Patent GB-1166783-A (GB)
Title: Evaporative Spinning Process and Apparatus
IPC: D01D5/04
Filed: 1968-05-10
Abstract: 1,166,783. Dry spinning apparatus. E. I. DU PONT DE NEMOURS & CO. 10 May, 1968 [11 May, 1967], No. 22433/68. Heading B5B. A dry spinning process comprises extruding a solution of a fibre-forming polymer in a volatile solvent through the orifices of a spinneret to form a multiplicity of streams of the solution, and causing a gas at a higher temperature than at least some of the streams to impinge on them, at least part of the gas flowing transversely to the streams, to evaporate the solvent and form filaments of the polymer, in which the streams are extruded at different temperatures and the gas impinges first on the cooler or coolest streams and subsequently on the hotter or hottest. Suitably the streams of solution are arranged in a cylindrical pattern, the streams at the lower or lowest temperature being in the peripheral portion of the cylindrical pattern and the gas impinging first on the peripheral portion of the cylindrical pattern and then on its interior portion. The solution may be extruded at two, or at at least three different temperatures. Suitably the difference between the highest and lowest temperatures of the solution is greater than 5‹ C. and the temperature difference is preferably between 5‹ and 75‹ C. and especially between 10‹ and 50‹ C. The solution may be heated to different temperatures before reaching the spinneret through which it is extruded, or alternatively a solution at a substantially uniform temperature may be brought to different temperatures by non-uniform heat transfer between the solution and the spinneret through which it is extruded. Specified fibres include acrylic, spandex, "Vinyon" (Registered Trade Mark), and cellulosic, e.g. cellulose acetate. Where acrylic fibres are made, the solvent is preferably dimethyl formamide and the gas Kemp gas, essentially a mixture of about 87% nitrogen and 13% carbon dioxide. The impinging gas may be at a higher temperature than any of the extruded streams, and suitably its temperature is at least 100‹ C. higher than that of any of the extruded streams. In a modification, at least two solutions, each of a different fibre-forming polymer, are extruded. In apparatus as shown, a dry, heated gas is introduced in to spinning cell 1 from an annular gas source 2 supplied by gas inlet 3. Outer streams 4 and inner streams 4<SP>1</SP> of a solution of a fibre-forming polymer dissolved in a volatile solvent are extruded through outer orifices 5 and inner orifices 5<SP>1</SP>, respectively, of spinneret plate 6. Inner shells 7 and 7<SP>1</SP> are mounted in cavities 8 and 8<SP>1</SP> of outer shell 9. Inner shell 7 is slightly smaller than cavity 8 in the outer shell and the space between the inner shell and the wall of cavity 8 constitutes the heating chamber for one portion of the spinning solution. Solution inlet 10 at the top of the inner shell communicates with annular groove 11 around the outside of the inner shell, at the top of the heating chamber. Channel 12 leads from the bottom of the heating chamber to a passage 13 and annular supply chamber 14 in an upper distribution plate 21, communicating in turn with outer passages 15 and outer annular recess 16 in a lower distribution plate 22 just above the outer orifices 5. Similarly, the space between the wall of cavity 8<SP>1</SP> and inner shell 7<SP>1</SP> constitutes a heating chamber for the other portion of the spinning solution fed by solution inlet 101 through annular groove 11<SP>1</SP>. Channel 12<SP>1</SP> leads from the bottom of the heating chamber to central passage 17 and central supply chamber 18 in the upper distribution plate 21, which communicates in turn with inner passages 19 and inner annular recess 20 in the lower distribution plate 22 just above the inner orifices 5<SP>1</SP>. The solution fed through inlet 10<SP>1</SP> is heated to a higher temperature than that fed through solution inlet 10. The solution heated to the higher temperature is passed from channel 12<SP>1</SP> to inner annular recess 20 and extruded through orifices 5<SP>1</SP> on concentric circles nearest the centre of the spinneret. The solution fed through solution inlet 10, and heated to a lower temperature, is passed from channel 12 to outer annular recess 17 and extruded through orifices 5 on concentric circles towards the periphery of the spinneret plate. Inner shell 7 and 7<SP>1</SP> are hollow. Steam or other condensable vapour is introduced into wells 25 and 25<SP>1</SP> through vapour inlets 26 and 26<SP>1</SP>, flows through pipes 27 and 27<SP>1</SP> and channels 28 and 28<SP>1</SP> to annular wells 29 and 29<SP>1</SP>, and is exhausted through outlets 30 and 30<SP>1</SP>. Condensate collects in wells 25 and 25<SP>1</SP> to the level of the bottom of pipes 27 and 27<SP>1</SP> and in lower wells 31 and 31<SP>1</SP> communicating with annular wells 29 and 29<SP>1</SP>, any excess condensate being exhausted by the steam through outlets 30 and 30<SP>1</SP>. Thermocouple wells 32 and 321 permit accurate determination of the temperature to which each portion of the solution is heated. The pressure of the steam supplied to each of the vapour inlets is regulated by means not shown to regulate the temperature of the solutions which are to be spun, the temperature in well 25<SP>1</SP> and the remainder of its circulatory system being higher than that in well 25 and its circulatory system. In another heating method, all parts of the solution may be at substantially the same temperature prior to being extruded, acquiring different temperatures during extrusion. A non-uniform degree of heat transfer between the solution and the spinneret will provide this. Thus a heat source such as an electrical core, placed at the centre of the spinneret, may be used to heat the interior streams to a greater extent than the peripheral streams. In the above heating techniques, the temperature differential is created by adding heat to the solution before or during extrusion. Differential cooling removal of heat from a hot solution may also be used to achieve the same result. If desired, the condensate wells may be extended more closely to the spinneret to maintain the polymer solutions at precisely regulated temperatures as closely as possible to the actual moment of extrusion. Insulation may be employed around and within the spinneret and distribution plates; thus, the ring nuts surrounding the spinneret may be highly polished, or covered with aluminium foil or other insulation, to protect the spinneret from over-heating by the hot gas passing by it. By the process of the invention, spinning output can be greatly increased as compared with conventional dry spinning methods at given standards of filament uniformity in the product, or alternatively product quality may be improved without sacrificing output.