GB1264072A - - Google Patents

Abstract

1,264,072. Moulding strapping. E. I. DU PONT DE NEMOURS & CO. 6 May, 1970 [7 May, 1969], No. 21866/70. Heading B5A. [Also in Divisions A4 and C3] In a crystalline thermoplastic resin strapping which is longitudinally oriented by rolling of an extruded billet, is of a tensile strength greater than 28 kg./mm.<SP>2</SP>, and is of at least 0À25 mm. thickness and 6À35 mm. width, the transverse propagation of longitudinally extending tears is prevented by grooves 36, Fig. 7, formed by the orienting rolls and extending longitudinally in a strapping surface, or in opposed surfaces, which are of a depth of 10 to 35% of the strapping thickness and the bottoms of which define a flat, or rounded, notch which is of an effective radius of curvature, of less than 0À075 mm., and preferably less than 0À025 mm. The grooves may be oppositely disposed as shown, or staggered. In the Fig. 8 embodiment (not printed) the notches are defined in the flat bottom of generally rectangular shaped grooves. The groove sides may also be inclined at 45 degrees. The resin may comprise polyethylene terephthalate which is preheated at 30‹ to 80‹ C. to cause conversion upon rolling, to the crystalline form from the amorphous extrudate, but in the preferred embodiment the resin comprises polyamide such as polycaprolactam, polyhexamethylene adipamide, or sebacamide, advantageously including 0À2 to 5% by weight of plasticizer (see Division C3) which is oriented by the rolling of the extruded billet, to 3À9 to 4À5 times its length, and to 0À7 to 1À5 times its width. The resin, extruded as a rectangular billet from a die orifice 21, is drawn by rolls 6, 7 through a water quench bath 4, in which it is linearly guided through pins intermediate entry and exit rolls, which it leaves at an angle to the water surface of 8 to 15 degrees and is fed across dancer arm 9, through a preheater 10 for heating to 15‹ C. below the crystalline melting point. The heated billet is then drawn by minimal tensioning rolls 14, 14<SP>1</SP>, through one or more pairs of orienting rolls 12, 13, each comprising a nip between spaced roll flanges 22 which limit the width 29 of the strapping, one or both of the final roll pair 12, 13 having circumferentially continuous projections which define the strapping grooves. The strapping is then fed through heat conditioner 15, having an exhaust 31, and wash tank 17 to be taken up on a spool 18.