Patent GB-1233763-A (GB)
IPC: D01D4/06
Filed: 1968-07-25
Abstract: 1,233,763. Spinneret. E. I. DU PONT DE NEMOURS & CO. 25 July, 1968 [11 Aug., 1967], No. 35595/68. Heading B5B. A spinning assembly for spinning a liquid such as a polymer melt or solution, and useful in dry-, wet- and melt-spinning comprises a spinneret plate 12 having orifices 27 for spinning liquid into filaments and a support member 11 having channels 26 for supplying liquid to the spinneret orifices 27, a thin metering plate 33 being sealed between the spinneret plate and the support member, the metering plates having apertures 35 which form metering passages to the spinneret orifices, each orifice being connected to a channel in the support member by one of said metering passages in the metering plate, the nearest edges of the channel and orifice being spaced from each other by a distance of 0À4 to 12 times the orifice diameter, each passage having a width W from 1 to 12 times the diameter (D) of the spinneret orifice and from 1 to 12 times the thickness H of the metering plate, said metering plate having a thickness within the range of 0À004 to 0À05 inch, the arrangement being such as to provide metering passages having a resistance to the flow of the spinning liquid at least as great as that of the corresponding spinneret orifices. Preferably, the nearest edges of a channel and its corresponding orifice are spaced a distance of from 0À7 to 6À6 times the diameter of the spinneret orifice, and the width of the metering passages is from 1À1 to 4À0 times the diameter of the corresponding spinneret orifice. Suitably, the metering plate is about 0À01 inch thick. The apertures in the metering plate are preferably non-round, and the metering plate is preferably so apertured and arranged as to provide metering passages of substantially rectangular cross-section. Thus in Fig. 2, metering plate 33 contains metering passages 35, through which the polymer flows radially, and which terminate at the spinneret capillaries 27. An oblong shape of passage is shown in Fig. 2, but it may also be elliptical, circular or irregular when viewed as in Fig. 2, provided all of the passages are alike. In any event, the passages will have substantially rectangular crosssections. Suitably, the ratio of the effective metering length L (see Fig. 3) to the diameter (D) or the hydraulic diameter, if the spinneret orifice is non-round, of the spinneret aperture is from 0À8 to 12, and especially from 1À0 to 6À6. In Fig. 4, each spinneret orifice 27 is connected to two spinning liquid supply channels 26 by the metering passage 35 and the channels are arranged to supply different spinning liquids for spinning bi-component filaments. In Fig. 5 (not shown) a metering passage (35) is shown having one portion of greater width (W) than another portion and thus, in the case of spinning bicomponent filaments as with the apparatus of Fig. 4, making it possible to allow for differences in the flow rates of the two polymers or differences in viscosities; the polymers merge at the upstream portions of spinning capillaries 27 at substantially the same pressure. In the alternative embodiment of Fig. 7, a very thin spinneret plate 12 is shown just underneath metering plate 33. The spinneret plate and the metering plate are stretched transversely in their assembly in the spinning pack the bottom of the spinneret plate resting against ring 15 and being supported by rings 14 and 15. In this form, a metering passage 35 of such proportions that the polymer pressure drop occurring in the passages 35 is substantially in excess of the pressure drop occurring in the spinning capillaries 27, is preferred, such factor being suitably at least 2 to 1. The length of the capillaries is usually very short owing to the use of the very thin spinneret plate 12, so that the pressure drop is usually small; pressure drop in the capillary 27 may be minimized by making the diameter (or equivalent hydraulic diameter of capillary 27 is not round) large in proportion to the height H and width W of the passage 35. The apertured metering plates may be constructed of any suitable rigid material, stainless steel being preferred. The plates are preferably about 0À010 inch thick. Use of the metering plates of the invention enables greater accuracy of metering to be obtained, since as contrasted to the conventional round cross-section metering passages where the pressure drop is proportional to the fourth power of the passage diameter so that slight variations in diameter affect metering accuracies substantially, the present metering plates are so apertured as to provide rectangular cross-section metering passages, the pressure drop being then proportional only to about the third power of the plate thickness, and to only about the first power of the passage width.