IL32862A - A continuous polyamide filament yarn having high elongation and high tenacity and process for producing the same - Google Patents

Description

mantmn ^pa T-PPK^IBP nn ¾p»3 rrnop ww» Vwm an mini nn ax A CONTINUOUS POLYAMIDE FILAMENT YARN HAVING HIGH ELONGATION AND HIGH TENACITY AND PROCESS FOR PRODUCING SAME Elongation of high tenacity yarn is increased by heating the yarn to a temperature between 180° and 235 eC, while under a tension between 0.05 and 0.35 grams per denier, for a period of 0.003 to 0.15 seconds.

The invention relates to a high tenacity yarn having a high elongation, and to a process for making such yarn. The yarn is particularly suitable for use in tire construction.

Present known polyamide tire yarns have tenacities of approximately 8.8 - 9.3 grams per denier and elongations of about 12.1 - 17.3%, the higher tenacities corresponding generally to lower elongations. A minimum acceptable tenacity is about 8.5 grams per denier. Somewhat higher tenacities can be produced by increasing the draw ratio, but this is at the expense of a corresponding decrease in elongation in the usual process. Tire makers poly-twist the yarn to make tire cord, and then hot stretch or "tensilize" the cord. A high elongation is desirable since it renders the yarn and tire cord more resistant to impact breaks, as well as affording more efficient use of the expensive hot stretching apparatus.

Elongation of a drawn yarn is a measure of the degree to which the yarn can be stretched before it breaks, and is the length by which the yarn can be stretched divided by the original drawn length of the yarn. Thus, if a yarn of unit length can be stretched to a length of 1.20 units before breaking, the elongation is 0.20.

Merely increasing either tenacity or elongation, while suffering a corresponding decrease in the other, does high values. A more useful indication of yarn desirability than either of these properties considered alone is their product. Thus, in a yarn having a tenacity of 9.3 grams and an elongation of 0.17, the product would be 1.58. Substantially improved properties are achieved when the tenacity-elongation product is at least 1.65, and preferably at least 1.70, provided that the tenacity is at least 8,5 grams per denier.

Applicants have- discovered that elongation can be substantially increased by subjecting the yarn to a specified temperature range while the yarn is under certain tensions, for specified time lengths, as is more fully disclosed below, and that this increased elongation can be attained with little if any loss in tenacity.

Accordingly a primary object of the invention is to provide a high tenacity yarn having unusually high elongation.

A further object is to provide a yarn of the above character wherein the product of tenacity and elongation values are greater than L65, whereby improved yarn · properties are achieved.

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

* For a more complete understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, wherein the FIGURE is a simplified perspective view of exemplary yarn drawing apparatus incorporating is fed to drawing apparatus 22 which draws the yarn and orients the molecules therein. The drawn yarn is next passed over and in thermal contact with a heated element illustrated as plate 24 to increase its elongation, and then is collected in an orderly fashion by means illustrated as a conventional twister takeup mechanism 26 including the usual ring and traveller.

Referring more specifically to the FIGURE, nip rolls 28 feed yarn 20 at a predetermined rate. Yam 20 next passes in one.or more wraps about fixed draw pin 30 and across a fixed heater block 32 positioned below draw pin 30 in the zone of high tension between draw pin 30 and draw roll 34. Yarn 20 slides across the surface of plate 32 and then in a plurality of wraps about draw roll 34 and its associated freely rotatable separator roll 36. The peripheral speed of draw roll 34 is selected to draw yarn 20 to a tenacity of at least 8.5 grams per denier. Drawing apparatus 22 as thus far specifically described is conventional.

According to the invention, yarn 20 next contacts hot plate 24 while under reduced tension. Yarn 20 next passes over guide roll 38 and through pigtail guide 40 to apparatus 26 where it is wound on bobbin 42. The size and temperature of plate 24 are selected in accordance with the speed of yarn 20 so that yarn 20 is exposed to between 180 β and 235 °C. for a period between 0.003 and 0.15 seconds, while the yarn is under a tension between 0.05 and 0.35 grams per denier. relative viscosity of 73, as determined by ASTM method D-789-53T. Using the illustrated apparatus, the relative speeds of nip rolls 28 and draw roll 34 were selected to provide a draw ratio of 5.2 t 1 when roll 34 had a peripheral speed of 280 yards (255 meters) per minute. Block 32 was maintained at 190eC. , and was 1.5 inches (3.8 cms) long in the path contacted by the yarn. Ceramic pin 30 was 0.75 inch (1.91 cms) in diameter and was heated by yarn friction to about 100 °C. Block 24 extended 6.5 inches (16.5 cms) along the yarn path, and was maintained at 210ec. The yarn tension while contacting block 24 was 0.14 grams per denier, and was substantially the same as the tension between roll 38 and pigtail guide 40.

Ring 44 was traversed back and forth parallel to the axis of bobbin 42 between limits which converge as a function of time, as generally illustrated in FIGURE 9 of U. S. Patent 2,764,363. Such a package construction is called "warp-wound", and is desirable in providing relatively uniform wind-on tension.

The tension on the yarn contacting block 24 can be maintained at a value within the tension range specified above by selection of traveller weight and shape, and spindle x.p.m. If necessary, the spindle r.p.m. can be decreased as the bob-, bin diameter increases, to keep the tension within the desired range. In this specific example, spindle r.p.m. is linearly decreased from 3150 r^p.m. at startup to 2700 r.p.m. at doff, maintaining uniform tension of 125 grams on the 840 drawn denier, 140 filament yarn. process as compared to a control yarn made the same process but without block 24 are as follows; Yarn Tenacity, g.p.d. Elongation Product Control 9.05 0.157 1.42 A 9.15 0.190 1.74 B 9.10 .193 1.75 C 8.88 .196 1.74 D 9.06 .182 1.65 E 9.90 .181 1.79 P 8.84 .193 1.71 G 8.82 .187 1.65 H 8.73 .204 1.76 The yarns prepared according to the present process have substantially higher impact strength than do yarns such as the control yarn having a tenacity-elongation product of less than about 1.65, and permit more efficient use of the hot-stretching apparatus. Those yarns having a tenacity-elongation product greater than 1.70 are particularly advantageous.

The terms "tenacity" and "elongation" as used in the specification and claims refer to breaking tenacity and breaking elongation as determined by ASTM test method D-2256, using a constant rate of elongation testing machine as set forth therein..

Other drawing apparatus and string-ups can be used to provide the drawn yarn which is fed to hot plate 24. For example, the undrawn yarn can be supplied directly from the more stages as desired, with or without use of a hot block such as 32 in the draw zone. However, the configuration illustrated in the FIGURE is preferred for its simplicity. Similarly, although the warp wound package is preferred because of its uniformity of winding tension, other package constructions could be used, including packages wound without twisting. Advantageously, nip rolls or a driven roll with cooperating separator roll could be added between the takeup mechanism 26 and plate 24, to isolate the yarn contacting plate 24 from tension variations originating in takeup mechanism 26. The inertia of roll 38 performs this isolation function to a sufficient extent in the illustrated preferred embodiment.

Claims (4)

WHAT IS CLAIMED IS:

1. A continuous polyamide filament yarn having at least 500 denier, characterised by a tenacity of at least 8.5 grams per denier, and an elongation such that the product of tenacity and elongation equals at least 1.65.

2. A process for producing high tenacity polyamide yarn having high elongation, characterised by: (a) drawing said yarn to a tenacity of at least 8.5 grams per denier, (b) reducing the tension on said yarn to a level between 0.05 and 0.35 grams per denier, (c) subjecting said yarn while at said reduced tension level to a temperature between 180° and 235°C. for a period between 0.003 and 0.15 seconds, and (d) collecting said yarn in an orderly fashion.

3. A process for producing high tenacity polyamide yarn having high elongation, substantially as hereinbefore described.

4. Continuous polyamide filament yarn as defined in Claim 1, whenever obtained by a process as claimed in Claims 2 or 3.