GB1063509A - Binding - Google Patents

Abstract

1,063,509. Twisting polypropylene film. SOC. NORMANDE DE MATIERES PLASTIQUES. Nov. 3, 1965 [Nov. 4, 1964], No. 46636/65. Heading BSB. [Also in Division D1] Binding is made by twisting and drawing a film of polypropylene having reduced viscosity 1À1-5À0. The twisting may be performed before drawing, or between two drawing steps. The draw ratio may be 0À9xe<SP>0À4</SP>, where e is the film thickness in microns. The drawing may be performed at 80‹-160‹ C. with draw ratio 2À5-12; if two drawing steps are performed, the first may be at 140‹-160‹ at 70% of the total draw ratio, and the second at 95‹- 140‹ C. The twist should be 1/#m turns/metre, where m is wt. in g/metre. The preferred thickness of the film is 0À015-0À30 mm.; the width may be 10-250 mm. The binding may then be flexibilized by (1) untwisting and retwisting; (2) rolling; (3) rolling and twisting, combined with untwisting and retwisting; or (4) rolling and twisting. In method 1 a string 1 of the strapping passes from braked rollers 2, 4, 5 through ring 6 to a revolving platform comprising free rotatable pulleys 7 and 8 which rotate rapidly about spindle 9, serving to untwist the string coming from roller 4 and to retwist that proceeding to driven roller 12. In method 2, the string is drawn through a train of meshing gear-wheels (Fig. 2, not shown). In method 3 the string passes between two endless bands oppositely inclined to the path of the string, forming an X (Fig. 3, not shown). The bands may be made of a number of close parallel rollers (Fig. 4, not shown) which may be covered with a flexible non-slip belt. In method 4, the apparatus of method 1 is modified by replacement of the revolving platform by a sequence of parallel rollers disposed alternately in two mutually perpendicular planes, the line of intersection of the planes being the direction of movement of the string (Fig. 5, not shown). The nip decreases along the train.