EP1608803B1 - Method and device for producing post-stretched cellulose spun threads - Google Patents

Abstract

The invention relates to a method and device for producing Lyocell fibres from a spinning solution containing water, cellulose and tertiary amine oxide. The spinning solution is extruded to form spun threads ( 10 ). The spun threads ( 10 ) are stretched and passed through a precipitation bath ( 16 ) in order to precipitate the cellulose. It has been surprisingly revealed that the tenacity of the Lyocell fibres produced in this way can be increased when the stretched fibres are subjected to post-stretching in a post-stretching means. The post-stretched Lyocell fibres have a wet modulus of at least 260 cN/tex.

Description

The invention relates to a method for the production of lyocell threads from a spinning solution containing water, cellulose and tertiary amine oxide and the spun threads produced by this method.

Furthermore, the invention relates to an apparatus for producing filaments of a spinning solution containing cellulose, water and tertiary amine oxide, with a spinneret through which the spinning solution is extrudable into filaments during operation, with a precipitating bath with a precipitant precipitating a cellulose, through which the filaments in the Operation with a first drawing means, by means of which the filaments are stretchable in operation, with a second drawing means, through which the stretched filaments drawn by the first drawing means are nachverstreckbar during operation, and with a arranged in the region of the second drawing means heating device by the Operation the spun yarns are heatable during Nachverstreckung.

In the manufacturing process, the spinning solution is first extruded into filaments, then the filaments are drawn and passed through a precipitation bath, after which the cellulose of the filaments coagulates.

The production process of fibers (hereinafter the terms "fibers" and "filaments" are used synonymously) from cellulose dissolved in a tertiary amine oxide such as N-methyl-morpholine-N-oxide and water, also called lyocell process, refers to the patents US-A-4 142 913 . US-A-4,144,080 . US-A-4 211 574 . US-A-4,246,221 , US-A-4,261,943 and US-A-4,416,698 back. In these patent publications, which are based on McCorsley, the basic principle of the production of lyocell fibers is described for the first time with the three process steps of extruding the spinning solution into filaments into an air gap, drawing the extruded filaments in the air gap and precipitating the cellulose in a precipitation bath.

After precipitation and coagulation of the cellulose, the filaments can be fed to further processing steps. Thus, the filaments can be washed, dried and treated with additives or impregnated. To produce staple fibers, the filaments can be cut.

The advantage of the Lyocell process lies in the good environmental compatibility and in the excellent mechanical properties of the spun threads or fibers. Various advances in the process developed by McCorsley have greatly improved profitability.

The lyocell fiber differs in terms of their structure and their textile properties of the other cellulose fibers and their production, as for example in the DE-A-100 16 307 . WO-A-01/58960 . DE-A-197 53 806 . DE-A-197 21 609 . DE-A-195 11 151 and DE-A-43 12 219 are described.

A particular problem of the Lyocell process compared to the processes described therein lies in the high surface tack of the freshly extruded filaments: As soon as the filaments touch the air gap, they stick together, resulting in either unsatisfactory fiber quality or even disruption of the spinning process and re-spinning leads. McCorsley himself uses this, as in the DE-A-284 41 63 described, the filaments in the air gap on a roller with Fällbadlösung. However, this arrangement is impractical at high spinning speeds. A series of further developments of the McCorsley process therefore deals with measures to reduce the surface tackiness of the spun yarns in the air gap and to improve the operational reliability, also called spin security, of the production process.

One widely used technique in the art of making lyocell fibers or filaments is to blown the filaments in the air gap with a cooling gas to cool the surfaces of the freshly extruded filaments and reduce their stickiness. Such Kühlbeblasungen are for example in the WO-A-93 19230 . WO-A-94 28218 . WO-A-95 01470 and in the WO-A-95 04173 described. As will be apparent from these references, depending on the arrangement of the extrusion orifices through which the spinning solution is extruded, different types and designs of blowing are used.

Another problem in the production of lyocell fibers is the design of the precipitation bath. Due to the high extrusion speeds, the filaments immerse at high speed in the Fällbadlösung and tear the Fällbadlösung in their environment. As a result, a flow is generated in the precipitation bath, which stirs the surface of the precipitation bath and mechanically loads the filaments when immersed in the precipitation bath to thread breaks.

In order to keep the Fällbadoberfläche as quiet as possible in the case of annularly arranged extrusion openings, in the DE-A-100 60 877 and in the DE-A-100 60 879 the filaments passed through specially designed spinning funnel filled with precipitation bath. In the spinning towers, the precipitating bath solution flows out together with the spun threads at the lower end. This gravity driven flow can, as in the DE-A-44 09 609 is described, be exploited to stretch the filaments.

When arranged on a rectangular surface extrusion openings were in accordance with the DE-A-100 37 923 achieved good results when the spun yarns form a substantially flat curtain and are deflected as a flat curtain in the precipitation bath to Fällbadoberfläche out. In this embodiment, a deflecting body is arranged in the precipitation bath.

The post-processing of lyocell threads after extrusion and the coagulation of the cellulose to achieve certain mechanical properties of the filaments is less well documented in the patent literature.

By doing Basic article "What is new about the new fibers of the genus Lyocell?", Lenzinger reports 9/94, pp. 37-40 It is believed that the fiber structure and fiber properties are determined by the molecular orientation during extrusion and the post-extrusion draw. Here, the Lyocell fibers differ significantly from the fibers, as in the DE-A-197 53 806 . DE-A-197 21 609 . DE-A-195 11 151 . DE-A-100 16 307 and the DE-A-43 12 219 are described.

This idea is taken up in the new patent literature and put into practice. So are in the EP-A-823 945 , in the EP-A-853 146 and in the DE-A-100 23 391 Devices are described in which after stretching of the extruded filaments and after the coagulation of the cellulose in the drawn filaments these are kept de-energized during further processing. These developments are based on the idea that the mechanical properties of the drawn and coagulated filaments can no longer be changed.

A path that is only opposite at first sight becomes alone in the EP-A-494,851 In this document, a method is described in which the substantially tensionless extruded and coagulated cellulose is stretched. It is essential in this process that no stretching of the freshly extruded filaments takes place. Through this, for the lyocell processing unusual method of EP-A-494,851 , which apparently was not further developed, a subsequent shaping of the filaments is to be made possible. The procedure of EP-A-494,851 thus resembles a plastic deformation process, wherein the starting material, the unstretched lyocell threads, has a rubbery consistency. The mechanical properties of the according to the method of EP-A-494,851 produced fibers, however, do not meet today's requirements.

In the DE-A-102 23 268 is described that a multi-stage precipitation and at the same time a multi-stage drawing of the filaments can be realized if the wetting device is used simultaneously for drawing the filaments. Although this measure can reduce the need for treatment medium and improve the control of the failure process, the textile properties remain substantially unaffected by this type of re-stretching.

In the JP-A-03-076822 a process for producing fire-resistant fibers is described. After coagulation of the undrawn fibers, the filaments are drawn for a first time, then oiled and dried, then re-stretched under steam and then dried again.

To modify the mechanical properties, such as the loop strength, fibrillation tendency and the tensile strength of lyocell fibers, the repertoire is currently used essentially as described in the article " Structure formation of cellulose fibers from amine oxide solutions. "Lenzinger reports 9/94, pp. 31-35 , is described. Thereafter, the textile-physical properties of lyocell fibers by changes in the cellulose concentration in the spinning solution (see. WO-A-96 18760 ), by varying the deduction conditions (cf. DE-A-42 19 658 ) and the use of additives (cf. DE-A-44 26 966 . DD-A-218 121 . WO-A-94 20656 ) and by changing the precipitation conditions (cf. AT-B-395 724 ). All of these methods, however, only an indirect and in the process management only very inaccurate control of the mechanical properties of the lyocell threads or fibers.

The invention is therefore based on the object to improve the known methods and apparatus for producing lyocell fibers in that the mechanical properties, such as the loop strength and the tensile strength of the lyocell fibers can be selectively influenced by an easy-to-control process.

This object is achieved according to the invention for the production process mentioned at the outset in that the drawn filaments are post-stretched and at the same time heat-treated.

For the device mentioned above, this object is achieved in that the filaments are stretched by the first drawing means in an air gap before entering the precipitation bath.

Surprisingly, the post-stretching or stretching of the filaments, which have already been drawn once in the air gap and then coagulated, can considerably improve the mechanical properties, in particular the wet modulus, compared with the conventional lyocell fibers. Due to the heat treatment during the post-drawing, the wet module is lowered a little after the first attempts and the fiber becomes somewhat more elastic again.

In contrast to the method and the device of DE-A-102 23 268 allows the heat treatment carried out during the post-stretching process a decisive improvement in the textile properties of the lyocell fibers.

Thus, lyocell fibers having a wet modulus of at least 250 cN / tex and a wet rubbing rate per 25 fibers of at least 18 can be obtained by the process of the present invention. Even wet modules of at least 300 cN / tex or 350 cN / tex can be achieved with the process according to the invention. The wet maximum tensile force extension can assume relatively low values, for example at most 12%.

The higher the predetermined tensile stress with which the spun threads are stretched or stretched, the higher the wet modulus of the finished threads and fibers seems to be. A considerable increase of the wet modulus compared to conventional fibers can be achieved according to an advantageous process control if the predetermined tensile stress with which the post-stretching is carried out amounts to at least 0.8 cN / tex. Higher values for the wet modulus can be achieved if, according to a further embodiment, the predetermined tensile stress during the post-drawing is at least 3.5 cN / tex.

In general, higher values for the wet modulus result when the filaments are coagulated before the post-drawing.

The heat treatment can be carried out subsequent to a washing or impregnation process as a drying process, so-called tension drying. Alternatively, the heat treatment may also take place in a steam or dry steam atmosphere. The steam or dry steam may contain impregnating agents which act on the filaments and lead to a chemical aftertreatment.

The heat treatment is preferably carried out in an oven in which the drawn and coagulated filaments are post-stretched between two godets with a predetermined tensile stress. In this case, a hot inert gas, such as hot air, or steam or dry steam may be passed through the surfaces of the godets and the filaments lying thereon.

After the post-stretching, the spun threads can be crimped, since the natural crimp of the spun threads is substantially reduced due to the post-stretching. At the same time a treatment with dry steam is possible simultaneously with the crimping.

For the production of staple fiber, the filaments can finally be cut.

In the following the invention will be explained in more detail by means of an embodiment and by means of test results and test examples with reference to the drawings.

Fig. 1

eine schematische Übersicht über eine Anlage zur Herstellung von nachverstreckten Lyocell-Fasem;

Fig. 2

eine Ausführungsform eines Mittels zur Nachverstreckung in einer schematischen Ansicht;

Fig. 3

eine weitere Ausführungsform eines Mittels zur Nachverstreckung in einer schematischen Ansicht.

Show it:

Fig. 1

a schematic overview of a plant for the production of post-stretched lyocell fibers;

Fig. 2

an embodiment of a means for Nachverstreckung in a schematic view;

Fig. 3

a further embodiment of a means for Nachverstreckung in a schematic view.

First, the basic structure of a plant 1 for the production of lyocell fibers on the basis of the schematic representation of Fig. 1 described. The plant 1 of Fig. 1 is used to produce staple fibers from Lyocell.

Via a pipeline system 2, a high-viscosity spinning solution containing water, cellulose and tertiary amine oxide, for example N-methyl-morpholine-N-oxide, passed. The line system 2 is modularly constructed from fluid line pieces 2a of predetermined length, which are connected to each other via standard flanges 2b.

The fluid line pieces 2a are provided with an internal temperature control device 3, which is mounted in the fluid line pieces 2 instead of the core flow of the spinning solution and is regulated by the temperature of the spinning solution in the pipeline system 2.

A temperature-controlled fluid is passed through the inner temperature control device via feed modules 4 arranged between two adjacent fluid line sections, as indicated by the arrows 5. The feed modules 4 essentially have the dimension of the standard flanges and are designed to be connectable with these.
At predetermined intervals, also replace by the arranged between the fluid line sections 2a Berstmodule 6, the feed modules 4. The bursting modules 6 have essentially the same configuration as the feed modules 4. You are in the Fig. 1 Not shown Berstkörpem provided that break when exceeding a predetermined pressure in the piping system 2, in case of bursting, and allow a pressure discharge to the outside. The bursting event may be especially at a spontaneous exothermic Reaction of the spinning solution due to overaging or overheating occur. The spinning solution which escapes in the event of a burst is collected in collecting containers 7, from where it can be recycled or disposed of.

Through the piping system 2, the spinning solution is fed to a spinner 8. The spinner head 8 is provided with a spinneret 9 having a large number of extrusion orifices (not shown), usually several thousand extrusion orifices. Through the extrusion openings, the spinning solution is extruded into filaments 10. The arrangement of the extrusion openings in the spinneret 9 may be circular, circular or rectangular; In the following, reference will be made, by way of example only, to a rectangular arrangement.

So that optimum spinning conditions prevail at the extrusion openings, in addition to the tempering device 3 in the piping system 2 further baffles can be provided, which can also be connected via the standard flanges, simply with the fluid line pieces 2a or with the feed modules 4 or bursting modules 6. Thus, in the pipeline system 2, a surge tank 11 a may be arranged, which compensates for pressure fluctuations and volume flow fluctuations of the spinning solution in the pipe 2 via a change in its internal volume and ensures a uniform extrusion pressure at the extrusion openings of the spinner head 8.

Furthermore, a mechanical filter device 11b with a backwashable filter element (not shown) may be provided in the pipeline system 2. The filter element has a fineness between 5 microns and 25 microns. Through the filter device 11 b takes place during the transport of the spinning solution, a continuous or - using alternately operated buffer (not shown) - a discontinuous filtering of the spinning solution instead.

The extrusion openings adjoin an air gap 12 which the freshly extruded spun threads 10 pass through and in which the spun threads are hidden by a tensile stress. In the air gap 12, a cooling gas flow 13 is directed to the spun yarns 10, which is generated by a blowing device 14. Temperature, humidity and composition of the cooling gas flow 13 can be regulated by an air conditioning device 15 to predetermined or variably predeterminable values.

The cooling gas stream 13 acts at a distance from the spinneret 9, on the spun yarns 10 and has a velocity component in the extrusion direction E, so that the spun yarns are mitverstreckt by the cooling gas stream 13. In order to allow a good heat transfer, the cooling gas flow 13 is turbulent.

After passing through the air gap 12, the spun threads 10 enter a precipitation bath 16. In order to avoid disturbing the surface of the precipitation bath 16, the cooling gas flow 13 is sufficiently spaced from the surface 17 of the precipitation bath, so that it does not impinge on the surface.

In the precipitation bath 16, the spun threads 10 are deflected by a substantially roller-shaped deflecting member 18 to a bundling member 19 above the precipitation bath, so that they again pass through the Fällbadoberfläche 17. The deflection can be rigid or fixed, or rotate with the threads. The bundling member 19 is rotatably driven and exerts as the first drawing means via the deflection member 18 a back to the extrusion openings of the spinneret 9 retrospective tensile stress on the spun yarns 10, which stretches the spun yarns 10. Of course, as the stretching means and the deflecting member 18 may be driven.

In order to stretch the spun yarns 10 as gently as possible, the tensile stress can also be generated only by the cooling gas stream 13 as the first drawing agent. This has the advantage that the tensile stress is introduced into the spun threads 10 by a friction stress acting on the surface of the spun threads.

From the bundling member 19, the filaments 10 are combined to form a bundle of fibers 20. Subsequently, the still wetted with the Fällbadlösung 16, combined to form the bundle of fibers 20 spun yarns 10 are placed without tension on a conveyor 21 and transported largely tensionless on this. During the transport of the filaments on the conveyor 21, the complete or almost complete coagulation of the cellulose filaments can take place under the lowest possible voltage influence.

The conveyor 21 may, as in Fig. 1 is shown to be configured as a vibrating conveyor, which transports the bundle of fibers 20, or optionally a plurality of bundles of fibers 20 at the same time, by vibrations in the conveying direction F. The vibrations of the conveyor 21 are indicated by the double arrow 22. By the reciprocating motion 21, the spun-thread bundle 20 is deposited in an orderly manner on the conveyor. Instead of the vibrating conveyor 22, other conveying devices, such as a plurality of godets arranged one behind the other, can be used with almost the same or peripheral speed decreasing in the conveying direction.

During transport on the conveyor 21, various treatments of the bundle of fibers 20 can be carried out, for example, the bundle of fibers 20 washed once or more times, dried and aviviert, for example by a sprinkler 23 from a treatment medium 24 is sprayed onto the filament bundle 20.

The bundle of fibers 20 is received by a godet 25 of the conveyor 21 and fed to a second Nachverstreckungsmittel 26 through which the durchkoagulierten filaments 10 are nachverstreckt.

In the embodiment of Fig. 1 If the post-stretching takes place during a simultaneous heat treatment or drying in the form of a voltage drying, as this the mechanical properties of the spun yarns 10 are influenced most favorable. Slightly worse properties, but still distinguished from the state of the art, are achieved by omitting the heat treatment during re-drawing.

The second Nachverstreckungsmittel 26 may also be provided immediately after the bundling means 19, ie between the conveyor 21 and the precipitation bath 16, so that only the nachverstreckten filaments are subjected to further treatment steps.

To carry out the heat treatment, the post-stretching means 26 in the entry region of the spun yarn 20 may have a heating device 27 which brings the spun-fiber bundle 20 to a predetermined temperature and at the same time dries the spun-fiber bundle 20 at least superficially.

In Nachverstreckungsmittel 26, the spun yarns are guided over two godets 28, 29, which are driven so that the spun yarn bundle 20 between them with a predetermined Nachverstreckungs tensile stress Z _{N is} applied. The spunbond bundle charged with this tension is maintained at a predetermined high temperature and can be impregnated during post-stretching, in particular by a hot inert gas, such as air, or by steam, for example dry steam, and swelling agents or other chemical fiber treatment means, such as Arrows 30 is indicated. To support the drying effect, the godets 28, 29 may also be heated.

As a result of the post-stretching, the spun-thread bundle 20 has a reduced crimp compared with conventional fibers, so that it is crimped over a stuffer box 31. Subsequently, the fiber bundle 20 is cut by a cutting device 32. If an endless fiber to be generated, of course, can be dispensed with the crimping and / or cutting.

After crimping and cutting, the crimped staple fibers can be transported in random orientation in the form of a crimped endless cable 33 on a conveyor 34 for further method steps.

In Fig. 2 an embodiment of a post-stretching means 26 is shown schematically. In this embodiment, a post-stretching takes place in the form of a voltage drying.

As already at Fig. 1 has been described, the Nachverstreckungsmittel 26 two godets 28, 29, which are driven so that the thread bundle 20 between them with a predetermined tensile stress Z _N of at least 0.8 cN / tex, preferably at least 3.5 cN / tex stretched or stretched. For this purpose, for example, the following in the conveying direction F godet 29 with a predetermined, higher speed to be rotated as the galette 28 located in the conveying direction F; wherein between the godet 29 and the looped around the godet thread bundle 20, a slip can prevail, which essentially determines the tensile stress Z _N.

To stretch the bundle of fibers 20 and its shrinkage during drying can be exploited: Since the bundle of fibers shortened during the drying process, an expansion or re-stretching takes place even if this shortening is not compensated by the rotational speeds of the godets 28, 29. In this way, a Nachverstreckung also take place when the godets 28, 29 rotate at substantially the same or only slightly different speed.

One or both godets 28, 29 can be provided with an at least gas-permeable surface 30, through which a hot inert gas, steam or dry steam from the interior of the godet 28, 29 is pressed by the spun-thread bundle 20 looped around the godet 28, 29.

Alternatively or in addition to a wrap, as described in the Fig. 2 is shown, each Galette 28, 29 may also be associated with a steam-permeable, actively or passively co-rotating roller 28a, 29a in opposition, as shown schematically in FIG Fig. 3 is shown. The rollers 28a, 29a also have permeable surfaces through which the inert gas or the vapor is sucked off. Instead of rollers and large drums can be provided.

Instead of the godets 28, 29 and larger drums or suction drums can be used with perforated surface, through which the hot gas is sucked.

In the area between the godets 28, 29 also hot air or another intertes hot gas, steam or dry steam is passed through gas or the filament bundles 20. The effectiveness of post-stretching has been demonstrated in a number of experiments.

The tests were carried out on a bundle of 79,270 filaments and a total titer of 110,978 dtex, corresponding to a single denier of 1.4 dtex. Table I gives an overview of the test results.

In a first series of experiments (Experiments 1 to 7), the filament bundle was dried at 73 ° C for 15 min under various conditions.

In experiment 1, the bundle of fibers was dried without tension.

In experiment 2, the bundle of fibers was dried without tension, remoistened and dried under tension. For this purpose, the bundle of fibers was passed through two eyelets at a distance of 50 cm and was weighted during drying on both sides with 19 kg each.

In experiment 3, the bundle of fibers was dried without tension, remoistened and dried under tension. For this purpose, the bundle of fibers was passed through two eyelets at a distance of 50 cm and weighted on both sides with 38 kg each.

In experiment 4, the bundle of fibers was clamped between two clamps at a distance of 38 cm and then dried.

In experiment 5, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 9 kg.

In experiment 6, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 19 kg.

In experiment 7, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 38 kg.

In a second series of experiments, the bundle of fibers was subjected to treatment with sodium hydroxide solution (NaOH) before drying. First, the filament bundle was treated with 5% NaOH solution for 5 minutes and then washed with completely deionized water. The NaOH solution was neutralized with 1% formic acid and washed again with deionized water.

The spunbond bundle was then dried in the dryer at 73 ° C for 30 minutes.

In experiment 8, the bundle of fibers was dried without tension.

In experiment 9, the bundle of fibers was dried without tension, remoistened and dried under tension. For this purpose, the bundle of fibers was guided through two eyelets at a distance of 50 cm and weighted on both sides with 19 kg each.

In experiment 10, the bundle of fibers was dried without tension, remoistened and dried under tension. For this purpose, the bundle of fibers was passed through two eyelets at a distance of 50 cm and weighted on both sides with 38 kg each.

In experiment 11, the bundle of fibers was stretched between two clamps at a distance of 38 cm and then dried.

In experiment 12, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 9 kg.

In experiment 13, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 19 kg.

In experiment 14, the bundle of fibers was dried wet under tension. The thread bundle was guided through two eyelets at a distance of 50 cm and weighted on both sides, each with a weight of 38 kg.

For the dried bundles of fibers, the titer, the tenacity, the maximum tenacity, the wet denier, the wet maximum tenacity, the tenacity at break, the wet modulus, and the wet abrasion number were then determined. The procedure was as follows.

The titer was determined according to DIN EN ISO 1973. The (wet) maximum tensile strength and the (wet) maximum tensile elongation were determined in accordance with DIN EN ISO 5079. The maximum loop tension was determined in accordance with DIN 53843 Part 2.

The wet modulus was determined on a fiber bundle, which is usable according to DIN EN 1973. The procedure is based on the test specification ASG N 211 of Alceru Schwarza GmbH. The tests for determining the wet modulus were carried out on a tensile testing machine with constant strain rate and low-path electronic force measurement. The gripping length of the thread bundle was 10.0 mm ± 0.1 mm. The fineness biasing force was 2.5 mN / tex ± 0.5 mN / tex for a titer greater than 2.4 dtex. At a titer of up to 2.4 dtex, a biasing mass of 50 mg was used. The elongation rates were 2.5 mm / min with an average wet elongation at break up to 10%, 5.0 mm / min with an average wet elongation at break of more than 10 to 2% and 7.5 mm / min with a mean wet elongation at break of over 20%.

Five spunbond bundles were placed in a shallow dish of wetting agent solution for at least 10 seconds, with the biasing mass previously clamped to one end of each spunbond bundle. The test specimen that has been inserted the longest is removed from the tray and used for the tensile test; after each test, a new specimen is to be inserted for the purpose of netting.

The spun yarn bundle to be clamped is clamped with its end opposite the biasing mass piece in the tensile testing machine, then the lower clamping clamp is closed and the submerged vessel with the wetting agent solution is raised so that the liquid level reaches as far as possible to the upper clamping clamp without them however, to touch. The distance between the grips is at the strain rate indicated above to increase steadily until an elongation of 5% is reached. At this moment, stop the movement of the lower clamp and determine the wet pull force in mN down to one decimal.

The wet modulus M is calculated from the arithmetic mean of the wet tensile force F in millinewtons and the mean fineness T in tex of the tested staple fibers and expressed in millinewtons per tex rounded to integers: M = F / (T * 0.05).

The wet scrubbing number was determined using a Fasemassscheuerprüfgerät FNP SMK Präzisionsmechanik Gera GmbH. The wet scrub number is the number of revolutions of the scrubbing shaft until the breakage of the fiber clamped under defined pretension in the wet scrub tester. The pretensioning weight is 70 mg at a titer between 1.2 and 1.8 dtex. The speed of the scouring shaft was 400 rpm, the wrap angle 45 °. The scouring shaft is provided with a fabric hose.

The tests according to Table 1 show a surprising increase in the wet modulus and the wet scrubbing number of the post-stretched fibers compared with the conventional, non-postdrawn fibers (Experiment 1). In the case of tension-free dried bundles of fibers, which are then moistened again and dried under tension (tests 2, 3 and 9, 10), the load of 38 kg (equivalent to 3.12 cN / tex) compared to the load of 19 kg (corresponds to 1, 6 cN / tex) achieved an increase of the wet modulus with a slight decrease in the wet rubbing number. It can be at the high load higher wet modules achieve than the wet under tension dried thread bundle of experiments 5 to 7 and 12 to 14.

The maximum tensile force, measured both wet and dry, is essentially unchanged from the non-post-stretched fibers of Experiment 1. The reduced maximum tensile force elongation and the reduced maximum loop tensile force, in conjunction with the wet modulus and wet scrub number, suggest that the post-stretched fibers are more brittle and ductile than the non-postdrawn fibers.

Thus, the experiments demonstrate that re-stretching or stress-drying can produce fibers with improved wet modulus and wet scrub number.

Claims (17)

1. A method for the production of Lyocell fibres from a spinning solution containing water, cellulose and tertiary amine oxide, wherein the following steps in the method are carried out:

   - extrusion of the spinning solution to spun threads (10),

   - stretching of the spun threads (10),

   - passage of the spun threads through a precipitation bath (16),
   characterised by the following step in the method:

   - post-stretching and simultaneous heat treatment of the stretched spun threads (10) after passage through the precipitation bath (16).
2. The method according to Claim 1, characterised by the following step in the method:

   - coagulation of the cellulose of the spun threads (10) before stretching.
3. The method according to Claim 1 or 2, characterised by the following steps in the method:

   - post-stretching with a tensile stress of at least 0.8 cN/tex.
4. The method according to Claim 3, characterised by the following step in the method:

   - post-stretching with a tensile stress of at least 3.5 cN/tex.
5. The method according to one of the aforementioned claims, characterised by the following step in the method:

   - treatment of the spun threads during heat treatment with hot inert gas.
6. The method according to one of the aforementioned claims, characterised by the following step in the method:

   - treatment of the spun threads during heat treatment with steam.
7. The method according to one of the aforementioned claims, characterised by the following step in the method:

   - passage of the spun threads (10) through an air gap (12) before the precipitation bath (16).
8. The method according to Claim 7, characterised by the following step in the method:

   - blowing of the spun threads (10) in the air gap (12) with a flow of cooling gas (13).
9. The method according to one of the aforementioned claims, characterised by the following step in the method:

   - conveyance of the spun threads free of tensile stress between the stretching and the post-stretching.
10. The method according to one of the aforementioned claims, characterised by the following step in the method:

    - crimping of the post-stretched spun threads (10).
11. The method according to one of the aforementioned claims, characterised by the following step in the method:

    - cutting of the post-stretched spun threads to form staple fibres.
12. A device (1) for the manufacture of spun threads (10) from a spinning solution containing cellulose, water and a tertiary amine oxide, with a spinneret (9), through which the spinning solution can be extruded in operation to form spun threads (10), with a precipitation bath (16) with a precipitating agent to precipitate cellulose, through which the spinning threads (10) are passed in operation, with a first stretching means (13, 18, 19), through which the spun threads can be stretched in operation, and with a second stretching means (28, 29), through which the spun threads (10) stretched by the first stretching means (13, 18, 19) can be post-stretched in operation, and a heating device (27, 30) arranged in the region of the second stretching means (28, 29) and by which the spun threads (10) can be heated in operation during the post-stretching, characterised in that the spun threads (10) can be stretched by the first stretching means (13, 18, 19) in an air gap (12) before entering the precipitation bath (16).
13. A lyocell fibre, in particular manufactured by the method according to one of the Claims 1 to 11, characterised by a wet modulus of at least 250 cN/tex and by a wet abrasion number per 25 fibres of at least 18.
14. The lyocell fibre according to Claim 13, characterised by a wet modulus of at least 300 cN/tex.
15. The lyocell fibre according to Claim 14, characterised by a wet modulus of at least 350 cN/tex.
16. Cellulose fibres according to one of the Claims 13 to 15, characterised by a wet tensile force elongation of at the most 12%.
17. Cellulose fibres according to one of the Claims 13 to 16, characterised by a wet abrasion number per 25 fibres of at the most 25.

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