Patent GB-573324-A (GB)
Title: Improvements relating to the extrusion of fused filament-forming compositions
IPC: D01D1/04
Filed: 1943-11-24
Abstract: Artificial filaments, foils, films and the like are obtained in a continuous operation by the extrusion of fused thermoplastic compositions, means being provided to introduce at intervals, fresh solid thermoplastic composition into the fusion vessel without interrupting the melting or extrusion of the composition. The solid composition is introduced into the fusion vessel through a lock-chamber capable of being closed to the vessel while open to the outer air for the purpose of charging the lock, or being closed after charging whilst its atmosphere is adjusted as regards pressure and/or composition to that of the fusion vessel, and of being opened to the fusion vessel while shut to the outer air for <PICT:0573324/IV/1> p <PICT:0573324/IV/2> <PICT:0573324/IV/3> <PICT:0573324/IV/4> <PICT:0573324/IV/5> feeding solid composition to the fusion vessel. The molten material is extruded by an inert atmosphere under pressure or by a pump, and in the former case the melting operation and extrusion temperature may be controlled in the manner described in Specification 540,967, whilst in the latter case they may be effected in the manner described in Specification 565,489.  The composition may be fed to the apparatus in the form of pellets, small uniform pieces, powder or grains, and any free atmospheric oxygen is displaced therefrom by flushing the lock chamber with the inert gas or by exhausting the chamber.  Means may be provided to ensure that the lock chamber cannot be opened to the fusion vessel or to the source of inert gas whilst open to the outer air and operation of the lock chamber closures may be effected manually or automatically.  The need for charging fresh composition to the chamber may be detected and visually or otherwise indicated in the manner described in Specification 573,325.  To prevent premature melting the lock chamber may be cooled.  The extruded materials may be drawn by winding up at speeds greater than that of extrusion.  Specified thermoplastic materials which may be employed are superpolymers formed by condensation of aminocarboxylic acids or of diamines and dicarboxylic acids or other condensation superpolymers, a polyvinyl compound, e.g. polymerized vinylidene chloride or vinyl chloride-acetate copolymer, or a polymerized ester of an unsaturated acid, e.g. those of the acrylic or methacrylic acid series, or cellulose derivatives, e.g. cellulose acetate, propionate, butyrate, aceto-propionate, aceto-butyrate, aceto-stearate, and ethyl or benzyl cellulose, or cellulose ether-esters.  Pigments, dyes and the like may be added to the compositions.  The meltspinning apparatus of Fig. 1 comprises a vessel 1 forming a melt chamber 2 and containing an inert liquid 3 which serves to melt the composition, a pool 4 of which collects at the base of the chamber.  The molten material is extruded by pump 6, through filter 8 and jet 9.  A heating jacket 10 surrounds vessel 1. Nitrogen or other inert gas under pressure is supplied to chamber 2 through passage 14.  A thermocouple 16 is connected to relay 17 and serves to indicate when the level of liquid 3 falls below its upper junction.  The solid composition enters chamber 2 from lock chamber 20 and intermediate chamber 21 which is provided with cooling jacket 22.  The chamber 20 is closed to fusion chamber 2 by conical valve 23 carried in stem 24 which passes through disc 26, Fig. 2, and hollow shaft 27, the valve 23 being held in position by spring 31.  The disc 26 pressed upwardly by spring 32 is secured to rotatable shaft 27 and has a port 33 adapted to coincide with port 34 in cover 29 through which a measured charge of composition is fed to the lock chamber. The shaft 27 is rotated by worm gear 36, and causes interrupted bevel gear 41 to engage with successive bevel gears 42, 43, Fig. 3, operating plug valves 46, 47 which in turn control a vacuum main and compressed nitrogen supply respectively connected to chamber 20.  By the mechanism 41, 42, 43 valve 46 is closed before valve 47 is opened.  Cam mechanism 57, 58 engages pin 59 in valve stem 24 and thereby opens the valve 23 after valve 46 has been closed. The shaft 27 is driven from a shaft 60 by an electrically-operated clutch 61 connected to the relay 17.  The relay is also connected to a switch (not shown) which is operated by cam 57 after the shaft has performed one revolution, thereby disengaging the clutch 61.  Fig. 4 shows a modification in which the composition is brought to a uniformly fused state by passing to the spinneret 73 through a tube 72 heated by liquid 74.  The chamber 70 is heated by condensate at the top of jacket 75.  The melt chamber 70 is supplied with nitrogen under pressure in order to extrude the material through spinneret 73.  Lock chamber 80 is supplied with nitrogen under the same pressure as that supplied to chamber 70. Valve 81 is actuated by lever 88.  The solid composition is fed to chamber 80 through manually-operated plug valve 93, the spindle of which has an extension 95, Fig. 5, in which a slot 96 serves to accommodate the lever 88 and so permit opening of the valve 81, when valve 93 is shut.  When valve 93 is open the lever is locked by extension 95 so that valve 81 cannot be opened.  In the Provisional Specification it is stated that the valve connecting the lock chamber with the melt chamber may automatically open under the weight of the charge of material on equalising the pressures in the melt and lock chambers.