U.S. patent number 3,676,540 [Application Number 05/124,583] was granted by the patent office on 1972-07-11 for wet-spinning shaped fibers.
This patent grant is currently assigned to American Cyanamid Company. Invention is credited to Howard Bundegaard, Richard Neil Story.
United States Patent |
3,676,540 |
Story , et al. |
July 11, 1972 |
WET-SPINNING SHAPED FIBERS
Abstract
A process for wet-spinning filaments of diversiform
cross-sectional configuration comprising; extruding a fiber-forming
polymer solution through orifices of diversiform cross-sectional
configuration in a spinnerette of low thermal conductivity into a
cold aqueous coagulating liquid while simultaneously and
continuously withdrawing the resulting coagulum from said
coagulating liquid at a linear velocity at least 0.5 times the
average linear velocity of said polymer solution through said
orifices.
Inventors: |
Story; Richard Neil
(Cincinnati, OH), Bundegaard; Howard (Norwalk, CT) |
Assignee: |
American Cyanamid Company
(Stamford, CT)
|
Family
ID: |
22415717 |
Appl.
No.: |
05/124,583 |
Filed: |
March 15, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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696495 |
Jan 9, 1968 |
|
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Current U.S.
Class: |
264/177.13;
264/177.18; 264/182; 428/399 |
Current CPC
Class: |
D01F
6/18 (20130101); D01D 5/06 (20130101); Y10T
428/2976 (20150115) |
Current International
Class: |
D01D
5/06 (20060101); D01F 6/18 (20060101); B28b
021/54 (); D01f 007/00 () |
Field of
Search: |
;264/177F,182
;161/177 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Woo; Jay H.
Parent Case Text
This is a continuation of Ser. No. 696,495, filed Jan. 9, 1968 and
now abandoned.
Claims
We claim:
1. A process for wet-spinning filaments of diversiform
cross-sectional configuration comprising; extruding a hot
fiber-forming acrylonitrile polymer solution in aqueous solution of
a solvent-forming salt or organic solvent through orifices of
diversiform cross-sectional configuration in a spinnerette of low
thermal conductivity directly into a cold aqueous coagulating
liquid within which said orifices are disposed to coagulate said
acrylonitrile polymer by leaching solvent out of the extrudate so
produced while simultaneously and continuously withdrawing the
resulting coagulum from said coagulating liquid at a linear
velocity at least 0.5 times the average linear velocity of said
polymer solution through said orifices but below that at which the
freshly forming coagulum breaks.
2. A process as defined in claim 1 wherein said polymer solution
comprises an acrylonitrile polymer dissolved in a concentrated
aqueous solution of a solvent-forming salt at about 60.degree. C.
to about 80.degree. C. and said coagulating liquid comprises a
dilute aqueous solution of the same salt maintained at a
temperature below about +10.degree. C.
3. A process as defined in claim 2 wherein said salt is zinc
chloride or a water-soluble thiocyanate.
4. A process as defined in claim 1 wherein said coagulum is
withdrawn from said coagulating liquid at a linear velocity of
between 0.5 and 2.0 times the average linear velocity of said
polymer solution through said orifices.
5. A process as defined in claim 1 wherein said coagulum is
withdrawn from said coagulating liquid at a linear velocity of
between 0.7 and 1.5 times the average linear velocity of said
polymer solution through said orifices.
6. A process as defined in claim 1 wherein said spinnerette
comprises a plastic material which is inert to said polymer
solution and said coagulating liquid.
7. A process as defined in claim 6 wherein said plastic material is
an epoxy resin.
8. A process as defined in claim 3 wherein said polymer solution
has a dope consistency index of between 10.5 and 15.0.
Description
This invention relates to a process for wet-spinning filaments of
diversiform cross-sectional configuration. More particularly, this
invention relates to producing such filaments from solutions of
polymers, such as acrylonitrile polymers, by a wet-spinning process
wherein the extrudate from the spinnerette is coagulated by
leaching solvent therefrom.
Recently, synthetic fiber technology has advanced to the stage
wherein it has become recognized that useful properties can be
imparted to synthetic fibers by making them of diversiform
cross-sectional configuration. Such "diversiform cross-sectional
configurations" include multi-lobal fibers (e.g. trilobal or
tetra-lobal cross-section), ribbon fibers (rectangular or
substantially rectangular cross-section), and dog-bone fibers
(something like a figure "8" cross-section). Fibers of such
diversiform cross-section configurations may be monocomponent
(i.e., uniform composition across the cross-section) or
multi-component (i.e., two or more discrete areas of different
composition across the cross-section) fibers. Numerous recent
references exist disclosing many diversiform cross-sectional
configurations and the advantages thereof.
In general, synthetic filaments can be produced from polymeric
materials by melt-spinning, dry-spinning, or wet-spinning
processes. In the "melt-spinning process" for forming synthetic
filaments, polymer liquefied by melting is extruded through
spinnerette orifices to form an extrudate which is coagulated by
cooling. Typically, polyamide, polyester, and glass fibers are
produced by melt-spinning. In the "dry-spinning process" for
forming synthetic filaments, polymer liquefied by dissolving in a
volatile solvent is extruded through spinnerette orifices to form
an extrudate which is coagulated by evaporation of the volatile
solvent. Typically, cellulose acetate solutions in acetone,
acrylonitrile polymer solutions in dimethylformamide, etc. are spun
into fibers by dry-spinning. In the "wet-spinning process" for
forming synthetic filaments, polymer liquefied by dissolving in a
solvent is extruded through spinnerette orifices to form an
extrudate which is coagulated by removal of solvent in a liquid
coagulating medium. In wet-spinning fibers of some polymers, such
as from solutions of acrylonitrile polymers in aqueous nitric acid,
aqueous salt, or organic solvents, the solvent is removed by
leaching it out of the extrudate in a cold aqueous coagulant. In
wet-spinning fibers of other polymers, such as from viscose
(aqueous sodium hydroxide solution of cellulose xanthate), the
solvent is removed by chemical reaction with an aqueous sulfuric
acid coagulant.
The various synthetic filaments of diversiform cross-sectional
configuration found in the recent prior art were made by
melt-spinning or dry-spinning processes since, with these
processes, it was generally necessary only to replace the
spinnerettes having round orifices with other spinnerettes having
appropriately shaped orifices. Because of the numerous well-known
advantages of wet-spinning processes, it would be highly desirable
to be able to spin such fibers by a wet-spinning process. However,
when attempts were made to similarly modify wet-spinning processes,
particularly ones wherein coagulation was effected by leaching
solvent out of the extrudate with a cold aqueous coagulant, fibers
of substantially circular cross-sectional configuration were still
produced. Perhaps this anomalous result arises because coagulation
is a much slower process when solvent has to be leached out of the
extrudate as compared to evaporation of solvent or cooling molten
polymer.
Accordingly, it is an object of the present invention to provide a
wet-spinning process for preparing filaments of diversiform
cross-sectional configuration. It is a further object of this
invention to provide a wet-spinning process for forming such fibers
of acrylonitrile polymers by suitable and minimal modifications to
existing wet-spinning processes involving extruding solutions of
acrylonitrile polymers into cold aqueous coagulating liquids.
These objects, and others as will appear or become evident from
this specification, are mainly obtained by (a) use of a spinnerette
of low thermal conductivity having orifices of diversiform
cross-sectional configuration in combination with (b) withdrawing
the freshly formed coagulum (into which the extrudate is converted
by the cold aqueous coagulating liquid) at a linear rate in excess
of 0.5 times the average linear velocity with which the polymer
solution passes through said orifices.
While the present invention is not limited to spinning fibers of
any particular diversiform cross-sectional configuration, numerous
such shapes for fibers and spinnerette orifices are known and
illustrated in such U.S. Pats. as Nos. 1,773,969; 1,964,659;
2,000,388; 2,508,799; 2,302,555; 2,746,839; 2,637,893; 2,816,349;
2,825,120; 2,831,748; 2,838,365; 2,939,201, 2,939,202; 3,017,686;
3,077,633; 3,097,416; 3,109,195; 3,117,906; 3,131,428; 3,156,085;
and 3,204,290. In the practice of the present invention, the
spinnerette orifices may have any of such diversiform
cross-sectional configurations as may be appropriate to the
cross-sectional configuration of the fibers to be spun
therethrough.
It must be recognized, however, that the cross-sectional
configurations of the fibers produced in accordance with the
present invention are not necessarily identical to the
cross-sectional configurations of the orifices through which they
are spun, since, depending upon other conditions, there is a
variable tendency for the extrudate to assume a cross-sectional
configuration during coagulation which is rounder or more compact
than the orifices through which extrusion occurred.
For wet-spinning acrylonitrile polymers, numerous solvents are
known. Illustrative of commercially utilized solvents are
concentrated aqueous salt solutions of zinc chloride or sodium
thiocyanate, concentrated nitric acid solution, and
dimethylacetamide although numerous others can be found in such
U.S. Pats as Nos. 2,140,921; 3,124,629; 2,698,646 through
2,698,649; 2,558,730 through 2,558,735; 2,790,700; and many others.
To form fibers, solutions of acrylonitrile polymers in such
solvents are normally extruded into aqueous coagulants which may be
water, dilute aqueous solutions of the same materials which are
solvents for acrylonitrile polymers when more concentrated or
substantially anhydrous, or dilute aqueous solutions containing
other materials.
When wet-spinning into aqueous coagulants, it has generally been
found important to keep the coagulant cold to convert the extrudate
into a clear, strong, flexible coagulum which could be dried to
form fibers relatively free of porosity. As pointed out in Craig et
al. "Characterization of Acrylic Fiber Sturcture" Textile Research
Journal, Vol. 32 No. 6, June 1962, pages 435-448, commercial
wet-spinnings of acrylonitrile polymers have long utilized cold
aqueous coagulants for this reason.
In such spinning systems, the simple substitution of metal
spinnerettes with orifices of diversiform cross-sectional
configuration for the metal spinnerettes with circular orifices
still yielded round fibers. Thus, until the present invention, it
was believed that the highly desirable fibers of diversiform
cross-sectional configuration could not be produced by wet-spinning
into cold aqueous coagulating liquids. Surprisingly, we have found
that such fibers can be formed by the process of the present
invention.
In the practice of the process of present invention, it is
essential that the spinnerette be of low thermal conductivity.
Illustrative of materials of low thermal conductivity of which
spinnerettes can be made are plastic materials (e.g. epoxy resins,
formaldehyde resins, polyesters, polyamides,
polytetra-fluoroethylene, etc.), ceramics, and glass. We have found
that metal spinnerettes, such as are usually used for wet-spinning
synthetic fibers of circular cross-section and for dry-spinning or
melt-spinning synthetic fibers of circular or diversiform
cross-sectional shapes, have too high a thermal conductivity to be
useful for the present invention.
In the practice of the process of the present invention, it is also
essential that the extrudate prior to becoming and as a nascent
coagulum, formed upon extruding the fiber-forming polymer solution
directly into the cold aqueous coagulating liquid, be withdrawn
from the coagulating liquid at a linear velocity at least 0.5 times
the average linear velocity of the polymer solution passing through
the spinnerette orifices. In other words, it is essential that the
"jet stretch" be at least 0.5X. At jet stretches below about 0.5X,
even with spinnerettes of low thermal conductivity, there is too
great a tendency for the coagulum to assume a circular
cross-sectional configuration. We have found that, other things
remaining constant, the higher the jet stretch the less the fiber
cross-section deviates from the cross-sectional shape of the
spinnerette orifice. The upper limit of jet stretch useful herein
is a function of factors extrinsic to the present invention.
Obviously, one cannot utilize a jet stretch so high that the
freshly forming coagulum breaks. We have found that jet stretches
above about 2.0X tend to produce undesirable fiber properties in
the final product. To achieve good balance of cross-sectional
configuration retention and fiber properties, jet stretches between
0.7X and 1.5X are generally preferred for wet-spinning processes
utilizing the present invention.
Except for the aforementioned modifications, the present invention
makes use of conventional wet-spinning process technology. Known
techniques may be utilized for preparation of the solutions of
fiber-forming polymers and for forwarding such solutions to the
spinnerette orifices. Also, known techniques for treating the
freshly formed coagulum may be utilized for converting it into a
fiber suitable for its intended uses. For example, the coagulum
formed upon extrusion of an acrylonitrile polymer into a cold
aqueous coagulant may then be stretched while still in the wet gel
form and containing solvent, washed free of solvent, further
stretched at elevated temperature, dried in a relaxed
free-to-shrink condition, steam relaxed, etc. as is well known in
making fibers of circular cross-section. Alternatively, it may be
subjected to any other known processing sequence.
For a more detailed understanding of the present invention,
reference may be had to the following examples illustrative of a
preferred embodiment thereof. In these examples, all compositions
are expressed in weight percentages unless otherwise stated.
The "relative viscosity" (Nr) of each acrylonitrile polymer
solution used may be determined in accordance with the procedure
published in the Journal of Polymer Science, Part A, Vol. 3, pages
1,359-1371 (1965) where
Generally, polymer solutions whose relative viscosities are between
about 50 and about 20,000 are utilized for wet-spinning processes.
The "dope consistency index" (I) of such a solution may be
calculated by the following formula
I = log.sub.10 [C.sup.5 .times. M.sup.3.4 ]
wherein C = polymer concentration in solution in grams/cc. and M =
weight average molecular weight of polymer. When a concentrated
aqueous sodium thiocyanate solution is utilized as the solvent for
the acrylonitrile polymer, a dope consistency index of between
about 10.5 and about 15.0 represents a relative viscosity of
between about 50 and about 20,000. The "aspect ratio" of a
generally rectangular cross-sectional configuration (whether of a
spinnerette orifice or of a fiber) is calculated by dividing the
length of the rectangle by its width.
EXAMPLE 1
An acrylonitrile polymer (89.2 percent acrylonitrile, 10.8 percent
methyl methacrylate) was dissolved in a 40 percent aqueous sodium
thiocyanate solution to form a spin dope containing 11.3 percent
polymer and having a dope consistency index of 13.061. This spin
dope was heated to 60.degree. C. and extruded through an epoxy
resin spinnerette provided with orifices of rectangular
cross-section measuring 2.3 mils .times. 14.6 mils (aspect ratio =
6.35) into a cold aqueous coagulating liquid which was a 10 percent
solution of sodium thiocyanate maintained at about -2.degree. C.
The thus formed filamentary coagulum was withdrawn from the bath at
a linear velocity of 1.2 times the average linear velocity of the
spin dope through the spinnerette orifices (jet stretch = 1.2X).
Thereafter, this filamentary coagulum was stretched to two times
its original length, washed with water until free of sodium
thiocyanate, restretched to about 6 times its previous length in
water at about 100.degree. C., dried in a relaxed free-to-shrink
condition under controlled temperature and humidity conditions (as
described in U.S. Pat. No. 2,984,912), and then relaxed about 36
percent in pressurized steam. The thus formed fibers had good
textile properties and an average aspect ratio of about 3.0. This
example illustrates a preferred embodiment of the present
invention.
EXAMPLE 2
The process of Example 1 was repeated using the same plastic
spinnerette except that the jet stretch was reduced to 0.5X. The
fibers so produced had good textile properties with an average
aspect ratio of about 1.7. This example (when compound with Example
1) illustrates the functional relationship between jet stretch and
degree of fiber cross-sectional modification. This is about the
minimum aspect ratio useful for modifying yarn and fabric
esthetics.
EXAMPLE 3
The process of Example 2 was repeated using a jet stretch of 0.5X
except for the substitution of a platinum-rhodium spinnerette
provided with orifices of rectangular cross-section measuring 2.4
mils .times. 15.6 mils (aspect ratio = 6.5). The fibers so produced
were essentially round in cross-section. This example (when
compared with Example 2) illustrates the criticality of using
spinnerettes of low thermal conductivity in obtaining fibers of
diversiform cross-sectional configuration at jet stretches near the
low end of the range useful for the present invention.
EXAMPLE 4
The process of Example 3 was repeated using the same metal
spinnerette except that the jet stretch was raised back up to 1.2X.
No fibers could be obtained due to breakage of all filaments at the
face of the spinnerette. This example (when compared with Example
1) also illustrates the criticality of using spinnerettes of low
thermal conductivity in obtaining fibers with higher jet stretches.
Under the spinning conditions of Example 1, when using metal
spinnerettes, the maximum jet stretches obtainable were found to be
about 0.5X whereas, with plastic spinnerettes, jet stretches
exceeding 2.5X were possible. However, with plastic spinnerettes,
some losses in textile properties were observed when jet stretches
above about 2.0X were used.
EXAMPLE 5
The process of Example 1 was repeated using the same plastic
spinnerette (orifice aspect ratio = 6.35) but with variations in
(a) jet stretch and (b) coagulating liquid concentration. Four runs
were made, viz., Run A using a jet stretch of 0.8X through a cold
aqueous coagulating liquid of 6 percent sodium thiocyanate solution
to yield fibers having an average aspect ratio of about 2.5; Run B
using a jet stretch of 1.6X through the same 6 percent solution to
yield fibers having an average aspect ratio of about 4.0; Run C
using a jet stretch of 0.8X through a cold aqueous coagulating
liquid of 18 percent sodium thiocyanate solution to yield fibers
having an average aspect ratio of about 2.2; and Run D using a jet
stretch of 1.6X through the same 18 percent coagulating solution to
yield fibers having an average aspect ratio of about 3.4. All these
fibers had good textile properties. This example (especially when
taken with Examples 1 and 2) illustrates the effects of variations
in jet stretch and coagulant concentrations to be expected in
practicing this invention and illustrates the wide range over which
some variables can vary.
EXAMPLE 6
Separate spin dopes were prepared by dissolving acrylonitrile
polymers (89.2 percent acrylontrile, 10.8 percent methyl
methacrylate) in 40 percent aqueous sodium thiocyanate solutions to
form (a) an 8.4 percent polymer solution having a dope consistency
index of 12.3,410 and (b) a 14.0 percent polymer solution having a
dope consistency index of 13.5,905. Each spin dope was heated to
80.degree. C. and extruded, in separate runs, through epoxy resin
spinnerettes provided with orifices of rectangular cross-section
measuring either (a) 3.0 mils .times. 15 mils (aspect ratio = 5.00)
or (b) 2.4 mils .times. 19.9 mils (aspect ratio = 8.3) into a
12percent aqueous sodium thiocyanate coagulating both maintained at
about -4.degree. C. In each run, the thus formed filamentary
coagulum was subjected to a jet stretch of 1.2X and thereafter
treated as in Example 1 to produce four separate fiber products.
The four runs made were Run E spinning the 8.4 percent polymer
solution through orifices of 5.00 aspect ratio to yield fibers
having an average aspect ratio of about 1.8; Run F spinning the
14.0 percent polymer solution through orifices of 5.00 aspect ratio
to yield fibers having an average aspect ratio of about 2.2; Run G
spinning the 8.4 percent polymer solution through orifices of 8.3
aspect ratio to yield fibers having an average aspect ratio of
about 3.4; and Run H spinning the 14.0 percent polymer solution
through orifices of 8.3 aspect ratio to yield fibers having an
average aspect ratio of about 4.4. All these fibers had good
textile properties. This example illustrates the effects of
variations in orifice configuration and spinning solution
consistency index to be expected in practicing this invention.
EXAMPLE 7
An epoxy resin spinnerette provided with +-shaped orifices of about
115,000.mu..sup.2 cross-sectional area was used to spin a spin dope
substantially the same as was spun in Example 1 under substantially
the same spinning conditions as in Example 1 except that the jet
stretch was 1.17X, the restretching was about 6.25X, and the final
relaxation step was omitted. The thus formed fibers had a generally
squarish cross-sectional shape with wavy sides. This example
illustrates the spinning of a fibers of a different diversiform
cross-sectional configuration than the preceding examples.
EXAMPLE 8
An epoxy resin spinnerette provided with Y-shaped orifices of about
90,000.mu..sup.2 cross-sectional area was used to spin a spin dope
substantially the same as was spun in Example 1 in three separate
runs under substantially the same spinning conditions as in Example
1 except that the jet stretches were 1.33X, 1.0X, and 0.75X in the
three runs, the restretching was about 6.25X and the final
relaxation was in water at about 100.degree. C. The thus formed
fibers ranged in cross-sectional configuration from substantially
the same shape as the orifices through "arrow head" cross-sections
and substantially triangular cross-sections with wavy sides to
gibbous triangular cross-sections with decrease in jet stretch.
This example illustrates production of fibers of yet another
diversiform cross-sectional configuration and the variation of
shape produced as a function of jet stretch with the higher jet
stretches yielding fibers whose cross-sectional configuration more
closely resembled the cross-sectional configuration of the orifices
through which they had been spun.
It will be appreciated by those skilled in the art to which the
present invention pertains that many modifications of this
invention can be made without departing from the spirit thereof. It
is intended that all modifications as are included in the foregoing
description or are made obvious thereby are to be considered as
encompassed within the scope of the subjoined claims.
* * * * *