CA2280872A1

CA2280872A1 - Drawing device and method for producing drawn synthetic filaments

Info

Publication number: CA2280872A1
Application number: CA002280872A
Authority: CA
Inventors: Jean Baravian; Georges Riboulet; Helmut Leiner; Robert Groten
Original assignee: Individual
Current assignee: Carl Freudenberg KG
Priority date: 1997-02-12
Filing date: 1998-01-26
Publication date: 1998-08-20
Also published as: DE19705113A1; EP0961844A1; BR9807833A; WO1998036110A1; CN1247578A; DE19705113C2; JP2000509770A

Abstract

The invention relates to a drawing device and a method for the production of drawn synthetic filaments (2, 3), comprising a spinning device (1) and pulling-off device (10) with pneumatic means for producing a traction force on the synthetic filaments (2, 3), wherein a heating device (5) with a heating-medium flow (8) guided in counterflow to the synthetic filaments (2, 3) is placed between the spinning device (1) and the pulling-off device (10).

Description

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 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 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 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 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.

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 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, 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, 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 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:

_$_ 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 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 _g_ 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.

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 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).

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 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.

Claims

1. Drawing arrangement for producing drawn synthetic filaments (2, 3) comprising a spinning device (1), and a pulling-off device (10) comprising a pneumatic means (11) for producing a traction force on the synthetic filaments (2, 3), characterized in that a heating device (5) is positioned between the spinning device (1) and the pulling-off device (10) with a heating medium flow (8) guided in counter current to the synthetic filaments (2, 3).

2. Drawing device according to claim 1, characterized in that means for producing a spun fleece are provided.

3. Drawing device installation according to claim 1, characterized in that means for producing staple fibers, for example, for the producing of fiber fleeces, are provided.

4. Process for producing drawn synthetic filaments (2, 3), wherein melt spun filaments (2, 3) with an individual titer of larger than 1 dTex are cooled behind a spinning device (1) at least to the solidification temperature and drawn by way of a pneumatic pulling device (10), characterized in that the filaments after cooling and before entering into the pulling-off device are heated for purpose of the drawing in a heating device (5), whereby the filaments in the heating device (5) are blown at in counterflow with a gaseous fluid (8) heated to a temperature above the solidification point.

5. Process according to claim 4, characterized in that between the heating device (5) and the pulling-off device (10), a secondary drawing takes place with a drawing ratio of 1.1:1.5.

6. Process according to claim 4 or 5, characterized in that the filaments (2, 3) are blown at in counterflow at a temperature of 200°C to 350°C, preferably 225°C to 300°C.

7. Process according to one of claims 4 to 6, characterized in that the filaments are blown at in counterflow with an air volume of 5 m3/h to 25 m3/h.

8. Process according to one of claims 4 to 7, characterized in that the filaments are guided through the counterflow at a pulling-off speed of 2000 m/min to m/min.

9. Process according to one of claims 4 to 8, characterized in that the air volume and the temperature of the air counterflow is adjusted so that a fiber stretch of less than 60% is achieved.

10. Process according to one of claims 4 to 9, characterized in that the pulling-off speed of the filaments, the air volume and the temperature of the air counterflow is adjusted so that at even pulling-off speed, a relative increase in the tensile strength of the secondarily stretched filament of at least 20% is achieved relative to a singly stretched filament, whereby preferably a tensile strength of the filaments of at least 32 cN/Tex, especially preferably 40 to 50 cN/Tex is achieved.

11. Process according to one of claims 4 to 10, characterized in that the pulling-off speed of the filaments, the air volume and the temperature of the air counterflow is adjusted so that the transition of the region of elastic deformation into the region of plastic deformation only takes place at an at least 20% higher force.

12. Process according to one of claims 4 to 11, characterized in that the air volume and the temperature of the air counterflow is adjusted so that a hot air shrinking of at most 6% (at 180°C, 15 min) is achieved.

13. Process according to one of claims 4 to 12, characterized in that the filaments are secondarily stretched subsequent to the counter current treatment continuously or in a separate treatment step.

14. Process according to one of claims 4 to 13, characterized in that the synthetic filaments (2, 3) are laid down on a carrier for producing a fleece.

15. Process according to one of claims 4 to 13, characterized in that the synthetic filaments (2, 3) are cut for producing staple fibers.

16. Fleece including drawn synthetic filaments produced by using a drawing device according to one of claims 1 to 3 or with a process according to one of claims 4 to 15, characterized in that the filaments have a tensile strength of at least 32 cN/Tex and a stretch of less than 60%.

17. Fleece according to claim 16, characterized in that the synthetic filaments are deposited as endless threads.

18. Fleece according to claim 16, characterized in that the synthetic filaments are present as staple fibers.

19. Yarn including drawn synthetic filaments manufactured using a drawing device according to one of claims 1 to 3 or a process according to one of claims 4 to 15, characterized in that the filaments have a tensile strength of at least 32 cN/Tex and a stretch of less than 60%.

20. Yarn according to claim 19, characterized in that the synthetic filaments are endless threads.

21. Yarn according to claim 19, characterized in that the synthetic filaments are present as staple fibers.