastic polymer articles by adding metal oxide, particularly silica provided as a part of glass, to the polymer prior to extrusion of the polymer. The metal oxide may be added to particulate polymer prior to melting or to a polymer melt prior to extrusion. At least some of the metal oxide will remain in the resultant foamed polymer article produced.
1 . A method for foaming a thermoplastic polymer comprising the steps of:
providing pellets of a thermoplastic polymer;
mechanically mixing metal oxide particles with said thermoplastic polymer pellets to form a mixture;
heating said mixture so as to melt said thermoplastic polymer pellets but not said metal oxide particles, said heating resulting in the formation of a melt mixture;
extruding said melt mixture; and
allowing said extruded melt mixture to harden, said hardened mixture comprising a plastic foam.
2 . The method of claim 1 wherein said metal oxide is non-ionic and of the form X a O b where X represents an elemental metal atom and a and b are whole numbers.
3 . The method of claim 2 wherein said metal oxide comprises silica (SiO 2 ).
4 . The method of claim 3 wherein said silica is provided as part of glass.
5 . The method of claim 4 wherein said metal oxide particles comprise glass spherules.
6 . The method of claim 5 wherein said glass spherules are hollow glass microspheres.
7 . The method of claim 1 wherein said thermoplastic polymer comprises a fluoropolymer.
8 . The method of claim 7 wherein said fluoropolymer comprises FEP.
9 . The method of claim 1 further comprising the step of: adding a blowing agent to said melt mixture.
10 . A method for foaming a thermoplastic polymer comprising the steps of:
providing a thermoplastic polymer;
melting said thermoplastic polymer;
mixing a particulate metal oxide with said melted thermoplastic polymer to form a melt mixture;
extruding said melt mixture; and
allowing said extruded melt mixture to harden, said hardened mixture comprising a plastic foam.
11 . The method of claim 10 wherein said metal oxide is non-ionic and of the form X a O b where X represents an elemental metal atom and a and b are whole numbers.
12 . The method of claim 11 wherein said metal oxide comprises silica (SiO 2 ).
13 . The method of claim 12 wherein said silica is provided as part of glass.
14 . The method of claim 13 wherein said metal oxide particles comprises glass spherules.
15 . The method of claim 14 wherein said glass spherules are hollow glass microspheres.
16 . The method of claim 10 wherein said thermoplastic polymer comprises fluoropolymer.
17 . The method of claim 16 wherein said fluoropolymer comprises FEP.
18 . The method of claim 10 further comprising the step of: adding a blowing agent to said melt mixture.
19 . An extruded thermoplastic polymer article comprising
a thermoplastic foam including voids; and
a plurality of glass spherules;
wherein the volume of at least some of said voids is, at least in part, the result of the addition of said glass spherules prior to the extrusion of said thermoplastic polymer.
20 . The article of claim 19 wherein said object comprises electrical insulation media extruded onto a conductor.