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US 5,180,751 AGranted
Polypropylene foam sheets
AssigneeJames River Corporation of Virginia
InventorsJohn J. Park, Leon Katz, Norman G. Gaylord
Life of this patent
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Abstract
A thermoformable, rigid or semi-rigid polypropylene foam sheet having a smooth surface and a uniform cell structure and a density of at least 2.5 lbs/ft.sup.3 is prepared by extruding a mixture of a nucleating agent, a physical blowing agent and a polypropylene resin having a high melt strength and high melt elasticity.
Claims10
A process for producing a foam sheet of a polypropylene characterized by at least
- (a) either z - average molecular weight M.sub.z of at least 1.0.times.10.sup.6 or a ratio of the z - average molecular weight M.sub.z to weight average molecular weight M.sub.w, and
- (b) either equilibrium compliance J.sub.eo of at least 12.times.10.sup.-5 cm.sup.2 /dyne or recoverable shear strain per unit stress Sr/S of at least 5.times.10.sup.-5 cm.sup.2 /dyne at 1 sec.sup.-1,
- comprising the steps of
- mixing pelletized polypropylene with a nucleating agent, plasticating the mixture,
- introducing a physical blowing agent into the substantially
- plasticated mixture to form a foaming mixture,
- mixing and cooling the foaming mixture,
- extruding the foaming mixture into a foamed extrudate, and forming the foamed extrudate into a continuous foam sheet.
5 more elements
Dependencies are inferred from the claim text.