Hollow Filament Spinneret

Abstract

A spinneret provided with a spinning nozzle having a plurality of arcuate segments whose ends bear inner, inwardly tapered enlargements at the outer one-third portions of the segments.

Description

BACKGROUND OF THE INVENTION

This invention relates to an improved spinneret for the production of hollow filaments.

It is well known that spinnerets with specially arranged arc-like slots can be used in the manufacture of synthetic filaments having a hollow core. Molten polymer forced through a slot forms a bulge and as a consequence of the bulging and the special arrangement, the polymer issuing at adjacent slot ends coalesces a short distance below the spinneret face. While spinnerets of the prior art function to produce hollow filaments, their use has led to open or ribbonized filaments after a relatively short period of operation.

SUMMARY OF THE INVENTION

In a spinneret plate provided with at least one nozzle, said nozzle being defined by a substantially symmetrical pattern of arcuate end-to-end slots interrupted by webs, the improvement comprising, said slots having ends bearing inner inwardly tapered enlargements at the outer one-third portions thereof, the inner one-third portion of said slot being of substantially uniform width.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, bottom view of a spinneret showing the arcuate segments or orifices of one spinning nozzle.

FIG. 2 is a partial sectional view taken along irregular line 2--2 of FIG. 1 with the spinneret in its normal position.

FIG. 3 is a cross-sectional view of a filament produced with the spinneret of FIG. 1.

FIG. 4 is a view similar to FIG. 1 showing another arcuate orifice of the invention.

FIG. 5 is a cross-sectional view of a filament produced with the spinneret of FIG. 4.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Only one of the plurality of spinning nozzles usually provided in a spinneret plate 10 has been shown. The nozzle in FIGS. 1 and 2 has four arcuate orifices or slots 12 which are separated by webs 14 and otherwise surround a solid center portion 16. Each of slots 12 bear inner inwardly tapered enlargements 18 at their outer ends, these enlargements are within the area extending from the center of the nozzle bounding the outer one-third portions 12a of the slots. The inner one-third portion 12b of the slot is of substantially uniform width.

FIG. 3 shows a cross section of a filament of the type produced by the nozzles illustrated in FIG. 1. The filament has a substantially circular core free of protuberances. The dotted lines indicate where polymer from adjacent segments has coalesced and similarly FIG. 5 illustrates a cross section of a filament produced by the nozzles shown in FIG. 4.

FIG. 4 shows arcuate orifices having larger, blunt-tipped tapered enlargements 18' with corresponding one-third portions 12a', 12b'. The arcuate orifices in FIGS. 1 and 4 have dimensions represented by letters a through g. Nominal values, in inches, for dimensions indicated are: a, 0.033; b, 0.004; c, 0.003; d, 0.0065; e, 0.007; f, 0.002 and g, 45.degree. .

The spinnerets of the present invention will preferably have nozzles with four slots 12 since four webs 16 provide good strength and are readily adaptable to the production of hollow filaments with a relatively smooth, nearcircular core. However, two, three, five or more segments may be used if desired. For example, three-segment nozzles can be used to produce triangularly shaped cores. In some instances, for example, when relatively high-velocity cooling air is used to quench the molten polymer near the spinneret face, it may be desirable to increase the amount of polymer in the vicinity of the point of coalescence by increasing the size of the enlargements. Such increases can lead to the formation of squarish holes and although suitable for spirally crimped filaments arising from nonuniform quenching, such filaments are not desired for use in stuffer-box crimping.

The enlargements must begin at the ends of a slot and not extend beyond one third the length L of the slot. The enlargements are also tapered inwardly into the center portion 16 of the spinning nozzle. Preferably, the enlargement will not protrude more than about 35% of the distance from the inner boundary to the center of portion 16. The tapering angle g should be less than 80.degree. and more than about 5.degree.. Preferably, g will be 20.degree. to 60.degree.. The area ratio, o/ I, wherein 0 equals the area in square mils, of an outer one-third portion (i.e., 12a or 12a') and I equals the area, in square mils, of the inner one-third portion (12b or 12b') should be at least 1.1 and preferably should not exceed about 1.5. In addition, the total area of the slot should not exceed 400 square mils. Preferably, the area ratio should be from about 1.15 to about 1.40.

A spinneret having 450 nozzles similar to those of FIG. 1 but without the enlargements, having an area ratio of about 1.0, was used to make hollow filaments and in periodical determinations was found to produce hollow filaments (17% void) with up to 20 improperly coalesced filaments. Under identical conditions, a spinneret having 450 nozzles differing only in the presence of enlargements of the type shown in FIG. 1 with an area ratio of 1.16 produced hollow filaments (14% void) and no improperly coalesced filaments.

In the spinnerets of this invention, the tapered enlargements must be at the inner portion of the segment. This particular structure causes a velocity differential to occur in polymer flow through the nozzle to set up force moments in the segments that favors coalescence. Such polymer velocity differential is indicated by the arrows in FIG. 2.

The orifices are generally of symmetrical shape with all orifices in a nozzle being essentially the same. However, it is not necessary that all orifices be identical and variations may be introduced if desired, for instance, to produce unsymmetrical filaments.

It is not essential that the inner boundary of the segment be the arc of a circle. Straight or curving lines may also serve to define the inner boundary but should not differ too greatly from a circular boundary because of changes in polymer distribution. In the practice of the present invention, the width of the web is preferably less than the width of the arcuate segment but widths less than about 0.002 inch should be avoided because of mechanical inadequacy.

It has been found in practice that the viscosity of the molten polymer varies more than the other factors and when the coalescence performance is borderline, day-to-day variations in viscosity can lead to continuing interruptions of the process. The spinnerets of the present invention are less sensitive to fluctuations in viscosity and have been much more effective in producing hollow filaments having a low denier per filament.

The spinneret of the present invention may be used to produce hollow filaments from any melt spinnable synthetic polymer exhibiting bulging during spinning and is particularly suitable for use with polyesters such as polyethylene terephthalate and its copolyesters. What is claimed is: 1. In a spinneret plate provided with at least one nozzle, for melt spinning filaments from molten polymers, said nozzle being defined by a substantially symmetrical pattern of four arcuate end-to-end slots interrupted by webs, said nozzle forming a filament having a single hollow core the improvement comprising, said slots having ends bearing inner inwardly-tapered enlargements at the outer one-third portions thereof, adjacent ends having proximate sides straight and parallel throughout their entire lengths, said slots having outer boundaries, said outer boundaries being the arc of a circle, the inner one-third portion of said slot being of substantially uniform width, the ratio of the distance c between adjacent slots and the width b of the slots being less than unity, said single hollow core being relatively smooth. 2. The spinneret plate as defined in claim 1, the ratio of the area of an outer one-third portion to the area of the inner one-third portion being in the range of from about 1.15 to about 1.40. 3. The spinneret plate as defined in claim 2, said ratio being 1.16. 4. The spinneret as defined in claim 1, said enlargements being inwardly tapered at an angle with respect to the end of the slot of less than 80.degree. and more than about 5.degree.. 5. The spinneret as defined in claim 4, said angle being between 20.degree. to 60.degree. .

Claims

What is claimed is:

1. In a spinneret plate provided with at least one nozzle, for melt spinning filaments from molten polymers, said nozzle being defined by a substantially symmetrical pattern of four arcuate end-to-end slots interrupted by webs, said nozzle forming a filament having a single hollow core the improvement comprising, said slots having ends bearing inner inwardly-tapered enlargements at the outer one-third portions thereof, adjacent ends having proximate sides straight and parallel throughout their entire lengths, said slots having outer boundaries, said outer boundaries being the arc of a circle, the inner one-third portion of said slot being of substantially uniform width, the ratio of the distance c between adjacent slots and the width b of the slots being less than unity, said single hollow core being relatively smooth.

2. The spinneret plate as defined in claim 1, the ratio of the area of an outer one-third portion to the area of the inner one-third portion being in the range of from about 1.15 to about 1.40.

3. The spinneret plate as defined in claim 2, said ratio being 1.16.

4. The spinneret as defined in claim 1, said enlargements being inwardly tapered at an angle with respect to the end of the slot of less than 80.degree. and more than about 5.degree..

5. The spinneret as defined in claim 4, said angle being between 20.degree. to 60.degree. .