Method and apparatus for manufacture of a polymer film, which is oriented under an angle to its longitudinal direction

Flexible tubular film (10) is helically cut into a flat strip by unwinding the tubular film in flattened form by a tumbling unwinder (1), advancing the flat film tube to a tube expansion zone (17) in which the flat tube is expanded into a circular cylindrical tube and is passed axially over a hollow mandrel (14) slightly lower in external diameter than the diameter of the expanded tube to be cut by knife (18) helically while on the mandrel into a flat strip that is removed at an angle to the mandrel axis. The flat tube is longitudinally stretched by stretching rollers (107-112), which tumble with the tumbling unwinder. The apparatus further comprises stabilization means for stabilizing the orientation applied by the tumbling stretching rollers, applied to the helically cut film strip after it has been drawn from the mandrel.