US3418199A - Crimpable bicomponent nylon filament - Google Patents

Description

Dec.'24, 1968 A. ANTON :TAL 3,418,199

CRIIPABLE BICOMPONENT NYLON FILAMENT Filed nec. 2?. 1967 y rfv/MP zas/Gmo@ ff United States Patent O 3,418,199 CRIMPABLE BICOMPONENT NYLON FILAMENT Anthony Anton, Wilmington, Del., and Emil John Volcheck, Jr., Chattanooga, Tenn., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Continuation-impart of application Ser. No. 494,556, Oct. 11, 1965. This application Dec. 27, 1967, Ser. No. 693,810

6 Claims. (Cl. 161-175) ABSTRACT F THE DISCLOSURE A bicomponent, nylon filament with continuous, adherent, eccentric components, one a homopolyamide, the other a copolyamide, the latter being a 6/6-6 or a 6/6-10 copolymer containing either 6--6 or 6410 in the ranges of either 8-l8% or 57-87%, the filament being crimpable against fabric restraints and having a crimp elongation of at least 30% This is a continuation-impart of Ser. No. 494,556, filed Oct. 11, 1965, now abandoned, which in turn is a continuation-inpart of Ser. No. 400,810, filed Oct. 1, 1964, now abandoned. The invention relates to crimpable polyamide filaments which are particularly suitable for the production of hosiery.

Polyamide filaments have been predominant in the eld of womens hosiery for many years, having almost completely displaced silk and other fibers in this market. Although conventional nylon hosiery are excellent in most respects, there is need for improvement, especially in connection with such factors as appearance, fit and comfort. This need arises from the fact that the standard sizes of seamless hose which are available do not provide a completely satisfactory lit for all wearers. ln many cases, the hose which provides a good fit for one part of the leg does not provide an adequate fit in other places, e.g., if the hose fits properly at the ankle the knee Will be too tight. These factors have led to the production of stretch hose which provide improvement in fit and comfort due to their ability to give enough to fit the larger parts of the leg without discomfort. However, in actual use, most stretch hose are lacking in stitch clarity and have a rather coarse appearance when compared with regular nonstretch hose.

Recently, semi-stretch and stretch hosiery having improved appearance have been produced by knitting the hose from crimpable bicomponent filaments which crimp during the hose finishing steps to produce the desired stretch characteristics. However, to produce the so-called miniature stretch hose, a higher degree of crimping under a slight load, as imposed by the knit fabric construction, is desired. Such high degrees -of crimping are difficult to attain, especially with sheath-core bicomponent structures which are desirable to prevent sticking in the high speed production of such filaments.

lt is an object of this invention to provide an improved bicomponent filament for the production of stretch hosiery. Other objects will become apparent from the examples and discussion to follow.

The several objectives and advantages disclosed herein have been achieved in a crimpable filament comprising continuous, adherent, eccentric components, one component consisting essentially of a homopolyamide and anther component consisting essentially of a copolymer hexamethylene adipamide or hexamethylene sebacamide and epsilon-caproamide, the copolymer containing, by weight, an amount of hexamethylene adipamide or hexamethylene sebacamide in one of the ranges 818% and 57-87%, the filament having a crimp elongation of at least 30% when exposed to steam at 118 C. Preferably, the homopolymer component is selected from the group comprising polyhexamethylene adipamide, polyepsiloncaproamide, polyhexamethylene sebacamide and polyhexamethylene dodecanediomide. However, other homopolyamides having a lower shrinkage potential than the copolyamide may also be used. Upon employing the resulting filaments for the manufacture of stretch hosiery in the usual manner, the resulting products are found to provide good fit and comfort and are 4of superior appearance.

For preparing hosiery yarn having an excellent combination of high tenacity for improved hose durability, low moisture sensitivity for good fit at high humidity levels and a satisfactory level of crimp elongation, the copolymer component is preferably a copolymer of hexamethylene adipamide and epsilon-caproamide containing 79-81% hexamethylene adipamide. For optimum results, compositions in the range of ill-85% hexamethylene adipamide should be employed. Where compositions in these ranges are employed, particularly in the production of sheathcore filaments, the relative viscosity of the copolymer should be higher than that of the homopolymer.

The wearer of a stocking experiences comfortable fit sensation when stresses from the strained fabric on the leg are satisfactory. Stretch hose tend to provide for many wearers a better fit in this respect. However, under conditions of high humidity, stretch hose tend to increase in dimension and excessive expansion will lead to a hose prone to bag. The following test gives a good indication of how a particular yarn will perform in a hose at high humidity. ln this test, hose are conditioned at 70 F. at relative humidities of 20% and 80%. The increase in circumference in the knee region of the hose conditioned at 80% RH in comparison with the 20% RH conditioned hose is determined on a beam stretch tester. An increase in excess of about 60% is undesirable, and preferably the increase is about 50% or lower. A beam stretch tester holds a stocking taut at the outside extremities of the welt and of the sole while measurements are taken with a two-arm probe inserted inside the stocking. The first arm of the probe does not move within the stocking and the second (contiguous with the first arm) is supported on a fulcrum. The inside ends of both arms are in juxtaposition when the apparatus is not loaded. A load of 468 grams is applied to the outside end of the second arm and the stocking is placed in tension locally by the two inside ends. The distance separating the two inside ends is measured and the circumference calculated.

The term eccentric as used in this application means both side-by-side and sheath-core structures.

Both the homopolyamide and copolyarnide components of filaments of this invention are formed lof polymer in fiber-forming molecular weight ranges. One of the components should have a relative viscosity of at least 35; for ease in spinning, the other should not differ thererom by more than about 10 units in relative viscosity. The term relative viscosity as used herein is the ratio of flow time in a viscometer of a polymer solution containing 8.2i0.2% by weight of polymer to the ow time of the solvent by itself. Measurements of relative viscosity are made with 5.5 grams of polymer in 50 ml. of formic acid at 25 C.

The polymers from which filaments of this invention are made are produced in accordance with techniques now known in the art and universally available in the patent literature. Similarly, the filaments are spun and processed according to known techniques with known apparatus. However, in preparing the preferred sheathcore filaments, a particularly satisfactory spinneret that can be employed has been illustrated in FIG. 2 of U.S.

Patent No. 3,244,785 to Hollandsworth. It will also be appreciated that the filaments preferably are formed in the deniers usually made for hosiery applications, that is to 30 d.p.f. (denier per filament) for leg yarns, though multi-filament yarns such as 15 denier, 3 filament or denier, 3 filament can also be made. Welt yarns are usually higher denier multi-filament yarns, such as denier, 7 filament.

The invention will be described in conjunction with the following specific examples in which the details are given by way of illustration and not by way of limitation. The properties of crimp elongation and shrinkage are determined by winding loops to give a skein of about cm. length when suspended with a Weight attached. The skein is held on a hook with a weight suspended from the other end, the weight being adjusted to impose a stress of 0.33 g.p.d. (grams per denier) on the skein. After one minute, the length A of the skein is measured. The load is then removed and a smaller weight substituted so that the skein is under a tensile load of 0.0012 g.p.d. i.e., a tension slightly in excess of that on the yarn when knitted into a fabric. The skein is then subjected to steam at 118 C. (245 F.) in a conventional hosieryboarding oven. The skein is then allowed to dry in air for ten minutes, after which the skein length B is measured. The 0.0012 g.p.d. load is then removed and the 0.33 g.p.d. load is again applied for one minute Iand the length C of the skein determined. The crimp elongation and shrinkage of the filament are then calculated as follows:

Crimp elongation, percent: 100 (C-B /B Shrinkage, percent: 100(AC) /A EXAMPLE I A 49.6% aqueous solution of hexamethylene diam.

monium adipate (6-6 nylon salt solution) is charged into an evaporator with sufficient epsilon-caprolactam to give the desired copolymer ratio and heat is applied to dissolve the caprolactam. The hot charge is transferred to an autoclave, heated to a temperature of about 210 C. and brought to a pressure of 250 p.s.i. (17 atmospheres). At this point, sufiicient 20% aqueous slurry of titanium dioxide is added to give a concentration of 0.3% TiOz in the final polymer. The solution is then heated at 250 p.s.i. (17 atmospheres) until the temperature reaches 274 C. After the heating period, pressure is reduced over a period of 90 minutes to atmospheric and the temperature is increased to 279 C. The polymer is then held minutes at this temperature after which it is extruded under nitrogen pressure in the form of a ribbon Which is quenched on a water-cooled casting Wheel and cut into 1/s (3 mm.) fiake in the conventional manner. Proceeding in this fashion, copolymers having the compositions given in Table I below are prepared. Those compositions prepared with more than 50% caprolactam are water extracted to remove residual monomer by placing the flake in a container, passing water at about 100 C. into the bottom of the container and permitting it to overow at the top for a period of eight hours.

Polyhexamethylene adipamide (6-6 nylon) flake having a relative viscosity of 45 is prepared in the conventional manner. The two flakes, 6 6 and one of the 6-6/ 6 copolymer compositions, are conditioned by drying and then melted and pumped to a spinneret assembly where the two polymers are extruded to form sheath-core filaments. The relative viscosities of the 6-6 ake and the 6-6/6 copolymer fiake after conditioning are shown in Table I. The two polymers are extruded with the 6-6/ 6 copolymer as the core, to form eccentric sheath-core hosiery monolils using a spinneret arrangement as shown in the Hollandsworth patent, FIG. 2, hereinbefore identified. The monofils contain equal amounts of the copolymer and homopolymer. The sheath at is thinnest point has a thickness equivalent to about 2% of the total filament diameter. The filaments are set by air quenching, using a 36-inc'h chimney and an air temperature of 24 C.,

steam conditioned as described in U.S. Patent No. 2,289,860 and each filament is wound into a package at 461 yds/min. (420 meters/min.) in the conventional manner. The monofil is subsequently withdrawn from the package and drawn to a ratio of 4.74 over an unheated draw pin located between a feed roll and a draw roll to give a final denier of 15. The filament is then passed under low tension from the draw roll through a tubular crimping chamber three inches in length at 790 yds/min. (720 meters/ min.). In the chamber, the monofil is heated by passing yapproximately 0.4 cu. ft./min. (11 liters/min). of heated air at 30 p.s.i.g. (2 atmospheres) through the chamber to give an air temperature at the exit of 180-185 C. The filament, which is under low tension in the crimping chamber, is crimped into helical `form and then led over into snubbing pins and around a power driven withdrawal roll to remove the crimp by stretching the filament slightly. The crimpable, substantially straight monofil is then wound into a package. The relative speeds of the draw roll and withdrawal roll permit 22% retraction in the length of the yarn between these points.

When the crimp elongations of the various crimpable filaments prepared as described above are measured as previously described, the vaverage values shown in Table I are obtained Shrinkage values for these filaments fall n the range of 5-10%.

TABLE I Copolymer, Relative Viscosity Crimp Tenacity, Weight Elongation, g.p.d.

Percent 6-6/6 Homopolymer Copolymer Percent The crimp elongation data have been plotted and the resulting curve of crimp elongation vs. polymer composition is attached hereto. As may be seen in the curve, unexpectedly high crimp elongations are obtained in the critical composition ranges as indicated by the sharp peaks in the curve.

Ladies minature hose are knit in the usual manner from the sheath-core laments prepared from the 6-6 and the /30, 60/40, 15/85 `and 10/90 6-6/ 6 copolymer compositions. After knitting, the hose are steamed at 118 C. in a relaxed condition for one minute. The hose are then scoured and dyed in the conventional manner and post-boarded at 121 C. for one minute. Inspection and testing of the hose indicated they would be very satisfactory from the standpoint of fit and comfort and superior in appearance to many of the conventional stretch hose.

EXAMPLE II Two copolymers having relative viscosities of about 35 and 52, respectively, are prepared from an aqueous solution of hexamethylene diammonium sebacate (6-10 salt) and epsiloncaprolactam following the general procedure of Exa-mple I, the relative amounts of 6-10 salt and caprolactam being adjusted to give a weight ratio of 15/85, 6-10/6 copolymer in one case (RV 35) and a ratio of 25/75, 6-10/6 in the other (RV 52).

Following the procedure of Example I, each of these copolymers is extruded in combination with 6-6 nylon flake having a relative viscosity of 45 to form eccentric sheath-core filaments, the coplymer being the core. After processing as described in Example I, the filaments are found to have an average crimp elongation of 45.8% in the case of the 15/ 85 ratio copolymer and 11.5% for the 25/75 copolymer. These values have been plotted and correspond, within experimental error, to the attached curve of crimp elongation vs. polymer composition for the filaments of Example I, indicating that substitution of the carbon, sebacic acid for the 6 carbon, adipic acid has little effect on the relationship between crimp elongation and polymer composition.

EXAMPLE III Various batches `of copolymer having the compositions shown in Table Il are prepared substantially as described in Example I. Except for the 50/50 composition, all copolymers are extruded and cut into pellets as described by Cooper and Zimny in their U.S. Patent 2,975,483. The 50/ 50 copolymer is cut to flake as `described in Example I. Pellets of 6 6 nylon are prepared in the conventional manner. The two polymers, 6 6 and one of the 6-6/ 6 copolymer compositions, lare fed separately to a dual screw melter where the pellets are first conditioned by exposure to humidified nitrogen at 125 C. and then melted and pumped to a spinneret assembly where the two polymers are extruded to form sheath-core filaments. The relative lviscosities of the pellets after conditioning are shown in Table II. Each filament is extruded, quenched and wound into a package substantially as described in Example I. The relative weight ratio of the sheath polymer to the core polymer is 60 except for the filament prepared from the /50 6-6/ 6 copolymer where the ratio is 5 0/ 5 O. The filaments are subsequently drawn and passed through a crimping chamber as described in Example I, except that the speed of passage through the crimping chamber is 843 y.p.m.

Cri-mp elongations of the various filaments prepared as described above are measured and recorded in Table II and hf-.ve been plotted. The tenacities of the filaments are also determined and recorded in Table II.

Ladies miniature hose are knit in the usual manner from the above-prepared filaments ywith the exception of the 50/ 5 0 copolymer composition. The hose are processed after knitting as described in Example I, except that after knitting the hose are placed in a bag and tumbled in atmospheric steam for 30 minutes in place of the 118 C. steam treatment. These hose are all found to be satisfactory from the standpoint of fit and comfort. The increase in hose circumference is determined as previously the filaments to moderate tension prior to winding into a package.

As already noted, the homopolymer component in the filament may consist of any homopolyamide having a lower shrinkage potential than the copolyamide. Polyhexa-methylene adipamide and polyepsilon-caproamide are particularly suitable in view of their shrinkage characteristics and ready availability. Other suitable polyamides include polyhexamethylene sebacamide and polyhexamethylene dodecaned-ioamide. Obviously, homopolymers containing very small amounts of a second or third polymer unit may be employed, if desired. Likewise, copolymers which are isomorphous may exhibit the shrinkage characteristics necessary for the second component to be used in combination with the 6-6/6 or 6/6-10 copolymers of this invention.

Although good results may be obtained with copolymers containing either 8-l8% or 57-87% of the 6-6 or 6-10 constituent, the 8-18% and 79-87% ranges are presently preferred from the standpoint of developing high crimp elongation and optimum yarn strength. For the best results in hose under conditions of high humidity, the range of 79-87% 6-6 is preferred and 8l-85% 6-6 is optimum.

The filament components may be extruded in either side-by-side or sheath-core relationship. An eccentric sheath-core filament with the copolyamide as the core is preferred for high speed spinning since difficulty is encountered with filaments sticking together when side-byside filaments are employed in such processes. In sheathcore structures, the core should be highly eccentric in order to achieve the highest level of crimp elongation and the copolymer component should have a higher (preferably about 5 units higher) relative viscosity than the homopolymer component. From a standpoint of processing, it is preferred that the copolymer component is the core and the homopolymer the sheath in sheath-core filaments.

While the relative amounts of the two components may be varied somewhat yas may be desired, it is generally preferable that the copolymer component constitute at least about 50% of the total weight.

While the invention has been described with reference to specific details, it will be appreciated that changes can described and is recorded in Table II. 45 be made without departing from its scope.

TABLE II Copolymer, Hose Cir- Relative Viscosity Crimp Weight cumterence, Elongation- Tenacity, Percent 6-6/6 Percent Homopolymer Copolymer Percent g.p.d.

Increase /15 46. 2 66. 7 35. 1 1 5. 5 82/1 S 48 48. 0 57.0 43. 5 5. 3 '7S/22 63 48. 0 57. 0 67. 8 5. 0 'I0/30 73 48. 0 57. 0 80. 0 4. 3 50/50 41. 4 53. 5 6. 9 5. 9

1 Estimated.

The yarns of this invention exhibit an outstandingly high degree of crimp under slight stress and are consequently especially suitable for the production of stretch hosiery. However, they may be used to an advantage in other fabrics, such as tricot knit fabrics, where improved covering power and hand are desired.

As illustrated in the examples and in the attached curve, the composition of the copolymer must be carefully selected to realize the advantages Of this invention. Also, the filaments must be subjected to heat in a relatively relaxed condition after drawing to develop the required retractive force on crimping. This may be accomplished by passing the filaments through a chamber or jet where the filaments are exposed to steam, hot air or other heated gas and permitted to crimp. The temperature of the treating atmosphere should be above about C. but below the softening point of the copolymer, and the temperature and time of exposure should be suflicient to permit full crimp development. After crimping, the crimp is preferably removed by subjecting Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A substantially straight, orientation drawn, nylon filament comprising continuous, adherent, eccentric, fiberforming components consisting essentially of a homopolyamide and a. copolyamide, the copolyamide consisting essentially of a member of the group consisting of hexamethylene adipamide and hexamethylene sebacamide in one of the weight ranges 8 to 18% and 57 to 87% and the remainder epsilon caproamide, the filament being crimpable into a helical configuration upon exposure to a heated atmosphere, and having a crimp elongation of at least 30% after exposure to steam at 118 C., the homopolyamide 'hav-ing a lower shrinkage potential than the copolyamide.

2. A filament according to claim 1 in sheath-core form with the copolyamide being the core.

3. The crimpable filament of claim 1 in which the homopolyamide is selected from the group consisting of polyhexamethylene adipamide, polyepsilon caproamide,

7 polyhexamethylene sebacamide and polyhexamethylene dodecanedioamide.

4. The crimpable lament of claim 3 in which the member of said group .is present in the copolyamide in an amount of 8 to 19% by weight.

5. The crimpable filament of claim 3 in which the member of said group is present in the copolyamide in an amount of 57 to 87% by weight.

6. The crimpable -lament of claim 3 in which the member of said group is present m the copolyamide in an amount of 79 to 87% and the copolyamide component has a relative viscosity greater than that of the homo-v polyamide.

References Cited UNITED STATES PATENTS 2,987,797 671961 Breen 28-82 5 3,038,235 6/.1962 Zimmerman 28-82 3,038,236 6/ 1962 Breen 28-82 3,145,133 8/1964 Barton et al. 161-168 ROBERT F. BURNETT, Primary Examiner.

R. L. MAY, Assistant Examiner.

U.S.v Cl. X.R.

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