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

An apparatus for manufacturing a polymer film comprising:

• an unwinding stand (1) including:
• a reel (9) having lay-flat tubular film mounted thereon,
• a tumbling unwinding device arranged to unwind the lay-flat tubular film and rotate it about its longitudinally extending middle line (23),
• a mandrel (14),
• stretching rollers (107-112, 101-106) mounted for tumbling with the tumbling unwinding device and for stretching the lay-flat tubular film in a longitudinal direction after it has been unwound from the reel (9) and before it is opened for dragging over the mandrel (14),
• a means for opening the drawn-off film to form an open tube and for dragging the open tube over the mandrel (14) in a screwing movement,
• a knife (18) located in a fixed position for helically cutting the open tube and means for pulling the helically cut film away from the mandrel, and
• a stabilization means for stabilizing the orientation applied by the longitudinal stretching rollers in the helically cut film after it has been pulled from the mandrel.

An apparatus for helically cutting a flexible tubular polymer film of predetermined diameter into a flat strip comprising:

• an unwinding stand having mounting means for mounting a reel of tubular film in lay-flat form, and an unwinding device for unwinding the flat tubular film from the reel, the unwinding device being mounted for tumbling about a predetermined tumbling axis whereby the flat tubular film is unwound from the reel and delivered to an expansion zone with its longitudinal middle line aligned with the predetermined tumbling axis and rotating about the longitudinal middle line,
• an expansion zone with a means for opening the lay-flat tubular film into a film tube of substantially circular section,
• a mandrel having an outer diameter less than the film tube diameter and being coaxial with said predetermined tumbling axis,
• means for dragging the film tube over the mandrel in a screwing movement,
• a knife in a predetermined fixed position relative to the mandrel for cutting the film of the tube at a predetermined angle to form a helically cut flat film strip,
• means for drawing off the helically cut flat film strip from the mandrel,
• stretching rollers for longitudinally stretching the lay-flat film after it has been unwound from the reel and before it reaches the expansion zone, the stretching rollers being mounted on the tumbling unwinding device for tumbling therewith about the predetermined tumbling axis, and
• a stabilization means for stabilizing the orientation applied by the said stretching rollers in the helically cut flat film strip after it has been drawn from the mandrel.