Process for forming improved foamed fibers

A method of forming foamed fibers which comprises the steps of forming a melt of a polymer of fiber-forming molecular weight in which is admixed a blowing agent, and a closed-cell-forming additive, extruding said melt through a spinnerette, quenching said melt downstream of said spinnerette under conditions at which bubbles form in said melt, and drawing said melt as it is quenched to produce a foamed fiber having fine bubbles contained therein is disclosed. The product fibers may contain substantially only closed-cells and/or substantially uniform cross sectional area cells.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for forming foamed fibers, and 
especially to processes employing a combination of molten polymer 
containing therein a dissolved decomposable compound or gaseous blowing 
agent and a closed-cell-forming additive which is extruded and 
subsequently quenched under conditions to produce an improved foamed 
fiber. The present invention also includes novel foamed fibers having 
essentially only closed-cell bubbles contained therein, and novel foamed 
fibers having substantially uniform cross sectional area cells formed 
therein. 
Foamed thermoplastic (and especially polyamide) fibers have been produced, 
especially for the purpose of being broken (fibrillated) into 
three-dimensional structures of interrelated fiber elements. See, for 
example, U.K. Patent Specifications Nos. 1,316,465, 1,221,488, 1,296,710, 
and 1,318,964. In addition, foamed polyester and polyamide fibers for 
textile applications are disclosed in DOS No. 2,148,588 (Apr. 5, 1973) 
(See Example 7). See also Chem. Abstract 90:24692m (1979) of Japanese 
Kokai No. 78,106,770. 
Hollow fibers, also known in the art, contain elongated voids extending 
generally or the entire length of the fiber in the longitudinal direction. 
Some of these fibers contain large diameter voids with low total void 
volume and find use in thermal insulation. The elongated voids are 
generally produced by the use of a modified spinning die. 
U.S. application Ser. No. 490,070, entitled "Producing Foamed Fibers, " to 
H. L. Li et al., filed Apr. 29, 1983 and commonly assigned now U.S. Pat. 
No. 4,562,022, discloses improved methods of forming fine-celled foamed 
fibers which employs at least one additional member arranged above the 
spinnerette which, with extruding a polymer melt having a blowing agent 
admixed therewith, produces excellent foamed fiber products. 
We have discovered a method of forming foamed fibers which contain fine, 
closed-cell bubbles, and/or cells of uniform cross sectional area. To that 
end, we have discovered a class of additives (hereinafter referred to as 
closed-cell-forming additives) which, when included in the polymer melt, 
produce improved foamed fibers. The use of the additive in a process for 
foaming fibers also dramatically enhances the ability to draw the fibers 
to produce very fine (on the order of 1 dpf) fibers (comprising open 
and/or closed cells) which are particularly useful as, for example, filter 
material, acoustic insulation, and apparel fiber. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method of forming foamed fibers 
which comprises the steps of: 
(a) forming a melt of a polymer of fiber-forming molecular weight in which 
is admixed a blowing agent and a closed-cell-forming additive; 
(b) extruding said melt through a spinnerette; 
(c) quenching said melt downstream of said spinnerette under conditions at 
which bubbles form in said melt; and 
(d) drawing said melt as it is quenched to produce a foamed fiber having 
fine, closed-cell bubbles contained therein and/or cells of uniform 
effective diameter. The closed-cell-forming additive comprises any one or 
more compounds selected from the group of siloxane polymers or copolymers 
thereof terminated at least at one end thereof by a group selected from 
relatively short (1-10 carbon) functionalized aliphatics, polyether 
alcohols and polyether amines. Preferably, the closed-cell-forming 
additive comprises any one or more compounds selected from the group of 
polydimethylsiloxane or copolymers thereof terminated at one end by 
polyether alcohols or polyether amines. The present invention also 
includes a foamed fiber having essentially closed-cell bubbles formed 
therein and/or cells of uniform cross sectional area. Foamed fibers 
(containing open and/or closed cell bubbles) may be formed as fine as 
about 1 dpf.

DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention involves the extrusion of a polymer 
melt containing, or having dissolved or dispersed therein, a blowing agent 
which is a decomposable compound or a dissolved gas and a 
closed-cell-forming additive. The polymer may be any of a variety of 
conventional thermoplastics used in fiber production, for example: 
polyesters such as polyethylene terephthalate; polyamides such a nylon 6, 
nylon 6/6, nylon 4/6 and nylon 6/12; polyolefins; poly(vinylchloride) 
polystyrenes; and blends thereof. The preferred thermoplastics for use in 
the present invention are polyamides, especially nylon 6 and nylon 6/6. 
The polymers should be of fiber-forming molecular weight, a term well 
understood in the art. In the case of nylon 6 and nylon 6/6, a generally 
acceptable number average molecular weight is at least about 10,000. 
The blowing agent may be a compound dissolved or dispersed in the molten 
polymer which, before reaching the spinning temperature, decomposes to 
form gases such as carbon dioxide, nitrogen, carbon monoxide or mixtures 
thereof. Materials which totally decompose to produce gaseous products 
such as nitrogen, ammonia, carbon dioxide, carbon monoxide and water 
vapor, or combinations of these are preferred. For example, 
azodicarbonamide decomposes to form nitrogen, carbon dioxide and ammonia 
in a 6:3:1 molar ratio. Azodicarbonamide, ethylene carbonate and oxalic 
acid are among the preferred materials. Oxalic acid, FICEL.RTM. 
azodicarbonamide, and Expandex.RTM. 5 PT (a 5-phenyl tetrazole, releasing 
N.sub.2 only) are the most preferred materials. Less preferred, but 
suitable, are materials such as alkali metal carbonates and bicarbonates 
which decompose to form carbon dioxide and at least one nonvolatile 
by-product, or, for example, other sodium salts. 
The blowing agent may also be a normally gaseous or volatile compound, such 
as a fluorocarbon or water mixed or injected into the polymer melt before 
or during extrusion. Samples of such blowing agents include carbon 
dioxide, nitrogen, noble gases, dichlorodifluoromethane, 
trichlorotrifluoroethane, water and volatile hydrocarbons, with nitrogen 
being the preferred blowing agent. 
The decomposition temperature of the decomposable compound and boiling 
point of the normally-gaseous or volatile compound should be selected to 
assure that cells form in the polymer at the spinning temperature at the 
outlet of the spinnerette (as the pressure drops). These cells should not 
collapse or redissolve in the extended fiber prior to polymer 
solidificatron. 
The concentration of the blowing agent or decomposable compound added to 
the polymer must be maintained above a certain amount in order to yield a 
sufficient number of cells to produce quality foamed fiber. The specific 
concentration is dependent upon a variety of factors including the degree 
of decomposition of the agent, the solubility of the gas(es) in the 
polymer, the amount of nucleating agent, the jet velocity of the fibers 
emerging from the spinnerette and the spinnerette design, among others, 
and can be determined by routine experimentation from the disclosure 
provided herein and/or upon viewing the cross sectional area of the fiber 
product to determine the presence or absence of closed and/or 
substantially uniform cross sectional area cells. Generally speaking, the 
concentration of blowing agent should be at least about 0.1% by weight and 
normally not more than about 0.6%. With FICEL.RTM. EPA, (which contains 
about 50% nucleating agent) the amount is ordinarily at least about 0.3% 
by weight, with Expandex.RTM. 5 PT the amount is normally at least about 
0.2% by weight, and with oxalic acid the amount is normally above about 
0.2% by weight. 
To the polymer melt is ordinarily added a nucleating agent such as talc, 
silica (powdered or fumed), or magnesium or calcium carbonate. The 
nucleating agent may also be premixed with the decomposable compound as is 
the case of azo-compounds premixed with silica and sold by BFC Chemicals 
Inc., Wilmington, Del. as FICEL.RTM. EPA, EPB, EPC, and EPD nucleating 
blowing agents. Alternatively, the nucleating agents may be separately 
mixed with the solid or molten polymer. A preferred nucleating agent is 
sold under the tradename MicroPflex.RTM. 1200 by Pfizer. Ordinarily, the 
nucleating agent should be maintained at about 0.2% by weight or more. 
Generally, an azodicarbonamide/silica concentration ratio of about 2:1 is 
preferred. When employing an oxalic acid and talc combination, a 
concentration ratio of about 2:1 is preferred. The absence of nucleating 
agent tends to increase the size of the cells and may interfere in the 
production of extremely fine denier foamed fiber. 
Admixed with the polymer, blowing agent and nucleating agent is a 
closed-cell-forming additive. The closed-cell-for-forming additive 
functions to stabilize and reduce the effective diameter of the bubbles 
formed in the polymer melt and results in the production of a molten 
foamed fiber having fine, substantially uniform cross sectional area, 
closed-cell bubbles formed therein. The closed-cell-forming additive 
comprises any one or more compounds selected from the group of siloxane 
polymers or copolymers thereof terminated at least at one end by a group 
selected from relatively short (1-10 carbon atoms, preferably 1-5 carbon 
atoms and most preferably 1-3 carbon atoms) functionalized aliphatics, 
polyether alcohols and polyether amines. The additive is represented by 
the formulae 
EQU A, (1) 
EQU AB, (2) 
EQU ABA, (3) 
EQU BAB, (4) 
and 
EQU (AB).sub.x (5) 
or mixtures thereof where R.sub.1 and R.sub.2 are independently selected 
from alkyl, hydroxy alkyl, aminio alkyl, alkoxy, alkoxy polyether, 
polyether alcohol, polyether amine and phenyl groups, R.sub.3 -R.sub.6 are 
independently selected from alkyl and phenyl groups or mixtures thereof, n 
is an integer, A is a block polymer having the general formula: 
##STR1## 
B is a polyether or polyamine, and x is an integer. 
Preferably, the closed-cell-forming additive is any one or more compounds 
selected from the group of polydimethylsiloxane (i.e., where R.sub.3 
-R.sub.6 are methyl groups) or copolymers thereof terminated at least at 
one end thereof by a polyether alcohol, polyether amine or a relatively 
short functionalized (1-5 carbon atom containing) aliphatic group. More 
preferably, the polydimethylsiloxane based polymer is terminated at least 
at one end by a substituted alkyl having one to three carbon atoms, a 
polyether alcohol or a polyether amine. Most preferably, the substituted 
alkyl (R.sub.1 and/or R.sub.2) is propylamine or propanol. The 
closed-cell-forming additive is normally provided in an amount between 
about 5:1 to about 1:5 (ratio of additive to blowing agent). Preferably, 
the closed-cell-forming additive is provided in an amount between about 
0.05% and about 1.0% by weight based on the polymer. More preferably, the 
additive is provided in an amount between about 0.15%-0.35%, and most 
preferably the additive is provided in an amount between about 0.2 and 
about 0.25% by weight. 
The effect of the closed cell forming additive is two-fold. Firstly, the 
additive is particularly useful in forming foamed fiber products 
containing substantially only closed cell bubbles. Fiber having a denier 
as low as about 1-3 dpf may be produced which exhibit this feature. 
Secondly, the closed-cell-forming additive unexpectedly enhances the 
ability to draw the spun fiber to produce extremely fine denier products 
(on the order of 1 dpf) due at least in part to the ability of the 
additive to decrease bubble size and increase the uniformity of the cross 
sectional area of the cell (open or closed). In accordance with this 
second advantage, a fiber cross section (normal to the fiber axis) will 
ordinarily show a decrease in cell size (diameter), an increase in the 
average number of voids and, perhaps more importantly, a range of void 
sizes larger than the average size which is decreased relative to a fiber 
formed in the absence of the closed-cell-forming additive. 
Spinning apparatus used in practicing the extrusion step of our process may 
be conventional extrusion apparatus for spinning ordinary fibers of the 
same polymer with minor modifications. Thus, for example, in spinning 
nylon 6 fibers, ordinary powder or pellet feed systems, extruders and 
spinnerettes may be used. The spinnerette may have any number of 
apertures. Each aperture may have various L/D (length to diameter) ratios 
and various cross sectional shapes (e.g., circular, Y-shaped, dog-boned, 
hexalobal, and preferably trilobally-shaped). Regardless of the shape 
used, the effective diameter (in the case of a circle, an equivalent 
dimension giving the same cross sectional area for the other shapes) may 
vary widely from about 0.1 mm to about 2.0 mm, with an effective diameter 
from about 0.1 mm and about 1.0 mm being preferred, and between about 0.1 
mm and about 0.6 mm being more preferred. Preferred 1/d ratios for the 
present invention are between about 30:1 and about 1:1, the lower range 
which is substantially less than that normally used for spinning polyamide 
fibers. Most preferably, the process employs a conventional extrusion 
apparatus having, as a principal modification thereof, at least one 
structure with a plurality of small openings defined therein, normally 
with a major cross sectional dimension of about 0.1 mm (the pore size of a 
porous member such as, for example, a sand pack or the mesh size of a 
screen) arranged upstream, and more preferably immediately upstream of the 
spinnerette. The most preferred modification is the employment of at least 
one screen pack as described in application Ser. No. 490,070 id., now U.S. 
Pat. No. 4,562,022, (the disclosure of which is hereby incorporated by 
reference to the extent not consistent herewith). Preferably, the screen 
pack should comprise screens having between about 20 mesh/in and about 400 
mesh/in. Most preferably, we employ an eight layered screen pack 
comprising a 90 mesh top layer, followed by two 200 mesh layers, followed 
by two 400 mesh layers, followed by two 200 mesh layers, followed by a 90 
mesh bottom layer. 
For a particular polymer/blowing agent/nucleating agent/closed-cell forming 
additive combination, spinning pressures will generally have a particular 
minimum value below which good quality foamed fibers will not form. While 
spinning pressure can be controlled by a positive displacement melt pumps, 
the aperture size and arrangement in the spinnerette and the structural 
addition (e.g., screen pack) and its arrangement will have a significant 
effect on the spinning pressure. Consequently, the spinning pressure is 
ordinarily controlled by reference to the jet velocity of the polymer 
through the spinnerette (throughput rate of the polymer through the 
spinnerette in length/sec.). Although jet velocities as high as about 150 
cm/sec may be used, jet velocities used in the process ordinarily range 
from about 2 cm/sec. to about 50 cm/sec., with 10-35 cm/sec. being the 
preferred range of velocity. Generally, an increase in the jet velocity 
will decrease the bubble size. More importantly, over the entire practical 
(ordinary) range of jet velocities, the closed-cell-forming additive 
functions to substantially reduce the cell (bubble) size as compared to 
the bubble size in an equivalent foamed fiber formed in the absence of the 
additive, and increases the uniformity of the cross sectional area 
thereof. 
The extrusion technique generally used to form the molten foamed polymer 
may be any technique used in the extrusion of thermoplastics. Devices for 
blending the blowing agent or decomposable compound, nucleating agent and 
additive can be those well known in the art of fiber extrusion. For 
example, the decomposable compound may be master-batched with some of the 
polymer material in one extruder, which is then fed at right angles to a 
main extruder containing polymer material. The polymer material can be fed 
to the main extruder as a powder or as pellets. The extruder would 
generally feed a melt pump or other similar apparatus to create the high 
pressure (jet velocity) needed for fiber production. Additional 
conventional features include, for example, the polymer being heated in 
stages through the main extruder, and further heating of the polymer 
immediately before or after the melt pump. 
Once the fiber is extruded through the spinnerette, the resultant molten 
fiber is quenched downstream of the spinnerette under conditions at which 
bubbles will form and are stabilized in the molten fiber. Such bubbles 
will contain, for example, carbon dioxide, may contain other by-products 
of compound decomposition (e.g., nitrogen and ammonia) and may also 
contain other volatile materials which are added as such to the polymer 
melt (e.g., fluorocarbons). The quench temperature should be below the 
temperature at which the molten fibers solidify. Furthermore, the quench 
temperature is generally within several degrees of room temperature (e.g., 
about 20.degree. C.) and should be chosen such that bubble coalescence, 
bubble diffusion to the polymer surface and redissolution are minimized. 
As the melt is quenched, it is normally drawn (melt drawn) so as to control 
the diameter (or the denier) of the fiber to a desired degree. Because of 
the high viscosities of most fiber-forming polymer materials, it is 
conventional to extrude through spinnerette apertures of major cross 
sectional dimensions much larger than the desired final fiber product 
dimension. Furthermore, since, once the molten fiber has solidified, it is 
relatively difficult to draw to a large extent (e.g., more than about 
5:1), the most appropriate place to draw is during the molten state and 
the quenching operation. In the present process, melt drawing is affected 
at a draw ratio of between about 2:1 and about 1000:1; and, at least in 
the case of polyamides, it is preferably between about 4:1 and about 
200:1. As one aspect of our invention, we have discovered that an 
essentially closed-cell bubble structure can be formed during the 
quenching operation which is neither destroyed nor rendered open cell by 
the drawing step, even when producing fibers having a denier as fine as 
about 1-3 dpf. Instead there may be some tendency for bubbles to elongate 
somewhat in the longitudinal direction. 
Because of the addition of the closed-cell forming additive, the product 
fibers from the above process generally exhibit a generally of very fine, 
uniform diameter bubble structure and hence are of more substantial 
physical properties than fibers produced in accordance with any previously 
mentioned process. Thus, for example, in product fibers having a denier 
(grams per 9000 meters) of between about 1 and 100, a representative cross 
section of each filament normally exhibits between about 50 and about 200 
percent more bubbles than would be possible in the absence of the 
closed-cell forming additive. Ordinarily, the total cross sectional area 
of the bubbles per given cross sectional area of, for example, nylon fiber 
product will amount to between about 10 and about 40 percent of the cross 
sectional area of the fiber. Moreover, we have discovered that the 
uniformity of and decreased cross sectional area of the fine cells 
increases the drawability of the spun fiber. Consequently, fibers on the 
order of 1 dpf can be continuously produced. 
The fiber product ordinarily has an effective diameter of between about 
0.01 mm and about 1.0 mm, preferably between about 0.01 mm and about 0.1 
mm. Effective diameter corresponds generally to a denier which can range 
from about 0.8 to about 8000, and which preferably ranges between about 
0.8 and about 80. Excellent carpets can be formed from such fibers, 
especially with deniers from about 15 to about 30. Not only would such 
carpets have added coverage without the loss of such properties as 
wearability and resilience, but they would also exhibit excellent 
resistance to accumulating dirt due to the essentially closed-cell 
structure of the fiber product. Moreover, continuous fibers of extremely 
low denier (on the order of 1 dpf) may be produced which would be 
especially useful in the production of apparel and as filter elements. 
The density of the foamed fibers will normally be between about 60 and 
about 90 percent of the density of unfoamed fibers of the same 
composition. In other words, the volume of polymer in the foamed fiber is 
ordinarily at least about 10% and normally between about 10% and about 40% 
less than the volume of polymer in an unfoamed fiber of the same cross 
sectional dimension and length. Accordingly, since denier is based upon 
weight, lower denier fibers of the same cross sectional area are created. 
The cells (bubbles) in such fibers have an effective diameter (as measured 
in a cross section of the fiber taken generally normal to the fiber axis) 
less than about 10 microns, normally less than about 2 micron, and in many 
instances less than or equal to about 1 micron. In essentially all 
instances, the foamed fiber produced in accordance with our process 
comprises bubbles of substantially smaller size and relatively uniform 
cross sectional area as compared to the bubbles in foamed fibers formed 
without the use of the additive. Moreover, except for extremely low denier 
fiber (i.e., less than about 1 denier), the cells may exist as essentially 
only closed cells (in the sense that a photograph of the cross section of 
the product fiber would show that essentially all the bubbles present over 
the given cross section of the fiber are substantially closed). 
In addition to the uses mentioned above for the foamed fibers, they may 
also be used in upholstery, camping equipment (e.g., tents and sleeping 
bags), luggage, ropes, or nets. The foamed fibers may be formed for such 
applications in woven and nonwoven fabrics, or they may be tufted or 
otherwise fabricated in ways conventional for nonfoamed fibers. 
The following Examples describe the production of essentialy 
closed-cell-containing and/or substantially uniform cross section cell 
containing foamed fibers which were spun using an apparatus of the type 
schematically illustrated in the FIG. 1. The apparatus comprises a heated 
extruder barrel 1 containing an extrusion screw 2 which propels a mixture 
3 of polymer, decomposable compound, nucleating agent and closed-cell 
forming additive (fed to the barrel via the hopper 4) toward a spinning 
apparatus 5. Within the spinning apparatus 5, a positive displacement melt 
pump 6 feeds the molten polymer mixture through a distributor plate 7 and 
a screen pack 8 toward the spinnerette 9. A continuous fiber product is 
produced by the spinnerette and is subsequently stretched and quenched 
(melt drawn) by suitable means not shown, and thereafter the solidified 
fiber is drawn to the final desired denier by suitable means (e.g., 
rollers, not shown). The Examples should not be construed in any way as 
limiting the scope of applicants' invention to anything less than that 
which is defined by the appended claims. 
COMATIVE EXAMPLE 1 
2 Kg of nylon 6 polymer pellets were coated with 9 g of a chemical blowing 
agent, Expandex.RTM. 5 PT (a 5-phenyltetrazole produced by Olin 
Corporation) and 9 g of a nucleating agent, MicroPflex-1200 (a submicron, 
chemically treated synthetic magnesium silicate), using 4 g of vegetable 
oil as a binder. The coating was done by adding the ingredients to a jar, 
which was sealed and tumbled (for about 30 min.) until the blowing and 
nucleating agents were uniformly distributed onto the polymer pellets. On 
a polymer basis, the concentration of the additives are, respectively, 
0.45 wt. %, 0.45 wt. %, and 0.20 wt. %. The anhydrous mixture was placed 
in the hopper of a one inch diameter extruder which was preheated to the 
desired temperature profile along the barrel of the extruder to yield a 
polymer melt temperature at the exit of the extruder of about 500.degree. 
F. The extruder was equipped with a metering pump and a spinning block 
containing the screens (eight layers, 90, 200, 200, 400, 400, 200, 200, 90 
mesh, top to bottom) and a spinnerette. The spinnerette had five (5) 
symmetrical trilobal orifices, wherein each lobe has dimensions (mils) of 
5 (width).times.20 (length).times.20 (depth). The area per orifice was 
1.8.times.10.sup.-3 cm.sup.2. The polymer-additive mixture was extruded at 
a rate of 13.6 g/m which translated into a jet velocity of 25 cm per sec. 
per orifice. It required a metering pump setting of 12.5 rpm and an 
extruder screw rpm sufficient to maintain about 2000 psi at the entrance 
to the metering pump. The pressure after the metering pump, but before the 
screen and spinnerette, was measured to be about 1180 psi. The filaments 
exiting from the spinnerette orifices were drawn down (melt drawn) to a 
29:1 ratio (56 dpf) while being cooled in air to a temperature at which 
the filaments did not stick to the surface of a first take-up roll, less 
than about 50.degree. C. Just above the first take-up roll, a finish was 
applied to the yarn to aid further processing and to dissipate any static 
charge buildup. The yarn on the first take-up roll was then drawn in line. 
The yarn on the first roll which turned at 874 rpm (437 MPM yarn speed) 
was advanced to a second roll which turned at 960 rpm (480 MPM) and from 
the second roll onto a third roll which turned at 1786 rpm (yarn speed of 
893 MPM). The yarn was then advanced from the third roll to a winder at 
893 MPM, which wound the yarn upon a sleeve. The temperature of the rolls 
(heated by induction heating) were 55.degree. C. 163.degree. C. and 
23.degree. C. for rolls 1, 2, and 3, respectively. The difference in roll 
speeds resulted in an overall draw ratio of 2.04:1. The final drawn foamed 
yarn floated in a liquid with a density of 0.9 g/cc and had a denier of 
135/5 (27 dpf). An analysis of 60 cross sections showed an average number 
of voids of 7.3 per cross section with an average size of 11.3 microns, 
and a range of voids (9) having a cross section larger than the average of 
13-16.7 microns. 
EXAMPLE 2 
The vegetable oil which functioned to bind the Expandex.RTM. 5 PT blowing 
agent and the nucleating agent to the polymer pellets was replaced by 0.25 
wt. % of a polydimethylsiloxane containing a secondary hydroxyl function 
(Dow Corning DC-Q1-8030). The polymer, additives, and resulting yarn were 
processed in the same manner as in Example 1. The resulting yarn had a 
denier of 135/5 (27 dpf) and also floated in a liquid with a density of 
0.9 g/cc. An analysis of 60 cross sections revealed an average number of 
12 voids per cross section. The void size averaged 10 microns. The 
addition of the closed-cell-forming additive substantially increased the 
average number of voids from 7.3 in Example 1 to 12 in this test. 
Moreover, the voids were substantially closed. In addition, the range of 
voids (13) having a cross section larger than the average decreased to 
11-13.8. 
EXAMPLE 3 
Nylon 6 polymer pellets were coated with Expandex.RTM. 5 PT blowing agent 
and MicroPflex-1200 nucleating agent, using the Dow Corning Q1-8030 
additive. The coating was accomplished as in Example 1, except that on a 
polymer basis, the concentration of the additives were respectively, 0.40 
wt. %, 0.30 wt. %, and 0.20 wt. %. The apparatus of Example 1 was 
employed, except that the spinnerette used had ten (10) symmetrical 
trilobal orifices having dimensions (mils) of 5.times.20.times.20. The 
area per orifice was 1.8.times.10.sup.-3 cm.sup.2. The polymer-additive 
mixture was extruded at a rate sufficient to yield a jet velocity of 41 
cm/sec per orifice. It required a metering pump setting of 34.5 rpm and an 
extruder screw rpm sufficient to maintain about 2450 psi (polymer 
temperature about 555.degree. F. at the exit of the extruder) at the 
entrance to the metering pump. The pressure after the meter pump, but 
before the screen and spinnerette was measured at about 1100 psi. The 
filaments exiting from the spinnerette orifices were drawn down at a 27:1 
ratio while being cooled in air to a temperature where the filaments (53 
dpf) did not stick to the surface of the first take-up roll. Again, just 
above the first take-up roll, a finish was applied to the yarn to aid 
further processing and to dissipate any static charge buildup. The yarn on 
the first roll was drawn in line. The yarn on the first roll which turned 
at 672 MPM was advanced to a second roll which turned at 1746 MPM and from 
the second roll onto a third roll which turned at 1746 MPM. The yarn was 
then advanced from the third roll to a winder at 1746 MPM, which wound the 
yarn upon a sleeve. The temperature of the rolls was approximately 
43.degree. C., 161.degree. C., and 23.degree. C. for rolls 1, 2, and 3, 
respectively. The difference in roll speeds resulted in overall draw ratio 
of 2.6:1. The final drawn yarn floated in a liquid with a density of 0.85 
g/cc and had a denier of 200/10 (20 dpf). An analysis of 60 cross sections 
revealed a average number of 13 voids per cross section with an average 
size of 6.6 microns, and a range of voids (10) having a cross section 
larger than the average of 7.5-9.2 microns. 
COMATIVE EXAMPLE 4 
Nylon polymer pellets were coated with the chemical blowing agent 
comprising caprolactam, oxalic acid, and a nucleating agent 
(MicroPflex-1200). The coating was accomplished by adding the ingredients 
to a jar which was then closed and tumbled until all additives were 
uniformly distributed onto the polymer pellets (about 30 min). On a 
polymer basis, the concentration of the additives was 0.2 wt. % oxalic 
acid, 0.2 wt. % MicroPflex-1200 and 0.4 wt. % caprolactam. The anhydrous 
mixture was placed in the hopper of a one inch diameter extruder which was 
preheated to the desired temperature profile along the barrel of the 
extruder to yield a polymer melt temperature at the exit of the extruder 
of about 503.degree. F. The extruder was equipped with a metering pump and 
a spinning block containing the screen (designed as in Example 1) and a 
spinnerette. The spinnerette had five (5) symmetrical trilobal orifices 
having dimensions (mils) of 5.times.20.times.20. The area per orifice was 
1.8.times.10.sup.-3 cm .sup.2. The polymer-additive mixture was extruded 
at a rate of 27 g/m which translated into a jet velocity of 50 cm/sec per 
orifice. It required a metering setting of 24 rpm and an extruder screw 
rpm sufficient to maintain about 2000 psi at the entrance to the metering 
pump. The pressure after the metering pump, but before the screen and 
spinnerette, was measured to be about 1209 psi. The filaments exiting from 
the spinnerette orifices were drawn down to a 28:1 ratio (59 dpf) while 
being cooled in air to a temperature below about 50.degree. C. Again, as 
in the previous examples, a finish was applied to the yarn to aid further 
processing and to dissipate any static charge buildup. The yarn on the 
first roll was then drawn in line. The yarn on the first roll which turned 
at 830 MPM was advance to a second roll which turned at a yarn linear 
velocity of 900 MPM and from the second roll onto a third roll which 
turned at a yarn speed of 1890 MPM. The yarn was then advanced from the 
third roll to a winder at 1890 MPM, which wound the yarn upon a sleeve. 
The temperature of the rolls was 65.degree. C., 162.degree. C., and 
23.degree. C. for roll 1, 2, and 3, respectively. The difference in roll 
speeds resulted in an overall draw ratio of 2.27. The final drawn yarn 
floated in a liquid with density of 0.9 g/cc and had a denier of 130/5 (26 
dpf) An analysis of 60 cross sections showed an average number of voids of 
4.1 per cross section with an average size of 12.5 microns, and a range of 
voids (8) having a cross section larger than the average of 14-23.6 
microns. 
EXAMPLE 5 
Nylon 6 polymer pellets were coated with oxalic acid, a nucleating agent 
(MicroPflex-1200), and the additive of Example 2 (Dow Corning DC-Q1-8030). 
On a polymer basis, the concentrations of the additions were 0 175 wt. % 
oxalic acid, 0.2 wt. % Microflex-1200, and 0.2 wt. % closed-cell-forming 
additive. The mixture was extruded through the barrel of the extruder 
described in Example 4. The polymer melt temperature at the exit of the 
extruder was about 518.degree. F. The spinnerette had twenty (20) 
symmetrical trilobal orifices having dimensions (mils) of 
4.times.10.times.10. The area per orifice was 6.2.times.10.sup.-4 
cm.sup.2. The polymer additive mixture was extruded at a rate of 23.4 
g/min which translated into a jet velocity of 32 cm/sec per orifice. It 
required a metering pump setting of 20 rpm and an extruder screw rpm 
sufficient to maintain about 1800 psi of pressure at the entrance to the 
metering pump. The pressure after the metering pump, but before the screen 
and spinnerette, was measured to be about 600 psi. The filaments exiting 
from the spinnerette orifices were drawn down to a 46.6:1 ratio (12 dpf) 
while being cooled in air to below 50.degree. C. As in the previous 
examples, a finish was applied to the yarn to aid further processing and 
dissipate any static charge buildup. The yarn of the first roll was then 
drawn in line. The yarn on the first roll which turned at 880 MPM was 
advanced. to a second roll which turned at a velocity of 1653 MPM and from 
the second roll to a third roll which also turned at a speed of 1653 MPM. 
The yarn was then advanced from the third roll to a winder at 1653 MPM, 
which wound upon a sleeve. The temperature of the rolls were 79.degree. 
C., 98.degree. C., and 23.degree. C. for roll 1, 2, and 3, respectively. 
The difference in roll speeds resulted in an overal draw ratio of 1.87:1. 
The final drawn yarn floated in a liquid with the density of 0.9 g/cc and 
had a denier of 128/20 (6.4 dpf) An analysis of 60 cross sections showed 
an average number of voids of 11.2 per cross section with an average size 
of 3.4 microns, and a range of voids (9) having a cross-section larger 
than the average of 4.1-5.1 microns. 
EXAMPLE 6 
Polyethylene terepthalate pellets were blended with 0.3 wt. % Expandex.RTM. 
5 PT blowing agent, 0.3 wt. % MicroPflex-1200 (nucleating agent) and 0.15 
wt. % of the additive of Example 2 (Dow Corning DC-Q1-8030). The mixture 
was extruded through a one inch diameter extruder which was preheated to 
the desired temperature profile along the barrel of the extruder to yield 
a polymer melt temperature at the exit of the extruder of about 
553.degree. F. The extruder was equipped with a metering pump at a 
spinning block containing the screens (designed as in Example 1) and the 
spinnerette. The spinnerette had twenty (20) symmetrical trilobal orifices 
having dimensions (mils) of 4.times.15.times.14. The area per orifice was 
1.1.times.10.sup.-3 cm.sup.2. The polymer-additive mixture was extruded at 
a rate of 24.5 g/min which translated into a jet velocity of 18.6 cm/sec 
per orifice. It required a metering pump setting of 18 rpm and an extruder 
screw rpm sufficient to maintain about 2400 psi at the entrance to the 
metering pump. Pressure after the metering pump, but before the screen and 
spinnerette, was measured to be about 1890 psi. The filaments exiting from 
the spinnerette orifices were drawn down to 22.5 denier per 20 fil. (6.2 
dpf). The yarn was then drawn in line to a final draw ratio of 1.96. The 
final drawn yarn floated in water (density 1.00 g/cc) and had a final 
denier of 64/20 (3.2 dpf). A visual inspection of the yarn cross sections 
showed an average number of voids of 11 per filament cross section with a 
size ranging from very small to medium diameter. 
COMATIVE EXAMPLE 7 
The closed-cell-forming additive employed in the process described in 
Example 6 was replaced with vegetable oil. The polymer, additives, and 
resulting yarn were processed in essentially the same manner as in Example 
6. The resulting yarn had a denier of 136 (6.8 dpf) and floated in a 
liquid with a density of 1.10 g/cc. A visual inspection of the yarn cross 
section revealed an average number of 6 voids per filament cross section. 
The size of the voids ranged from medium to large in diameter. 
EXAMPLE 8 
Nylon 6 polymer pellets were coated with Expandex.RTM. 5-PT blowing agent, 
MicroPflex-1200 nucleating agent, and a low molecular weight silicone with 
terminal hydroxyl groups (produced by Goldschmidt and distributed under 
the tradename Goldschmidt CK 150). The coating was accomplished as in 
Example 1, except that on a polymer basis, the concentrations of the 
additions were, respectively, 0.40 wt. %, 0.30 wt. %, and 0.20 wt. %. The 
apparatus of Example 1 was employed, except that the spinnerette used had 
ten (10) symmetrical trilobal orifices having dimensions (mils) of 
5.times.20.times.10. The area per orifice was 1.8.times.10.sup.-3 
cm.sup.2. The polymer-additive mixture was extruded at a rate sufficient 
to yield a jet velocity of 36.1 cm/sec. per orifice. It required a 
metering pump setting of 34.5 rpm and an extruder screw rpm sufficient to 
maintain about 2800 psi at the entrance to the metering pump. The pressure 
after the metering pump, but before the screen and spinnerette was 
measured at about 1300 psi. The filaments exiting the spinnerette were 
drawn while being cooled in air to a temperature where the filaments did 
not stick to the surface of the first take-up roll. Just above the first 
take-up roll, a finish was applied to the yarn to aid further processing 
and to dissipate any static charge buildup. The yarn on the first roll was 
drawn in line. The yarn on the first roll which turned at 1624 rpm was 
advanced to a second roll which turned at 3492 rpm and from the second 
roll onto a third roll which turned at 3492 rpm. The yarn was then 
advanced from the third roll to a winder of 3492 rpm, which wound the yarn 
upon a sleeve. The temperature of the rolls was approximately 65.degree. 
C., 150.degree. C., and 23.degree. C. for the rolls 1, 2, and 3, 
respectively. The differences in roll speeds resulted in an overall draw 
ratio of 2.15:1. The final yarn floated in a liquid with a density of 0.85 
g/cc and had a denier of 200/10 (20 dpf). A visual count of 10 cross 
sections revealed an average of 35 voids per cross section. 
EXAMPLE 9 
Nylon 6 polymer pellets were coated with Expandex.RTM. 5-PT blowing agent, 
MicroPflex-1200 nucleating agent, a solution of a silicone containing 
amine functionality in 50% white mineral spirits (produced by Goldschmidt 
and distributed under the tradename Goldschmidt Tegosivin L49). The 
coating was accomplished as in Example 1, except that on a polymer basis, 
the concentration of the additive were respectively, 0.40 wt. %, 0.30 wt. 
%, and 0.40 wt. %. The apparatus of Example 1 was employed, except that 
the spinnerette used had ten (10) symmetrical trilobal orifices having 
dimensions (mils) of 5.times.20.times.10. The area per orifice was 
1.8.times.10.sup.-3 cm.sup.2. The polymer-additive mixture was extruded at 
a rate sufficient to yield a jet velocity of 36.1 cm/sec. per orifice. It 
required a metering pump setting of 34.5 rpm and an extruder screw rpm 
sufficient to maintain about 2600 psi at the entrance to the metering 
pump. The pressure after the metering pump, but before the screen and 
spinnerette was measured at about 1170 psi. The filaments existing from 
the spinnerette were drawn while being cooled in air to a temperature 
where the filaments did not stick to the surface of the first take-up 
roll. Just above the first take-up roll, a finish was applied to the yarn 
to and further processing and to dissipate any static charge buildup. The 
yarn on the first roll was drawn in line. The yarn on the first roll which 
turned at 1624 rpm was advanced to a second roll which turned at 3492 rpm 
and from the second roll onto a third roll which turned at 3492 rpm. The 
yarn was then advanced from the third roll to a winder of 3492 rpm, which 
wound the yarn upon a sleeve. The temperature of the rolls was 
approximately 65.degree. C., 150.degree. C., and 23.degree. C. for the 
rolls 1, 2, and 3, respectively. The differences in roll speeds resulted 
in an overall draw ratio of 2.15:1. The final yarn floated in a liquid 
with a density of 0.85 g/cc and had a denier of 200/10 (20 dpf). A visual 
count of 10 cross sections revealed an average of 23 voids per cross 
section. 
COMATIVE EXAMPLE 10 
Nylon 6 polymer pellets were coated with Expandex.RTM. 5-PT blowing agent, 
and and MicroPflex-1200 nucleating agent, and a solution of a silicone 
containing amine functionally in 50% white mineral spirits (produced by 
Goldschmidt and distributed under the tradename Goldschmidt Tegosivin 
L50). The coating was accomplished as in Example 1, except that on a 
polymer basis, the concentration of the additive were, respectively, 0.40 
wt. 0.30 wt. %, and 0.67 wt. %. The apparatus of Example 1 was employed, 
except that the spinnerette used had ten (10) symmetrical trilobal 
orifices having dimensions (mils) of 5.times.20.times.10. The area per 
orifice was 1.8.times.10.sup.-3 cm.sup.2. The mixture was extruded at a 
rate sufficient to yield a jet velocity of 36.1 cm/sec. per orifice. It 
required a metering pump setting of 34.5 rpm and an extruder screw rpm 
sufficient to maintain about 2400 psi at the entrance to the metering 
pump. The pressure after the metering pump, but before the screen and 
spinnerette was measured at about 1260 psi. The filaments existing from 
the spinnerette were drawn while being cooled in air to a temperature 
where the filaments did not stick to the surface of the first take-up 
roll. Just above the first take-up roll, a finish was applied to the yarn 
to and further processing and to dissipate any static charge buildup. The 
yarn on the first roll was drawn in line. The yarn on the first roll which 
turned at 1624 rpm was advanced to a second roll which turned at 3492 rpm 
and from the second roll onto a third roll which turned at 3492 rpm. The 
yarn was then advanced from the third roll to a winder of 3492 rpm, which 
wound the yarn upon a sleeve. The temperature of the rolls was 
approximately 65.degree. C., 150.degree. C., and 23.degree. C. for the 
rolls 1, 2, and 3, respectively. The differences in roll speeds resulted 
in an overall draw ratio of 2.15:1. The final yarn floated in a liquid 
with a density of 0.79 g/cc and had a denier of 200/10 (20 dpf). A visual 
count of 10 cross sections revealed an average of 34 voids per cross 
section.