Splittable elastane yarns

Details Splittable elastane yarns Splittable elastane yarns

1997-10-29

2003-05-13

Edwards, N. (Department: 1774)

Stock material or miscellaneous articles

Coated or structually defined flake, particle, cell, strand,...

Rod, strand, filament or fiber

C428S357000, C057S225000, C057S226000

Reexamination Certificate

active

06562456

ABSTRACT:

The invention relates to a manufacturing process for splittable elastane multifilament yarns whereby coalescence of the individual filaments forming the yarn due to fusion, sticking or mechanical entangling or plying is prevented. The individual filaments obtainable from the process can be split after take-off the multifilament yarn bobbin and be further processed separately in textile production processes.
Elastane fibers are fibers consisting of segmented polyurethanes in at least 85% by weight. Their typical property spectrum is the result of using polyurethane-polyureas from oligomeric polyester- or polyether-diols, aromatic diisocyanates and short-chain aliphatic diamines. Filament formation is customarily effected by spinning solutions of the polyurethanes by the wet spinning process or preferably by the dry spinning process, suitable solvents in both cases being polar solvents such as dimethyl sulphoxide, N-methylpyrrolidone, dimethylformamide or preferably dimethylacetamide.
Commercial elastane yarns are well known. Owing to their elastic properties they are used for manufacturing functionalized textile products, i.e. articles exhibiting a combination of extensibility and retractive or shaping power. For this, the elastane filament yarn is combined, for example by overwrapping, overspinning or interlacing, with other inelastic yarns to form combination yarns, or the elastane filament yarn is knitted up directly with inelastic yarn.
It order that these processing operations may proceed without problems, the elastane yarns have to be virtually free of fluff, thin places and defects. The prior art teaches that the elastane yarns are produced as coalesced multifilament yarns. This means that the individual filaments forming the overall yarns are virtually stuck together during spinning, for example in the dry spinning process. A process for producing coalesce elastane yarns is described for example in U.S. Pat. No. 3,094,374 and European Patent Application 182,615. The former expressly describes the advantages of a multifilament with high interfilamentary adhesion with regard to consistent processing and discloses methods for achieving this property spectrum.
It was therefore not to be expected that elastane multifilament yarns having good processing properties could be obtained if the process used for producing them is deliberately geared to minimize or eliminate interfilamentary adhesion.
Laid-Open Document JP 03-059 112 describes bundled polyurethane multifilaments or monofilaments which are wound up on a bobbin in an oriented manner so that the bundled multi- or monofilaments require 15 mg or less for separation from the bobbin. They are further processed as separate multifilaments or monofilaments at a speed of at least 150 m/min. These products are obtained by subjecting the dry-spun filaments to cooling below 60° C. and additionally adding a metal soap to the product. It is immaterial for the process of JP 03-059 112 whether multi- or monofilaments are separated.
It is an object of the present invention to produce multifilament yarns which are splittable into their individual filaments on unwinding from the bobbin. These individual filaments must not be mutually plied, entangled, or locally or longitudinally stuck together. The problem is to completely suppress such rare effects which occur every several hundred meters.
This object is achieved by a manufacturing process for producing splittable elastane multifilament yarns from conventional polyurethane-polyureas by means of a modified dry spinning process, which is characterized by the steps of
1) deploying in the spinning head of a conventional dry spinning apparatus one or more multihole spinning jets whose individual capillaries are located on one plate, the distance x between capillaries on one plate and the distance y between capillaries on adjacent multihole spinning jet plates conforming to the following relationship:
40 mm<
x<y
<500 mm,
2) laminarizing the spinning gas flow in the dry spinning apparatus to prevent entangling of the individual filaments from one multihole jet and from adjacent multihole jets,
3) passing the resulting elastane yarns leaving the spinning shaft through a first thread guide with one opening per individual filament and then through a second thread guide which gathers a plurality of individual filaments together to form a multifilament, and
4) winding up the multifilament yarn.
The polyurea-polyurethanes are prepared by methods known per se. An advantangeous method is the synthesis of the fiber raw materials by the prepolymer process, in which, in a first step, a long-chain diol is reacted, in a solvent or in the melt, with a diisocyanate to form a prepolymer so that the reaction product contains isocyanate end groups (NCO groups).
Preferred long-chain diols are polyesterdiols on the one hand and polyetherdiols on the other. It is also possible to choose mixtures of the two kinds of diols. These generally have a number average molecular weight of 1000-6000.
Suitable polyesterdiols are for example dicarboxylic acid polyesters which may contain not only a plurality of different alcohols but also different carboxylic acids. Of particular suitability are copolyesters of adipic acid, hexanediol and neopentylglycol in a molar ratio of 1:0.7:0.43. Suitable polyesters have a molecular weight of 1000-4000.
Suitable polyetherdiols are for example polytetramethylene oxide diols, preferably with a molecular weight of 1000-000 (all stated molecular weights are number averages, unless otherwise indicated).
It is also possible to use polyester- and/or polyether-diols in combination with diols which contain tertiary amino groups. Particularly suitable are for example N-alkyl-N,N-bishydroxyalkylamines. Examples are the compounds:
4-tert-butyl-4-azaheptane-2,6-diol, -methyl-4-azaheptane-2,6-diol, -ethyl-3-azapentane-1,5-diol, -ethyl-2-dimethylaminoethyl-1,3-propanediol, -tert-pentyl4-azaheptane-1,6-diol, 3-cyclohexyl-3-azapentane-1,5-diol, 3-methyl-3-azapentane-1,5-diol, 3-tert-butylmethyl-3-azapentane-1,5-diol and 3-tert-pentyl-3-azapentane-1,5-diol.
The elastane raw materials are synthesized using the customary aromatic diisocyanates in admixture with small proportions of aliphatic and/or cycloaliphatic diisocyanates, if desired. Particularly good results are obtained with the following diisocyanates:
2,4-toluylene diisocyanate and also corresponding isomer mixtures, and
4,4′-diphenylmethane diisocyanate (MDI) or corresponding isomer mixtures. It is of course possible to use mixtures of aromatic diisocyanates.
Another form of the synthesis of elastane raw materials comprises mixing polyester- and polyether-polyurethane prepolymer and then reacting in a conventional manner to form polyurea-polyurethanes. The mixing ratio of polyester- and polyether-diols advantageous for the particular technical purpose is easily determined in preliminary experiments.
In the polyurea-polyurethane synthesis, the urea groups are introduced into the macromolecules by a chain-extending reaction. Customarily, the prepolymers (“macrodiisocyanates”) synthesized in the prepolymer stage to contain NCO end groups are reacted with diamines in solution. Suitable diamines are for example ethylenediamine, tetramethylenediamine, 1,3-cyclohexanediamine, isophoronediamine and also mixtures thereof. By using a small amount of monoamines, for example diethylamine or dibutylamine, during the chain extension, it is possible to achieve the molecular weight desired for the polyurea-polyurethanes. The chain extension itself can be carried out batchwise or continuously and with or without the use of CO
2
as retarder.
A mixture of polyester- and polyether-polyurethane-ureas can also be formed following completion of the synthesis of the individual components.
The reactions are customarily carried out in an inert polar solvent, such as dimethylformamide or dimethylacetamide.
The polymer solution intended for spinning may additionally include a whole series of customary additives, for example antioxidants and light stabiliz

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