Process and apparatus for producing thick and thin filaments

A process and apparatus for producing thick and thin filaments wherein the deniers of the thick portions of the filaments are randomized by passing an undrawn nylon feed yarn from a supply package under tension through the nip in a feed/cott roll combination, the cott roll having at least one peripheral slot periodically opening the nip. The yarn is forwarded from this nip by a draw roll assembly operated at a peripheral velocity of 3-5X that of the feed roll to fully draw the drawn portions. A snubbing device is used upstream of the feed/cott roll assembly to provide a yarn tension immediately upstream of the nip.

BACKGROUND OF THE INVENTION 
This invention relates to the production of yarns having thick and thin 
sections. More particularly it relates to process and apparatus for 
preparing nylon filament yarns having thick and thin sections. 
The production of thick and thin yarns is known in the art. For example, 
Nicita et al., U.S. Pat. No. 3,491,418, utilizes a cott roll with a 
plurality of series of slots of different length and traverses the yarn 
across this series. The thin (fully drawn) portions of each filament have 
substantially constant denier and the same is true for the thick (undrawn 
or partially drawn) portions. In order to avoid patterning when these 
yarns are used in textile fabrics a randomness of the alternating thick 
and thin filaments is required. The randomness apparently obtained by 
Nicita et al. is a variation in lengths of the thick and the thin 
sections. 
SUMMARY OF THE INVENTION 
It has now been found that an improvement in the randomness obtained by the 
prior art can be obtained by randomly varying the denier of the thick 
sections of the thick and thin yarns thus avoiding patterning in textile 
fabrics without having to provide a variation in the lengths of the thick 
and thin sections. The process includes the steps of passing an undrawn 
nylon feed yarn from a supply package while under tension into the nip of 
a feed roll assembly comprising rotating driven feed and presser rolls, 
the presser roll having at least one peripheral slot periodically opening 
the nip whereby the presser and feed rolls intermittently engage the yarn 
between them and forward it then release the yarn when the slot is over 
the filament. The filament is continuously removed from the nip under 
tension by a draw roll assembly operated at a peripheral velocity of 3-5X 
that of the feed roll assembly to fully draw the drawn portions and then 
collected. The yarn passes only once through the nip along a path 
substantially tangential to the feed roll surfaces. Both entering and 
leaving the nip the filament is in a single plane. A snubbing device is 
used upstream of the feed roll assembly to provide yarn tension 
immediately upstream of the nip which is in the range of from 0.005 to 
about 0.015 grams per denier based on the denier of the undrawn yarn or 
filament. The yarn is also snubbed between the feed and draw rolls for 
localizing the draw point.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawings show a yarn 10 being withdrawn from a supply package 12 
through a pigtail guide 14 and around a snub guide 16 to the feed roll 
assembly comprising feed roll 18 and cott or presser roll 20. The feed 
roll 18 is driven in the direction shown by the arrow by a conventional 
drive means (not shown). The presser roll 20 is provided with a slot 22 
and is driven by engagement with roll 18. 
Slot 22 of presser roll 20 is shown more clearly in FIG. 2. It extends 
along the surface of the presser roll from about 10% to about 40% of the 
circumference and allows the yarn to deliver directly with nip disengaged 
from the friction guide 16 to draw pin 24 with negligible contact and 
friction when it is over the yarn in the nip. At other times the presser 
roll is pressing against the feed roll and engages the yarn passing 
through the nip. The yarn then slows to feed roll speed and is drawn. Yarn 
10 passing from the tangency of the rolls 18 and 20 then passes over a 
draw pin 24 to draw roll 26 and over associated idler roll 28. Yarn 10 
leaving draw roll passes through a guide 30 and then on to windup 
mechanism 32 and package 34. 
Operation of this process with a given cake of undrawn yarn provides a 
drawn thick/thin yarn which varies in skein denier over a limited but 
definite range. Since the thin portions have substantially constant denier 
the variation is attributable to variation in deniers of the thick 
portions both within a package and among packages. 
While the invention applies equally to monofilament and multifilament yarns 
and may be superimposed on alternate length randomness of the prior art, 
it is best exemplified by using a 6,6 nylon filament for which nip 
disengagement times producing thick sections alternate with nip engagement 
times producing thin sections with the nip engagement times being greater 
than the nip disengagement times. 
The monofilament feed yarn is generally from 100 to 200 denier filament. 
The tension guide 16 may be of a pin variety. However, it is preferred 
that it be of such configuration as to contain the filament 10. The 
presser roll 20 may have a rubber surface while the feed roll may have a 
metal surface. The draw ratio will, of course, be determined by the 
respective speeds of the draw and feed rolls. For this process and with 
nylon 6,6 it will generally range from about 3.2 to 5. The degree to which 
the thick portions become drawn has been found to vary substantially all 
the way from essentially undrawn to almost completely drawn. 
EXAMPLE 
A 6,6 nylon flake having a RV of 36 is used to spin a monofilament. RV is 
solution-to-solvent ratio of absolute viscosities at 25.degree. C when the 
solvent is aqueous 90% formic acid and the solution has 8.4% by weight 
polymer. The monofilament is spun at 276 .+-. 2 yd/min (252 .+-. 2 m/min) 
and wound onto spin cakes containing about 2.4 lb (1.1 kg) of undrawn 
monofilament. Denier of the undrawn monofilament is about 111. 
The undrawn monofilament on its package is stocked on a creel and processed 
substantially as shown in FIG. 1. Because the feed action is so erratic, 
the spin bobbin is mounted in a loosely fitting can with an Alsimag eyelet 
guide, i.e., 14, for its exit opening. Then the yarn makes 1.25 turns 
around the snubbing guide 16 which is a 3/4-inch (1.9 cm) diameter 
cylindrical guide with 30-40 .mu. AA surface roughness, with discs at 
each end to prevent loss of yarn and with a post of guide material 
extending from the middle of the cylindrical guide for separating 
individual wraps. The post is located 10 degrees from vertical. The yarn 
then tangentially enters and leaves the nip between the driven feed roll 
18 and follower cott roll 20. The cott-roll 20 is a hard-rubber roll 
3-7/16-inch (8.73 cm) in diameter. It has a one-inch (2.54 cm) wide slot 
centered on its face to remove 1/8 of the roll circumference. Between the 
snubbing guide and the feed-roll, another Alsimag eyelet guide 17 is 
positioned to make sure the yarn enters the nip tangentially. Departing 
the nip, the yarn makes two wraps around a cylindrical 0.195 inch (0.495 
cm) diameter draw pin 24 with an AA surface roughness of 20-30 .mu.. At 
least one wrap is required both for localizing the draw point and for 
isolating the drawing tension from the feed/cott roll assembly. Peripheral 
velocity of the draw roll is 701 yd/min (641 m/min) to provide a draw 
ratio (for the fully drawn segments) of 4.285X. The drawn thick-thin 
monofilament is wound onto pirns using a standard ring-and-traveller 
windup. 
FIG. 3 represents 1483 separate denier determinations of random samples 
taken from the yarn produced during a prolonged test under the above 
conditions. The denier ranged from a minimum of 26.6 to a maximum of 44.5. 
The mean denier was about 36. 
Skein denier is determined by weighing a 90 meter length of yarn then 
converting to the weight in grams of 9000 meters.