Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-05-21
2003-12-02
Edwards, N (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S364000, C428S395000, C264S176100, C264S177130, C264S210800
Reexamination Certificate
active
06656583
ABSTRACT:
The invention relates to high-strength polyester filaments having a tear strength of >70 cN/tex, and to a process for the production of these filaments.
High-strength filaments made from polyethylene terephthalate and processes for the production thereof have been known for some time (F. Fourné, Synthetische Fasern [Synthetic Fibres], Hanser Verlag, Munich [1995] 584-586; U.S. Pat. Nos. 3,758,658, 4,374,797 and 4,461,740).
In these high-strength filaments, particular properties, especially high tear strength, low elongation at break and a low number of filament flaws, are required. These requirements are linked in technological terms to the use of high stretching ratios of at least 1:5 in raw yarn production. However, higher stretching ratios have their limit if the filament is already damaged by the stretching and filament breakage occurs. The higher the production speed, the lower this limit. However, the technical and economic value of the spin-stretch process on use of high production speeds can only be regarded as positive if the textile filament qualities are not impaired at the same time, but instead are even improved. Thus, the spinning take-off speed in commercial processes is limited to a maximum of 700 m/min, in general from 500 to 600 m/min. The wind-up speed is, corresponding to the stretching ratio, from greater than 2500 m/min to less than 3800 m/min.
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, preferably from 3000 to 6000 m/min, can be increased by the addition of amorphous, thermo-plastic 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. However, the process cannot be applied to spun filaments produced at take-off speeds of less than 2500 m/min since these, in contrast to POY, are of low crystallinity (<12%) and have low orientation (birefringence<25·10
−3
) and high elongation at break (>225%). No data are given on the production of high-strength yarns in the integrated 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. The crucial factor for the effect is said to be the interaction of three properties—the chemical structure of the additive, which hardly allows any elongation of the additive molecules, 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, 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 also known to the person skilled in the art that the tear strength can be dramatically affected by changing the relaxation proportion with the same spinning and stretching conditions. In practice, the thermal shrinkage of high-strength filaments of this type is adjusted, depending on the industrial area of application, by means of the relaxation ratio. The thermal shrinkage is reduced with increasing relaxation ratio, but so are the tear strength and LASE 5, whereas the elongation at break increases.
The present invention has the object of providing high-strength polyester filaments having a tear strength of >70 cN/tex and a process for the production thereof in which it is possible to use spinning take-off speeds and wind-up speeds which are significantly above those of the prior art. In particular, it should be possible to achieve tear strengths of >80 cN/tex at a relaxation ratio RR of ≧0.97, tear strengths of >77 cN/tex at a relaxation ratio of 0.95<RR<0.97, and tear strengths of >70 cN/tex at a relaxation ratio RR of <0.95.
This object is achieved in accordance with the invention by high-strength polyester filaments and by a process for the production thereof as indicated 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 dials, such as, for example, isophthalic acid, adipic acid, diethylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, 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, a copolymer is added to the polyester in an amount of from 0.1 to 2.0% by weight, where the copolymer must be amorphous and substantially insoluble in the polyester matrix. The two polymers are essentially incompatible with one another and form two phases which can be differentiated microscopically. Furthermore, the copolymer must have a glass transition temperature (determined by DSC at a heating rate of 10° C./min) of from 90 to 170° C. and must be thermoplastic.
The melt viscosity of the copolymer should be selected here so that the ratio of its melt viscosity extrapolated to the measurement time zero, measured at an oscillation rate of 2.4 Hz and a temperature which is equal to the melting point of the polyester plus 34.0° C. (290° C. for polyethylene terephthalate) relative to that of the polyester, measured under the same conditions, is between 1:1 and 7:1, i.e. the melt viscosity of the copolymer is at least equal to or preferably greater than that of the polyester. The optimum effectiveness is only achieved through the choice of a specific viscosity ratio of additive to polyester. At a viscosity ratio optimised in this way, it is possible to minimize the amount of additive added, making the economic efficiency of the process particularly high. Surprisingly, the viscosity ratio determined as ideal in accordance with the invention for the use of polymer mixtures for the production of high-strength yarns is above the range indicated as favourable in the literature for the mixing of two polymers. In contrast to the prior art, polymer mixtures with high-molecular-weight copolymers were highly suitable for spinning.
Due to the high flow activation energy of the additive polymers, the viscosity ratio after exit of the polymer mixture from the spinneret increases dramatically in the filament formation zone. The flow activation energy (E) here is a measure of the rate of change of the zero viscosity as a function of the change in measurement temperature, where the zero viscosity is the viscosity extrapolated to the shear rate 0 (M. Pahl et al., Praktische Rheologie der Kunststoffe und Elastomere [Practical Rheology of Plastics and Elastomers], VDI-Verlag, Düsseldorf (1995), pages 256 ff.). Through the choice of a favourable viscosity ratio, a particularly narrow particle size distribution of the additive in the polyester matrix is achieved, and by combining the viscosity ratio with a flow activation energy which is significantly greater than that of the polyes
Cziollek Joachim
Janas Wolfgang
Mrose Werner
Schwind Helmut
Ude Werner
Edwards N
Lurgi Zimmer AG
Norris & McLaughlin & Marcus
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