Stretch polyester/cotton spun yarn

Abstract

The invention provides a spun yarn comprising cotton and a bicomponent polyester staple. The fiber of the invention exhibits unusually high stretch characteristics and has excellent cardability and uniformity.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to spun yarn comprising polyester staple fiber and cotton, more particularly such a yarn in which the polyester staple is a bicomponent that imparts desirable properties to the yarn.

[0003] 2. Discussion of Background Art

[0004] Polyester bicomponent fibers are known from U.S. Pat. Nos. 3,454,460 and 3,671,379, which disclose spun yarns made from bicomponent staple having certain ranges of crimp properties outside of which the yarns are said to be boardy, harsh, and aesthetically undesirable.

[0005] Spun yarns comprising bicomponent staple fibers are disclosed in Japanese Published Patent Applications JP62-085026, and JP2000-328382 and U.S. Pat. No. 5,874,372, but such fibers can have little recovery power and need to be mechanically crimped, which adds to their cost.

[0006] Polyester fibers having longitudinal grooves in their surfaces are described in U.S. Pat. Nos. 3,914,488, 4,634,625, 5,626,961, and 5,736,243, and Published International Patent Application WO01/66837, but such fibers can lack good stretch and recovery properties.

[0007] Spun yarns of polyester bicomponent staple fibers and cotton that have high stretch and uniformity characteristics are still needed.

SUMMARY OF THE INVENTION

[0008] The present invention provides a spun yarn having a total boil-off shrinkage of at least about 22% and comprising cotton and a bicomponent staple fiber comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate) wherein the bicomponent fiber has, a crimp development value of at least about 35% and no higher than about 70%, a crimp index value at least 15% and no higher than about 45%, a length of at least about 1.3 cm and no higher than about 5.5 cm, a linear density of at least about 0.7 decitex per fiber, and no higher than about 3.0 decitex per fiber, and wherein the bicomponent fiber is present at a level of at least about 20 wt % and no higher than about 65 wt %, based on total weight of the spun yarn and wherein the cotton is present at a level of at least about 35 wt % and no higher than about 80 wt %, based on total weight of the spun yarn.

[0009] The invention also provides a process for making the spun yarn of claim 1 comprising the steps of:

[0010] a) providing the bicomponent staple fiber;

[0011] b) providing cotton;

[0012] c) combining by intimate blending at least the cotton and the bicomponent staple fiber so that:

[0013] the bicomponent fiber is present at a level of at least about 20 wt %,

[0014] the bicomponent fiber is present at a level no higher than about 65 wt %,

[0015] the cotton is present at a level of at least about 35 wt %, and

[0016] the cotton is present at a level no higher than about 80 wt % based on total weight of the blended fibers;

[0017] d) carding the blended fibers to form a card sliver;

[0018] e) drawing the card sliver;

[0019] f) doubling and redrawing the card sliver up to about 3 times;

[0020] g) converting the drawn sliver to roving; and

[0021] h) ring-spinning the roving to form the spun yarn.

[0022] The invention further provides a fabric selected from the group consisting of knits and wovens and comprising such a spun yarn as made by such a process.

BRIEF DESCRIPTION OF THE FIGURE

[0023] The FIGURE shows a schematic cross-section of a spinneret pack useful in making bicomponent polyester fiber tow.

DETAILED DESCRIPTION OF THE INVENTION

[0024] It has now been found that spun yarn comprising cotton and a bicomponent staple fiber which in turn comprises poly(ethylene terephthalate) and poly(trimethylene terephthalate) and has selected mechanical properties, has unexpectedly high stretch characteristics, cardability, and uniformity.

[0025] As used herein, ‘bicomponent fiber’ means a fiber in which two polymers are in a side-by-side or eccentric sheath-core relationship and includes both spontaneously crimped fibers and fibers with latent spontaneous crimp that has not yet been realized.

[0026] “Intimate blending” means the process of gravimetrically and thoroughly mixing dissimilar fibers in an opening room (for example with a weigh-pan hopper feeder) before feeding the mixture to the card or of mixing the fibers in a dual feed chute on the card, and is to be distinguished from draw-frame blending.

[0027] The spun yarn of the invention comprises cotton and a polyester bicomponent staple fiber comprising poly(ethylene terephthalate) (“2G-T”) and poly(trimethylene terephthalate) (“3G-T”) and has a total boil-off shrinkage of at least about 22%. When the total boil-off shrinkage is less than about 22%, the stretch-and-recovery properties of the yarn can be inadequate. The bicomponent staple fiber has a crimp development (“CD”) value of at least about 35% and no higher than about 70% and has a crimp index (“CI”) value of at least 15%, preferably at least about 20%, when substantially free of interlacing, and no higher than about 45%, preferably no higher than about 42%, more preferably no higher than about 30%.

[0028] When the CD value is lower than about 35%, the spun yarn has too little total boil-off shrinkage to generate good recovery in fabrics made therefrom. When the CI value is low, mechanical crimping can be necessary for satisfactory carding and spinning. When the CI value is high, the bicomponent staple can have too much crimp to be readily cardable, and the uniformity of the spun yarn can be inadequate.

[0029] The bicomponent staple fiber has a length of about at least about 1.3 cm and no higher than about 5.5 cm. When the bicomponent fiber is shorter than about 1.3 cm, it cannot be readily carded, and when it is longer than about 5.5 cm, it cannot be readily spun with cotton. The cotton can have a length of about 2-4 cm. The bicomponent fiber has a linear density of at least about 0.7 dtex and preferably at least about 0.9 dtex per fiber and no higher than about 3.0 dtex per fiber. When the bicomponent staple has a linear density above about 3.0 dtex per fiber, the yarn can have a harsh hand, and it can be hard to blend with the cotton, resulting in a poorly consolidated, weak yarn. When it has a linear density below about 0.7 dtex per fiber, it can be difficult to card. For a spun yarn of higher uniformity, it is preferred that the bicomponent staple have a linear density less than about 2.5 dtex per fiber.

[0030] In the spun yarn, the bicomponent staple fiber is present at a level of at least about 20 wt %, preferably at least about 35 wt %, and no more than about 65 wt %, preferably less than 50 wt %, based on the total weight of the spun yarn. When the yarn of the invention comprises less than about 20 wt % polyester bicomponent, the yarn can exhibit inadequate stretch and recovery properties, as indicated by low total boil-off shrinkage. When the yarn comprises more than about 65 wt % bicomponent staple fiber, the blended fibers can be difficult to card.

[0031] In the spun yarn of the invention, the cotton is present at a level of at least about 35 wt % and no higher than about 80 wt %, based on total weight of the spun yarn. Optionally, up to about 30 wt %, based on total weight of the spun yarn, can be other staple fibers, for example poly(ethylene terephthalate) staple.

[0032] When the CI of the bicomponent staple fiber is lower in the range of acceptable values, higher proportions of polyester bicomponent staple fibers can be used without compromising cardability and yarn uniformity. When CD is higher in the range of acceptable values, lower proportions of bicomponent staple can be used without compromising total boil-off shrinkage. In particular, since the fiber blend level, CI, and cardability are inter-related, satisfactory cardability can be retained even with high CI values (for example as high as about 45%) if the amount of bicomponent fiber in the blend is low (for example as low as about 20 wt %, based on total weight of spun yarn). Similarly, since the fiber blend level, CD, and total boil-off shrinkage are inter-related, satisfactory total boil-off shrinkage can be retained even at about 20 wt % bicomponent fiber, based on total weight of spun yarn, if the CD is high, for example at about 55% or more.

[0033] It is preferred that the spun yarn of the invention have a Coefficient of Variation (“CV”) of linear density of no higher than about 22%. Above that value, the yarn is less uniform than 100% cotton and can become less desirable for use in some types of fabrics.

[0034] The bicomponent staple fiber can have a weight ratio of poly(ethylene terephthalate) to poly(trimethylene terephthalate) of about 30:70 to 70:30, preferably 40:60 to 60:40. One or both of the polyesters comprising the bicomponent fiber can be copolyesters, and “poly(ethylene terephthalate)” and “poly(trimethylene terephthalate)” include such copolyesters within their meanings. For example, a copoly(ethylene terephthalate) can be used in which the comonomer used to make the copolyester is selected from the group consisting of linear, cyclic, and branched aliphatic dicarboxylic acids having 4-12 carbon atoms (for example butanedioic acid, pentanedioic acid, hexanedioic acid, dodecanedioic acid, and 1,4-cyclo-hexanedicarboxylic acid); aromatic dicarboxylic acids other than terephthalic acid and having 8-12 carbon atoms (for example isophthalic acid and 2,6-naphthalenedicarboxylic acid); linear, cyclic, and branched aliphatic diols having 3-8 carbon atoms (for example 1,3-propane diol, 1,2-propanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, and 1,4-cyclohexanediol); and aliphatic and araliphatic ether glycols having 4-10 carbon atoms (for example, hydroquinone bis(2-hydroxyethyl) ether, or a poly(ethyleneether) glycol having a molecular weight below about 460, including diethyleneether glycol). The comonomer can be present to the extent that it does not compromise the benefits of the invention, for example at levels of about 0.5-15 mole percent based on total polymer ingredients. Isophthalic acid, pentanedioic acid, hexanedioic acid, 1,3-propane diol, and 1,4-butanediol are preferred comonomers.

[0035] The copolyester(s) can also be made with minor amounts of other comonomers, provided such comonomers do not have an adverse affect on the benefits of the invention. Such other comonomers include 5-sodium-sulfoisophthalate, the sodium salt of 3-(2-sulfoethyl) hexanedioic acid, and dialkyl esters thereof, which can be incorporated at about 0.2-4 mole percent based on total polyester. For improved acid dyeability, the (co)polyester(s) can also be mixed with polymeric secondary amine additives, for example poly(6,6′-imino-bishexamethylene terephthalamide) and copolyamides thereof with hexamethylenediamine, preferably phosphoric acid and phosphorous acid salts thereof.

[0036] There is no particular limitation on the outer cross-section of the bicomponent fiber, which can be round, ovoid, triangular, ‘snowman’ and the like. A “snowman” cross-section can be described as a side-by-side cross-section having a long axis, a short axis and at least two maxima in the length of the short axis when plotted against the long axis. In one embodiment, the spun yarn of the invention comprises cotton and a bicomponent staple fiber comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate) and having a plurality of longitudinal grooves in the surface thereof. Such a bicomponent staple fiber can be considered to have a “scalloped oval” cross-section which can improve the wicking properties of the polyester bicomponent.

[0037] The polyester bicomponent staple fibers in the spun yarn of the present invention can also comprise conventional additives such as antistats, antioxidants, antimicrobials, flameproofing agents, dyestuffs, light stabilizers, and delustrants such as titanium dioxide, provided they do not detract from the benefits of the invention.

[0038] It is preferred that the bicomponent staple fiber of which the spun yarn of the invention is comprised have a tenacity-at-break of at least about 4 dN/tex and no higher than about 5.5 dN/tex. When the tenacity is too low, carding and spinning can be difficult, and when it is too high, fabrics made from the spun yarn of the invention can exhibit undesirable pilling. It is also preferred that the linear density of the spun yarn be in the range of about 100 to 700 denier (111 to 778 dtex).

[0039] Knit (for example circular knit and flat knit) and woven (for example plainwoven and twill) stretch fabrics can be made from the spun yarn of the invention.

[0040] The process of the invention comprises the steps of mixing by intimate blending cotton (which can optionally be combed) with a polyester bicomponent staple fiber having the composition and characteristics described hereinbefore, wherein the bicomponent staple fiber is present at a level of at least about 20 wt % and no more than about 65 wt %, preferably less than 50 wt %, based on the total weight of the blended fibers. The cotton is present at a level of at least about 35 wt % and no higher than about 80 wt %, based on total weight of the blended fibers. Optionally, up to about 30 wt %, based on total weight of the spun yarn, can be other staple fibers, for example poly(ethylene terephthalate) staple.

[0041] Use of bicomponent staple fiber exhibiting follow-the-leader crimp is preferred because such staple is believed to improve carding due to its lower CI level. Correspondingly, it is preferred that the bicomponent fibers in the tow precursor to the staple fiber be ‘in register’ with each other and not be ‘de-registered’.

[0042] The blended fibers are further processed by carding the blended fibers to form a card sliver, drawing the card sliver, doubling and redrawing the card sliver up to 3 times, converting the drawn sliver to roving, and ring-spinning the roving with a twist multiplier of 3 to 5.5 to form the spun yarn having a total boil-off shrinkage of at least about 22%.

[0043] Intrinsic viscosity (“IV”) of the polyesters was measured with a Viscotek Forced Flow Viscometer Model Y-900 at a 0.4% concentration at 19° C. and according to ASTM D-4603-96 but in 50/50 wt % trifluoroacetic acid/methylene chloride instead of the prescribed 60/40 wt % phenol/1,1,2,2-tetrachloroethane. The measured viscosity was then correlated with standard viscosities in 60/40 wt % phenol/1,1,2,2-tetrachloroethane to arrive at the reported intrinsic viscosity values.

[0044] Unless otherwise noted, the following methods of measuring tow Crimp Development and tow Crimp Index of the bicomponent fiber were used in the Examples. To measure tow Crimp Index (“C.I.”), a 1.1 meter sample of polyester bicomponent tow was weighed, and its denier was calculated; the tow size was typically of about 38,000 to 60,000 denier (42,000 to 66,700 dtex). Two knots separated by 25 mm were tied at each end of the tow. Tension was applied to the vertical sample by applying a first clamp at the inner knot of the first end and hanging a 40 mg/den (0.035 dN/tex) weight between the knots of the second end. The sample was exercised three times by lifting and slowly lowering the weight. Then a second clamp was applied at 100 cm down from the inner knot of the first end while the weight was in place between the knots of the second end, the 0.035 dN/tex weight was removed from the second end, and the sample was inverted while maintaining the tension so that the first end was at the bottom. A 1.5 mg/den (0.0013 dN/tex) weight was hung between the knots at the first end, the first clamp was removed from the first end, the sample was allowed to retract against the 0.0013 dN/tex weight, and the (retracted) length from the clamp to the inner knot at the first end was measured in cm and identified as Lr. C.I. was calculated according to Formula I. To measure tow Crimp Development (“C.D.”), the same procedure was carried out, except that the 1.1 meter sample was placed—unrestrained—in boiling water for 1 minute and allowed fully to dry before applying the 40 mg/den (0.035 dN/tex) weight.

C.I. and C.D. (%)=100×(100cm−Lr)/100cm   (I)

[0045] To determine the total boil-off-shrinkage of the spun yarns in the Examples, the yarn was made into a skein of 25 wraps on a standard skein winder. While the sample was held taut on the winder, a 10 inch (25.4 cm) length (“Lo”) was marked on the sample with a dye marker. The skein was removed from the winder, placed in boiling water for 1 minute without restraint, removed from the water, and allowed to dry at room temperature. The dry skein was laid flat, and the distance between the dye marks was again measured (“Lbo”). Total boil-off shrinkage was calculated from formula II:

Total B.O.S. (%)=100×Lbo/Lo   (II)

[0046] Using the same sample that had been subjected to the boil-off total shrinkage test, the ‘true’ shrinkage of the spun yarn was measured by applying a 200 mg/den (0.18 dN/tex) load, measuring the extended length, and calculating the percent difference between the before-boil-off and extended after-boil-off lengths. The true shrinkage of the samples was generally less than about 5%. Since true shrinkage constitutes only a very minor fraction of total boil-off shrinkage, the latter is used herein as a reliable measure of the stretch characteristics of the spun yarns. Higher total boil-off shrinkage corresponds to desirably higher stretch.

[0047] The uniformity of the mass of the spun yarns along their length (that is, of their linear density) was determined with a Uniformity 1-B Tester (made by Zellweger Uster Corp.) and reported as Coefficient of Variation (“CV”) in percentage units. In this test, yarn was fed into the Tester at 400 yds/min (366 m/min) for 2.5 minutes, during which the mass of the yarn was measured every 8 mm. The standard deviation of the resulting data was calculated, multiplied by 100, and divided by the average mass of the yarn tested to arrive at percent CV.

[0048] Spun yarn tensile properties were determined using a Tensojet (also made by Zellweger Uster Corp.)

[0049] The cardability of the fiber blends used to make the spun yarns in the Examples was assessed with a Trutzschler Corp. staple card for which a rate of 45 pounds per hour (20 kg/hour) was considered “100% speed”. Cardability was rated “Good” if the card could be run at 100% speed with no more than 1 stop in a 40 pound (18 kg) test run, “Satisfactory” for at least 80% speed with no more than 3 stops in a run, and “Poor” if the speed was lower or the number of stops higher than for “Satisfactory”. Stops were generally caused by web breaks or coiling jams.

[0050] To determine available stretch in the fabrics of Examples 6A and 6B, three 60×6.5 cm sample specimens were cut from each of the fabrics in Examples 4A and 4B. The long dimension corresponded to the stretch direction. Each specimen was unraveled equally on each side until it was 5 cm wide. One end of the fabric was folded to form a loop, and a seam was sewn across the width to fix the loop. At 6.5 cm from the unlooped end of the fabric a first line was drawn, and 50 cm away (“GL”) from the first line, a second line was drawn. The sample was conditioned for at least 16 hours at 20+/−2° C. and 65+/−2% relative humidity. The sample was clamped at the first line, and hung vertically. A 30 newton weight was hung from the loop, and the sample was exercised 3 times by alternately allowing it to be stretched by the weight for 3 seconds and then supporting the weight so the fabric was unloaded. The weight was re-applied, and the distance between the lines (“ML”) was recorded to the nearest millimeter. The available stretch was calculated from formula III, and the results from the three specimens were averaged

% Available Stretch=100×(ML−GL)/GL   (III)

[0051] To measure percent growth (a measure of recovery after stretching) in Examples 6A and 6B, three new specimens were prepared as described for the Available Stretch test, extended to 80% of the previously determined Available Stretch, and held in the extended condition for 30 minutes. They were then allowed to relax without restraint for 60 minutes, and the length (“L2”) between the lines was again measured. Percent Fabric Growth was calculated from Formula IV, and the results from the three specimens were averaged.

% Fabric Growth=100×(L2−GL)/GL   (IV)

[0052] In the Examples, the cotton was Standard Strict Low Midland Eastern Variety with an average micronaire of 4.3 (1.5 denier per fiber (1.7 dtex per fiber)). The cotton and the polyester bicomponent staple fiber were blended by loading both into a dual feed chute feeder, which fed the Trutzschler card. The resulting card sliver was 70 grain wt. (about 4950 dtex). Six ends of sliver were drawn together 6.5× in each of two passes to give 60 grain (about 4250 dtex) drawn sliver which was then converted to roving, unless otherwise noted. The total draft in the roving process was 9.9×. Unless otherwise noted, the roving was ring-spun on a Saco-Lowell frame using a back draft of 1.35 and a total draft of 29 to give a 22/1 cotton count (270 dtex) spun yarn having a twist multiplier of 3.8 and 17.8 turns per inch. When 100% cotton was so processed, the resulting spun yarn had a CV of 22% and a total boil-off shrinkage of 5%.

[0053] Within each bicomponent staple fiber sample, the fibers had substantially equal linear densities and polymer ratios of poly(ethylene terephthalate) to poly(trimethylene terephthalate). No mechanical crimp was applied to the bicomponent staple fibers in the Examples.

[0054] In the Tables, “Comp.” indicates a Comparison Sample, not of the invention, and ‘nm’ indicates ‘not measured’.

EXAMPLE 1A

[0055] Polyester bicomponent staple fiber was made from bicomponent continuous filaments of poly(ethylene terephthalate) (Crystar® 4415-763, a registered trademark of E. I. du Pont de Nemours and Company), having an intrinsic viscosity (“IV”) of 0.52 dl/g, and poly(trimethylene terephthalate) (Sorona®, a registered trademark of E. I. DuPont de Nemours and Company), having an IV of 1.00, which were melt-spun through a 68-hole post-coalescing spinneret at a spin block temperature of 255-265° C. The weight ratio of the polymers was 60/40 2G-T//3G-T. The filaments were withdrawn from the spinneret at 450-550 m/min and quenched with crossflow air. The filaments, having a ‘snowman’ cross-section, were drawn 4.4×, heat-treated at 170° C., interlaced, and wound up at 2100-2400 m/min. The filaments had 12% CI (a value believed to be considerably depressed by the interlacing), 51% CD, and a linear density of 2.4 dtex/filament. For conversion to staple fiber, filaments from wound packages were collected into a tow and fed into a conventional staple tow cutter, the blade spacings of which were adjusted to obtain a 1.5 inch (3.8 cm) staple length.

EXAMPLE 1B

[0056] The polyester bicomponent staple fiber from Example 1A was intimately blended with cotton to obtain various weight percents of the two fibers. The blended fibers were carded, drawn, converted to roving, and ring-spun. The resulting spun yarns had the CV and total Boil-Off Shrinkage (“B.O.S.”) values shown in Table I. 1 TABLE I Staple Total Bicomponent, B.O.S., Spun Yarn wt % Cardability CV, % % Comp. Sample 1A 30 Good 17 18 Sample 1B 40 Good 18 24 Sample 1C 50 Satisfactory 19 34 Sample 1D 60 Satisfactory 22 36 Comp. Sample 1F 70 Poor 25 nm

[0057] Interpolation of the data in Table I shows that total boil-off shrinkage was low when this particular bicomponent staple was less than about 35 wt % of the weight of the spun yarn. The data also show that cardability suffered when the amount of polyester bicomponent staple fiber exceeded about 65 wt %, based on weight of the spun yarn. Uniformity was improved if the proportion of polyester bicomponent was less than 50 wt %.

Comparison Example 1

[0058] Polyester bicomponent staple fiber was made as described in Example 1A, with the following differences. The weight ratio of 2G-T/3G-T was 40/60, the spinneret had 34 holes, and the resulting filaments had a 4.9 dtex/fil linear density. The CI was 16% and the CD was 50%, but cardability with cotton at levels of 65 wt %, 40 wt %, and even 20 wt % polyester bicomponent staple was very poor, showing the unsatisfactory results obtained when the polyester bicomponent staple had high linear density.

Comparison Example 2

[0059] Polyester bicomponent staple fiber was made substantially as described in Example 1A, except that the continuous filaments used were drawn 2.6× and had only 3% CI and 29% CD. Cardability was good in a 60/40 polyester/cotton blend, but the boil-off shrinkage of the yarn spun from such a blend was only 15%, showing the inadequate spun yarn properties that result when CD is too low.

EXAMPLE 2

[0060] To make the polyester bicomponent staple fibers used in Examples 3 and 4, poly(ethylene terephthalate) of 0.58 IV was prepared in a continuous polymerizer from terephthalic acid and ethylene glycol in a two-step process using an antimony transesterification catalyst in the second step. TiO2 (0.3 wt %, based on weight of polymer) was added, and the polymer was transferred at 285° C. and fed by a metering pump to a 790-hole bicomponent fiber spinneret pack maintained at 280° C. Poly(trimethylene terephthalate) (1.04 IV Sorona®) was solid-phase polymerized, dried, melt-extruded at 258° C., and separately metered to the spinneret pack.

[0061] FIG. 1 shows a cross-section of the spinneret pack that was used. Molten poly(ethylene terephthalate) and poly(trimethylene terephthalate) entered distribution plate 2 at holes 1a and 1b, distributed radially through corresponding annular channels 3a and 3b, and first contacted each other in slot 4 in distribution plate 5. The two polyesters passed through hole 6 in metering plate 7 and through counterbore 8 in spinneret plate 9, and exited the spinneret plate through capillary 10. The internal diameters of hole 6 and capillary 10 were substantially the same.

[0062] The fibers were spun at 0.5-1.0 g/min per capillary into a radial flow of air supplied at 142 to 200 standard cubic feet per minute (4.0 to 5.6 cubic meters per minute) so that the mass ratio of air:polymer was in the range of 9:1 to 13:1. The quench chamber was substantially the same as that disclosed in U.S. Pat. No. 5,219,506 but used a foramineferous quench gas distribution cylinder having similar sized perforations so that it provided ‘constant’ air flow. Spin finish was applied to the fibers with a conical applicator at 0.07 wt % to 0.09 wt % based on fiber weight, and then they were wound onto packages.

[0063] About 48 packages of the resulting side-by-side, round cross-section fibers were combined to make a tow of about 130,000 denier (144,400 dtex), passed around a feed roll to a first draw roll operated at less than 35° C., passed to a second draw roll operated at 85° C. to 90° C. and supplied with a hot water spray, heat-treated by contact with six rolls operated at 170° C., optionally over-fed by up to 14% to a puller roll, and, after application of 0.14 wt % finish based on weight of fiber, passed through a continuous, forced convection dryer operating at below 35° C. The tow was then collected into boxes under substantially no tension and cut to 1.5 inches for blending with cotton in Examples 3 and 4. The first draw was 77-90% of the total draw applied to the fibers. Additional spinning and drawing conditions and fiber properties are given in Table II. 2 TABLE II Unload Sock Fabric Bicomponent Force Knit Sample Spun Yarn Weight, g/m{circumflex over ( )}2 Content, wt % (kg) 5A Sample 1D 180 60 0.10 5B Sample 1C 177 50 0.09 5C Sample 1B 165 40 0.08 Comp. 5E None 127 0 0.04 *Bicomponent Staple Sample 2A had a 70/30 2G-T/3G-T weight ratio; all others were 60/40 2G-T/3G-T. **(Draw Roll 2 speed - Puller Roll speed)/(Puller Roll speed)

EXAMPLE 3

[0064] Selected bicomponent staple samples made in Example 2 were ring spun at a 60/40 polyester/cotton weight ratio to make 22/1 cotton count spun yarns. Bicomponent staple fiber properties, cardability when blended with cotton, and properties of the resulting spun yarns are given in Table TABLE III 3 TABLE III Bicomponent C.I. C.D. B.O.S. CV, Staple % Cardability % Spun Yarn % % Comp. 9 Good 26 Comp. 20 15 Sample 2J Sample 3A Sample 2B 16 Good 35 Sample 3B 24 19 Sample 2A 28 Satisfactory 49 Sample 3C 34 20 Sample 2H 34 Satisfactory 53 Sample 3D 39 19 Sample 2E 36 Satisfactory 53 Sample 3E 38 22

[0065] Interpolation and extrapolation of the data in Table III show that when CI is below 15%, boil-off shrinkage can be inadequate, and that when CI is as high as about 42%, cardability remains satisfactory.

Comparison Example 3

[0066] Bicomponent staple Sample 2B was blended with cotton at a polyester bicomponent/cotton weight ratio of 60/40, and the blend was carded and drawn as described hereinabove, but without making a roving. The drawn sliver was air-jet spun into 22/1 yarn on a Murata 802H spinning frame at an air nozzle pressure ratio (N1/N2) of 2.5/5.0, a total draft of 160, and a take-up speed of 200 meters/min. The total boil-off shrinkage of the yarn was only 14%, showing that air-jet spun yarn had unsatisfactory stretch and recovery.

EXAMPLE 4

[0067] Selected bicomponent staple samples made in Example 2 were ring-spun at 60/40 and 40/60 polyester/cotton weight ratios to make 22/1 cotton count spun yarns. Bicomponent staple fiber properties, cardability of the fiber blends, and properties of the resulting spun yarns are given in Table IV. 4 TABLE IV Bicomponent Bicomponent C.I., C.D., B.O.S., CV, Staple staple wt % % Cardability % Spun Yarn % % Sample 2I 60 24 Satisfactory 48 Sample 4A 28 18 Sample 2C 60 34 Satisfactory 56 Sample 4B 37 19 Sample 2F 60 28 Satisfactory 49 Sample 4C 31 20 Comp. 60 47 Poor 57 Comp. 38 25 Sample 2D Sample 4D Sample 2G 60 44 Poor 54 Comp. 28 22 Sample 4E Sample 2F 40 28 Good 49 Sample 4F 24 18 Sample 2G 40 44 Satisfactory 54 Comp. 25 22 Sample 4G

[0068] The data in Table IV show that, when CI is above about 42%, carding can be impractically difficult at 60 wt % bicomponent staple but satisfactory at 40 wt % bicomponent staple. Extrapolation of the data shows that at about 20 wt % bicomponent staple having CI as high as about 45%, carding would be good and total boil-off shrinkage and yarn uniformity (CV) would still be acceptable.

EXAMPLE 5

[0069] Women's 3×1 quarter socks with a ½ cushion foot were knit on a Lonati 454J, 108 needle, 4 inch (10 cm) cylinder machine, using only spun yarns from Example 1. Each sock was bleached with aqueous hydrogen peroxide at 180° F. (82° C.) and boarded at 250° F. (121° C.) for 1.5 minutes with dry heat.

[0070] The unload power of the socks was determined as follows. To avoid edge effects, the sock was not cut. It was marked with a 2.5 inch×2.5 inch (6.4 cm×6.4 cm) square, centered on the foot, between the toe and heel. The grips of an Instron tensile tester were placed at the sock foot top and bottom, avoiding the heel and toe and leaving the centered square between the grips so that the test sample had a 2.5 inch (6.4 cm) gauge. Each sample was cycled 3 times to 50% elongation at a speed of 200% elongation per minute. The unload force was measured at 30% remaining available stretch on the 3rd cycle relaxation and reported in kilograms force and is reported in Table V. In this test, “30% remaining available stretch” means that the fabric had been relaxed 30% from the maximum force on the 3rd cycle. 5 TABLE V Unload Sock Fabric Bicomponent Force Knit Sample Spun Yarn Weight, g/m{circumflex over ( )}2 Content, wt % (kg) 5A Sample 1D 180 60 0.10 5B Sample 1C 177 50 0.09 5C Sample 1B 165 40 0.08 Comp. 5E None 127 0 0.04

[0071] The data in Table V show that knit fabric comprising spun yarn of the invention has high fabric unload force and good stretch-and-recovery properties which are retained even in knits made with spun yarns comprising lower levels of the polyester bicomponent staple fiber.

EXAMPLE 6A

[0072] A 3/1 twill fabric was made on an air jet loom with a warp of 100% ring-spun cotton of 40/1 cotton count, reeded to 96 ends/inch (38 ends/cm). The filling yarn consisted of a 22/1 cotton count ring-spun yarn of 40 wt % cotton and 60 wt % of bicomponent staple Sample 2H, inserted at 65 picks per inch (25½ picks per cm) and 500 picks/minute. The fabric was scoured for an hour at the boil and conventionally dyed with direct and disperse dyes. The available stretch was 21%, and the growth was 3.8%, both desirable properties.

EXAMPLE 6B

[0073] Example 6A was repeated but with a spun yarn of bicomponent staple Sample 2E ring-spun at the same blend ratio with cotton, inserted at 45 picks per inch (18 picks/cm). The fabric was scoured for hour at the boil and conventionally dyed with direct and disperse dyes. The available stretch was desirably high at 25%, and the growth was desirably low at 4.6%.

[0074] The yarns produced in the examples and fabrics made therefrom in accordance with the invention were soft and aesthetically pleasing.

Claims

1. A spun yarn having a total boil-off shrinkage of at least about 22% and comprising cotton and a bicomponent staple fiber comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate) wherein the bicomponent fiber has:

a crimp development value of at least about 35%;

a crimp development value no higher than about 70%;

a crimp index value at least 15%;

a crimp index value no higher than about 45%;

a length of at least about 1.3 cm;

a length no higher than about 5.5 cm;

a linear density of at least about 0.7 decitex per fiber; and

a linear density of no higher than about 3.0 decitex per fiber;

wherein the bicomponent fiber is present at a level of at least about 20 wt %, based on total weight of the spun yarn;

wherein the bicomponent fiber is present at a level no higher than about 65 wt %, based on total weight of the spun yarn;

wherein the cotton is present at a level of at least about 35 wt %, based on total weight of the spun yarn; and

wherein the cotton is present at a level no higher than about 80 wt %, based on total weight of the spun yarn.

2. The spun yarn of claim 1 wherein the bicomponent fiber has a crimp index value of at least about 20% and the bicomponent fiber has a crimp index value no higher than about 30%.

3. The spun yarn of claim 1 wherein a coefficient of variation of linear density is no higher than about 22%, and the bicomponent fiber has a decitex per fiber no higher than about 2.5.

4. The spun yarn of claim 1 wherein the bicomponent fiber is present at a level of less than 50 wt %, based on the total weight of spun yarn.

5. The spun yarn of claim 1 wherein the bicomponent staple fiber has a tenacity-at-break of at least about 4.0 dN/tex, and the bicomponent staple fiber has a tenacity-at-break of no higher than about 5.5 dN/tex, and the bicomponent staple fiber is present at a level of at least about 35 wt %, based on the total weight of spun yarn.

6. A process for making the spun yarn of claim 1 comprising the steps of:

a) providing the bicomponent staple fiber;

b) providing cotton;

c) combining by intimate blending at least the cotton and the bicomponent staple fiber so that:

the bicomponent fiber is present at a level of at least about 20 wt %;

the bicomponent fiber is present at a level no higher than about 65 wt %;

the cotton is present at a level of at least about 35 wt %; and

the cotton is present at a level no higher than about 80 wt % based on total weight of the blended fibers;

d) carding the blended fibers to form a card sliver;

e) drawing the card sliver;

f) doubling and redrawing the card sliver up to about 3 times;

g) converting the drawn sliver to roving; and

h) ring-spinning the roving to form the spun yarn.

7. The process of claim 6 wherein the bicomponent fiber has a crimp index value of at least about 20% and is present at a level of less than 50 wt %, based on the total weight of the blended fibers, and the ring-spinning provides a twist multiplier of about 3 to 5.5.

8. The process of claim 6 wherein the bicomponent fiber has a decitex per fiber no higher than about 2.5.

9. The process of claim 6 wherein the spun yarn has a coefficient of variation of linear density of no higher than about 22% and the bicomponent staple fiber is present at a level of at least about 35 wt %, based on the total weight of the blended fibers.

10. A fabric selected from the group consisting of knits and wovens and comprising the spun yarn of claim 1.