Method of manufacturing a strainable thermoplastic film material, product resulting therefrom, and apparatus to carry out the method

A method of manufacturing a thermoplastic film which exhibits rubberlike strain properties mainly in one direction (1) comprising the steps of:

• extruding or casting a film,
• stretching the film below its melting range so that the entire film is oriented or an area of the entire film is oriented, where the stretching has a component in the direction (1) to make the film shrinkable in the direction (1),
• simultaneously or subsequently, giving the film or the film area a pleated or waved shape having an average pitch of pleating or an average wavelength of the waves is 5 mm or less, whereby the extension of the pleats or waves is perpendicular to the direction (1),
• heating the film or the film area in a pattern comprising regions (A) and allowing the film or the film area to shrink in the pattern along the direction (1), while a shrinkage perpendicular to the direction (1) is prevented by a holding means, if the film or the film area tends to shrink in the direction perpendicular to the direction (1) so that the regions (A) become flattened, while unheated film regions (B) of the film or the film area remain pleated or waved where the regions (B) are discontinuous or disrupted.