Process for producing yarn having reduced heatset shrinkage

Details Process for producing yarn having reduced heatset shrinkage Process for producing yarn having reduced heatset shrinkage

1998-09-08

2003-03-04

Juska, Cheryl A. (Department: 1771)

Stock material or miscellaneous articles

Pile or nap type surface or component

Composition of pile or adhesive

C428S092000, C428S369000, C428S370000, C428S373000, C428S397000, C442S200000, C442S311000, C442S364000, C028S219000, C028S247000

Reexamination Certificate

active

06528139

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of fibers. More particularly, the present invention relates to a process for producing yarn having reduced heatset shrinkage.
BACKGROUND OF THE INVENTION
Polyamide, particularly nylon 6, has been used extensively as a synthetic fiber. Its structural and mechanical properties make it attractive for use in such capacities as face fiber for carpeting.
Polyamide fibers, yarns, carpets, and fabrics are often heatset using either moist or dry heat to provide the fibers, yarns, carpets, and fabrics with dimensional stability. A steaming unit made by Superba of Mulhouse, France or American Superba, Inc. of Charlotte, N.C. is typical of the equipment employed in heatsetting with moist heat. Typically, the heatsetting temperature for nylon 6 is in the range of 124° C. to 127° C. Polyamide fibers, yarns, carpets, and fabrics often shrink during heatsetting. The typical heatset shrinkage encountered with 100 percent nylon 6 fibers, etc. is about 24 percent to about 32 percent. High heatset shrinkage can hurt carpet wear performance and appearance; therefore, less heatset shrinkage is desirable. One way of obtaining less shrinkage is to heatset nylon 6 fibers, yarns, carpets, and fabrics at a lower temperature. Heatsetting at a lower temperature is advantageous because it provides an environment that is not as harsh and results in a savings of both energy and energy costs. Commonly, however, lower heatset temperatures are undesirable because the resulting carpet product lacks the characteristics of acceptable appearance and wear performance required by the marketplace. For example, the resulting carpet product sometimes shows streaks and chevrons when dyed and may lack properties such as good tip definition and good cover.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to reduce the heatset shrinkage that results during the production of fibers, yarns, carpets, and fabrics.
Another object of the present invention is to reduce the temperature at which fibers, yarns, carpets, and fabrics are heatset while still obtaining a desirable end product.
Thus, according to the present invention, there is provided a process for producing yarn having reduced heatset shrinkage comprising the steps of texturing a yarn of bicomponent fibers having a nylon 6 sheath and a core of a fiber-forming polyolefin selected from the group consisting of polypropylene and copolymers thereof to a spinnerette and applying steam at a temperature to the yarn of bicomponent fibers using a steaming unit, wherein the heatset shrinkage of the yarn of bicomponent fibers is about one third to about one half of the heatset shrinkage of a yarn formed of 100 percent nylon 6 fibers and having steam applied thereto at said temperature.
Most preferably, the bicomponent fibers are concentric sheath/core structures having a polyamide sheath and a polyolefin core, wherein the sheath comprises from about 70 percent by weight to about 85 percent by weight of the fibers. Such bicomponent fibers exhibit desirable physical properties that are comparable to and even better than fibers formed of 100 percent nylon 6. The polyolefin core may optionally include one or more inert organic fillers so as to affect the total fiber density (compensating for the lower density of the polyolefin core as compared to the polyamide sheath).
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
To promote an understanding of the principles of the present invention, descriptions of specific embodiments of the invention follow, and specific language is used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended by the use of this specific language and that alterations, modifications, equivalents, and further applications of the principles of the invention discussed are contemplated as would normally occur to one of ordinary skill in the art to which the invention pertains.
As used herein, the term “fiber” includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple fibers). The term “yarn” refers to a continuous strand or bundle of fibers.
As used herein, the term “bicomponent fiber” refers to a fiber having at least two distinct cross-sectional domains respectively formed of from two or more polymer types. The term “bicomponent fiber” is, therefore, intended to include concentric and eccentric sheath/core fiber structures, symmetric and asymmetric side-by-side fiber structures, island-in-sea fiber structures, and pie wedge fiber structures. Preferred fiber structures according to the present invention are bicomponent sheath/core fiber structures having a nylon 6 sheath and a core comprised of polypropylene or copolymers thereof. While the following disclosure will be directed to such a preferred embodiment, the present invention is equally applicable to other bicomponent fiber structures having a polyamide domain and a polyolefin domain.
As used herein, the term “cover” refers to the degree to which the underlying structure is concealed by the surface material. With respect to carpets, cover is the degree to which pile covers the backing. A lack of cover means that, upon visual examination, the backing can be seen.
Broadly, the present invention is a process for producing yarn having reduced heatset shrinkage comprising the steps of texturing a yarn of bicomponent fibers having a nylon 6 sheath and a core of a fiber-forming polyolefin selected from the group consisting of polypropylene and copolymers thereof and applying steam at a temperature to the yarn of bicomponent fibers using a steaming unit, wherein the heatset shrinkage of the yarn of bicomponent fibers is about one third to about one half of the heatset shrinkage of a yarn formed of 100 percent nylon 6 fibers and having steam applied thereto at said temperature.
The polyamides useful to form the sheath of the sheath/core bicomponent fibers of the present invention are those long chain synthetic polymers containing amide (—CO—NH—) linkages along the main polymer chain that are generically known as nylon 6. Suitable polyamides can also be copolymers of nylon 6, as well as other polyamides having heatset shrinkage properties similar to nylon 6 and copolymers thereof.
Importantly, the core of the fibers according to this invention comprises a fiber-forming polyolefin. Preferred polyolefins are polypropylene and copolymers thereof.
Preferably, the sheath comprises from about 70 percent by weight to about 85 percent by weight of the fibers, while the core comprises from about 15 percent by weight to about 30 percent by weight of the fibers. More preferably, the sheath comprises from about 74 percent by weight to about 79 percent by weight of the fibers, and the core comprises from about 21 percent by weight to about 26 percent by weight of the fibers. Weight ratios of the sheath to the core in the fibers may range from about 2.3:1 to about 10:1. A ratio greater than about 3:1 is particularly preferred.
The core may optionally include an inert organic particulate filler material dispersed therein. The filler material must have an average particle size that is sufficiently small to pass through the polymer filter of the spinnerette without affecting filter pressure. In this regard, particulate filler materials having a particle size in the range between about 0.05 &mgr;m and 1.00 &mgr;m, and preferably less than about 0.50 &mgr;mm, may be employed. When used, the filler material may be blended in a melt of the polyolefin core resin prior to the co-melt spinning of the polyolefin core resin and the polyamide sheath resin using conventional melt-blending equipment. For example, the filler material may be introduced via a side arm associated with an extruder that melts the polyolefin and blends the introduced fill

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