Patent GB-1427281-A (GB)
Title: Network structures
IPC: B29D28/00
Filed: 1974-01-02
Abstract: 1427281 Making nets by moulding, stretching and laminating HERCULES Inc 2 Jan 1974 [16 Jan 1973 (2)] 00152/74 Headings B5A B5B and B5N [Also in Division Dl] To make a net from a sheet of thermoplastics material by stretching to rupture thinner portions of the sheet, parallel continuous main ribs 61, Fig. 9, or 65, Fig. 10, are moulded on one side of the sheet and parallel continuous or discontinuous tie ribs 59 or 67 at an angle to the main ribs are moulded on the other side, so that stretching splits the webs between the ribs and converts the ribs into oriented filaments 53, 54, Fig. 6, forming a net. A polyolefin, PVC, polyamide or polyester sheet is supplied to a pair of rolls directly from an extruder die, or a preformed sheet is reheated. Main ribs 61 transverse to the machine direction are formed by a longitudinally grooved roll 55 (Fig. 7, not shown), co-operating with a circumferentially grooved roll (58) for forming the tie ribs 59. The tie ribs may be continuous or they can be made discontinuous by underfeeding the nip of the rolls (55, 58) so that there is insufficient pressure to force material into the tie rib forming grooves where they intersect with the larger main rib forming grooves. Alternatively, Fig. 10, longitudinal main ribs 65 are formed by circumferentially or helically grooved roll 62 and discontinuous transverse tie ribs 67 are formed by recesses 66 in roll 63. Discontinuous tie ribs prevent thickening of the intersections of the filaments of the web. The main ribs may be closer together or further apart than the tie ribs, and similarly shaped. Their cross-sectional area may be equal to that of the tie ribs but is preferably 1¢ to 100 times greater. The tie ribs may lie at any angle from 15 to 90 degrees to the main ribs and both may be inclined to the machine direction. The sheet may be drawn on a tenter to from 1¢ to over 10 times in two directions at once or in a first direction parallel, perpendicular or inclined to the main ribs and then in a second direction preferably perpendicular to the first during which neck-down may be permitted. The stretching may also be achieved by running the rolls at different speeds to create actual or incipient splits. One net may have laminated to it another having main ribs perpendicular to the first or two further nets 88 and 93, Fig. 18, having their main ribs oppositely inclined at angles of 60 degrees to the first net 91. In Fig. 18 the three nets 88, 91, 93 are passed through a preheater 95, heated laminating rolls 96, 97, and an annealing unit 98. The constructions of Figs. 19 and 21 are obtained by laminating a previously laminated net. Also paper, foil and non-woven fabrics may be laminated to the nets using adhesive, heat or ultrasonic bonding. The nets are used for reinforcing masking tape, wallpaper, fabrics, plastic bags and sanitary and medical pads. A net 110, Fig. 23, may be split into strips 110a to 110d or into individual fibres by lease rods 114 which break the tie filaments 112, Fig. 27. The strips can be fibrillated by a beater bar 116 to partly or completely separate the main filaments 111. The yarn produced may be wound directly on to a spool 122, passed through an air-jet entrainer 123 on to a spool 124, or passed through a down-twister on to a spool 126. Bicomponent filaments may be crimped by passing through a heater 119 so that one component shrinks. A false twist may be imparted to the yarn by a false twisting head 120. The fibres may be cut to staple length and spun. Unfibrillated strips produce maximum coverage when knitted or woven.