Process and device for the formation of monofilaments produced by melt-spinning

A continuous process and apparatus for the production of melt-spun monofilaments having a diameter of 60 .mu.m to 2500 .mu.m from fiber-forming polymers, wherein the polymer melt is spun into air from a spinning head, laterally quenched in a spinning cabinet with a defined air velocity profile and then cooled in a liquid bath.

This invention relates to a continuous process and an apparatus for the 
production of melt-spun monofilaments having a diameter of 60 .mu.m to 
2500 .mu.m from fibre-forming polymers, in particular polyamide. In this 
process, the polymer melt is spun into air from a spinning head, laterally 
quenched in a spinning cabinet with a defined air velocity profile and 
then cooled in a liquid bath. 
BACKGROUND OF THE INVENTION 
Processes for the production of monofilaments from thermoplastic polymers 
without additional air quenching between the spinning head and spinning 
vat containing a liquid coolant are known in principle. Handbuch der 
Kunststoff-Extrusionstechnik II [manual of plastics extrusion II], Carl 
Hanser Verlag, Munich, Vienna, 1986, pages 295 to 319 describes the known 
process stages in detail. According to this reference, thermoplastic 
monofilaments (having a diameter of greater than 60 .mu.m) may be produced 
by spinning, for example in water, at a delivery speed of the finished 
monofilaments of at most 600 m/min. 
Monofilaments of a substantially smaller cross-section and multi-filament 
fibres are directly spun into air as the coolant at a distinctly higher 
delivery speed using other processes. German published patent application 
DE 41 29 521 A1 thus describes an apparatus for high speed spinning 
multi-filament fibres at a windup speed of at least 2000 m/min. 
In the latter-stated process. monofilaments or multi-filament fibres are 
spun into air and directly wound up. One particular feature of this 
process is the cooling apparatus used therein. It consists of a porous 
pipe open in the direction of spinning and arranged concentrically 
relative to the tow. Given the elevated windup speed, no cooling medium is 
actively supplied. The process described therein relates to filament yarns 
with the filaments having an individual linear density of 0.1 to 6 dtex 
and is not applicable to monofilaments having a diameter of greater than 
50 .mu.m (approx. 22 dtex). 
International patent application WO 91/11547 describes a process and 
apparatus for high speed spinning of monofilaments having an individual 
linear density of 1 to 30 dtex (corresponding to approx. 10 to 57 .mu.m). 
In this process, the melt-spun monofilaments are cooled with an air blast, 
drawn over a friction element, provided with a finish and wound up at a 
speed of up to 6000 m/min. This process differs fundamentally from the 
process according to DE 41 29 521 A1 with regard to the active cooling of 
the monofilament by an air blast and by the use of a friction element, by 
means of which fibre tension is adjusted. 
Both direct spinning/stretching processes (according to DE 41 29 520 A1 and 
WO 91/11547) are in principle limited to the production of small diameter 
monofilaments (i.e. having a fibre diameter of &lt;57 .mu.m) due to 
unfavourable heat dissipation brought about by air cooling and the poor 
internal thermal conductivity of the fibres. 
German patent application bearing the file number P 43 36 097.1 describes a 
continuous high speed production process for the production of melt-spun 
monofilament fibres having a diameter of 60 .mu.m to 500 .mu.m. In this 
process, the polymer fibres formed are laterally quenched over a zone of 1 
to 10 cm beneath the spinning head with temperature-controlled air from 
nozzles in order to stabilise the smooth running of the fibres. After the 
air cooling, the polymer filaments are cooled in a liquid bath. 
The surface of the melt fibres which have only passed through a short air 
zone, for example as in the last-stated process, and have then been 
directly spun into a liquid exhibits a texture similar to orange peel. The 
monofilaments exhibit a loss of strength and a wide dispersion of their 
knot strength. 
Moreover, the sudden cooling of the monofilaments in the cooling liquid 
gives rise to a pronounced core/shell structure in the filaments which 
also degrades the mechanical properties of the filaments. 
Due to the unfavourable dissipation of heat on air cooling and poor 
internal thermal conductivity in such processes in which only air is used 
as the cooling medium, monofilament production is limited to a diameter of 
&lt;57 .mu.m. 
Additional air quenching between the spinning head and spinning bath by 
nozzles over an air zone of 1 to 10 cm (corresponding to DE 43 36 097) 
gives rise to satisfactory textile characteristics in thin monofilaments 
(having a diameter of &lt;200 .mu.m) spun at high speed. Use of the stated 
air cooling zone is not sufficient for thicker monofilaments. Moreover, 
the process is extremely sensitive to air movement in the fibre forming 
zone, so impairing the operational reliability of the plant. 
SUMMARY OF THE INVENTION 
The object underlying the invention is to improve the stated spinning 
processes for monofilaments in such a manner that spinning reliability and 
the textile characteristics of the resultant monofilaments, in particular 
the knot strength thereof, are improved. 
This object is achieved according to the invention bit a continuous process 
for the production of monofilament fibres having a diameter of 60 .mu.m to 
2000 .mu.m from fibre-forming thermoplastic polymers by melt-spinning of 
the molten polymer from a spinning head into air, lateral quenching with 
cooling gas in a spinning cabinet, cooling of the formed fibres in a 
liquid bath, removal of adhering liquid, optionally applying a finish, 
stretching the fibres in one or more stages, setting and winding the 
fibres at a delivery speed of the set fibres of 100 to 4000 m/min, 
characterised in that the cooling gas has a temperature of 0 to 50.degree. 
C. and that the cooling gas exhibits a velocity profile which decreases in 
the running direction of the fibres, measured perpendicularly to the 
running direction of the fibres, and that the cooling liquid has a 
temperature of -10 to 150.degree. C. 
DETAILED DESCRIPTION 
The fibre-forming polymer is in particular melt-spun into air from a 
melt-spinning head which is known per se, quenched laterally in a spinning 
cabinet with temperature-controlled air (of a temperature of 0.degree. C. 
to 50.degree. C.) following a defined air velocity profile, preferably 
from one side from nozzles or, in the case of round spinnerets, from 
annular nozzles and then cooled in a liquid bath at a temperature of 
5.degree. C. to 50.degree. C. 
In a preferred variant, the transverse air velocity relative to the 
monofilaments immediately below the spinneret (for example at a distance 
of 0.5 to 6 cm from the spinneret) is 0.1 to 10 m/sec, in particular of 
0.1 to 2 m/sec, and falls over the length of the spinning cabinet to a 
lower, but, relative to the longitudinal section of the spinning cabinet, 
extremely uniform air velocity of 0.001 m/sec to 1 m/sec, in particular of 
0.01 to 0.2 m/sec. 
In a preferred process, the cooling gas flows from nozzles, which are 
arranged annularly around the fibres in the spinning cabinet, into the 
spinning cabinet and the cooling gas, together with the vapours released 
by the spun fibres, is exhausted below the nozzles. 
In another variant of the process, the nozzles are arranged on one side of 
the spinning cabinet and the cooling gas, together with the vapours 
released by the spun fibres, is exhausted opposite the nozzles. 
Another preferred process is that using a spinning cabinet which covers the 
distance between the spinning head and the liquid bath. The spinning 
cabinet may have a length of 2 to 200 cm. The spinning cabinet preferably 
has a length of 8 to 60 cm. 
In a preferred variant of the process, the transverse air velocity in the 
spinning cabinet relative to the monofilaments is 0.05 to 10 m/sec, in 
particular 0.1 to 2 m/sec, at a distance of 0.5 to 6 cm from the 
spinneret. In particular at a distance of 6 to 200 cm from the spinneret. 
the air velocity in the spinning cabinet is 0.001 m/sec to 1 m/sec, 
preferably 0.01 to 0.2 m/sec. 
The monofilaments are preferably quenched in the spinning cabinet with 
emperature-controlled air of a temperature of 0 to 50.degree. C., in 
particular of 10 to 30.degree. C. 
In another preferred variant of the process, the air introduced into the 
spinning cabinet, together with the vapours released by the spun fibres, 
is exhausted opposite the air inlet uniformly over the entire spinning 
cabinet. In particular when the spinning gas is exhausted from the 
spinning cabinet, a pressure differential of the order to 10 to 100 Pa 
relative to ambient pressure is produced. 
The temperature of the cooling bath is preferably 5 to 50.degree. C. 
The delivery speed of the fibres is preferably 1000 to 3500 m/min. The 
monofilaments obtainable from the process in particular have a diameter of 
100 to 400 .mu.m, preferably of 180 to 250 .mu.m. 
Fibre-forming polymers which may be considered are in particular polyamide, 
polyethylene terephthalate, polybutylene terephthalate, polypropylene and 
polyethylene. The preferred polymer is polyamide, in particular polyamide 
6, polyamide 6,6, polyamide 6,10, polyamide 6,12, polyamide 11, polyamide 
12, a blend of the stated polyamides or a copolyamide of the stated 
polyamides. Particularly preferred polymers are a copolyamide consisting 
of polyamide 6 and polyamide 6,6, a copolyamide of polyamide 6 and 
polyamide 12 and a copolyamide consisting of polyamide 6 and polyamide 11. 
Another preferred copolyamide consists of polyamide 6, polyamide 6,6 and 
either polyamide 11 or polyamide 12. 
In another preferred variant, the bottom of the spinning cabinet ends at 
the surface of the cooling liquid in the spinning bath. 
After leaving the liquid bath, the monofilaments have any adhering cooling 
liquid removed in the conventional manner and are post-treated by optional 
application of a finish, stretching and setting. The monofilaments are 
then wound onto reels. 
The monofilaments produced using the described novel "dry/wet" 
melt-spinning process are distinguished by a smoother surface and a higher 
work capacity (defined as the product of breaking tenacity and maximum 
tensile elongation). 
By means of the described defined air cooling, in particular in the event 
of compliance with the preferred flow profile, a smooth fibre surface is 
produced and the monofilament shell is gently cooled such that the 
core/shell structure is less pronounced than in conventional processes 
(spinning through a small air gap into a liquid bath). 
The described spinning process according to the invention is in particular 
required at a higher production speed of 600 to 3000 m/min in order to 
achieve the textile characteristics required of monofilaments. 
The melt-spinning process according to the invention is preferably used for 
the production of fishing lines, in particular for high-strength, 
transparent fishing lines and for the production of industrial 
monofilaments, in particular at a relatively high production speed (&gt;600 
m/min) or an increased number of spinneret holes. 
The transparency and especially the knot strength of, for example, fishing 
lines made from the monofilaments are substantially improved by the 
spinning process according to the invention. 
The present invention also provides an apparatus for the performance of the 
process according to the invention consisting of a melt-spinning head with 
a spinneret, a spinning cabinet with a quenching unit and exhausting unit, 
a liquid bath with fibre guides and baffles, wipers and an adhering liquid 
aspirator, optionally a finish application station, one or more stretching 
units, in particular for hot stretching, a setting zone and windup 
stations. The apparatus is characterised in that the spinning cabinet 
surrounds the space between the spinning head and surface of the cooling 
liquid bath or in particular encloses it in a gas-tight manner. 
In particular, gas nozzles for quenching the monofilaments in the spinning 
cabinet are provided on one side of the cabinet, which nozzles are 
optionally provided with flow smoothers in the area of the monofilaments. 
In a preferred apparatus, the first nozzle in the spinning cabinet below 
the spinneret is a flat nozzle with an adjustable slot. Preferably, all 
the spinning cabinet air nozzles may be separately controlled so that the 
air streams may be adjusted in accordance with the required air flow 
profile. 
One variant of the apparatus has an annular nozzle to quench the 
monofilaments in the spinning cabinet with flow smoothers to render the 
gas velocity profile uniform upstream from the nozzle. Another preferred 
apparatus has an annular exhaust below the annular nozzle, by means of 
which the air introduced into the spinning cabinet together with the 
vapours released by the spun fibres may be exhausted. A preferred 
apparatus is one in which the exhaust unit in the spinning cabinet is 
arranged opposite the air inlet nozzles. 
FIGS. 1 to 3 below provide a more detailed. non-limiting illustration of 
the invention.

EXAMPLES 
General Process Description 
The polymer melt is introduced via a line into the melt-spinning head 17 
with the spinneret 1 (c.f FIG. 1). The spinning cabinet 2 has an air 
quenching unit 3 and exhaust unit 4, which introduce and remove the 
cooling air and are arranged opposite each other as shown in FIG. 1. An 
additional slot nozzle 19 with flow smoothers 21 to render the gas 
velocity profile uniform upstream from the nozzle 19 is arranged above the 
quenching unit. 
In one variant of the apparatus according to FIG. 2, the exhaust unit 4 has 
an annular exhaust channel 22 which passes around the spinning cabinet 2, 
which channel ensures spatially uniform discharge of the spinning gas. The 
slot nozzle 19 is replaced by an annular nozzle 20 and annular nozzles 
with flow smoothers are provided as the quenching unit 3. 
In both variants, the tow 23 of monofilaments is precooled in the spinning 
cabinet 2 by quenching with air. 
The tow 23 is then further cooled and solidified in a liquid bath 5. A 
fibre guide 6 ensures a gentle change in the running direction of the tow 
23 by means of a plurality of guide bars. Baffles 16 in the cooling bath 
calm the cooling bath liquid at elevated production speeds in order to 
avoid turbulence in the cooling bath liquid brought about by liquid 
entrained by the monofilaments and to prevent impact on the monofilaments, 
which are still soft (c.f. FIG. 1). Since cooling bath liquid is entrained 
from the cooling bath 5 at high monofilament delivery speeds, liquid 
wipers 7 are arranged downstream from the exit of the monofilaments 23 
from the cooling bath liquid and upstream from the pair of haul-off rolls 
8. which wipers, together with an adhering liquid aspirator 9, remove the 
entrained cooling bath liquid from the monofilaments 23. The spinning 
apparatus furthermore has a finish application station 10 and subsequent 
aspirator 11 for excess finish. a hot stretching zone 13, a setting zone 
14 and winders 15 to wind the monofilaments. The running speed of the 
seven-roller units 12, 24 and 25 determine the extent of drawing in the 
hot stretching zone 13 and the setting zone 14 (c.f. FIG. 3). 
In both variants of the apparatus, the spinning cabinet 2 of the spinning 
apparatus is arranged in such a manner that the spinning cabinet 2 
encloses the space between the spinning head 17 and liquid surface 18 of 
the cooling liquid bath 5, in which the monofilaments are formed, in a 
gas-tight manner. 
A variant of the apparatus as shown in FIG. 1 was used for the following 
Examples. However, gas-tight enclosure of the space between the spinning 
head 17 and liquid surface 18 was not provided by the spinning cabinet 2. 
One or three opposing nozzles 19 and 3a, 3b were used for quenching. The 
width of the nozzles in each case covered the width of the tow. 
The nozzle 19 was a slot nozzle at the heights stated in each of the 
Examples. Nozzles 3a and 3b were nozzles equipped with flow smoothers, the 
height of which approximately covered the remaining height beneath the 
spinneret. 
Example 1 
Monofilaments of a diameter of 0.40 mm were produced under the above-stated 
standard conditions from a commercially available copolyamide with the 
trade name Ultramid C 35 (manufacturer: BASF AG, Ludwigshafen). The 
distance between the discharge of the melt from the spinneret orifice and 
the surface of the cooling medium (water) was 60 mm. 
A slot nozzle 19 having a slot height of 25 mm was installed in this zone, 
by means of which the monofilaments were quenched with air in a defined 
manner between leaving the spinneret and entering the cooling medium. 
Table 1 shows the measured linear and knot strengths of the resultant 
monofilaments. 
Quenching nozzles were omitted for the Comparative Example in Table 1. In 
the zone between the spinning head 17 and the surface of the cooling 
liquid, the tow was passed through ambient air for a distance of 15 mm. 
TABLE 1 
______________________________________ 
Maximum Maximum Breaking 
tensile tensile tenacity 
Monofilament 
force elongation 
[cN/tex] 
diameter [mm] 
[daN] [%] linear/knot 
______________________________________ 
Comparison 
0.40 11.99 20.15 80.05/60.29 
Process according 
0.40 12.33 21.53 81.53/65.66 
to the invention 
______________________________________ 
Example 2 
Monofilaments of a diameter of 0.20 mm were produced under the stated 
standard conditions from a commercially available polyamide with the trade 
name Durethan B 31 (manufacturer: BASF AG, Ludwigshafen). The distance 
between the discharge of the melt from the spinneret orifice and the 
surface of the cooling medium (water) was 280 mm. 
Quenching nozzles were omitted for the Comparative Example in Table 2. In 
the zone between the spinning head 17 and the surface of the cooling 
liquid, the tow was passed through ambient air for a distance of 15 mm. 
TABLE 2 
__________________________________________________________________________ 
Air velocities Maximum 
Maximum 
Breaking tenac- 
Air [m/sec] 
Slot height 
[mm] tensile 
tensile 
ity 
Nozzles: 
[mm] Monofilament 
force 
elongation 
[cN/tex] 
19/3a/3b 
(slot nozzle 19) 
diameter 
[daN] 
[%] linear 
__________________________________________________________________________ 
Comparison 
none/none/ 
none 0.20 1.58 26.6 42.1 
none 
Process accord- 
1.5/0.5/0.5 
5.0 " 1.72 27.8 45.9 
ing to the inven- 
tion 
Process accord- 
1.5/0.5/0.5 
25.0 " 1.84 30.2 50.6 
ing to the invent- 
ion 
Process accord- 
5.0/1.5/1.5 
25.0 " 1.76 29.2 47.4 
ing to the inven- 
tion 
__________________________________________________________________________ 
Example 3 
Monofilaments of various diameters were produced under the stated standard 
conditions from a commercially available copolyamide with the trade name 
Ultramid C 35 (manufacturer: BASF AG, Ludwigshafen). The distance between 
the discharge of the melt from the spinneret orifice and the surface of 
the cooling medium (water) was 60 mm. 
A slot nozzle 19 having a slot height of 25 mm was installed in this zone, 
by means of which the monofilaments were quenched with air in a defined 
manner between leaving the spinneret and entering the cooling medium. 
Quenching nozzles were omitted for the Comparative Example in Table 3. In 
the zone between the spinning head 17 and the surface of the cooling 
liquid, the tow was passed through ambient air for a distance of 15 mm. 
The linear and knot strengths measured on the resultant monofilaments are 
as follows: 
TABLE 3 
______________________________________ 
Maximum Maximum Breaking 
tensile tensile tenacity 
Monofilament 
force elongation 
[cN/tex] 
diameter [mm] 
[daN] [%] linear/knot 
______________________________________ 
Comparison 
1.00 64.58 18.35 72.46/40.54 
Process according 
1.00 66.25 19.1 77.87/53.58 
to the invention 
Process according 
0.30 7.83 21.04 90.63/67.75 
to the invention 
0.30 7.72 22.84 91.35/74.15 
Process according 
0.20 3.66 20.41 94.53/73.71 
to the invention 
0.20 3.69 21.58 94.00/77.96 
Process according 
0.16 2.31 21.73 90.45/73.96 
to the invention 
0.16 2.36 22.78 90.80/77.07 
______________________________________