Method and device for longitudinal drawing of a film web

Device for drawing a film web of thermoplastic polymer comprising a driven roller (2) driven at a speed of V1 and a second driven roller (3) driven at a speed of V2, V1<V2, and the rollers (2)/(3) being arranged in such a way that a drawing gap (4) is formed between the two rollers (2)/(3), and wherein between the two rollers (2)/(3), a width-maintaining device is arranged which mechanically grips peripheral areas of the film web in such a way that the width of the film web remains essentially unchanged during longitudinal drawing in the drawing gap (4), and wherein the width-maintaining device includes two pairs of carriages (5a) and (5b), one pair of carriages (5a) and (5b) being positioned on one film periphery and each of the four carriages having a plurality of rolls (6a) and (6b) arranged in sequence, one carriage being arranged on each film periphery above and one carriage opposite below the film web and the carriages (5a) and (5b) arranged above and below a film periphery being positioned vis-à-vis each other in such a way that the rolls (6a) and (6b) are aligned in the direction of advance (9) of the film and the pairs of rolls (6a) and (6b) lying opposite each other touching the film web lying inbetween in the peripheral area (10).