Patent GB-975235-A (GB)
Title: Biaxial stretching of beaded edge film
IPC: B29C55/16
Filed: 1960-11-29
Abstract: 975,235. Biaxial stretching of beaded edge film. FMC CORPORATION. Nov. 29, 1960 [March 16, 1960], No. 41021/60. Heading B5B. An apparatus for biaxially stretching a beaded edge film in a continuous manner comprises a stretching zone 17 (Fig. 1) into which a preheated film 11 having a web 13 and beaded longitudinal edges 15 is advanced by a metering device. The stretching zone 17 is defined by a pair of flexible tracks 19 and 21 supported by a frame 23 positioned between the metering device (not shown) and a pair of take-up rolls 25 and 27. The tracks 19 and 21 each consist of a pair of spaced flexible plates 29 and 31 (Fig. 2) between which the film web travels as the film is advanced through the stretching zone. To facilitate transverse adjustment of the tracks 19 and 21 towards and away from each other, the terminal portions of the plates 29 and 31 are each provided with lugs 33 (Figs. 1 and 3) which are pivotally mounted by pins 35 on carriages 37 and 39 disposed adjacent to the exit and entrance of the stretching zone respectively. The carriages 39 are simultaneously adjusted towards and away from each other by screw 41 rotatably supported in bearings 43 and 45 and meshing with threads formed in the carriages 37. A guide rod 53 fixed to the bearing plates 43 slidably supports the carriages 37 and prevents their rotation as the screw 41 is turned by the crank 55. The carriages 39 at the entrance of the stretching zone 17 are generally similar to the carriages 37 and are adjusted in a similar manner by rotation of the crank 69. The end bearing plates 59 (Fig. 3) and the centre support bearings 61 are fixed to a slide block 71 which rides along angle bars 73 and 75 of the frame 23 and is guided along a longitudinal path by the roller 79. Prior to the commencement of the stretching operation the flexible plates 29 and 31 forming each of the tracks 19 and 21 are adjusted to provide a desired gap therebetween and the tracks 19 and 21 are positioned parallel to one another. The film 11, preferably preheated, is then laced between the flexible plates of the respective tracks (Fig. 2) and then passed through the nip of the take-up rolls 25 and 27. The speed of these is then gradually increased until the desired longitudinal tension is exerted on the film. The carriages 37 are then moved away from one another by means of the crank 55 until the desired degree of transverse stretching of the film web is obtained. As the film is advanced through the stretching zone, the transverse tensions exerted on the tracks 19 and 21 as the film beads move along them flex the tracks into a contour which the film beads tend to assume in response to the longitudinal and transverse tensions exerted on the film. In a second illustrated embodiment of the apparatus, relatively short tracks are provided at the entrance and exit portions of the stretching zone only. In a third embodiment of the invention the film beads are engaged during the passage of the film through the stretching zone by a number of pairs of co-operating rollers, the rollers 165 of each pair (Fig. 8) being of identical construction and fixedly mounted on vertical shafts 171 which are rotatably mounted in yoke 173. The rollers of each pair are spaced apart sufficiently to allow the film web to pass freely therebetween and are preferably provided with roughened or knurled peripheral surfaces to prevent slipping of the film beads. The pairs of rollers at the entrance to the stretching zone are preferably positively driven as by gears 175. Specifications 969,005 and 969,852 are referred to.