Patent GB-1445981-A (GB)
Title: Net and method of producing same
IPC: B29C48/305
Filed: 1972-08-11
Abstract: 1445981 Fishing net BEGHIN-SAY 10 Aug 1973 [11 Aug 1972] 37499/72 Heading A1A [Also in Divisions B5 and Dl] A fishing net comprises a regular array of longitudinal continuous filaments A of ribbonlike cross-section and a regular array of transverse stems 21 of a second polymer, the filaments being embedded along all or part of their length in a material 22 consisting of or including the second polymer.  Preferably the net is formed by fibrillation. Using the die of Fig. 2 a film is extruded comprising longitudinal ribbons of material A separated by and covered on one side by a lower melting polymer B and covered on the other side by lower melting polymer B 1 . In example 1 A is nylon 6 (nylon 66 and polyethylene terephthalate are also mentioned) and B and B 1  are polypropylene, the ratio being 30% nylon 6 and 70% polypropylene. The film is cooled by air then by haul-off and cooling roller 10. The film is drawn longitudinally X2 between nip rollers 11, 12 and roll 14, simultaneously contracting laterally by X1.4. The film is embossed between heated smooth roll 15 and embossed roll 16 which is at a lower temperature than and rotates at a lower peripheral speed than roll 15. If the nylon filaments are closer to one surface of the film that surface contacts the embossed roll. At 155C the polypropylene is semimolten whilst the nylon 6 is still solid. The differential velocities shear the embossed polypropylene, producing holes bordered by stems. The embossing causes a longitudinal contraction of X1.4. The net is drawn longitudinally X2.8 between pairs of rollers 24, 25 and 26, 27 then drawn transversely X7 at 130C by a tenter. The product has a weight of 5 g/m<SP>3</SP> and both the longitudinal filaments and the transverse stems are of orientated polymers. In this example the two polymers are incompatible i.e. form distinct phases in the molten state which do not stick together on cooling. These bonds are ruptured during the drawing steps so that the nylon filaments can slip within the polypropylene matrix. Specified modifications include calendering the net before stretching transversely to produce ribbon-like stems, deleting the transverse stretching when the stems comprise an elastic polymer e.g. polypropylene having both atactic and iso or syndiatactic components and block copolymers of polyurethane or polystyrenebutadiene and incorporating up to 25% of polyamide or polyethylene terephthalate into phases B, B 1  to permit a higher production rate. Fibrillation then occurs after embossing. In example 2 an ethylene acrylic polymer is used for component B (polypropylene again being used for B 1 ) and in example 3 a 20% vinylacetate 80% ethylene copolymer is used. These polymers are binders for cellulose fibres hence the nets may be laminated to sheets of cellulosic fibres. The die of Fig. 4 (not shown) produces a sheet having outermost layers of a fourth polymer. Where the stems comprise layers of different polymers and the filaments are spaced widely apart differential shrinkage curls the stems and thereby bulks the net. Alternative processes are briefly specified. Thus a film of ribbons of polymer A interspersed with polymer B may be extruded and surface layers extruded or calendered on. An array of filaments of polymer A may be produced by extrusion or by splitting and drawing a film and a matrix applied by calendering. Finally a film of polymer A sandwiched be-  tween films of matrix polymer(s) is slit to an  array of ribbons which are drawn and then squeezed to form the matrix in the space between the ribbons either during a hot embossing step to form the net or during a prior hot calendering step.