GB875019A - Polyamide melt spinning process - Google Patents

Abstract

<PICT:0875019/IV (a)/1> In melt-spinning synthetic linear polyamides, the polyamide is melted in a closed heated chamber or fed in molten condition into a melt storage chamber and the pool of melt which, in either case, is formed in the lower portion of the chamber is exposed to a mixture of a gas and dry superheated steam, which occupies the free space in the chamber above the pool of melt, until it no longer evolves or absorbs water vapour and its water content remains constant, the volumetric rate of flow of melt through the chamber being sufficiently low to ensure that the period of residence of the melt in the chamber is sufficient to allow a condition of equilibrium to be reached with respect to the migration of water between the melt and the atmosphere in the chamber. The mixture of gas and steam in the melting or melt storage chamber is in free communication with the gas space in the upper portion of a second closed chamber which is at the same pressure as the first chamber but is maintained at a temperature below the boiling point of water at that pressure, the gas being saturated with water vapour in this second or humidifying chamber by introducing steam or water into the chamber in sufficient quantity to cause a pool of water to collect at the bottom of the chamber. The pressure of the atmosphere in both chambers is maintained at a constant predetermined value. As shown, the melt is introduced into a melt storage chamber 8 through a pipe 1 into an annular channel 2 from which it overflows, runs down the wall 3 of the chamber and collects in a sump 4, from which it is fed by a screw metering pump 5 through the outlet 6 to a spinning nozzle. The chamber 8 is closed by a cover plate 7 and is maintained at a constant predetermined temperature above the melting point of the polyamide by the circulation of a heating fluid through a jacket 7a. It communicates through a large diameter pipe 9 with a second closed chamber 10 into which water is sprayed by a pump 13 through the spray nozzle 11. Water collects in a sump at the bottom of the chamber 10 to form a pool of water 12 from which water is recycled by the pump 13, a small supply of fresh water being added to the circulation system through a valve 14. The level of the pool of water 12 is maintained constant by means of a float 16 and regulator 17 which controls an outlet valve 15. The chamber 10 is maintained at a constant temperature by means of a jacket 18 through which a fluid at a constant predetermined temperature is circulated. At the beginning of the spinning process the whole apparatus is evacuated and is then filled with an inert gas such as nitrogen through pipe 1. During spinning additional gas is introduced with the melt from a melting chamber through the pipe 1 and makes up for loss of gas during spinning. The pressure of the gas is preferably maintained slightly above atmospheric. In an alternative arrangement, the second or humidifying cylindrical chamber is provided with a central vertical tube concentric with the vertical walls of the chamber and the annular space between this tube and the walls of the chamber is filled with Raschig rings which are sprayed from above with water raised by means of a circulating pump from a pool of water formed in a sump at the bottom of the chamber. An inert gas such as nitrogen is circulated through the annular column of Raschig rings by means of an axial fan disposed in the central tube. Specification 730,617 is referred to.