Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-06-24
2003-06-10
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S395000
Reexamination Certificate
active
06576339
ABSTRACT:
DESCRIPTION
The invention relates to polyester staple fibres and to a process for the production of these staple fibres.
Staple fibres made from polyethylene terephthalate and processes for their production have been known for some time (F. Fourné. Syntheti-sche Fasern [Synthetic Fibres], Hanser Verlag. Munich [1995] 91-94 and 462-486).
Besides the quality of the staple fibres, the spin factor SF, i.e. the throughput (g/min) per spinneret field area (cm
2
), is of importance here, where
SF=HD·d·DR·v·
10
−4
·K
and
HD denotes the hole density (n/cm
2
)=number of spinneret holes per spinneret field area,
d denotes the titre of the staple fibres (dtex),
d
0
denotes the titre of the spun filaments (dtex),
DR denotes the overall stretching ratio=1: . . . ,
v denotes the spinning take-off speed (m/min),
K denotes a polyester-dependent constant, where
K
=
d
d
0
·
DR
=
100
-
relaxation
(
%
)
100
,
for example about 0.92 for PET and about 0.73 for PTT.
The aim is the highest possible spin factor, preferably in the range from 2.9 to 10.0.
The hole density HD is determined by the available spinning machine and cannot be increased as desired, even for geometrical reasons. The spinning take-off speed is restricted to speeds below 2500 m/min by the tow baling system of the spun filaments and their further conversion into staple fibres. The stretching ratio is, to a first approximation, proportional to the elongation at break of the spun filament, the elongation at break for a specific polymer being lower the higher the spinning take-off speed. Low titres, in particular microfilaments of <1 dpf, or intensive cooling also reduce the elongation at break and thus the stretching ratio and the spin factor: reductions in capacity are the consequence. For a specified spinning take-off speed, the spin factor can consequently be increased by selecting a polymer of higher elongation at break. On the other hand, the polymer determines the quality of the staple fibres and therefore can only be changed minimally or not at all.
WO 99/07927 Al discloses that the elongation at break of pre-orientated polyester yarns (POYs) which have 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, 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. However, the process cannot be applied to spun filaments produced at take-off speeds of below 2500 m/min since these, in contrast to POY fibres, are of low crystallinity (<12%) and have high shrinkage on boiling (>40%) and high elongation at break (>225%).
In EP 0 080 274 B and EP 0 154 425 B, the same effect is achieved by addition of polyolefins or PA-66 to polyethylene terephthalate. According to EP 0 080 274 B, the effect increases with increasing spinning take-off speed, where the wind-up speed must be at least 2000 m/min. According to EP 0 154 425 B, the effect can also be achieved, albeit to a lesser extent, at lower wind-up speeds if the polyethylene terephthalate has an intrinsic viscosity of greater than 0.70 dl/g.
EP 0 631 638 B describes filaments made from polyethylene terephthalate containing imidated poly(alkyl methacrylates) which have subsequently been subjected to final stretching. Although the industrial yarn spun at 510 m/min has increased elongation at break, the stretching is, however, not improved, and the yarn otherwise has worse properties than filaments without additive.
It is furthermore known that it is possible to spin polypropylene terephthalate (EP 745 711 A, WO 96/00808 A) and polybutylene terephthalate (U.S. Pat. No. 4,877,572) to give continuous filaments. However, no mention is made of their suitability for the production of staple fibres.
The object of the present invention is to maximize the spin factor in the production of polyester staple fibres, where the staple fibres must have the same or better quality values than staple fibres produced by known processes.
This object is achieved in accordance with the invention by polyester staple fibres and by a process for their production as described in the patent claims.
The term polyester here is taken to mean poly(C
2-4
-alkylene) tere-phthalates, 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-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 0.5 to 0.7 dl/g, polypropylene terephthalate having an I.V. of from 0.6 to 1.2 dl/g and polybutylene terephthalate having an I.V. of from 0.6 to 1.2 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 10:1, 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 and meaning that particularly favourable processing properties are achieved. Surprisingly, the viscosity ratio determined as ideal in accordance with the invention for the use of polymer mixtures for the production of staple fibres 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. Surprisingly, it has been found that the melt viscosity of the mixture does not increase significantly under the conditions according to the invention. A positive result of this is avoidance of increases in the pressure drop in the melt lines.
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. 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 polyester (PET about 60 kJ/mol), i.e. greater than 80 kJ/mol, a fibril structure of the additive is obtained in the spun filament. The high glass transition temperature compared with the polyester ensures rapid solidification of this fibril structure in the spun filament. The maximum particle sizes of the additive polymer here immediately after exiting from the spinneret are about 1000 nm, while the mean particle size is 400 nm or less. After drawing beneath the spinneret, fibrils having a
Cordes Ingo
Janas Wolfgang
Schwind Helmut
Ude Werner
Wandel Dietmar
Edwards N.
Lurgi Zimmer AG
Norris & McLaughlin & Marcus
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