Partially Oriented Nylon Yarn and Process

Other aspects will in part appear hereinafter and will in part be apparent from the following detailed description taken together with the accompanying drawings, wherein:

FIG. 1 is a schematic front elevation view of an exemplary spinning position for making PON yarns according to the invention; and

FIG. 2 is a graph showing crimp development of yarns of the present invention as compared to various other yarns.

As shown in FIG. 1, molten streams 20 of nylon 66 polymer are extruded through capillaries in spinneret 22 downwardly into quench zone 24 supplied with transversely directed quenching air at room temperature. Streams 20 solidify into filaments at some distance below the spinneret within the quench zone. Filaments 26 are converged to form yarn 28 below quench zone 24. A conventional spin-finish is applied to yarn 28 by finish applicator 30. If desired, the filaments may be converged simultaneously with application of the finish. Yarn 28 next passes through interfloor conditioner tube 32 and in partial wraps about godet 34 and 36 prior to being wound on bobbin 38. The filaments may be entangled if desired, as by pneumatic tangle chamber 40.

Ordinarily, godets 34 and 36 perform the functions of withdrawing filaments 26 from quench zone 24 at a spinning speed determined by the peripheral speed of godet 34, and of reducing the tension in yarn 28 from the rather high level just prior to godet 34 to an acceptable level for winding onto package or bobbin 8. The winding tension range of 0.03 to 0.25 grams per denier is preferred, with tensions of about 0.1 grams per denier being particularly preferred. Godets 34 and 36 may be dispensed with if the yarn winding tension immediately prior to the winder in the absence of the godets is within the yarn tension ranges indicated in this paragraph. "Winding tension" as used herein means the yarn tension as measured just prior to the yarn traversing and winding mechanism. Some commercially available winders include an auxiliary roll designed to both assist in yarn traversing and to permit reducing the yarn tension as the yarn is wound onto the bobbin or package. Such winders may be of assistance when using the upper portions of the yarn tension ranges indicated in the paragraph.

Spinneret 22 contains 34 capillaries having lengths of 0.012" (0.3 mm.) and diameters of 0.009" (0.229 mm.). Quench zone 24 is 44 inches in height, an is supplied with 18.degree. C. quench air having an average horizontal velocity of about 1 foot (30.5 cm.) per second. Filaments 26 are converged into yarn 28 about 37.5 inches (95 cm.) below the spinneret, and conventional spin finish is applied to yarn 28 by finish applicator 30. Conditioner tube 2 is 77 inches (183 cm.) long and is of the type disclosed in Koschinek U.S. Pat. No. 4,181,697, i.e., a steamless tube heated to 120.degree. C. through which yarn 28 passes. The speed of godets 34 and 36 are 3500 meters per minute and 3535 meters per minute, respectively, to prevent the yarn from wrapping on godet 34. The winder used is the Barmag SW4SLD, and the winder speed is adjusted to provide a winding tension of 0.1 grams per denier. Four different nylon 66 polymers are spun at a temperature of about 295.degree. C. into PON yarns with polymer metering rates selected such that the final drawtextured yarns have nominal deniers of about 70. All polymers contain between 0.1 and 0.35 mol % acetic acid as a viscosity stabilizer, and in this range of concentration the level of acetic acid has little effect on yarn properties.

Item 1 is a control within the range of conventional commercial PON practice, having no branching agent. Yarn RVs and amounts of branching agent are given below in Table 1. The PON elongations for items 1-4 are, respectively, 71%, 97%, 91%, and 109%. Normalized lamellar dimensional products for items 2 and 4 are 2.4 and 3.1 respectively, while normalized SAXS peak intensities for items 2 and 4 are 6.1 and 11.8 respectively. Normalized lamellar dimensional product and normalized SAXS peak intensity for item 1 are each approximately 1.0. The data indicates a substantial increase in crimp development (% CD) by incorporating a small amount of branching agent in the polymer.

The spun yarns are then simultaneously drawn and friction-twist textured on a texturing machine using a 21/2 meter primary heater and a Barmag disc-aggregate with Kyocera ceramic discs in a draw zone between a feed and a draw or mid roll. The heater temperature is 230.degree. C., and the ratio of the peripheral speed of the discs to draw roll speed (the D/Y ratio) is 1.910. The draw roll speed is set at 800 meters per minute, and the feed roll speed is adjusted to some lower speed to control the draw ratio and hence the draw-texturing tension (the yarn tension between the exit of the heater and the aggregate). In order to maximize the crimp development, the draw ratio is changed by adjustment of the feed roll speed so that the drawtexturing tension is high enough for stability in the false twist zone and yet low enough that the filaments are not broken, this being the operable texturing tension range. Within the operable tension range, the "maximum texturing tension" is defined as the tension producing the maximum initial crimp development without an unacceptable level of broken filaments (frays). More than 10 broken filaments per kilogram are unacceptable in commercial use.

With these yarns, the operable texturing tension range is quite narrow when draw-texturing at 800 meters per minute. The maximum texturing tension is found to be about 0.43 grams per draw roll denier. The draw roll denier is defined as the spun yarn denier divided by the mechanical draw ratio provided by the different surface speeds of the feed roll feeding the yarn to the heater and of the draw or mid roll just downstream of the false-twist device. When the texturing tension is more than 0.45 grams per draw roll denier, an unacceptable level of broken filament is produced.

Properties of the textured yarns measured about 2 weeks after texturing are given in Table 1.

In the table, "Elong." means elongation in percent, while "Ten." means tenacity in grams per denier. "Stress" is the texturing tension in grams per draw roll denier. "% TAN" is the mol % of the trifunctional branching agent 4(aminomethyl)-1,8-diaminooctane (referred to herein as "TAN") incorporated in the polymer. TAN has the following structural formula: ##STR2##

A decrease in textured yarn tenacity is indicated at the highest level in Table 1 (0.125 mol %), suggesting that higher levels of branching agent may involve a reduction in tenacity below the level required by some end uses. Furthermore Item 4 above exhibits a severe bobbin crushing problem, crushing the bobbin on the winder chuck after about 10-20 minutes run time. When repeating Item 4 with no heat applied in tube 32, four hour doffs are possible without crushing the bobbin. In this case the crimp development obtained is 18%, and the textured yarn tenacity is 3.97. It is accordingly preferred to use TAN at a level of about 0.075 to about 0.10 mol %, or to apply heat in tube 32. That is, the use of TAN in this manner avoids requirements for heat conditioning.

This qualitatively illustrates the effect of PON yarn RV on crimp development in the textured yarn, both with and without a branching agent according to the present invention. Flake from modified nylon 66 polymers having different RVs and containing 0.075 mol percent TAN are spun as in Example 1 above, with the PON yarn denier selected such that the drawtextured yarn has 70 denier. The PON yarns are textured under the conditions used for Example 1 above. The textured yarns are aged on the bobbin for 2-3 weeks and the resulting crimp development is compared to similarly aged textured yarns made from conventional linear (i.e., without a branching agent) 40 RV PON and linear 65 RV PON in FIG. 2. As illustrated, the present yarns provide for greatly increased crimp development as compared to conventional 40 RV linear PON, and, with comparable RV's up to about 65 or 70, provide equivalent or somewhat higher crimp development than yarns made with high RV linear polymer. PON yarns with a branching agent and having RV's lower than about 55 or so can be spun using a conventional melt grid, and do not require a screw extruder or the like as does, for example, 65 or 70 RV PON without a branching agent.

While the above examples use TAN for exemplifying the invention, numerous other branching agents may be used. Bishexaethylene triamine is an alternative branching agent. Trimesic acid is an example of a material reactive with the amine end groups in the polymer. Any necessary adjustment in the amount of branching agent can readily be done by trial and error. Suitable branching agents generally contain three or more functional groups reactive with amine or carboxylic end groups under the conditions used for polymerizing the polymer, and generally increase the polymer RV. Alpha-amino-epsilon-caprolactam is noted as another suitable material which under polymerizing conditions has the requisite minimum number of reactive functional groups. If the branching agent contains more than three such functional groups, it may be necessary to reduce the level of branching agent significantly below those indicated above as preferred with TAN.

All yarn packages to be tested are conditioned at 21 degrees C. and 65% relative humidity for one day prior to testing.

The yarn elongation-to-break is measured one week after spinning. Fifty yards of yarn are stripped from the bobbin and discarded. Elongation-to-break is determined using an Instron tensile testing instrument. The gage length (initial length) of yarn sample between clamps on the instrument) is 25 cm., and the crosshead speed is 30 cm. per minute. The yarn is extended until it breaks. Elongation-to-break (or elongation) is defined as the increase in sample length at the time of maximum load or force (stress) applied, expressed as a percentage of the original gage length (25 cm.).

Crimp development is measured as follows. Yarn is wound at a positive tension less than 2 grams on a Suter denier reel or equivalent to provide a 11/8 meter circumference skein. The number of reel revolutions is determined by 2840/yarn denier, to the nearest revolution. This provides a skein of approximately 5680 skein denier and an initial skein length of 9/16 meter. A 14.2 gram weight or load is suspended from the skein, and the loaded skein is placed in a forced-air oven maintained at 180.degree. C. for 5 minutes. The skein is then removed from the oven and conditioned for 1 minute at room temperature with the 14.2 gram weight still suspended from the skein, at which time the skein length L.sub.2 is measured to the nearest 0.1 cm. The 14.2 gram weight is then replaced with a 650 gram weight. Thirty seconds after the 650 gram weight is applied to the skein, the skein length L.sub.3 is measured to the nearest 0.1 cm. Percentage crimp development is defined as (L.sub.3 -L.sub.2)L.sub.3 .times.100. Crimp development decreases with time as the textured yarn ages on the bobbin, rapidly for the first hours and days, then more slowly. Normalized crimp development is the ratio of the crimp development of the yarn sample to that of a 40 RV reference yarn of the same denier and denier per filament spun and textured under the same conditions as the yarn sample, with both crimp development values being determined 14 days after the yarns are textured.

Relative viscosity (RV) is determined by ASTM D789-81, using 90% formic acid.

Broken filaments are determined visually, by counting the number of broken filaments on the exposed surfaces of the package.

The reference polymer is nylon 66 formed from stoichiometric amounts of hexamethylene diamine and adipic acid, further containing as the sole additives 44 parts per million manganese hypophosphite monohydrate, 898 parts per million acetic acid as a molecular weight stabilizer and 3000 parts per million titanium dioxide pigment, all parts being parts by weight. Polymerization is conventional, to provide a nominal polymer RV of 38-40.

The reference yarn is prepared by appropriately adjusting the moisture level in the reference polymer, then spinning under the same spinning conditions as the yarn being tested to provide a 40 RV reference yarn having the same denier and denier per filament as the yarn sample being tested.

The X-ray diffraction patterns (small angle X-ray scattering, or SAXS) are recorded on NS54T Kodak no-screen medical X-ray film using evacuated flat plate Laue cameras (Statton type). Specimen to film distance is 32.0 cm.; incident beam collimator length is 3.0 inches, exposure time is 8 hours. Interchangeable Statton type yarn holders with 0.5 mm. diameter pinholes and 0.5 mm. yarn sheath thickness are used throughout as well as 0.5 mm. entrance pinholes. The filaments of each sheath of yarn are aligned parallel to one another and perpendicular to the X-ray beam. A copper fine focus X-ray tube (.lambda.=1.5418 .ANG.) is used with a nickel filter at 40 KV and 26.26 MA, 85% of their rated load. For each X-ray exposure a single film is used in the film cassette. This film is evaluated on a scanning P-1000 Obtronics Densitometer for information concerning scattering intensity and discrete scattering distribution characteristics in the equatorial and meridional directions. A curve fitting procedure, using Pearson VII functions [see M. H. Heuvel and R. Huisman, J. Appl. Poly. Sci., 22, 2229-2243 (1978)] together with a second order polynomial background function, is used to fit the experimental data prior to calculation. A meridional scan is performed, the discrete scattering fitted, equatorial scans are performed through each discrete scattering maxima and then again the data is fitted via a parameter fit procedure.

The peak height intensity is taken as an average of the four fitted intensity distributions (i.e., the two mirrored discrete scattering distributions in the meridional directions and the two equatorial distributions through these meridional maxima). The normalized SAXS peak intensity is then simply the ratio of the measured peak intensity to that of the measured peak intensity of a 40 RV reference yarn of the same denier and denier per filament spun under the same conditions.

The SAXS discrete scattering X-ray diffraction maxima are used to determine the average lamellar dimensions. In the meridional direction this is taken here to be the average size of the lamellar scattered in the fiber direction and in the equatorial direction, the average size of the lamellar scattered in a direction perpendicular to the fiber direction. These sizes are estimated from the breadth of the diffraction maxima using Scherrer's method,

where K is the shape factor depending on the way .beta. is determined, as discussed below, .lambda. is the X-ray wave length, in this case 1.5418 .ANG., .theta. is the Bragg angle, and .beta. the spot width of the discrete scattering in radians,

where

r=the fiber to film distance 320 mm.

w=the corrected half width of the scattering as discussed below

HW=peak to peak distance (mm.) between discrete scattering maxima

The Scherrer equation is again used to calculate the size of the lamellar scattered in the equatorial direction through the discrete scattering maxima,

where

Warren's correction for line broadening due to instrumental effects is used as a correction for Scherrer's line broadening equation,

where W.sub.m is the measured line width, W=0.39 mm. is the instrumental contribution obtained from inorganic standards, and w is the corrected line width (either in the equatorial or meridional directions) used to calculate the spot width in radians, .beta.. The measured line width (W.sub.m is taken as the width at which the diffraction intensity on a given film falls to a value of one-half the maximum intensity and is the half width parameter of the curve fitting procedure. Correspondingly, a value of 0.90 is employed for the shape factor K in Scherrer's equations. Any broadening due to variation of periodicity is neglected.

The lamellar dimensional product is given then by

and the normalized lamellar dimensional product is then simply the ratio of the lamellar dimensional product to that of a 40 RV reference yarn of the same denier and denier per filament spun under the same conditions.