EP3692189A1

EP3692189A1 - Flame retardant lyocell filament

Info

Publication number: EP3692189A1
Application number: EP18779722.0A
Authority: EP
Inventors: Robert Malinowsky; Martin Neunteufel; Marina Crnoja-Cosic; Clemens Bisjak; Dieter Eichinger; Christoph Schrempf
Original assignee: Lenzing AG; Chemiefaser Lenzing AG
Current assignee: Lenzing AG
Priority date: 2017-10-06
Filing date: 2018-10-08
Publication date: 2020-08-12
Also published as: JP2023101736A; RU2020114311A; RU2020114311A3; US20200240043A1; KR20220071296A; KR20200059291A; MX2020003621A; US20230080038A1; AU2018346452B2; CN111148864A; BR112020004363A2; BR112020004363B1; WO2019068927A1; AU2018346452A1; JP2020536186A; PE20210233A1

Abstract

The invention relates to a filament having flame retardant properties, as well as methods for its preparation and its use. The filament according to the invention are Lyocell filaments.

Description

Flame Retard ant Lyocell Filament

[0001] The invention relates to flame retardant lyocell filaments as well as a method for producing same and uses of the flame retardant filaments.

Background Art

[00002] Flame retardant fibers are used in a great variety of fields of applications, from technical fabrics to outerwear of clothing articles. While cellulosic fibers have long been used in these fields of application, cellulosic filaments, due to their reported unsatisfactory dimensional stability and low wet strength have not yet gained much attention and use in this field. The term filament as employed herein, defines, in accordance for example with BISFA (The International Bureau For The Standardization Of Man-Made Fibres) terminology (also the further terminology used in this specification and in the claims is as defined in the BISFA publication, see also below), a fibre of very great length considered as continuous (endless), which distinguishes filaments for shorter types of fibers, such as staple fibers, flocks . For such shorter types of fibers dimensional stability concerns as well as strength concerns are of lesser relevance, so that cellulosic staple fibers etc. have gained widespread use, also in versions containing additives, including flame retardants. However, for filaments concerns relating to dimensional stability and strength properties, in particular wet strength, are of greater concern. That is one of the reasons why cellulosic filaments, in particular flame retardant filaments have not yet found widespread use.

[0003] In the prior art, viscose, staple fibers have been prepared using flame retardants as additives. US 2012/0156486 A1 and US 2013/0149932 A1 are examples of descriptions of such prior art staple fibers. However, cellulosic filaments, such a viscose filaments, when being prepared with flame retardants, have not shown required properties, such as dimension stability as well as sufficient dry and wet strength. This is necessary in order to survive demanding textile processes like weaving and dyeing and finishing as well as achieving a proper textile performance in respect to shrinkage when washed or used when teared.

Object of the present invention [0004] In view of the above problems, it is the object of the invention to provide a flame retardant filament (FR filament) which satisfies high quality standards with regard to strength and dimensional stability. The term flame retardant filament as employed herein defines a filament which is not merely coated with a flame retardant material but which incorporates the flame retardant in the matrix of the filament.

Brief description of the invention

[0005] This problem is solved according to the invention by a filament according to claim 1. Preferred embodiments are given in claims 2 to 5. The invention further provides a method according to claim 6, for which again preferred embodiments are given in claims 7 to 9. Finally the present invention provides the use according to claim 10 and the product according to claim 1 1 , for which preferred embodiments are defined in claims 12 to 15. Further explanation is provided in the following description.

Detailed description of the invention

[0006] It has been found surprisingly that flame retardant lyocell filaments do overcome the shortcomings of the prior art and the perceptions and concerns in relation with flame retardant cellulosic filaments, such as viscose filaments. Lyocell filaments as describe herein surprisingly do show a highly satisfactory balance of properties and can reliably be prepared in the form of flame retardant filaments. These FR filaments have shown great promise for producing a variety of products, including filament yarns, as well as fabrics for protective clothing or e.g. fabrics or non-wovens for other technical applications produced from filaments and yarns in accordance with the present invention.

[0007} Lyocell fibers are well known in the art and the general methodology to produce same is for example disclosed in US 4,246,221 and in the BISFA (The International Bureau for the Standardization of Man-Made Fibers) publication " Terminology of Man-Made Fibres", 2009 edition. Both references are included herewith in their entirety by reference.

Reference is also made to WO 02/18682 A1 and WO 02/72929 A1 , which relate to a method for producing cellulose filament yarns, and are also included in their entirety.

[0008] As indicated above, the FR filament according to the present invention is a lyocell filament, i.e. a filament produced using the lyocell process. This process is well known to the skilled person and therefore is not further described herein in detail. The examples provide illustration for this process, as well as the patent literature described herein. The filament may have any desired linear density, with suitable values being in the range of from 0.6 and 4 dtex, with preferred values being in the range of from 0.8 to 2 dtex. The cellulose raw product employed for preparing the FR filament of the present invention is not critical, and any type of raw product suitable for the lyocell process may be employed.

[0009] As indicated above, the present invention is in particular characterized in that the novel and inventive FR filament does show a highly surprising balance of mechanical (strength/ tenacity) properties, in dry as well as in wet state, and in addition a very satisfactory dimensional stability. At the same time the desired flame retardancy can be obtained even in filaments without overly sacrificing mechanical properties. Strength properties which may be obtained in the filaments of the present invention are typically determined in conditioned state and for the FR filaments of the present invention these properties typically are as follows:

Average dry tenacity (FFk) of at least 22 cN/tex, The average dry elongation at break (FDk) of the filaments is at least 6 %, preferably between 6 % and 8 %. These properties are evaluated using the following test equipment and parameters:

Test apparatus: USTER© Tensorapid 4 2.4.2 UTR4/500N:

Test length: 500 mm

Clamp speed: 60 mm/min

Clamp pressure: 30 %

Pre-tension: 4.1 cN

[0010] Filaments in accordance with the present invention accordingly do show a favorable high dimensional stability, which benefits yarns and fabrics prepared therefrom. In this manner, high quality flame retardant products can be manufactured using the FR filament of the present invention.

[001 1] As indicated above, the filaments of the present invention are FR filaments, i.e. filaments incorporating flame retard ants. As the filaments of the present invention are lyocell filaments, the incorporation of the flame retardants may be achieved by including the flame retardant in a suitable manner into the spinning solution (or at least into the composition prior to spinning the filaments), as further illustrated in the Example contained herein. The type of flame retardant is not critical as long as it in particular can be included in the spinning solution or spinning composition, typically in the form of a solution of the flame retardant, preferably an aqueous solution. However, the flame retardant may also be included in form of a finely ground powder, or dispersion of such a finely ground powder. If such solid forms of flame retardants are to be employed, it is preferable that the average particle diameter of the flame retardant is at most 50% of the filament diameter, more preferably at most 30 %, even more preferably at most 10% of the filament diameter.

[0012] The amount of flame retardant in the final filament typically is in the range of from 2 to 50 wt.-% of the filament, preferably 10 to 40, even more preferably 15 to 30 wt.-%. This amount may be tailored according to need (for example in relation to the degree of flame retardancy desired) and can be adjusted by means of the ratio of cellulose and flame retardant in the spinning solution or spinning composition.

[0013] The type of flame retardant, as indicated above is not critical. Preferred however are flame retardants based on nitrogen and phosphorous containing compounds, such as those commercially available under the trademark Aflammit ®. In particular preferred are organic phosphourous compounds, such as Aflammit KWB. Any flame retardants employed may be subjected to pre- treatments, such as milling, in order to obtain flame retardants having a particle size (if they are not soluble in the spinning composition) suitable for the spinning process, typically depending from the filament diameter aimed at. Such processes are known to the skilled person.

[0014] In one embodiment of the present invention a flame retardant being an oxidized condensate of a tetrakis hydroxyalkyl phosphonioum salt with ammonia and/or a nitrogenous compound which contains one or several amine groups is excluded

[0015] As outlined above, the FR filament according to the present invention is a lyocell filament. Accordingly the process for preparing a filament according to the present invention comprises the provision of a spinning solution comprising at least cellulose, water, NMMO and the flame retardant, and spinning the solution and regenerating the filaments in a manner known to the skilled person. In accordance with the present invention it has been determined that spinning velocities of about 250 to 750 m/min may be employed, such as from 300 to 600, preferable 350 to 450 m/min. During the process any further required additives and stabilizers, such as dyes and pigments etc. may be added as required.

[0016] The filaments may of course be subject to any usual post spinning processing, such as coating, finishing etc. A skilled person will be able to select appropriate processes depending on the intended use of the FR filaments. However, preferred and illustrative spinning processes, including detailed outlines of the various process steps are outlined in the following. [0017] The present invention provides a process for producing the herein described lyocell filaments, as well as for example lyocell multifilament yarns. The process will be described in detail referring to the individual process steps. It is to be understood, that these process steps and their respective preferred embodiments can be combined as appropriate and that the present application covers these combinations and discloses same, even if not explicitly described herein.

• Manufacture of spinning solution.

[0018] It has been found that it is preferred to employ a cellulose starting material which complies with the following requirement

[0019] The rheological properties of known lyocell spinning solutions may not be compatible with the demands of high speed filament yarn production. For example, unacceptable numbers of filament breakages are encountered when using spinning solution compositions known for staple fiber production. It has been found that using a broader molecular weight distribution of the cellulose raw material than previously disclosed overcomes this problem, namely by blending 5-30 wt.- %, preferably 10 to 25 wt.-% of cellulose having a scan viscosity in the range of 450-700 ml/g with 70-95 wt.-%, preferably 75 to 90 wt.-% cellulose having a scan viscosity in the range of 300-450 ml/g, wherein the two fractions have a difference in scan viscosity of 40 ml/g or more, preferably 100 ml/g or more. The scan viscosity is determined in accordance with SCAN-CM 15:99 in a cu- priethylenediamine solution, a methodology which is known to the skilled person and which can be carried out on commercially available devices, such as the device Auto PulplVA PSLRheotek available from psl-rheotek.

[0020] To obtain such a cellulose raw material (for example from woodpulp) to achieve required molecular polydispersity blends of different types of starting materials may be used. Optimum blend ratios will depend on actual molecular weight of each blend component, filament production conditions and specific product requirements of the filament yarn. Alternatively, required cellulose polydispersity could also be obtained for example during manufacture of woodpulp, via blending prior to drying. This would remove the requirement to carefully monitor and blend pulp stocks during lyocell manufacture.

[0021] The overall content of cellulose in the spinning solution typically is from 10 to 20 wt.-%, preferably 10 to 16 wt.-%, such as from 12 to 14 wt.-%. As the skilled person is aware of the required components for spinning solutions for a lyocell process, no further detailed explanations of the components and the general production method is deemed to be required here. Reference in this respect is made to US 5,589, 125, WO 96/18760, WO 02/18682 and WO 93/19230, incorporated herein by reference.

[0022] To further control the process in accordance with the present invention, it is preferred to employ high levels of process monitoring and control to ensure uniformity of composition of the spinning solution. This may include in-line measurement of spinning solution composition/pressure/temperature, in-line measurement of particulate content, in-line measurement of spinning solution temperature distribution in jets/nozzles and regular off-line cross-checks.

[0023] It is further preferred to control and, if required to improve the quality of the lyocell spinning solution used in the present invention, as contents of large particles can result in unacceptable breaks in individual filament as they are being formed. Examples of such particles are impurities, such as sand, etc. but also gel particles comprising cellulose not sufficiently dissolved. One option to minimize the content of such solid impurities are filter processes. Multi-stage filtration of the spinning solution is the optimum way to minimize solid impurities. A skilled person will understand that greater filter stringencies are required for finer filament titers. Typically, for example, depth filtration with an absolute stopping power around 20 microns has been found to be effective for 1 .3 decitex filaments. 15 micron absolute stopping power is preferred for finer filament decitex. Devices and process parameters for carrying out filtering are known to the skilled person.

In addition it has been found suitable to adjust the viscosity of the spinning solution to a range of from 500-1350 Pa s, measured at a shear rate of 1 .2 (1/s) at 1 10°C.

[0024] The temperature of the spinning solution during its preparation typically is in the range of form 105 to 120 °C, preferably 105 to 1 15 °C. Prior to the actual spinning/extrusion the solution, optionally after filtering, is heated to a higher temperature, using processes and devices known to the skilled person, of typically from 1 15 to 135°C, preferably 120 to 130°C. This process, together with a filtering step increases the homogeneity of the spinning solution after its initial preparation in order to provide the spinning solution (sometimes called spinning mass) suitable for extrusion through the spinning nozzles. This spinning solution preferably is then, prior to extrusion/spinning, brought to a temperature of from 1 10°C to 135°C, preferably 1 15°C to 135°C, a process which may include intermediate cooling and heating stages as well as tempering stages (stages where the spinning solution is kept at a given temperature for a certain time). Such processes are known tot eh skilled person. • Extrusion of filaments

[0025] It has been found that uniformity and consistency of flow of the spinning solution through each spinneret nozzle hole further improves the process and helps to meet the quality requirements for the individual cellulose filaments and in turn also those for multifilament yarns. This is in particular relevant in view of the very high production speeds required for filament and filament yarn production, which are in the range of from 200 m/min and upwards. In accordance with the present invention production speeds of 200 m/min und upwards can be achieved, such as 400 m/min or more, preferably 700 m/min or more and even up to 1000 m/min or more. Suitable ranges are from 200 to 1500 m/min, such as from 400 to 1000 m/min or from 700 to 1000 m/min, including ranges such as from 700 to 1500 m/min.

[0026] Each spinneret piece used for extrusion of lyocell spinning solution has a number of nozzle holes corresponding to the number of filaments required for a continuous filament yarn. Multiple yarns can be extruded from a single jet by combining multiple spinneret pieces into a single spinneret plate, for example as disclosed in WO03014429 A1 , incorporated herein by reference.

[0027] The number of nozzle holes for each filament yarn may be selected depending on the type of yarn intended, but the number is typically in the range of from 10 to 300, preferably 20 to 200, such as from 30 to 150.

[0028] Uniformity of spinning solution flow may be improved by providing a good temperature control within the spinneret and the individual nozzles. It is preferred, that during spinning the temperature variance within the nozzles (and between the nozzles is as small as possible, and preferably within ±2°C or less. This may be achieved via a means of providing direct heating to the spinneret and the individual nozzles in a series of different zones, to enable compensation for any local differences in temperature of spinning solution and to give precise control of the temperature of the spinning solution as it is extruded from each spinneret nozzle .Examples of such temperature control means are disclosed in WO 02/072929 and WO 01 /81662, incorporated herein by reference.

[0029] Spinneret nozzle profiles preferably are designed to maximize smooth acceleration of spinning solution through the nozzle while minimizing pressure drop. Key design features of the nozzle include, but are not limited to, a smooth inlet surface and sharp edges at nozzle outlet. • Initial cooling

[0030] After exiting the spinning nozzles, the individual filaments are typically subjected to a cooling process, typically using an air flow. Accordingly, it is preferred to cool the filaments in this step by using an air draught, preferably a controlled cross draught in an air gap. The air draught should have a controlled humidity in order to obtain the desired cooling effect without detrimental effect on the quality of the fibers. Suitable humidity values are known to the skilled person. However, a direct application of known lyocell staple fiber procedures in this step does not work, as this would require, taking the high filament production speeds into account, a very long air gap (over 200 mm). Such an air gap however is not feasible, as the individual filaments would move and touch, leading to filament fusion and poor product quality. For the same reason, it has been found that the high velocity air cross draughts disclosed for staple fiber production may pose problems. In addition, greater uniformity and consistency of extension is required for filament products compared to staple fibers.

[0031] Thus, the present invention provides new means to adjust the filament production processing in order to meet quality requirements of filament yarn production.

[0032] For example, WO03014436 A1 , incorporated herein by reference, discloses a suitable cross draught arrangement. Uniform filament cooling over the full length of the air gap is preferred.

[0033] As outlined above, the longer air gaps which would be considered as being required in accordance with the common understanding of the spinning process in particular under consideration of the high production velocities are not feasible. However, it has been found that a longer air gap length than typically employed for staple fiber production may be used successfully, such as around 40-130 mm. Preferably the air gap is in the range of from 40 to 120 mm, such as from 50 to 100 mm. In embodiments this may be combined with wider filament separation at the spinneret face (around twice the nozzle separation employed in lyocell staple fiber production). Such an arrangement has been found to be beneficial for filament production. An increase in filament separation in this manner reduces the opportunity for filaments to touch and enables the required uniform filament cooling to be achieved. [0034] Cross-draught velocities are preferably much lower than used in lyocell staple fiber production. Suitable values are 0.5-3 m/sec, preferably 1 -2 m/sec. Humidity values may be in the range of from 0.5 to 10 g water per kg air, such as from 2 to 5 g water per kg air. The air temperature preferably is controlled to a value of below 25°C, such as below 20°C.

• Initial coagulation of filaments

[0035] After exiting the spinneret nozzles and having been cooled in the air gap, the filaments produced have to be treated to further initiate coagulation. This is achieved by means of entering the individual filaments into a coagulation bath, also called spinning bath or spin bath. It has been found that in order to achieve a high degree of uniformity of product quality, this further initial coagulation of the filaments preferably occurs within a small window, i.e. with only a minor variability, preferably at precisely the same point.

It has been found that traditional spin bath designs are often not suitable for this purpose because the hydrodynamic forces due to high filament speeds (above around 400m/min) disturb the bath surface resulting in uneven initial coagulation (and variable air gap size) as well as potential filament fusion and other damage. It has been determined that in case of such problems it is preferable to use shallow spin baths, having a depth of below 50 mm.

[0036] Such spin baths are disclosed for example in WO03014432 A1 , incorporated herein by reference, which discloses shallow spin bath depths in the range of from 5-40 mm, preferably 5 to 30 mm, more preferably 10-20 mm. The use of such shallow spin baths enables to control contact point of the spun filaments with the coagulation solution in the spin bath, thereby avoiding the problems, which may occur when using conventional spin bath depths.

[0037] In addition it has been found that filament quality can also be improved if the concentration of amine oxide within the spin bath is controlled to values smaller than typically used in lyocell fiber production. Spin bath concentrations of below 25 wt.-%, more preferably below 20 wt.-% amine oxide, even more preferably preferably below 15 wt.-% have been found to improve filament quality. Preferred ranges for the amine oxide concentration are from 5 to 25 wt.-%, such as from 8 to 20 wt.-% or from 10 to 15 wt.-%. This is significantly below the range disclosed for lyocell staple fiber production. To enable the maintenance of such a low amine oxide concentration continuous monitoring of the composition of the spin bath is preferred, so that for example adjustments of the concentration may be carried out by replenishing water and/or by selective removal of excess amine oxide.

The temperature of this spin bath typically is in the range of from 5-30°C preferably 8-16°C.

[0038] Similar to the preferred embodiments disclosed above for the spinning solution, high stringency spin bath liquor filtration is possible, to minimize potential to damage freshly-formed tender filaments by undesired solid impurities within the spin bath. This is particularly important at very high production speeds, in excess of 700m/min

[0039] Within the spinning bath the individual filaments of a target final yarn are brought together and are bundled into an initial multifilament bundle by means of the exit from the spinning bath, which is typically a ring shaped exit, which brings the filaments together and also serves to control the amount of spinning bath solution exiting the bath together with the filament bundle. Suitable arrangements are known to the skilled person. The shape as well as the choice of material for the ring shaped exit influences the tension applied to the filament bundles, as at least some of the filaments are in contact with the ring shaped exit. A skilled person will be aware of suitable materials and shapes for those exits from the spinning bath in order to minimize any negative impact on the filament bundle.

[0040] Accordingly, in a preferred embodiment of the process in accordance with the present invention, the process comprises the steps of manufacture of a spinning solution suitable for the lyocell process comprising from 10 to 15 wt%, preferably from 12 to 14 wt% of cellulose, wherein the cellulose is the above-described blend of celluloses having different scan viscosity values. This process furthermore comprises the step of extrusion of the spinning solution through extrusion nozzles while maintaining a temperature variability through the extrusion nozzles within a range of ± 2°C or less. The filaments thus produces are subjected to an initial cooling as described above, followed by the initial coagulation of filaments obtained in this manner occurs in a coagulation bath (spin bath) having a depth of less than 50 mm, preferably from 5 to 40 mm, more preferably from 10 to 20 mm.

[0041] The composition of the coagulation liquor employed in this coagulation bath shows a concentration of amine oxide of 23 wt% or less, more preferably below 20 wt%, and even more pref- erably below 15 wt%. Adjustment of this amine oxide content may be achieved by means of selective removal of amine oxide and/or by replenishing fresh water to adjust the concentration to the preferred ranges.

[0042] Such a process ensures that filaments with a high quality and, in particular, a high uniformity can be obtained, which particularly enter the coagulation bath in a manner ensuring uniform coagulation and therefore uniform filament properties. In addition, in embodiments of the process described above, it is preferred to adjust the distance between the individual filaments upon extrusion, for example by employing a wider nozzle separation, compared with standard lyocell staple fiber production processes, as further described below. These preferred process parameters and conditions enable, as indicated herein, the production of lyocell filaments with a high uniformity, while also enabling the desired high process velocities (spinning velocities of 200 m/min or more, more preferably 400 m/min or more, and in embodiments as high as 700 m/min or more). In this context, the present invention furthermore enables the continuous and long-term production of cellulose lyocell filaments and corresponding yarns as the process parameters and conditions as explained above avoid filament breakage etc. , which would require stoppage of filament and yarn production.

• Filament extension

[0043] After exiting the spinning bath the multifilament bundles are taken up, typically by means of a guidance roller which directs the bundle, which will yield the final yarn, towards the subsequent processing stages, such as washing, drying and winding. During this step preferably no stretching of the filament bundle occurs. The distance between the exit from the spinning bath and the contact with the guidance roller may be selected according to need and distances of between 40 and 750 mm, such as from 100 to 400mm have been shown as being suitable. It has been found that this process step can provide further options to control and influence product quality. In this process step for example filament crystalline structure may be adjusted, thereby achieving the desirable properties of lyocell continuous filament yarns. As indicated above, and as derivable form the wording of claim 1 , success in this process step has been found to be closely linked to spinning solution rheology and consistency of extrusion from nozzles, a described above.

[0044] As indicated above, a means such as a guidance roller takes up the filaments, assembles same to form the initial yarn and guides the yarn thus obtained towards further processing steps. In accordance with the present invention it is preferred, that a maximum tension applied to the filament bundle at the contact point of the filament bundle (yarn) with the guidance roller is (4.2 x filament number / filament titer)^{0 69} (cN) or less. This tension means the tension applied to the filaments / filament bundle from the point of exit from the spinning nozzles to the fist contact point, for example with the guidance roller provided after the coagulation step. The formula provided above defines, by means of illustration, that the maximum tension, for example for a filament bundle of 60 filaments with a yarn titer of 80 dtex (inividual filaments have a titer of 1.33 dtex), that the maximum tension is (4.2 x 60 : 1.33)° ⁶⁹, accordingly 37.3 cN.

[0045] By maintaining such a specified maximum tension it can be ensured that filament breakage is prevented so that high quality yarns may be obtained. In addition this helps to ensure that the filament production process can run for the required times without disturbance. A skilled person will understand that the tension referred to herein is a tension which is to be measured using samples taken from the overall process by using a three roll testing apparatus Schmidt-Zugspan- nungsmessgerat ETB-100. The tension measured for filaments and filament bundles at the designated point of contact referred to herein may, using the process parameters disclosed here in the context of the present invention, be used to control product quality and process stability, in particular by adjusting the composition of the spinning solution, the spin bath depth and the spin bath liquor (coagulation bath) composition, the air cross draught as well as spinneret design, such as nozzle design and nozzle separation, in order to adjust the tension values to values conforming to the equation provided above.

• Filament washing.

[0046] As the filaments after initial coagulation and cooling still contain amine oxide, the filaments and/or yarns obtained typically are subjected to washing. Amine oxide may be washed from the newly formed yarns via a counter- current flow of demineralised water or other suitable liquid, typically at 70-80°C. As with the earlier process steps, it has been found that traditional washing techniques, for example use of troughs, may pose problems in view of the high production speeds above around 400m/min. In addition, uniform application of wash liquor to each individual filament is preferred, to obtain a high quality product. At the same time minimal contact between the tender filaments and washing surfaces is preferable in order to maintain integrity of the filaments, to achieve target yarn properties. Further, individual filament yarns must be washed close together and line length should be minimized to enable viable process economics. In view of the above it has been found that a preferred washing process involves the following, alone or in combination: [0047] Washing preferably is carried out using a series of driven rollers and each yarn is subjected individually to a series of wash liquor impregnation/liquor removal steps.

[0048] It has been found beneficial to provide a means of stripping or spinning liquor uniformly from each yarn filament, without damaging the tender filaments, after each wash impregnation step. This may for example be achieved via a suitably designed and positioned pin guides. The pin guides may, for example be constructed with a matt chrome finish. The guides allow close spacing of filament yarns (around 3mm), good contact with filaments to give uniform liquor removal and low tension to minimize filament damage.

[0049] Optionally, an alkaline washing step may be included to increase removal efficiency of residual solvent from the filaments.

[0050] Used wash liquor (after first pin guide) typically has a concentration of 10-30%, preferably 18-20% amine oxide prior to return to solvent recovery.

[0051] A 'soft finish' may be applied to aid further processing. Types and application methods will be known to those skilled in the art. For example, a 'lick-roller' arrangement applying around 1 % finish on the filaments, followed by a nip roller to control yarn tensions into the dryer has been found to be effective.

• Yarn drying

[0052] Again, good control of this step assists in the development of optimal yarn properties and minimizing potential for filament damage. Drying means as well as drying parameters are known to the skilled person. Preferred embodiments are defined in the following:

[0053] The dryer consists for example of 12-30 heated drums of around 1 m diameter. Individual speed control is preferred to ensure filament tension is kept low and constant, preferably below 10cN, preferably below 6cN. Spacing between yarns through drying may be around 2 to 6 mm.

[0054] Initial temperature in dryer is around 150°C. In later stages of the drying process temperatures may be lower, as drying progresses. [0055] An antistatic agent and/or a soft finish may be applied to the filament yarns after drying, by means known to those skilled in the art.

[0056] Further process steps, for example combining, texturising or intermingling yarns, may be applied after drying and prior to collection, using processes known to the skilled person. If desired, a soft finish may be applied to the yarns prior to the above identified steps.

• Collection of yarns

[0057] Yarns may be collected using standard winding equipment. A suitable example is a bank of winders. Winder speed is used to fine tune process speeds upstream to maintain low and constant yarn tension.

[0058] A skilled person will understand that various modifying substances, such as dyestuffs, antibacterial products, ion-exchanger products, active carbon, nanoparticles, lotions, fire-retardant products, superabsorbers, impregnating agents, dyestuffs, finishing agents, crosslinking agents, grafting agents, binders; and mixtures thereof can be added during preparation of the spinning solution or in the washing zone, as long as these additions do not impair the spinning process. This allows to modify the filaments and yarns produced in order to meet individual product requirements. The skilled artisan is well aware of how to add such above-referenced materials in which step of the lyocell filament yarn production process. In this regard it has been found that many desirable modifying substances which would normally be added at the washing stage will not be effective with the filament yarn route because of the high line speeds and hence short residence times. In order to introduce these modifying substances an alternative approach is to collect fully washed but 'never-dried' filament yarns and submit these to further processing batch-wise where residence time would not be a limiting factor.

[0059] The FR filaments according to the present invention may be used for producing further products, such as yarns, fabrics and non-wovens. Yarns may comprise varying numbers of the filaments of the present invention, suitable examples are from 10 to 200 filaments, such as from 15 to 150, and in embodiments from 25 to 100. Yarn titers may cover a broad range, depending from the intended field of use, and examples are titers in the range of from 30 to 150 denier, such as from 50 to 120 denier. Due to the unique balance of properties, such as high mechanical strength and rather low elongations at break, high quality products with a high dimensional stability may be prepared using the filaments of the present invention.

[0060] The FR filaments of the present invention may be used alone when producing further (textile) products, the filaments any however also be blended with other types of fiber, in order to generate filament mixture with a desired property profile. In particular it may be an option to blend the FR filaments of the present invention with other fibers if the intended product does not require a high degree of flame retardancy. Another option is to blend the FR filaments with high strength filaments if high strength fabrics are desired. In any case. The FR filament so for the present invention has shown to provide good properties, as explained above, also in blends with other types of fibers.

[0061] The following examples do illustrate the present invention. Examples

The following examples demonstrate the superior properties of the FR Lyocell filament of the present invention compared with non flame retardant viscose, cupro and Lyocell filaments.

Example 1 shows the properties of an FR Lyocell filament in accordance with the present invention.

Comparative Examples 1 to 3 show the properties of a viscose filament, a cupro filament and a Lyocell filament, respectively, all not containing a flame retardant component.

The filaments according to the present invention according to Example 1 were generated as follows:

Pulp (cellulose) was impregnated with a 78 % watery N-methyl-morpholine-N-oxide (NMMO) solution, and low amounts of stabilizers. The resulting suspension contained 1 1.6 % cellulose, 68 % NMMO, 20.4 % water and stabilizer GPE. The pulp consisted of a mixture of sulfite and sulfate cellulose. A flame retardant (Aflammit KWB, suspension of 20% milled Aflammit KWB in 50% aqueous NMMO) was added to prepare the final spinning solution, excess water was removed form the slurry under shear and heating to obtain a fiber free spinning solution comprising 12.7% cellulose, 73.8% NMMO, 10.7% water, and 2.8% flame retardant (all % refer to the weight, based on the total composition). The spinning solution was filtered and extruded at 1 14°C in a dry-wet process, wherein the spinning solution was extruded through nozzles into an air gap. For stabilizing the extrusion process, the air gap was provided with an air stream. Spinning velocity was 400 m/min.

After crossing the air gap, the cellulose precipitated in a spinning bath containing 10 % NMMO, the rest being water.

The endless filaments thus obtained were washed with water, impregnated with finish, dried and winded to a bobbin. Washing took place in fully de-salted water in counterflow. For drying, a contact dryer was used which reduced humidity to 10.5 %.

Using these filaments a multi-filament consisting of single filaments was generated. From the multi-filaments, untwisted filament yarn was manufactured. From the filament yarns fabrics may be produced. The linear density of the yarn produced was between 20 and 200 dtex, preferably between 50 and 150 dtex.

For other details of the manufacturing process, reference is made to US 4,246.221 , WO 02/18682 A1 and WO 02/72929 A1.

The filaments comparative examples 1 to 3 were produced using conventional processes, the Lyocell filaments were produced using the experimental setup as described for Example 1 , except for using no flame retardant component.

The respective properties are reported below:

Example 1

Lyocell filament

Material

(FR)

Min dtex 1 ,36 dtex

Max dtex

2,31 dtex

FFk 33.2 cN/tex

FFn 19.5 cN/tex Comparative Comparative ExComparative ExExample 1 ample 2 ample 3

Viscose (Non Lyocell Filament

material Cupro (Non FR)

F ) (Non FR)

Mln dtex 2.29 1.46 1.84

Max dtex 3.02 1.92 3.92

FFk cN/tex 21.1 18.7 40.9

FFn cN/tex 9.2 10.6 27.3

Comparative Examples 1 and 2 show that viscose and cupro filaments, even without added flame retardant agent do show completely unsatisfactory properties. On the other hand, FR Lyocell filaments do display highly satisfactory properties, even though mechanical properties are somewhat lower, compared to Comparative Example 3, i.e. the non FR Lyocell filament. However, the properties for the FR Lyocell filament in accordance with the present invention are significantly improved, as compared to the non FR viscose and cupro filaments. The comparative examples using other types of cellulose filaments do suffer from a great imbalance of mechanical properties, so that no dimensionally stable products can be prepared for these filaments. At the same time the flame retardant filaments of the present invention, in addition to showing highly satisfactory flame retardant properties, also do show a great balance of mechanical properties.

Flame retardant Lining

From a yarn (den90/40 (multifilament with 40 filaments having a total titer of 90 denier), yarn titer dtex100f40), obtained by using the FR Lyocell filament of the present invention, a lining with 75 g/m² was produced. This lining was used in an three-layer assembly, comprising a moisture barrier (Laminate, 148 g/m², 50% Meta Aramid / 50% Lenzing FR (flame retardant viscose staple fiber)/PU membrane), an outer fabric ( 260 g/m²; 50% Lenzing FR, 38% Para Aramid, 12% PA) and the above identified lining (100% FR Lyocell filament) was evaluated in relation to flame re- tardancy. The three layer assembly passed the flame spread test according to EN ISO 15025: 2002 Procedure A (test flame to outer fabric as well as test flame to lining) and fulfilled all requirements according to EN 469 (EN 533 Index 3).

Claims

1. Flame retardant filament (FR filament), comprising a flame retardant and cellulose, characterized in that the filament is a lyocell filament.

2. FR filament according to claim 1 , having an average dry tenacity of at least 22 cN/tex.

3. FR filament according to claim 1 or 2, having an average wet tenacity of at least 1 1 cN/tex.

4. FR filament according to any one of claims 1 to 4, wherein the amount of flame retardant is form 2 to 50 wt.-%.

5. Method for producing a FR filament according to any one of claims 1 to 4, comprising: providing a composition comprising pulp, NMMO, water and a flame retardant, and spinning the solution to produce filaments.

6. Method according to claim 5, wherein the amount of flame retardant and pulp in the spinning solution is in the range of from 12 to 25% of the spinning solution.

7. Method according to claim 5 and/or 6, wherein the spinning velocity is in the range of from 250 to 750 m/min.

8. Method according to any one of claims 5 to 7, wherein the pulp comprises sulphite and sulphate cellulose.

9. Use of the FR filament according to any one of claims 1 to 4 or produced according to any one of claims 5 to 8 for the preparation of yarn, fabrics and textile products.

10. Yarn, fabric or textile product comprising the FR filament according to any one of claims 1 to 4 or produced according to any one of claims 5 to 8.

1 1 . Use or product according to any one of claims 9 or 10, wherein the FR filament is blended with other types of fibers.

12. Use or product according to any one of claims 9 to 1 1 , satisfying the demands according to EN ISO 14 1 16 classification "limited flame spread index 3" when tested according to EN ISO 15025:2002 Process B - edge flaming. Use or product according to any one of claims 9 to 12, being a multi filament yarn.

Use or product according to any one of claims 9 to 13, wherein the FR filament comprises a resin finish.