High speed spinning of sheath/core bicomponent fibers

Details High speed spinning of sheath/core bicomponent fibers High speed spinning of sheath/core bicomponent fibers

2000-02-14

2001-12-25

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With twining, plying, braiding, or textile fabric formation

C264S172120, C264S172150, C264S172170, C264S172180, C264S210800

Reexamination Certificate

active

06332994

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to melt-spinning of synthetic fibers. More specifically, the present invention relates to melt-spinning processes by which sheath/core bicomponent polyamide fibers are produced.
BACKGROUND AND SUMMARY OF THE INVENTION
Polyamide fibers are relatively inexpensive and offer a combination of desirable qualities such as comfort, warmth and ease of manufacture into a broad range of colors, patterns and textures. As a result, polyamide fibers are widely used in a variety of household and commercial articles, including, for example, carpets, drapery material, upholstery and clothing. Carpets made from polyamide fibers are a popular floor covering for both residential and commercial applications.
Sheath/core polyamide fibers are, in and of themselves, well known. For example, U.S. Pat. No. 5,447,794 (incorporated by reference herein) discloses sheath/core polyamide filaments which are resistant to staining. According to the '794 patent, the core component may be nylon 6, nylon 6,6 and copolymers thereof, while the sheath component may be high carbon nylons, such as nylon 12,12, nylon 6,12, nylon 6,10, nylon-11 and the like.
The current wisdom in the fiber-spinning art is that conventional sheath/core polyamide bicomponent fibers must be melt-spun at relatively slow melt-spinning speeds. In this regard, relatively low speed spinning of sheath/core bicomponent fibers is thought to be necessary in order to ensure that the sheath component provides complete coverage of the core component (i.e., so that the sheath component completely surrounds the core component along the entirety of the fiber length). For example, the '794 patent discloses that spinning speeds of less than 500 meters per minute were employed. (See, column 5, lines 23-24 of the '794 patent.)
Because of the attractive properties that sheath/core polyamide bicomponent fibers have or can be made to have, it would be highly desirable if they could be melt spun at relatively high melt-spinning rates, for example, about 4000 meters per minute or greater, and more preferably about 4500 meters per minute or greater. High speed spinning of bicomponent fibers would thus greatly contribute to lower cost fiber production. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in processes whereby sheath/core bicomponent fibers are melt-spun at relatively high spinning rates. In particularly preferred forms, the present invention is embodied in melt-spinning polyamide sheath/core bicomponent fibers at melt-spinning speeds of about 4000 meters per minute or greater, and more preferably about 4500 meters per minute or greater. Most preferably, the sheath is formed of nylon 6,12 while the core is formed of nylon 6.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.
DETAILED DESCRIPTION OF THE INVENTION
As used herein and in the accompanying claims, the term “fiber-forming” is meant to refer to polymers which are capable of being formed into a fiber structure having a length at least 100 times its width. The term “fiber” includes fibers of extreme or indefinite length (filaments) and fibers of short length (staple). The term “yarn” refers to a continuous strand or bundle of fibers. The term “bicomponent fiber” is a fiber having at least two distinct cross-sectional domains respectively formed of different polymers and is therefore intended to include concentric and eccentric sheath-core fiber structures.
Virtually any melt-spinnable polymer may be employed in the practice of the present invention. Classes of suitable polymeric materials include polyamides, polyesters, acrylics, olefins, maleic anhydride grafted olefins, and acrylonitriles.
The preferred polymers used in forming the core and sheaths of the bicomponent fibers of this invention are polyamides. In this regard, those preferred polyamides are generically known by the term “nylon” and are long chain synthetic polymers containing amide (-CO-NH-) linkages along the main polymer chain. Suitable melt spinnable, fiber-forming include those which are obtained by the polymerization of a lactam or an amino acid, or those polymers formed by the condensation of a diamine and a dicarboxylic acid. Typical polyamides useful in the present invention include nylon 6, nylon 6/6, nylon 6/9, nylon 6/10, nylon 6T, nylon 6/12, nylon 11, nylon 12, nylon 4,6 and copolymers thereof or mixtures thereof. Polyamides can also be copolymers of nylon 6 or nylon 6/6 and a nylon salt obtained by reacting a dicarboxylic acid component such as terephthalic acid, isophthalic acid, adipic acid or sebacic acid with a diamine such as hexamethylene diamine, methaxylene diamine, or 1,4-bisaminomethylcyclohexane. Preferred are poly-&egr;-caprolactam (nylon 6) and polyhexamethylene adipamide (nylon 6/6). Most preferred is nylon 6. The preferred polyamides will exhibit a relative viscosity of between about 2.0 to about 4.5, preferably between about 2.4 to about 4.0.
The fiber-forming polymers used to form the core and sheath of the bicomponent fibers are different from one another. The particular fiber-forming polymer that is used may be selected based on the final fiber physical property that may be desired. Most preferably, the core polymer is nylon 6 and the sheath polymer is nylon 6,12.
Most preferably, the sheath is relatively thin as compared to the core. That is, the sheath polymer completely surrounds the core polymer and accounts for less than about 30 wt. %, usually less than about 15 wt. %, and typically less than about 10 wt. % of the total fiber weight. Most preferably, the sheath polymer is present in an amount between about 3 wt. % to about 30 wt. %, typically between about 3 wt. % to about 15 wt. % and usually between about 3 wt. % to about 10 wt. % of the total fiber weight. Conversely, the core polymer is present in an amount of between greater than about 70 wt. % to about 97 wt. %, usually between about 85 wt. % to about 97 wt. %, and usually between about 90 wt. % to about 97 wt. % of the total fiber weight.
The sheath-core fibers are spun using conventional fiber-forming equipment. Thus, for example, separate melt flows of the sheath and core polymers may be fed to a conventional sheath-core spinnerette pack such as those described in U.S. Pat. Nos. 5,162,074, 5,125,818, 5,344,297 and 5,445,884 (the entire content of each patent being incorporated expressly hereinto by reference) where the melt flows are combined to form extruded multi-lobal (e.g., tri-, tetra-, penta- or hexalobal) fibers having sheath and core structures. Preferably, the fibers have a trilobal structure with a modification ratio of at least about 2.0, more preferably between 2.2 and 4.0. In this regard, the term “modification ratio” means the ratio R
1
/R
2
, where R
2
is the radius of the largest circle that is wholly within a transverse cross-section of the fiber, and R
1
is the radius of the circle that circumscribes the transverse cross-section. The fibers could also have a substantially circular cross-section (i.e., a modification ratio of substantially about 1.0).
The extruded fibers are quenched, for example with air, in order to solidify the fibers. The fibers may then be treated with a finish depending on the particular end-use application envisioned. For example, the fibers may be treated with a finish which comprises a lubricating oil or mixture of oils and antistatic agents. The thus formed fibers are then combined to form a yarn bundle which is then wound on a suitable package.
While the melt-spinning equipment is conventional, the spinning speed employed to spin the bicomponent fibers of this invention is quite unconventional. Specifically, unlike the prior art, the present invention melt-spins the bicomponent fibers at relatively high melt-spinning rates. Preferably, the fibers are melt-spun at rates of about 4000 meters per minute or grea

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