Patent ID: 8003031

Claim:
A method for producing oriented slit film tapes, comprising the following steps: a) extruding melt polyolefin polymer through a die; b) simultaneous quenching and melt-drawing of the molten polymer in a cooling device to form a film sheet; c) slitting the initial film sheet into a plurality of relatively narrow slit film tapes; d) stretching at elevated temperature, by passing the slit film tapes through a heating medium at a temperature just below the softening temperature of the slit film tapes; e) annealing and cooling the oriented slit film tapes; f) winding the slit film tapes; wherein before the stretching step, the method further comprises a stage of pre-stretching made by passing the slit film tapes through one set of holding rollers turning at a given speed and one set of pre-stretch rollers turning faster than the holding rollers, wherein at least one of the rollers of the set of holding rollers is heated at a temperature between 48° C. to 85° C. and at least one of the rollers of the set of pre-stretch rollers is cooled to a temperature between 15° C. to 45° C.