Patent GB-1117946-A (GB)
Title: Melt-spinning process and apparatus
IPC: D01D5/084
Filed: 1966-01-19
Abstract: 1,117,946. Melt spun poly-#-caproamide filaments. ALLIED CHEMICAL CORP. 19 Jan., 1966 [19 Jan., 1965], No. 2520/66. Heading B5B. A process for spinning continuous filaments from a filament forming poly-#-caproamide melt containing volatile impurities, comprises extruding said melt at a temperature of 250‹ to 300‹ C., downwardly, to form continuous filaments, through a spinneret and into a zone wherein the resulting filaments contact hot quiescent gas and wherein the temperature, at a point ¢ inch below said spinneret, is at least 40‹ C. higher than the temperature of said melt and at least 315‹ C. but not above the temperature where degradation of the poly-#-caproamide sets in; passing the said filaments through the said hot quiescent gas at at least 315‹C. for not over ¢ sec.; then passing the filaments into contact with a gas in a zone having a temperature below the temperature of the said melt; and finally into contact with a gas having a temperature at least 30‹ C.below the melting point of the said poly-caproamide. Preferably, the polycaproamide spun has a number average molecular weight of at least 24,000, the gas supplied to the quiescent zone contains water vapour at a partial pressure of 10 to 100 mm. of mercury, the gas temperature ¢ inch down from the spinneret is at 320‹ to 380‹ C.; the filaments pass in not over 2 inches of travel from contact with gas having a temperature equal to the melting point of the polycaproamide, into contact with gas having a temperature 30‹ C. below the melting point of the polycaproamide; and gas from the quiescent zone, containing lactam, is withdrawn from the spinning chamber. Polycaproamide melts spun by the process of the invention may contain various dissolved or finely dispersed additives such as stabilizing agents, delustrants, pigments, blended-in polymers, latent crosslinking agents, adhesion-promoting agents and anti-static agents. Apparatus as shown comprises a spinning tower divided into an upper section 20, a mid-section 22, and a lower section 24. A horizontal spinneret 14, has a multiplicity of orifices 16 therein; sealed around said spinneret and closely surrounding the area immediately below the outermost orifices thereof, is a downwardly extending shield 12, the vertical length of which may be adjustable, open at its lower end and provided, at least at its upper end 38, with heating means 44; a chamber 30 surrounding said shield and in communication with the interior thereof via its open lower end, said surrounding chamber having at least one outlet 32 for withdrawing gas therefrom; and extending downward below said shield and gas outlet, walls 42 forming the remainder of the spinning tower and provided with at least one inlet 26 for gas. Outer wall section 28 terminates below in an inwardly projecting lip 34, forming a bottom for outer chamber 30, and is removably connected to outer wall section 60 by a liquid seal 62 or deformable gasket or packing, to allow ready dismantling. The upper section 38 of the shield is in tight physical contact with the lower section 40 to transfer heat from the heated upper portion to the unheated lower portion, thus providing a thermal gradient from the end of band heater 44 to the bottom of lower section 40. This upper section preferably closely surrounds the area immediately below the outermost spinneret orifices, being at a radial distance from these orifices suitably of “ “ inch to 2 inches. Lower section 40 of the heated shield 12 is vertically adjustable by set screw 46 so that the vertical distance from the face of spinneret 14 to the lower edge, 48 of section 40 may be adjusted. The heated shield is sealed around the spinneret face, to prevent air currents thereat, by means of packing retainer 50 for receiving a circular gasket or packing 52; alternatively a liquid seal may be used. Pistons 54 attached to section 38 and received in cylinders 56, contain compression springs 58, which bear against lip 34, urge pistons 54 and wall section 38 upward so as to urge packing 52 into engagement with the face of the spinneret. Below lip 34, lower wall section 42 extends downward forming the lip section 22 of spinning chamber 10, down to gas inlets 26. Below inlets 26, walls 42 continue downward to form the lower section 24 of spinning chamber 10. In operation, heating element 44 is first turned on and allowed to reach thermal equilibrium; filaments 18 are extruded from spinneret 14 and relatively cool gas, suitably air enters spinning chamber 10 through inlets 26. A minor portion of the air moves upwardly through midsection 22 towards heated shield 12, while the remainder of the air moves downwardly through lower section 24 in the direction of travel of filaments 18. Generally from 5 to 20% of the total volume of entering gas passes upwardly through mid-section 22. Gas from this section 22 and from within shield 12 is drawn through the space between the bottom of the heated shield and the annular lip 34, into outer chamber 30 and thence out of the outlets 32. Gas entering through inlets 26 can be maintained at any desired temperature, generally at least 30‹ C. below the polycaproamide melting point so as to effect the desired quick cooling of the filaments when their temperature is near the melting point. The entering gas may be made to enter the chamber uniformly throughout the entire periphery of the chamber, while the flow through inlets 26 can be adjusted so as to be unequal around the periphery. Gas may enter from only one inlet, the gas outlet being opposite thereto, to produce cross-flow quenching, and gas distributing means, e.g. grids, screens or cloths, will advantageously cover inlets 26 to control the gas flow pattern. The humidity of the entering gas may be controlled as desired. Examples are given.