GB1499899A - Bonded non-woven fabrics - Google Patents

Abstract

1499899 Polypropylene filaments E I DU PONT DE NEMOURS & CO 24 June 1975 [24 June 1974] 26770/75 Heading B5B [Also in Division D1] An autogeneously bonded non-woven fabric of isotactic polypropylene filaments comprises a layer M at each surface in which the filaments are preferentially orientated in the machine direction and a layer X, constituting 40 to 60% of the total fabric weight, in which the filaments are preferentially orientated in the cross machine direction, each layer consisting of 65 to 90% by weight of matrix filaments and 10 to 35% of lower melting binder filaments, or of filaments having matrix and binder segments in the above proportions, the matrix filaments of the M layers having an average denier of 6 to 20 and a tenacity of at least 2 gm./denier and the matrix filaments of the X layer having an average denier of 26 to 60 and a tenacity of at least 3 gms/denier which is at least 10% higher than the tenacity of the matrix filaments in the M layer, the filaments being disposed so that the ratio MD/45 is at least 1À5 where "MD" is the total length of filament lengths that are in the machine direction and "45" is the total length of filament lengths that are in the bias direction, and XD/45 is at least 1À5 and (MD+XD)45 is 3À5 to 30. The ratios are obtained by the randometer light scattering method described in Specification 1,244,754. Melt-spun polypropylene filaments 4 are quenched by a counter current of air as the pass through elliptical cross-section flow restrictors 5, 6. The elliptical bundle of filaments becomes a ribbon of parallel filaments as it passes over roll 22. The filaments are drawn by passage over rolls 23-27, each roll rotating faster than the proceeding one. Roll 25 and optionally roll 23 is heated. Roll 25 has grooves running along its surface in the axial direction. Segments of the filaments which touch the hot surface of the roll between grooves are additionally drawn and thus increased in tenacity compared to the segments suspended over the grooved portions. The latter become the binder segments. The filaments are electrostatically charged at corona charger 29 and laid on to travelling belt 41 by air jets 30. A pulse of air is supplied at the jet exit alternatively from one side of the ribbon of filaments and then from the other to deflect the ribbon back and forth, thereby depositing filaments predominantly aligned in the crossmachine direction. Similar jets or lines of jets (Fig. 3, not shown) are disposed in front of and behind the cross laying jets but are turned through 90 degrees to produce the machine direction (M) layers. The web is thermally bonded by passage through the nip formed by a resilient roll and a perforated steam emitting roll, the calender of U.S. Specification 3,313,002 being used. The binder segments have an elongation at break of 400 to 800%.