Process for producing synthetic filaments

A process for producing spin-oriented filaments at a draw-off speed of more than 2400 m/min, whereby the filaments extruded from a spinneret are solidified in a cooling shaft solely by the ambient air entrained by the suction effect of the filaments and the cooling shaft having a zone where the walls are air permeable directly beneath the spinneret and has a following zone where the peripheral walls are completely closed.

BACKGROUND OF THE INVENTION 
This invention concerns a process for spinning and cooling spin-oriented 
multifilaments by means of a spinning apparatus having spinning heads 
containing spinnerets and cooling shafts with an air-permeable wall 
through which a stream of air is sucked into the interior of the cooling 
shaft solely by the frictional entrainment of air by the filaments. 
Multifilament continuous filaments of synthetic polymers are produced from 
a melt at the spinning temperature by means of a spinning device. The melt 
is forced through boreholes in a spinneret. The resulting melt streams are 
then cooled and combined to form a filament bundle, which is treated with 
a spin finish oil, then drawn off with a fiber draw-off device and finally 
wound onto tubes to form a bobbin. 
Cooling is especially important here. The uniformity of cooling has a 
direct influence on the physical characteristics of the filaments such as 
uniformity of the Uster-value or dyeing receptivity. Trouble is caused by 
nonlaminar or turbulent flow of the cooling air. Before the melt streams 
which are extruded at a high spinning temperature have cooled below the 
solidification point, contact with each other or with the thread guides 
has to be avoided because they would stick. 
PRIOR ART 
Systems with cool air processing in a climate-controlled installation and 
feeding of the air through air ducts to cooling shafts and blowing the air 
by means of fans into the area of the melt streams below the spinnerets 
have proven successful. However, complicated air distribution systems, 
controls and homogenization equipment must be used in order to guide the 
turbulent cooling air and maintain laminar flow. 
Practical examples of these systems include those with cross flow, i.e., 
essentially air flow at right angles to the filaments and direct removal 
of the heat of melting on the leeward side (U.S. Pat. No. 4,529,368) as 
well as those with radial flow, i.e., air is directed from the outside 
into the filament bundle and heat is dissipated essentially in the 
direction of travel of the filament (U.S. Pat. No. 4,712,988 and German 
Patent A 3,406,347). 
Another method of producing a stream of cooling air consists of passing the 
filaments through a suction device where the stream of cooling air is 
produced by the reduced pressure (U.S. Pat. No. 4,496,505 and 
International Patent WO 90-02222A). 
Conventional currently-used techniques for cooling the melt streams in 
order to combine them into a filament bundle and process them further 
consist of blowing air onto them either by means of forced air pressure or 
reduced pressure. 
German Patent A 1,914,556 discloses a device for spinning and cooling 
synthetic continuous filaments whereby the required stream of cooling air 
is created inside a shaft provided with a number of perforations and 
through which shaft a bundle of melt streams extruded from a spinneret is 
guided. The shaft consists exclusively of an air barrier shaft without 
perforations for a length of 300 to 500 mm just down stream of the 
spinning head. In the next stage it consists of a shaft with flow control 
and with ventilation openings for the remaining total length. The short 
unperforated zone at the lower end of the shaft shown in FIG. 5 is not 
mentioned anywhere in the patent specification and could serve only to 
provide mechanical stability for the cooling shaft. Because the portion of 
the shaft next to the spinning head is imperforate, access of outside air 
into this region of the shaft is completely prevented. The melt streams 
thus are not be subjected to any cooling at all immediately after leaving 
the spinning head. The result is a lengthening of the required cooling 
zone accordingly, for example, to about 2000 mm. 
THE INVENTION 
The object of this invention is to provide a process for spinning and 
cooling synthetic continuous filaments that will not require much energy 
consumption, will require minimal equipment and control technology, and 
will be especially suitable for high draw-off speeds. This object is 
achieved by sucking the air stream directly into the cooling shaft 
directly below the spinnerets solely by the frictional entrainment of the 
air by the filaments, where the walls of the cooling shaft are subdivided 
into two different zones in the longitudinal direction and the filaments 
are drawn off at speeds of at least 2400 m/min. The wall of the first zone 
directly below the spinneret is air permeable and the wall of the second 
following zone is closed or imperforate. 
In a departure from the teachings of German Patent DE A 1,914,556 cited 
above, cooling air derived from outside ambient air is provided for the 
melt streams directly beneath the spinnerets. This cooling air is sucked 
into the shaft because of the friction between the air and the filaments 
being guided through the respective zones of the cooling shaft. To a 
certain extent this is comparable to an injector effect. This entrainment 
effect extends along the entire length of the cooling shaft and includes 
the area directly beneath the spinnerets so the melt streams to be cooled 
are subjected to cooling immediately after they leave the spinneret. 
Subdividing the cooling shaft into two zones results in a channelizing 
effect on the air stream along the direction of the filaments such that 
air is sucked in through the perforated wall of the shaft and supplied 
into the directed stream along the length of the first zone. A convective 
exchange of heat and flow through the walls is suppressed along the length 
of the second zone. 
It has surprisingly been found that especially at high draw-off speeds a 
cooling effect created by the injector action described above produces 
filaments having a spin orientation in part because of the high draw-off 
speed. This orientation cannot be obtained when using the device according 
to German Patent A 1,914,556 because of the relatively low draw-off speed 
of 1000 m/min preferred in that device. Secondly, the filaments have a 
uniformity which cannot be achieved when using the device according to 
German Patent A 1,914,556 even in combination with a draw-off speed of 
more than 2400 m/min. The uniform cooling in the area directly beneath the 
spinnerets which is obtained according to the present invention, results 
in filaments having a high uniformity along their entire length as well as 
between one monofilament and the next. Especially when using draw-off 
speeds of more than 4500 m/min. there is less trouble in the spinning 
process-in other words, there was a lower incidence of breakage of single 
filaments due to the disturbance in drawing off the filaments. Preventing 
convective heat exchange and flow exchange through the walls of the second 
zone also acts as a buffer against external interference, causes an 
alignment of the air flow in the direction of the filaments and delays the 
subsequent cooling effect. In this zone the filaments are already highly 
drawn and already have a velocity close to the draw-off speed. The 
interaction of these two conditions evidently yields conditions that are 
otherwise achieved only by actively supplying heat from the outside, for 
example, with the help of a heated spinning shaft as described in German 
Patent A 2,117,659. 
Furthermore, this process yields an important practical advantage compared 
with traditional cooling systems, where cooling air is directed against 
the filaments by means of excess pressure or a reduced pressure. Those 
systems require a considerable technical expense, especially for fans, 
which expense is completely eliminated with the present invention. The 
process according to this invention makes it possible to produce superior 
filaments in a practical and advantageous manner at greatly reduced cost. 
It is possible to eliminate separate climate control installations which 
consume a great deal of energy in processing cooling air, also the use of 
air ducts and homogenization equipment to create a laminar flow of the 
turbulent air as well as heating equipment for after treatment of the 
thread. 
When using the process according to this invention, the average distance 
between the single filaments in a filament bundle on leaving the cooling 
shaft can be less than 6 mm because of the particularly high uniformity of 
the air flow and the rapid cooling of the filaments. Preferably a bundle 
filament guide that combines the filaments to form a thread is installed 
directly at the outlet of the cooling shaft. This permits a short spinning 
length which in turn permits a low thread tension when using a high 
draw-off speed and also permits an advantageous design of the spinning 
apparatus. 
Favorably, the process according to this invention is suitable for 
producing single filament titers of 0.3 to 3.0 dtex at a draw-off speed of 
2400 to 8000 m/min. 
The device for carrying out the process according to this invention is 
designed so that the cooling shafts are connected directly at the lower 
end of the spinning heads, the walls of the cooling shafts are provided 
with perforations to permit access of air over the length of the first 
zone and the second zone is designed with imperforate walls. 
The air permeable walls can be formed of a metal mesh or with small holes 
or perforations. 
The length of the cooling shaft is at least 200 mm and normally is a 
maximum of 1500 mm. The length of the second zone ranges from somewhat 
shorter than the first zone to approximately twice the length of the first 
zone. Preferably, the length of the second zone is approximately 80% to 
200% of the length of the first zone. 
Preferably the device is designed in such a way that the cooling shaft has 
two telescoping sections that can move relative to each other in the 
longitudinal direction. One section is perforated and forms the first 
zone, whereas the other section is imperforate. By simply sliding one 
section with respect to the other, the length ratio of the two zones and 
the total length can be adjusted easily. The cross-sectional shape of the 
cooling shaft depends on the shape of the spinnerets which may be round, 
oval or rectangular. Accordingly the cooling shaft may have a circular, 
oval or rectangular cross section which is preferably 10 to 60 mm larger 
than the cross section of the orifice field of the spinneret. When using 
circular spinnerets, the cooling shaft and its walls are designed so they 
are cylindrical and surround the filament bundle concentrically.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
Although a commercial spinning apparatus has multiple spinning heads, the 
drawing illustrates only a single head and a single cooling shaft. 
FIG. 1 shows in schematic form an example of a cooling shaft extending from 
the lower side 1 of the spinning head and concentrically surrounds the 
filaments 5 leaving the spinneret. The shaft is essentially a metal 
cylinder 3. 
Metal cylinder 3 has holes or perforations distributed uniformly over the 
walls of the first zone 2, whereby the air permeability can be varied over 
a wide range. However, the air resistance should not be so great as to 
impair the suction effect. Excessively large perforations should also be 
avoided in order to buffer the movement of air in the vicinity. A 
perforated, open area which comprises a maximum of 50% of the total 
surface area of the wall has proven appropriate. 
Since each filament bundle is surrounded by the cylinder wall 3 of the 
cooling shaft, the cooling air drawn in through the suction effect of the 
moving filaments (note the arrows in FIG. 1) is directed essentially 
radially from the outside to the inside. It is drawn from the environment 
and therefore has a temperature corresponding to the temperature of the 
spinning area. 
The walls surrounding the second zone 4 are closed or imperforate so that 
air can flow through the zone only from the filament inlet end to the 
outlet end of the shaft. 
Below the cooling shaft, there is a thread oiling device (not shown) or 
some other type of thread guide for bundling the solidified filaments to 
form a thread which is then guided to a draw-off device and wound onto 
tubes to form a bobbin. 
The cooling shaft shown schematically in FIG. 2 has a design similar to 
that in FIG. 1. A second perforated metal cylinder 6 is arranged 
concentric with the first cylinder 3 and is spaced from it in the area of 
the air permeable walls of the first zone. This construction provides an 
additional buffering effect for air movements in the spinning area--for 
example, in opening and closing doors. A maximum wall distance of 20 mm 
between the two perforated metal cylinders is recommended. 
EXAMPLE 1 
Polyethylene terephthalate (PET) chips with an intrinsic viscosity (I.V.) 
of 0.63 dl/g were melted, and the melt was extruded through the orifices 
or nozzles of a spinneret at a temperature of 294.degree. C. The spinneret 
had a diameter of 80 mm. The orifice field diameter was 70 mm and the 
diameter of each orifice was 0.25 mm, the length L=2 D. The number of 
orifices in the spinneret was 34. 
The polymer delivery rate was 39.5 g/min, thus yielding a titer of 76f34 
dtex, corresponding to a spinning titer of 2.24 dtex per single filament. 
Directly beneath the spinneret there was a cooling shaft in the form of a 
metal cylinder with a diameter of 100 mm. The length of the first zone was 
500 mm and it was perforated. The diameter of each hole was 5 mm. The 
holes (2730 holes) were distributed uniformly over the wall. The open area 
amounted to 34%. The length of the second zone was 500 mm and the zone was 
designed with closed walls. 
The cooling shaft was surrounded by ambient air at a temperature of 
29.degree. C. The filaments were bundled in a filament thread oiler 100 mm 
from the cooling cylinder. 
Then the filament bundle was drawn off at a speed of 5200 m/min by a bobbin 
winder equipped for compensation of tension by means of a grooved roller 
operated with an overfeed of 6%. 
The thread characteristics and uniformity values were as follows: 
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Titer (dtex) 76.1 
Breaking Load (cN) 256.6 
CV Breaking Load (%) 1.8 
Tenacity at Break (cN/tex) 
33.7 
Elongation at Break (%) 
62.8 
CV Elongation (%)* 3.0 
Uster Half Inert (%) 0.32 
Single Filament CV Titer (%) 
3.1 
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*(CV = Coefficient of Variation) 
EXAMPLES 2 AND 3 
The procedure followed was the same as described in Example 1, but the 
delivery rate was increased slightly to 42.5 g/min. In addition, the 
length of the second zone was shortened to 150 mm in one case (Example 2) 
while in the other case (Example 3) this zone was lengthened to 800 mm. 
The individual characteristics of the POY (Partially Oriented Yarn) were as 
follows: 
______________________________________ 
Example 2 
Example 3 
______________________________________ 
Titer (dtex) 82.6 82.5 
Breaking Load (cN) 265.0 288.9 
CV Breaking Load (%) 
3.2 1.8 
Tenacity at Break (cN/tex) 
32.1 35.0 
Elongation at Break (%) 
59.9 66.6 
CV Elongation (%) 4.7 3.5 
Uster Half Inert (%) 
0.7 0.34 
______________________________________ 
With the greatly shortened length of the second cooling zone according to 
Example 2, the values obtained for product uniformity are inferior to 
those of Example 1. 
With the greatest length according to Example 3, the highest values for 
tenacity and elongation are obtained, which is equivalent to a good 
resistance of the yarn to stress. 
EXAMPLE 4 
The procedure and equipment were the same as in Example 1 but the delivery 
was reduced to 34.9 g/min. 
At the same time the draw-off speed was reduced to 4200 m/min so the titer 
of the wound thread was approximately the same as that in Examples 2 and 
3. 
Even at this speed, a uniform quality of the product could be achieved. 
The fiber characteristics and uniformity data were as follows: 
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Titer (dtex) 83.3 
Breaking Load (cN) 260.0 
CV Breaking Load (%) 
2.1 
Tenacity at Break (cN/tex) 
31.2 
Elongation at Break (%) 
87.1 
CV Elongation (%) 3.6 
Uster Half Inert (%) 
0.31 
______________________________________ 
The product of tenacity times the square root of elongation equals 291. 
This is of the same order of magnitude as the product in Example 3.