Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-06-06
2004-05-25
Niland, Patrick D. (Department: 1714)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C264S176100, C264S177130, C264S210800, C428S364000, C428S395000
Reexamination Certificate
active
06740404
ABSTRACT:
The invention relates to HMLS polyester filaments having a tear strength of >70 cN/tex, an LASE 5 of >35 cN/tex and a hot-air shrinkage at 160° C. of 1.5-3.5%, and to a spin-stretch process for the production of the HMLS filaments. The term HMLS filaments here is taken to mean stretched polyester multifilaments of
h
igh
m
odulus and
l
ow
s
hrinkage.
Polyethylene terephthalate multifilaments of high LASE 5 (the specific force which corresponds to an elongation of 5% in the stress-strain diagram) and low thermal shrinkage are known, as are processes for their production, the yarns being employed for industrial applications, such as tyre cord. Processes of this type are described, inter alia, in the patent specifications U.S. Pat. No. 5,067,538. EP 0 423 213 B, U.S. Pat. Nos. 4,101,525 and 5,472,781. It is clear in these publications that the stretching ratio that can be used drops, the steepness of the stress-strain diagram. i.e. the LASE 5, increases, the thermal shrinkage drops and the achievable strength drops with increasing spinning take-off speed. The drop in the usable stretching ratio is due to the increase in the orientation in the spun filament and is characterized by an increase in the birefringence of the spun filament.
U.S. Pat. No. 4,491,657 only achieves tear strengths of 62 cN/tex in the subsequent stretching process at a spinning speed of 3000 m/min. In EP 0 423 213 B. Tables 2 and 5 show that at the stretching ratios that can be used in practice, a tear strength of 69 cN/tex is already achieved at spinning speeds of 2900 m/min.
The drop in the usable stretching ratio with increasing spinning speed is exacerbated by higher spinning viscosities, as shown by U.S. Pat. No. 5,067,538. In this, the usable stretching ratio at an intrinsic viscosity of the polymer of 0.88 dl/g is already so low that end speeds of greater than 6000 m/min are no longer possible. EP 0 169 415 A describes a polyester spun filament having an intrinsic viscosity of greater than 0.9 dl/g. The stretching ratios that can be used for the various spinning speeds are so low that efficient end speeds of greater than 6000 m/min in spin-stretching are only possible at very high spinning take-off speeds of greater than 3500 m/min. In EP 0 546 859 A, a polyester filament is produced at spinning take-off speeds of from 2500 to 4000 m/min. Here too, the low stretchability, even at spinning take-off speeds of 4000 m/min, during high-speed spin-stretching give end speeds of just 6000 m/min, with the tear strength being lower than 65 cN/tex.
In addition, EP 0 438 421 B1 makes it clear that high-speed spin-stretching to give filaments results in a large number of capillary breaks. For this reason, a device which determines the stretching point is introduced there, reducing the capillary breakage level of HMLS filaments of this type to 20 defects/10 km in the best case.
Stretched yarns having tear strengths of greater than 70 cN/tex and low thermal shrinkage, produced at spinning speeds of greater than 2500 m/min, are also described in EP 0 526 740 B. These yarns consist of a polyester raw material based on a polyethylene terephthalate modified by copolymerization. These modifying components are incorporated into the polymer chain during the polymer formation process, which impairs the flexibility of the spinning operation.
It is furthermore known from WO 99/07927 A1 that the elongation at break of polyester pre-oriented yarn (POY) which has been spun at take-off speeds of at least 2500 m/min can be increased by the addition of amorphous, thermoplastic copolymers based on styrene, acrylic acid and/or maleic acid or derivatives thereof compared with the elongation at break of polyester filaments spun under identical conditions without addition. No data are given on the production of HMLS filaments by the spin-stretch process.
EP 0 047 464 B relates to an unstretched polyester yarn where improved productivity is obtained at speeds of between 2500 and 8000 m/min by increasing the elongation at break of the spun filament by addition of 0.2-10% by weight of a polymer of the —(—CH
2
—CR
1
R
2
—)—n type, such as poly(4-methyl-1-pentene) or polymethyl methacrylate. Fine and uniform dispersion of the additive polymer by mixing is necessary, where the particle diameter must be ≦1 &mgr;m in order to avoid fibril formation. Besides the chemical structure of the additive, which hardly allows any elongation of the additive molecules, the crucial factor for the effect is said to be the low mobility and the compatibility of polyester and additive.
EP 0 631 638 B describes fibres predominantly comprising PET which comprises 0.1-5% by weight of a polyalkyl methacrylate which has been imidated to the extent of 50-90%. The fibres obtained at speeds of 500-10,000 m/min and subsequently subjected to final stretching are said to have a relatively high initial modulus. In the examples of industrial yarns, however, the effect on the modulus is not readily evident; in general, the strengths achieved are low, which is a considerable disadvantage of this product.
It is an object of the present invention to provide HMLS filaments having a tear strength of >70 cN/tex, an LASE 5 of >35 cN/tex and a hot-air shrinkage at 160° C. of from 1.5 to 3.5%, and to provide a spin-stretch process for the production thereof in which end speeds of greater than 6000 m/min can be achieved, even in the case of ultrahigh-viscosity polyester, with minimization of the number of capillary breaks. It should be possible to produce the desired HMLS filaments at high spinning speeds without the need for chemical modification of the polyester raw material, which would reduce the flexibility of the spinning machine. In addition, it should be possible to produce the HMLS filaments in a customized manner for the particular application by adjustment of the birefringence in the spun filament substantially independently of the spinning take-off speed. It should be possible to set birefringence values here in the range from 30·10
−3
to 55·10
−3
.
The object on which the invention is based is achieved by HMLS polyester filaments and a spin-stretch process for their production as defined in the patent claims.
The term polyester here is taken to mean poly(C
2-4
-alkylene) terephthalates, which may comprise up to 15 mol % of other dicarboxylic acids and/or diols, such as, for example, isophthalic acid, adipic acid, diethylene glycol, polyethylene glycol. 1,4-cyclohexane-dimethanol, or the respective other C
2-4
-alkylene glycols. Preference is given to polyethylene terephthalate having an intrinsic viscosity (I.V.) in the range from 0.8 to 1.4 dl/g, polypropylene terephthalate having an I.V. of from 0.9 to 1.6 dl/g and polybutylene terephthalate having an I.V. of from 0.9 to 1.8 dl/g. Conventional additives, such as dyes, matting agents, stabilizers, antistatics, lubricants and branching agents, may be added to the polyester or polyester/additive mixture in amounts of from 0 to 5.0% by weight without any disadvantage.
In accordance with the invention, the polyester is treated in the melt with an amorphous, thermoplastic, incompatible, polymeric additive which has a glass transition temperature of from 90 to 170° C., where the ratio of the melt viscosity of the additive to the melt viscosity of the polyester is from 1:1 to 7:1, the mixture is treated in a static mixer with shearing, with the shear rate being from 16 to 128 s
−1
, and the product of the shear rate and the residence time in seconds to the power 0.8 is set to a value of at least 250, and the mixture is subsequently spun at a, spinning take-off speed v of from 2500 to 4000 m/min, stretched, thermally treated and wound up at ≧6000 m/min.
The additive polymers to be added to the polyester may have a different chemical composition so long as they have the above-mentioned physical properties. Three different types of polymer are preferred, namely
1. A polymer which comprises the following monomer units:
A=acrylic acid, methacrylic acid or CH
2
═CR—COOR
1
, where R
Cziollek Joachim
Janas Wolfgang
Mrose Werner
Schwind Helmut
Ude Werner
Niland Patrick D.
Norris McLaughlin & Marcus P.A.
Zimmer AG
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