Process for steam-conditioning spin-oriented polyamide filaments

An improved high-speed spinning process for making steam-conditioned partially-oriented polyamide draw-texturing feed yarns involves controlling the wall temperature of the lower portion of a steam conditioning tube independently of the steam flow and temperature in the upper tube.

TECHNICAL FIELD 
This invention relates to an improved process for conditioning 
partially-oriented polyamide filaments with steam while being spun at high 
speed. More particularly, it relates to such a process which provides 
improved control of filament dyeability within predetermined limits. 
BACKGROUND 
U.S. Pat. No. 3,994,121 (Adams) discloses a process for making filaments of 
poly(hexamethylene adipamide) having a birefringence of at least 0.040 by 
withdrawing the filaments from the spinneret at a high spinning speed and 
conditioning the freshly cooled filaments with steam to increase their 
thermal shrinkage and to improve their package-forming characteristics 
prior to being wound up. The acid dyeability of filaments spun in this 
manner can be quite sensitive to the steaming conditions. Consequently, 
when steaming conditions change, such as in order to provide a desired 
draw-tension, boil-off shrinkage, or improved package formation, the acid 
dyeability of the filaments also can change resulting in a need to 
segregate products where dye mergeability is critical. In general, as the 
degree of steaming is increased, the acid dyeability of the filaments 
increases. 
U.S. Pat. No. 4,181,697 (Koschinek et al.) teaches a similar high-speed 
spinning process wherein the filaments are heat-treated under specified 
conditions in a steamless spinning duct prior to being wound. Such a 
process provides for no control of acid-dyeability independently of the 
heating conditions required for other yarn properties such as package 
stability. 
Partially oriented polyamide yarns made by either of the above processes 
are especially useful as draw-texturing feed yarns in the trade. 
Improvements in draw-texturing apparatuses are continually being made to 
permit them to operate at higher speeds which provide economies in 
overhead and operating expenses. Consequently, there is an accompanying 
demand for improved yarns which operate satisfactorily at these higher 
processing speeds in order to take advantage of the apparatus 
improvements. Important in this regard are uniformity improvements in yarn 
drawing tension and package formation, especially with regard to larger 
packages, while maintaining a uniform dyeability. 
Consequently, an object of this invention is a process which facilitates 
the uniform preparation of partially-oriented draw-texturing polyamide 
feed yarns within predetermined limits of yarn properties such as 
draw-tension and packageability independently of acid dyeability.

DESCRIPTION OF THE INVENTION 
This invention provides an improved high-speed spinning process for making 
partially oriented polyamide draw-texturing feed yarns within 
predetermined standards including the steps of extruding molten filaments 
of a synthetic fiber-forming polyamide from a spinneret assembly, cooling 
the molten filaments to a non-tacky state in a quench chimney, 
conditioning the cooled filaments with steam by passage through a 
substantially vertical conditioning tube having heated upper and lower 
inner wall portions, introducing steam into the tube within its heated 
upper wall portion and winding up the conditioned filaments under tension 
into a yarn package at a speed of from 3000 to 4000 ypm (2743 to 3658 mpm) 
wherein the improvement comprises regulating the temperature of the lower 
heated wall portion independently of the upper steam-heated portion to 
maintain yarn properties that vary with changes in the lower heated wall 
portion, within predetermined limits while maintaining steam flow in the 
tube substantially constant whereby the acid dyeability of the yarn 
remains substantially unchanged. 
The invention is particularly effective with respect to yarns of aliphatic 
polycarbonamides, commonly called nylon, such as poly(epsilon-caproamide) 
and poly(hexamethylene adipamide) and especially the latter because of its 
importance to the textured yarn hosiery industry. 
The upper wall portion of the conditioner can be heated conveniently, as is 
known, with a superatmospheric steam supply which surrounds and heats the 
upper wall portion and provides a source of steam into the tube by means 
of an appropriately sized orifice or orifices leading into the tube 
through a plug in its heated wall. The lower wall may be heated most 
conveniently by an electrical heating element or elements with a 
conventional temperature control means. 
For the preparation of conventional low denier hosiery yarns suitable rates 
of steam flow in the conditioning tube have been found within the range of 
from 0.25 to 1.25 lbs. per hour (113.4-567 gm/hr.) with lower wall 
temperatures appropriately selected within the range of 60.degree. to 
115.degree. C. 
A preferred conditioning tube is comprised of an upper wall portion 
conventionally heated by a superatmospheric steam jacket about 20 inches 
(0.508 m) long and a total tube length of about 6.5 feet (1.98 m), with 
the length below the steam jacket being wrapped with an electrical heating 
element. Steam can be introduced into the tube by means of an orifice in a 
replaceable plug in the tube wall between the steam jacket and the tube 
interior with steam flow being regulated by the size of the orifice. The 
orifice suitably can have a diameter of from about 0.028 to 0.040 inch 
(7.1.times.10.sup.-4 to 1.02.times.10.sup.-3 m) with a steam supply 
maintained at a pressure of about 7.5 psig (51.7 kPa gauge). 
The process of this invention is especially useful for regulating yarn 
draw-tension and/or yarn package bulge within predetermined limits 
independently of the MBB acid dyeability of the yarn. The need for such 
control can come about through normal process changes which can accompany 
a change in spinning speed, an increase in yarn package size, and so forth 
for higher productivity. With this invention such changes can be 
accommodated while maintaining yarn dyeability within acceptable limits 
and thereby maintaining its dye mergeability with other yarns. 
TEST METHODS 
Draw tension is a function of the level of molecular orientation and 
crystallinity which relate to physical properties of a yarn. These 
physical properties relate not only to how the yarn will process during 
later operations, such as in texturing, but also to properties of the 
textured yarn and characteristics of fabrics made therefrom. Draw tension 
is measured using the apparatus described in U.S. Pat. No. 4,295,360. The 
yarn is drawn 1.33.times.; feed roll surface velocity is 200 ypm (182.88 
mpm) and heater temperature is 185.degree. C. 
Package bulge is a measure of non-uniformity of a package of yarn. Package 
bulge is the extent that yarn bulges or protrudes from the package 
shoulder. The yarn package consists of the yarn wound onto a 2.5" 
(6.35.times.10.sup.-2 m) cylindrical rigid paper core. The package surface 
forms essentially a right cylinder having a diameter of 5.25 inches 
(0.13335 m). A straightedge is positioned along the package shoulder 
normal to the package axis of rotation. The axial distance in inches 
between the point the yarn touches the straightedge (the tip of the bulge) 
and the normal package shoulder (unbulged yarn) is the "Package Bulge". A 
package bulge of up to 1/16 inch (1.5875.times.10.sup.-3 m) is acceptable 
while a bulge of greater value than 4/16 inch (6.35.times.10.sup.-3 m) is 
intolerable causing such handling and processing difficulties that the 
package has to be put to waste. 
For MBB dye testing in the following example yarn samples are prepared by 
loosely winding 3.00 gram skeins. Thirty-six of these skeins, consisting 
of 6 control samples and 30 test samples, are scoured by immersing them in 
a vessel containing 21 liters of room temperature scouring solution 
comprised of 160 ml ammonium hydroxide, 100 ml 10% Merpol HCS, (a liquid, 
non-ionic detergent from E. I. du Pont de Nemours and Co.), with the 
remainder of the solution being demineralized water. This bath has a pH of 
10.4. The bath containing the yarn samples is heated to 95.degree. C. at 
the rate of 3.degree. per minute. The samples are removed and the bath 
discarded when the temperature reaches 95.degree. C. 
The yarns are then dyed by placing the 36 samples in 21 liters of an 
aqueous dye solution comprised of 200 ml of a standard buffer solution at 
3.8 pH, 100 ml of 10% Merpol HCS (a liquid, nonionic detergent from E. I. 
du Pont de Nemours and Co.), 5 ml Depuma (a silicone defoaming agent), and 
500 ml of 0.18% Anthraquinone Milling Blue BL (abbreviated MBB) (C.I. Acid 
Blue 122). The final bath pH is 4.4. The solution temperature is increased 
at 3.degree./min from room temperature to 75.degree. C., and held at that 
temperature for 30 minutes. The dyed samples are rinsed, dried, and 
measured for dye depth by reflecting colorimeter. 
The dye values are determined by computing K/S values from reflectance 
readings. The equations are: 
##EQU1## 
when R=the reflectance value. The 180 value is used to adjust and 
normalize the control sample dyeability to a known base. 
EXAMPLE 
This example tests yarn responses to changes in steam flow and in lower 
wall temperatures of a conditioning process for partially-oriented 
draw-texturing feed yarns of poly(hexamethylene adipamide) made according 
to this invention. 
The yarns are spun using the process as represented by FIG. 1. In reference 
to FIG. 1, filaments 10 are extruded from spinneret assembly 20 into 
quench chimney 30 and are cross-flow quenched by room temperature air 
(flowing from right to left as represented). After cooling to a non-tacky 
state, the filaments are converged into a yarn by guide 40, passed through 
steam-conditioner tube 50, through guide 60 and over finish roller 70 
which is immersed in finish bath 80. Yarn 10 then passes through guide 90, 
wraps around high-speed puller roll 100 and associated roller 110 and is 
wound up as package 120. Steam-conditioner tube 50 is comprised of an 
upper portion surrounded by a steam jacket 52 having a steam inlet 54 and 
steam outlet 56 for steam maintained at a superatmospheric pressure. Steam 
also flows from steam jacket 52 into the inside of the conditioning tube 
through an orifice which is located in a replaceable plug (not shown) in 
the upper tube wall. The lower portion of tube 50 is heated by electrical 
heating element 58 which is wrapped around the tube in a helical manner. 
The temperature of heating element 58 is controlled by means of a 
conventional temperature controller 59. The steam-jacketed section of the 
tube is 20 inches (0.508 m) long and the electrically heated lower portion 
is 6 feet (1.83 m) long. Such an apparatus arrangement makes it possible 
to investigate the effects of steam flow and lower conditioner wall 
temperatures independently of one another. The pressure of the steam 
supply is maintained at 7.5 psig (51.7 kPa gauge) and flow of steam into 
the tube is controlled by replacing the orifice through the tube wall. 
The yarns are wound up using a single cam windup, a helix angle of 
8.5.degree. and a windup speed of 3500 ypm (2200 mpm). 
The yarns are spun under otherwise substantially conventional conditions 
selected to provide a yarn of 27 denier (30 dtex) containing 7 filaments. 
Yarns are made with no steam and with three different steam flow rates, 
each at four different lower wall temperatures. The different flow rates 
are obtained using no steam orifice, a single orifice of 0.028 inch 
(7.1.times.10.sup.-4 m) diameter, a single orifice of 0.040 inch diameter, 
and two orifices of 0.040 inch (1.02.times.10.sup.-3 m) diameter which 
provide flow rates respectively of 0.00, 0.26, 0.57, and 1.14 lbs/hr 
(0.118, 0.259, 0.517 kg/hr) of steam. The four lower wall temperatures are 
60.degree., 79.degree., 96.degree., and 115.degree. C. 
Yarn responses of MBB acid dye level, draw-tension, package bulge, are 
obtained as represented in FIGS. 2-4. 
From these results it is apparent that draw-tension responds both to steam 
flow and lower wall temperature. Changes in lower wall temperature cause a 
larger response at lower steam flow rates. MBB dye level responds 
surprisingly substantially only to steam flow rate; i.e., changes in the 
lower wall temperature cause substantially no MBB dye level change. 
Package bulge responds to both steam flow and lower wall temperature. A 
100% reduction in bulge can be obtained with less than 1 gram change in 
draw tension by a reduction in lower wall temperature without changing MBB 
dye level. 
Independently controlling the lower conditioner wall temperature is a novel 
way to adjust package bulge and draw-tension variations without affecting 
MBB dye level. Process problems associated with changes in package bulge 
caused by draw-tension shifts during manufacture can be returned to 
predetermined limits by small changes in conditioner wall temperature on a 
machine or position basis. Electrical wall temperature control can be 
varied infinitely and variable more conveniently versus the conventional 
step changes in steam flow through changing the orifice diameter.