US3769669A - Method of making a helically crimped continuous filament yarn - Google Patents

Abstract

One side of a drawn homogeneous filament having at least 17 percent boiling water shrinkage is heated above its melting point while under high tension. The filament is then prebulked while under substantially no tension by being exposed to hot air at a temperature above the yarn glass transition temperature, soon after the initial heat treatment, and preferably before being wound. This produces a tighter crimp when the yarn is later subjected to hot water.

Description

United States Patent 11 1 Self et a1. Nov. 6, 1973 METHOD OF MAKING A HEL ICALLY 3,457,613 7/1969 McClure 28/72.1 C IM E CONTINUOUS FILAMENT YARN 3,602,951 9/1971 Stanley 28/1.2

[75] Inventors: Joseph A. Self, B21101] Rouge La; FOREIGN PATENTS 0 APPLCATIONS g z f g x i fzz' i'zk g ig z 1,064,765 4/1967 Great Britain 28/13 '7 Court, N.C. Primar Examiner--Louis K. Rimrodt [73] Asslgneez Monsanto Company, St. Louls, Mo. Atmmgv Keny O Corley et aL [22] Filed: Feb. 22, 1972 [21] Appl. No.: 228,144 [57] ABSTRACT R l t 62 e 3 ed U s Apphcatlon Data One side of a drawn homogeneous filament havlng at 1 g gg g g g 1968 least 17 percent boiling water shrinkage is heated above its melting point while under high tension. The filament is then prebulked while under substantially no (g1. tension y being exposed to hot air at a temperature [58] Field 1 3 above the yarn glass transition temperature, soon after the initial heat treatment, and preferably before being wound. This produces a tighter crimp when the yarn is [56] References cued later subjected to hot water. 7

UNITED STATES PATENTS 12/1967 Daniel 28/12 2 Claims, 4 Drawing Figures METHOD OF MAKING A HELICALLY CRIMPED CONTINUOUS FILAMENT YARN This is a division of application Ser. No. 772,766 filed Nov. 1, 1968, now U.S. Pat. No. 3,663,352, granted May 16, 1972.

11 The invention relates to a helically crimped continuous filament yarn, and to a process for making such yarn. More particularly, the invention relates to such yarn having an enhanced bulk level.

Numerous types of helically bulked or crimped yarn have been proposed in the prior art, and are particularly useful when the yarn is to have substantial stretch. One such helically crimped yarn is produced by conjugate spinning, i.e., extruding two polymer components in parallel relationship in a single filament. If the polymer components have different shrinkages, the drawn filament will develop helical crimp when heated. Conjugate spinning has a number of disadvantages, such as the necessity for metering the two components to the spinneret orifices, and the elaborate distribution passageways required for properly distributing both polymer components to each orifice.

Another helically crimped yarn is produced by drawing a hot nonconjugate or homogeneous yarn while under tension over a sharp edge. In this process-the edge produces a flattened surface on the yarn, which flattened surface will be On the inside of the resulting helix when the yarn is bulked.

A further prior art process is disclosed in U.S. Pat. No. 3,226,792 to Starkie, wherein nylon 66 yarn is stretched, heated on one side to a temperature below the melting point of the yarn while being cooled on the opposite side, and wound. The yarn is later unwound and immersed in boiling water to develop the bulk. When such a process is applied to nylon 66, the degree of bulk obtainable is limited because of the relatively small shrinkage of nylon 66.

Another approach is disclosed in U.S. Pat. No. 2,974,391 to Speakman, wherein one side ofa homogeneous filament is heated above the melting point while the yarn is under a tension stretching the filaments not more than percent of their length. The yarn is wound, and later unwound and heated to develop the crimp.

According to the present invention, the drawn homogeneous yarn fed to the texturing operation has a boiling water shrinkage (excluding the immediate elastic recovery upon elimination of tension) in excess of 17 percent. One side of the yarn is heated to a temperature above its melting point, while the opposite side of the yarn, is maintained below 100 C., to impart latent bulk to the yarn. The yarn is then prebulked, i.e., subjected to a temperature above its glass transition temperature while under minimum tension to crystallize the yarn in its bulked configuration, preferably before the yarn is wound on a package. The yarn is subsequently unwound and subjected to boiling water. The degree of final bulk obtainable is considerably enhanced by the prebulking step, and is substantially higher than is attained by the prior art.

Accordingly, a primary object of the invention is to provide a helically crimped yarn.

A further object is to provide a yarn of the above character wherein the crimps are in the form of a tightly coiled helix.

A further object is to provide a yarn wherein the ratio of the helix coil length to the filament radius is less than 45.

A further object is to provide processes for making yarns of the above character.

Other objects will in part appear hereinafter and will in part be obvious from the following disclosure and the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view of preferred apparatus for practicing the invention;

FIG. 2 is a perspective view of a bulked filament according to the invention;

FIG. 3 is an end view of the helix shown in FIG. 2, and,

FIG. 4 is a developed view of the helix shown in FIG. 2, illustrating the relationships between the coil radius, the coil pitch, and coil length.

As schematically shown in FIG. 1, spun yarn 20 is withdrawn from package 22 and fed to feed rolls 24 driven at a constant speed. Spun yarn 20 next passes through a pigtail guide 26 and around draw pin 28. Yarn 20 next passes in a plurality of wraps about draw roll 30 and its associated separator roll 32. A heated roll 34 contacts yarn 20 just before yarn 20 contacts draw roll 30 for the second time, for a purpose to be explained hereinafter. After leaving draw roll 30 for the last time, yarn 20 is fed by a pair of nip rolls 36 downwardly through a heated prebulking chamber 38 to a second pair of nip rolls 40. Upon leaving nip rolls 40, yarn 20 is taken up in an orderly fashion, as by the illustrated conventional ring and twister assembly 42. With the exceptions of the temperature of roll 34, and the presence of rolls 36 and 40 and chamber 38, the illustrated apparatus is identical to that disclosed in greater detail in U.S. Pat. No. 3,317,978 to McIntosh et al.

Referring more specifically to FIG. 1, yarn 20 is drawn by the cooperation of feed rolls 24, draw pin 28 and draw roll 30, as will be apparent to those skilled in the art. According to the present invention, roll 34 is heated to a temperature in excess of the melting temperature of yarn 20, and contacts and melts one side of the yarn. The temperature of the opposite side of the yarn is maintained below 100 C., and preferably below C., by being contacted almost immediately thereafter by draw roll 30. Yarn 20 at the time it is contacted by roll 34 is under a tension in excess of 50 percent of the tension between draw pin 28 and draw roll 30. In the illustrated configuration, the tension on yarn 20 when contacted by roll 34 is substantially equal to the tension of the yarn leaving draw pin 28. The temperature of roll 34 is selected with respect to the yarn speed so that a small portion of the yarn periphery is melted, for example, a portion subtending an angle of about 30 at the filament center.

Yarn 20, being heated on one side by roll 34 and being cooled on its opposite side by draw roll 30, is subjected to a severe thermal gradient. The surface contacted by roll 34 is melted, as noted above, and accordingly its crystalline structure is destroyed or disoriented. The probable states of the polymer across the the cross section from hot side to cold side are: (A) melted and disoriented, (B) disoriented, (C) oriented, crystalline and heat set, and (D) oriented and crystalline but not heat set. To some depth, the heated side has little or no elastic recovery after removal of the tension, and little or no shrinkage in subsequent relaxation treatments. The opposite side of the filament, however,

retains elastic recovery and shrinkage. Accordingly, when tension is removed from the yarn, a helical crimp develops with the flattened portion on the outside of the helix (see FIG. 2) due to the elastic recovery difference across the filament. The direction of the helix randomly reverses at short intervals along the filament. On treatment with a relaxing medium such as steam or boiling water, the crimp frequency increases due to the shrinkage difference across the filament.

In womens seamless hosiery a crimp frequency of at least 27.5 (preferably 30 or more) crimps per inch is desirable in order to obtain at least two crimps per knit stitch in the hose. This relationship provides good stretch and fit, and optimum stitch clarity. It has been found that in order to obtain 30 crimps per inch in the final product when using 15 drawn denier yarn, the untextured drawn yarn must possess a boiling water shrinkage of at least 17 percent, which requirement eliminates nylon 66 and nylon 6 (shrinkage about 11-12 percent) as a satisfactory polymer. When a 15 denier monofilament yarn with at least 17 percent shrinkage is textured on roll 34 and then relaxed in boiling water without passing through chamber 38, it will form a helical coil with a radius R (see FIG. 3) of 0.15 to 0.21 millimeter. The crimp frequency can be further increased according to the invention by passing the yarn while under substantially zero tension through heating chamber 38, wherein the yarn is subjected to a temperature higher than its glass transition temperature to crystallize the filament while in its crimped condition, before the filament is exposed to boiling water.

As shown in FIGS. 2-4, the helix is characterized by the pitch P (the distance between corresponding points on adjacent coils), the coil radius R as measured between the axis or center of the helix and the center of the filament, and the radius r of the filament. The circumference C of the cylinder on which the center of the filament lies is given by 2 1r R. As shown in FIG. 4, the length S of one complete coil equals \KZ'IrR) +1)". The helix angle a which the filament makes with a plane perpendicular to the helical axis is equal to arctan P/2 1r R.

Prebulked filaments according to the present invention, after being withdrawn from the bobbin and relaxed two minutes in boiling water, are characterized by a ratio of S/r less than 45, and a coil length less than 0.924 millimeter. The ratio S/r takes account of the filament dimensions, since it is more difficult to achieve a given helical radius R and coil length S with, for example, a 15 denier filament than with a smaller filament such as one of only 2 or 3 denier. The ratio of (Rr/R+r) is within the range of 0.66 to 0.75.

EXAMPLE I Nylon 66 is spun as monofilament yarn and then drawn at a draw ratio of 3.2 to a drawn denier of 15, passing under roll 34 at 1,800 feet per minute. Roll 34 has a surface temperature of 280 C., which is above the 262 C. melting point of this polymer. The yarn is then passed through prebulking chamber 38 and subjected to hot air at 265 C. for a distance of 10 inches. About pounds of air per hour are supplied at 5 p. s. i. g. to chamber 38. Nip rolls 40 are driven at one-half the peripheral velocity of rolls 36, to insure essentially zero tension on the yarn during prebulking. A sample of this yarn withdrawn from the bobbin and relaxed in boiling water forms a helix with a radius R of 0.146 millimeter, and a pitch P of 0.578 millimeter. This corresponds to a helical coil length S of 1.08 millimeter, or 23.4 helical crimps per inch of filament length along the helix. The ratio of S/r is 50.2. This yarn thus develops inadequate crimp for use in seamless hosiery as noted above, since drawn nylon 66 yarn has a boiling water shrinkage of about 11 percent.

Although this yarn is not suitable for seamless hose, the crimp is noticeably enhanced by the prebulking treatment. The same yarn drawn and treated by roll 34 under the conditions noted above, but not prebulked by chamber 38, forms in boiling water a closely packed helix having a radius R of 0.26 millimeter. This corresponds to a length 5 of 1.63 millimeter, or 15.6 crimps per inch. The prebulking step thus increases the number of crimps per inch by about 50 percent.

EXAMPLE II Nylon 66-610 copolymer (formed from mols hexamethylene diamine, 8O mols adipic acid, and 20 mols sebacic acid) is spun as monofilament yarn and drawn at a draw ratio of 3.82 to a denier of 13.1. The yarn is passed under roll 34 at 1,275 feet per minute. Roll 34 is maintained at a surface temperature of 262 C., as compared to the polymer melting point of 240 C. The yarn is then passed through prebulking chamber 38 and subjected to hot air at 235 C. for a distance of 10 inches. About 1 9% pounds of air per hour are supplied at 3 p. s. i. g. to chamber 38. Nip rolls 40 are driven at one-third the speed of rolls 36. A sample of this yarn withdrawn from the bobbin and relaxed in boiling water forms a helix with a radius R of 0.122 millimeter and a pitch P of 0.358 millimeter. This corresponds to a helical coil length S of 0.847 millimeter, or 29.9 helical crimps per inch of filament measured along the helix. The ratio of S/r is 42.3. The boiling water shrinkage of this polymer is about 19 percent.

Seamless hosiery knit from the resulting yarn has ex cellent appearance, stretch and fit. The improvement in crimp by the prebulking treatment is shown by a comparison with the same yarn drawn and treated by roll 34 under the same conditions, except that the yarn is directly wound after leaving the draw roll for the last time, without being prebulked by chamber 38. A segment of this latter yarn, removed from the bobbin and placed in boiling water, forms a closely packed helix with radius R of 0.21 millimeter. This corresponds to a length S of 1.32 millimeter, or 19.2 crimps per inch. Accordingly, the prebulking step increases the number of helical crimps per inch by about 55 percent.

EXAMPLE III Nylon terpolymer is formed from 50 mols of hexamethylene diamine, 35 mols of adipic acid, 5 mols of terephthalic acid, and 10 mols of isophthalic acid. The polymer is spun as a monofilament yarn, and then drawn at a draw ratio of 3.51 to a draw denier of 13.9, passing under roll34 at 1,275 feet per minute. Roll 34 has a surface temperature of 240 C., as compared to the terpolymer melting point of 220 C. The yarn is then passed through prebulking chamber 38 and subjected to hot air at C. for a distance of 10 inches. About 3 pounds of air per hour are supplied at 3 p. s.

i. g. to chamber 38. Nip rolls 40 are driven at one-third the speed of rolls 36, to insure substantially zero tension on the yarn in chamber 38. A sample of this yarn withdrawn from the bobbin and relaxed in boiling water forms a helix with a radius R of 0.112 millimeter and a pitch P of 0.333 millimeter. These dimensions correspond to a helical coil length S of 0.775 millimeter, or 32.6 helical crimps per inch of filament measured along the helix. The ratio of S/r is 37.2, and the boiling water shrinkage is 26 percent for drawn yarn from this polymer.

Seamless hosiery knit from the resulting yarn has excellent appearance due to the high degree of crimp obtained. This particular yarn, however, has low tensile recovery which results in inadequate stretch recovery of the knit hose. The yarn is suitable for knit sheer scarves. The improvement in bulk by the prebulking treatment is shown by a comparison with the same yarn drawn and treated by roll 34 under the same conditions, except that the yarn is directly wound after leaving the draw-roll for the last time, without being prebulked by chamber 38. A segment of this latter yarn, removed from the bobbin and placed in boiling water, forms a closely coiled helix with a radius of 0.15 millimeter. This corresponds to a length S of 0.942 millimeter, or 27 crimps per inch. Accordingly, the number of helical crimps per inch is increased by approximately 21 percent by the prebulking step.

Nearly comparable improvement in final bulking level can be obtained if the latently bulked yarn is prebulked after winding in a separate operation, if the prebulking operation is performed promptly. That is, the latently bulked yarn can be initially wound, then unwound and fed under substantially zero tension through the prebulking chamber as a separate operation. However, the effectiveness of the prebulking decreases as a function of the time during which the latent bulked yarn is subjected to tension before prebulking. For a substantial improvement in bulking level, the prebulking should therefore be performed in less than 2 days after the latent bulk is imparted to the yarn, with best results being obtained if the prebulking is performed before the latent-bulked yarn is wound, as illustrated.

The prebulking medium can be hot air, steam,'or radiant heat. Polymer boiling water shrinkage as used herein is determined by drawing a filament to at least three times the spun length and measuring the drawn filament length before and after immersion of the filament in boiling water for 2 minutes. The shrinkage is the reduction in length divided by the original drawn length immediately before immersion in water. The term homogeneous is used herein as opposed to conjugate, and includes homopolymers and random or ordered copolymers, etc.

We claim:

1. A process for making a stretch yarn, comprising A. drawing a spun yarn at a given drawing tension to a length at least three times the length of said spun yarn, to thereby provide a drawn yarn, said spun yarn being so selected that said drawn yarn has a boiling water shrinkage of at least 17 percent;

B. imparting latent crimp to said drawn yarn by heating one side thereof, while said drawn yarn is under at least 50 percent of said drawing tension, to a temperature above the melting point of the yarn while keeping the opposite side of said drawn yarn below C;

C. feeding said yarn at a given speed to a treatment zone;

D. prebulking said yarn by subjecting said yarn in said treatment zone to a temperature above the glass transition temperature of said yarn while said yarn is under substantially no tension;

E. withdrawing said yarn from said treating zone at a speed between 30 and 60 percent of said given speed; and

F. collecting said yarn in an orderly fashion.

2. The process defined in claim 1, wherein said step of prebulking is performed before said drawn yarn is collected.

Claims (2)

1. A process for making a stretch yarn, comprising A. drawing a spun yarn at a given drawing tension to a length at least three times the length of said spun yarn, to thereby provide a drawn yarn, said spun yarn being so selected that said drawn yarn has a boiling water shrinkage of at least 17 percent; B. imparting latent crimp to said drawn yarn by heating one side thereof, while said drawn yarn is under at least 50 percent of said drawing tension, to a temperature above the melting point of the yarn while keeping the opposite side of said drawn yarn below 100* C; C. feeding said yarn at a given speed to a treatment zone; D. prebulking said yarn by subjecting said yarn in said treatment zone to a temperature above the glass transition temperature of said yarn while said yarn is under substantially no tension; E. withdrawing said yarn from said treating zone at a speed between 30 and 60 percent of said given speed; and F. collecting said yarn in an orderly fashion.

2. The process defined in claim 1, wherein said step of prebulking is performed before said drawn yarn is collected.

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