US3129272A - Melt-spinning synthetic polymer filaments - Google Patents

Description

April 14, 19-64 D. c. FERRIER ETAL 3,129,272

MELT-SPINNING SYNTHETIC POLYMER FILAMENTS Filed April 28, 1961 2 SheetsSheec 1 K S E m r m m M 58 M; 4F my M 58 MM UL in mm w April 14, 1964 D. c. FERRlER ETAL 3,129,272

MELT-SPINNING SYNTHETIC POLYMER FILAMENTS Filed April 28. 1961 2 Sheets-Sheet 2 lnvenlprs g3 37 He. Z

Attorneys United States Patent Ofifice 3,129,272 Patented Apr. 14, 1964 3,129,272 MELT-SPHNNING SYNTHETKC POLYMER FELAMENTS Duncan Cameron Ferrier, Lian-yr-avon, Cwmbran, and

William Geotfrey Parr, Ahergavenny, England, assignors to British Nylon Spinners Limited, Pontypool, England Filed Apr. 28, 1961, Ser. No. 106,344 Claims priority, application Great Britain May 19, 1960 3 Claims. (Cl. 264-435) The present invention concerns improvements in or relating to melt-spinning synthetic polymer filaments.

In the melt-spinning process, which is the process used for the extrusion of filaments from such fibre-forming materials as the synthetic linear polyamides, polyesters, polyethylenes and polypropylenes, molten fibre-forming material is continuously supplied from a melter or a continuous polymerisation apparatus to a spinneret containing one or more small orifices, and the material is extruded through the orifice or orifices under the pressure exerted on it at the back of the spinneret, such pressure usually being brought about by the action of a rotary metering pump in the supply line of the molten material. It is a common practice in such melt-spinning processes to include a fine grain filter between the metering pump and the spinneret in order that the material to be extruded shall be as free from air bubbles as possible and in order that any foreign bodies in the molten material may be prevented from reaching the spinneret. Such a filter often comprises sand or other fine-grain, inert, particulate substance; and the filter and spinneret are often combined in apparatus known as a pack which can be handled as a unit for insertion in, or removal from, a port in the meltspinning unit itself.

When inserted in a port of the melt-spinning unit, the pack, which in addition to the spinneret and the filter may also contain wire mesh or perforated plate screens above and below the filter, has to be screwed tightly home in order that there shall be a liquid-tight seal between the output pipe of the metering pump and the top of the pack itself. To this end, the pack may, for instance, be carried in a holder which is capable of being screwed into the pack-receiving port of the melt-spinning unit; and subsequently the pack itself is forced upwardly, relative to its holder and against a gasket, by tightening-up a number of grub screws in the bottom lip of the holder which screws bear against a metal ring positioned between said lip and the bottom of the pack. Laterally, the pack is a relatively loose fit within the holder, although, of course, there is no actual looseness between them once the pack has been forced into position by the tightening of the grub screws.

Discontinuity in the melt-spinning operation may arise from several causes, of greater or lesser frequency. Thus, the whole spinning unit itself will have to be removed for internal cleaning after some weeks of spinning; but, prior to that complete cessation, interruptions in normal spinning can, and often will, occur due to metering pump failures, pack leakage or blockage and spinneret defects.

It is with the lessening of the frequency of the latter type of interruption that this invention is principally concerned.

Despite very great care being taken in the manufacture and use of spinnerets, there are always likely to be minor blemishes either in the orifices of the spinneret or on the face of it, which may lead to irregular flow of the molten material through and out of the orifices. But even such blemishes are not themselves responsible for the most frequent interruptions in normal spinning arising from spinneret defects, the primary cause of which, in the case of polyhexamethylene adipamide certainly, is now thought to be the build-up, in time, of a black deposit at the discharge end of an orifice and depending from the spinneret face, which deposit forms an uneven ruff around the filament emerging from the orifice. In the course of the build-up, which may take only a few hours, it is likely that one side of the ruff will become longer than the other, and the effect of this will be to cause the line of flow of the filament to become bent out of the vertical, first to form what is known as a knee, and finally to be bent to such an extent that the filament touches the spinneret face, ceases to flow as a filament, and forms instead what is known as a drip. Apart from the blemishes of the spinneret above referred to, the factors most likely to give rise to a propensity for dripping are the nature of the synthetic polymer itself, including the amount of delustrant which it contains, and the size and shape of the orifices, for instance whether they are circular or are tri-dentate, tri-lobal or other complex shapes, the latter being particularly prone to drips.

The actual occurrence of a drip will normally be forestalled by the routine procedure known as wiping, in which the face of the spinneret is cleaned; naturally, however, such a procedure involves a disruption to the normal spinning operation and is consequently a wasteful and limiting necessity, the frequency of which is desirably kept as low as possible.

Although other methods of ameliorating the trouble are known and practised, one line of approach which has previously been described is to blanket the face of the spinneret with an inert gas, such as nitrogen, so as substantially to exclude free oxygen from polyamine filaments as they emerge from the orifices 0f the spinneret. It is at the basis of such a line of approach that the dripping phenomenon is caused initially by oxidative degradation of some of the fibre-forming material as it emerges from an orifice, at the high temperatures involved, e.g., 280 C. The manner of blanketing the spinneret face previously described was to inject the gas radially inwardly towards the centre of the spinneret face from a number of equi-spaced jets at the top of a cylindrical shield surrounding the said spinneret face.

For a number of reasons, the above-described method of blanketing the spinneret face has not been found to be successful. Probably the main trouble is that the desired conditions of extrusion and cooling of the filaments are too greatly interfered with, either by reason of the provision of too stagnant and deep an atmosphere near to the spinneret or because the method of introducing the gas from a number of jets below the spinneret is not adequate to exclude free oxygen and is actually prejudicial to the proper flow of the filaments. As a result, the previously-described method, even if it were to have been carried-out such that a proper blanketing of the spinneret face occurred, was prone to introduce substantial physical irregularities in the filaments extruded, for example too Wide a range of denier variation; or, alternatively, the blanketing was not adequate enough substantially to reduce the frequency of drips.

Whatever the reasons for this comparative failure, however, we have now found that the drip frequency of certain synthetic linear polymer melt-spinning processes, particularly processes for melt-spinning polyhexamethylene adipamide filaments, can be reduced many times by a process according to the invention involving the introduction of an inert gas immediately below the spinneret face in such a manner that the face is uniformly and completely blanketed by the gas without, however, bringing about any substantial alteration to the normal extrusion and cooling conditions of the filaments in the process concerned. By an inert gas we mean a gas, such as steam or nitrogen, having no chemical action on the molten filaments as extruded.

The invention, therefore, comprises a process for meltspinning a synthetic linear polymer in which molten polymer is extruded through an orifice or orifices in a spin neret plate, and which is characterised by the continuous and uniform provision immediately below the spinneret plate of a substantially homogeneous and laterally unconfined shallow layer of an inert gas in contact with the entire surface area of said spinneret plate.

Thus, the layer of gas should only be at the most an inch or two in depth, in order that the ordinary effects of the ambient atmosphere on the filaments shall not be substantially excluded in the critical region around the point of extrusion. Also the gas must be introduced in a steady uniform manner such that the layer of gas immediately beneath the spinneret face is substantially complete and uniform, and not turbulent.

Super-heated steam is the preferred inert gas, owing to its low density compared with air which permits a shallow layer of the gas automatically to be maintained in close contact with the spinneret plate. This critical feature is not achieved without especial care with other, less buoyant, gases. Steam is also cheap and convenient owing to its availability at the melt-spinning machines.

If the gas, like super-heated steam, is pre-heated to a temperature equivalent to that of the spinneret itself, the gas blanket will neither heat up, nor cool, the spinneret from the desired extrusion temperature of the synthetic polymer in question, nor will the gas, if cold, draw heat from the melt-spinning unit if its supply pipe is led therethrough. Preferably, the gas is introduced into the vicin ity of the spinneret plate via an uninterrupted annular slot, for instance one formed between the lip of the packholder and the spinneret. No specific means, such as a cylindrical shield, is employed laterally to bound the layer of gas; but, if desired, a perforated diffuser ring may be fitted inwardly of the aforementioned slot, such ring being shallow and not having any actual confining effect. In certain constructions of pack, it may be possible to fit, say, a porous sintered metal ring actually within the annular slot, instead of an inner diffuser ring.

Instead of introducing the gas annularly, it may sometimes be desired to introduce it from one side only of the spinneret plate, to travel thereacross in a uniform transverse stream.

In one convenient form of apparatus for carrying out the invention, which will be described in greater detail hereafter, superheated steam at a pressure of lbs. per square inch (gauge) and temperature of 280 C. is led through a pipe fitted in drillings within the metal block at the lower end-portion of the melt-spinning unit to a position above the pack and outside the top gasket between the pack and the output pipe of the metering pump. Steam from the pipe is allowed to emerge into the space between the pack casing and the walls of the port, at a rate controlled by the size of an orifice within a plug fitted in the output end of this pipe, and finds it way down between the pack casing and the walls of the pack-holder, the screwed joint between the latter and the port serving as a crude seal to prevent steam from escaping, and finally emerges through the annular slot between the lower lip of the holder and the spinneret, to converge from all sides uniformly towards the centre of the spinneret face. This is a convenient arrangement, since, prior to starting to extrude through a new pack, the spinning parts including the pack may be purged with the inert gas, in this case steam, so as to remove any air bubbles therefrom. The purging must be effected before the pack has been screwed completely home, so that the gas can enter the top of the pack itself, whence it is normally excluded by the tight fit of the pack, gasket and melt block. Gas can then, if desired, be drawn through the pack by applying suction to the spinneret face, although simply diffusing it through the pack from the top thereof will normally be sufficient.

The above-mentioned convenient form of apparatus will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic side elevation of melt spinning apparatus for spinning molten filaments according to the embodiment and winding them;

FIGURE 2 is a diagrammatic sectional view of the lower end-portion of the melt-spinning unit of FIG- URE l; and

FIGURE 3, is a diagrammatic view looking up at the lower end-portion of the apparatus of FIGURE 2.

Referring firstly to FIGURE 1, there is shown the lower end-portion of a melt-spinning unit comprising a metal block 1 in which is housed melter 2 in which fibreforrning material, such as polyhexamethylene adipamide, is melted and is then withdrawn from a pool of molten material by rotary metering pump 4 and fed via pipe 5 to filter pack 7. The molten material is forced through the filtering medium of the pack (to be described in greater detail below) and emerges from holes in a spinneret plate in the form of continuous filaments 12. A laterally unconfined atmosphere of super-heated steam 10 is maintained in the immediate vicinity of the spinneret plate, the steam having been brought to that region via super-heater 8 and thence through a pipe 29 in block 1 to the top of the pack 7. As will be described with reference to FIGURES 2 and 3, the steam then ilows through the pack-securing parts, to emerge as a substantially uninterrupted circular stream just below, and di rected towards the mid-point of, the face of the spinneret plate. Platen heater 35 surrounds the pack 7, serving to maintain the latter at the correct temperature for extrusion of the molten material. Filaments 12 are cooled by a transverse air stream, solidify, and are brought together into a converged bundle to pass downwardly through stream conditioning tube 14. The converged bundle of filaments is drawn down by godets 16, and is then wound up on package 18 driven frictionally by drive roll 20.

Referring now to FIGURES 2 and 3, the pack 7, fitted within port 3, comprises a casing 9 containing within it layers of sand or other inert particulate matter, of graduated grain-size, having the layer of coarsest grain size at the top. The sand, or other particulate material, is bounded at top and bottom by fine mesh metal screens; and the spinneret plate, with orifices 6, is located bcneath the lower screen at the bottom 11 of the pack. A so-called metal bottle cap" 13 having a serrated top edge 15 surrounds the lower half of the pack to hold together the spinneret, lower screen and casing, and the serrations serve accurately to locate the pack centrally within its holder 17, which holder is screwed into the block 1 at the lower end of the port 3. The final tightening of the pack against a gasket 19, surrounding the outlet of the pipe 5, is elt'ected by a plurality of grub screws, two of which, 21, are shown, in the lip 23 of the holder 17. The grub screws are tightened against a metal bearing ring 25 fitted between the bottom 11 of the pack and the lip 23, so that the pack is forced hard upwardly against the gasket 19, thus forming a liquid-tight seal between the pipe 5, containing the molten polymer material, and the top of the pack, and creating a substantially continuous annular slot 27 between the ring 25 and the lip 23. The superheated steam at 25 lbs. gauge pressure is supplied through pipe 29 at the top of the port 3. A plug 31, having a small orifice 33 through the middle thereof, is screwed into the pipe 29 near to its emergence through the top wall of the port; and the size of the orifice determines the amount of steam allowed to escape into the empty spaces of the port, in unit time. An orifice of a diameter between 0.025 inch and 0.035 inch may prove to be satisfactory, allowing for a steam supply of, say, 1 /2 pounds of steam per hour. Too great a supply of steam must be avoided, as it may create too deep a layer beneath the spinneret plate.

Surrounding the spinneret and the pack holder 17 is platen heater 35; and a steam diffusing ring 37, of wire mesh, is inserted inside the lip 23, having the effect of slightly impeding the steam flow and of thus removing any slight discontinuities, say, in the region of grub screws 21, which there may be in the annular supply of steam emerging from the gap 27, as explained hereafter.

The steam passing through the orifice 33 passes downwardly between the casing 9 and the walls of the port 3, thence between the serrations 15 of the bottle cap, or gasket 13, and between that cap and the pack holder 17, and finally behind the bearing ring 25 and thence inwardly radially through the diffusion ring 37, as indicated by the arrows in FIGURE 3, towards the midpoint of the face of the spinneret plate, in a continuous annular stream from the gap 27. It will be observed that this arrangement provides a relatively shallow homogeneous layer of steam in contact with the entire surface area of the face of the spinneret plate, the flow of which can be controlled so as to allow for at least substantially complete blanketing of the spinneret face without any adverse effect on the filament flow from the spinneret, and without having any material effect on the conditions, particularly of temperature, of extrusion and cooling of the filaments, owing to the practically normal impingement of the ambient atmosphere on the spinning unit.

As an example of the efficacy of the process according to the invention, there are compared the results achieved when melt-spinning 40 denier/ 13 filament yarns of polyhexamethylene adipamide, containing 2% by weight of titanium dioxide delustrant and having a relative viscosity of 33.5, both with and without the specified atmosphere of the preferred inert gas, superheated steam, in the vicinity of the face of the spinneret plate.

Two filament bundles of 13 filaments each were spun from the 26 holes of each of the spinneret plates employed, the holes being of 0.013 inch diameter, such that the polymer throughput was 4 pounds weight per hour. The bundles were wound up separately at a speed of 3930 feet per minute.

A steam atmosphere was maintained continuously in the close vicinity of half the number of spinneret plates employed in the trial, whilst the remainder had no such inert gas atmosphere. No routine wiping of the faces of the spinneret plates that were steamed was undertaken; whilst the others were wiped every 4 hours (with consequential interruption to the spinning process). Even without such routine wiping, the drip rate of the steamed spinuerets was less than that of the others, with a figure of 0.03 per 100 pounds of polymer spun compared with 0.05 per 100 pounds.

Such a trial demonstrates clearly that not only does the invention avoid the waste incumbent in routine wiping procedure, but also enables much larger spinning cakes to be wound than normally, owing to the increased continuity allowed to the spinning process. In addition, such increased continuity is valuable when, instead of winding-up into cakes at the spinning machine, the yarn is forwarded directly and continuously to a draw ing (stretching) stage before winding.

We claim:

1. In a melt-spinning process of the type in which molten synthetic linear polymer is delivered from a source thereof to and through a spinneret pack which includes a spinneret plate having extrusion orifices therein, the improvement which comprises: supplying an inert gas under pressure to the exterior of said spinneret pack at a location upstream of said spinneret plate; guiding and dispersing the inert gas along said pack to the vicinity of said plate and around the periphery of said plate to form a substantially unbroken stream for flowing across the face thereof; and flowing the unbroken stream across the face of said plate to form and maintain a homogeneous and laterally unconfined shallow layer of the inert gas in contact with the entire surface area of said plate.

2. A process as in claim 1 further comprising subsequently cooling the filaments issuing from the spinneret plate by directing against them a transverse stream of air.

3. In a process of operating a melt-spinning machine of the type which includes a spinneret pack fitted into a recess in the body of the machine, said pack having a spinneret plate for discharging extruded filaments from the machine, the improvement which comprises: supplying an inert gas under pressure to the recess upstream of said spinneret pack; guiding and dispersing the inert gas along said pack to the vicinity of said spinneret plate and around the periphery of said plate to form a substantially unbroken stream for flowing across the face thereof; and flowing the unbroken stream across the face of said plate to form and maintain a homogeneous and laterally unconfined shallow layer of the inert gas in Contact with the entire surface area of said plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,252,689 Bradshaw Aug. 19, 1941 2,335,922 Dreyfus Dec. 7, 1943 2,821,744 Spohn et al Feb. 4, 1958 2,841,821 Phipps July 8, 1958 2,918,347 Netarbartole et a1 Dec. 22, 1959 2,957,747 Bowling Oct. 25, 1960

Claims (1)

1. IN A MELT-SPINNING PROCESS OF THE TYPE IN WHICH MOLTEN SYNTHETIC LINEAR POLYMER IS DELIVERED FROM A SOURCE THEREOF TO AND THROUGH A SPINNERET PACK WHICH INCLUDES A SPINNERET PLATE HAVING EXTRUSION ORIFICES THEREIN, THE IMPROVEMENT WHICH COMPRISES: SUPPLYING AN INERT GAS UNDER PRESSURE TO THE EXTERIOR OF SAID SPINNERET PACK AT A LOCATION UPSTREAM OF SAID SPINNERET PLATE; GUIDING AND DISPERSING THE INERT GAS ALONG SAID PACK TO THE VICINITY OF SAID PLATE AND AROUND THE PERIPHERY OF SAID PLATE TO FORM A SUBSTANTIALLY UNBROKEN STREAM FOR FLOWING ACROSS THE FACE THEREOF; AND FLOWING THE UNBROKEN STREAM ACROSS THE FACE OF SAID PLATE TO FORM AND MAINTAIN A HOMOGENEOUS AND LATERALLY UNCONFINED SHALLOW LAYER OF THE INERT GAS IN CONTACT WITH THE ENTIRE SURFACE AREA OF SAID PLATE.

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