EP1320638A1

EP1320638A1 - Stretchable polymeric fibers and articles produced therefrom

Info

Publication number: EP1320638A1
Application number: EP01981385A
Authority: EP
Inventors: Garret Daniel Figuly; Anthony J. Soroka
Original assignee: EI Du Pont de Nemours and Co; Invista Technologies SARL USA
Current assignee: Invista Technologies Saerl
Priority date: 2000-09-29
Filing date: 2001-09-28
Publication date: 2003-06-25
Anticipated expiration: 2021-09-28
Also published as: AU2002213030A1; JP2004518828A; KR100760796B1; CN1466635A; TW567258B; DE60111548T2; KR20030061371A; DE60111548D1; EP1320638B1; MXPA03002752A; ATE298015T1; WO2002027083A1; CN1250787C

Abstract

A stretchable synthetic polymer fiber comprises an axial core formed from an elastomeric polymer, and two or more wings formed from a non-elastomeric polymer attached to the core. The fiber has a substantially radially symmetric cross-section. Such fibers can be used to form garments, such as hosiery.

Description

TITLE OF INVENTION

STRETCHABLE POLYMERIC FIBERS AND ARTICLES

PRODUCED THEREFROM

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to stretchable fibers, including multiwing, stretchable synthetic polymer fibers formed from at least two types of polymers. The invention also relates to methods of producing such fibers. The invention also relates to articles formed from the fibers, including yarns, garments, and the like.

DESCRIPTION OF RELATED ART

It is desired to impart stretchability into many products formed from synthetic fibers, including various garments, such as sportswear and hosiery.

As disclosed in U.S. Patent No. 4,861 ,660 to Ishii, various methods are known for imparting stretchability to synthetic filaments. In one method, the fibers are two- or three-dimensionally crimped. In another such method, stretchable filaments are produced from elastic polymers, for example, natural or synthetic rubber, or a synthetic elastomer, such as polyurethane elastomer. However, there are drawbacks associated with either of these methods. Ishii attempts to overcome the drawbacks of such filaments by imparting asymmetry to filaments which are formed from two polymers. Asymmetry causes the composite lobe filamentary constituents to be spirally coiled around the axial filamentary constituent in alternately reversed different directions. Thus, the resultant composite filament exhibits an improved stretchability and a good touch and gloss. However, due to their asymmetrical cross section, the Ishii fibers can develop, after mild heat treatment, substantial three-dimensional or helical crimp in addition to their axial spiral twist. This three-dimensional crimp characteristic imparts a torque to the fibers and has been found to impart a substantial and often undesirable 'edge curl' to fabrics constructed of such fibers. The inherent bulk and non-uniformity of such fibers also makes it difficult to construct uniform low basis weight or sheer fabrics from them. For these reasons the Ishii fibers are often unsatisfactory in fabrics knitted or woven from them.

U.S. Patent No. 3,017,686 to Breen et al. also discloses a filament made from two polymers. These polymers are thermoplastic hard polymers, each having no elastomeric property. The polymers are chosen in order to have a sufficient difference in shrinkage so that the fin of the filament has a sinuous configuration, or "ruffle". Breen is concerned with the frequency by which the fins on a filament change direction so that close packing between adjacent filaments is not possible, and is not concerned with stretchability. Thus, the fiilaments disclosed in Breen do not exhibit the high recovery desired in many of today's fabrics.

Thus, there is still a need for fibers and articles therefrom, that are stretchable and have excellent stretch and recovery power, preferably without undesired two- or three-dimensional crimping characteristics, and for convenient methods of making such fibers and articles.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with the prior art by providing a stretchable synthetic polymer fiber having a substantially radially symmetric cross-section. This imparts an unexpected combination of high stretch and high uniformity without significant levels of 2- or 3- dimensional crimp. As a result, the fibers of the invention are well-suited for use in smooth, non-bulky, highly stretchable fabrics. Such a finding was unexpected in view of the teaching to the contrary by U.S. Patent No. 4,861 ,660 to Ishii.

Thus, in accordance with the present invention, there is provided a stretchable synthetic polymer fiber having a substantially radially symmetric cross-section and comprising an axial core comprising a thermoplastic elastomeric polymer and a plurality of wings comprising at least one thermoplastic, non-elastomeric polymer attached to the core. There is further provided in accordance with the invention a garment comprising the stretchable synthetic polymer fiber described above. The invention further provides a melt spinning process for spinning continuous polymeric fibers comprising: passing a melt comprising at least one thermoplastic non-elastomeric polymer and a melt comprising a thermoplastic elastomeric polymer through a spinneret to form a plurality of stretchable synthetic polymeric fibers, each having a substantially radially symmetric cross-section and comprising an axial core comprising the elastomeric polymer and a plurality of wings comprising the non- elastomeric polymer attached to the core; quenching the fibersafter they exit the capillary of the spinneret to cool the fibers, and collecting the fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional profile drawing of a six-wing fiber of the invention.

Figs. 2A and 2B show fibers of the invention in which the spiral twist is almost completely circumferential (2A) and in which the spiral twist is almost completely noncircumferential (2B).

Fig. 3 shows a fiber of the invention in which the fiber is slightly wavy.

Fig. 4 is a representation of the cross-sectional shape of a particular symmetrical two-wing fiber having a thin sheath around the core and between the wings according to the invention.

Fig. 5 is a process schematic of an apparatus useful for making fibers of this invention.

Fig. 6 is a representation of a stacked plate spinneret assembly, in side elevation, that can be used to make the fiber of the invention.

Fig. 6A is a representation of orifice plate A in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 6, and taken across lines 6A - 6A of Fig. 6. Fig. 6B is a representation of orifice plate B in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 6, and taken across lines 6B - 6B of Fig. 6. Fig. 6C is a representation of orifice plate C in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 6, and taken across lines 6C - 6C of Fig. 6.

Fig. 7 is a representation of a stacked plate spinneret assembly, in side elevation, that can be used to make certain fibers according to another embodiment of the present invention.

Fig. 7A is a representation of orifice plate A in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7A - 7A of Fig. 7.

Fig. 7B is a representation of orifice plate B in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7B - 7B of Fig. 7.

Fig. 7C is a representation of orifice plate C in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7C - 7C of Fig. 7. Fig. 7F is a representation of orifice plate F in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7F - 7F of Fig. 7.

Fig. 7G is a representation of orifice plate G in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7G - 7G of Fig. 7.

Fig. 7H is a representation of orifice plate H in plan view at 90° to the stacked plate spinneret assembly shown in Fig. 7, and taken across lines 7H - 7H of Fig. 7.

Fig. 8 is a cross-sectional profile drawing of a fiber of the invention as exemplified in Example 7.

Fig. 9 is a cross-sectional profile drawing of a six-wing fiber of the invention as exemplifed in Example 7. DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided a stretchable synthetic polymer fiber, shown generally at 10 in Figs. 1 , 2A, 2B, 3, 4, 8 and 9. The fiber of the present invention includes an axial core, shown at 12 in Fig. 1 , and a plurality of wings, shown at 14 in Fig. 1. According to the present invention, the axial core comprises a thermoplastic elastomeric polymer, and the wings comprise at least one thermoplastic, non-elastomeric polymer attached to the core. Preferably, the thermoplastic, non-elastomeric polymer is permanently drawable.

As used herein, the term "fiber" is interchangeable with the term "filament". The term "yarn" includes yarns of a single filament. The term "multifilament yarn" generally relates to yarns of two or more filaments. The term "thermoplastic" refers to a polymer which can be repeatedly melt-processed (for example melt-spun). By 'elastomeric polymer' is meant a polymer which in monocomponent fiber form, free of diluents, has a break elongation in excess of 100% and which when stretched to twice its length, held for one minute, and then released, retracts to less than 1.5 times its original length within one minute of being released. The elastomeric polymers in the fiber of the invention can have a flex modulus of less than about 14,000 pounds per square inch (96,500 kPascals), more typically less than about 8500 pounds per square inch (58,600 kPascals) when present in a monocomponent fiber spun according to ASTM standard D790 Flexural Properties at RT or 23° C and under conditions substantially as described herein. As used herein, "non- elastomeric polymer" means any polymer which is not an elastomeric polymer. Such polymers can also be termed "low elasticity", "hard: and "high modulus". By "permanently drawable" is meant that the polymer has a yield point, and if the polymer is stretched beyond such point it will not return to its original length.

The fibers of the invention are termed "biconstituent" fibers when they are comprised of at least two polymers adhered to each other along the length of the fiber, each polymer being in a different generic class, e.g., polyamide, polyester or polyolefin. If the elastic characteristics of the polymers are sufficiently different, polymers of the same generic class can be used, and the resulting fiber is a "bicomponent" fiber. Such bicomponent fibers are also within the scope of the invention. The fiber of the present invention is twisted around its longitudinal axis, without significant two- or three-dimensional crimping characteristics. (In such higher-dimensional crimping, a fiber's longitudinal axis itself assumes a zig-zag or helical configuration; such fibers are not of the invention). The fiber of the present invention may be characterized as having substantially spiral twist and one dimensional spiral twist.

"Substantially spiral twist" includes both spiral twist that passes completely around the elastomeric core and also spiral twist that passes only partly around the core, since it has been observed that a fully 360° spiral twist is not necessary to achieve the desirable stretch properties in the fiber. Fig. 2A shows a fiber 10 with a substantially spiral twist which is almost completely circumferential, and Fig. 2B shows a fiber 10 with a substantially spiral twist which is almost completely noncircumferential. "One dimensional" spiral twist means that while the wings of the fiber can be substantially spiral, the axis of the fiber is substantially straight even at low tension, in contrast to fibers having 2- or 3-dimensional crimp. However, fibers having some waviness are within the scope of the invention, as illustrated by fiber 10 in Fig. 3.

The presence or absence of two- and three-dimensional crimp can be gauged from the amount of stretch needed to substantially straighten the fiber (by pulling out any non-linearities) and is a measure of the radial symmetry of fibers having spiral twist. The fiber of the invention can require less than about 10% stretch, more typically less than about 7% stretch, for example about 4% to about 6%, to substantially straighten the fiber. The fiber of the present invention has a substantially radially symmetric cross-section, as can be seen from Fig. 1. By "substantially radially symmetric cross-section" is meant a cross-section in which the wings are located and are of dimensions so that rotation of the fiber about its longitudinal axis by 360/n degrees, in which "n" is an integer representing the "n-fold" symmetry of the fibers, results in substantially the same cross-section as before rotation. The cross-section is substantially symmetrical in terms of size, polymer and angular spacing around the core. This substantially radially symmetric cross-section impartes an unexpected combination of high stretch and high uniformity without significant levels of two- or three-dimensional crimp. Such uniformity is advantageous in high-speed processing of fibers, for example through guides and knitting needles, and in making smooth, non-'picky' fabrics, especially sheer fabrics like hosiery. Fibers which have a substantially radially symmetric cross-section possess no self-crimping potential, i.e., they have no significant two- or three-dimensional crimping characteristics. See generally Textile Research Journal, June 1967, p. 449.

For maximum cross-sectional radial symmetry, the core can have a substantially circular or a regular polyhedral cross-section, e.g., as seen in Figs. 1 , 4, 8, and 9. By "substantially circular" it is meant that the ratio of the lengths of two axes crossing each other at 90° in the center of the fiber cross-section is no greater than about 1.2:1. The use of a substantially circular or regular polyhedron core, in contrast to the cores of U.S. Patent No. 4,861 ,660, can protect the elastomer from contact with the rolls, guides, etc. as described later with reference to the number of wings. The plurality of wings can be arranged in any desired manner around the core, for example, discontinuously as depicted in Fig. 1, i.e., the wing polymer does not form a continous mantel on the core, or with adjacent wing(s) meeting at the core surface, e.g., as illustrated in Figs. 4 and 5 of U.S. Patent No. 3,418,200. The wings can be of the same or different sizes, provided a substantially radial symmetry is preserved. Further, each wing can be of a different polymer from the other wings, once again provided substantially radial geometric and polymer composition symmetry is maintained. However, for simplicity of manufacture and ease of attaining radial symmetry, it is preferred that the wings be of approximately the same dimensions, and be made of the same polymer or blend of polymers. It is also preferred that the wings discontinuously surround the core for ease of manufacture. While the fiber cross-section is substantially symmetrical in terms of size, polymer, and angular spacing around the core, it is understood that small variations from perfect symmetry generally occur in any spinning process due to such factors as non-uniform quenching or imperfect polymer melt flow or imperfect spinning orifices. It is to be understood that such variations are permissible provided that they are not of a sufficient extent to detract from the objects of the invention, such as providing fibers of desired stretch and recovery via one-dimensional spiral twist, while minimizing two- and three-dimensional crimping. That is, the fiber is not intentionally made asymmetrical as in U.S. Patent No. 4,861 ,660.

The wings protrude outward from the core to which they adhere and form a plurality of spirals at least part way around the core especially after effective heating. The pitch of such spirals can increase when the fiber is stretched. The fiber of the invention has a plurality of wings, preferably 3- 8, more preferably 5 or 6. The number of wings used can depend on other features of the fiber and the conditions under which it will be made and used. For example, 5 or 6 wings can be used when a monofilament is being made, especially at higher draw ratios and fiber tensions. In this case the wing spacing can be frequent enough around the core that the elastomer is protected from contact with rolls, guides, and the like and therefore less subject to breaks, roll wraps and wear than if fewer wings were used. The effect of higher draw ratios and fiber tensions is to press the fiber harder against rolls and guides, thus splaying out the wings and bringing the elastomeric core into contact with the roll or guide; hence the preference for more than two wings at high draw ratios and fiber tensions. In monofilaments, five or six wings are often preferred for an optimum combination of ease of manufacture and reduced core contact. When a multifiber yarn is desired, as few as two or three wings can be used because the likelihood of contact between the elastomeric core and rolls or guides is reduced by the presence of the other fibers.

While it is preferred that the wings discontinuously surround the core for ease of manufacture, the core may include on its outside surface a sheath of a non-elastomeric polymer between points where the wings contact the core. Fig. 4 shows a fiber 10 having a sheath 16. The sheath thickness can be in the range of about 0.5% to about 15% of the largest radius of the fiber core. The sheath can help with adhesion of the wings to the core by providing more contact points between the core and wing polymers, a particularly useful feature if the polymers in the biconstituent fiber do not adhere well to each other. The sheath can also reduce abrasive contact between the core and rolls, guides, and the like, especially when the fiber has a low number of wings.

The core and/or wings of the multiwinged cross-section of the present invention may be solid or include hollows or voids. Typically, the core and wings are both solid. Moreover, the wings may have any shape, such as ovals, T-, C-, or S-shapes (see, for example, Fig. 4). Examples of useful wing shapes are found in U.S. Patent No. 4,385,886. T, C, or S shapes can help protect the elastomer core from contact with guides and rolls as described previously.

The weight ratio of total wing polymer to core polymer can be varied to impart the desired mix of properties, e.g., desired elasticity from the core and other properties from the wing polymer. For example, a weight ratio of non-elastomeric wing polymer to elastomeric core polymer in the range of about 10/90 to about 70/30, preferably about 30/70 to about

40/60, can be used. For high durability combined with high stretch in uses in which the fiber is not used with a companion yarn (for example hosiery), a wing/core weight ratio in the range of about 35/65 to about 50/50 is often preferred. As noted above, the core of the fiber of the invention can be formed from any thermoplastic elastomeric polymer. Examples of useful elastomers include thermoplastic polyurethanes, thermoplastic polyester elastomers, thermoplastic polyolefins, thermoplastic polyesteramide elastomers and thermoplastic polyetheresteramide elastomers. Useful thermoplastic polyurethane core elastomers include those prepared from a polymeric glycol, a diisocyanate, and at least one diol or diamine chain extender. Diol chain extenders are preferred because the polyurethanes made therewith have lower melting points than if a diamine chain extender were used. Polymeric glycols useful in the preparation of the elastomeric polyurethanes include polyether glycols, polyester glycols, polycarbonate glycols and copolymers thereof. Examples of such glycols include poly(ethyleneether) glycol, poly(tetramethyleneether) glycol, poly(tetramethylene-co-2-methyl-tetramethyleneether) glycol, poly(ethylene-co-1 ,4-butylene adipate) glycol, poly(ethylene-co-1 ,2- propylene adipate) glycol, poly(hexamethylene-co-2,2-dimethyl-1 ,3- propylene adipate), poly(3-methyl-1 ,5-pentylene adipate) glycol, poly(3- methyl-1 ,5-pentylene nonanoate) glycol, poly(2,2-dimethyl-1 ,3-propylene dodecanoate) glycol, poly(pentane-1 ,5-carbonate) glycol, and poly(hexane-1 ,6-carbonate) glycol. Useful diisocyanates include 1- isocyanato-4-[(4-isocyanatophenyl)methyl]benzene, 1-isocyanato-2-[(4- isocyanato-phenyl)methyl]benzene, isophorone diisocyanate, 1 ,6- hexanediisocyanate, 2,2-bis(4-isocyanatophenyl)propane, 1 ,4-bis(p- isocyanato,alpha,alpha-dimethylbenzyl)benzene, 1 ,1 '-methylenebis(4- isocyanatocyclohexane), and 2,4-tolylene diisocyanate. Useful diol chain extenders include ethylene glycol, 1 ,3 propane diol, 1 ,4-butanediol, 2,2- dimethyl-1 ,3-propylene diol, diethylene glycol, and mixtures thereof. Preferred polymeric glycols are poly(tetramethyleneether) glycol, poly(tetramethylene-co-2-methyl-tetramethyleneether) glycol, poly(ethylene-co-1 ,4-butylene adipate) glycol, and poly(2,2-dimethyl~1 ,3- propylene dodecanoate) glycol. 1-lsocyanato-4-[(4- isocyanatophenyl)methyl]benzene is a preferred diisocyanate. Preferred diol chain extenders are 1 ,3 propane diol and 1 ,4-butanediol. Monofunctional chain terminators such as 1-butanol and the like can be added to control the molecular weight of the polymer.

Useful thermoplastic polyester elastomers include the polyetheresters made by the reaction of a polyether glycol with a low-molecular weight diol, for example, a molecular weight of less than about 250, and a dicarboxylic acid or diester thereof, for example, terephthalic acid or dimethyl terephthalate. Useful polyether glycols include poly(ethyleneether) glycol, poly(tetramethyleneether) glycol, poly(tetramethylene-co-2-methyltetramethyleneether) glycol [derived from the copolymerization of tetrahydrofuran and 3-methyltetrahydrofuran] and poly(ethylene-co-tetramethyleneether) glycol. Useful low-molecular weight diols include ethylene glycol, 1 ,3 propane diol, 1 ,4-butanediol, 2,2- dimethyl-1 ,3-propylene diol, and mixtures thereof; 1 ,3 propane diol and 1 ,4-butanediol are preferred. Useful dicarboxylic acids include terephthalic acid, optionally with minor amounts of isophthalic acid, and diesters thereof (e.g., <20 mol%).

Useful thermoplastic polyesteramide elastomers that can be used in making the core of the fibers of the invention include those described in U.S. Patent No. 3,468,975. For example, such elastomers can be prepared with polyester segments made by the reaction of ethylene glycol, 1 ,2-propanediol, 1 ,3-propanediol, 1 ,4-butanediol, 2,2-dimethyl-1 ,3- propanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,10-decandiol, 1 ,4- di(methylol)cyclohexane, diethylene glycol, or triethylene glycol with malonic acid, succinic acid, glutaric acid, adipic acid, 2-methyladipic acid, 3-methyladipic acid, 3,4-dimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, or dodecandioic acid, or esters thereof.

Examples of polyamide segments in such polyesteramides include those prepared by the reaction of hexamethylene diamine or dodecamethylene diamine with terephthalic acid, oxalic acid, adipic acid, or sebacic acid, and by the ring-opening polymerization of caprolactam. Thermoplastic polyetheresteramide elastomers, such as those described in U.S. Patent No. 4,230,838, can also be used to make the fiber core. Such elastomers can be prepared, for example, by preparing a dicarboxylic acid-terminated polyamide prepolymer from a low molecular weight (for example, about 300 to about 15,000) polycaprolactam, polyoenantholactam, polydodecanolactam, polyundecanolactam, poly(11- aminoundecanoic acid), poly(12-aminododecanoic acid), poly(hexamethylene adipate), poly(hexamethylene azelate), poly(hexamethylene sebacate), poly(hexamethylene undecanoate), poly(hexamethylene dodecanoate), poly(nonamethylene adipate), or the like and succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, terephthalic acid, dodecanedioic acid, or the like. The prepolymer can then be reacted with an hydroxy-terminated polyether, for example poly(tetramethylene ether) glycol, poly(tetramethylene-co-2- methyltetramethylene ether) glycol, polypropylene ether) glycol, poly(ethylene ether) glycol, or the like. As noted above, the wings can be formed from any non- elastomeric, or hard, polymer. Examples of such polymers include non- elastomeric polyesters, polyamides, and polyolefins. Useful thermoplastic non-elastomeric wing polyesters include poly(ethylene terephthalate) ("2G-T") and copolymers thereof, poly(trimethylene terephthalate) ("3G-T"), polybutylene terephthalate ("4G- T"), and poly(ethylene 2,6-naphthalate), poly(1 ,4- cyclohexylenedimethylene terephthalate), poly(lactide), poly(ethylene azelate), poly[ethylene-2,7-naphthalate], poly(glycolic acid), poly(ethylene succinate), poly(.alpha.,.alpha.-dimethylpropiolactone), poly(para- hydroxybenzoate), poly(ethylene oxybenzoate), poly(ethylene isophthalate), poly(tetramethylene terephthalate, poly(hexamethylene terephthalate), poly(decamethylene terephthalate), poly(1 ,4-cyclohexane dimethylene terephthalate) (trans), polyethylene 1 ,5-naphthalate), poly(ethylene 2,6-naphthalate), poly(1 ,4-cyclohexylidene dimethylene terephthalate)(cis), and poly(1 ,4-cyclohexylidene dimethylene terephthalate)(trans).

Preferred non-elastomeric polyesters include poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(1 ,4-butylene terephthalate) and copolymers thereof. When a relatively high-melting polyesters such as poly(ethylene terephthalate) is used, a comonomer can be incorporated into the polyester so that it can be spun at reduced temperatures. Such comonomers can include linear, cyclic, and branched aliphatic dicarboxylic acids having 4-12 carbon atoms (for example pentanedioic acid); aromatic dicarboxylic acids other than terephthalic acid and having 8-12 carbon atoms (for example isophthalic acid); linear, cyclic, and branched aliphatic diols having 3-8 carbon atoms (for example 1 ,3-propane diol, 1 ,2-propanediol, 1,4-butanediol, and 2,2-dimethyl-1 ,3- propanediol); and aliphatic and araliphatic ether glycols having 4-10 carbon atoms (for example hydroquinone bis(2-hydroxyethyl) ether). The comonomer can be present in the copolyester at a level in the range of about 0.5 to 15 mole percent. Isophthalic acid, pentanedioic acid, hexanedioic acid, 1 ,3-propane diol, and 1 ,4-butanediol are preferred comonomers for poly(ethylene terephthalate) because they are readily commercially available and inexpensive.

The wing polyester(s) can also contain minor amounts of other comonomers, provided such comonomers do not have an adverse affect on fiber properties. Such other comonomers include 5-sodium- sulfoisophthalate, for example, at a level in the range of about 0.2 to 5 mole percent. Very small amounts, for example, about 0.1 wt% to about 0.5 wt% based on total ingredients, of trifunctional comonomers, for example trimellitic acid, can be incorporated for viscosity control.

Useful thermoplastic non-elastomeric wing polyamides include poly(hexamethylene adipamide) (nylon 6,6); polycaprolactam (nylon 6); polyenanthamide (nylon 7); nylon 10; poly(12-dodecanolactam) (nylon 12); polytetramethyleneadipamide (nylon 4,6); polyhexamethylene sebacamide (nylon 6,10); poly(hexamethylene dodecanamide) (nylon 6,12); the polyamide of dodecamethylenediamine and n-dodecanedioic acid (nylon 12,12), PACM-12 polyamide derived from bis(4-aminocyclohexyl)methane and dodecanedioic acid, the copolyamide of 30% hexamethylene diammonium isophthalate and 70% hexamethylene diammonium adipate, the copolyamide of up to 30% bis-(P-amidocyclohexyl)methylene, and terephthalic acid and caprolactam, poly(4-aminobutyric acid) (nylon 4), poly(8-aminooctanoic acid) (nylon 8), poly(hapta-methylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poiy(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(decamethylene sebacamide (nylon 10,10), poly[bis(4-amino-cyclohexyl)methane-1 ,10-decanedicarboxamide], poly(m-xylene adipamide), poly(p-xylene sebacamide), poly(2,2,2- trimethylhexamethylene pimelamide), poly(piperazine sebacamide), poly(11-amino-undecanoic acid) (nylon 11), polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, and poly(9- aminononanoic acid) (nylon 9) polycaproamide. Copolyamides can also be used, for example poly(hexamethylene-co-2-methylpentamethylene adipamide) in which the hexamethylene moiety can be present at about 75-90 mol% of total diamine-derived moieties. Useful polyolefins include polypropylene, polyethylene, polymethylpentane and copolymers and terpolymers of one or more of ethylene or propylene with other unsaturated monomers. For example, fibers comprising non-elastomeric polypropylene wings and an elastomeric polypropylene core are within the scope of the present invention; such fibers are bicomponent fibers.

Combinations of elastomeric and non-elastomeric polymers can include a polyetheramide, for example, a polyetheresteramide, elastomer core with polyamide wings and a polyetherester elastomer core with polyester wings. For example a wing polymer can comprise nylon 6-6, and copolymers thereof, for example, poly(hexamethylene-co-2- methylpentamethylene adipamide) in which the hexamethylene moiety is present at about 80 mol % optionally mixed with about 1 % up to about 15% by weight of nylon-12, and a core polymer can comprise an elastomeric segmented polyetheresteramide. "Segmented polyetheresteramide" means a polymer having soft segments (long-chain polyether) covalently bound (by the ester groups) to hard segments (short- chain polyamides). Similar definitions correspond to segmented polyetherester, segmented polyurethane, and the like. The nylon 12 can improve the wing adhesion to the core, especially when the core is based on PEBAX™ 3533SN from Atofina. Another preferred wing polymer can comprise a non-elastomeric polyester selected from the group of poly(ethylene terephthalate) and copolymers thereof, poly(trimethylene terephthalate), and poly(tetramethylene terephthalate); an elastomeric core suitable for use therewith can comprise a polyetherester comprising the reaction product of a polyether glycol selected from the group of poly(tetramethyleneether) glycol and poly(tetramethylene-co-2-methyl- tetramethyleneether) glycol with terephthalic acid or dimethyl terephthalate and a low molecular weight diol selected from the group of 1 ,3-propane diol and 1 ,4-butane diol.

An elastomeric polyetherester core can also be used with non- elastomeric polyamide wings, especially when an adhesion-promoting additive is used, as described elsewhere herein. For example, the wings of such a fiber can be selected from the group of (a) poly(hexamethylene adipamide) and copolymers thereof with 2-methylpentamethylene diamine and (b) polycaprolactam, and the core of such a fiber can be selected from the group of (a) polyetheresteramide and (b) the reaction products of poly(tetramethyleneether) glycol or poly(tetramethylene-co-2- methyltetramethyleneether) glycol with terphthalic acid or dimethyl terephthalate and a diol selected from the group of 1 ,3-propane diol and 1 ,4-butene diol.

Methods of making the polymers described above are known in the art and may include the use of catalysts, co-catalysts, and chain- branchers, as known in the art.

The high elasticity of the core permits it to absorb compressional, torsional, and extensional forces as it is twisted by the attached wings when the fiber is stretched and relaxed. These forces will cause delamination of the wing and core polymers if their attachment is too weak. Bonding can be enhanced by selection of one or more of the wing(s) and core compositions or by the use of a sheath as earlier described and/or the use of additives to either or both polymers which enhance bonding. Additives can be added to one or more of the wings, such that each wing has the same or different degrees of attachment to the core. Thus, typically the core and wing polymers should be selected such that they have a sufficient compatibility that they will bond to each other such that separation is minimized while the fibers are made and used. Also, additives can be added to the wing and/or core polymers to improve adhesion, for example, nylon 12, e.g., 5% by weight, based on total wing polymer, i.e., poly(12-dodecanolactam), also known as "12" or "N12", commercially available as Rilsan "AMNO" from Atofina. Also, maleic anhydride derivatives (for example Bynel® CXA, a registered trademark of E. I. du Pont de Nemours and Company or Lotader® ethylene/acrylic ester/maleic anhydride terpolymers from Atofina) can be used to modify a polyether-amide elastomer to improve it adhesion to a polyamide. As another example, a thermoplastic novolac resin, for example HRJ12700 (Schenectady International), having a number average molecular weight in the range of about 400 to about 5000, could be added to an elastomeric (co)polyetherester core to improve its adhesion to (co)polyamide wings. The amount of novolac resin should be in the range of 1 - 20 wt%, with a more preferred range of 2 - 10 wt%. Examples of the novolac resins useful herein include, but are not limited to, phenol-formaldehyde, resorcinol-formaldehyde, p-butylphenol- formaldehyde, p-ethylphenol-formaldehyde, p-hexylphenol-formaldehyde, p-propylphenol-formaldehyde, p-pentylphenol-formaldehyde, p- octylphenol-formaldehyde, p-heptylphenol-formaldehyde, p-nonylphenol- formaldehyde, bisphenol-A-formaldehyde, hydroxynapthaleneformaldehyde and alkyl- (such as t-butyl-) phenol modified ester (such as penterythritol ester) of rosin (particularly partially maleated rosin). See allowed U.S. Patent Application Serial No. 09/384,605, filed August 27, 1999 for examples of techniques to provide improved adhesion between copolyester elastomers and polyamide.

Polyesters functionalized with maleic anhydride ("MA") could also be used as adhesion-promoting additives. For, example, poly(butylene terephthalate) ("PBT") can be functionalized with MA by free radical grafting in a twin screw extruder, according to J.M. Bhattacharya, Polymer International (August, 2000), 49: 8, pp. 860-866, who also reported that a few weight percent of the resulting PBT-g-MA was used as a compatibilizer for binary blends of poly(butylene terephthalate) with nylon 66 and poly(ethylene terephthalate) with nylon 66. For example, such an additive could be used to adhere more firmly (co)polyamide wings to a (co)polyetherester core of the fiber of the present invention.

The polymers and resultant fibers, yarns, and articles used in the present invention can comprise conventional additives, which can be added during the polymerization process or to the formed polymer or article, and may contribute towards improving the polymer or fiber properties. Examples of these additives include antistatics, antioxidants, antimicrobials, flameproofing agents, dyestuffs, light stabilizers, polymerization catalysts and auxiliaries, adhesion promoters, delustrants such as titanium dioxide, matting agents, and organic phosphates. Other additives that may be applied on the fibers, for example, during spinning and/or drawing processes include antistatics, slickening agents, adhesion promoters, hydrophilic agents antioxidants, antimicrobials, flameproofing agents, lubricants, and combinations thereof. Moreover, such additional additives may be added during various steps of the process as is known in the art.

The fibers of the invention can be in the form of continuous filament (either a multifilament yarn or a monofilament) or staple (including for example tow or spun yarn). The drawn fibers of the invention can have a denier per fiber of from about 1.5 to about 60 (about 1.7- 67dtex). Fully drawn fibers of the invention with polyamide wing typically have tenacities of about 1.5 to 3.0 g/dtex, and fibers with polyester wing, about 1-2.5 g/dtex, depending on wing/core ratios. The resulting fibers of the invention can have an after boil-off stretch of at least about 20%, preferably of at least about 40% for improved comfort and fit in the final garment.

While the above description focuses on advantages when the fiber has a substantially radially symmetric cross-section, such symmetry, while often desired, is not required for embodiments of the invention where: (a) the stretchable synthetic polymer fiber has at least about 20% after boil-off shrinkage and requires less than about 10% stretch to substantially straighten the fiber;

(b) the stretchable synthetic polymer fiber comprises an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein the core includes on its outside surface a sheath of a non-elastomeric polymer between points where the wings contact the core;

(c) the stretchable synthetic polymer fiber comprises an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein the core has a substantially circular or regular polyhedron cross section; or

(d) the stretchable synthetic polymer fiber comprises an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein at least one of the wings has a T, C, or S shape. Such fibers according to these four embodiments can be made and used and can provide one or more of the advantages described herein. When a yarn comprising a plurality of fibers is made, the fibers can be of any desired fiber count and any desired dpf, and the ratios of the elastomeric to non-elastomeric polymers can differ from fiber to fiber. The multifilament yarn can contain a plurality of different fibers, for example, from 2 to 100 fibers. In addition, yarns comprising the fibers of the present invention can have a range of linear densities per fiber and can also comprise fibers not of the invention.

The synthetic polymer fibers of the present invention may be used to form fabrics by known means including by weaving, warp knitting, weft (including circular) knitting, or hosiery knitting. Such fabrics have excellent stretch and power of recovery. The fibers can be useful in textiles and fabrics, such as in upholstery, and garments (including lingerie and hosiery) to form all or a portion of the garment, including narrows. Apparel, such as hoisiery, and fabrics made using the fibers and yarns of the present invention have been found to be smooth, lightweight, and very uniform ("non-picky") with good stretch and recovery properties. Further in accordance with the present invention, there is provided a melt spinning process for spinning continuous polymer fibers. This process will be described with respect to Fig. 5, which is a schematic of an apparatus which can be used to make the fibers of the present invention. However, it should be understood that other apparatus may be used. The process of the present invention comprises passing a melt comprising an elastomeric polymer through a spinneret to form a plurality of stretchable synthetic polymeric fibers including an axial core comprising the elastomeric polymer and a plurality of wings attached to the core and comprising the non-elastomeric polymer. With reference to Fig. 5, a thermoplastic hard polymer supply, which is not shown, is introduced at 20 to a stacked plate spinneret assembly 35, and a thermoplastic elastomeric polymer supply, which is not shown, is introduced at 22 to a stacked pflate spinneret assembly 35. Precoalescence or post coalescence spinneret packs can be used. The two polymers can be extruded as undrawn filaments 40 from stacked plate spinneret assembly 35 having orifices designed to give the desired cross section. The process of the present invention further includes quenching the filaments after they exit the capillary of the spinneret to cool the fibers in any known manner, for example by cool air at 50 in Fig. 5. Any suitable quenching method may be used, such as cross-flow air or radially flowing air.

The filaments are optionally treated with a finish, such as silicone oil optionally with magnesium stearate using any known technique at a finish applicator 60 as shown in Fig. 5. These filaments are then drawn, after quenching, so that they exhibit at least about 20% after boil-off stretch. The filaments may be drawn in at least one drawing step, for example between a feed roll 80 (which can be operated at 150 to 1000 meters/minute) and a draw roll 90 shown schematically in Fig. 5 to form a drawn filament 100. The drawing step can be coupled with spinning to make a fully-drawn yarn or, if a partially oriented yarn is desired, in a split process in which there is a delay between spinning and drawing. Drawing can also be accomplished during winding the filaments as a warp of yarns; called "draw warping" by those skilled in the art. Any desired draw ratio, (short of that which interferes with processing by breaking filament) can be imparted to the filament, for example, a fully oriented yarn can be produced by a draw ratio of about 3.0 to 4.5 times, and a partially oriented yarn produced by a draw ratio of about 1.2-3.0 times. Herein, draw ratio is the draw roll 90 peripheral speed divided by the feed roll 80 peripheral speed. Drawing can be carried out at about 15-100°C, typically about 15- 40°C.

The drawn filament 100 optionally can be partly relaxed, for example, with steam at 110 in Fig. 5. Any amount of heat-relaxation can be carried out during spinning. The greater the relaxation, the more elastic the filament, and the less shrinkage that occurs in downstream operations. The drawn, final filament, after being relaxed as described below, can have at least about 20% after boil-off stretch. It is preferred to heat-relax the just-spun filament by about 1-35% based on the length of the drawn filaments before winding it up, so that it can be handled as a typical hard yarn. The quenched, drawn, and optionally relaxed filaments can then be collected by winding at a speed of 200 to about 3500 meters per minute and up to 4000 meters per minute, at a winder 130 in Fig. 5. Or if multiple fibers have been spun and quenched, the fibers can be converged, optionally interlaced, and then wound up for example at up to 4000 meters per minute at winder 130, for example in the range of about 200 to about 3500 meters per minute. Single filament or multifilament yams may be wound up at winder 130 in Fig. 5, in the same manner. Where multiple filaments have been spun and quenched, the filaments can be converged and oprtionally interlaced prior to winding as is done in the art.

At any time after being drawn, the biconstituent filament may be dry- or wet-heattreated while fully relaxed to develop the desired stretch and recovery properties. Such relaxation can be accomplished during filament production, for example during the above-described relaxation step, or after the filament has been incorporated into a yarn or a fabric, for example during scouring, dyeing, and the like. Heat-treatment in fiber or yarn form can be carried out using hot rolls or a hot chest or in a jet-screen bulking step, for example. It is preferred that such relaxed heat-treatment be performed after the fiber is in a yarn or a fabric so that up to that time it can be processed like a non-elastomeric fiber; however, if desired, it can be heat-treated and fully relaxed before being wound up as a high-stretch fiber. For greater uniformity in the final fabric, the fiber can be uniformly heat-treated and relaxed. The heat-treating/relaxation temperature can be in the range of about 80°C to about 120°C when the heating medium is dry air, about 75°C to about 100°C when the heating medium is hot water, and about 101 °C to about 115°C when the heating medium is superatmospheric pressure steam (for example in an autoclave). Lower temperatures can result in too little or no heat-treatment, and higher temperatures can melt the elastomeric core polymer. The heat- treating/relaxation step can generally be accomplished in a few seconds.

As noted above, the spinneret capillary has a design corresponding to the desired cross-section of the fibers of the present invention, as described above, or to produce other biconstituent or bicomponent fibers. The capillaries or spinneret bore holes may be cut by any suitable method, such as by laser cutting, as described in U.S. Patent No. 5,168,143, drilling, Electrical Discharge Machining (EDM), and punching, as is known in the art. The capillary orifice can be cut using a laser beam for good control of the cross-sectional symmetry of the fiber of the invention. The orifices of the spinneret capillary can have any suitable dimensions and can be cut to be continuous (pre-coalescence) or non-continuous (post- coalescence). A non-continuous capillary may be obtained by boring small holes in a pattern that would allow the polymer to coalesce below the spinneret face and form the multi-wing cross-section of the present invention.

For example, the filaments of the invention can be made with a precoalescence spinneret pack as illustrated in Figs. 6, 6A, 6B and 6C. In Fig. 6, a side elevation of the stacked plate spinneret assembly as shown in Fig. 5, the polymer flow is in the direction of arrow F. The first plate in the spinneret assembly is plate D containing the polymer melt pool and is of a conventional design. Plate D rests upon metering plate C (shown in cross sectional view Fig. 6C), which in turn rests upon optional distribution plate B (shown in cross sectional view Fig. 6B), which rests on spinneret plate A (shown in cross sectional view Fig. 6A), which is supported by spinneret assembly support plate E. Metering plate C is aligned and in contact with distribution plate B below the metering plate, the distribution plate being above, aligned with, and in contact with spinneret plate A having capillaries there through but lacking substantial counterbores, the spinneret plate(s) being aligned and in contact with a spinneret support plate (E) having holes larger than the capillaries. The alignments are such that a polymer fed to the metering plate C can pass through distribution plate B, spinneret plate A and spinneret support plate E to form a fiber. Melt pool plate D, which is a conventional plate, is used to feed the metering plate. The polymer melt pool plate D and spinneret assembly support plate E are sufficiently thick and rigid that they can be pressed firmly toward each other, thus preventing polymer from leaking between the stacked plates of the spinneret assembly. Plates A, B, and C are sufficiently thin that the orifices can be cut with laser light methods. It is preferred that the holes in the spinneret support plate (E) be flared, for example at about 45°-60°, so that the just-spun fiber does not contact the edges of the holes. It is also preferred that, when precoalescence of the polymers is desired, the polymers be in contact with each other (precoalescence) for less than about 0.30 cm, generally less than 0.15 cm, before the fiber is formed so that the cross-sectional shape intended by the metering plate C, optional distribution plate D, and spinneret plate design E is more accurately exhibited in the fiber. More precise definition of the fiber cross-section can also be aided by cutting the holes through the plates as described in U.S. Patent No. 5,168,143, in which a multi- mode beam from a solid-state laser is reduced to a predominantly single- mode beam (for example TMoo mode) and focused to a spot of less than 100 microns in diameter and 0.2 to 0.3 mm above the sheet of metal. The resulting molten metal is expelled from the lower surface of the metal sheet by a pressurized fluid flowing coaxially with the laser beam. The distance from the top of the uppermost distribution plate to the spinneret face can be reduced to less than about 0.30 cm.

To make filaments having any number of symmetrically placed wing polymer portions, the same number of symmetrically arranged orifices are used in each of the plates. For example in Fig. 6A, spinneret plate A is shown in a plan view oriented 90° to the stacked plate spinneret assembly of Fig. 5. Plate A in Fig. 6A is comprised of six symmetrically arranged wing spinneret orifices 140 connected to a central round spinneret hole 142. Each of the wing orifices 140 can have different widths 144 and 146. Shown in Fig. 6B is the complementary distribution plate B having distribution orifices 150 tapering at an open end 152 to optional slot 154 connecting the distribution orifices to central round hole 156. Shown in Fig. 6C is metering plate C with metering capillaries 160 for the wing polymer and a central metering capillary 162 for the core polymer. Polymer melt pool plate D can be of any conventional design in the art. Spinneret support plate E has a through hole large enough and flared away (for example at 45-60°) from the path of the newly spun filament so that the filament does not touch the sides of the hole, as is shown in Figs. 5 and 6 side elevation. The stacked spinneret plate Assembly, plates A through D, are aligned so that core polymer flows from polymer melt pool plate D through central metering hole 162 of metering plate C and through the 6 small capillaries 164, through central circular capillary 156 of distribution plate B, through central circular capillary 142 of spinneret assembly plate A, and out through large flared hole in spinneret support plate E. At the same time, wing polymer flows from polymer melt pool plate D through wing polymer metering capillaries 160 of metering plate C, through distribution orifices 150 of distribution plate B (in which, if optional slot 154 is present, the two polymers first make contact with each other), through wing polymer orifices 140 of spinneret plate A, and finally out through the hole in spinneret assembly support plate E.

The spinneret pack of the invention can be used for the melt extrusion of a plurality of synthetic polymers to produce a fiber. In the spinneret pack of the present invention, the polymers can be fed directly into the spinneret capillaries, since the spinneret plate does not have a substantial counterbore. By no substantial counterbore is meant that the length of any counterbore present (including any recess connecting the entrances of a plurality of capillaries) is less than about 60%, and preferably less than about 40%, of the length of the spinneret capillary. Directly metering multicomponent polymer streams into specific points at the backside entrance of the fiber forming orifice in the spinneret plate eliminates problems in polymer migration when multiple polymer streams are combined in feed channels substantially before the spinneret orifice, as is the norm.

It can be useful to combine the functions of two plates into one through the use of recessed grooves, on one or both sides of the single plate with appropriate holes through the plate to connect the grooves. For example, recesses, grooves and depressions can be cut in the upstream side of the spinneret plate (for example by electrodischarge machining) and can function as distribution channels or shallow, insubstantial counterbores.

A variety of fibers comprising two or more polymers can be made with the spinneret pack of the present invention. For example, other biconstituent fibers and bicomponent fibers not disclosed and/or claimed herein can be so made, including the cross-sections disclosed in U.S. Patent Numbers 4,861 ,660, 3,458,390, and 3,671 ,379. The resulting fiber cross-section can be for example side-by-side, eccentric sheath-core, concentric sheath-core, wing-and-core, wing-and-sheath-and core, and the like. Moreover, the spinneret pack of the invention can be used to spin splittable or non-splittable fibers.

In Fig. 7 a side elevation of the spinneret assembly stacked plates as shown in Fig. 5 is represented, where the polymer flow is in the direction of the arrows. The use of this assembly is exemplied in Example 6 below. The first plate in the spinneret assembly is plate D containing the polymer melt pool. This plate is of a conventional design known in the art and contains passages 20 and 22 for introduction of the non-elastomeric wing and sheath polymer and the elastomeric polymer respectively. Plate D rests upon metering plate H, which in turn rests upon distribution plate G, which rests on spinneret plate F, which rests upon plate C, which rests upon plate B, which rests upon the spinneret or plate A, which is supported by spinneret assembly support plate E. The polymer melt pool plate D and spinneret assembly support plate E are sufficiently thick and rigid and pressed firmly toward each other, thus preventing polymer from leaking between the stacked plates of the spinneret assembly. All other plates are sufficiently thin so that the orifices can be cut using laser light machining methods. Figs. 7A -7C and Figs. 7F-7H represent a plan view an alternative stacked plate spinneret assembly useful in making certain fibers of the present invention represented by the cross sectional view in Fig. 5. The elastomeric core polymer and non-elastomeric wing and sheath polymers are joined in Figs. 7A -7C and Figs. 7F - 7H using a precoalescence spinneret plate pack assembly of the same general type illustrated in the side elevation view of Fig. 6. In this alternative stacked plate spinneret assembly, a spinneret assembly support plate E, spinneret plate A, and polymer melt pool plate D are used, but five plates replace distribution plate B and metering plate C. Through spinneret plate A, shown in Fig. 7A are cut wing orifices 210, a central core polymer and sheath polymer hole 214, and connecting slots 212. Plate B, as shown in Fig. 7B, is cut through with wing orifices 220 and a central core polymer and sheath polymer hole 222 centered above spinneret plate A. Centered above plate B is plate C, as shown in Fig. 7C, cut through it are cone- shaped wing and sheath polymer orifices 230, a central core polymer and sheath polymer hole 232. An annular shaped portion of the plate 234 remains connected to the plate. Centered above plate C is plate F, shown in Fig. 7F, cut through with wing orifices 240 and central core polymer and sheath polymer hole 242. Centered above plate F is plate G, as shown in Fig. 7G, cut through with wing orifices 250, cone-shaped wing polymer and sheath polymer orifices 252, and a central core polymer hole 254. Centered above plate G is plate H, as shown in Fig. 7H, cut through it are wing polymer orifices 260, wing polymer and sheath polymer orifices 262, and a central core polymer hole 264. The invention is illustrated by the following non-limiting examples.

The following test methods were used in the Examples.

Test Methods

The term after boil-off stretch is used interchangeably in the art with the following terms: "% stretch", "recoverable stretch", "recoverable shrinkage" and "crimp potential". The term "non-recoverable shrinkage" is used interchangeably with the following terms: "% shrinkage", "apparent shrinkage" and "absolute shrinkage".

Stretch properties (after boil-off stretch, after boil-off shrinkage and stretch recovery after boil-off) of the fibers prepared in the Examples were determined as follows. A 5000 denier (5550 dtex) skein was wound on a 54 inch (137 cm) reel. Both sides of the looped skein were included in the total denier. Initial skein lengths with a 2 gram weight (length CB) and with a 1000 gram weight (0.2 g/denier) (length LB) were measured. The skein was subjected to 30 minutes in 95°C water ("boil off"), and initial (after boil off) lengths with a 2 gram weight (length CA_initiai) and with a 1000 gram weight (length LAinw_ai) were measured. After measurement with the 1000 gram weight, additional lengths were measured with a 2 gram weight after 30 seconds (length CA_30sec) and after 2 hours (length CA_2hrs)- Shrinkage after boil-off was calculated as 100 x (LB - LA) / LB. Percent after boil-off stretch was calculated as 100 x (LA - CA@30 sec) / CA@30 sec. Stretch recovery after boil-off was calculated as100 x (LA - CA_{2 rs}) / (LA - CAtnttiai)- The test for unload force at 20% and 35% available stretch was performed as follows. A biconstituent fiber skein having a total denier of 5000 (5550 dtex) after boil off was prepared. Both sides of the looped skein were included in the total denier. An Instron tensile tester (Canton, MA) was used at 21 °C and 65% relative humidity. The skein was placed in the tester jaws, between which there was a 3 inch (76 mm) gap. The tester was cycled through three stretch-and-relax (load-and-unload) cycles, each load cycle having a maximum of 500 grams force (0.2 grams per denier), and then the force on the 3^rd unload cycle was determined. An effective denier (that is, the actual linear density at the test elongation) was determined for 20% and 35% available stretch on the 3^rd unload cycle. "20% and 35% available stretch" means that the skein had been relaxed 20% and 35%, respectively, from the 500 gram force on the 3^rd cycle. The unload force at 20% and 35% available stretch was recorded in milligrams per effective denier (mg/denier).

Delamination of the wings from the core of a fiber was determined by first winding a 5000 denier (5550 dtex) skein (the skein size included both sides of the resulting loop) on a 1.25 meter reel. The skein was subjected to 102 °C steam in an autoclave for 30 minutes. A 20 cm length individual fiber was selected from the skein and folded once in half. The open end of the resulting loop was taped together at the bottom, and the taped loop was hung vertically on a hook. A weight of 1 gram per denier (50 grams for a 25 denier loop) was attached to the bottom (taped) end of the loop. The weight was raised to the point at which the loop was slack, and then lowered gently to stretch the loop and apply the full weight. After 10 such cycles the loop was examined for delamination under magnification and rated. Three samples were rated as follows:

0 = No wing / core delamination visable along the fiber

1 = Slight delamination observed at one or more of the node reversals 2 = Delamination observed where the fiber rubbed against the hook from which it was hanging

3 = Marginal delamination (in small loops, and only in a few spots) 4 =Small loops indicating delamination along the entire fiber

5 = Gross delamination (large loops all along the fiber) The results from the three samples were averaged.

Ri and R₂ were measured by superimposing two circles on a photomicrograph of a cross-section of the fiber so that one circle (Ri) circumscribed the approximate outermost extent of the core polymer and the other circle (R₂) inscribed the approximate innermost extent of the wing polymer.

Example 1.A A biconstituent fiber of the invention having a symmetrical six-wing cross-section substantially as shown in Fig. 1 was spun using an apparatus as illustrated in Fig. 5. A single fiber 40 was spun using spinneret plate 35 and a spinneret temperature of 265°C. At 20 in Fig. 5 a melted nylon polymer conventionally prepared and having a relative viscosity of about 45-60, was introduced to the spin pack assembly 30. The nylon polymer which formed the wing portion of the biconstituent filament was poly(hexamethylene-co-2-methylpentamethylene adipamide) in which the hexamethylene moiety was present at 80 mol% (6/MPMD(80/20)-6) to which 5% by weight based on total wing polymer, nylon 12 (poly(12-dodecanolactam)) (also known as "12" or "N12")

(Rilsan^® "AMNO" from Atofina) had been added. The nylon 12 was added to aid wing-to-core cohesion. The wing portions were 45 wt% of the fiber. A second polymer, which formed the core of the fiber, was introduced at 22 to spin pack assembly 30 in Fig. 5. The core polymer was an elastomeric segmented polyetheresteramide (PEBAX™ 3533SN from Atofina; flex modulus 2800 psi (19,300 kPascals) ) and was metered volumetrically to create a core which was 55 wt% of the biconstituent fiber.

Precoalescence spinneret pack assembly 30 was comprised of stacked plates labeled A through E in Fig. 6. Orifices were cut through 0.015 inch (0.038 cm) thick stainless steel spinneret plate A as six wings arranged symmetrically at 60 degrees, around a center of symmetry using a process as described in U.S. Patent No. 5,168,143. As illustrated in Fig. 6A, each wing orifice 140 was straight with a long axis centeriine passing through the center of symmetry and had a length of 0.049 inches (0.124 cm) from tip to the circumference of a central round spinneret hole 142 (diameter 0.012 inches [0.030 cm]) with origin of radius the same as the center of symmetry. There was no counterbore at the entrance to the spinneret capillary. The wing length 144 from tip to 0.027 inches (0.069 cm) was 0.0042 inches (0.0107 cm) wide; the remaining length 146 of 0.022 inches (0.056 cm) was 0.0032 inches (0.0081 cm) wide. The tip of each wing was radius-cut at one-half the width of the tip. Distribution plate B of 0.015 inches (0.038 cm) thickness was aligned with the spinneret plate A so that its distribution orifices were congruent with the spinneret orifices in the spinneret plate A. The six wing orifices of plate B were 0.094 inch (0.239 cm) long and 0.020 inch (0.051 cm) wide, and their wing tips were rounded to a radius one-half their width. As illustrated in Fig. 6B, each of the six wing orifices 150 of distribution plate B tapered to a rounded (0.006 inch [0.015 cm] diameter) open end 156 and then continued as a slot of 0.013 inch (0.033 cm) length and 0.0018 inch (0.0046 cm) length to central hole 156. The central hole 156 in this plate was 0.0125 inches (0.032 cm) in diameter. A slot 154 connected the central hole with the end of each wing distribution orifice. Metering plate C was of 0.010 inch (0.025 cm) thickness (see Fig. 6C). Each of the metering holes was centered above a wing long axis centeriine or above the center of symmetry in distribution plate B. The central metering hole 152 and one hole per wing 160 were 0.010 inch (0.025 cm) diameter; the centers of holes 160 were 0.120 inch (0.305 cm) from the center of hole 162. The central metering hole was fed filtered melted elastomeric polymer from a conventional melt pool plate D (see Fig. 6) and formed the core element within the final fiber. The outer six metering holes of plate C were fed a non-elastomeric polymer from melt pool plate D to become the polymer wings. Large holes (typically 0.1875 inches (0.4763 cm) in diameter) in spinneret support plate E (see again Fig. 6) were aligned with the spinneret orifices in spinneret plate A and were flared at 45°. Spinneret plate A, distribution plate B, and metering plate C were sandwiched by melt pool plate D and spinneret support plate E. Typically, plate E was 0.2-0.5 inches (0.4-1.3 cm) thick, and plate D was 0.02-0.03 inches (0.05-0.08 cm) thick.

A single freshly spun fiber 40 (see Fig. 5) was cooled to solidify it by a flow of air 50, and a finish (about 5 wt% based on fiber) comprising silicone oil and a metal stearate was applied at 60. The fiber was forwarded to a draw zone between feed roll 80 and draw roll 90, taking several wraps about each roll. The speed of draw roll 90 was four times that of feed roll 80 for a draw ratio of 4X; the latter speed was 350 meters per minute. The fiber was then treated with steam at 6 pounds per square inch 0.87 kilopascal) in a chamber 110; winder 130 was operated at a speed 20% lower than that of draw roll 90 so that the fiber was partly (20%) relaxed in order to reduce shrinkage in the final fiber. The drawn and partly relaxed fiber 120 was wound up at winder 130 and had a linear density of 27 denier (30 dtex).

Example 1.B

A biconstituent yarn of the invention having 10 fibers, each with 6 radially symmetric wings of nylon 6-12 (poly(hexamethylene dodecanamide)), (intrinsic viscosity 1.18), Zytel® 158, a registered trademark of E. I. du Pont de Nemours and Company; flex modulus 295,000psi (2.0 million kPascals) and a core of PEBAX™ 3533SA was spun using the apparatus of Fig. 5 in substantially the same way as in Example 1.A, except that the spinneret temperature was 240 °C, distribution plate B had no slot 154, and 4 wt% of a polyetherester-based finish was applied in place of the finish applied in Example 1.A, the draw ratio was 3.75X, and the yarn was relaxed 15%. The drawn and partly relaxed yarn had a linear density of 80 denier (88 dtex). A photomicrograph of the cross-section of the resulting fiber is shown in Fig. 8. Example 1.C

A biconstituent yarn of the invention of 10 filaments with five radially symmetric wings on each filament of poly(butylene terephthalate) (4G-T) (Crastin® Type 6129, a registered trademark of E. I. du Pont de Nemours and Company; 350,000 psi flex modulus (2.4 million kPascals)) and having a HYTREL^® (a registered trademark of E. I. du Pont de Nemours & Company, Inc.) 3078 elastomeric polyetherester core was prepared analogously to that of Example 1.A except that: each plate had five holes for wing polymer supply arranged symmetrically at 72° apart; the metering plate C had an additional set of holes, one per wing on the centeriine of the wing; the 4G-T wings had no cohesion additive; 4 wt% of a finish comprising polysiloxane as described in United States Patent No. 4,999,120 was used in place of the finish applied in Example 1.A; the feed roll speed was 250 meters per minute; the draw ratio was 3.6X; and the steam pressure for relaxation was 20 pounds per square inch 2.9 kilopascal). The drawn and partly relaxed yarn had a linear density of 150 denier (165 dtex).

With regard to the additional set of holes on the metering plate C, one per wing on the centeriine of the wing, each hole was 0.005 inches (0.013 cm) in diameter and 0.0475 inches (0.121 cm) from the center of symmetry of the holes. However, the additional holes were not fed melted polymer by melt pool plate D.

The yarns prepared in Example 1.A - C were compared for after boil-off stretch, after boil-off shrinkage, and stretch recovery after boil-off. The test was carried out by first preparing a 5000 denier (5550 dtex) skein of yarn which was wound on a 54 inch (137 cm) reel. Both sides of the looped skein were included in the total denier. The initial skein length with a light and a heavy weight were measured and the following measurements were recorded:

CB = measured skein length with 2 gram weight

LB = measured skein length with 1000 gram weight (0.2 grams per denier). The following initial and final lengths were measured after hot aqueous treatment or "boil off which subjected the skein to a 30 minute dip in 95°C water:

CA (initial) = measured skein length after treatment with 2 gram weight

LA = measured skein length after treatment with 1000 gram weight applied (0.2 grams per denier) CA (30 seconds) = measured skein length 30 seconds after LA measured with 1000 gram weight removed and 2 gram weight applied

CA (2 hrs) = measured skein length 2 hours after LA measured, with 2 gram weight applied

These measurements were used to calculate the yarn characteristics as follows:

Percent Stretch after boil off = 100 x (LA - CA@30sec) / CA@30sec

Boil-Off Shrinkage = 100 x (LB - LA) / LB.

Percent Recovery after boil-off = 100 x (LA - CA@2hrs) / (LA -

CA@initial)

The yarn properties of boil-off shrinkage, percent after boil-off stretch and stretch recovery reported in Table 1 for the yarns of Example 1.A - 1.C are suitable for hosiery and apparel applications.

TABLE 1.

Example 2 A sheer hosiery leg blank was knitted using four fibers prepared in

Example 1.A. A commercial four-feed hosiery machine (Lanoti Model 400, 402 needles) was used. The fibers were knit in a typical four-feed, every-course jersey leg construction typical for commercial pantyhose. The filaments were knit directly from the wound package and behaved like a "hard" yarn, that is, without elastomeric character. The four filaments were independently fed to the machine needles directly through standard creel guides, each of which had a conventional dancer ring tensioner typically used for feeding non-elastomeric yarns to hosiery knitting machines. The hose blanks were knit at 700 rpm in the thigh area and 800 rpm in the ankle. Each blank was knit in about 2 minutes, including a panty portion in a standard nylon spandex panty style.

The griege size of the hose blank was adjusted by conventional means to meet standard size specifications. Next, the greige hosiery leg blanks were heat-treated to activate the latent stretch characteristic in the biconstituent fiber. This was done in one of two ways. In one method, the greige pantyhose blanks were placed in a cloth bag and agitated in a water bath at room temperature. The bath was raised in temperature with steam to 85°C over 45 mintues and then cooled with room temperature water while agitated. The bagged blanks were dewatered in a centrifuge and dried in an oven at 100°C. In another method, the blanks were shrunk by tumble steaming using atmospheric pressure steam for 30 minutes. In either case, the fiber of the invention was made highly stretchable but not bulky by the relaxed hot treatment. The blanks were then removed from the bags and sewn into pantyhose in a conventional way. The garments were then rebagged and dyed using standard acid dye procedures for nylon hosiery with a maximum dye bath temperature of 99° C. The dyed garments were dewatered, dried, and boarded on standard 4 inch (10.2 cm) base width hosiery boards. The boarding autoclave was set to treat the hose for 4 seconds at 102°C, followed by drying at 99°C for 30 seconds. The pantyhose were placed on the boards so that they remained as small as possible while holding the fabric in a wrinkle -free state. The appearance of the finished garments was suitable for sheer hosiery applications, and they showed good stretch and recovery. Their shrinkage at each stage of finishing was measured as described below, and the magnitude and consistency of sizing of the finished goods was found suitable for the commercial manufacture of hosiery products.

Cross-stretch measurements were taken on the greige fabric and again after a ten-minute hot aqueous treatment (boil off) to assess shrinkage and potential to meet typical size standards. The cross-stretch measurements were made by slipping each blank over the jaws of a Dinema S.R.L. instrument, separating the jaws, and measuring the percent stretch when the force on the jaws reached 4500 grams. Measurements were taken 3 inches (7.6 cm) below the crotch ("Thigh"), ¹Λ way between the toe and the crotch ("Knee"), and about 3.5 inches (8.9cm) up from the toe ("Foot"). The leg pull stretch was measured similarly except that each blank was clamped length-wise between the jaws of the instrument. The stretch values were 22% for the thigh, 21 % for the knee, 17% for the foot, and 138% for the leg pull. A shrinkage level of approximately 17-24% from greige to boil-off dimension was determined for the thigh, knee, foot, and leg pull and was little changed after further boarding and dyeing, indicating that the blanks were dimensionally stable, as needed for commercial use.

Example 3

Yarns from Example 1.B were used to construct a weft-stretch woven fabric on a shuttle loom in a "Crowfoot" construction with TACTEL^® a registered trademark of E. I. du Pont de Nemours and Company) 70 denier (78 decitex) 6-6 nylon in the warp with 102 ends per inch (40/cm). The Example 1.B 80 denier (89 decitex) 10 filament biconstituent yarn was the weft fiber at 100 picks per inch (39/cm). The greige woven fabric width was 62.5 inches (159 cm). This fabric was finished using a relaxed state scour at 71 °C, followed by a second relaxed scour at 118°C. After drying, this fabric had a relaxed width of 36 inches (91 cm). This fabric was dyed at 100°C with standard acid dyes for nylon. The after dyeing wet width was 33 inches (84 cm). Finally, this fabric was air dried without heat setting. The final width was 33.25 inches (84 cm). This fabric was non- bulky, smooth and non-wrinkled after only air drying. The fabric showed good stretch and recovery, and excellent hard fiber hand and aesthetics. In the relaxed finished state, this fabric had the following properties:

Basis weight: 4.45 oz./yard² (151 grams/m²);

Thickness: 0.0103 inch (0.0262 cm);

Fill Count: 112 weft threads per inch (44/cm); Warp Count: 192 warp threads per inch (76.8/cm).

A 5 cm width by 10 cm length of this fabric was evaluated for hand stretch to full extension in the weft. The fabric could be stretched 65% of its relaxed length and showed recovery after hand stretching of greater than 95% of the difference between its stretched and relaxed length.

Example 4

Yarns from Example 1.C were used to construct a weft-stretch woven fabric on a shuttle loom in a plain weave construction with DuPont TACTEL^® 70 denier (78 decitex) 6-6 nylon in the warp with 102 ends per inch (40/cm). The Example 1.C 150 denier (166 decitex) 10 filament biconstituent yarn was the weft fiber at 50 picks per inch (19.7/cm). The greige woven fabric width was 63.5 inches (161 cm). This fabric was finished using a relaxed state scour at 82°C for 20 minutes. The fabric was dyed at 100 °C for 60 minutes with standard acid dyes for nylon, and dried at 93°C. The final dry width was 33.5 inches (85 cm). This fabric was non-bulky, smooth and non-wrinkled. The fabric showed good stretch and recovery, and excellent hard fiber hand and aesthetics. In the relaxed finished state, this fabric had the following properties:

Basis weight: 4.5 oz./yard² (152 grams/m²);

Thickness: 0.0115 inch (0.0292 cm);

Fill Count: 60 weft threads per inch (23.6/cm); Warp Count: 204 warp threads per inch (80/cm).

A 5 cm width by 10 cm length of this fabric was evaluated for hand stretch to full extension in the weft. The fabric could be stretched 72.8% of its relaxed length and showed recovery after hand stretching of greater than 97% of the difference between its stretched and relaxed length.

Example 5

This example illustrates the benefit of using an adhesion promoter (see Example 5B) in making the fiber of the invention. Biconstituent fibers were spun using the apparatus illustrated in Fig. 5 and the conditions and spinneret pack analogous to those described for Example 1.A. Each drawn fiber had a linear density of 26 denier (28.6 dtex). After- boil-off properties and delamination ratings are reported in Table 2.

Example 5. A.

The elastomeric core polymer was an elastomeric polyetheresteramide (PEBAX™ 3533SN, from Atofina) and was metered volumetrically during spinning to create a core which was 51 wt% of each fiber. The nylon blend, which formed the six wings, was poly(hexamethylene-co-2-methylpentamethylene adipamide), as described in Example 1.A. A photomicrograph of the cross-section of the resulting fiber is shown in Fig. 9.

Example 5.B.

A fiber having 6 wings of 6/MPMD(80/20)-6 polyamide (poly(hexamethylene-co-2-methylpentamethylene adipamide) in which the hexamethylene moiety was present at 80 mol%) and a core of elastomeric polyetheresteramide (PEBAX™ 3533SN) was spun substantially as in Example 5.A. except that 5 wt% poly(12-dodecanolactam as described in Example 1.A was added to the wing polymer to aid in wing-to-core cohesion.

Delamination of the wings from the core of a fiber was determined by first winding a 5000 denier (5550 dtex) skein (the skein size included both sides of the resulting loop) on a 1.25 meter reel. The skein was subjected to 102 °C steam in an autoclave for 30 minutes. An individual fiber having a length of 20 cm was selected from the skein and folded once in half. The open end of the resulting loop was taped together at the bottom, and the taped loop was hung vertically on a hook. A weight of 1 gram per denier (0.9 dN/tex) (50 grams for a 25 denier [28 dtex] loop) was attached to the bottom (taped) end of the loop. The weight was raised to the point at which the loop was slack, and then lowered gently to stretch the loop and apply the full weight. After 10 such cycles the loop was examined for delamination under magnification and rated. Three samples were rated as follows:

0 = No wing / core delamination visable along the fiber

3 = Marginal delamination (in small loops, and only in a few spots)

4 = Small loops indicating delamination along the entire fiber

5 = Gross delamination (large loops all along the fiber) The results from the three samples were averaged and are reported in Table 2.

TABLE 2

The results show that using selected pairs of core and wing polymers can give a fiber that resists delamination (Example 5.A) and that using an adhesion promoter can have a beneficial effect on further reducing the delamination rating of the fiber, for example to below a rating of about 2.5 (Example 5.B).

Example 6

This example illustrates a fiber of the invention having a particular two-wing cross-section and the use of a thin sheath comprising the same polymer as the wings and continuously connecting the wings. In this case a side of each wing (as distinct from an end of the wing) is attached to the core so the wing has a T-shape (See Fig. 4). The thin sheath encapsulates the core and eliminates the contact of the elastomer with surfaces.

In making the fiber in this Example, poly(hexamethylene dodecanamide) (Zytel^® 158) was used as the wing polymer and a polyetherester having a poly(tetramethylene-co-2-methyltetramethylene ether) glycol soft segment and butylene terephthalate (4G-T) hard segment, prepared substantially as described in United States Patent 4,906,721 was used as the core. The amount of 3-methyltetrahydrofuran incorporated into the copolyether glycol was 9 mol%, the glycol number average MW was 2750, and the mole ratio of 4G-T to copolyether glycol was 4.6:1.

The polymers were spun using the configuration of spinneret plates as shown in Figs. 7A - 7C and Figs. 7F - 7H. In spinneret plate A (Fig. 7A), the sheath-core hole had a diameter of 0.011 inches [0.028 cm]. The core-and-sheath hole of first plate B (Fig. 7B) had a diameter of 0.008 inches [0.020 cm]. The core-and-sheath hole of first plate B (Fig. 7B) had a diameter of 0.025 inches [0.064 cm], and the annulus of this plate had an outer diameter of 0.100 inches [0.254 cm]. The core-and-sheath hole of third plate F (Fig. 7F) had a diameter of 0.125 inches [0.318 cm]. The central core hole of fourth plate G (Fig. 7G) had a diameter 0.025 inches [0.064 cm]) and the annulus of this plate had an outer diameter of 0.100 inches [0.254 cm]. The central core hole of the fifth plate H (Fig. 7H) had a diameter of 0.033 inches [0.084 cm]. The central holes and annuli were of dimensions such that the polymer flows were as follows. Core polymer was fed straight through the central core holes of each of the plates. Wing-and-sheath polymer was fed to the wing orifices and outer part of the core hole of spinneret plate A by the wing orifices and the outer part of central hole of plate B, respectively. The first contact between wing and core was therefore in spinneret plate A. The cone-shaped wing-and-sheath orifices of plate C fed part of the polymer downward into the wing orifices of plate B and fed part of the polymer upward to the outer edge of central hole of plate F, thus forming part of the sheath. The cone-shaped wing-and-sheath orifices of plate C were fed by the orifices of plate F. The orifices of plate F were fed by the orifices of plate G. The cone-shaped orifice of plate G fed the outer edge of the central hole of plate F, thus forming the other part of the sheath. The first contact between sheath and core was therefore at plate F. The orifices in plate H fed the orifices, respectively, in plate G. In the fibers made in this example, the weight ratio of wing to core was 56/44, and the sheath was about 10 wt% of the total wing content. This percent can be varied from about 2 to about 20 wt%. Ten filaments were spun, drawn 3.6X without relaxation, and wound up at 900 meters per minute. Upon relaxed exposure to atmospheric pressure steam, the fiber immediately shrank and thereafter exhibited good stretch and recovery.

Example 7

This example shows that fully circumferential spiral twist is unnecessary to achieve the stretch and recovery desired in the fiber of the invention.

The wing and core polymers used in Example 1.C were spun through a spinneret pack similar to that used in Example 1.A, with the following differences: the wing orifices in spinneret plate A had a length of 0.023 inches (0.058 cm), and the central round hole had a diameter of 0.008 inches (0.200 cm); distribution plate B lacked slots 154 (see Fig. 6B); ten fibers were spun to form a yarn, each fiber being 33 wt% wing polymer; the yarn was drawn 3.3X without relaxation and wound up at 1040 meters/minute. Figs. 8 and 9 are photomicrographs of the resulting fibers in the yarn, showing both circumferential spiral twist and noncircumferential spiral twist of the wings. Circumferential twist sections and noncircumferential twist sections had similar responses to full relaxation: a 10 cm length subjected to atmospheric pressure steam shrank to 4.8 cm. Repeated stretch-and-relax cycles (to 10 cm) resulted in a length of 6.5 cm, which however again shrank to 4.8 cm on renewed exposure to atmospheric pressure steam, indicating a reversible set. While the invention has been described in conjunction with the detailed description thereof, it is to be understood that the foregoing description is exemplary and explanatory in nature, and is intended to illustrate the invention and its preferred embodiments. Through routine experimentation, the artisan will recognize apparent modifications and variations that may be made without departing from the spirit of the invention.

Claims

WHAT IS CLAIMED IS:

1. A stretchable synthetic polymer fiber having a substantially radially symmetric cross-section and comprising an axial core comprising a thermoplastic, elastomeric polymer, and a plurality of wings comprising at least one thermoplastic, non-elastomeric polymer attached to the core.

2. The fiber of claim 1 , which comprises from 3 to 8 wings, has an after-boil-off stretch of at least about 20%, requires less than about 10% stretch to substantially straighten the fiber, has a substantially circular core cross-section, and wherein the weight ratio of non-elastomeric wing polymer to elastomeric core polymer is in the range of about 10/90 to about 70/30.

3. The fiber of claim 1 , wherein the non-elastomeric polymer is selected from the group consisting of non-elastomeric polyamides, polyolefins and polyesters, and the elastomeric polymer is selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyester elastomers, thermoplastic polyolefins, thermoplastic polyesteramide elastomers and thermoplastic polyetheresteramide elastomers.

4. The fiber of claim 1 , wherein the non-elastomeric polymer is selected from the group consisting of a) poly(hexamethylene adipamide) and copolymers thereof with 2-methylpentamethylene diamine and b) polycaprolactam, and the elastomeric polymer is a polyetheramide.

5. The fiber of claim 1 , wherein the non-elastomeric polymer is selected from the group consisting of poly(ethylene terephthalate) and copolymers thereof, poly(trimethylene terephthalate), and poly(tetramethylene terephthalate), and the elastomeric polymer is selected from the group consisting of the reaction products of poly(tetramethyleneether) glycol or poly(tetramethylene-co-2- methyltetramethyleneether) glycol with terephthalic acid or dimethyl terephthalate and a diol selected from the group consisting of 1 ,3-propane diol and 1 ,4-butane diol.

6. The fiber of claim 1 , wherein the core includes on its outside surface a sheath of a non-elastomeric polymer between points where the wings contact the core.

7. The fiber of claim 1 further comprising an additive added to the non- elastomeric polymer of the wings to improve adhesion of the wings to the core, wherein this fiber has a delamination rating below about 2.5.

8. The fiber of claim 7, wherein the non-elastomeric polymer is selected from the group consisting of (a) poly(hexamethylene adipamide) and copolymers thereof with 2-methylpentamethylene diamine and (b) polycaprolactam, and the elastomeric polymer is a polyetheresteramide.

9. A stretchable synthetic polymer fiber having at least about 35% after boil-off shrinkage and which requires less than about 10% stretch to substantially straighten the fiber.

10. A stretchable synthetic polymer fiber comprising an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein the core includes on its outside surface a sheath of a non-elastomeric polymer between points where the wings contact the core.

11. A stretchable synthetic polymer fiber comprising an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein the core has a substantially circular or regular polyhedron cross section.

12. A stretchable synthetic polymer fiber comprising an axial core comprising an elastomeric polymer and a plurality of wings comprising a non-elastomeric polymer attached to the core, wherein at least one of the wings has a T, C, or S shape.

13. A garment comprising the fiber of claims 1 , 9, 10, 11 or 12.

14. A melt spinning process for spinning continuous polymeric fibers comprising: passing a melt comprising at least one thermoplastic non- elastomeric polymer and a melt comprising a thermoplastic elastomeric polymer through a spinneret to form a plurality of stretchable synthetic polymeric fibers having a substantially radially symmetric cross-section and comprising an axial core comprising the elastomeric polymer and a plurality of wings comprising the non-elastomeric polymer attached to the core; quenching the fibers after they exit the capillary of the spinneret to cool the fibers, and collecting the fibers.

15. The process of claim 14, comprising an additional step, after quenching, of heat-relaxing the fiber so that it exhibits at least about 20% after-boil-off stretch.

16. The process of claim 15, wherein the heat-relaxing is carried out with a heating medium of dry air, hot water or superatmospheric pressure steam at a temperature in the range of about 80°C to about 120°C when the heating medium is said dry air, about 75°C to about 100°C when the heating medium is said hot water, and about 101°C to about 115°C when the heating medium is said superatmospheric pressure steam.

17. The process of claim 14, comprising an additional step, after the quenching, of drawing the fiber so that it exhibits at least about 20% after- boil-off stretch.

18. The process of claim 14, comprising an additional step, after the quenching, of relaxing the fiber by in the range of about 1-35% based on the fiber length before relaxing.