US2753594A - Apparatus for use in the melt-spinning of synthetic polymers - Google Patents

Description

July 10, 1956 A. BUCK 2,7

APPARATUS FOR USE IN THE MELT-SPINNING OF SYNTHETIC POLYMERS Filed May 3, 1952 1 k INVENTOR:

5 g J $2M Bum Reuben Kv fig & W I) ATTORNEYS,

APPARATUS FOR USE 1N THE MELT-SPINNING OF SYNTHETIC POLYMERS Alfred Buck, Kusnacht, Zurich, Switzerland, assignor to lnventa A.-G., fiir forschuug und Patentverwertung Luzern, Lncerne, Switzerland Application May 3, 1952, Serial No. 285,949

6 Claims. (Cl. 18-8) This invention consists in an apparatus for use in the melt-spinning of synthetic polymers as is hereinbelow de scribed. To refer first to the prior art, in the polymerisation of e-caprolactam it has long been known that a state of equilibrium occurs between the polymerised fraction and the lactam fraction. Consequently, the polymerisate of E-caprolactam always contains a definite percentage of monomeric lactam, a substantial proportion least of which must be removed from the polyamide if textile threads or bristles of high quality are to be spun. For removing such monomer, the solid polymerisate can be treated, in the form of lumps, granules or other pieces, With an extraction agent, such as water or alcohol, whereby not only can the monomer be completely extracted, but the dimers and trimers also can be at least partly extracted. Another known method of removal consists in the vacuum distillation of the monomer. These two known processes are described in the U. 3. Patent No. 2,241,321 of Schlack of May 6, 1941; the specification of which discloses that the polymerisation and the spinning can be carried out continuously if the monomer is removed directly beyond the polymerisation vessel or chamber or in a separate vacuum vessel. This Schlack process, however, has not proved suitable or successful as a commercial process, because the large size vessels required can only be closed vacuum-tightly with much difficulty, whereas the melt is extremely sensitive to oxygen even when the latter is present in only the smallest traces. Further, the period of time required for the removal of the monomer by the above-mentioned process is so extended that, owing to the rapid establishment of a state of equilibrium, monomers are re-formed to a substantial extent, and the material being treated becomes seriously unhomogeneous.

In addition to the above-mentioned Schlack process, two further processes have also been heretofore proposed and tried, in which the monomer is removed in a continuous spinning process. In the first of these latter two processes the melt coming from the polymerisation vessel is converted into thread form before being spun, in order to be able quickly to evaporate the lactam from the large surface which is thereby formed. However, this process cannot be successfully carried out on a commercial scale without the use of very expensive apparatus. In the second or final one of the aforesaid so-called direct spinning processes the spinning head contains a thin-layer evaporator. It is possible to carry out this latter process in such a manner as to obtain a material which remains homogeneous for a time as regards the monomer content. The latter process has, however, certain disadvantages when carried out on a usefully large scale; and these drawbacks are obviated by employing the apparatus, to be described, according to the present invention. Thus, for example, the output of the prior spinning head was limited, and only small amounts, such as are used for example for producing silk, could be spun. Further, after the spinning head had been in operation for some time, trouble occurred because the melt from time to time States Patent ice A main object of the present invention is to obviate the unhomogeneity of the polymerisate caused by the mentioned inclusions. Further objects are, first, to enable themonomers to be removed quickly and thoroughly, and

second, to obtain a production output rate which is sub-- stantially greater than with the hitherto known apparatus. and can at the same time be adapted within wide limits tothe desired throughputs, while still maintaining a high.

quality of product.

The aforesaid objects are realized, and the former drawbacks overcome, by the use of the apparatus of thepresent invention.

According to the invention, the melt is caused and allowed to flow, as by gravity, in thin layers over the; inner surface of the process chamber or closed vessel used, and over other interior surfaces, such as the outer and I inner surfaces of a number of co-axial cylinders arranged i within the vessel, all in such a manner that there are no surfaces within the vessel which are not covered by themelt, and under these conditions, an inert gas is passed.

through the vessel. With these principles in effect the melt is conducted to the said interior surfaces, for example through co-axial, annular nozzles which. communicate 1 with a distributing passage to which the melt is supplied. The melt layers seal interiorly the reaction chamber walls,

minimizing access of oxygen.

The melt is spread interiorly over the outside and in side surfaces of the coaxial cylinders by means of a suit-- able distributing system and the melt runs off from the cylinders under the action of gravity. The various cylinders should be about equally supplied with the melt and all of them may have the same length, namely a length which is adapted to suit the optimum state of equilibrium of the polymerisate with normal charge. The melt is supplied thoroughly in such a manner that thereis no surface which is not covered by the melt between the nozzle outlet and the outlet from the vessel in which the nozzles are disposed, including the surface of the vessel itself. This prevents the deposit at any place of polyamide particles which would become oxidized in the course of time and would be thereby entrained in the melt in the form of inclusions and so cause unhomogeneity in the polymerisate.

In order to accelerate the evaporation of the monomer by partial pressure and to eifect its removal. a filling gas is blown in countercurrent through the system under a slight superatmospheric pressure. For this purpose an inert gas or gas mixture which contains less than 0.003% oxygen is used.

In one aspect the invention is for the progressive meltspinning of caprolactum polymerisate wherein, within a gas-tight chamber, the melt, in fluent condition, is caused to flow in protective layers over the inner wall surface of the chamber and over any other interior surfaces such as surfaces of special cylindrical elements; whereby such interior surfaces are maintained covered by the melts; and in such method causing an inert gas to flow into, through and out from such chamber, operative to accelerate the evaporation of the monomer and effects its removal; suit able filling gases for this purpose being nitrogen, carbon dioxide, steam and others.

The apparatus of the invention is illustrated, by way of example, in the accompanying drawing, in which Fig. 1

is a sectional elevation of the apparatus, and Fig. 2 is a detail view on a larger scale.

Referring to the drawing, the melt is supplied by the pipe 1 to a ring-shaped distributor or manifold chamber 2 in a vessel d, said chamber equalizing the pressure of the melt. A series of annular concentric rings 6 define a series of annular concentric channels 4. Passageways 3' branch off from the chamber 2 into the channels 4. A series of concentric cylinders 8 have their upper ends 5 in the form of guides extending into the channels 4 and forming with the rings 6 annular slit nozzles 7 communicating with said channels. The melt is discharged from these slit nozzles 7 in the form of thin annular films and runs down over the guides 5 and down on the inside and also on the outside surfaces of the cylinders 8 and also on the inside surface of the vessel 9 but does not flow over the inner surface of the inside cylinder. The film flows into the lower part of the vessel 9 which preferably formsa casingfor the apparatus.

An inert gas is introduced through the pipe 12 and is led away through a pipe 10. The melt is withdrawn together with the evaporated monomer through the pipe 11.

Example A polymerisate of e-caprolactam having an extract content of ll percent was passed on to seven surfaces through a spinning head as described above having an average diameter of 34 centimeters and evaporating surfaces of a length of 18 centimeters. The throughput amounted to 109 grams per minute of polymerisate and 60 liters per minute of filling gas. The temperature was of the order of 245 centigrade. A slight excess pressure was present in the apparatus. The extract content of the threads obtained amounted to 6 percent.

What is claimed is:

1. An apparatus for the treatment of polyamides containing monomers preliminary to meltspinning, comprising an upright gas-tightly closed vessel, a number of upright coaxial cylinders disposed in the vessel, nozzles near the upper ends of said cylinders from which the melt flows downwardly in thin layers for distribution over the outer surface of the cylinder of smallest diameter and over the inner and outer surfaces of the other cylinder or cylinders and over the inner surface of the vessel, while maintaining all surfaces between the nozzle outlets and the outlet from the vessel covered by the melt and means for conducting the melt to the spinning nozzles.

2. An apparatus according to claim 1 comprising a distributing passageway communicating with the nozzles, i

and means for conducting the melt to the passageway for distribution to the nozzles.

3. An apparatus according to claim 1 in which the nozzles define channels, the upper ends of the walls of the cylinders extending into said channels respectively, the walls of the channels being spaced a short distance from the surfaces of the cylinders, and from the surface of the vessel to form openings through which the melt is adapted to be discharged from said nozzles and over said surfaces in the form of thin layers.

4. A distributor system for the treatment of polyamid'es containing monomers preliminary to melt-spinning comprising a vessel, a ring-shaped distributor or manifold chamber in said vessel, an inlet for the melt in said chamber, rings defining a series of annular concentric channels, passageways branching off from said chamber and leading into said channels, annular concentric guides extending into said channels to form with said rings annular slit nozzles'communicating with said channels, said guides extending down in said vessel from said rings in annular form to cause the melt discharged from said slit nozzles to flow downward as thin annular films over said guides, and means for passing an inert gas through said vessel countercurrent to the downwardly descending films and in contact therewith to carry away the evaporated monomers from the melt.

5. A distributor apparatus employed in connection with the melt-spinning of polyamides comprising a vessel, a ring-shaped distributor or manifold chamber in said vessel, an inlet for the melt to said chamber, a series of rings in encompassing relationship defining annular channels, passageways leading from said chamber into said channels, annular guides extending between adjoining rings and into positions opposite said channels to form with said rings on opposite sides of the guides, slit nozzles for the discharge of the melt therethrough from said channels, said guides defining surfaces extending downward in said vessel and along which the melt is adapted to flow after discharge from said nozzles to allow the monomer to evaporate oil, and means for discharging the evaporated monomer from said vessel.

6. A distributor apparatus employed in connection with the melt-spinning of polyarnides comprising a vessel, an annular distributor or manifold chamber in said vessel, an inlet for the melt to said chamber, a series of circular rings of different diameters in concentric relationship defining on opposite sides circular channels opening on inner andouter cylindrical surfaces, whereby the confronting channels of adjoining rings conjointly form annular spaces, passageways leading from said chamber into said spaces, cylindrical concentric guides with their axes substantially vertical extending at their upper ends between adjoining rings and into said spaces to form with said rings on opposite sides of the guides, slit nozzles for over the surfaces of said guides as thin cylindrical films,

and means for discharging the evaporated monomers from said vessel,

References Cited in the file of this patent UNITED STATES PATENTS 2,089,945 Converse et a1. Aug. l7, 1937 2,253,176 Graves Aug. 19, 1941 2,687,552 Gabler Aug. 31, 1954

Claims (1)

1. AN APPARATUS FOR THE TREATMENT OF POLYAMIDES CONTAINING MONOMERS PRELIMINARY TO MELT-SPINNING, COMPRISINGING AN UPRIGHT GAS-TIGHTLY CLOSED VESSEL, A NUMBER OF UPRIGHT COAXIAL CYLINDERS DISPOSED IN THE VESSEL, NOZZLES NEAR THE UPPER ENDS OF SAID CYLINDERS FROM WHICH THE MELT FLOWS DOWNWARDLY IN THIN LAYERS FOR DISTRIBUTION OVER THE OUTER SURFACE OF THE CYLINDER OF SMALLEST DIAMETER AND OVER THE INNER AND OUTER SURFACES OF THE OTHER CYLINDER OR CYLINDERS AND OVER THE INNER-SURFACE OF THE VESSEL, WHILE MAINTAINING ALL SURFACES BETWEEN THE NOZZLE OUTLETS AND THE OUTLET FROM THE VESSEL COVERED BY THE MELT AND MEANS FOR CONDUCTING THE MELT TO THE SPINNING NOZZLES.

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