US3558767A - Controlled polyamide filament stretching process - Google Patents

Abstract

HIGH DRAW RATIOS CAN BE ACHIEVED TO YIELD HIGHSTRENGTH POLYAMIDE HOSIERY YARN WHICH EXHIBITS UNIFORM LUSTER BY MAINTAINING THE RATIO

AT LESS THAN 1.02 GRAMS PER DENIER-CM T1 IS TENSION ON A FILAMENT APPROACHING THE DRAW ZONE; T2 IS THE TENSION ON A FILAMENT RECEDING FROM THE DRAW ZONE; D IS THE DRAWN DENIER OF THE FILAMENT AND D IS THE DIAMETER OF THE DRAW PIN OR SNUBBING ELEMENT IN CM.

Description

Jan. 26, 1971 F. GOPEZ, JR I 3,553,767

' CONTROLLED POLYAMIDE FILAMENT STRETCHING PROCESS I Filed Nov. 19, 1968 INVENTOR F2 0901/00 cop/52, JR

United States Patent O U.S. Cl. 264290 2 Claims ABSTRACT OF THE DISCLOSURE High draw ratios can be achieved to yield highstrength polyamide hosiery yarn which exhibits uniform luster by maintaining the ratio at less than 1.02 grams per denier-cm. T is the tension on a filament approaching the draw zone; T is the tension on a filament receding from the draw zone; D is the drawn denier of the filament and d is the diameter of the draw pin or snubbing element in cm.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the production of nylon filaments, and more particularly, to an improved process for the production of such filaments for use in ladies hosiery.

Description of the prior art In the manufacture of ladies nylon hosiery, monofilaments are commonly used as the leg yarn with rnultifilament yarns used in the welt, heel and toe. In the United States 15 monofils prevail, while in Europe higher deniers such as 20 denier are more commonly used. Although nylon filaments dominate the field of ladies hosiery in view of their relatively high strength and other desirable qualities, the use of relatively low denier yarns needed to provide sheer hose which the market demands results in a lower'hose wear life than is desirable.

Increased hose durability may be achieved by increasing the strength of the filaments. This may be accomplished by increasing the molecular weight of the polymer and the draw ratio employed in processing the filaments However, when high draw ratios are used in conventional pin drawing of nylon filaments of this type, the hose prepared from the filaments tend to have a streaky appearance which is apparently due to occasional changes in luster, ie, the manner in which the filaments reflect light. These luster streaks are highly undesirable and must be eliminated in order to achieve a commercially acceptable hosiery yarn. In addition, the use of high draw ratios leads to a high incidence of broken filaments such that the process is commercially unacceptable.

SUMMARY OF THE INVENTION High draw ratios can be achieved without deleterious eifect on a polyamide filament by drawing an undrawn Patented Jan. 26, 1971 polyamide filament by passing it from a feeder roll at a tension, T to and around an unheated snu bbing element of substantially circular cross section having a diameter, d, withdrawing the filament at tension, T from the snub- 5 bing element with a draw roll, heating the filament between the snubbing element and draw roll to efiect additional draw. This process must be carried out under the following conditions: the drawn denier, D, of the filament must be in the range of from 10 to 30; the absolute draw ratio must be at least 5.4; and the ratio 'must be no greater than 1.02 grams per denier-cm. Preferably the diameter of the snubbing element is from 2.5 to 5 centimeters and the relative viscosity of the undrawn polyamide filament is at least 50. Under normal process conditions the filament is heated at a temperature in the range of from 170 C. to 230 C.

BRIEF DESCRIPTION OF THE DRAWING The figure is a simplified schematic representation of the apparatus by which the process of this invention can be practiced.

DEFINITIONS The expression relative viscosity as used herein signifies the ratio of flow time in a viscometer of a polymer solution relative to the flow time of the solvent by itself. Measurements of relative viscosity are made with 5.5 gms. of polyamide in 50 ml. of formic acid at 25 C.

Machine draw ratio, as referred to herein, is calculated by dividing the speed of the yarn leaving the draw zone by the entering speed. Where feed and draw rolls are employed, the yarn speed is assumed to be the same as the surface speed of the rolls.

Yarn birefringence, as employed herein, refers to the birefringence of the extruded and quenched, but undrawn, filament. Birefringence is a measure of the orientation of the polymer chains relative to the fiber axis. It is determined from observation of the filament between crossed plane-polarizing elements, e.g., Nicol prisms, using a Soleil compensator for accuracy. The method is described in detail by Heyn in Textile Research Journal 22, 5-13 (1952).

Since the undrawn yarn is oriented to some degree, and this may vary considerably depending on polymer viscosity and extrusion conditions, the orientation of the drawn yarn is not accurately reflected by the machine draw ratio. Hence, it is desirable to use an absolute draw ratio which takes into account orientation prior to drawing. It has been found that an absolute draw ratio calculated from the following empirical equation, satisfactorily reflects the contribution of the undrawn filament orientation to the total orientation existing in the drawn yarn:

Absolute Draw Ratio: (1+22.2B 284B R where B is undrawn yarn birefringence and R is machine draw ratio.

DESCRIPTION OF PREFERRED EMBODIMENTS Nylon hosiery yarn is prepared by extruding and quenching molten polyamide to form monofilaments. For

purposes of this invention the monofilaments at this stage should preferably have a relativeviscosity of'at least 50 and a denier suflicient to yield a final drawn denier in the range of to 30. The newly formed filaments are usually wound into a package and transported to a drawing apparatus.

Referring to the figure, the undrawn nylon filament 4 is supplied from yarn package 2. The yarn need not be taken from a package as shown, but may be taken directly from a spinning machine to continuously process the yarn. The yarn 4 is passed from the package through guide 6 to a feed roll 8, about which the yarn is wrapped. The feed roll is positively driven and may be associated with a nip roll, if desired. From the feed roll the yarn is advanced to and around draw pin or snubbing element 10. The yarn is pulled away from or withdrawn from the snubbing element across a curved heated plate 12 by driven draw roll 14 and its associated separator roll 16. The yarn can be wrapped around draw pin 10 one and one-half times or any other amount necessary to effectuate drawing of the filament at the snubbing element. The plate 12 can be heated by any conventional means. As the yarn is heated when it passes over the plate, additional drawing is accomplished, The relative peripheral speeds of the draw roll 14 and the feed roll 8 determine the mechanical draw ratio of the filament. The drawn yarn is taken from the draw roll 14, passed through guides 18 and 22, and wound on bobbin 24.

The tension on the filament prior to and after contact with the snubbing element is determined by a number of factors, including the peripheral speeds of the draw roll 14, the feed roll 8, the denier of the filament and the friction between the snubbing element 10 and the filament. The tension between the feed roll and snubbing element is represented in the figure by T the tension between the draw roll and snubbing element is represented by T The snubbing element friction is proportional to the diameter, d, of the element.

The filament is heated during the drawing process by passing it from the snubbing element over a curved hot plate between the snubbing element and draw roll whereby the filament is subjected to additional drawing without substantial snubbing action which would tend to distort the filament cross-section.

Excess transverse pressure on the filaments should be avoided both on the snubbing element in the first draw zone and in the second draw zone to prevent fabric luster streaks which are believed to result from distortion of the cross-section. Excessive pressure in the first draw zone may be avoided by correct sizing of the drawing element in relation to the tension imposed on the filament in this zone. However, in order to provide adequate snubbing action, diameters greater than 5 cm. should be avoided and the minimum diameter should be at least about 2.5 cm. to avoid the necessity for low tensions which are not practical Where a high draw ratio is desired. The tension, T on the filament leaving the first draw zone is regulated primarily by the temperature imposed in the second draw zone and to a lesser extent by the friction between the filament and the heating element in this zone.

It is especially important that excessive transverse pressures on the filament be avoided in the heated draw zone. Consequently, substantial snubbing of the filaments should be avoided. While heating in this zone may be varied to suit the polymer used to prepare the filaments, temperatures in the range of 170 C. to 230 C. are usually required for satisfactory results. The heating and frictional contact with any surface in the heating zone should be adjusted so that the drawing in the heated zone is substantially less than that in the unheated draw zone.

Where it is necessary to reduce the shrinkage in aqueous solution of the filaments, as may be required with certain polyamides and particularly with copolyamides, this may be accomplished by passing the filaments through a heated zone under low tension. Filaments may be heated at con.- stant length or retraction of the filaments may be permitted, the latter procedure being preferred where a copolymer filament having a low shrinkage tension is desired. In some cases it may be desirable to employ heating at constant length followed by further heating under conditions which permit retraction of the filament. With most copolyamides, a retraction in the range of 11-18% will prove satisfactory. I

It is highly desirable that the relative viscosity of the extruded filament be at least 50 in order to achieve high strength, and consequently a high level of durability in hose. I

EXAMPLES The examples are intended as illustrative of preferred modes of carrying out the process of this invention. They are not intended to be in any way delimitative 0f the inventive concept.

EXAMPLE I A copolyamide flake is prepared from hexamethylenediammonium adipate and epsilon-caprolactam following the general procedure of Example I of U. S. Pat. 3,322,- 721. The copolymer contains 6-6 polymer units and 15%' 6 polymer units. The relative viscosity of the flake is 44. The flake is heated in a nitrogen atmosphere to remove additional water, thus increasing the relative viscosity, as measured on the extruded filaments, to the level shown in Table I. The flake is melted in a screw melter and extruded to form 15 denier (drawn denier) monofil. A heated baflie of 17.8 cm. depth is placed around the spinneret to reduce the quenching rate near the spinneret, and the spinneret is blanketed with stream at 290 C. The filament is then quenched with cross flow air, passed over a finish roll where a lubricating finish is applied, and wound into a package. The filament is subsequently unwound from the package, passed around a feed roll, then around an unheated draw pin for 1 /2 wraps, then directly over a hot plate of 3 in. length to a draw roll rotating at a peripheral speed of 771 meters/ min. The draw roll assembly consists of a stepped roll,

the larger diameter portion of which acts as the draw.

roll, a separator roll and a heating element mountedbetween the stepped roll and separator roll to contact the yarn for a distance of about 4 in. as it passes to and from the separator roll. The yarn is given 5-12 passes around the draw roll portion of the stepped roll and the associated separator roll, and is then passed to the smaller diameter portion of the stepped roll. where it is given 5-8 passes around this roll and the separator roll, the number of passes being adjusted to give the desired yarn shrinkage. The difference in the diameters.

of the two portions of the roll is sufficient to permit the yarn to retract 13%. The yarn, after drawing, is thus subjected to constant length heat treatment and then per mitted to retract 13% under the influence of heat. The filament is then wound into a package in the conventional manner. The above process is run under various conditions of draw pin diameters, hot plate temperature and draw ratio, as shown in Table I below. For comparison,

samples of filaments, it is found that those filaments havmg distorted cross-sections produce hose with luster streaks, while those with round, undistorted filaments do not.

In all cases where a hot plate was employed, the draw ratio in the heated zone was substantially less than the draw ratio in the unheated zone.

TABLE I Undrawn yarn Draw ratio Hot Draw pin Plate Tz-T1, denier Filament Relat ve Birefrln- Diameter, Temp., Xdiameters cross- Tenacity, vlscosities gence Mach ne Absolute m. C. T|,g. T2, g. Denier cm. section g.p.d.

0.0080 4.54 5. 2 33 15.3 1.07 Distol'ted 7.53 0.0080 4. 95 5. 91 6 54 14.5 1 74 d 0. 0080 4. 95 5. 91 6 55 14. 0. 0078 5. 40 6. 43 11 50 1 14. 6 0. 0046 5. 24 5. 85 1 25 14. 9

1 Estimated based on spun denier and draw ratio.

7 EXAMPLE II he in the range from 25 to 75 grams, that the absolute Following the general procedure of Example I, except draw who be at least and that the who of that no heating or relaxation of the yarn subsequent to drawing is employed, polyhexamethylene adipamide (66 T --T nylon) yarns having relative viscosities as shown in Table II are produced. Process variations, results of microscopic examination of the filament cross-sections, etc., are shown in Table II below. Draw ratios in the heated zone were be no greater than grams P substantially less than in the unheated draw zone. 5? P t r of i 1 l P a 55 3" EXAMPLE HI am1 e amen as a re a we vlscosity 0 at east Starting with polycaprolactam (6 nylon) flake having a relative viscosity of 59, an 80 relative viscosity flake is produced and processed into filaments following the procedure of Example I except that no heating or relaxation of the yarn subsequent to drawing is employed. Process variables, results of microscopic examination of these filaments, etc. are shown in Table III below. Draw ratios in the heated zone were substantially less than in the unheated draw zone.

TABLE II Undrawn yarn Draw ratio Hot Draw pin Plate Tz-T1, denier Filament Relative Birefrin- Diameter, Temp., XDiameters cross- Tenacity, viscositie gence Machine Absolute em. 0. T1, g. T2,g- Denier cm. section g.p.d.

0. 0020 4.95 5. 3.81 175 7 29 13.0 0.442 Round 7 4 0.0039 4.67 5.10 3.81 200 3 48 17.3 0.683 d0 0.0039 5.09 5.55 3.81 200 7 65 15.5 0.96 .do 7 62 0. 0039 5.24 5.71 3.81 200 7 72 15.0 1 14 Distorted 8 12 0.0040 5.24 5.72 3.81 '230 13 68 14.4 1.005 Round 9.0 0. 0040 5.40 5.90 3.81 230 14 75 14.2 1.13 Distorted-.. 9.3

1 Estimate based on draw ratio vs. elongation for 63 and 53 RV yarns.

TABLE III Undraw'n yarn Draw ratio Hot Draw pin Plate Tz-T1, Denier Filament Birefrin- Diameter, Temp., X Diameter, cross- Tenacity, Relative viscosities gence Machine Absolute em. C. T1,g- T2,g- Denier 0111- seetion g.p.d.

80 0.0062 4.88 5. 59 3.81 200 0 36 16.4 0. 575 Round 7.77 80 0.0062 5.17 5.9 3.81 200 0 42 15.7 0.705 .....d@ 8.48

STATEMENT OF UTILITY References Cited 7 The process of this invention delineates conditions by UNITED STATES PATENTS which filamentary nylon can be subjected to higher draw 3 011 215 12 19 1 Alley 2 7 ratios than heretofore could be achieved without filament 3 091 015 5 9 3 Zimmerman deformation. Draw ratios of greater than 5.4 can now be 3 303 1 9 2 19 7 pitzl 264 290 achieved without crushing the filament by utilizing the 3 3 2 307 5 19 Ciceri et 1 264 210 process e e disclosed- 3,400,194 9/1968 Boone et a1 264-210 The splnt and scope of thls invention shall only be 3,414 4 12/19 3 Pitzl 2 4 0 limited by the appended claims and any equivalents or 3,441,642 4/1969 Engelman et a1 modifications thereof within the purview of the art. 3,452,130 6/1969. Pitzl 264 210 What IS clalmed 3,452,131 6/1969 'Geerdes et a1. 264-290 1. A process for drawing an undrawn polyamlde fila- 3 472 016 10/1969 Robertson ment comprising drawing the said filament by passing it from a feeder roll at a tension, T to and around'a 65 34914l8 1/1970 Nlclta et a1 264290 snubbing element of substantially circular cross-section FOREIGN PATENTS having a diameter d, withdrawing the filament'at a tension 889,144 2/1962 Great Britain 264 290 T from the said snubbing element with a draw roll, and 636,095 2/1962 Canada heating the filament between the snubbing element and draw roll to a temperature in the range of from 170 C. DONALD ARNOLD, Primary Examiner to 230 C. to eifect additional draw, with the provisos that the drawn denier D, of the filament be in the range MINTZ Asslstant Exammer of from 10 to 30, the diameter of the snubbing element U S Cl X R d, be in the range of from 2.5 to 5 cm., the tension T be in the range of from 0 to 14 grams, the tension T 28-71.3, 72.17; 264210

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