POLYESTER YARN

Abstract: A terephthalate polyester yarn containing at least two types of filament is described. The filaments of the first type have in cross-section no more than one axis of planar symmetry whereas the filaments of the second type, which are stronger and have a higher elongation at break point than the filaments of the first type, have a plurality of axes of planar symmetry. The resultant yarn may be draw textured to produce a yarn that has free ends but is low in piling.

Description: Polyester yarn This invention relates to a polyester yarn that may be draw textured to produce a fabric having a spun-like feel similar to that of cotton or wool. It is known to treat polyester yarn in a texturing jet to give it a more natural spun-like feel - see U.S. Patent 4,100,725 to Magel. It is also known to produce filaments having body and wing portions. Filaments in such yarns when treated in a texturing jet tend to split longitudinally so that the wing portions are at least intermittently separated from the body portion. The wing portion also splits transversely giving a product with free ends - see U.S. Patent 4,245,001 to Phillips et al. U.S. Patent 4,157,419 to Mirhej discloses a polyester draw texturing feed yarn having three types of filaments, one of which is a bicomponent filament. When this yarn is hot drawn the the bicomponent filaments break and the ends form a helical crimp. Bradley et al. U.S. Patent 4,110,965 discloses a polyester yarn having a spun-like hand made by breaking in a false twist operation one type of filaments (nonround filaments) while the second type of filaments (round filaments) remain unbroken. It is an object of the present invention to provide a yarn that may be draw textured to produce a yarn that has free ends, but that is low in pilling. According to the present invention there is provided a terephthalate polyester yarn containing at least two different types of filaments, one of said types, the first type of filament, having no more than one axis of planar symmetry and a nonuniform orientation profile across its cross section as shown by birefringence, said first type filaments having a tenacity of 0.8 to 2.0 grams per denier, the composition of said first type of filament being a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5-(sodium-sulfo) isophthalate units, and another of said types, the second type of filament, having plurality of axes of planar symmetry, a tenacity of 1.6 to 3.6 grams per denier said tenacity being 30 to 200% higher than the tenacity of said first type of filament, and an elongation at break of at least 30% higher than the elongation at break of said first type of filament, the composition of said second type of filament being a copolymer of poly(ethylene terephthalate) units and about 2 mole percent ethylene 5-(sodium-sulfo) isophthalate units or a homopolymer of poly(ethylene terephthalate). The yarn of the present invention suitably contains from 30 to 65% by weight of filaments of the first type. If desired, the filaments of the second type may be of different cross-sectional shape, for example, some may be circular and other symmetrically multilobal. Preferably the filaments of the first type have an elongation at break of between 30% and 100% A highly desirable cross-sectional shape for filaments of the first type is a keyhole shape. This shape will be more fully desribed in the examples which will follow. The first type of filaments in the feed yarn of the invention has in its cross section no more than one axis of planar symmetry. The phrase "no more than one axis of planar symmetry" eans that not more than one straight line can be drawn in the plane of the filament cross section that will divide the filament cross section into two equal parts each being the mirror image of the other. - < amples of cross sections having no more than one axis of planar symmetry, are a keyhole shape, a triskelion shape, or a fan shape. The first type of filaments in the feed yarn of the invention have a nonuniform orientation profile across its cross section, as measured by birefringence, and an overall higher orientation than the second type of filaments. The method of measuring birefringence of textile fibers is disclosed in U.S. Patent 3,963,678 issued to Conrad et al. This nonuniform and higher orientation is purposely created in the first type of filament of the yarns -of the present invention by quenching the filaments rapidly. These orientation differences between the first and second type of filaments is exploited in using the yarns of the present invention in that when the first type of filaments are broken in the draw texturing operation, the broken ends twist and curl. These broken ends give the yarn and fabric made from the yarn a "natural" spun feel similar to cotton or wool depending on total number of filaments and average denier per filament. Because the broken ends twist and cul they become somewhat entangled with the other filaments, and as a result there tend to be very fe long protruding free ends. Long protruding free ends are partial: responsible for the pilling problem in polyester fabrics. The second type of filament in the yarn has a lower overall orientation and a higher elongation at break than the first type, and also a higher tenacity. Thus when the yarn containing both types of filament is draw-textured the filaments of the second type just elongate, while some of the filaments of the first type break. The higher elongation property in the second type filaments is "built in" to them by spinning them at a higher temperature, and by attenuating them (drawing them down) at a slower rate over a longer distance. An efficient means of accomplishing this is by use of the stepped spinneret shown in the accompanying drawing, and which is the subject of the Applicants' co-pending European Patent Application No.83300677.8 filed 10 February 1983, published under serial No. EP A, a copy of which is on the European Patent'Office file for the instant application. The tenacity of the second type of filament is also greater than the tenacity of the first type of filament. A tenacity difference between the second type of filament and the first type of filament can be insured if each of the two types of filament are spun from different polymers, for example if the polymer of the first type of filament is a copolymer of poly(ethylene terephthalate) and ethylene 5-(sodium-sulfo) isophthalate, and the second type of filament is spun from a polymer that is a homopolymer of about the same melt viscosity as the copolymer (it being well-known in the art that the homopolymer filaments are higher in tenacity in grams per denier than copolymer). The second type of filament will also have a higher tenacity than the first type of filament, even if spun from the same chemical composition, if the spinning conditions are properly adjusted. For example, when using a stepped spinneret, the filaments that are spun cooler and are quenched more quickly have lower tenacity than the filaments that are spun hotter and quenched more slowly. Pilling is also affected by tenacity, in that if tenacity is low, the free ends tend to break off before pills become fully formed - thus shedding the partially formed pill. According to a further aspect of the present invention there is thus provided a process for the preparation of a terephthalate polyester yarn containing at least two different types of filaments, the said process comprising (a) melt-spinning into filaments of a first type through a first set of spinneret capillaries the cross sections of which each have no more than one axis of symmetry a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5-(sodium-sulfo) isophthalate units, (b) melt-spinning into filaments of a second type through a second set of spinneret capillaries which are recessed in relation to the spinneret capillaries of the said first set and whose cross-sections each have a plurality of axes of symmetry a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5- (sodium-sulfo) isophthalate units or a homopolymer of poly(ethylene terephthalate), and (c) directing a stream of quenching gas to strike the said filaments of the first type before striking the said filaments of the second type, whereby the said filaments of the first type are formed having no more than one axis of planar symmetry and a non-uniform orientation profile across their cross-section as shown by birefringence and having a tenacity of 0.8 to 2.0 grams per denier and the said filaments of the second type are formed having a plurality of axes of planar symmetry, a tenacity of 1.6 to 3.6 grams per denier said tenacity being 30 to 200% higher than the tenacity of the said first type of filament, and an elongation at break of at least 30% higher than that of the said first type of filament. In the examples which follow the relative viscosity was measured in hexafluoro isopropanol, at 25 + 0.003 C at a concentration of 4.75 weight percent and is designated LRV. The birefringence reported is the average of 10 measurements, and the "percent coefficient of variation" is determined by the formula Standard Deviation X 100. % Coefficient of Variation = Birefringence Mean The spinning of yarns of the invention will now be described by way of Example with reference to the accompanying drawing in which: Figure 1 shows a stepped spinneret of a type useful in the spinning of the yarn of the invention. Figure 1 shows a stepped spinneret 1 having mounting holes 2 and a boss 5 on planar surface 6. Outlet orifices 7 penetrate the boss and the planar surface 6. The arrow shows the preferred direction of flow of quenching gas, generally air. Example 1 A spinneret plate of the type illustrated in Figure 1 had the following dimensions: the plate is approximately 1.25 cm thick having a boss 5 approximately 1.25 cm thick. The boss has about 6.5 cm in its longest dimension, and 1.75 cm wide. The boss has three rows of capillaries, 10 in the first row and 12 in each of the second and third rows The rows are about 6 mm apart and are offset so that the capillaries in the second row when viewed laterally to the length of the row appear to be midway between the capillaries in the first row. The capillaries in the third row are aligned with those in the first row. The capillaries are keyhole shaped, about 30 mils (.76 mm) long, 3 mils (.076 mm) wide and having an enlarged circular end about 9 mils (.23 mm) in diameter. The enlareent is located at the end adjacent round caLDlllaries. These capillaries have a circular counterbore on the melt side (the side without the boss) about .16 cm in diameter and about 2.3 cm deep. Three additional rows of capillaries which penetrate the spinneret plate in the area not covered by the boss, are located in three lines that are parallel to the rows of capillaries that penetrate the boss. The two rows adjacent the boss contains 12 capillaries, and the other row contains 10 capillaries. These capillaries have a circular counterbore on the melt side (the side without the boss) about .16 cm in diameter and about 1 cm deep. The rows are about 1.25 cm apart. These rows of capillaries are not offset. These capillaries are round and have a diameter of approximately 13 mils (.33 mm). The spinneret plate was mounted on the spinning machine in such a way that the stream of quenching air will. first strike the filaments that originate from capillaries that penetrate the boss--the Reyhole-shaped capillaries. Using the above-described spinneret, a polyester yarn was melt-spun from copolyester of poly(ethylene terephthalate) and ethylene 5-(sodium-sulfo) isophthalate, containing about 2 mole percent of the latter component. The copolymer had an LRV of between 14 and 14.5. The polymer contained 0.3as of finely divided TiO2. The block temperature of the spinning machine operated at 3000C. The polymer was spun at 3,200 meters per minute. The filaments were quenched with air having a temperature of 210C at an air flow of 65 cubic feet (1-.84rn3)'per inuta per spinning pack. The flow of the quenching air was such that it first contacted the keyhole filaments and the boss initially shielded the round filaments from the quenching air. Both the filaments having a round cross-sectional shape and the filaments having the keyhole cross-sectional shape had a denier of 4.0. The round filaments had a birefringence of 0.0279. The keyhole filament had a birefringence of 0.0467, and a percent coefficent of variation cf 15.4. The round filaments had a break elongation cf 146 percent, and the keyhole filaments a break elongation of 88 percent. The round filaments had a tenacity of 2.00 grams per denier, and the keyhole filament had a tenacity of 1.27 grams per denier. The resulting feed yarnas draw textured on a Lesson095 false twist texturing machine at a speed of 91 meters per minute, a twist of 2360 turns per meter at a texturing temperature of 2000C and a draw ratio of 1.65. The draw textured yarn had 5 broken filaments per centimeter, an elongation at break of 12.6 percent, a tenacity of 1.38 grams per denier and a boil-off shrinkage of 4.8%. Double knit fabric from this yarn zzhen boiled in an acid bath, pre3, will give an excellent random tumble pill test rating--a rating of 5. The rating schedule is set forth in U.S. Patent 4,157,419 at column 10. Example 2 Using the same spinning equipment and spinneret as described in Example 1, except that one row of 12 of the keyhole spinneret apertures was blocked, the same copolyester as Example 1 was spun at 2950C and 3,200 meters per minute. The filaments were quenched with air at 2100 flowing at 75 cubic feet (2.12m3) per minute per spinning pack. The round fila ments had a denier of 4.9, a break elongation of 139%, a tenacity of 1.67 grams per denier, a bierfringence of 0.0268 with a percent coefficient of variation of 4.5. The keyhole filaments had a denier of 3.4, an elongation at break of 85 percent, a tenacity of 1.17 grams per denier, a birefringence of 0.0686 with a percent coefficient of variation of 23.0. This yarn was draw textured on the same machine and under the same conditions as the yarn of Example 1, and had a break elongation of 15.0, a tenacity of 1.83, a boil-off shrinkage of 4.8 and 5.9 broken filaments per centimeter. Double knit poplin fabrics from this yarn when boiled in an acid bath, pH3, will have an excellent random tumble pill test rating. Example 3 Using the same spinning equipment as in Example 2, including the spinneret with 12 of the keyhole spinneret apertures blocked off, but with the homopolyester of poly(ethylene terephthalate) having an LRV of 22, and containing 0.3% finely divided TiO2 being fed to the round spinneret capillaries, and the copolyester of Example 1 being fed to the keyhole spinneret capillaries, a yarn was spun at 3000C at a speed of 3,200 meters per minute. The filaments were quenched with air at 21 C flowing at 75 cubic feet (2.12m3-) per minute per spinning pack. The round filament had a denier of 3.5, an elongation at break of 141 percent, tenacity of 2.95 gram per denier and a birefringence of 0.0423 with a coefficient of variation of 7.1. The keyhole-shaped filaments had a denier of 3.2, an elongation at break of 70 percent and a tenacity of 1.07 grams per denier, and a birefringence of 0.0612 with a coefficient of variation of 14.2. This yarn was draw tetured on the same equipment and at the sane condition as the earlier examples, except that the draw ratio was 1.55. The textured yarn had an elongation at break of 25.8 percent a tenacity of 3.00 grams per denier, a boil-off shrinkage of 4.1, and 3.3 broken filaments per centineter. Double knit poplin fabrics of this yarn had acceptable random tumble pill test ratings without boiling in an adid bath, p3.

Claims: Claims 1. A terephthalate polyester yarn containing at least two different types of filaments, one of said types, the first type of filament, having no more than one axis of planar symmetry and a nonuniform orientation profile across its cross section as shown by birefringence, said first type filaments having a tenacity of 0.8 to 2.0 grams per denier, the composition of said first type of filament being a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5-(sodium-sulfo) isophthalate units, and another of said types, the second type of filament, having a plurality of axes of planar symmetry, a tenacity of 1.6 to 3.6 grams per denier said tenacity being 30 to 200% higher than the tenacity of said first type of filament, and an elongation at break of at least 30% higher than the elongation at break of said first type of filament, the composition of said second type of filament being a copolymer of poly(ethylene terephthalate) units and about 2 mole percent ethylene 5-(sodium-sulfo) isophthalate units or a homopolymer of poly(ethylene terephthalate). 2. A yarn as claimed in claim 1 wherein the said first type of filament has an elongation at break of between 30% and 100%. 3. A yarn as claimed in either of claims 1 and 2 wherein the said first type of filament has a triskelion cross section. 4. A yarn as claimed in either of claims 1 and 2 wherein the said first type of filament has a keyhole cross-sectional shape. 5. A yarn as claimed in any one of claims 1 to 4 wherein the said second type of filament has a round cross-sectional shape. 6. A yarn as claimed in any one of claims 1 to 4 wherein the said second type of filament is multilobal symmetrical. 7. A yarn as claimed in any one of claims 1 to 6 containing from 30 to 65% by weight of filaments of the said first type. 8. A process for the preparation of a terephthalate polyester yarn containing at least two different types of filaments, the said process comprising (a) melt-spinning into filaments of a first type through a first set of spinneret capillaries the cross sections of which each have no more than one axis of symmetry a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5-(sodium-sulfo) isophthalate units, (b) melt-spinning into filaments of a second type through a second set of spinneret capillaries which are recessed in relation to the spinneret capillaries of the said first set and whose cross-sections each have a plurality of axes of symmetry a copolymer of poly(ethylene terephthalate) units and about 2 mol percent ethylene 5-(sodium sulfo)isophthalate units or a homopolymer of poly(ethylene terephthalate), and (c) directing a stream of quenching gas to strike the said filaments of the first type before striking the said filaments of the second type, whereby the said filaments of the first type are formed having no more than one axis of planar symmetry and a non-uniform orientation profile across their cross-section as shown by birefringence and having a tenacity of 0.8 to 2.0 grams per denier and the said filaments of the second type are formed having a plurality of axes of planar symmetry, a tenacity of 1.6 to 3.6 grams per denier said tenacity being 30 to 200% higher than the tenacity of the said first type of filament, and an elongation at break of at least 30% higher than that of the said first type of filament. 9. A process as claimed in claim 8 wherein the yarn is subsequently draw-textured.

Inventors: MIRHEJ, MICHAEL EDWARD
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1983
Main classification: D02G3
IPC codes: D01F6, D01D4, D01D5