Process for melt spinning a plurality of eccentric sheath-core filaments

The sticking between an array of melt spun eccentric bicomponent filaments converged together into yarn is avoided by selecting the filaments being converged so that the thin sheath regions of the filaments do not contact one another and conducting the convergence in two steps if the number of filaments required for the yarn is too great for convergence in one step while avoiding the aforesaid contact.

BACKGROUND OF THE INVENTION 
This invention is directed to a process of melt spinning eccentric 
bicomponent filaments. 
Eccentric bicomponent filaments have the property of self-crimpability, by 
virtue of the differential between the shrinkage of the two components of 
the filament. This property is useful in textiles for making stretch 
fabrics such as hosiery. Preferably, one component is eccentrically 
disposed entirely within the other component, whereby the first-mentioned 
component is the core component and the other component is the sheath 
component, such a shown in FIG. 5 of U.S. Pat. No. 3,244,785. This 
surrounds the lower melting core component with the higher melting sheath 
component to prevent the filaments from sticking together when converged 
after melt spinning. Because of the eccentric disposition of the core 
within the sheath, the sheath has a cross section that varies from a thin 
region to a thick region relative to one another. 
U.S. Pat. No. 3,244,785 discloses a process for making an eccentric 
sheath-core filament by first forming a concentric arrangement of a core 
of one molten polymeric component in a sheath of another molten polymeric 
component, and while this concentric arrangement is still in molten form, 
injecting additional molten sheath polymeric component along one side of 
the concentric arrangement to force the core polymeric component to an 
eccentric position within the sheath. A row of the eccentric bicomponent 
filaments is melt spun and gas quenched during convergence (bringing 
together) of the filaments into yarn, and then the yarn is wound into a 
package. Between convergence and windup, the filaments can be treated, 
such as with steam, for dimensional stabilization. The yarn is then cold 
drawn at least about 4X and then heated at as low tension as possible to 
precrimp the yarn, followed by stretching to temporarily suppress the 
crimp and then making a fabric out of the yarn. In the case of the special 
filament compositions disclosed in Segraves and Mulholland, U.S. Pat. 
application Ser. No. 581,158, filed May 27, 1975 (Belgian Pat. No. 
831,930), the cold drawn yarn can be made into the fabric directly, i.e., 
without precrimping, and then the fabric can be heated to develop the 
crimp for the first time. 
U.S. Pat. No. 3,535,844 discloses a spinneret assembly for melt spinning a 
pair of rows of the sheath-core eccentric filaments of the type disclosed 
in U.S. Pat. No. 3,244,785, to thereby increase melt spinning capacity 
without undesirable crowding of the filaments and without increasing 
spinneret size. This is done by alternating the direction of the passages 
for injecting the sheath polymer along the side of the concentric 
sheath-core arrangement. The resultant filaments are spun with the thin 
sheath regions oriented to face the quench gas flow in one row and to face 
the opposite direction in the other row. 
U.S. Pat. No. 3,704,971 discloses a spinneret assembly which doubles the 
production capacity of the spinneret assembly of U.S. Pat. No. 3,535,844 
by providing a second pair of rows of orifices for melt spinning the 
filaments, with the orientation of the thin sheath regions of the 
filaments in this second pair of rows being a repetition of the opposite 
facing arrangement of U.S. Pat. No. 3,535,844 in the first pair of rows. 
In the embodiment shown in the patent, the distance between the pairs of 
rows is greater than the distance between the rows in each pair. 
The spinneret assembly of U.S. Pat. No. 3,704,971 has operated 
satisfactorily to produce 18 denier yarn composed of eight eccentric 
sheath-core filaments (5.85 dpf as spun) converged together in a single 
step from two orifices in each of the four rows of orifices. When the 
spinneret assembly was used to make 17-3 yarn (22.3 dpf as spun), by 
grouping two adjacent filaments from one row with another filament from 
the adjacent row of the same pair of rows, the filaments randomly stuck to 
one another in the yarn converged therefrom. These stuck together portions 
would not crimp adequately, and the resultant poorly crimped portions 
caused appearance defects in fabric made therefrom. This sticking problem 
was unpredictable in the sense that sometimes it occurred under a given 
set of operating conditions, e.g., melt (spinning) temperature, windup 
rate, quench air temperature and velocity, and convergence guide friction, 
all of which affect the condition of the filament at convergence into a 
bundle, and sometimes the sticking did not occur. Summary of the Present 
Invention 
The present invention involves the discovery that this sticking of 
filaments together occurs only when the thin sheath region of one filament 
comes into contact with the thin sheath region of another filament during 
convergence, despite the fact that the entire outer surface of each 
filament is of the same sheath polymer. This sticking occurs under the 
same operating conditions as when sticking does not occur upon contact 
between the thin sheath region of one filament with the thick sheath 
region of another filament or between two thick sheath regions. 
Consequently, the present invention involves the selection of filaments 
from an array of melt spun filaments for convergence into bundles in which 
contact betwen thin sheath regions during convergence does not occur. 
More specifically, the process of the present invention arises in the 
process of melt spinning a plurality of filaments each having a core 
component eccentrically disposed within a sheath component, the 
eccentricity of the core component within the sheath component providing 
the sheath component with a cross section varying from a thin region to a 
thick region relative to one another, gas quenching said filaments and 
converging said filaments together into yarn, wherein the converged 
together filaments randomly stick together, the improvement comprising 
selecting the filaments to be converged into said yarn to avoid contact 
between the thin sheath regions of the filaments during convergence, the 
number of filaments required for said yarn being at least three and 
requiring the convergence into at least one bundle to avoid said contact, 
said one bundle being said yarn when the number of filaments therein is 
equal to the number required for said yarn, and when more than one bundle 
is formed by said convergence to obtain avoidance of said contact, 
converging the resultant bundles together into said yarn, whereby the thin 
sheath regions of the filaments in said yarn do not stick together. 
The selection of the filaments and the number of bundles formed from the 
filaments for subsequent convergence into the yarn will depend on the 
number of filaments required for the yarn and on the thin sheath 
orientation of the filaments in the array of filaments being melt spun. 
For example, with proper selection of filaments from the array, a three 
filament yarn will require only one convergence step into the yarn. On the 
other hand, a seven filament yarn will require convergence first into 
bundles of the desired number of filaments in each, wherein thin-sheath to 
thin-sheath contact during convergence is avoided, followed by convergence 
of the bundles into the yarn. The solution to the problem provided by the 
present invention does not involve expensive reconstruction of equipment 
such as the quench chimney and does not require any sacrifice in 
production capacity. This solution also eliminates the sensitivity of 
filament-to-filament sticking to slight and sometimes undetected changes 
in the above described operating conditions. The sticking of melt spun 
filaments together is in essence a condition of overcrowding. The present 
invention alleviates this overcrowding without requiring an increase in 
spinneret size.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an eccentric bicomponent filament 2 in which a core 4 of one 
component of the filament is eccentrically disposed, e.g., in the D-shaped 
cross section shown, within a sheath 6 of the other component of the 
filament. Because of the eccentric disposition of the core 4 within the 
sheath 6, the cross section of the sheath varies from a thin region 8 to a 
thick region 10 relative to one another. The thin region 8 preferably has 
a thickness of only about 1% of the filament diameter. 
In FIG. 2 a multiplicity of filaments each like that of FIG. 1 are melt 
spun and converged in a method which does not avoid filaments sticking 
together, such method therefore not being within the process of the 
present invention. More specifically, from a spinneret assembly 12 like 
that of U.S. Pat. No. 3,704,971 are melt spun four rows of eccentric 
bicomponent filaments, the first row represented for purposes of 
simplicity and clarity by filaments 14 and 16, the second row by filament 
18, the third row by filament 20, and the fourth row by filaments 22 and 
24. As in U.S. Pat. No. 3,704,971, the orientation of the eccentric core 
and thus the thin-sheath regions in the melt spun filaments is as follows: 
first and third row, facing the quench gas flow; second and fourth row, 
facing away from the quench gas flow. This orientation is the same as 
shown in FIG. 5. The first and second and the third and fourth rows form 
two pairs of rows of orifices and filaments spun therefrom, with the 
distance between these two pairs of rows being greater than the distance 
between the rows in each pair. 
The filaments pass through a quench chimney 26 where they are converged, 
cooled and solidified from the molten condition to nonsticky state by cool 
gas, which is usually air, flowing in the cross direction indicated by 
arrows in the drawing. While the filaments are depicted as straight lines 
passing through the quench chimney, the filaments are in fact undergoing 
some random lateral movement during convergence, due to such influences as 
velocity variations in the quench gas striking the filaments. During 
passage through the quench chimney 26, the six filaments shown are 
converged between the fingers of a convergence guide 28 to form two yarns 
30 and 32. The yarns are passed through a steam chamber 33 for dimensional 
stabilization and are then wound onto their respective packages 34 and 36. 
As shown in FIG. 2, yarn 30 is made from filaments 14, 16, and 18 which are 
melt spun from adjacent rows of orifices in the spinneret plate and yarn 
32 is made from filaments 20, 22, and 24 which are also melt spun from 
adjacent rows of orifices. The filaments 22 and 24 are melt spun from 
adjacent orifices in the fourth row and the filaments 14 and 16 are melt 
spun from adjacent orifices in the first row of orifices. The filaments 20 
and 18 are melt spun from orifices that lie between the aforementioned 
adjacent orifices, respectively. The result of this approach used to make 
the 17-3 yarn hereinbefore described has been unpredictable random 
sticking of filaments together when converged into their respective yarns, 
particularly when the as-spun denier of the filaments exceeded about 10 
dpf. This sticking has occurred because filaments 14 and 16 of yarn 30 are 
adjacent in the same row and have the same thin-sheath region orientation, 
and during convergence, the resultant random lateral movement of the 
filaments leads to side-by-side contact of the thin sheath regions thereby 
causing sticking. The same has occurred for filaments 22 and 24 of yarn 
32. 
One embodiment of the present invention for avoiding this filament sticking 
result is shown in FIG. 3 wherein like elements are numbered the same as 
in FIG. 2. In this embodiment, yarn 38 is converged from filaments 14, 18, 
and 22 and yarn 40 is converged from filaments 16, 20, and 24. The 
filaments are melt spun from the same orifices as in FIG. 2. Interfilament 
sticking is avoided because in the grouping of filaments selected for 
convergence into yarns 38 and 40, there is no thin-sheath to thin-sheath 
contact between filaments, either face to face or side by side during 
convergence. For example, the thin sheath regions of filaments 14 and 18 
face in opposite directions and the thin sheath region of filament 22 
faces away from the thin sheath region of filament 18. The selection of 
filaments in this embodiment is of one per row. Since only three filaments 
are required for the yarn, it is possible to converge these filaments 
together in one step at convergence guide 28 to form the yarn. 
An additional feature of filament selection in the embodiment of FIG. 2 is 
the selection of at least one filament from a row on each side of the 
centerline 25 of the spinneret assembly 12. This widens the angle of 
convergence of the filaments into their respective yarns, which maintains 
in filaments apart longer in the quench chimney giving them further 
opportunity for the thin sheath regions of the filaments to lose their 
stickiness before convergence together. 
In another embodiment of the present invention shown in FIG. 4, wherein 
like elements are numbered the same as in FIGS. 2 and 3, a single yarn 42 
is formed at convergence guide 44 at the exit end of the steam chamber 33 
by converging two bundles 46 and 48 of yarns formed at convergence guide 
28 in the same manner as yarns 38 and 40, respectively. This stepwise 
convergence of the melt spun filaments first into filament bundles prior 
to dimensional stabilization treatment and then the bundles into the 
desired yarn after completion of such treatment prevents the thin sheath 
regions of all six filaments from coming into contact with one another 
during initial convergence which would inevitably occur during single-step 
convergence of six filaments. 
Another embodiment incorporating filament selection and stepwise 
convergence of the selected melt spun filaments into yarn in accordance 
with the present invention is shown in FIG. 5 depicting a portion of the 
face of spinneret plate 50 from which is melt spun a plurality of 
eccentric bicomponent filaments 52 in an array of four rows 54, 56, 58, 
and 60 corresponding to the four rows of the same total number of orifices 
in the spinneret assembly of U.S. Pat. No. 3,704,971 to make four 
seven-filament yarns. Since the same number of orifices is involved, this 
embodiment represents no loss of production capacity from that of the 
patent. In this embodiment, the difference from the patent spinneret 
assembly is the location of the orifices in the rows, which aids filament 
selection to avoid thin-sheath to thin-sheath contact. The eccentric core 
62 is shown for each filament (cross-section shading of filaments 52 is 
omitted for clarity) to show the opposite orientation of the thin sheath 
region of each filament from row to row, which is the same orientation as 
produced by the spinneret assembly of U.S. Pat. No. 3,704,971. The thin 
sheath regions in row 54 face the quench gas flow coming from the 
direction indicated by the arrows in the drawing, which is from the back 
of the apparatus, and the thin sheath portions in row 56 face in the 
opposite direction. This orientation is repeated for rows 58 and 60 of 
filaments. 
The filaments 52 melt spun from spinneret plate 50 are divided into four 
groups 64, 66, 68, and 70 of seven filaments each to form four 
seven-filament yarns. The selection of the filaments for each group runs 
across the centerline 65 of the plate 50 rather than in the direction of 
the rows or in groupings in closely spaced rows, e.g., rows 54 and 56. 
Each group of filaments is converged stepwise to yarn similar to the 
embodiment of FIG. 4 except that the convergence is first into three 
bundles of filaments indicated by the filaments encompassed within the 
phantom lines for groups 64 and 68 in FIG. 5, and then these three bundles 
of filaments are converged into their respective seven-filament yarn. As 
shown for group 64, the bundles are of two groups of two filaments each 
and one group of three filaments. This convergence pattern is repeated for 
group 70 and the convergence pattern of group 68 is repeated for group 66. 
The selection of filaments for each bundle is such that no thin sheath 
regions face one another as can be seen from FIG. 5. The thin sheath 
regions either face in opposite directions or in the same direction, and 
no filaments from the same row are in the same bundle. 
In another embodiment of the present invention, the selection step to avoid 
interfilament sticking is aided by changing the core orientation of the 
array of filaments. For example, as shown in FIG. 7, the cores 72 and 
thereby the thin sheath regions of the filaments 74 in row 76 of the 
filaments face the same direction, i.e., towards the quench gas flow shown 
by the arrows, as in row 78, while the core orientation in rows 80 and 82 
of filaments is the same as in rows 58 and 60 of FIG. 5. In this 
embodiment, it is possible to group four filaments into one bundle or 
yarn, one filament from each row without thin-sheath to thin-sheath 
contact to thereby prevent interfilament sticking. 
The reorientation of the cores 72 in row 76 of filaments shown in FIG. 7 
can be obtained by a modification of the spinneret assembly of U.S. Pat. 
No. 3,704,971 which modification is shown in FIG. 6. More specifically the 
spinneret assembly 90 includes a distribution plate 92 which has upper 
recesses 94 and 96 in communication with each other to form a flow channel 
for core component of the sheath-core filament. The distribution plate 
also has a lower recess 98 to form a flow channel for the sheath component 
of the filament. The recesses 94 and 96 and 98 can be supplied with their 
respective components in molten form in the same manner as shown in U.S. 
Pat. No. 3,704,971. 
The core component from recesses 94 and 96 passes through core meter holes 
100, each such hole representing a row thereof, the holes in one row being 
in staggered relationship with the holes in an adjacent row. The holes 100 
terminate in cylindrical projections 102 in the recess 98. The core 
component exiting the holes 100 at projections 102 enter spinneret 
passages 104 in line therewith along with a concentric sheath of sheath 
component from recess 98. 
For each spinneret passage, there is an angled passage 106 communicating 
between recess 98 and its respective spinneret passage 104 for injecting 
additional sheath component into the spinneret passage. This additional 
sheath component is combined in substantially side-by-side relation with 
the molten concentric sheath core arranged in the passage to be melt spun 
from the orifices of the spinneret passages at the face 108 of the 
spinneret as filaments having the cross section shown in FIG. 1. 
The orifices of the four spinneret passages 104 correspond to the four rows 
of filaments of FIG. 7 as shown in FIG. 6. The alternating direction of 
the angled passages 106 for rows 80 and 82 is in accordance with U.S. Pat. 
No. 3,704,971. The angled passages 106 for rows 76 and 78 all extend in 
the same direction to obtain the core orientation for these rows of 
filaments shown in FIG. 7. In this embodiment, too, the filaments to be 
converged into each bundle are selected from rows on opposite sides of the 
centerline of the spinneret plate to provide at the same time a larger 
convergence angle to the converging filaments. 
The foregoing discussed embodiments all involve a pattern of selecting 
filaments to be converged together into yarn or into bundles and then into 
yarn in accordance with the principle of avoiding contact between thin 
sheath regions of the filaments during convergence. The selection pattern 
depends on the orientation of the thin sheath regions, so as to avoid the 
selection of filaments in which the thin sheath regions are side-by-side, 
such as in adjacent orifices in any of the rows shown in FIGS. 5 and 7, or 
are face-to-face, for convergence in one step. As shown in the embodiments 
of FIG. 6 and 7, the thin sheath orientation can be changed to aid in the 
selection step. Whether or not stepwise convergence of filaments is 
required to make the yarn will depend on the number of filaments required 
to make the yarn. Generally, as many as four filaments can be converged in 
one step into one bundle by proper selection without thin-sheath to 
thin-sheath contact. A greater filament count, i.e., five filaments, for 
the yarn will require at least two bundles in the first converging step. 
As many as four and as few as one filament can be in each bundle but 
preferably each bundle is composed of 2 to 4 filaments for simplification 
purposes. 
Generally, the melt spinning of eccentric bi-component filaments can be 
done in a multi-row array from a spinneret plate without requiring the 
process of the present invention when the as-spun denier per filament is 
less than about 10 measured on yarn prior to cold draw. Consequently, the 
present invention is most applicable when at least three of the melt spun 
filaments are to be converged into each yarn and when the as-spun denier 
per filament is at least about 10. 
The principle of the present invention is applicable to all eccentric 
bicomponent filaments wherein the thin sheath regions remain sticky for a 
longer time than the remainder of the filament. Typically, the core is a 
low melting polymeric material and the sheath is a higher melting 
polymeric material. An example of such a sheath-core composition is 
disclosed in the aforementioned Segraves and Mulholland patent application 
particularly wherein the core is a copolymer of 25-45% by weight 
epsilon-caproamide units with 75-55% (to total 100%) by weight of 
hexamethylene dodecanedioamide units and the sheath polymer is 
polyhexamethylene dodecanedioamide. The process of the present invention 
is particularly applicable to making yarns of filaments of drawn denier 
greater than 31/2 per filament, which yarns are especially useful in such 
applications as welt and leg yarn for hosiery. Typically such yarn will 
have a total drawn denier of at least 15 as a leg yarn and at least 35 as 
a welt yarn. 
The presence or absence of sticking between filaments is evaluated by 
single end knitting the yarn from each yarn package into a tube about 16 
cm long and having a relaxed diameter of about 15 cm. A succession of yarn 
packages can be evaluated by successively knitting the lengths of tubing, 
end-to-end and one length of tubing per package. The crimp in the fabric 
is developed by immersing the fabric in a boiling aqueous dye (hosiery 
brown color) bath. The fabric is dried in the relaxed condition and then 
visually inspected. Portions of the filaments that are stuck together for 
lengths of about 2.54 cm and longer do not crimp and are easily visible as 
a defect in the fabric. One such defect per length of tubing is counted as 
a rejection of the entire package, and the yarn is rated as a percent of 
packages rejected of the total packages tested. For commercial operation, 
a rejection rate of 0% for at least 50 packages of the yarn being 
evaluated is desired. 
The process of the present invention is illustrated by the following 
example in which parts and percents are by weight unless otherwise 
indicated. 
EXAMPLE 
The following general procedure was used for spinning filaments from 
different spinneret orifice arrangements. The eccentric bicomponent 
filament had a cross section like that of FIG. 1 and had the following 
composition: The core was a copolymer of 30% by weight epsilon caproamide 
units and 70% by weight hexamethylene dodecanedioamide units and the 
sheath was 100% polyhexamethylene dodecanedioamide units, both prepared 
essentially by the procedure of Example 1 of the aforementioned Segraves 
and Mulholland patent application. The core copolymer had a relative 
viscosity of 44.2 .+-. 2.2 and the sheath polymer had a relative viscosity 
of 39.2 .+-. 2.1, the relative viscosities being measured on samples taken 
from the melt of each polymeric material just before entering the 
spinneret assembly. The filament was composed of 60% by weight core 
copolymer and 40% by weight sheath polymer. The melt temperature measured 
at the point where the relative viscosity samples were taken was 
268.degree. C for both polymeric materials. The windup speed was 421 yards 
per minute (385 m/min) and the as-spun denier per filament was about 27. 
The 60 inch (1.52 meter) quench chimney used cross air flow at 49.degree. 
.+-. 1.degree. F (9.5.degree. .+-. 0.5.degree. C). Before windup into 
packages the yarn was passed through a 75.6 inch (1.92 meter) long chamber 
containing saturated steam at atmospheric pressure for dimensional 
stabilization. The yarns were withdrawn from their packages and drawn at a 
draw ratio of 4.285X over an unheated draw pin located between the feed 
and draw rolls of a conventional draw twister to a denier per filament of 
7.1 (7.9 dtex). The draw roll peripheral velocity was 790 yarns per minute 
(722.4 meters per minute). After drawing, the yarn was immediately passed 
through a 5.8 inch (14.7 cm) long tube through which hot air was jetted 
cocurrently at 0.7 .+-. 0.1 ft.sup.3 /min (19.8 .+-. 2.8 liters/min) to 
provide an exit-air temperature of 150.degree. .+-. 3.degree. C. At the 
point of air entry, the tube was 0.08 inch (0.20 cm) in diameter, 
increasing gradually to 0.20 inch (0.51 cm) at a distance of 2.8 inch (7.1 
cm). There the tube diameter increased abruptly to 0.25 inch (0.63 cm) and 
remained constant for the last 3 inches (7.6 cm) of tube length. The yarn 
after exit from the tube passed in zig-zag fashion over three snub pins at 
a total contact angle of 390.degree. .+-. 15.degree. . The resultant 
annealed yarn was immediately packaged under tension, as described 
hereinafter. The ring and traveler windup following annealing was at a 
spindle speed of 7710 rpm to provide 0.271 turns per inch (0.107 turns per 
centimeter) of inserted twist. The resultant drawn yarns were then knitted 
into the tubes and crimped as hereinbefore described and these tubes were 
visually inspected for defects. 
In a control experiment of this Example using the foregoing-described 
general procedure, the orifices of the spinneret had the four row 
arrangement of the spinneret assembly of U.S. Pat. No. 3,704,971. In a 
second experiment using the general procedure of this Example, the 
orifices of the same spinneret assembly were arranged in accordance with 
the embodiment of FIG. 5 of the present invention with the centerline 
distance between rows of each pair being about 0.6 cm and between each 
pair of rows being about 2.0 cm. 
In the control experiment, the yarn was made by converging filaments 
selected from a pattern of two from one row, two from the adjacent row, 
two from a row on the opposite side of the spinneret centerline and one 
from the adjacent row thereto. These seven filaments were converged in one 
step at a convergence guide positioned between the quench chimney and 
steam chamber into seven-filament yarn. In the second experiment, the 
filaments were converged into bundles of two filaments, two filaments and 
three filaments selected in accordance with FIG. 5 prior to entering the 
steam chamber, and at the exit of the steam chamber, these bundles of 
filaments were converged into four seven-filament yarns. At least 50 
packages of yarn were wound up and knitted into test tubing for each 
experiment. 
The results of these experiments were as follows: For the control 
experiment, the percent of packages that were defective was 121/2 %. For 
the second experiment, none of the packages were defective. 
Instead of packaging the yarn between the melt spinning and drawing 
operations, these operations can be coupled, in which case the dimensional 
stabilization following convergence could be omitted. 
As many apparently widely different embodiments of this invention may be 
made without departing from the spirit and scope thereof, it is to be 
understood that this invention is not limited to the specific embodiments.