Method for producing filaments of high tenacity

A molten polymer is extruded through at least one orifice to produce a filament which is immediately cooled to a temperature below its glass transition temperature by contacting the filament with a gas having a temperature ranging from about +10.degree. C. to about -20.degree. C.

The invention relates to a filament and to a method for producing a 
filament from thermoplastic polymers. In another aspect, the invention 
relates to gas quenching thermoplastic filaments produced by melt 
spinning. 
The process of melt spinning thermoplastic synthetic filaments by extruding 
a molten polymer through a spinneret having at least one orifice to 
produce a filament, cooling the filament to a temperature below the glass 
transition temperature of the polymer and heating and drawing the filament 
to substantially improve the physical properties of the filament such as 
tenacity, modulus, elongation, etc. is well known in the art. Further, it 
is recognized in the art, such as for example U.S. Pat. No. 3,489,832 
issued to Bruton et al on Jan. 13, 1970, that the temperature of the 
medium employed to cool the freshly spun filament to a temperature below 
the glass transition temperature of the polymer is important. Burton et al 
broadly teach that in spinning polycaproamide yarns the temperature of the 
quenching air should not be above 35.degree. C. and in a specific example 
employ quench air at a temperature of 28.degree. C. 
In two other patents, U.S. Pat. No. 3,118,012 and U.S. Pat. No. 3,213,171 
issued to J. J. Kilian on Jan. 4, 1964 and on Oct. 19, 1965 respectively, 
quenching freshly spun filaments with a gas having a temperature ranging 
from 15.degree. C. to 40.degree. C. is described. In addition, the patent 
teaches that the use of the cooler medium simply adds undue cost to the 
process. 
Dutch Pat. No. 7,307,431 describes a process for producing fibers from 
crystalline plastic materials which have extraordinarily good properties. 
The patent describes a process employing a liquid quenching medium as 
compared to the gaseous quenching medium used in the previously discussed 
patents. The liquid quenching medium is maintained at very low 
temperatures. For example, the patent teaches that the cooling bath must 
be kept at a temperature of less than -30.degree. C., and preferably less 
than -50.degree. C. Several examples are described in the patent in which 
the temperature of the quenching liquid ranged from -75.degree. C. to 
-100.degree. C. Although it is well known in the art that generally the 
use of a liquid quenching bath alters the properties of the filaments and 
particularly the surface of the fiber as compared to a gas quenching 
medium, the Dutch patent does teach that the properties of filaments 
quenched with a liquid bath can be improved by lowering the temperature of 
the bath; however, extremely low temperatures are required. 
It was found that the properties of filaments quenched or cooled with a 
gas, such as air, nitrogen, carbon dioxide or other gas inert to the 
process, can be substantially improved if the temperature of the gas is 
somewhat colder than that taught by Burton et al or Kilian. Such a result 
is surprising in view of the prior art discussed above, and particularly 
in view of the teaching of Kilian that temperatures of the quenching gas 
below about 15.degree. C. simply added undue cost to the process and in 
view of the fact that a substantial improvement in the properties of the 
fibers can be realized without employing quenching liquid baths operated 
at temperatures of -30.degree. C. and lower. 
It is an object of the invention to produce gas quenched thermoplastic 
filaments having improved properties as compared to filaments produced in 
accordance with the prior art. 
Another object of the invention is to improve the properties of gas 
quenched thermoplastic filaments and at the same time minimize the expense 
in producing the filaments. 
SUMMARY OF THE INVENTION 
According to the invention, a molten polymer is extruded through at least 
one orifice to produce a filament and the filament is immediately cooled 
to a temperature below its glass transition temperature by contacting the 
filament with a gas having a temperature ranging from about -20.degree. C. 
to about 10.degree. C., wherein the polymer is selected from the group 
consisting of polyethylene terephthalate, polycaprolactam, and the 
condensation product of 5-methyl-1,9-nonanediamine and terephthalic acid. 
The present invention is applicable to a specific group of thermoplastic 
polymers. The polymers suitable for use in the invention are polyethylene 
terephthalate, polycaprolactam and poly(5-methyl-1,9-nonamethylene 
terephthalamide) which is the condensation product of 
5-methyl-1,9-nonanediamine and terephthalic acid. 
Further, the invention is limited to the use of gas quenching processes as 
compared to liquid quenching processes. The gases that can be employed 
according to the invention vary widely, the only requirement being that 
the gas is inert with respect to the polymer being extruded. Some of the 
gases suitable for use in the invention include for example air, nitrogen, 
helium, and carbon dioxide; however, air was used in the Example 
hereinafter described with good success and because it is readily 
available, air is the preferred gas quenching medium. 
According to the invention the temperature of the gas quenching medium 
broadly is within the range of from about -20.degree. C. to about 
10.degree. C.; however, good results were obtained employing a gas 
temperature ranging from about -10.degree. C. to about 0.degree. C. 
Although it may be possible to obtain filaments with improved properties 
when employing quenching gas temperatures below -20.degree. C., one object 
of the invention is to minimize the cost of the process while obtaining an 
improvement in the properties of the filaments as compared to filaments 
obtained employing prior art processes. Based upon the good results 
obtained employing a gas temperature ranging from about -10.degree. C. to 
about 0.degree. C., it is believed that the lowest temperature that should 
be employed from an economic standpoint is -20.degree. C. 
Most any spinning apparatus used for melt spinning thermoplastic filaments 
known in the art can be used in the present invention provided it is 
capable of providing quenching gas within the temperature ranges defined 
above. Also the filament or filaments produced in accordance with the 
invention are drawn employing apparatus known in the art. No special 
equipment is required to draw the filaments produced in accordance with 
the present invention. 
Generally the filaments produced by the process of the invention are drawn 
employing heater temperatures ranging from about 2.degree. C. to about 
40.degree. C. below the glass transition temperature of the polymer. Based 
upon the results of the Example hereinafter described, it is believed that 
good results can be obtained employing heater temperatures ranging from 
about 5.degree. C. to about 20.degree. C. below the glass transition 
temperature of the polymer.

EXAMPLE 
Four runs were carried out to demonstrate the invention. Runs 1 and 3 were 
carried out in accordance with the invention and runs 2 and 4 were carried 
out outside the scope of the invention. In all the runs the polymer 
employed was the condensation product of 5-methyl-1,9-nonanediamine and 
terephthalic acid. The polymer was extruded using a piston extruder having 
approximately a 20 gram capacity and using a 6 hole spinneret with 0.009 
inch (0.023 cm) diameter holes and with a capillary length of 0.012 inches 
(0.030 cm). The extrusion rate was 1 cc/min and the spinning temperature 
was 300.degree. C. Two take up speeds were employed, 280 feet/min (85.34 
meters/min) in runs 1 and 2 and 400 feet/min (121.92 meters/min) in runs 3 
and 4. The filaments were drawn employing two godet rolls with a heat 
positioned between the rolls and operated at 100.degree. C. The glass 
transition temperature of the polymer employed in the runs was 112.degree. 
C. In runs 2 and 4, the non-inventive runs, ambient air was used as the 
quenching air which had a temperature ranging from about 20.degree. C. to 
25.degree. C. In the invention runs, runs 1 and 3, the freshly spun 
filaments were passed through an insulated double wall cylindrical chamber 
having an inside diameter of 4 inches (10.16 cm) and an outside diameter 
of 6 inches (15.24 cm) to provide an annular space of approximately 1 inch 
(2.54 cm). The cylindrical chamber was positioned immediately below the 
spinneret and had a length of 2 feet (0.609 meters). In the runs carried 
out in accordance with the invention, runs 1 and 3, the annulus was filled 
with dry ice so that the air inside the cylindrical chamber was maintained 
with in the range of -10.degree. C. to 0.degree. C. The results of runs 1 
to 4 are provided in Table I below: 
TABLE I 
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Temp. of Draw 
Take up Speed 
Tenacity.sup.(1) 
Percent.sup.(2) 
Modulus 
Run # 
Quench Air 
Ratio 
(feet/min) 
Denier 
g/denier 
Elongation 
(initial) 
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1 -10.degree. C. to 0.degree. C. 
4.5 280 25 3.7 19.1 34 
2 20.degree. C. to 25.degree. C. 
4.5 280 25 3.3 17.5 32 
3 -10.degree. C. to 0.degree. C. 
4.5 400 20 3.35 19.0 29.6 
4 20.degree. C. to 25.degree. C. 
4.5 400 21 2.81 16.5 24.6 
__________________________________________________________________________ 
.sup.(1) Tenacity was determined employing ASTM test D 2101-72 
.sup.(2) Percent Elongation was determined employing ASTM test D 2256-72 
.sup.(3) Modulus was determined employing ASTM test D 885-72 
Runs 2 and 4 employing a quench air temperature within the range of 
temperatures described in Burton et al and Kilian discussed in the 
background of the invention produced filaments having a lower tenacity, 
percent elongation, and initial modulus as compared to the filaments 
produced in Runs 1 and 3 respectively. Of course, the comparison is made 
only between yarns of approximately the same denier, i.e., run 1 with run 
2 and run 3 with run 4.