Abstract:
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.