Process for melt-spinning acrylonitrile polymer fiber

Melt-spinning of a fusion melt of an acrylonitrile polymer and water through a crowded hole spinnerette plate having small orifice diameters is achieved using low molecular weight polymer to provide fiber of desirable physical properties.

This invention relates to a process for melt-spinning fiber-forming 
polymers at an increased production rate per spinnerette. More 
particularly, this invention relates to such a process wherein a 
spinnerette with a greater number of smaller orifices per given area is 
employed. 
In conventional melt-spinning of fibers, a fiber-forming polymer is heated 
to a temperature at which it melts, is extruded through a spinnerette 
plate to form filaments which rapidly cool to become solid, and the 
resulting filaments are then further processed to provide the desired 
fiber. The spinnerette plate that is employed in such processing must 
contain capillaries to provide the desired filaments while satisfying two 
additional requirements. The capillaries must be of such dimensions as to 
satisfy back-pressure requirements and must be sufficiently spaced from 
one another as to prevent premature contact between the emerging fibers 
that would result in sticking together or fusion of filaments with one 
another. To satisfy the back-pressure requirements, the capillaries are 
provided with counterbores of sufficient diameter and depth. 
Recent developments in the field of fiber spinning, especially acrylic 
fibers, has led to the development of fusion melts which can be extruded 
through a spinnerette plate to provide filaments. These fusion melts 
comprise a homogeneous composition of a fiber-forming polymer and a melt 
assistant therefor. The melt assistant is a material which enables the 
polymer to form a melt at a temperature below which the polymer would 
normally melt or decompose and becomes intimately associated with the 
molten polymer so that a single phase melt results. The melt assistant 
must be used in proper proportions with the polymer to provide the 
single-phase fusion melt. If a low boiling melt assistant is used the melt 
assistant in proper amounts and the polymer often must be heated at 
pressures above atmospheric pressure to provide the fusion melt. Since the 
temperature at which the fusion melt forms is above the boiling point of 
the melt assistant at atmospheric pressure, consequently super-atmospheric 
pressures are necessary to keep the melt assistant in the system. Such 
fusion melts have been effectively spun into fiber using spinnerette 
plates similar to those employed in conventional melt-spinning. 
Because of the requirement for adequate spacing of the capillaries in 
spinnerette plates used for melt-spinning to prevent premature contact 
between the nascent filaments which would result in their sticking 
together, the number of capillaries that can be provided in a given 
spinnerette plate is greatly restricted. As a result, production capacity 
of a spinnerette with a given surface area is limited and usually large 
tow bundles can only be produced by combining the outputs from a series of 
spinnerettes. This, in turn, requires costly installations of additional 
spinnerettes, specially designed conduits and spin packs to ensure an even 
distribution of the melt to all spinning holes, provision of space for 
installation, and further power consumption to operate the increased 
number of spinnerettes. 
There exists, therefore, the need for processes for providing fiber by melt 
spinning which enables the productivity of spinnerettes to be increased. 
Such provision would fulfill a long-felt need and constitute a significant 
advance in the art. 
In accordance with the present invention, there is provided a process for 
melt-spinning acrylonitrile polymer fiber which comprises providing a 
homogeneous melt of an acrylonitrile fiber-forming polymer of kinematic 
molecular weight in the range of about 30,000 to 60,000 and water at a 
temperature above the boiling point of water at atmospheric pressure and 
at a temperature and pressure which maintains water in single phase with 
said polymer and extruding said fusion melt through a spinnerette assembly 
containing a spinnerette plate having a density of orifices of a diameter 
of about 60 to 160 microns of at least about 18 per square centimeter 
directly into a steam-pressurized solidification zone maintained under 
conditions such that the release of water from the nascent extrudate 
avoids deformation thereof. 
The process of the present invention provides filamentary extrudates which 
do not stick together as they emerge from the spinnerette orifices. Since 
the filaments have no tendency to stick together, the orifices of the 
spinnerette plate can be located closer together and more orifices can be 
provided in the spinnerette plate. As a result, the productivity of a 
spinnerette can be greatly increased without negatively affecting the 
quality of the resulting fiber. The present invention also employs 
orifices of reduced cross-section relative to those conventionally 
employed in melt-spinning. As a result an even greater number of orifices 
can be present in the spinnerette plate. In order to overcome 
back-pressure difficulties that would arise with the orifices of narrow 
cross-section, the process of the present invention employs fiber-forming 
polymers of lower molecular weight than conventionally employed. 
Unexpectedly, the fiber obtained possesses good fiber properties in spite 
of the low molecular weight of the fiber-forming fiber. It is believed 
these good fiber properties are the result of processing steps employed. 
The spinnerette plate used in the process of the present invention has two 
distinguishing features over conventional spinnerette plates used in 
conventional melt-spinning processes. First, the spinnerette has a much 
greater density of orifices per unit area than do the conventional plates 
used in melt-spinning by conventional procedures. Typically, prior art 
melt-spinning spinnerette plates have a density of about 5-10 orifices per 
square centimeter. In the process of the present invention, the 
spinnerette plate contains at least about 18 orifices per square 
centimeter. Second, the conventional melt-spinning spinnerette plates have 
orifices of about 200-400 microns or larger diameter at their exit ends. 
The process of the present invention, contrary to this, uses orifices in 
the range of about 60-160 microns diameter at their exit ends. This 
provision not only allows a greater number of orifices to be positioned in 
the spinnerette plate to increase productivity but also enables finer 
denier fiber to be provided at a given stretch ratio. 
In carrying out the process of the present invention, it is necessary to 
provide a homogeneous fusion melt of a fiber-forming acrylonitrile polymer 
and water. Any fiber-forming acrylonitrile polymer of the specified 
molecular weight range that can form a fusion melt with water at a 
temperature above the boiling point of water at atmospheric pressure and 
at a pressure and temperature sufficient to maintain water and the the 
polymer in a single, fluid phase can be used in the process of the present 
invention. Polymers falling into this category are known in the art. The 
fusion melt is prepared at a temperature above the boiling point at 
atmospheric pressure of water and eventually reaches a temperature and 
pressure sufficient to maintain water and the polymer in a single, fluid 
phase. 
The homogeneous fusion melt is extruded through the spinnerette plate of 
high orifice density and reduced orifice diameter directly into a 
steam-pressurized solidification zone maintained under conditions such 
that the rate of release of water from the nascent extrudate avoids 
deformation thereof. By controlling the release of water from the nascent 
extrudate, such deformations thereof as foamed structure, inflated 
structure, pock-marked structure, and the like which adversely affect 
processability are avoided and continuous processing can be effected in 
spite of the high density of orifices and low diameter thereof in the 
spinnerette plate. The extruded filaments are also free of any tendency to 
stick together due to their nature. The homogeneous fusion melt is a 
special type of melt that requires the combination of proper amounts of 
water and polymer, high temperature, and superatmospheric pressure. Slight 
variations in these critical features leads to solidification of the 
polymer which in solidification form exhibits no tendency toward 
stickiness. The extrudate filaments are processed further according to 
conventional procedures to provide desirable filamentary materials which 
may have application in textile and other applications.

The invention is more fully illustrated in the examples which follow 
wherein all parts and percentages are by weight unless otherwise 
specified. 
Kinematic average molecular weight (M.sub.k) is obtained from the following 
relationship: 
##EQU1## 
wherein .mu. is the average effluent time (t) in seconds for a solution of 
1 gram of the polymer in 100 milliliters of 53 weight percent aqueous 
sodium thiocyanate solvent at 40.degree. C. multiplied by the viscometer 
factor and A is the solution factor derived from a polymer of known 
molecular weight and in the present case is equal to 3,500. 
EXAMPLE 1 
A fusion melt of 14% water and 86% of an acrylonitrile polymer of the 
following composition was prepared: 
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Acrylonitrile 84.98 
Methyl methacrylate 12.0% 
Polyvinyl alcohol (Trademark 
Elvanol 71-30G) 3.0% 
Acrylamidomethylpropane 0.1% 
sulfonic acid 
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This polymer had a kinematic molecular weight value of 40,000. The fusion 
melt was spun through a spinnerette plate having the following 
characteristics: 
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Capillary Diameter 120 microns 
Capillary spacing, center to center 
1.3 millimeters 
Counterbore Diameter 1.2 millimeters 
Counterbore spacing center to 
1.2 millimeters 
center 
Capillary Density 54 per square 
Centimeter 
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The extrusion temperature was 170.degree. C. and extrusion was directly 
into a steam-pressurized solidification zone maintained at 13 pounds per 
square inch gauge. The extrudates were stretched at a stretch ratio of 4.2 
in a first stage and 9.8 in a second stage, dried at 138.degree. C. and 
steam relaxed at 116.degree. C. No filament breakage or sticking occurred. 
The fiber obtained had the following properties: 
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Denier per filament 3.15 
Straight tenacity 3.2 grams/denier 
Straight elongation 30% 
Loop tenacity 2.6 grams/denier 
Loop Elongation 23% 
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COMATIVE EXAMPLE A 
Following the procedure of Example 1 in every material detail, an 
additional run was made using a polypropylene melt free of melt assistant 
and designated as fiber grade having a melt index of 3 (Trademark Rexene 
PP-3153) in place of the fusion melt of example. Extrusion was conducted 
at 260.degree.-280.degree. C. directly into air. The extrudates stuck 
together as they emerged from the spinnerette and the desired individual 
filaments could not be obtained. 
EXAMPLES 2-5 
Again following the procedure of Example 1 in every material detail except 
for the spinnerette plate, a series of runs were made using spinnerettes 
of the characteristics given in Table I which also indicates the example 
number. In each instance, no filament breakage or sticking occurred and 
the fiber obtained had properties substantially similar to those of the 
fiber of Example 1. 
TABLE I 
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Overall 
Plate Capillary COUNTERBORES 
Diam. 
Diameter 
Total 
SING 
DENSITY* 
DIAM. 
SING 
Example 
mm .mu. No. mm NO./cm.sup.2 
mm mm 
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2 381 200 5016 
2.2 18 1.8 2.2 
3 279 120 9060 
1.7 25 1.5 1.7 
4 279 100 5016 
2.2 18 2.0 2.2 
5 76 85 2937 
1.2 67 1.0 1.2 
6 432 120 30000 
1.3 54 1.2 1.3 
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*Spinnerette capillary density was calculated based on effective area of 
plate used (flange area not included). 
EXAMPLE 7 
The process of Example 1 was again repeated in every material detail except 
that the polymer employed was copolymer of 94% acrylonitrile and 6% methyl 
acrylate having a kinematic molecular weight of 48,000. No filament 
breakage or sticking occurred during extrusion and the fiber obtained had 
substantially the same properties as those of Example 1.