Note: Descriptions are shown in the official language in which they were submitted.
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DRAWING DEVICE AND METHOD FOR PRODUCING
DRAWN SYNTHETIC FILAMENTS
Technical Field
The invention relates to a drawing device including a spinning device and a
pulling-
off device with pneumatic means for producing a traction force on the
synthetic
filaments and a method for producing drawn synthetic filaments according to
which
melt spun filaments with an individual titer of more than 1 dTex are cooled to
the
solidification temperature behind the spinning device and drawn by way of a
pneumatic drawing device for the manufacture of synthetic threads, staple
fibers or
fleeces.
Prior Art
The manufacture of synthetic filaments by melt spinning consist essentially of
three
process steps. Initially, the polymer is melted by way of an extruder,
subsequently
follows the spinning of the filaments by way of a spinning nozzle provided
with
capillary bores or several spinning nozzles. Finally, a drawing of the spun
filaments
follows to achieve a reduction of the cross section. The reduction in cross
section of
the spun filaments is an essential requirement for many technical and textile
applications. The drawing, which represents a deciding process step for the
further
possible uses of these filaments can be directly, continuously and/or
automatically,
incorporated into the spinning process or can be carried out as separate
processing
step in the production sequence.
The drawing of the filaments is carried out by way of a pulling-off device in
mechanical manner through galettes or in pneumatical manner through a nozzle.
Independent of the type of the integrated pulling-off device, pneumatic or
mechanical, the filaments spun at a high spinning speed, which means larger
than
3500 m/min, in a single step installation have significantly worse mechanical
properties, for example, strength and elasticity modulus, than the filaments
spun at a
lower spinning speed, which means lower than 3500 m/min, which have been
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subjected to a secondary drawing in an additional process step.
Although in the one step process a high spinning speed favours the formation
of
improved mechanical properties compared to a lower spinning speed, structural
differences befinreen the surface and the interior of the filament are also
simultaneously created within the filament itself, which are responsible for a
reduction of the strength or the elasticity modulus of the filaments relative
to a
secondarily drawn filament.
US 2,604,667 teaches the manufacture of oriented threads without special
drawing
device for secondary drawing using a pulling-off speed of at least 4700 m/min.
This
high speed is required in order to reach high strength. If the speed remains
lower,
the filaments produced have a high stretch. In order to reach this pulling of
speed,
driven rollers or an air nozzle can be used. US 2,604,667 deals foremost with
the
manufacture of yarns, mentions, however, also the manufacture of staple fibers
with
the use of an air nozzle a pulling-off device.
For the manufacture of spun fleeces from spun, endless filaments, it is known
to
carry out a drawing of the filaments exiting the spinning nozzle by way of a
pneumatic nozzle of a pulling-off arrangement operating in the supersonic
region.
Several solidified filaments are respectively guided by way of the nozzle to a
laying
down arrangement for the manufacture of the spun fleece. The force exerted
onto .
the filaments by the air friction enables the adjustment of the pulling-off
arrangement
and, thereby, the influencing of the mechanical properties of the filaments.
It has
hereby been shown that the influencing of the properties of the filaments has
limits.
Despite the increase in the pulling-off speed which is achieved by the
increase of the
pressure of the air supplied to the nozzle, the strength can barely be further
increased and the stretch can barely be further reduced.
A process is known from the DE-OS 2 117 659 for the manufacture of threads and
fibers of synthetic, linear polymers by melt spinning from capillaries which
operates
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with pulling-off speeds of up to 3500 m/min. The pulling-off speed is preset
by the
speed of a galette pair. To influence the stretch, a heating device is
positioned
between a spinning nozzle and the pulling-off galettes in which a synthetic
fiber
consisting of 50 filaments is heated to temperatures above the solidification
point
and below the melting temperature, whereby a drawing ratio of up to 1:2 is
reached.
Further mentioned is the manufacture of spun fleeces of filaments with fine
individual titer and especially adapted strength and stretch, however, without
describing it further.
DE-OS 29 25 006 goes into the effect of the drawing on the strength on the one
hand and on stretch and shrinking on the other hand. It is explained that the
filaments obtain a higher strength through the drawing, while stretch and
shrinking
are reduced. The relative to the DE-OS 21 17 659 higher pulling-off speeds of
4100
to 6000 m/min are achieved through the use of slightly red glowing heating
elements
in direct contact with the filaments.
For the manufacture of synthetic fibers of polymers, especially polyamides,
polyester
or polypropylene, by way of melt spinning, an installation is known from the
DE 40
21 545 with at least one spinning nozzle, a blowing duct, a heating duct, a
preparation arrangement, galettes and one spool arrangement, whereby the
heating
duct includes counterflow producing arrangements, for example, blow jets.
Fully
drawn synthetic threads or fibers can be manufactured with this arrangement
whereby the individual fibers or filaments have an individual titer of less
than 1 dTex.
Fully drawn synthetic threads are produced in this installation and according
to this
process without additional treatment, which can be manufactured into an
especially
fine and conformable material whether the installation provides sufficient
drawing
properties for higher titer ranges is not disclosed.
It is an object of the invention to provide a device and process suited for
the
production of drawn synthetic filaments with a titer of larger than 1 dTex and
generates filaments with higher strength and reduced stretch.
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A process is known from DE 2 205 273 OS for the production of a fiber fleece
wherein the threads exiting the spinning nozzle are cooled by way of cooling
air and
guided over a contact surface placed at a distance from the spinning nozzle,
whereby the threads are heated to a temperature below the melting point. In
this
process, the threads are furthermore guided through an injector supplied with
pressurized air so that the threads are exposed to traction forces by the
pressurized
air flowing to the injector. The threads are thereby drawn. It is here a
disadvantage
that because of the contact of the thread with the contact surface, only one-
sided
friction tensions are formed on the thread.
The DE-Z: Chemical Fibers International, Volume 46, January 1996, Pages 37 to
40
describes a process for the manufacture of drawn yarns, wherein the yarn prior
to
the spinning of the filaments to a thread and the subsequent winding up onto a
galette is guided through a heating channel with hot air guided in counterflow
to the
direction of movement of the individual filaments. Because the air friction
acts on the
whole outer surface of the individual filaments, the stretch and strength of
the
manufactured yarn can be influenced.
Description of the Invention
In accordance with the invention, the drawing device includes a heating device
positioned between the spinning device and the pulling-off device with a
heating
medium flow guided in counterflow to the synthetic fiber.
In this installation, endless filaments can be manufactured of a thermoplastic
synthetic material, for example, polyester, polyamide, polypropylene,
polyethylene,
etc., through single or multiple spinning (dual layer, segmented, coaxial,
etc.) for
technical or textile applications. The mechanical properties of the filaments
manufactured through melt spinning are significantly improved at even titer,
especially the ultimate strength, stretch, elasticity modulus and thermal
shrinking.
The heating device can be operated with hot air fed in counterflow or other
hot,
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preferably neutral gases, but also with gas mixtures admixed with additives.
The air
is heated to a temperature which is above the solidification temperature of
the
filaments.
The operating principle of the heating device resides in that between the
spinning
device and the pulling-off device, the heating medium guided in counterflow
creates
a region for the "holding" or "breaking" of the heated filament bundle. The
application
of a further drawing force by way of the pulling-off device positioned in
series after
the region is thereby possible and it results in an additional drawing. The
drawing is
defined by the difference between the entry speed of the filaments into the
heating
device and the entry speed of the filaments into the pulling-off device.
It has been surprisingly found that the pneumatic pulling-off arrangement
which
operates according to the principle of air friction can also be combined with
a
heating device which operates in countertlow. The filaments so obtained have
at
even pulling-off speed an increased strength and a reduced stretch. It is also
an
essential advantage that the pulling-off speed can be drastically reduced for
the
production of filaments with specific properties.
In an advantageous further development, means for the production of a spun
fleece
can be provided. These means cause a laying down of the synthetic filaments
conveyed through the pneumatic pulling-off device to a lofty product, a spun
fleece,
whereby no further mechanical conveying means for the synthetic filaments are
necessary.
The drawing arrangement, however, can also be complemented with means for the
generation of staple fibers, whereby the synthetic filaments are cut into
short fibers.
These fibers are especially suited for the manufacture of fiber fleeces.
Synthetic filaments which have a higher strength at reduced stretch can be
produced through a process for the manufacture of drawn synthetic filaments,
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wherein melt spun filaments after a spinning device are cooled at least to the
solidification temperature and drawn by way of a pneumatic pulling-off
arrangement,
with a subsequent heating in a heating device for the purpose of drawing,
whereby
the filaments in the heating device are blown at by a gaseous medium heated to
a
temperature above the solidification point and in counterflow. These filaments
do not
require a further secondary drawing and enable the carrying out of the process
at
lower pulling-off speeds than previously.
The process is preferably carried out in such a way that between the heating
device
and the pulling-off device, a secondary drawing takes place at a drawing ratio
of
1.1:1.5.
It is further advantageous when the filaments are blown at in counterflow at a
temperature of 200°C to 350°C, in the case of PET (polyethylene)
or PA 66
(polyamide) preferably 225°C to 300°C. The amount of air can be
varied from 5 m3/h
to 25 m3/h.
In order to achieve a significant improvement of the strength and stretch, it
is
sufficient when the filaments are guided through the counterflow at a pulling-
off
speed of 2000 m/min to 4700 m/min. Nevertheless, the improvement of the
properties also occurs at higher speeds.
With this process, the properties of the synthetic filaments to be produced
can be
influenced. It is thus possible to adjust the amount of air and the
temperature of the
counterflow air such that a thread stretch of less than 60% is achieved, or to
adjust
the pulling-off speed of the filaments, the amount of air and the temperature
of the
countertlow air such that at the same pulling-off speed, a relative increase
of the
traction strength of the subsequently drawn filaments of at least 20% is
achieved
compared to a singly drawn filament, whereby preferably a tractive strength of
the
filaments of at least 32 cN/Tex is achieved, especially preferably 34 to 45
cN/Tex, or
the amount of air and the temperature of the counterflow air is adjusted such
that a
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hot air shrinking of at most 6% (at 180°C, 15 min) is achieved. This is
true especially
when PES (polyester) is used as the material.
It is further advantageous to adjust the pulling-off speed of the filaments,
the air
amount and the temperature of the counterflow air such that the transition of
the
range of elastic deformation into the range of plastic deformation takes place
only
under a force which is at least 20% higher.
Although the filaments are highly drawn, it is possible to subsequently draw
the
filaments again subsequent to the counterflow treatment either continuously or
in a
separate treatment step.
As further process steps, the filaments can be laid down on a carrier for the
generation of a fleece or cut for the manufacture of staple fibers, whereby
the cut
filaments can be packaged for the processing in further processes.
Especially advantageous is the use of the synthetic filaments for the
manufacture of
a fleece, whereby the filaments have a tractive strength of at least 32 cN/Tex
and a
stretch of less than 60%. For the manufacture of a spun fleece, the synthetic
filaments can be deposited as endless threads, for the manufacture of a fiber
fleece,
the synthetic filaments can be deposited as staple fibers.
Further advantageous is the use of the synthetic filaments for the manufacture
of
yarns, whereby the filaments have a tractive strength of at least 32 cNITex
and a
stretch of less than 60%. The yarns can thereby be manufactured from endless
synthetic filaments or spun from staple fibers.
Brief Description of the Drawings
In the drawing, a drawing device for the production of drawn synthetic
filaments is
schematically illustrated. It shows the:
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Figure 1 the essential components of the installation, the
Figure 2 a course of the speed of a filament bundle according to the invention
in
comparison to conventional systems, and
Figure 3 the characteristic curves of different mechanical properties.
Embodiment of the Invention
The drawing device illustrated in Figure 1 for the production of drawn
synthetic
filaments includes a spinning device 1 to which molten synthetic material is
fed in a
known manner. Through spinning nozzles positioned in a spinning device 1,
filaments 2 exit which correspond in number to the number of openings in the
spinning nozzles, and which together form a filament bundle 3. Normally, 16,
32 or
64 filaments are combined to a filament bundle. After exiting from the
spinning
nozzle, filaments 2 are cooled to below the solidification temperature,
whereby an
additional cooling device 4 can be provided. Crystalline and amorphous zones
are
thereby formed in the individual filament.
The cooled filaments 2 are now guided to a heating device 5 and bundled
therein so
that a parallel path through the heating device 5 results. The heating device
5
includes a heating duct 6 at the lower end 7 of which, relative to the
spinning device,
hot air 8 is supplied and at the upper end 9 of which the air exits again. The
air 8 is
thus guided in counterflow to the filament bundle 3 in the heating duct 6.
The drawing-off device 10 by which a traction force is exerted onto the
filament
bundle 3 is positioned at a predetermined distance from the heating duct 6.
This is
done pneumatically through a venturi nozzle 11 to which air 12 is supplied
under
high pressure so that at the smallest cross section, the speed of sound is
reached
and in the further course the speed of sound is surpassed.
The filament bundle exiting the drawing-off arrangement 10 can be processed
into a
synthetic thread in a known manner, cut for the production of staple fibers,
or used
for the manufacture of a spun fleece. The latter is described, for example, in
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FR 74 20 254.
Figure 2 illustrates an overview over the course of the speed of the spun
filaments
for different installations or processes. Under the conventional conditions of
a direct
spinning and drawing of the filaments in one step and under high speed, here a
pulling-off speed of 6000 m/min, the filaments are subjected to a shock-type
cooling
because of the very high speed gradients in longitudinal and transverse
direction,
see curve A. The speed gradient along the spinning path is larger than 2 x 104
1/s,
and the cooling speed is in the order of 26000°C /s. These extreme
conditions cause
a different, heterogenous structure in the filament between the mantle and the
core
of the filament. Compared to secondarily drawn filaments drawn in a multi-step
process, this causes the decrease of specific mechanical properties.
A reduction of the speed to 4400 m/min pulling-off speed significantly reduces
the
speed gradient and the cooling speed, as can be read from curve B. However,
the
rupture load also decreases and the elongation at rupture increases.
In order to achieve an increase in the rupture load and a decrease in the
elongation
at rupture despite advantageously low pulling-off speeds, two step mechanical
processes are used which have a first region with a high speed gradient and a
second region with high speed gradients. This is illustrated in curve C.
By using a heating device with filaments blown at by heated air guided in
countertlow between the spinning nozzle and the pulling-off device, the course
illustrated in curve D is achieved at a pulling-off speed of 4400 m/min. A
further
stretch of the filaments heated above the solidification point takes place
over a
length L of the heating device 5.
Different experimental results are compared in Table 1 achieved with and
without a
heating device for different mass flows of polyethyleneterephthalate (PET)
with a
melting point of 256°C and a viscosity of 190 Pa s at 290°C.
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In a first experimental set up T, a drawing device consisting of a spinning
device 1
and a pulling-off device 10 was used for the manufacture of filaments.
The second experimental setup V is distinguished from the first in that a
heating
device 5 was provided between the spinning device 1 and the pulling-off device
10,
in which the filaments are heated by heated air guided in counterflow and to a
temperature above the solidification temperature. It is possible that the
filaments 3
are thereby heated to above their solidification temperature, but that the
melting
temperature is nevertheless not reached.
The experiments were carried out for both experimental setups, first with a
mass
flow of 1 g/min per capillary opening of the spinning nozzle (T1, V1.1, V1.2)
and then
with a mass throughput of 0.62 g/min per capillary opening of the spinning
nozzle
(T2, V2).
Upon comparison of the essential properties of the filament produced in the
first
series of experiments, it is first noted that the pulling-off speed of the
filaments in the
experiments V1.1, V1.2 has significantly decreased compared to T1. This can be
explained by an incomplete compensation of the friction forces in the heating
device
by the increase in pressure in the pulling-off device. A direct comparison of
the
mechanical properties of two filaments manufactured with the same pulling-off
speed
according to the two experimental setups T, V is therefore not possible here.
It is apparent that despite a pulling-off speed reduced from 4770 m/min to
3330
m/min, the strength was increased from 30.3 cN/Tex to 39.7 cN/Tex and the
stretch
was reduced from 72.6% to 57.1 % (T1 and V1.2). It is thereby possible to
operate in
a region of medium pulling-off speed for the production of filaments of high
strength.
An increase of the speed in the experimental setup with heating device to 4000
m/min leads to an additional improvement of the strength from 39.7 cN/Tex to
42.5
cN/Tex and a reduction of the stretch from 57.1 % to 43.7% (V1.2 compared to
V1.1).
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In the second experimental series V2, T2, a mass throughput of polymer/hole of
0.62 g/min was adjusted. Even in the finer titer range, the pulling-off speed
was
reduced. The strength was improved in a significant way from 27.7 cN/Tex to
36.6
cN/Tex, and the stretch was also significantly reduced from 82.6% to 47.6%.
Table 1
Experiment V 1.1 V 1.2 T 1 V 2 T 2
Mass Flow Polymer/Hole 1.00 1.00 1.00 0.62 0.62
(g/min Hole)
Titer 2.5 3.0 2.1 2.0 1.5
(dTex)
Pulling-off Speed 4000 3330 4770 3100 4130
(m/min)
Strength 42.5 39.7 30.3 36.6 27.7
(cN/Tex)
Stretch 43.7 57.1 72.6 47.6 82.6
(%)
Thermal Shrinking 4.5 4.5 3.4 4.4 3.2
(%) (180C, 15 min Hot
Air)
The force-stretch curve of the filaments arising from the experiments T1,
V1.1, V1.2;
T2, V2 is compiled in Figure 3. One recognizes the extrodinarily high
influence of the
heating device both on the strength as well as the stretch. Especially
important is the
significant improvement of the stretch in the range of forces higher than 10
cN/Tex.
The improved filaments can here take on significantly more flow without being
overly
stretched. This behaviour is still essentially present even with filaments
manufactured at a reduced pulling-off speed according to V1.2 or V2.
The cooling of the filaments exiting the spinning device having a temperature
of
about 300°C was carried out through cross flow with air at room
temperature, the
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heating of the filaments in the heating device was carried out with a volume
flow
between 10 and 15 m3/h of air heated to 270 to 300°C. It goes without
saying that
the temperature of the gaseous fluid 8 must be adjusted for polyolefins
according to
the respective melting temperature. The mass throughput of gaseous fluid 8
depends, among other things, on the amount of the filaments to be drawn, the
polymer or polymers used, the degree of drawing and the pre-drawing between
the
spinning device 1 and the heating device 5.
The filaments, because of their improved mechanical properties, are especially
suited for the manufacture of fleeces, whereby thermol plastic synthetic
materials
are used as the material, especially PET, but also polyester (PES), polyamide
(PA),
polyamide 6.6 (PA 6.6), polypropylene (PP) or polybutyleneterephthalate (PBT).
The
filaments can also be made of several different materials, whereby known
spinning
techniques are used.
