GB934336A - Melt-spinning of polymers - Google Patents

Abstract

<PICT:0934336/IV(a)/1> In the melt-spinning of fibre-forming polymers a similar electrical potential is applied to each filament during extrusion, so that the filaments repel one another. The polymer may be melted by heating and forced under pressure through a plurality of fine holes in a spinneret plate, the plate being electrically insulated from ground and having applied thereto a substantial electrical potential, i.e. a positive or negative but not alternating voltage above 500 volts and in general up to about 20 kv. Polymers specified include nylons, polyformaldehyde, polyurethanes, polyvinylidene chloride, and polyesters, e.g. polyethylene terephthalate, polyethylene and polypropylene. In apparatus as shown, the spinneret plate 6, together with its supporting block 7, bolt 8 and filter 9, is electrically insulated from the pack 1 by insulating sheath 14 and insulating ring 15. A D.C. voltage is applied to the plate 6 by the lead 17 from the voltage source 18, lead 17 being insulated from pack 1 by insulating bushing 19. The spinneret pack 1 is grounded at 20. The filaments 10 thus repel one another, and the chance of filament coalescence is reduced. Horn 21, which is also raised to the potential of plate 6 prevents the charged filaments being attracted to ground on the spinning pack at, e.g. point 22. The spinning pack may alternatively be so designed as to eliminate the need for horn 21. In a modification, lead 17 does not pass through pack 1 via bushing 19, but is attached directly to bolt 8 or horn 21. When spinning polymer melts having significant electrical conductivity, e.g. nylons, it is necessary to insulate not only plate 6 but also the spinning pack 1 to prevent an excessive leak of current to ground. This is suitably effected by putting the electrical insulation before the heater 5 (Fig. 1, not shown) and raising all the apparatus downstream of the hopper 3 (Fig. 1, not shown) to a high voltage, the ground connection at 20 being removed. When spinning polymer melts having very high electrical resistance, e.g. polyethylenes, the charged spinneret plate 6 does not provide an adequate time of contact for charge collection by the filaments. In this case also the spinning pack 1 is insulated so that the whole part can be charged, but it is not necessary to insulate the pump 2 and heater 5 (Fig. 1, not shown). The apparatus of Fig. 2, in which only the spinneret plate 6 and its surroundings are charged, is especially suitable for polymers of intermediate properties, e.g. polyethylene terephthalate. A spin finish may be applied to the yarn before it reaches guide 11, suitably by electrostatic spraying, the nozzle of the spin finish applicator being charged to an opposite polarity to that of the spinneret plate.