Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-02-23
2003-09-23
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S180000, C264S105000, C264S210800, C057S200000, C057S362000, C057S400000
Reexamination Certificate
active
06623585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of preparing a coalesced spandex. More particularly, it relates to a method for dry-spinning a solution of a high-melting thermoplastic polyurethane, bundling the resulting spandex, and fusing the resulting bundle to form the coalesced multifilament spandex by a method which does not employ false-twisting.
2. Description of the Background Art
In the conventional production of a coalesced spandex by dry spinning, a solution of polyurethane or polyurethaneurea is prepared and extruded through spinneret holes into a spinning column. Heat is applied to the inside of the column to drive off the solvent and form filaments. Such filaments are customarily quite small in diameter in order to permit rapid evaporation of solvent. In order to make filaments with larger diameters and to improve the uniformity of the final product, a plurality of filaments are normally bundled together and cohered to each other (“coalesced”) along their lengths by passing them through a jet such as described in U.S. Pat. No. 3,353,344. Such a false twist coalescence method is described in, for example, U.S. Pat. No. 3,094,374. Due to the random distribution of any nonuniformities along the length of individual filaments, such irregularities are effectively cancelled out when a number of filaments are thus coalesced, and the resulting coalesced multifilament spandex has improved uniformity over the individual filaments.
European published Patent Application Number 756026 discloses a method wherein immediately after dry-spinning of segmented polyurethaneureas which are not thermoplastic, the filaments are slightly bonded by passing them through a “thread control element with comb-like shape” immediately after spinning to form a multifilament which can be readily and easily split into single filaments.
Japanese published Patent Application Number 53-139847 describes melt-spinning of a low-melting polyurethane from widely spaced spinneret holes and the bonding of the resulting filaments into a coalesced multifilament spandex by passing them through a guide placed at a selected distance from the face of the spinneret.
Spandex is widely used in various applications such as apparel because it has desirable characteristics including high stretch and recovery. Expanding applications have led to new needs such as high uniformity combined with mechanical properties that are available from, for example, thermoplastic polyurethanes and polyurethaneureas. Spandex with desirable properties such as good heat settability, high elastic recovery, and good resistance to environmental conditions can be the prepared by dry-spinning a high-melting thermoplastic polyurethane to make a spandex such as that disclosed in International Patent Application Number WO95/23883. Good heat settability is an advantage, for example, when the spandex is to be used in combination with other fibers such as wool which should not be exposed to the temperatures necessary to heat-set such spandex.
However, spandex uniformity tends to be unsatisfactorily low when filaments of such a polyurethane are dry-spun and coalesced by the conventional false-twist coalescence method, perhaps due to fluctuations in the twisting force. As a result, the combination of good uniformity with the desirable properties of a dry-spun thermoplastic polyurethane is still needed.
SUMMARY OF THE INVENTION
In the method of the present invention a solution of high-melting thermoplastic polyurethane is extruded from a spinneret into a heated atmosphere to produce a plurality of filaments which are then brought into a side-by-side relationship with each other and fused into a coalesced multifilament by passing the filaments over or through a guide by a method which does not employ false-twisting.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
As used herein “spandex” has its usual meaning, that is, 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. “Thermoplastic polyurethane” and “thermoplastic polyurethaneurea” mean a polyurethane and a polyurethaneurea, respectively, with a melting point (“T
m
”) in the range of 150-270° C., preferably in the range of 160° C. to 250° C. and most preferably in the range of 230° C. to 250° C. when measured by differential scanning calorimetry (hereinafter “DSC”) and a DSC-measured glass transition temperature (“T
g
”) of no more than 0° C., preferably no more than −20° C.
The present invention provides a method for preparing a coalesced multifilament spandex comprising:
dry spinning a thermoplastic polyurethane to form as-spun filaments;
bundling a plurality of the as-spun filaments in a first guide;
passing the bundled filaments through a second guide to form a coalesced multifilament, neither the first guide nor the second guide creating false-twist in the filaments; and
winding up the coalesced multifilament;
wherein the thermoplastic polyurethane has a melting point in the range of about 230° C. to 250° C. and a glass-transition temperature no higher than about 0° C. Preferably, the first guide is a comb-shaped guide and the second guide is a slit guide.
The method of the present invention can be applied to filaments comprising primarily polyurethanes, polyurethaneureas, or blends of polyurethanes and polyurethaneureas, so long as the polyurethane, polyurethaneurea or mixture thereof has a T
m
in the range of about 150-270° C., preferably in the range of about 160-250° C., and most preferably in the range of about 230° C. to 250° C., and has a T
g
of no more than about 0° C., preferably no more than about −20° C. Such high melting temperatures generally require even higher (and therefore impractical) processing temperatures for melt-spinning and, therefore, the resulting spandex is best prepared by dry-spinning from solution.
In order to combine good coalescence by the method of the present invention with good heat settability and satisfactory heat resistance in use, polyurethanes with melting points below 150° C. or above 270° C. should be avoided. If the melting point is too low, the heat resistance is insufficient. If the melting point is too high, the heat settability and fusability by the method of the present invention are insufficient.
Spandex can be prepared by reacting a polymeric glycol with a diisocyanate to form a “capped glycol”, dissolving the capped glycol in a suitable solvent, reacting the dissolved capped glycol with a difunctional chain extender to form the polyurethane or polyurethaneurea in solution, and dry-spinning the solution through a heated spinning column. Suitable solvents include dimethylacetamide (DMAc), dimethyl-formamide, N-methylpyrrolidone, and the like. This “prepolymer method” is preferred when the chain extender is a diamine. Alternatively, when the chain extender is a diol, melt polymerization can also be used. Reaction of all ingredients can also be carried out in solution for diamine- and diolextended polymers. When the chain extender is a diol, such polymers are polyurethanes, and when the chain extender is a diamine, such polymers are polyurethaneureas. In solution and melt polymerization, especially when the chain extender is a diol, the ingredients can be added sequentially or all at once (the “one shot method”). In order to make the spandex according to the method of the present invention when the polymer is made in the melt, the polymer is dissolved in a suitable solvent by any suitable method prior to dry-spinning. The solution can also be prepared from one type of polyurethane or two or more types of polyurethane.
The polymeric glycol can be a polyether diol or a polyester diol. Suitable polyether diols include those derived from butanediol, 3-methyl-1,5-pentanediol, tetrahydrofuran, 3-methyltetrahydrofuran, and copolymers thereof. Preferred polyether dials include polytetramethyleneether glycol (PTMEG) and PTMEG having copolymerized therein minor amounts of 3-methyltetrahydrofur
Matsuda Toshikazu
Nakanishi Hideki
Umezawa Masao
DuPont-Toray Co. Ltd.
Yao Sam Chuan
LandOfFree
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