US20050087900A1

US20050087900A1 - Spundbonding spin pack characterized by uniform polymer distribution and method of use

Info

Publication number: US20050087900A1
Application number: US10/960,371
Authority: US
Inventors: Martin Allen; Rachelle Bentley
Original assignee: Nordson Corp
Current assignee: Saurer AG
Priority date: 2003-10-23
Filing date: 2004-10-07
Publication date: 2005-04-28

Abstract

A meltspinning apparatus that provides for uniform distribution of a flow of a melt-processable thermoplastic polymer in a machine direction of the meltspinning apparatus. The meltspinning apparatus includes a spin pack having a plurality of side-by-side coathanger-shaped distribution chambers. Each of the distribution chambers uniformly distributes the polymer flow in the machine direction so that the molten polymer has a substantially uniform residence time in the chamber during distribution.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/513,676 filed on Oct. 23, 2003, the disclosure of which is hereby incorporated in its entirety by reference herein.

FIELD OF THE INVENTION

The invention relates generally to melt-spinning apparatus and methods, and more particularly, to a spin pack for a melt-spinning apparatus and methods of forming nonwoven webs with a melt-spinning apparatus.

BACKGROUND OF THE INVENTION

The spunbonding process is a melt-spinning technology used for forming nonwoven webs of filaments or fibers composed of one or more thermoplastic polymers such as polyethylene, polypropylene, and polyester. Spunbond nonwoven webs are fashioned into many consumer and industrial products, including disposable hygienic articles, disposable protective apparel, fluid filtration media, and household durables. Spunbonding processes generally involve pumping one or more molten thermoplastic polymers through a spin pack that distributes, filters, combines, and finally extrudes continuous filaments of the constituent thermoplastic polymer(s) through an array of thousands of spinneret orifices in a spinneret. After extrusion, the filaments are drawn or stretched by, for example, an impinging high-velocity airflow that accelerates the filament velocity and then quenched to cause solidification. The drawn filaments are propelled toward a forming zone and collected on a moving collector to form the spunbond nonwoven web.
Multicomponent filaments consist of two or more thermoplastic polymers that have separate flow paths that are manipulated as the molten thermoplastic polymers pass through the spin pack. More specifically, the spin pack distributes the flow of each constituent thermoplastic polymer in the machine and cross-machine directions before combining the polymers in a set of downstream configuration plates and extruding the combined polymers from the array of spinneret holes. Multi-component fibers enable a manufacturer to take advantage of the material-specific properties of different thermoplastic polymers simultaneously, often with synergistic results.
In conventional spin packs, the molten thermoplastic polymer from each inlet port is distributed initially in the cross-machine direction and then distributed by downstream flow passageways in the machine direction by multiple triangular or rectangular slots. A stream of thermoplastic polymer is supplied through an inlet communicating with each slot at its apex. Frequently, the inlet is angled relative to the apex so that the alignment of the fluid flow is not directed vertically toward the base of the slot opposite the apex. The thermoplastic material flows toward a slotted outlet at the base of each of the slots and is supplied to a set of holes positioned downstream of the outlet. The thermoplastic material in the slot spreads radially outward from the apex toward the base so that the fluid pressure and flow rate (i.e., mass flow) proximate the periphery of the slotted outlet is less than the fluid pressure and flow rate near the center of the slotted outlet. The non-uniformity in the fluid pressure and flow rate present at the slotted outlet is amplified as the thermoplastic polymer flows through downstream flow passages in the spin pack. Because of the variations in the fluid pressure of the thermoplastic polymer, unacceptable irregularities are observed in the nonwoven web.
Conventional configuration plates are formed by etching or electroforming thin metallic sheets with patterns of recesses, slots and throughholes configured to combine thermoplastic polymers to form multicomponent filaments. The configuration plates are typically thinner than about 0.060″ and, hence, lack robustness. Although relatively inexpensive, the inherent inability to adequately control the etching process produces inaccuracies that cause the geometries of the recesses, slots and throughholes in the configuration plates to be non-uniform and to not display reproducibility from plate to plate. Significant variations in fluid mass flow and pressure occur as the thermoplastic polymers flow through the configuration plates, which lead to observed nonuniformities in the nonwoven web. Another disadvantage of such thin configuration plates is that heating to a temperature sufficient to remove thermoplastic residue in the recesses, slots and throughholes may cause warpage that, if extreme, may prevent reuse.
It would be desirable, therefore, to provide a spin pack for a melt-spinning apparatus capable of more uniformly distributing the thermoplastic polymer in the machine direction.

SUMMARY

In one embodiment of the invention, a spin pack is provided for forming a molten polymer into filaments. The spin pack includes a distribution plate with a length, a width, and a plurality of distribution chambers. Each of the distribution chambers has an inlet receiving a flow of the molten polymer, a slotted outlet having a major axis oriented substantially parallel to the width, and a coathanger-shaped distribution passageway coupling the inlet with the slotted outlet. The spin pack further includes a spinneret downstream from the distribution plate. The spinneret has a plurality of channels and a plurality of spinning orifices from which the filaments are discharged. Each of the spinning orifices is associated with one of the channels. The channels are arranged in a plurality of columns aligned along the width. Each of the channels receives the flow of the molten polymer from the slotted outlet of one of the distribution chambers.
In another embodiment of the invention, a method of operating a meltspinning apparatus is provided for forming a plurality of filaments from a flow of a molten polymer. The method includes moving a collector in a travel direction, distributing the flow of the molten polymer in a first direction generally perpendicular to the travel direction, and distributing the flow of the molten polymer in a second direction generally parallel to the travel direction among a plurality of coathanger-shaped distribution chambers to form a corresponding plurality of sheets of the molten polymer spaced apart in the first direction. The distributed flow of the molten polymer in each of the plurality of sheets is supplied to a plurality of channels aligned in the travel direction for forming a plurality of filaments. The filaments are collected on the collector.
In accordance with the principles of the invention, the thermoplastic polymer(s) is/are distributed in the machine direction of the spin pack by a plurality of coathanger distribution chambers so that the flow rate and fluid pressure is substantially uniform in the machine direction before streams of the polymer(s) flow downstream for combining (if necessary) and extruding. As a result, the pressure of any single stream of thermoplastic polymer among the multiple streams flowing through the spin pack downstream of the coathanger distribution chambers is substantially equilibrated to the fluid pressure of any other stream from among the multiple streams. Because the thermoplastic polymer is more uniformly distributed in the machine direction, significantly greater uniformity is observed among the thermoplastic filaments extruded from the spinning orifices in the downstream spinneret. Each spinning orifice therefore receives a polymer stream having a similar thermal history and having more uniform physical and chemical properties. The distribution plate of the invention is easily scalable to conform to varying numbers and distributions of spinning orifices.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
FIG. 1 is a diagrammatic perspective view of a spunbonding apparatus with a spin beam assembly incorporating a spin pack in accordance with principles of the invention;
FIG. 2 is a perspective view partially in cross-section of the spin pack of FIG. 1;
FIG. 3 is an exploded view of the spin pack of FIG. 2;
FIGS. 4 and 5 are top and end views, respectively, of the assembled spin pack of FIG. 2;
FIG. 6 is a cross-sectional view of a transfer plate of the spin pack taken generally along line 6-6 of FIG. 4;
FIG. 7 is a cross-sectional view taken generally along line 7-7 of FIG. 4;
FIG. 8 is a detailed view of a portion of FIG. 7;
FIG. 9 is a cross-sectional view taken generally along line 9-9 of FIG. 7;
FIG. 9A is a cross-sectional view taken generally along line 9A-9A of FIG. 9;
FIG. 10 is a top view of the first configuration plate of the spin pack of FIG. 2;
FIG. 10A is a detailed view of a portion of FIG. 10;
FIG. 11 is a top view of the second configuration plate of the spin pack of FIG. 2;
FIG. 11A is a detailed view of a portion of FIG. 11;
FIG. 12 is a top view of the third configuration plate of the spin pack of FIG. 2;
FIG. 12A is a detailed view of a portion of FIG. 12;
FIG. 13 is a top view of the fourth configuration plate of the spin pack of FIG. 2;
FIG. 13A is a detailed view of a portion of FIG. 13;
FIG. 14 is a top view of the fifth configuration plate of the spin pack of FIG. 2;
FIG. 14A is a detailed view of a portion of FIG. 14;
FIG. 15 is a top view of the sixth configuration plate of the spin pack of FIG. 2;
FIG. 15A is a detailed view of a portion of FIG. 15;
FIG. 15B a cross-sectional view of a transfer plate of the spin pack taken generally along line 15B-15B of FIG. 15A;
FIG. 16 is a top view of the spinneret of the spin pack of FIG. 2; and
FIG. 16A is a cross-sectional view of the spinneret of the spin pack taken generally along line 16A-16A of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is directed generally to a spin pack for a meltspinning apparatus having improved polymer distribution in the machine direction. Although the filaments will be described herein as being formed using an exemplary meltspinning apparatus, it should be understood that modifications to the exemplary meltspinning apparatus described herein could be made without departing from the intended spirit and scope of the invention.
With reference to FIG. 1, a spunbonding apparatus 10 is equipped with an extruder 12 that converts a solid melt-processable thermoplastic polymer (Polymer A) into a molten state and transfers the molten polymer under pressure to metering pump(s) 16. A second solid melt-processable thermoplastic polymer (Polymer B) is converted by another extruder 14 into a molten state and transferred under pressure to metering pump(s) 18. Pellets of the solid thermoplastic polymers are placed in hoppers 11, 13 and fed to the corresponding one of extruders 12, 14 for melting and transfer.
The two melt-processable thermoplastic polymers may each be selected from among any commercially available spunbond grade of a wide range of thermoplastic polymer resins, copolymers, and blends of thermoplastic polymer resins including, but not limited to, polyolefins, such as polyethylene and polypropylene, polyesters, nylons, polyamides, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, and cellulose acetate. Additives such as surfactants, colorants, anti-static agents, lubricants, flame retardants, antibacterial agents, softeners, ultraviolet absorbers, polymer stabilizers, and the like may also be blended with either thermoplastic polymer. Each constituent thermoplastic polymer may be identical in base composition and differ only in additive concentration.
Metering pumps 16, 18 pump metered amounts of the corresponding thermoplastic polymer through distribution chambers 17, 19, respectively, extending through a die body 25 to a spin pack 20. Distribution chambers 17, 19, which may be coathanger distribution chambers, are oriented with a major dimension aligned in the cross-machine direction for distributing, preferably uniformly, the corresponding thermoplastic polymers in the cross-machine direction (CD). The spin pack 20 contains flow passageways that cooperate for distributing and combining the two polymers received from the distribution chambers 17, 19 for discharge from a spinneret 22. The thermoplastic polymers are typically raised to elevated temperatures in the extruders 12, 14 and maintained at such temperatures in the spin pack 20, which is heated and supported by the surrounding die body 25, to obtain an extrudable melt.
A descending curtain of filaments 24 is quenched to accelerate solidification by a cross-flow of cooling air from a quench duct 27. The filaments 24 are drawn into a filament-drawing device 26 that directs high velocity sheets of process air in a downwardly direction generally parallel to the length of the filaments 24. Because the filaments 24 are extensible, the converging, downwardly-directed sheets of high-velocity process air apply a downward drag that attenuates the filaments 24. Exemplary filament-drawing devices 26 are disclosed in U.S. patent application Ser. No. 10/072,550, U.S. Pat. No. 4,340,563, and U.S. Pat. No. 6,182,732, the disclosures of which are hereby incorporated herein by reference in their entirety. Other types of filament-drawing devices 26 are contemplated by the invention.
The filaments 24 discharged from filament-drawing device 26 are propelled toward a porous collector 28 and deposited in a substantially random manner as substantially flat loops on the collector 28 to aggregately form a nonwoven web 30. The collector 28 moves in a web direction, represented by the arrow labeled MD, parallel to the length of the nonwoven web 30. The width of the nonwoven web 30 deposited on collector 28 is approximately equal to the width of the curtain of filaments 24. Positioned below the collector 28 is an air management system 32 that supplies a vacuum transferred through the collector 28 for attracting the filaments 24 onto the collector 28 and disposing of the high-velocity process air discharged from the filament drawing device 26 so that filament laydown is relatively undisturbed. Exemplary air management systems 32 are disclosed in U.S. Pat. No. 6,499,982, the disclosure of which is hereby incorporated by reference herein in its entirety.
Additional spunbonding apparatus, not shown but similar to spunbonding apparatus 10, and meltblowing apparatus (not shown) may be provided downstream or upstream of spunbonding apparatus 10 for depositing one or more additional spunbond and/or meltblown nonwoven webs 30 of either monocomponent or multicomponent filaments either as a substrate for receiving nonwoven web 30 or onto an exposed surface of nonwoven web 30. An example of such a multilayer laminate in which some of the individual layers are spunbond and some meltblown is a spunbond/meltblown/spunbond (SMS) laminate made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer containing filaments 24.
With reference to FIGS. 2 and 3, the spin pack 20 includes a transfer plate 34, a distribution plate 36 downstream from the transfer plate 34 that divides the flow of each polymer in the machine direction (MD), a set 38 of configuration plates 40, 42, 44, 46, 48, and 50 downstream from the distribution plate 36 that combines polymer A and polymer B to form multicomponent filaments, and the spinneret 22 that has spinning holes from which the multicomponent filaments are extruded. The two polymers are segregated while in the die body 25, as well as while flowing in the transfer plate 34, the distribution plate 36, and configuration plates 40, 42, 44, 46, and 48, and combined at the downstream-most configuration plate 50 and spinneret 22. Threaded fasteners 54 are inserted through registered holes extending about the periphery of the assembled spin pack 20 and thread into internally threaded holes 56 contained in the spinneret 22. The holes in the transfer plate 34 may be countersunk to an extent that the heads of the fasteners 54 are below the upstream planar surface of the transfer plate 34. Alternatively, the fasteners 54 may be threaded into threaded holes 56 in the transfer plate 34 with the heads positioned in countersunk holes provided in the spinneret 22. Dowel pins 58 are inserted through registered holes in the assembled spin pack 20 to ensure proper positioning during assembly.
With reference to FIGS. 2-6, immediately downstream from the die body 25 is the transfer plate 34 that includes a first slotted port 60 that receives the machine-direction-distributed flow of polymer A from coathanger distribution chamber 17 and a second slotted port 62 that receives the machine-direction-distributed flow of polymer B from the coathanger distribution chamber 19. The slotted ports 60, 62 each have a major dimension extending in the cross-machine direction. Each of a plurality of throughholes 64 circumscribed by slotted port 60 transfers polymer A to a corresponding one of a plurality of slots 65 defined in the downstream face of the transfer plate 34. Similarly, each of a plurality of throughholes 66 circumscribed by slotted port 62 transfers polymer B to a corresponding one of a plurality of slots 67 defined in the downstream face of the transfer plate 34. Each of the slots 65, 67 has a closed end located near the transverse centerline of the transfer plate 34, which extends in the cross-machine direction, so that the polymer flows are centralized along the centerline.
Upstream ends of slotted ports 60, 62 are encircled by glands counter-bored to receive and hold respective seals 52 that prevent leakage between the die body 25 and the transfer plate 34. A screen 53 positioned in each of the slotted ports 60, 62 filters particles and other contamination from the flows of the two segregated thermoplastic polymers before the individual flows enter the distribution plate 36. Screen 53 may be made of a metal mesh or other suitable filter media. Each screen 53 is recessed in a corresponding countersunk area of the upstream surface of transfer plate 34 and is generally rectangular.
The transfer plate 34 includes only two slotted ports 60, 62 each receiving one of the two polymers in contrast to conventional transfer plates that include a single central slotted port for one polymer flanked on each side by one of a pair of slotted ports receiving the other polymer. In further contrast to conventional transfer plates, the polymers are directed by slots 65, 67 to the transverse centerline of the transfer plate 34 before being supplied to the downstream distribution plate 36.
With reference to FIGS. 2, 3, and 7-9, the distribution plate 36 is positioned immediately downstream from the transfer plate 34 and is disposed between transfer plate 34 and the set 38 of configuration plates 40, 42, 44, 46, 48, and 50. The distribution plate 36 operates to distribute the flows of the two thermoplastic polymers uniformly in the machine direction. The distribution plate 36 includes a plurality of individual, substantially rectangular plates 68 each of which includes a coathanger-shaped distribution chamber 70 and an inlet 72 coupling an apex of each of the distribution chambers 70 with a closed end of slot 65 if polymer A is supplied and a closed end of slot 67 if polymer B is supplied.
Dowel pins 74 extend in the cross-machine direction through aligned horizontal holes in the rectangular plates 68 for aligning and positioning plates 68. The plates 68 may be permanently bonded together to form a single entity or integral object, in which case the dowel pins 74 may be used for alignment and then removed from the assembly. The invention contemplates that, in an alternative embodiment, the distribution plate 36 may consist of a single unitary cast block that contains multiple coathanger distribution chambers 70 each having an inlet 72 rather than an assembly of multiple plates 68.
With reference to FIGS. 7-9, inlet 72 intersects an apex 76 of the distribution chamber 70 at the conjunction of a pair of lateral distribution passages or channels 78, 80 that convey the molten thermoplastic polymer laterally away from the inlet 72. The distribution channels 78, 80 are inclined downstream so as to diverge away from apex 76 in opposite directions substantially parallel to the machine direction. The distribution channels 78, 80 have a substantially circular cross-sectional profile that may narrow or taper in diameter with increasing distance from the apex 76.
The distribution chamber 70 transforms the circular section of the thermoplastic polymer entering inlet 72 to a thin sheet at a discharge outlet 86. To that end, distribution channels 78, 80 communicate via an inlet slit 82 of a relatively-narrow distribution passageway 71. A slotted discharge outlet 86 is defined at the base of the distribution passageway 71. The distribution passageway 71 has a length, L, in the machine direction, a height, H, measured in an upstream/downstream vertical direction, and a width, W, measured in the cross-machine direction. The length of distribution passageway 71 progressively lengthens from the apex 76 to discharge outlet 86 and the width of the distribution passageway 71 is substantially constant from slit 82 to discharge outlet 86. The height of distribution chamber 70 is greater when measured at the apex 76 than proximate the peripheral edges 86 a,b of discharge outlet 86. The diameter of the distribution channels 78, 80 is greater than the width of the distribution passageway 71.
The distribution chamber 70 is symmetrical laterally of the apex 76 to form a triangle having two sides consisting of distribution channels 78, 80 and a base defined by the discharge outlet 86 that is longer than either of the sides, although the invention is not so limited. In an exemplary embodiment, the sides and base of the distribution chamber 70 collectively define an isosceles triangle in which the sides are of equal length.
The distribution channels 78, 80 transfer the thermoplastic polymer from the inlet 72 laterally away from the centerline of the distribution plate 36, and the distribution passageway 71 channels the thermoplastic polymer axially in a downstream direction toward the discharge outlet 86. The polymer residence time from the apex 76 to the discharge outlet 86 is approximately uniform for polymer exiting at any point across the entire length of the discharge outlet 86. In addition, the fluid pressure of the thermoplastic polymer is substantially constant across the length of the discharge outlet 86. The design of the coathanger-shaped distribution chamber 70 may be optimized by three-dimensional mathematical modeling and numerical fluid-flow simulations using, for example, finite element analysis.
With reference to FIGS. 2, 3, 10 and 10A, positioned immediately downstream of the distribution plate 36 is the first configuration plate 40 that includes a plurality of circular bores or thoughholes 88 each extending vertically through the thickness of plate 40 from an upstream inlet to a downstream outlet. The throughholes 88 are arranged in alternating first and second linear rows 90, 92, respectively, extending in the machine direction and in staggered columns extending in the cross-machine direction. Throughholes 88 in each row 90 are registered vertically with the discharge outlet 86 of one of the distribution chambers 70 transferring polymer A. Throughholes 88 in each row 92 are registered vertically with the discharge outlet 86 of one of the distribution chambers 70 transferring polymer B. Accordingly, the throughholes 88 in each row 90 are supplied with polymer A and the throughholes 88 in each row 92 are supplied with polymer B.
With reference to FIGS. 2, 3, 11 and 11A, the second configuration plate 42 is positioned immediately downstream of the first configuration plate 40 and includes a plurality of first slots 94 and a plurality of second slots 96 each extending vertically through the thickness of the second configuration plate 42 from an upstream inlet to a downstream outlet. A major axis of each of the slots 94, 96 is aligned generally in the cross-machine direction. Slots 94 are aligned in rows oriented in the machine direction and slots 96 are aligned in separate rows also oriented in the machine direction. Each slot 94 is centered in substantial vertical alignment with one of the throughholes 88 in the linear rows 92 of the first configuration plate 40. Similarly, each slot 96 is centered in substantial vertical alignment with one of the throughholes 88 in the linear rows 90 of the first configuration plate 40. Accordingly, slots 96 transfer polymer A laterally in the cross-machine direction and slots 94 transfer polymer B laterally in the cross-machine direction.
With reference to FIGS. 2, 3, 12 and 12A, the third configuration plate 44 is positioned immediately downstream of the second configuration plate 42 and includes a plurality of first circular bores or throughholes 98 and a plurality of second circular bores or throughholes 99 each extending vertically through the thickness of configuration plate 44 from an upstream inlet to a downstream outlet. Throughholes 98, 99 are arranged in linear rows extending in the machine direction and are likewise spaced in the cross-machine direction. Each throughhole 98 is registered vertically in substantial vertical alignment with a closed end of one of the slots 94 in the second configuration plate 42 and each throughhole 99 is registered vertically in substantial vertical alignment with a closed end of one of the slots 96 in the second configuration plate 42. Consequently, throughholes 98 are supplied with polymer B and throughholes 99 transfer polymer A vertically in the downstream direction. Throughholes 98, 99 are more densely positioned with smaller center-to-center spacings than throughholes 88 in configuration plate 40.
With reference to FIGS. 2, 3, 13 and 13A, positioned immediately downstream of the third configuration plate 44 is the fourth configuration plate 46 that includes a plurality of X-shaped slots 100 and a plurality of circular bores or throughholes 102 each extending vertically through the thickness of the fourth configuration plate 46 from an upstream inlet to a downstream outlet. The X-shaped slots 100 and throughholes 102 are arranged in linear rows in the machine direction and are spaced in the cross-machine direction. The center of each X-shaped slot 100 is aligned vertically with one of the throughholes 98 in the third configuration plate 44 for receiving a flow of polymer B. Each throughhole 102 is registered with one of the throughholes 99 in the third configuration plate 44 for receiving a flow of polymer A.
With reference to FIGS. 2, 3, 14 and 14A, the fifth configuration plate 48 positioned immediately downstream of the fourth configuration plate 46 includes a plurality of first circular bores or throughholes 104 and a plurality of second circular bores or throughholes 106 each extending vertically through the thickness of the fifth configuration plate 48 between an upstream inlet and a downstream outlet. The first throughholes 104 are arranged in groups of four each situated at one corner of an imaginary rectangle, and one of the second throughholes 106 is positioned at the geometrical center point of the imaginary rectangle. Each of the second throughholes 106 is registered vertically with one of the throughholes 102 in the fourth configuration plate 46 for receiving a stream of polymer A. Similarly, each of the first throughholes 104 is vertically aligned with one of the four curved closed ends of the X-shaped slots 100 in the fourth configuration plate 46 for receiving a stream of polymer B.
With reference to FIGS. 2, 3, 15, 15A and 15B, the sixth configuration plate 50, which is immediately downstream of the fifth configuration plate 48, brings the flow path of polymer B received from the fifth configuration plate 48 into coaxial alignment with the flow path of polymer A received from the fifth configuration plate 48 so that polymer B forms a sheath that coats a core region of polymer A. To that end, the sixth configuration plate 50 includes a plurality of circular bores or throughholes 108 each of which is surrounded by a concentric substantially-circular recess 110. Adjacent recesses 110 merge together at opposite side edges. Each throughhole 108 is concentrically aligned with one of the second throughholes 106 in the fifth configuration plate 48. Throughhole 108 has a larger diameter than the second throughhole 106 to facilitate polymer combination.
Each recess 110 is registered with a group of throughholes 104 in the fifth configuration plate 48 so that polymer B is provided at multiple individual locations about its circumference defined by the arrangement of the throughholes 104. In the exemplary embodiment, polymer B is provided at four locations in which adjacent locations are separated by an angular arc of about 90 degrees. A raised circular wall 112 is positioned between each throughhole 108 and the corresponding surrounding recess 110. Polymer B flows radially inward over the circular wall 112, intersects the flow of polymer A about its circumference, and coats the core of polymer A as a sheath to form concentric sheath-core multicomponent filaments, which flow in their combined form downstream through throughholes 108 to the spinneret 22.
With reference to FIGS. 2, 3, 16 and 16A, the spinneret 22 has a densely-spaced array of spinning channels 114 each registered concentrically with one of throughholes 108 in the sixth configuration plate 50, which is immediately upstream from the spinneret 22. The spinning channels 114 are arranged in an array having aligned or staggered rows and/or columns from which a dense curtain of multicomponent filaments 24 each constituted collectively by the two polymers is discharged. Typically, the rows of spinning channels 114 are aligned in the cross-machine direction and the columns of spinning channels 114 are aligned in the machine direction. The spacing between adjacent spinning channels 114 in either the machine direction or cross-machine direction can be uniform or may change proportionally to either the width (W) or the length (L) of the spinneret 22. As detailed above, one of the coathanger distribution chambers 70 (FIG. 9) ultimately supplies polymer A and another of the coathanger distribution chambers 70 ultimately supplies polymer B to each column of spinning channels 114.
Each spinning channel 114 tapers or narrows near a downstream surface of spinneret 22 to a smaller diameter spinning orifice 116 from which multicomponent filaments 24 are extruded for subsequent solidification, attenuation and collection as a nonwoven web 30 (FIG. 1). The cross-sectional profile of the spinning orifices 116 can be selected to accommodate the cross-sectional profile desired for the extruded filaments 24 (FIG. 1), such as round, oval, trilobal, triangular, dog-boned, or flat.
In this exemplary embodiment of the invention, the filaments 24 produced are concentric sheath-core bicomponent filaments that are of uniform cross-sectional shape and area from filament to filament. The invention contemplates that additional thermoplastic materials may be combined with these two thermoplastic materials in the set 38 of configuration plates 40, 42, 44, 46, 48 and 50 to form multicomponent filaments 24 with more than two constituent thermoplastic materials and that the constituent thermoplastic materials may have other configurations, such as side-by-side. The designs and shapes of the channels (e.g., slots and throughholes) of the configuration plates 40, 42, 44, 46, 48 and 50 may be modified in accordance with various filament configurations. Such designs and modifications of the channels of configuration plates 40, 42, 44, 46, 48 and 50 are within general knowledge of a person of ordinary skill in meltspinning.
Any number of different configuration plate designs may be used and each configuration plate 40, 42, 44, 46, 48 and 50 may be formed by CNC machining of relatively-thick metal plates in accordance with one aspect of the invention. The specific construction of the configuration plates and the arrangement and shape of slots, recesses and throughholes in the configuration plates will depend on the desired multi-component filament configuration, e.g., concentric sheath-core, eccentric sheath-core, side-by-side, segmented pie, islands-in-the-sea, etc. While six configuration plates have been shown in the exemplary inventive embodiment, a greater or lesser number of configuration plates may be provided as desired to realize a specific filament configuration.
The invention contemplates that the set 38 of configuration plates 40, 42, 44, 46, 48, and 50 that combine the two polymers to fashion the multicomponent filaments 24 may be replaced by a different set of configuration plates with flow paths suitable for fashioning monocomponent filaments 24. Alternatively, the configuration plates 40, 42, 44, 46, 48, and 50 may be removed in their entirety for forming monocomponent filaments 24 without departing from the spirit and scope of the invention.
Each of the configuration plates 40, 42, 44, 46, 48, and 50 is formed by milling or drilling a thin rectangular sheet of a suitable metal using computer numerically controlled (CNC) machining. For example, the configuration plates 40, 42, 44, 46, 48, and 50 may be formed by CNC machining from sheets of a metal alloy, such as 17-4 stainless steel.
Alternatively, the sheets may be machined by other non-etching processes, such as laser cutting or electrical discharge machining (EDM). The sheets have a thickness greater than 0.060″, which is thicker than conventional sheets in which the flow channels are formed by an etching process. In one specific embodiment of the invention, the sheets have a thickness of about 0.078″. Flow channels formed by a machining process are significantly more uniform in center-to-center array positions than etched flow channels. Moreover, each flow channel is surrounded and defined by a smoother sidewall that has fewer defects.
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept. The scope of the invention itself should only be defined by the appended claims, wherein we claim:

Claims

1. A spin pack for forming a molten polymer into filaments, comprising:

a distribution plate including a length, a width, and a plurality of distribution chambers, each of said distribution chambers having an inlet receiving a flow of the molten polymer, a slotted outlet having a major axis oriented substantially parallel to said width, and a coathanger-shaped distribution passageway coupling said inlet with said slotted outlet; and

a spinneret downstream from said distribution plate, said spinneret having a plurality of channels and a plurality of spinning orifices from which the filaments are discharged, each of said spinning orifices associated with one of said channels, and said channels being arranged in a plurality of columns aligned along said width, each of said channels receiving the flow of the molten polymer from said slotted outlet of one of said distribution chambers.

2. The spin pack of claim 1 wherein said slotted outlet has opposite closed ends, and each of said distribution chambers includes a pair of distribution channels each diverging laterally away from said inlet toward a corresponding one of said opposite closed ends.

3. The spin pack of claim 2 wherein each of said distribution channels further includes a distribution passageway coupling said pair of distribution channels with said slotted outlet, said distribution passageway having a dimension measured parallel to said width that is smaller than a dimension measured parallel to said width of said pair of distribution channels.

4. The spin pack of claim 1 wherein said distribution passageway includes a major dimension measured parallel to said width that increases from said inlet to said slotted outlet.

5. The spin pack of claim 1 wherein said inlet of each of said plurality of distribution chambers is positioned on an imaginary line extending along said length.

6. The spin pack of claim 5 wherein said imaginary line bisects said distribution plate along said width.

7. The spin pack of claim 1 further comprising:

a transfer plate upstream from said distribution plate, said transfer plate including a plurality of passageways oriented parallel to said width, and each of said passageways providing the molten polymer to said inlet of a corresponding one of said distribution chambers.

8. The spin pack of claim 1 wherein said width is shorter than said length.

9. A melt spinning apparatus for forming a molten polymer into filaments, comprising:

a collector positioned for collecting the filaments and moving in a travel direction;

a spin pack including a distribution plate and a spinneret downstream from said distribution plate, said distribution plate having a length, a width aligned substantially parallel to said travel direction, and a plurality of distribution chambers, each of said distribution chambers having an inlet receiving a flow of the molten polymer, a slotted outlet having a major axis oriented substantially parallel to said width, and a coathanger-shaped distribution passageway coupling said inlet with said slotted outlet, and said spinneret having a plurality of channels and a plurality of spinning orifices from which the filaments are discharged, each of said spinning orifices associated with one of said channels, and said channels being arranged in a plurality of columns aligned along said width, each of said channels receiving the flow of the molten polymer from said slotted outlet of one of said distribution chambers; and

a drawing device positioned between said spin pack and said collector, said drawing device operative for attenuating the filaments discharged from said spinning orifices.

10. The melt spinning apparatus of claim 9 wherein said slotted outlet has opposite closed ends, and each of said distribution chambers includes a pair of distribution channels each diverging laterally away from said inlet toward a corresponding one of said opposite closed ends.

11. The melt spinning apparatus of claim 10 wherein each of said distribution channels further includes a distribution passageway coupling said pair of distribution channels with said slotted outlet, said distribution passageway having a dimension measured parallel to said width that is smaller than a dimension measured parallel to said width of said pair of distribution channels.

12. The melt spinning apparatus of claim 9 wherein said distribution passageway includes a major dimension measured parallel to said width that increases from said inlet to said slotted outlet.

13. The melt spinning apparatus of claim 9 wherein said inlet of each of said plurality of distribution chambers is positioned on an imaginary line extending along said length.

14. The melt spinning apparatus of claim 13 wherein said imaginary line bisects said distribution plate along said width.

15. The melt spinning apparatus of claim 9 wherein said spin pack further comprises:

16. The melt spinning apparatus of claim 9 wherein said width is shorter than said length.

17. A method of operating a meltspinning apparatus for forming a plurality of filaments from a flow of a molten polymer, comprising:

moving a collector in a travel direction;

distributing the flow of the molten polymer in a first direction generally perpendicular to the travel direction;

distributing the flow of the molten polymer in a second direction generally parallel to the travel direction so that the molten polymer has a substantially uniform residence time in a distribution chamber during distribution;

supplying the distributed flow of the molten polymer to a plurality of channels for forming a plurality of filaments; and

collecting the plurality of filaments on the collector.

18. The method of claim 17 wherein the distribution chamber has a slotted outlet with a major axis oriented in the travel direction, and distributing the flow of the molten polymer in the second direction comprises:

adjusting the flow of portions of the molten polymer within the distribution chamber to provide the substantially uniform residence time in the distribution chamber for molten polymer emerging at all points across the slotted outlet.

19. The method of claim 17 wherein each of the distribution chambers has a slotted outlet with a major axis oriented in the travel direction, and distributing the flow of the molten polymer in the second direction comprises:

adjusting the flow of portions of the molten polymer within the distribution chamber so that the molten polymer emerging from the slotted outlet has a substantially uniform pressure at all points across the slotted outlet.

20. The method of claim 17 wherein distributing the flow of the molten polymer in the second direction comprises providing flow paths of different length in the distribution chamber to provide the substantially uniform residence time.