US3438190A - Nontorque bulk yarn and process of forming same - Google Patents

Description

United States Patent 3,438,190 NONTORQUE BULK YARN AND PROCESS OF FORMING SAME George H. Collingwood, Hopewell, Va, assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Aug. 29, 1967, Ser. No. 663,994 Int. Cl. D02g 3/04, 3/26 U.S. Cl. 57-140 12 Claims ABSTRACT OF THE DISCLOSURE SPECIFICATION This invention relates to a process for preparing novel bulk yarns and to the products obtained thereby which comprises passing a multifilament yarn in two passes through a false-twisting apparatus, heat-setting the yarn at each pass and twisting in the second pass in a direction opposite to the first while maintaining critical parameters.

More specifically, this invention is directed to a process and the products obtained thereby which comprises spinning and drawing in a continuous operation synthetic fila ments, e.g., nylon, followed by heat-setting at temperatures ranging from 93 to 230 C. while twisting to levels ranging from about 15 to 150 turns per inch, first in one direction and then in the opposite direction. The difference in twist between the first and second pass, plus or minus turns per inch, may be expressed as being approximately 1.455 times the differential in thermal seconds plus 10.5. The synthetic bulk yarns obtained in accordance with this process are characterized as having a uniform sine wave crimp, free of lOOpS, with a skein shrinkage of less than 30%, an ultimate elongation of less than 55% and a torque angle of 90 plus or minus 5 before and after wetting. The process is particularly applicable to synthetic filaments such as nylon or similar organic synthetic fibers including the linear polyamides, such as polycaproamide, polyhexamethylene adipamide and various melt blends of a linear polyester, i.e., polyethylene terephthalate with polycaproamide and polyhexamethylene adipamide.

It is known that by utilizing the technology presently available in the art, substantial torquing is obtained, in the dry state, which is undesirable. Moreover, unless specific and closely controlled conditions are employed, yarns having a torque angle greater than 90 are almost always obtained. If these yarns are used in such items as corduroys, rib knits, chevron design, jersey knits and the "ice like, there is a diiferential skewing of the fabric design which results in a less attractive or, in other words, an objectionable design. To overcome this, it becomes necessary to cut out the final product at an angle which obviously adds additional costs in the cutting operations and a loss of fabric. Moreover, wetting of the yarn prior to knitting results in prebulking which makes it difiicult to pass it through the eyelets of needles and results in entanglement and snagging due to the lofty nature of the individual ends during fabrication of the textiles.

Accordingly, to avoid these problems and to provide yarn of uniform sine wave crimp, free of loops, with a skein shrinkage of less than 30% and a torque angle of about 90, it was found necessary to utilize a process whereby the yarn passes through a false-twisting apparatus in two passes with heat-setting at each pass, the second pass including a twisting in the direction opposite from the first pass. The critical parameters of the process include the twist differential in relationship to the differential in thermal seconds in each pass, and the interrelationship between twist levels and heat treatment.

Accordingly, it is an object of this invention to provide a process for preparing synthetic, bulked yarns of uniform sine wave crimp which are free of loops, have a skein shrinkage of less than 30%, an ultimate elongation of less than 55% and a torque angle of 90 plus or minus 5 before and after wetting.

It is another object of this invention to provide a synthetic bulked apparel yarn containing at least by weight of polyamide filaments characterized as having a uniform sine wave crimp free of loops, a skein shrinkage of between 4 and 25%, ultimate elongation of between 25 and 52% and a torque angle of 90 plus or minus 5 before and after wetting.

These and other objects of the invention will become apparent from a further and more detailed description as follows.

This invention relates to a process and the products obtained thereby for preparing novel bulked yarns which comprises passing multifilament yarns, e.g., 15 to 280 multifilaments, in two passes through a false-twisting apparatus with heat-setting in each pass and with the second pass being twisted in the opposite direction of the first pass. The differential in twist between the passes plus or minus 5 turns per inch equals 1.455 times the differential in thermal seconds plus 10.5, and the total twist minus the diflerence in twist between the passes plus or minus 5 equals 1.42 times 2 times the thermal seconds of the second pass minus 23.7.

These novel synthetic yarns may be characterized as having a uniform sine wave crimp, free of loops, with an ultimate elongation of less than 55% and a torque angle of plus or minus 5 before and after wetting. Moreover, the bulked nontorque yarns of this invention have a skein shrinkage of less than 30% and in most instances, they are in the region of less than 20%. In comparison, other yarns prepared by known two-pass processes under conditions which exhibit a torque characteristic of greater than plus or minus 5 from 90, are characterized by a shrinkage. As an example, for a given twist level, the yarns of this invention exhibit at least 5% lower shrinkage than other yarns made by a two-pass process which have torque angles of less than plus or minus 5 deviation from the 90. In addition, the nontorque yarns of this invention are characterized by an ultimate elongation of less than 55%, and normally between 41 and 50%. The ultimate tensile strength of the yarns may range between 3.5 and 7 grams per denier, and more likely, between 4 /2 and 6 grams er denier.

As an example, a feeder yarn was prepared by passing the filaments in two passes at 188 C. for the first pass for a residence time of about 0.385 second and with a second pass at a temperature of 160 C. for about 0.385 second. This yarn had a crimp of about 16.4 crimps per inch at a crimp elongation of 16.9% and a crimp recovery of about 100%. The yarn having a torque angle of about 90 when observed under a lower power microscope was characterized as a plurality of filaments lying in a series of sine waves in a level plane. After wetting the yarn, the only significant difference was an intensification of the sine waves wtih no significant difference in the uniform nature of the sequential sine waves being noted before wetting and bulking. Moreover, the yarns were observed to be free of tight spots which normally would occur if the yarns were overheated in passing over the false-twist apparatus due to melting and fusing of the individual filamentary ends. These yarns, when converted into a knitted fabric, for example, were uniform, very soft and had a high quality surface texture which is desirable for many end use applications. Typical examples of yarns obtained in accordance with the process of this invention were found to have the following relationships:

TABLE 1 Midpoint Mean Total Range of Total Denier Average, Turns/ Twists Inch/Pass From the above data, it can be observed that as the denier increases, it was necessary to reduce the twist level. Thus, it is possible to obtain higher speeds and, therefore, increased productivity with the heavier denier products.

The relationship between the turns per inch, the residence time of the heater with a spindle operating at 350,000 r.p.m. and twist-setting heaters of 27.5 and 40 inches in length are illustrated by the data in Table 2. In the false-twist apparatus, the spindle speeds are maintained between 250,000 and 1,000,000 r.p.m., and more preferably, between 300,000 and 600,000 r.p.m.

TABLE 2 Turns Seconds 27.5 Inch 40 Inch Denier Range Per Inch Residence Heater, Heater, Time EL/min. FtJnin.

If the residence times are below 0.2 second without the use of a preheating device, it was found that this was insufficient to achieve the necessary twist-setting temperatures. Thus, it is preferred, in accordance with this invention, to provide residence times greater than 0.2 second if no preheating devices are to be employed. Generally, the multifilament yarns are twist-set at temperatures ranging between 93 and 230 C. However, at temperatures above 200 C., there is a tendency for the individual filaments of polycaproamide, for example, to fuse, giving evidence of tight spots. If this is permitted to happen, the yarn will result in a fabric characterized as having a rough hand which is unsatisfactory. For nylon 6, 6, temperatures as high as 230 C. may be employed before the individual filaments fuse. Thus, except for the preferred temperature differences, polyhexamethylene adipamide and polycaproamide may be processed in accordance with this invention in a similar manner with complete success. It is preferred, however, to twist-set polycaproamide at temperatures ranging between 93 C. and 200 C. while twist-setting polyhexamethylene adipamide at twist-set temperatures between 130 C. and 230 C. The twist-setting of a blend of polycaproamide and polyethylene terephthalate wherein the caproamide ranges from 50 to by weight may be carried out under the same conditions as those employed for polycaproamide yarns. Likewise, a blend containing polyhexamethylene adipamide and polyethylene terephthalate may be twist-set under the same conditions as those employed for polyhexamethylene adipamide.

As a specific example, the feed yarn passes over a feed roll in the range of 2 to +4% overfeed on a heater to the twist, then to a false-twist spindle and to the top feed roll which operates between a +3 and a +10% overfeed. The yarn may be wound up on a package or in the alternative, passed directly and continuously to the second stage where again the overfeed is between -2 and +4%. The yarn then passes over a twist-setting heater of 20 to 50 inches in length and through a false-twist spindle operating at speeds of between 200,000 and 1,200,000 r.p.m. The twist in the second pass is in the opposite direction of that in the first pass.

If desired, it is obvious that the yarn may be placed on a package after drawing, placed on one side of the machine and false-twisted to the desired level for the first pass, and then transferred to the second side of the machine and twisted in the opposite direction for the second pass. Alternatively, the yarn may be passed in one continuous operation from the front side of the machine to the back side of the machine Without a rewinding operation by utilizing a proper guide arrangement. Still further, a more efiicient form of the instant process comprises spin-drawing the filaments and passing the yarn continuously after the drawing stage over a feed roll at a forward feed percent of 3 to +4, then to a heater 27 /2 to 40 inches in length and to a twisting spindle operating between 350,000 and 1,200,000 r.p.m. Following the twisting spindle, the yarn is carried to a discharge roll from the first stage which operates at an overfeed between +2 and +10%, onto the feed roll for the second stage which operates at about the same overfeed, over a heater of 20 to 50 inches, and then on to the false-twisting spindle, also operating at approximately the same speed. Finally, the yarn is discharged on a feed roll operating between a +3 and a +10% overfeed. The yarn is taken up with any suitable windup means at tension between 0.005 to 0.05 gram per denier. As previously indicated, at low residence times, e.g., in the region of 0.1 to 0.2 second on the heater, it is desirable to use a preheating device which has significantly higher surface temperatures than the twist-setting heater to bring the yarn to the region of the twist-setting temperature. The temperatures employed on the preheating devices may range between 20 to 50 higher than that used as a standard twist-setting temperature.

When spin-draw feeder yarns are employed, it is desirable to use 2 to 8 fibers on a single heater in order to maximize the unit productivity of the feed roll and the heaters employed. Additionally, the discharge roll from the first twist stage may serve as a feed roll for the second stage, thereby eliminating one feed roll in the falsetwist train. False-twisting, as part of a continuous spindraw process, becomes economical when multiple ends are fed from a spin-draw position over a multiple-end feed roll, over a multiple-end heater and then to individual twist spindles and on to a multiple-end feed roll to the second stage. Maximum heater lengths are desirable in order to achieve the necessary time on the heater. It is not recommended to loop the yarn around the header,

since the-torque created interferes with obtaining maximum turns per inch for a given spindle speed.

If it is desirable to utilize a preheater in order to rapidly obtain the twist-setting temperatures desired at high speeds, the thermal seconds which are input from the preheaters are calculated as part of the total thermal seconds for the system.

The data in Table 3 illustrates the effects between the residence time, the spindle speeds, and the speed of travel over the twist-setting heaters for each stage.

TABLE 3 Spindle Process Speed, Conditions 27.5 Inch Heater 40 Inch Heater r.p.m.

350,000 Seconds .2 .4 .6 .2 .4 .6 F.p.m. 685 345 230 1, 000 500 335 T .p.i 3 40 84 127 29 58 87. 5 Secs. .15 .2 .3 .15 .2 .3 F.p.m 915 685 460 1,350 1, 000 670 T.p.i. 64 85 127 444 59 S8 Secs 10 15 .20 .10 .15 .20 1,000,000-... F.p.1n. 1,385 915 085 2, 000 1, 350 1, 000 1,000,000.-.. T.p.i. 61 100 121 42 A 82% 1 Seconds=Seconds in contact with the heater. 2 F.p.m.=1 eet per minute. 3 T.p.i.=Turns per inch. 4 Secs.=Yarn residence time in seconds on the twist-setting heater.

It can be seen from the data in Table 3 that with a 40 inch heater at residence times of between 0.1 and 0.15 seconds, yarn speeds of 1,000 to 2,000 feet per minute can be obtained with spindle speeds of 700,000 to 1,000,- 000 -r.p.m.

In preparing the O-torque yarns of this invention, there must be a relationship between the total twist and the total thermal seconds employed. It has been found that this relationship exists as shown by the data in Table 4. These examples were carried out by employing a 27 /2 inch heater, a 40-denier, 12-filament yarn, with spindle speeds of 350 rpm. Eighteen different runs produced yarns having essentially O-to-rque of 90 plus or minus 5.

TABLE 4 O-Torque Yarn 90i5 Prior Art Yarn With Total Thermal, Torques Having An As shown by the data in Table 4, at the higher twist levels, there is little difference between those yarns which have a high torque. However, as one approaches a total twist level under 100, then there is a difference between the O-torque yarn and that yarn which exhibits torque. The equation for the O-torque yarns may be expressed as total twist equals 1.445 times the total thermal seconds minus 35.7. The equation for the yarn which exhibits unsatisfactory torque may be expressed as total twist equals 1.465 times the total thermal seconds minus 41.

As shown by the data in Table 5, when the differential between the first and second pass twist levels employed and the differential in thermal seconds between the first and second pass are compared with each other, a significant trend is obtained which shows that to produce a successful low torque yarn, it is necessary to have a specific differential in thermal seconds. If significant variations above 15 thermal seconds are employed, then an unsatisfactory yarn which torques in both the wet and dry state is obtained. Comparison of data from 18 lots which exhibited essentially 0-torque with 26 lots which exhibited an unsatisfactory torque of greater than i or with an average of 21 differential from. torque angle is shown in Table 5.

TABLE 5 Differential in D fference in Thermal Seconds Twist Between 1st and 2d Pass The equation for the data for the yarn which exhibits essentially no torque may be expressed as: 1st pass twist minus second pass twist equals 1.455 times the difference in thermal seconds between the first and second pass plus 10.5. The equation for the yarn that exhibits a tendency to torque and when formed into fabric, shows substantial skewing may be expressed as: the twist in first pass twist in t.p.i. minus the twist t.p.i. for the second pass equals 1.495 times thermal seconds for the first pass minus the thermal seconds for the second pass plus 5.7.

If one, however, combines the effect of the total twist and the total thermal seconds with the effect of the differential twist and the differential thermal seconds, then the differences which exist between the process where essentially a O-torque yarn is produced and the process for the yarn which torques, becomes emphasized, as shown in Table 6. The difference which exists is larger at the lower twist level.

TABLE 6 O-Torque Yarn or 2 Times the Thermal Total Twist Yarn Having Torque Seconds for the 2d Minus Angles 90;l;5, 2 Pass for Yarn Which Differential Times the Thermal Has Torquing Seconds of the 2d Pass Characteristics In Table 6, it can be observed that the thermal seconds of the second pass is significantly lower for the 0-torque yarn than that for the yarns that have unsatisfactory torque characteristics. Thus, if the yarn is false-twisted under conditions where total twist minus the differential in twist equals 1.42 times two times the thermal seconds for the second pass, minus 23.7, a satisfactory nontorquing yarn will be produced. However, even though the yarn is made in two passes, if it :is characterized by the equation: total twist minus the differential twist equals 1.50 times two times the thermal seconds for the second pass, minus 43, then an unsatisfactory yarn will be produced. It is unexpected and could not have been predicted that these critical relationships exist.

If one decreases the differential in thermal seconds, a torque angie of less than 90 is obtained and the torque angle moves in the direction of 0. If one increases the differential in thermal seconds, compared to the differential in twist, one moves in an upward direction towards a angle. Thus, very small differences such as :5 thermal seconds difference between the first and second pass can, as compared with the twist differential employed, result in an unsatisfactory yarn which may deviate from a desired torque angle of 90 '-5.

The Examples 1 through 62 of Table 7 illustrate the wide variety of conditions under which a successful 0- torque yarn can be produced and also illustrate the small changes from the specific parameters, i.e., total twist, thermal seconds, differences between twist, difference between diiferential thermal seconds and total twist minus differential twist times the total thermal seconds for the second pass and their effect upon the ability to obtain a O-torque yarn.

TABLE 7.-Continued Differential Effects Fiber Properties 2 Thermal Example Number T.p.i. Percent Thermal Torque Total Twist Secs., 2d Pass UTS, Ultimate Percent Breaking Twist Shrinkage Secs. Angle Minus Delta g./d. Elongation Strength Twist Retained Differential Effects Fiber Proeprties 2 Thermal Example Number T.p.i. Percent Thermal Torque Total Twist Secs., 2d Pass UTS, Ultimate Percent Breaking Twist Shrinkage Secs. Angle Minus Delta g./d. Elongation Strength Twist Retained Example Diiferential Efiects Example Differential Etlects Example Difierential Effects Temperature Temperature Temperature Differential Effects 2 Thennal Polymer Type Thermal Torque Shrinkage, Total Twist Minus Secs, 2d Pass Secs. Angle Percent Delta Twist 14 220 172 Nylon 6. -21 152 124 Do.

-7 192 154 Nylon 6, 6. 10 160 Nylon 6.

-5 160 140 -10 160 130 20% Nylon 6, 80% PET.

7 130 108 Nylon 6. -7 100 87 0 +7. 5 150 Do 11 115 Do.

--7 96 84 Nylon 6, 6 24 36 52 Nylon 6. 14 76 70 70% PET, 30% Nylon 6.

1 5 x 5 x 3 False-twistMachine; Length of Heater 27.5.

TABLE 7 .Continued Example 1st Pass Fabric Fabric Gage Number Torque Angle, Thickness, 4 Layers Degrees Inches Thickness, In.

1 5 x 5 x 3 Falsetwist-Macl1ine; Length of Heater 27.5.

In Examples 1 through 50, spindle speeds of 350,000 r.p.m. were employed, with 40 denier, 12-filament 1/2Z semidull yarn. The yarns were twisted in two passes on a 5-5-3 false-twist machine having a heater length of 27 /2 inches. In all examples, an overfeed to the twisting zone 75 of +2% was maintained and a feed to the package was maintained at +5 for both passes. By examining the 50 data in Table 7, for the final yarn properties it can be noted that the skein shrinkage is below 25% for the non torquing yarn. The ultimate elongation is below 55% and the torque angles do not deviate greater than :5 from 90 angles. These properties are especially desirable in production of bulk fabrics which retain their dimensional shape, have a soft characteristic hand and have good drape characteristics. Additionally, they have excellent dimensional stability and elminate the additional operation of combining ends to avoid the torque characteristics of stretch yarns.

Fabric was knitted from the bulked yarns of the following examples in Table 8 and the dimensions were measured for a single thickness and for 4 folds of thickness. The method of measurement is as described in ASTM Dl77-64 (ASTM 1964 Standards, Part 24). A low pressure was employed on the test micrometer and the results are reported in inches thickness. In general, the bulk or thickness of the fabrics increases with increased skein 0 shrinkage. However, the increase in fabric thickness is at a considerably higher level than the change in skein shrinkage and the bulk characteristics of a yarn exhibiting 12% skein shrinkage is essentially equivalent to a yarn produced in an one-pass operation and having 70% skein shrinkage.

. Yarn Ultimate Elongation, Percent... 70220% TABLE 8 Turns Per Inch Percent Fakric Thickness Example Skein =T0rque Number First Pass 2d Pass Total Shrinkage Angle Single Thick- 4 Layers,

ness, Inches Inches 00 es 132 5 90 .014 05s The data in Table 9 illustrates the differences between suitable for many end-use applications. However, at a the prior art and the present invention of nontorque yarn torque angle of less than 85 or greater than 95, there is and conventional stretch yarns. In Table 9 it can be seen a noticeable and unsatisfactory skewing and wrinkling of that this invention differs from the prior art in terms of the fabrics knitted or Woven from false-twist bulked yarns. the freedom from torque before wetting, by absence of The apparent hand bulk factor is determined by a panel loops in the unstretch'ed yarn, by a skein shrinkage of jury of 6 skilled observers and 1s a measurement of the below 25%, by a significantly lower ultimate elongation, bulk properties of the fabric when held in ones hand. A by a torque angle of 90i5 before wetting, and by a rating of 4.5 to 5.0 indicates excellent bulk properties. A higher retained crimp retentivity. rating of 4.0 to 4.5 equals good bulk properties and a TABLE 0 Prior Art Two Passes This Invention 2d Pass, False- Stretch Yarns Conventional One-Pass Process Type False-Twist Twist Where Tlw-Delta False-Twist Tw=1.42 (2Ts )23.7

Nontorquing After Wetting. N ontorqning, Before and After Extensive Torquing.

Wettii Torque Characteristics...

Yarn Appearance Some Loops Urlrifoi'rn, Noncntangled Sine Wave. Many Loops in Yarn,

o oops. Yarn Skein Shrinkage, Percent Greater than 1-25% 42 7g% Torque Angle 90 After Wetting. 0;|:5 13 Crirnps Per Inch-.. 1220 1g 3 Crimp Elongation... 1o-24. 30430, Crimp Retentivity Bil-94%.. 88-100% /12 Denier Fabric Thickness, 1 1* .019 2 .020.

La er. 40/12 Denier Fabric Thickness, 4 1* .071 2* .076. P Iiii qui g skewed Fabric in D y tate. N o skewing before or after Wetting Yam must be doubled to avoid extensive fabric skewing.

*=Thickness in Inches.

In the false-twist process, it has been found that overrating of 3.5 to 4.0 equals commercially acceptable bulk feed to the twisting spindle and from the discharge rolls roperties. A rating of 0 to 3.5 is unacceptable commershould be kept within certain specific limits. Thus, a feed cially for many end-use applications. For 40-denier yarn, of the nontwisted yarn from the forward feed rolls toward the apparent hand bulk factor versus the turns per inch the heater and twisting spindles, should be in the region per pass are as follows. of to discharge condmolls greater h 45 Apparent hand bulk factor: Turns per inch per pass -4%, there results in increased mechanical down-time due to the 4% strain which is characterized by yarn break- .0 120 outs during the twisting process. In the discharging of the 4-75 100 yarns toward the takeup device, discharge feeds should be 4- 80 maintained within the region of +2 to +10 overfeed. At 60 above +10%, one tends to get crossovers and low package 3- 50 weights and sloughing of the package surface. In general, 3- 40 15 to 280 denier multifilament yarns are passed into a first .0 20 heat-treating zone at temperatures ranging from about 10 93 C. to 230 C. at speeds of about 150 to 2,000 feet per 0 0 minute, While twisting to levels of about 15 to 150 turns per inch in one direction, and subsequently passing said filaments through a second heat-treating zone at the same temperature range and speeds, while twisting in the op- In general, yarns which have a skein shrinkage of greater than 30% the skein shrinkage varies with denier in the following manner.

posite direction to levels of about 15 to 150 turns per inch. Demer: Skem shrmkage normal, Percent To understand the process of this invention, the terms 20 50 employed herein have the following definitions: 50 30 5 7 The torque angle is measured by knitting a yarn into 30440 45 55 a sleeve and measuring the wale lines or those lines which 140 250 3 545 run vertically at a angle from the stitch direction, this ,5 angle is measured with a protractor. At a torque angle of The term thermal seconds is defined as the total sec- 90i1, there are no significant differences in the fiber onds residence time on or in the twist-setting heat device characteristics and in the fabric properties when converted times the surface temperature of the heater employed and/ to a knitted or woven structure. At 90i3 and particuor alternately if a gas or steam is employed times the larly in the range of 87 to 88 torque angle and 92 to 93 70 temperature in C. of the gaseous medium employed. torque angle, there is very slight visible fabric skewing but The crimp frequency is the number of waves per inch of insufiicient quantity to cause difficulties in the subsecounted in a single filament under a pretension of .005 quent knitting and weaving operations. At a torque angle gram per denier employing a crimp frequency tester conin the region of 85 to 86 and 94 to 95 angle, there is sisting of 2 clamps, one rotatable and the other stationary.

noticeable torquing of the fabric but the product is still 75 The distance between clamps is adjusted to 4 inches. A

movable thread counter equipped with a pointer magnifying glass and thumb activated counter can be set so crimps are visually observed to count crimps. Every turning point or wave of the filament along the 4-inch gage length is counted. The crimps are fully developed by boiling in wator for 30 minutes.

The crimp elongation is measured by difference in length by applying to a 4-inch gage .5 gram tension using the same apparatus on a movable trolley as described above. Thus, the percent elongation which occurs on a 4-inch section of yarn, in increasing the tension from .005 g./d. to .5 equals the percent crimp elongation.

The skein shrinkage was determined by using 100 meters of yarn wound on a 44-inch Scott winder with a weight of .0016 gram per denier being attached to the skein while the skein is placed in a tank of water at 180 F. for a period of 10 minutes. The skein is then dried at a temperature of less than 150 F. and equivalated at 70 F. and 60% RH. for a period of 24 hours, the weight of .0016 gram per denier remaining attached. After the 24- hour period has elapsed, the length of the skein is again measured with the following computation:

LO-LF=LO X 100% =skein shrinkage LO=length of skein prior too removal from the reel, LF=the final length of the treated stretch yarn skein after conditioning.

The value obtained for this calculation should be less than 30% for nontorquing yarns and more preferably less than 25%.

The bulked nontorquing yarns of this invention in the relaxed state lie on a uniform plane in a series of relatively uniform, half-circle sine waves. Standard stretch yarn in a relaxed state produced on a one-pass operation exists as a series of entangled filaments with a considerable number of complete loops being present. Thus, the physical structure of the nontorquing yarns of this invention permits greater uniformity in passing over guides and through needles and as a result, more uniform fabrics are obtainable therefrom with less mechanical stoppage due to snagging or snarling of ends than for the typical false-twist yarns produced heretofore.

What is claimed is:

1. A process of preparing a continuous, synthetic multifilament bulked yarn having a torque angle of 90i5 and a skein shrinkage below 30%, which comprises spinning and drawing the synthetic filaments and passing same into a first heating zone at temperatures ranging from about 93 C. to 230 C. at speeds of about 150 to 2,000 feet per minute while twisting to levels of about 15 to 150 turns per inch in one direction: and subsequently passing said filament through a second heating zone at temperatures ranging from about 93 C. to 230 C. at speeds of about 150 to 2,000 feet per minute while twisting in the opposite direction to levels of about 15 to 150 turns per inch: the differential in twist between the first and second pass :5 turns per inch equals 1.455 times the differential in thermal seconds plus 10.5.

2. The process of claim 1 further characterized in that the synthetic multifilament yarn has a total denier ranging between 15 and 280 and contains at least by Weight of a polyamide.

3. The process of claim 2 further characterized in that the polyamide is selected from the group consisting of polycaproamide, polyhexamethylene adipamide and a blend of said amides with a linear polyester.

4. The process of claim 3 further characterized in that the polyester is polyethylene terephthalate.

5. The process of claim 2 further characterized in that the 15 to 280 denier multifilannent yarn is passed into the first and second heat-treating zones at temperatures ranging from about 120 C. to 230 C.

6. The process of claim 3 further characterized in that the multifilament yarn comprises polycaproamide and the temperatures in the first and second heat-treating zones range between 93 C. and 200 C.

7. The process of claim 3 further characterized in that the multifilament yarn comprises. polyhexamethylene adipamide and the temperatures in the first and second heat-treating zones range between 130 C. and 230 C.

8. The process of claim 1 further characterized in that the yarn is an to 280 denier multifilament yarn passed through the heating zones while twisting to levels of about 15 to 80 turns per inch.

9. A synthetic, bulk apparel yarn of uniform sine wave crimp, free of loops, with a skein shrinkage of less than 30%, an ultimate elongation of less than 55% and characterized as having a torque angle of i5 before and after wetting.

10. The yarn of claim 9 further characterized as containing at least 50% by weight of polyamide filament selected from the group consisting of polycaproamide, polyhexamethylene adipamide and blends of said amides with a linear polyester.

11. The yarn of claim 10 further characterized in that the polyester is polyethylene terephthalate which is present in the blend in amounts ranging from 10 to 50% by weight.

12. The yarn of claim 9 further characterized as having 12 to 20 crimps per inch, a skein shrinkage of less than 24% and a crimp retention of 80 to References Cited UNITED STATES PATENTS 2,711,627 6/1955 Leath et a1. 57157 3,041,814 7/1962 Held 57-34 3,137,119 6/1964 Crouzet 57157 3,318,083 5/1967 Gilcrist 57-157 3,367,101 2/1963 Garner et a1. 57--140 DONALD E. WATKINS, Primary Examiner.

U.S. Cl. X.R.