Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-06-30
2001-09-04
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S394000, C428S373000
Reexamination Certificate
active
06284371
ABSTRACT:
This invention relates to a spinning process, more particularly a dry spinning process, for the production of elastane fibers in which 0.8 to 2% by weight of polydimethylsiloxane with a viscosity of 50 to 300 cSt and 0.2 to 0.6% by weight of ethoxylated polydimethylsiloxane with a viscosity of 20 to 150 cSt are added to the elastane spinning solution before it is spun.
Elastane fibers are fibers of which at least 85% by weight consist of segmented polyurethanes. The elastic and mechanical properties of elastane fibers are established by the use of polyurea polyurethanes based on aromatic diisocyanates, for example, for the production of the elastane fibers. Elastanes of the type in question are typically produced by wet spinning or preferably dry spinning the solutions. Suitable solvents for both processes are polar solvents, for example dimethyl sulfoxide, N-methyl pyrrolidone, dimethyl formamide and preferably dimethyl acetamide.
Commercial yarns produced from such fibers have been known for many years. The most important application for fibers of the type in question is the elasticizing function for linen, corsetry and swimwear articles and their use in garter welts for socks and stockings and also elastic bands. By far the largest quantity of elastane filament yarns is processed in warp and raschel knitting machines for the major fields of fashion swimwear and girdles. To this end, up to 1,500 filaments are wound adjacent one another onto a warp beam under constant, controlled elongation, for example in an expander-type warping frame. A warp consisting of several warp beams is then processed together with one or more warps of non-elastic base yarns (for example polyamide) to form a full-width fabric. Elastane-containing materials with elastane fiber contents of up to at most around 20% are produced from these fabrics by dyeing and finishing, receiving not only their color and appearance, but also their final textile and mechanical (elastic) properties through these subsequent treatment steps.
At this stage of the production process, it has been found that, where they have been dyed in a single color, the textiles often show visible streaks so that they can only be used to a limited extent, if at all. This streakiness is assumed to be caused by irregularities in the thickness and elasticity of the elastane filaments used, although the exact cause is very difficult to pinpoint because the unwanted streakiness can only be detected after a plurality of process steps has been carried out.
The problem addressed by the present invention was to provide improved elastane fibers which, after processing on warp knitting machines, would produce distinctly less streakiness in dyed and finished textiles without any adverse effect on their processability in the intermediate steps required for the production of the textiles.
It has now surprisingly been found that this problem can be solved by adding a mixture of polydimethylsiloxane (PDMS) with a viscosity of 50 to 300 cSt and ethoxylated polydimethylsiloxane to the polyurethane urea solution before it is spun and then carrying out the spinning process.
The present invention relates to a process for the production of elastane fibers from polyurea polyurethanes by dry spinning or wet spinning comprising the steps of spinning, removal of the spinning solvent, finishing, optionally twisting and winding of the spun fibers, characterized in that
A) from 0.8 to 2% by weight of polydimethylsiloxane with a viscosity of 50 to 300 cSt and
B) from 0.2 to 0.6% by weight of ethoxylated polydimethylsiloxane with a viscosity of 20 to 150 cSt
(viscosities measured with a falling ball viscosimeter at 25° C.) are added to the spinning solution before it is spun, the percentages shown being based on the siloxane content of the final fiber. The viscosity of the PDMS used must not under any circumstances fall below 50 cSt because otherwise the desired effect would no longer occur. The ethylene-oxide-modified polydimethylsiloxanes suitable for use in accordance with the invention preferably correspond to general formula I:
in which PE is the single-bond unit CH
2
CH
2
—CH
2
O(Eo)
m
Z. In this formula, Eo stands for ethylene oxide and Z is either hydrogen or a C
1-6
alkyl radical and x, y and m are integers of or greater than 1 which are preferably selected so that formula (I) does not exceed a molecular weight of 4,000.
Products of this type are produced, for example, by Union Carbide under the trade name of Silwet®. Types with a viscosity of 20 to 150 cSt and a molecular weight of around 600 to 4,000 are suitable for use in accordance with the invention. Unless otherwise specifically stated, all molecular weights are number average molecular weights (M
n
).
The inclusion of pure polydimethylsiloxane (PDMS) in the spinning solution is known in principle and is described, for example, in DE-A-3 912 510, according to which elastanes are produced by a special spinning process, namely a dry spinning process for the production of coarse-denier elastane fibers with introduction of superheated steam. This document refers to silicone oils as flow promoters among other possible additives. U.S. Pat. No. 4,973,647 also mentions the inclusion of silicone oil in the spinning solution. Neither document makes any reference to the effects of the oil after further processing nor do they mention the inclusion of a special combination of oils with certain properties in the spinning solution.
The inclusion of amylsiloxane-modified polydimethylsiloxane oils in the spinning solution, which is not the subject of the present invention, is known from DE-AS 1 469 452.
It is not apparent from any of these documents whether the inclusion of pure or modified PDMS in the spinning solution is capable of influencing or improving the properties of the fibers, more particularly the optical uniformity of elastic warp-knitted fabrics of these elastane fibers.
The application of mixtures of polydimethylsiloxane and polyether-modified PDMS to the spun elastane filaments by dipping or spraying or by roller is also known (see JP 57 128 276 or JP 03 146 774).
The object of applying finishing oils such as these is to improve the take-off properties of the elastane fibers in warping and knitting processes. The inclusion of the mixtures in the spinning solution is not mentioned in these documents, nor do they contain any reference to the fact that mixtures, especially those having the composition according to the invention, included in the elastane spinning solution produce an improvement in the optical properties of warp-knitted fabrics obtained therefrom.
The polyurea polyurethanes are produced by methods known per se. A method which has proved to be particularly successful for the synthesis of these fiber raw materials is the prepolymer process in which, in a first step, a long-chain diol is reacted with a diisocyanate in a solvent or in the melt to form a prepolymer in such a way that the reaction product is terminated by isocyanate groups.
Preferred diols are, on the one hand, polyester diols and, on the other hand, polyether diols. Mixtures of polyester and polyether diols may also be used. The diols generally have a molecular weight of 1,000 to 6,000.
Suitable polyester diols are, for example, dicarboxylic acid polyesters which may contain both several different alcohols and also several different carboxylic acids. Mixed polyesters of adipic acid, hexanediol and neopentyl glycol in a molar ratio of 1:0.7:0.43 are particularly suitable. Suitable polyesters preferably have a molecular weight of 1,000 to 4,000.
Suitable polyether diols are, for example, polytetramethylene oxide diols, preferably having molecular weights of 1,000 to 2,000.
Polyester and/or polyether diols may also be used in combination with diols containing tertiary amino groups. N-alkyl-N,N-bis-hydroxyalkylamines for example are particularly suitable. Suitable components are, for example, 4-tert.butyl-4-azaheptane-2,6-diol, 4-methyl-4-azaheptane-2,6-diol, 3-ethyl-3-azapentane-1,5-diol, 2-ethyl-2-dimethylaminomethylpropane-1,3-d
Kausch Michael
Klein Wolfgang
Schmitz Konrad
Wolf Karl-Heinz
Bayer Aktiengesellschaft
Edwards N.
Norris McLaughlin & Marcus P.A.
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