EP1608803A1

EP1608803A1 - Method and device for producing post-stretched cellulose spun threads

Info

Publication number: EP1608803A1
Application number: EP04710007A
Authority: EP
Inventors: Stefan Zikeli; Klaus Weidinger; Lutz Glaser; Werner Schumann
Original assignee: ZiAG Plant Engineering GmbH
Current assignee: LL Plant Engineering AG
Priority date: 2003-04-01
Filing date: 2004-02-11
Publication date: 2005-12-28
Anticipated expiration: 2024-02-11
Also published as: BRPI0409544A; WO2004088010A1; CN1774527A; ATE400677T1; ZA200507946B; KR20050119675A; US20060083918A1; TW200422447A; KR100691913B1; DE10314878A1; CN100410430C; TWI278541B; EP1608803B1; BRPI0409544B1; DE502004007553D1

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

Process and device for producing post-stretched cellulose spinning threads

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

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 process for producing fibers (hereinafter the terms “fibers” and “threads” are used synonymously) from cellulose dissolved in a tertiary amine oxide such as N-methyl-morpholine-N-oxide and water, also called the Lyocell process, is based on the patents US-A-4 142 913, US-A-4 144 080, US-A-4211 574, US-A-4 246 221, US-A-4 261 943 and US-A-4416 698. In these patent publications based on McCorsley, the basic principle of producing lyocell fibers with the three process steps of extruding the spinning solution into filaments in an air gap, stretching the extruded filaments in the air gap and precipitating the cellulose in a precipitation bath is described for the first time.

After the cellulose has precipitated and coagulated, the spun threads can be passed on to further processing steps. The filaments can be washed, dried and treated with additives or impregnated. The spun threads can be cut to produce staple fibers.

The advantage of the Lyocell process is the good environmental compatibility and the excellent mechanical properties of the spun threads or fibers. Through various further developments of the process developed by McCorsley, the economy could be greatly improved. The structure and the textile properties of the lyocell fiber differ from the other cellulose fibers and their production, as described, for example, in DE-A-100 16 307, DE-A-197 53 806, DE-A-197 21 609, DE-A-195 11 151 and

DE-A-43 12 219 are described.

A special problem of the Lyocell process compared to the processes described there is the high surface tack of the freshly extruded spun threads: As soon as the spun threads touch in the air gap, they stick together, which either leads to unsatisfactory fiber quality or even to an interruption in the spinning process and a new piecing leads. McCorsley himself, as described in DE-A-284 41 63, uses the filaments in the air gap over a roller with a precipitation bath solution. However, this arrangement is not practical at high spinning speeds. A number of further developments of the McCorsley process are therefore concerned with measures to reduce the surface stickiness of the filaments in the air gap and to improve the operational safety, also known as spinning safety, of the production process.

One measure widely used in the prior art in the production of lyocell fibers or threads is to blow the spinning threads in the air gap with a cooling gas in order to cool the surfaces of the freshly extruded spinning threads and to reduce their stickiness. Cooling blows of this type are described, for example, in WO-A-93 9230, WO-A-942818, WO-A-95 01470 and in WO-A-95 01473. As can be seen from these documents, depending on the arrangement of the extrusion openings through which the spinning solution is extruded, different types and configurations of the blowing are used.

Another problem in the production of Lyocell fibers is the design of the coagulation bath. Due to the high extrusion speeds, the filaments are immersed in the coagulation bath solution at high speed and entrain the coagulation bath solution in their environment. As a result, a flow is generated in the precipitation bath, which agitates the surface of the precipitation bath and mechanically stresses the filaments when immersed in the precipitation bath up to thread tears. In order to keep the precipitation bath surface as still as possible in the case of circularly arranged extrusion openings, in DE-A-100 60 877 and in DE-A-100 60 879 the spinning threads are passed through specially designed spinning funnels filled with precipitation bath. In the spinning funnels, the precipitation bath solution flows out together with the spinning threads at the lower end. This flow, driven by gravity, can, as described in DE-A-44 09 609, be used to stretch the spun threads.

In the case of extrusion openings arranged on a rectangular area, good results have been achieved according to DE-A-100 37 923 if the spun threads form an essentially flat curtain and are deflected as a flat curtain in the precipitation bath toward the precipitation bath surface. In this embodiment, a deflecting body is arranged in the precipitation bath.

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

In the basic article "What is new about the new fibers of the Lyocell genus?", Lenzinger reports 9/94, pp. 37-40, it is assumed that the fiber structure and the fiber properties are due to the molecular orientation during extrusion and which are immediately related the extrusion subsequent stretching can be determined. The Lyocell fibers differ decisively from the fibers as described in DE-A-197 53 806, DE-A-197 21 609, DE-A-195 11 151, DE-A-100 16 307 and DE -A-43 12 219 are described.

This idea is taken up in the new patent literature and put into practice. Thus, in EP-A-823 945, in EP-A-853 146 and in DE-A-100 23 391 devices are described in which after stretching the extruded filaments and after coagulation of the cellulose in the elongated filaments, these be 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 glance is followed in EP-A-494851 alone: This publication describes a process in which the cellulose, which is extruded and coagulated essentially without tension, is stretched. It is essential in this process that the freshly extruded spun threads are not stretched. This method of EP-A-494 851, which is unusual for lyocell processing and does not seem to have been further developed, is intended to enable the filaments to be shaped subsequently. The process of EP-A-494 851 thus resembles a plastic deformation process, the starting material, the undrawn lyocell threads, having a rubber-like consistency. However, the mechanical properties of the fibers produced according to the process of EP-A-494 851 do not meet today's requirements.

DE-A-102 23 268 describes that multistage precipitation and, at the same time, multistage stretching of the spun threads can be achieved if the wetting device is simultaneously used to stretch the spun threads. This measure can reduce the need for treatment medium and improve the control of the failure process, but the textile properties remain essentially unaffected by this type of post-stretching.

To change the mechanical properties, such as the loop strength, the tendency to fibrillation and the tensile strength of Lyocell fibers, the repertoire is currently essentially used, as described in the article "Structure formation of cellulose fibers from amine oxide solutions", Lenzinger reports 9/94, p 31-35. Thereafter, the textile-physical properties of Lyocell fibers are changed by changing the cellulose concentration in the spinning solution (cf. WO-A-96 18760), by varying the take-off conditions (cf. DE-A-42 19 658) and by using additives (cf. DE-A-44 26 966, DD-A-218 21, WO-A-94 20656) and by changing the precipitation conditions (cf. AT-B-395 724). However, all of these methods only allow indirect and very imprecise control of the mechanical properties of the Lyocell threads or fibers. The invention is therefore based on the object of improving the known methods and devices for producing lyocell fibers in such a way that the mechanical properties, such as the loop strength and the tensile strength of the lyocell fibers, can be influenced in a targeted manner by an easily controllable process.

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

For the device mentioned at the outset, this object is achieved in that a second stretching means, by means of which the spinning threads drawn by the first stretching means can be post-stretched in operation, and a heating device arranged in the region of the second stretching means, by means of which, during operation, the spinning threads during post-stretching are provided are heatable.

Surprisingly, the post-stretching or stretching of the spun threads that have already been drawn and then coagulated in the air gap can considerably improve the mechanical properties, in particular the wet modulus, compared to the conventional Lyocell fibers. Due to the heat treatment during post-stretching, the wet module is lowered somewhat after the first attempts and the fiber becomes somewhat more elastic again.

In contrast to the method and device of DE-A-102 23268, the heat treatment carried out during post-stretching enables a decisive improvement in the textile properties of the Lyocell fibers.

Lyocell fibers produced with the method according to the invention can thus be achieved with a wet modulus of at least 250 cN / tex and a wet abrasion number per 25 fibers of at least 18. With the method according to the invention, even wet modules of at least 300 cN / tex or 350 cN / tex can be achieved. The maximum wet tensile strength can take on 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 appears to be. A significant increase in the wet modulus compared to conventional fibers can be achieved according to an advantageous process if the predetermined tensile stress with which the post-stretching is carried out is 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 post-stretching is at least 3.5 cN / tex.

In general, there are higher values for the wet modulus if the filaments are coagulated before being drawn.

The heat treatment can be carried out after a washing or impregnation process as a drying process, i.e. so-called stress drying. Alternatively, the heat treatment can also take place in a steam or dry steam atmosphere. The steam or dry steam can contain impregnation 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-drawn between two godets with a predetermined tensile stress. A hot inert gas, such as hot air, or steam or dry steam can be passed through the surfaces of the godets and the spun threads lying thereon.

After the post-stretching, the spun threads can be crimped, since the natural crimping of the spun threads is significantly reduced due to the post-stretching. Treatment with dry steam is also possible at the same time as crimping.

Finally, the staple threads can be cut to produce staple fiber.

The invention is explained in more detail below on the basis of an embodiment and on the basis of test results and test examples with reference to the drawings. "Show it:

Figure 1 is a schematic overview of a plant for the production of post-stretched Lyocell fibers.

2 shows an embodiment of a means for post-stretching in a schematic view;

Fig. 3 shows a further embodiment of a means for post-stretching in a schematic view.

First, the basic structure of a plant 1 for the production of Lyocell fibers is described using the schematic representation of FIG. 1. The system 1 in FIG. 1 is used for the production of staple fibers from Lyocell.

A highly viscous spinning solution containing water, cellulose and tertiary amine oxide, for example N-methyl-morpholine-N-oxide, is passed through a pipeline system 2. The line system 2 is constructed modularly from fluid line pieces 2a of a predetermined length, which are connected to one another via standard flanges 2b.

The fluid line pieces 2a are provided with an internal temperature control device 3, which is installed 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 piping system 2.

A temperature-controlled fluid is passed through the internal temperature control device via feed modules 4 arranged between two adjacent fluid line pieces, as indicated by the arrows 5. The feed modules 4 essentially have the dimensions of the standard flanges and are designed to be connectable to them. At predetermined intervals likewise replace the feed modules 4 by burst modules 6 arranged between the fluid line pieces 2a. The burst modules 6 have essentially the same configuration as the feed modules 4. They are provided with bursting bodies, not shown in FIG. 1, which break when a predetermined pressure in the pipeline system 2 is exceeded, in the event of a burst, and enable pressure to be discharged to the outside. The bursting can occur especially in the thermal reaction of the spinning solution may occur due to aging or overheating. The spinning solution emerging in the event of bursting is collected in collecting containers 7, from where it can be recycled or disposed of.

The spinning solution is guided through the piping system 2 to a spinning head 8. The spinning head 8 is provided with a spinneret 9, which has a large number of (not shown) extrusion openings, usually several thousand extrusion openings. The spinning solution is extruded into spun threads 10 through the extrusion openings. The arrangement of the extrusion openings in the spinneret 9 can be circular, circular or rectangular; In the following, reference is made to a rectangular arrangement only by way of example.

So that optimal spinning conditions prevail at the extrusion orifices, in addition to the temperature control device 3 in the piping system 2, further internals can be provided, which can also be easily connected to the fluid line pieces 2a or to the feed modules 4 or bursting modules 6 via the standard flanges. Thus, a pressure expansion tank 11a can be arranged in the piping system 2, which compensates for pressure fluctuations and volume flow fluctuations of the spinning solution in the pipeline 2 by changing its internal volume and ensures a uniform extrusion pressure at the extrusion openings of the spinning head 8.

Furthermore, a mechanical filter device 11b with a backwashable filter element (not shown) can be provided in the piping system 2. The filter element has a fineness between 5 μm and 25 μm. By means of the filter device 11b, during the transport of the spinning solution, the spinning solution is filtered continuously or - using alternately operated buffers (not shown) - discontinuously.

The extrusion openings adjoin an air gap 12 through which the freshly extruded spun threads 10 pass and in which the spun threads are hidden by tensile stress. In the air gap 12, a cooling gas stream 13 is directed onto the spun threads 10, which is generated by a blowing device 14. The 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 on the spinning threads 10 at a distance from the spinneret 9 and has a speed component in the extrusion direction E, so that the spinning threads are also stretched by the cooling gas stream 13. In order to enable good heat transport, the cooling gas flow 13 is turbulent.

After crossing 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 stream 13 is sufficiently spaced from the surface 1 of the precipitation bath so that it does not strike the surface.

In the precipitation bath 16, the spinning threads 10 are deflected by an essentially roller-shaped deflection member 18 to a bundling member 19 above the precipitation bath, so that they pass through the precipitation bath surface 17 again. The deflecting member can be rigid or fixed, or rotate with the threads. The bundling element 19 is rotatably driven and, as the first stretching means, exerts a tensile stress on the strands 10, which stretches the strands 10, via the deflecting element 18, which is retroactive to the extrusion openings of the spinneret 9. Of course, the deflection element 18 can also be driven as a stretching means.

In order to stretch the spinning threads 10 as gently as possible, the tension can also be generated only by the cooling gas stream 13 as the first stretching means. This has the advantage that the tensile stress is introduced into the spinning threads 10 by means of a frictional stress distributed over the surface of the spinning threads.

The spinning threads 10 are combined into a thread bundle 20 by the bundling element 19. Subsequently, the spinning threads 10, which are still wetted with the precipitation bath solution 16 and are combined to form the thread bundle 20, are deposited without tension on a conveyor device 21 and are transported there largely without tension. During the transport of the spun threads on the conveyor device 21, the complete or almost complete coagulation of the cellulose of the spin threads can take place with the least possible influence of tension. As shown in FIG. 1, the conveying device 21 can be designed as a vibration conveyor that transports the bundle of threads 20, or possibly a plurality of bundles of threads 20 simultaneously, by vibrations in the conveying direction F. The vibrations of the conveyor 21 are indicated by the double arrow 22. Due to the reciprocating movement 21, the bundle of spun threads 20 is deposited in an orderly manner on the conveyor. Instead of the vibration conveyor 22, other conveying devices such as a plurality of godets arranged one behind the other can be used with almost the same or decreasing circumferential speed in the conveying direction.

Various treatments of the thread bundle 20 can take place during the transport on the conveyor device 21, for example the thread bundle 20 can be washed, dried and finished once or several times, for example by a sprinkler system 23 from which a treatment medium 24 is sprayed onto the thread bundle 20.

The bundle of threads 20 is taken up by the conveying device 21 by a godet 25 and fed to a second post-stretching means 26, through which the coagulated spun threads 10 are post-stretched.

In the exemplary embodiment in FIG. 1, the post-stretching takes place during simultaneous heat treatment or drying in the form of tension drying, since this has the most favorable effect on the mechanical properties of the spinning threads 10. Slightly poorer properties, which are, however, still distinguished from the prior art, are achieved if the heat treatment during post-stretching is dispensed with.

The second post-stretching means 26 can also be provided immediately after the bundling means 19, that is to say between the conveying device 21 and the precipitation bath 16, so that only the post-stretched spun threads are subjected to further treatment steps. In order to carry out the heat treatment, the post-stretching means 26 can have a heating device 27 in the entry and entry area of the spinning thread 20, which brings the spinning thread bundle 20 to a predetermined temperature and at the same time dries the spinning thread bundle 20 at least on the surface.

In the post-stretching means 26, the spun threads are guided over two godets 28, 29, which are driven in such a way that a predetermined post-stretching tensile stress ZN is applied to the spun thread bundle 20 between them. The bundle of filaments subjected to this tensile stress is kept at a predetermined high temperature and can be impregnated during the post-stretching, in particular by a hot inert gas, such as air, or also by steam, for example dry steam, and with swelling agents or other agents for chemical fiber treatment, such as by the Arrows 30 is indicated. To support the drying effect, the godets 28, 29 can also be heated.

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

After crimping and cutting, the crimped staple fibers can be transported in a tangled position in the form of a crimped endless cable 33 on a conveyor device 34 for further process steps.

An embodiment of a post-stretching means 26 is shown schematically in FIG. 2. In this embodiment, post-stretching takes place in the form of stress drying.

As has already been described in FIG. 1, the post-stretching means 26 has two godets 28, 29 which are driven in such a way that the thread bundle 20 between them with a predetermined tensile stress Z _N of at least 0.8 cN / tex, preferably of at least 3 , 5 cN / tex is stretched. For this purpose, for example, the godet 29 following in the conveying direction F can have a predetermined, higher speed are rotated than the godet 28 lying in front of it in the conveying direction F; a slip may prevail between the godet 29 and the bundle of threads 20 wrapped around the godet, which essentially determines the tensile stress Z _N.

The stretching of the thread bundle 20 can also be exploited during the drying process: since the thread bundle shortens during the drying process, stretching or post-stretching also takes place if this shortening is not compensated for by the rotational speeds of the godets 28, 29. In this way, post-stretching can also take place if the godets 28, 29 rotate at essentially the same or only slightly different speeds.

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 is pressed out of the interior of the godet 28, 29 through the spun yarn bundle 20 wrapped around the godet 28, 29.

As an alternative or in addition to a loop, as shown in FIG. 2, each godet 28, 29 can also be assigned a roller 28a, 29a, which is also permeable to vapor, actively or passively rotating, as shown schematically in FIG. 3. The rollers 28a, 29a also have permeable surfaces through which the inert gas or the steam is sucked off. Instead of rollers, large drums can also be provided.

Instead of the godets 28, 29, larger drums or suction drums with a perforated surface can also be used, through which the hot gas is drawn off.

In the area between the godets 28, 29, hot air or another internal hot gas, steam or dry steam is likewise passed through gas or the thread bundles 20. The effectiveness of post-drawing has been demonstrated in a number of tests. The experiments were carried out on a bundle of threads consisting of 79,270 individual threads and a total titer of 110,978 dtex, corresponding to a single titer of 1.4 dtex. Table I gives an overview of the test results.

In a first series of tests (tests 1 to 7), the bundle of threads was dried at 73 ° C. for 15 minutes under various conditions.

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

In experiment 2, the bundle of threads was dried without tension, re-moistened and dried under tension. For this purpose, the bundle of threads was passed through two eyelets at a distance of 50 cm and was weighed down with 19 kg on each side during drying.

In experiment 3, the bundle of threads was dried without tension, re-moistened and dried under tension. For this purpose, the thread bundle was passed through two eyelets at a distance of 50 cm and weighed down on both sides with 38 kg each.

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

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

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

In experiment 7, the bundle of threads was dried wet under tension. The thread bundle was passed through two eyelets at a distance of 50 cm and weighted on both sides with a weight of 38 kg each. In a second series of experiments, the bundle of threads was subjected to a treatment with sodium hydroxide solution (NaOH) before drying: first, the spun thread bundle was treated with 5% NaOH solution for 5 minutes and then washed with fully deionized water. The NaOH solution was neutralized with 1% formic acid and again washed with fully deionized water.

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

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

In experiment 9, the bundle of threads was dried without tension, re-moistened and dried under tension. For this purpose, the thread bundle was passed through two eyelets at a distance of 50 cm and weighed down on both sides with 19 kg each.

In experiment 10, the bundle of threads was dried without tension, re-moistened and dried under tension. For this purpose, the thread bundle was passed through two eyelets at a distance of 50 cm and weighed down on both sides with 38 kg each.

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

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

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

In experiment 14, the bundle of threads was dried wet under tension. The thread bundle was passed through two eyelets at a distance of 50 cm and weighted on both sides with a weight of 38 kg each. The titer, the fineness-related «maximum tensile force, the maximum tensile force elongation, fineness-related wet maximum tensile strength, the wet maximum tensile force elongation, the fineness-related maximum loop tensile force, the wet modulus and the wet scrubbing number were then determined for the -dried bundles of threads. The following test regulations were used.

The titer was determined in accordance with DIN EN ISO 1973. The (wet) maximum tensile force and the (wet) maximum tensile force 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 that can be used in accordance with DIN EN 1973. The procedure is based on the test specification ASG N 211 from Alceru Schwarza GmbH. The tests for determining the wet modulus were carried out on a tensile testing machine with constant strain rate and low-displacement electronic force measurement. The clamping length of the thread bundle was 10.0 mm ± 0.1 mm. The fineness-related prestressing force was 2.5 mN / tex ± 0.5 mN / tex with a titer of over 2.4 dtex. For a titer up to 2.4 dtex, a pre-stress mass of 50 mg was used. The elongation rates were 2.5 mm / min for an average wet elongation at break of up to 10%, 5.0 mm / min for an average wet elongation at break of over 10 to 2% and 7.5 mm / min for an average wet elongation at break of over 20%.

Five bundles of spun threads were placed in a shallow dish with wetting agent solution for at least 10 seconds, the pretensioning piece being previously clamped to one end of each bundle of spun threads. The longest test specimen in each case is removed from the shell and used for the tensile test; after each test, a new test specimen must also be inserted for wetting.

The end of the spun thread bundle to be clamped is clamped in the tensile testing machine while the preload is applied, then the lower clamp is closed and the immersion vessel with the wetting agent solution is raised so that the liquid level as far as possible reaches the upper clamp without it however to touch. The distance between the clamping clamps can be steadily increase the speed until an elongation of 5% is reached. At this moment the movement of the lower clamp has to be stopped and the wet tensile force in mN has to be determined 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 is given in millinewtons per tex rounded to whole numbers: M = F / (T • 0.05) ,

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

The tests in Table 1 show a surprising increase in the wet modulus and the number of wet scrubs of the post-drawn fibers compared to the conventional, non-post-drawn fibers (Test 1). For tension-free dried thread bundles, which are then moistened again and dried under tension (tests 2, 3 and 9, 10), the load with 38 kg (corresponds to 3.12 cN / tex) compared to the load with 19 kg (corresponds to 1, 6 cN / tex) an increase in the wet modulus with a slight decrease in the number of wet scrubs. Higher wet modules can be achieved with the heavy load than with the thread bundles of tests 5 to 7 and 12 to 14 which have been dried under tension.

The maximum tensile force, measured both wet and dry, is essentially unchanged compared to the undrawn fibers after Experiment 1. The reduced maximum tensile force elongation and the reduced loop maximum tensile force in connection with the wet modulus and the wet abrasion count suggest that the post-drawn fibers are brittle and more ductile than the non-post-drawn fibers. Consequently, the tests prove that fibers with an improved wet modulus and an improved wet abrasion number can be produced by the post-stretching or tension drying.

Table I

Claims

Expectations

1. A process for producing Lyocell fibers from a spinning solution containing water, cellulose and tertiary amine oxide, the following process steps being carried out:

- extruding the spinning solution into filaments (10),

- stretching the spun threads (10),

Passing the filaments through a precipitation bath (16),

characterized by the following process step:

- Post-drawing and simultaneous heat treatment of the drawn filaments (10) after passing through the precipitation bath (16).

2. The method according to claim 1, characterized by the following step:

- Coagulation of the cellulose of the filaments (10) before stretching.

3. The method according to claim 1 or 2, characterized by the following process steps:

- Post-stretching with a tensile stress of at least 0.8 cN / tex.

4. The method according to claim 3, characterized by the following step:

- Post-stretching with a tensile stress of at least 3.5 cN / tex.

5. The method according to any one of the above claims, characterized by the following process step: - Treating the filaments during the heat treatment with hot inert gas.

6. The method according to any one of the above claims, characterized by the following process step:

- Treating the filaments during the heat treatment with steam.

7. The method according to any one of the above claims, characterized by the following process step:

- Passing the spun threads (10) in front of the precipitation bath (16) through an air gap (12).

8. The method according to claim 7, characterized by the following process step:

- Blowing the spun threads (10) in the air gap (12) with a cooling gas stream (13).

9. The method according to any one of the above claims, characterized by the following process step:

- Tension-free conveying of the spun threads between drawing and post-drawing.

10. The method according to any one of the above claims, characterized by the following process step:

- Crimping the post-drawn filaments (10).

11. The method according to any one of the above claims, characterized by the following process step:

- Cutting the post-drawn filaments into staple fiber.

12. Device (1) for producing spun threads (10) from a spinning solution containing cellulose, water and tertiary amine oxide, with a spinneret (9), through which the spinning solution can be extruded into spinning threads (10) during operation, with a precipitation bath (16 ) with a cellulose precipitating agent through which the spun threads (10) are guided in operation, with a first stretching means (13, 18, 19), through which the spun threads can be stretched during operation, and with a second stretching means (28, 29) , by means of which the spinning threads (10) stretched by the first stretching means (13, 18, 19) can be post-stretched in operation, characterized by a heating device (27, 30) arranged in the region of the second stretching means (28, 29), by which the Spinning threads (10) can be heated during the post-stretching.

13. Lyocell fiber, in particular produced by the method according to one of claims 1 to 11, characterized by a wet modulus of at least 250 cN / tex and by a wet scrubbing number per 25 fibers of at least 18.

14. Lyocell fiber according to claim 13, characterized by a wet modulus of at least 300 cN / tex.

15. Lyocell fiber according to claim 14, characterized by a wet modulus of at least 350 cN / tex.

16. Cellulose fibers according to one of claims 13 to 15, characterized by a wet tensile elongation of at most 12%.

17. Cellulose fibers according to one of claims 13 to 16, characterized by a wet abrasion number per 25 fibers of at least 25.