Patent GB-914489-A (GB)
Title: Improvements in and relating to non-woven fabrics
Inventor: SEYMOUR DONALD EDWIN
IPC: B29C55/14
Filed: 1960-07-19
Abstract: Non-woven openwork net materials are made from thermoplastic film of a long-chain molecular structure having at least one surface <PICT:0914489/IV(a)/1> <PICT:0914489/IV(a)/2> <PICT:0914489/IV(a)/3> <PICT:0914489/IV(a)/4> <PICT:0914489/IV(a)/5> embossed with small bosses or raised figures arranged with spaces between adjacent bosses in longitudinal and transverse rows, the row of bosses in each longitudinal row being in staggered arrangement with the bosses in each adjacent row, by stretching the embossed film longitudinally until it takes a permanent set and then transversely to produce a number of short splits extending longitudinally between adjacent longitudinally aligned bosses in each longitudinal row, so that the splits of one longitudinal row pass through the spaces between the transversely adjacent bosses of the two adjacent longitudinal rows, to leave each boss of a longitudinal row with four thinned narrow bands of the partly elongated material integral therewith and extending therefrom, each of these four bands being integral with and extending from an adjacent boss in the two adjacent longitudinal rows of bosses.  Specified materials include polyolefins, e.g. low-density or high-density polyethylene, polypropylene and ethylene-propylene copolymers.  Preferably the embossments are hexagons, arranged in parallel rows in the longitudinal direction of the film and with two parallel flat edges of each of the hexagons in the transverse direction of the film (Fig. 2), the parallel longitudinal rows of hexagons being arranged so that the centres of every four adjacent hexagons are at the angular corners 29, 30, 31, 32 of a rhombus with obtuse angles aligned longitudinally of the film and acute angles transversely of the film.  Fig. 4 shows such a film after longitudinal stretching, the rhombus 29, 30, 31, 32 being distorted as shown, and during transverse stretching, in which the splits 35 appear.  Further transverse stretching results in the formation of a net as in Fig. 5, the hexagons becoming generally circular and the rhombus 29, 30, 31, 32 becoming a square.  Regular hexagons are preferred but irregular hexagons of the form of Figs. 7 and 8 or circular or elliptical projections, possibly with hexagonal flats in the requisite positions, may also be used.  Embossments may be present on one or both faces of the film.  One face may be embossed, and the other may have a raised pattern such that it follows at least some of the lines of the net to be made, thus reinforcing the net. Spacing of the bosses may be non-uniform.  The thermoplastic material may include fillers, colouring agents and stabilizers. A laminated film of a number of layers of the same material, but of differing colours, may be embossed and treated as above.  A net having small holes may be made using a particular thermoplastic material of a gauge such that only a small degree of longitudinal stretching is necessary to cause a permanent set in the material, so that subsequent transverse stretching produces only small holes.  The pitch spacing of the bosses in the rows may be in the range of one hundred to several hundreds to the inch, and the film commensurately thin, to produce a net fabric resembling a porous film.  Longitudinal stretching may be effected on conventional stretching rolls, and transverse stretching on tenters (not shown).  Alternatively transverse stretching may be effected using a shaped former which presses downwardly on the centre of the film.  This method may be utilized to apply transverse stretching only to some portions of the longitudinally stretched film, to produce patterns and concave-convex formations.  The openwork net material, when made, may be given a setting or normalizing treatment by heating for a short period at a low temperature in relation to the fusing temperature of the material.