ANGULAR ANNEALING PROCESS

A procedure wherein a tubular high molecular weight polymer film which has been longitudinally stretched and therefore is longitudinally shrinkable, is converted by helical cutting to second polymer film, which then is heated and relaxed in order to partly or totally eliminate the shrinkability, whereby one edge of the helically cut film, inevitably becomes longer than the other edge, referring to a relaxed stated, characterised in that second film is converted to third film by continuously advancing second film in a first direction towards a lineary zone which extends perpendicularly to the edges of the cut film, while heating the film to a temperature lower than but close to its melting range, and in direct succession hereto moving the heated film at velocity (v) in a second direction which forms a small angle (a) to the first direction, the velocity (v) and angle (a) being selected to reduce or totally eliminate the difference between the lengths of the edges.