Patent GB-1144117-A (GB)
Title: Spinneret for the production of hollow filaments
IPC: D01F1/08
Filed: 1967-09-26
Abstract: 1,144,117. Spinneret for hollow filaments. E. I. DU PONT DE NEMOURS & CO. 26 Sept., 1967 [27 Sept., 1966], No. 43787/67. Heading B5B. A spinneret for the production of hollow filaments comprises a plate 11 having upper and lower surfaces connected by a passage having successively a cylindrical length 12 terminating at shoulder 14, a tapered length 16 continuing therefrom and a capillary length 18; and an insert 20, swaged into this passage and held in position by lip 23 which is formed as the insert is flared into the passage. The insert includes a first cylindrical portion 22 and a second cylindrical portion 24 continuing from bottom surface 21 of the first cylindrical portion. The cross-sectional dimensions of portion 24 are smaller than those of the capillary length 18 of the spinneret passage, thus forming a spinning orifice having the desired width of the wall of the filament to be spun. The insert 20 is also provided with a comparatively large central axial bore 26 that extends partially through the insert and terminates in a flat surface 30. Holes 32 lead straight through from flat surface 30 to bottom surface 21 of the insert and are substantially equispaced radially from the axis of bore 26 to provide uniform polymer flow into the continuous passage formed by cylindrical portion 24 of the insert 20 and capillary length 18. The insert 20 is provided with a lower axial bore 28 which connects to a lateral bore 34. When insert 20 is fitted into the spinneret as shown in Figs. 1 and 4, the bore 34 is aligned with a lateral bore 36 extending through spinneret 10, the combined bores 36, 34 and 28 forming a continuing passageway for supplying fluid to the interior of the hollow filament. When swaged in position, surface 21 of insert 20 engages shoulder 14 in the bore of the spinneret 10 and the upper surface 25 of insert 20 is engaged by lip 23. Thus a positive seal is formed between insert 20 and the spinneret to prevent polymer leakage into the core supply passageways 36, 34 and 28. In operation, the molten polymer composition moves initially into bore 26 of insert 20 and is then uniformly distributed through holes 32 (see Fig. 3) and passes through the passageway defined by cylindrical portion 24 of insert 20 and capillary length 18 to form a hollow filament. As the polymer coalesces around the outlet end of insert 20, a partial vacuum is formed causing a gravity flow of room air through the combined bores 36, 34 and 28 into the centre of the filament. The percentage of filament void may be controlled by capillary geometry, polymer viscosity and the rate of spinning and quenching. While the holes 32 are shown equispaced radially from the centre of an insert right section containing the holes they may alternatively be equi-spaced around the circumference of the right section. The tapered length 16 of the passageway is preferably conical. The apparatus as shown is suitable for the production of round cross-section filaments, but other filaments whose outer surface cross-sections are non-round (i.e. trilobal, tetralobal, or serrated) may be produced. Condensation polymers and copolymers, e.g. polyesters, polyamides and polysulphonamides. especially those that can be readily melt-spun, are preferred in the practice of the invention. If desired, inert gas may be used rather than room air in the production of the hollow filaments. The spinneret has the advantage of providing means accurately to control filament wall thickness, provide a positive seal between the insert and spinneret and enable visual inspection of the polymer passages to be made without removing the insert from the spinneret.