IMPROVED CATIONIC-DYEABLE COPOLYESTER DRAW-TEXTURING FEED YARNS

Abstract: An improved cationic-dyeable copolyester draw-texturing feed yarn that is novel in that the filaments are concentric sheath/core bicomponent filaments, the sheath consisting essentially of the cationic-dyeable polyester, whereas the core consists essentially of homopolymer, whereby such feed yarn may be draw-textured on commercially-available machines to give textured yarns with lower broken filament counts and improved bulk at economically viable costs.

Description: FIELD OF THE INVENTION This invention concerns improvements in and relating to improved cationic-dyeable copolyester draw-texturing feed yarns, and more particularly to such feed yarns that are novel on account of being concentric sheath/core bicomponent filaments, and are improved in that they are capable of being draw-textured at relatively high speeds without undesirably high numbers of broken filaments to give textured yarns having desirably high bulk, and the resulting textured yarns, and fabrics and garments containing such textured yarns. BACKGROUND OF THE INVENTION Synthetic polyester multifilament yarns have been known and used commercially for several decades, having been first suggested by W.H. Carothers, U.S. Patent No. 2,071,251, and then by Whinfield and Dickson, U.S. Patent No. 2,465,319. Most of the polyester polymer that has been manufactured and used commercially for such continuous filament yarns has been poly(ethylene terephthalate), sometimes referred to as 2G-T. This polymer is often referred to as homopolymer, although it is known that, in addition to the residues of ethylene, from ethylene glycol, and terephthalate residues, from dimethyl terephthalate or terephthalic acid, there are also residues from diethylene glycol. For textile (apparel) purposes, such commercial homopolymer is usually of intrinsic viscosity about 0.6; it can vary up to about 0.65 or even 0.67, and can also be of somewhat lower viscosity. Commercial homopolymer is notoriously difficult to dye. Such homopolymer is mostly dyed with disperse dyestuffs at high temperatures under elevated pressures, which is a relatively expensive and inconvenient process (in contrast to processes for dyeing several other commercial fibers at atmospheric pressure, e.g. at the boil), and so there have been several suggestions for improving the dyeability of polyester yarns. Accordingly, Griffing and Remington, U.S. Patent No. 3,018,272, suggested the use of cationic-dyeable copolyesters, in which the poly(ethylene terephthalate) structure is modified by inclusion of sulfonate groups that provide an affinity for cationic dyestuffs. Such cationic-dyeable copolyester consisting essentially of poly[ethylene terephthalate/5-(sodium sulfo) isophthalate] containing about 2 mole % of the 5-(sodium sulfo) isophthalate groups in the polymer chain has been used commercially as a basis for polyester yarns for some 20 years, and is sometimes referred to as 2G-T/SSI. Although this cationic-dyeable copolyester is significantly more expensive than the homopolymer, it has been used on a large scale for various applications, especially as staple fiber, and in heather multi-filament yarns, wherein the cationic-dyeable copolyester filaments are intermingled with homopolymer filaments. A very large amount of homopolymer has been used to make draw-texturing feed yarns. This concept was first suggested by Petrille in U.S. Patent No. 3,771,307 and Piazza and Reese in U.S. Patent No. 3,772,872. These draw-texturing feed yarns (DTFY) are substantially amorphous spin-oriented multi-filament (continuous filament) yarns prepared by spinning at withdrawal speeds of the order of about 3000 ypm (2743 metres per minute) or more, more or less as indicated by Petrille and by Piazza and Reese. These withdrawal speeds are used to obtain the spin-orientation that is required for the feed yarns to be stable (in storage and to heat, so that they may be draw-textured). It is also desirable, however, that the feed yarns be substantially amorphous, i.e. of relatively low crystallinity. It is this low crystallinity that distinguishes DTFY from drawn polyester yarns that are used in fabric formation, e.g. by weaving or knitting. The present invention is concerned with DTFY, i.e. with feed yarns that are spin-oriented, but of low crystallinity, as distinguished from crystalline yarns such as have been used directly in fabrics. Most commercial DTFY at this time has a crystallinity of the order of 10%, and relatively high boil-off shrinkage; such shrinkages have generally been of the order of about 40%. In contrast, commercial polyester yarns that are drawn have generally had crystallinity of more than 30%, and shrinkages of 15% or less. It is also possible to obtain crystalline spin-oriented yarns by spinning under different conditions, including very high speeds, e.g. as disclosed by Frankfort and Knox in U.S. Patent Nos. 4,134,882 and 4,195,051, and these yarns may be subjected to draw-texturing. However, according to the present invention, such crystalline yarns are not contemplated and it is preferred to use spin-oriented yarns of low crystallinity, as shown by a boil-off shrinkage of at least 15%, and preferably at least 25%. As indicated, conventional homopolymer DTFY has been manufactured in large quantities and has been draw-textured. Hitherto, however, although 2G-T/SSI copolymer has been used satisfactorily for other types of polyester yarns, customers have complained that 2G-T/SSI DTFY has given unacceptably high broken filament counts (BFC) in contrast to conventional homopolymer DTFY. This has been particularly true, for instance, when it has been desired to prepare a 150/68 denier/number of filaments (16.7 tex/number of filaments) textured 2G-T/SSI copolyester yarn by draw-texturing a 250-68 DTFY at a draw ratio of about 1.6 X on a Barmag FK6 machine at speeds of 500-600 m/min., which texturing conditions have been desirable commercially for several years, and have been desirable commercially for several years, and have long been attainable with regular homopolymer DTFY with acceptable BFC levels of about 0.5/1b (1.1/kg) or less (counted by examining the ends of the packages of textured yarn). Despite many efforts, hitherto, we have not found it practical to improve 2G-T/SSI copolyester DTFY by varying its process of manufacture so as to meet customer requirements in this regard at an economic price. It is an object of the invention to provide a cationic-dyeable copolyester DTFY that meets such requirements. It was suggested by Barmag (Schippers) in German DE OS 2335946 to manufacture crimped filaments by heating and simultaneous false-twisting with more than 2,000 turns per meter of filament length using multi-component filaments, in which at least one component had properties that affected its length or its length-behavior that differed from those of the other component or components. The bicomponent construction could be any made of usual and known materials. Example II shows the spinning of nylon 6 and a polyester component at 3 km/min. to provide concentric sheath/core filaments, and their draw-texturing using a draw ratio of 1: 1.25 (1.25 X), using a single heater at 220°C (the second heater was by-passed). The other Examples show side-by-side bicomponent filaments that are wholly polyamide. Barmag does not disclose the specific combination of a 2G-T/SSI copolyester in any bicomponent combination. Lee, U.S. Patent No. 4,059,949 discloses composite yarns exhibiting heather dyeing capability, comprised of two groups of filaments composed of two differently dyeable polymers, wherein filaments of one group are homofilaments of one polymer, and filaments of the other group are of a substantially concentric sheath/core structure with the sheath being of the other polymer and the core being of the same polymer as the homofilaments. The yarn dyes to give a heather appearance which is different from the appearance expected based on the polymer composition of the yarn. Lee makes no reference to DTFY, nor to draw-texturing. Example I shows the preparation of heather yarns form molten 2G-T of 22 HRV and molten 2G-T/SSI of 14 HRV to provide yarns of 34 filaments, 7 of which are single component filaments of 2G-T/SSI, whereas 27 of which are substantially concentric sheath/core bicomponent filaments of which the core is 2G-T/SSI ans the sheath is 2G-T, by a process of spinning, quenching and drawing in a continuous operation. These drawn heather yarns are then false-twist textured without drawing. Most of the dependent claims are directed to this combination, which is obviously preferred, as can be sen from the majority of the description. Claim 10, however, being dependent on Claim 1, is directed to the feature wherein the homofilaments are composed of 2G-T and the sheath/core filaments are composed of a 2G-T core and a sheath of 2G-T/SSI. There is also a reference in column 4, starting at line 28, to a reverse case with a basic dyeing component in the sheath and a disperse dyeable core component. In this reverse case, the 2G-T/SSI sheath takes up both disperse dyes and basic dyes, and the 2G-T core is dyed only with the disperse dyes. However, in the preferred case, both the sheath and core are dyed with disperse dyes, but neither sheath nor core is dyed with basic dyes (column 4, lines 16-28). SUMMARY OF THE INVENTION According to the invention, there is provided an improved cationic-dyeable copolyester draw-texturing feed yarn, wherein the cationic-dyeable copolyester consists essentially of poly[ethylene terephthalate/5-(sodium sulfo) isophthalate] containing about 2 mole % of the 5-(sodium sulfo) isophthalate groups in the polymer chain, and the feed yarn is a substantially amorphous spinoriented multi-filament yarn prepared by spinning at a withdrawal speed of the order of about 3000 ypm (2743 metres per minute) or more, the improvement characterized in that the filaments are concentric sheath/core bicomponent filaments, wherein the sheath consists essentially of the cationic-dyeable copolyester, and the core consists essentially of poly(ethylene terephthalate) of intrinsic viscosity about 0.6. The bicomponent filaments preferably consist essentially of approximately equal amounts by weight of sheath and of core. The advantages of the DTFY of the invention are particularly noted for filaments of lighter denier, being about 5 dpf (denier per filament or 0.55 tex per filament) or less. There is also provided a process for preparing a textured cationic-dyeable polyester yarn, wherein such feed yarn is subjected to draw-false-twist-texturing, and the resulting textured polyester yarns, and fabrics and garments containing at least 10% by weight of such texutred polyester yarns, and preferably consisting essentially of such textured polyesters yarns. BRIEF DESCRIPTION OF DRAWINGS The Figure is a photomicrograph of cross-sections of filaments of the bicomponent yarns of the invention. DETAILED DESCRIPTION OF THE INVENTION The preparation of monocomponent polyester DTFY has been amply described in the prior art, e.g. in the aforsaid U.S. Patent Nos. 3,771,307 and 3,772,872, the disclosures of which are hereby incorporated by reference, and these conventional techniques need only be modified by providing for the spinning of concentric bicomponent filaments, e.g. using a spinneret as disclosed on the left hand side of Figure 1 of aforesaid U.S. Patent N°. 4,059,949, the disclosure of which is also hereby incorporated by reference, it being recognized that U.S. Patent N°. 4,059,949 discloses the preparation of mixed yarns including drawn concentric bicomponent filaments (as well as monocomponent drawn filaments), and not of DTFY. The preparation of bicomponent filaments for polyester DTFY is disclosed in Mirhej, U.S. Patent N°. 4,157,419, it being recognized that Mirhej discloses the preparation of eccentric bicomponent filaments that are intended to break during draw-texturing and provide a helical crimp, on account of the excentric nature, whereas the bicomponent filaments according to the present invention are concentric, and are primarily intended to resist breaking during normal draw-texturing operations. Further details for preparing preferred concentric bicomponent filaments and DTFY according to the present invention are given in the following Example, as are details of their texturing. The preparation of fabrics and garments from the resulting textured yarns may be carried out by conventional techniques. The advantage of the improved (reduced) BFC is quite significant, as is the increased bulk obtained in comparison with monocomponent 2G-T/SSI copolymer filament yarns. A further advantage of the DTFY according to the invention is that the cost of the homopolymer, that provides the core of the novel bicomponent filaments, is considerably cheaper than for the 2G-T/SSI copolymer, so the cost of the raw materials for the bicomponent filaments is considerably less than for monocomponent filaments of 2G-T/SSI. In view of these economic incentives, and the many prior suggestions of using bicomponent filaments for various other purposes, it is quite surprising that no one has previously suggested the present invention. The invention is further described in the following Example. Reference may be made to Knox, U.S. Patent No. 4,156,071 for most of the various test measurements. For the tensile properties, however, there was used a six-inch sample length, without twist at a 200% per minute rate of extension. "Natural Draw Ratio "(NDR) is determined from a stress-strain curve as described by Ludewig in Polyester Fibres , Section 5.4.1 (pages 174-177), John Wiley & Sons, Ltd., 1971. "Natural Draw Force" (NDF) is the value of the tensile stress on the yarn taken from the straight-line portion of the stress-strain curve located in the yield zone below the natural draw ratio. As reported here, NDR and NDF are determined from a stress-strain curve measured on an Instron tensile testing machine at 70°F and 65% RH using a sample length of five inches and a rate of elongation of 400% per minute. Crimp Contraction (CCA₅) was measured essentially as in U.S. Patent No. 4,134,882. The method for determining LRV is disclosed in Most, U.S. Patent No. 4,444,710. EXAMPLE A 240/68 bicomponent feed yarn was prepared at a withdrawal speed of 3315 ypm, with 50/50 by weight of 2G-T of 19.4 LRV (intrinsic viscosity 0.61) in the core and with 98/2 2G-T/SSI copolyester of 12.8 LRV (intrinsic viscosity 0.49) in the concentric sheath, using a block temperature of 286°C, but otherwise essentially as described and illustrated in Lee U.S. Patent No. 4,059,949. The filaments were treated with a commercial draw-texturing finish and interlaced. The resulting yarns had the following properties, Tenacity 1.3 g/d (11.8 g/tex), Elongation 117%, Modulus 24 g/d (218 g/tex), Natural Draw Ratio 1.4, Natural Draw Force 150 g, Shrinkage 45%, Density 1.347 and Birefringence 0.02. Cross-sections of filaments are shown in the photomicrograph in the Figure. This yarn was draw-textured on a Murata machine under conventional conditions and compared with a control yarn prepared essentially similarly except that it has monocomponent, consisting only of the 2G-T/SSI copolyester. The bicomponent feed yarn of the invention gave significantly fewer broken filaments and better crimp, as can be seen from the Table. It was also found that there was consistent improvement in crimp contraction measured over various loadings (from 0.5 to 10 mg/denier - 45 to 90 mg/tex) which could be of advantage in providing a combination of greater bulk and/or less broken filaments, as desired, by using more or less rigorous texturing conditions. These textured yarns may be processed into fabrics by conventional techniques, such as knitting, or weaving if desired, and dyed to attractive shades with cationic and/or disperse dyes, despite the presence of a homopolymer core. As indicated in the foregoing Example, the sheath/core (DTFY) filaments of the invention contain about 50/50 by weight of homopolymer/copolymer, and correspondingly about equal amounts by area of cross-section, since the densities are approximately equal. The diameter of the core (which is the same as the internal diameter for the sheath) is about 10.5 µm, whereas the external diameter of the sheath (and of the total filament) is about 15 µm. In other words, the thickness of the sheath (on either side) is only about 2 µm. A decrease in the thickness of the sheath in the feed yarn may lead to more bulk in the textured product, and possibly lower broken filaments and lighter dyeing. Increased dyeing capability could possibly be achieved by increasing the proportion of SSI in the copolyester used for the sheath, if desired. Thus, although this description has emphasized the 2G-T/SSI copolymer that has been preferred for many years and has been available commercially, it will be understood that variations of the precise compositions and proportions of the polymers and of their conditions of preparation can be made without departing from the essence of the invention, both for the copolymer sheath and for the homopolymer core of the bicomponent filaments and yarns, according to the present invention. For instance, the viscosity of the homopolymer may vary from about 0.6 to about 0.67. It is also conventional to use additives, such as pigments or delustering agents, such as titanium dioxide, if desired.

Claims: 1. An improved cationic-dyeable copolyester draw-texturing feed yarn, wherein the cationic-dyeable copolyester consists essentially of poly[ethylene terephthalate/5-(sodium sulfo)isophthalate] containing about 2 mole % of the 5-(sodium sulfo)isophthalate groups in the polymer chain, and the feed yarn is a substantially amorphous spin-oriented multi-filament yarn prepared by spinning at a withdrawal speed of the order of about 3000 ypm (2743 metres per minute) or more, the improvement characterized in that the filaments are concentric sheath/core bicomponent filaments, wherein the sheath consists essentially of the cationic-dyeable copolyester, and the core consists essentially of poly(ethylene terephthalate) of intrinsic viscosity about 0.6. 2. A feed yarn according to Claim 1, wherein the average denier per filament is about 5 or less (about 0.55 or less tex par filament). 3. A feed yarn according to Claim 1 or 2, wherein the bicomponent filaments consist essentially of approximately equal amounts by weight of sheath and of core. 4. A process of preparing a textured cationic-dyeable polyester yarn, characterized in that a feed yarn according to Claim 1, 2 or 3 is subjected to draw-false-twist-texturing. 5. A textured polyester yarn prepared by draw-false-twist-texturing the feed yarn of any one of Claims 1 to 3. 6. A fabric containing at least 10% by weight of textured polyester yarn according to Claim 5. 7. A fabric consisting essentially of textured polyester yarn according to Claim 5. 8. A garment containing at least 10% by weight of textured polyester yarn according to Claim 5. 9. A garment consisting essentially of textured polyester yarn according to Claim 5.

Inventors: BUTLER, MICHAEL DOUGLAS, SIVILS, GEORGE LETE, JR.
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1988
Main classification: D01F8
IPC codes: D02G1, D02G3, D01F8