Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
1999-09-01
2001-06-05
Calvert, John J. (Department: 3741)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S002000, C057S003000, C057S006000, C057S010000, C057S012000, C057S207000, C057S225000, C057S230000, C057S244000, C428S370000, C428S373000, C428S375000, C428S377000
Reexamination Certificate
active
06240716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stable double covered elastomeric yarn, a process for making such a yarn, and fabric comprising such a yarn and, more especially, it relates to a yarn having a coordinated sheath twist orientation.
2. Discussion of the Background Art
Covered elastic yarns, such as single covered yarns obtained by winding an inelastic filament yarn or inelastic staple fiber around a core elastic yarn, and double covered yarns obtained by further winding around the single covered yarn a second inelastic filament yarn or inelastic staple fiber, are used in a variety of apparel applications. Such covered elastic yarns recently have come to be used in stretch woven applications that do not require a great deal of stretchability.
Japanese Published Patent Application No. 06-049736 (1994) discloses the use in elastic woven fabrics of an elastic polyurethane fiber covered with a multifilament yarn in which the weight ratio of the multifilament yarns to the elastic fiber is one to five. That is, the elastic fiber is 50% to about 80% of the weight of the covered yarn. However, the problems of fluff, stability, and hand that arise when the covering fiber is in staple form are not solved in this disclosure.
Further, typical stretch fabrics using conventional elastomeric polyurethane fibers have been deficient in that they have a low wet heat settability and tend to shrink on laundering. The covered yarn can also exhibit its instability in that the core yarn and sheath yarn can shift with respect to each other so that the elastic yarn slips in at cut edges of the fabric and the core yarn penetrates the covering yarn. Such yarns can also result in fluff formation and give fuzzy fabrics, or curl in the case of knit products. In order to enhance hot-wet stability, the heat-set temperature could be increased, but covered elastic yarns using thermally degradable fibers such as wool and acrylic staple as sheath yarns cannot tolerate wet temperatures of 100° C. or higher in dyeing and finishing or dry temperatures of 160° C. or higher because the soft hand can be lost and fabric strength reduced. A stable covered elastic yarn is still needed.
SUMMARY OF THE INVENTION
The double covered elastic yarn of this invention consists essentially of:
a spandex core wherein the spandex has a heat set of at least 50%;
a first sheath yarn wound around the spandex to form a single covered yarn not exceeding 40 percent of the total weight of the double covered yarn; and
a second sheath yarn wound around the single covered yarn;
wherein the first and second sheath yarns are wound in the same direction.
The process for making a double covered elastic yarn of this invention comprises the steps of:
providing a spandex having a heat set of at least 50% from a spandex supply package; stretching the spandex in the range of about 100 to 250%;
covering the stretched spandex with a first sheath yarn to form a single covered yarn;
covering the single covered yarn with a second sheath yarn wound in the same direction as the first sheath yarn to form a double covered yarn, wherein the single covered yarn is not more than 40 weight percent of the double covered yarn; and
heat setting the double covered yarn.
The woven fabric of this invention comprises the double covered yarn described above as the only warp yarn or as the only weft yarn.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, “spandex” means a manufactured fiber in which the fiber-forming substance is a long chain synthetic elastomer comprised of at least 85% by weight of a segmented polyurethane. Spandex in the range of about 20 to 166 decitex (about 18 to 150 denier) is suitable for use in making the double covered yarn of the present invention.
“Sheath yarn” means a relatively inelastic yarn comprising continuous filaments, bundled staple fibers, or spun staple fibers, or both filaments and staple fibers. The “first sheath yarn” is the sheath yarn wound around the spandex to form a single covered yarn. The “second sheath yarn” is the sheath yarn wound around the single covered yarn to form a double covered yarn.
Suitable filament sheath yarns include polyester, nylon, acrylic, rayon, acetate, silk, and the like. Suitable staple fibers include synthetic fibers such as polyester, nylon, acrylic, rayon, and acetate, and natural fibers such as cotton, wool, and the like, or blends thereof. Continuous filaments, for example nylon filament, are preferred as the first sheath yarn. Wool and staple acrylic fibers are preferred as the second sheath yarn.
“Heat set” means that a spandex, after being stretched to 100% elongation, is heat treated while in the elongated condition, and released from the elongation, returns to a length which is longer than the original length. Thus, for example, if a 10-cm length spandex returns to a 15-cm length after being stretched to 20 cm, exposed to elevated temperatures, and released, it is said to have 50% heat set.
“Fluff” means loose ends of staple fibers extending from the double covered yarn, resulting in an undesirably fuzzy yarn that is difficult to knit or weave.
To obtain the stable double covered yarn of the present invention, the yarn is made with a coordinated twist orientation of the first and second sheath yarns. The spandex core fiber has at least 50% set and preferably at least 55% set, as can be determined by water immersion heat treatment at 100° C. for 60 minutes at 100% elongation. In applications where the double covered yarn of this invention is to be set with dry heat, the spandex has at least a 50% set and preferably at least 55% set after dry heat treatment at 140° C. for 1 minute when elongated to 100% elongation.
In the stable double covered yarn of the present invention, the first and second sheath yarns are wound in the same direction, either both in the z-direction or both in the s-direction. Under such circumstances, the yarn bulkiness (distention) is small, and the covering will tighten while interlacing the fluffs. In turn, this results in fluff binding and in a reduction of the number of excessively long fluffs. Since size is not generally applied to a woven fabric made with a single wool yarn as the warp, weaving would be difficult unless the fluffs can be bound to the yarn. Because fluffs are bound in the yarn of this invention, it can be used without sizing as the only warp yarn in a woven. The is particularly useful for light weight stretch wovens for spring and summer wear, in which case, however, the single covered yarn preferably has a relatively high metric count such as 1/40 (“singles forty”). The double covered yarn of the present invention can also be used satisfactorily as the only yarn in the weft or in both warp and weft.
In contrast, when the twist directions of the two sheath yarns are different, the twists in the first sheath yarn can be de-twisted during covering with the second sheath yarn to give a bulky final yarn and increased fluffs, particularly excessively long fluffs. In addition, different twist directions can result in partial exposure on the yarn surface of the first sheath yarn.
The double covered yarn of the present invention contains not more than 40 weight percent of the single covered yarn. It is preferred that the single covered yarn be present not exceeding 30 weight percent of the double covered yarn and, more preferably, 25 weight percent. If the single covered yarn exceeds the above limitations when compared to the double covered yarn, the first sheath yarn can appear on the yarn surface or fabric surface, and the fabric then has the hand of the first sheath yarn. In addition, for example, if the second sheath yarn is wool, the number of wool fibers is reduced in the final cover, which worsens the interlacing of the wool and can cause many excessively long fluffs, which makes it difficult to use such a product, especially as the only yarn in the warp or weft.
In the yarn of the present invention, the spandex can comprise in the range of about 2-9 percent by weight of the double covered ya
Hayashi Shoichi
Yanagawase Takeshi
Calvert John J.
DuPont Toray Company, Ltd.
Frank George A.
Hurley Shaun R.
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