Filled, biaxially oriented, thermoplastic film having preferential shrinkage and method of making such film

a filled, biaxially oriented, void-containing thermoplastic film suitable for making heat-shrinkable bands is provided having shrinkage on heating to 100.degree. C. of greater than 5%, which shrinkage in turn is at least 5% greater than the shrinkage in a direction perpendicular thereto.A process for preparing this film with its preferential shrinkage is provided including the steps of:(a) melt-blending a C.sub.2 -C.sub.10 .alpha.-monoolefin polymer and at least 20 weight percent inert filler, based on the total weight of polymer and filler;(b) forming a film from the melt blend;(c) cooling the film to a temperature below the melting point;(d) biaxially stretching the film at least about twice its original forming dimensions in mutually perpendicular directions while the film temperature is above the line-drawing temperature and below the polymer melting temperature, until the film has at least about 30% voids;(e) cooling the film to room temperature; and(f) post-stretching the biaxially stretched film in a selected direction at a temperature below 100.degree. C. to an extent that provides the above-mentioned preferential shrinkage in the filled film.

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Description
Patent History
Patent number: T981003
Type: Grant
Filed: Jul 11, 1978
Date of Patent: Apr 3, 1979
Assignee: E. I. Du Pont de Nemours and Company (Wilmington, DE)
Inventors: Lester R. Bartron (Wilmington, DE), Samuel P. Anderson (Wilmington, DE), Rudolph H. Michel (Wilmington, DE)
Application Number: 5/923,569