JP2023101736A - Flame-retardant lyocell filament - Google Patents

Abstract

To provide a filament having flame retardancy, and moreover, a manufacturing method and use thereof.SOLUTION: A filament having flame retardancy is a flame-retardant filament (FR filament) containing a flame retardant and cellulose and is characterized by that the filament is a lyocell filament.SELECTED DRAWING: None

Description

The present invention relates to flame-retardant lyocell filaments, as well as to a method for producing the same and uses of said flame-retardant filaments.

Flame-retardant fibers are used in a wide variety of applications, from industrial fabrics to clothing outerwear. Although cellulosic fibers have long been used in these application areas, cellulosic filaments have not received much attention and have been used in this area due to their reportedly poor dimensional stability and low wet strength. As used herein, the term filament defines very long fibers that are considered continuous (endless), e.g. according to BISFA (The International Bureau For The Standardization Of Man-Made Fibers) terminology (further terminology used in the specification and claims is also defined in BISFA publications, see also below), as opposed to filaments of shorter types of fibers such as staple fibers, flock, etc. distinguished. For such shorter types of fibers, dimensional stability concerns and strength concerns are less important, so cellulosic staple fibers and the like have been widely used, even in versions containing additives, including flame retardants. However, for filaments, concerns about dimensional stability and strength properties, especially wet strength, are more of an issue. This is one of the reasons why cellulosic filaments, especially flame-retardant filaments, are still not widely used.

In the prior art, viscose staple fibers have been produced using flame retardants as additives. US2012/0156486A1 and US2013/0149932A1 are examples of such prior art staple fiber specifications. However, cellulosic filaments such as viscose filaments have not exhibited the required properties such as dimensional stability, as well as adequate dry and wet strength when produced with flame retardants. This is necessary to withstand demanding textile processing such as weaving and dyeing and finishing, as well as achieving adequate textile performance in terms of shrinkage when laundered or used in torn condition.

In view of the above problems, it is an object of the present invention to provide flame-retardant filaments (FR filaments) that meet high quality standards in terms of strength and dimensional stability. The term flame retardant filament, as used herein, defines a filament that has a flame retardant incorporated within the matrix of the filament, rather than simply being coated with a flame retardant material.

This problem is solved according to the present invention by the filament described in aspect <1> below. Preferred embodiments are described in aspects <2> to <5> below. The present invention further provides a method according to aspect <6> below, and preferred embodiments thereof are also described in aspects <7> to <9> below. Finally, the present invention provides a use according to aspect <10> below and a product according to aspect <11> below, and preferred embodiments thereof are described in aspects <12> to <15> below. Further extensions are provided in the description below.

Surprisingly, it has been found that flame retardant lyocell filaments overcome the shortcomings of the prior art as well as perceptions and concerns regarding flame retardant cellulosic filaments such as viscose filaments. The lyocell filaments described herein surprisingly exhibit a sufficiently high balance of properties that they can be reliably produced in the form of flame-retardant filaments. These FR filaments are very promising for the production of a variety of products including filament yarns, as well as fabrics for protective clothing made from the filaments and yarns according to the invention, or fabrics or nonwovens for other industrial applications.

Lyocell fibers are known in the art, and general methods for making them are disclosed, for example, in U.S. Pat. No. 4,246,221 and the 2009 edition of the BISFA (International Bureau for Standardization of Man-made Fibers) publication "Terminology of Man-Made Fibers." Both references are hereby incorporated by reference in their entirety.
Reference is also made to WO 02/18682 A1 and WO 02/72929 A1 relating to processes for producing cellulose filament yarns, which are also incorporated in their entirety.

As indicated above, the FR filaments according to the present invention are Lyocell filaments, i.e. filaments manufactured using the Lyocell process. This process is well known to those skilled in the art and therefore will not be described in further detail here. The examples, as well as the patent literature mentioned herein, provide a description of this process. Said filaments may have any desired linear density, suitable values being in the range of 0.6 to 4 dtex, preferred values being in the range of 0.8 to 2 dtex. The cellulosic raw material used to make the FR filaments of the present invention is not critical and any type of raw material suitable for the Lyocell process may be used.

As indicated above, the present invention is particularly characterized by the novel and inventive FR filaments exhibiting a surprisingly high balance of mechanical (strength/tensile strength) properties and in addition very satisfactory dimensional stability in dry as well as wet conditions. At the same time, the desired flame retardancy can be obtained even in filaments without excessively sacrificing mechanical properties. The strength properties obtainable with the filaments of the present invention are typically specified in the conditioned state, and for the FR filaments of the present invention these properties are typically as follows:
Average dry tensile strength (FFk) of at least 22 cN/tex. The average dry breaking elongation (FDk) of said filaments is at least 6%, preferably between 6% and 8%. These properties are evaluated using the following test equipment and parameters.
Test equipment: USTER® Tensorrapid 4 2.4.2 UTR4/500N:
Test length: 500mm
Clamping speed: 60mm/min Clamping pressure: 30%
Preload: 4.1cN

Filaments according to the present invention therefore exhibit a favorable high dimensional stability, which is beneficial for yarns and fabrics produced therefrom. Thus, the FR filaments of the present invention can be used to produce high quality flame retardant products.

As mentioned above, the filaments of the present invention are FR filaments, i.e. filaments with incorporated flame retardants. Since the filaments of the present invention are lyocell filaments, incorporation of the flame retardant can be accomplished by including the flame retardant in the spinning solution (or at least in the composition prior to spinning the filaments) in a suitable manner, as further illustrated in the examples contained herein. The type of flame retardant is not critical, as long as it can be included, typically in the form of a solution of said flame retardant, preferably in the form of an aqueous solution, especially in said spinning solution or spinning composition. However, the flame retardant may also be included in the form of finely divided powders or dispersions of such finely divided powders. If such a solid form of flame retardant is to be used, it is preferred that the average particle size of said flame retardant is no greater than 50% of the filament diameter, more preferably no greater than 30%, and even more preferably no greater than 10% of said filament diameter.

The amount of flame retardant in the final filament is typically in the range of 2-50%, preferably 10-40, even more preferably 15-30% by weight of said filament. This amount may be adjusted as needed (e.g., in relation to the degree of flame retardancy desired) and can be adjusted by the ratio of cellulose to flame retardant in the spinning solution or spinning composition.

The type of flame retardant is not critical, as noted above. However, flame retardants based on nitrogen and phosphorus containing compounds are preferred, such as those marketed under the Aflammit® trademark. In particular, organophosphorus compounds such as Aflammit KWB are preferred. Any flame retardant used may be subjected to a pretreatment such as milling to obtain a flame retardant with a particle size suitable for the spinning process (if not soluble in the spinning composition), typically depending on the filament diameter of interest. Such processes are known to those skilled in the art.

In one embodiment of the present invention, flame retardants that are oxidative condensation products of tetrakishydroxyalkylphosphonium salts and ammonia and/or nitrogen compounds that contain one or more amine groups are excluded.

As outlined above, the FR filaments according to the invention are lyocell filaments. Accordingly, a process for making filaments according to the present invention comprises providing a spinning solution comprising at least cellulose, water, NMMO, and said flame retardant, spinning said solution, and regenerating said filaments by methods known to those skilled in the art. According to the invention it has been determined that a spinning speed of about 250-750 m/min can be used, such as 300-600 m/min, preferably 350-450 m/min. During the course of said process, any further required additives and stabilizers such as dyes and pigments may be added as required.

Said filaments may of course undergo any of the usual post-spinning treatments such as coating, finishing, and the like. A person skilled in the art can select an appropriate process depending on the intended use of the FR filament. However, a preferred exemplary spinning process is outlined below, including a detailed overview of the various process steps.

The present invention provides processes for making the lyocell filaments described herein, as well as, for example, lyocell multifilament yarns. The process is described in detail with reference to individual process steps. It is to be understood that these process steps and corresponding preferred embodiments may be combined as appropriate, and that the present application encompasses and discloses these combinations even if not explicitly recited herein.

Preparation of the Spinning Solution It has been found preferable to use a cellulose starting material which meets the following requirements.

The rheological properties of known lyocell spinning solutions may not meet the demands of high speed filament yarn production. For example, an unacceptable number of filament breaks occur when using spinning solution compositions known in staple fiber production. By using a cellulose feedstock with a broader molecular weight distribution than previously disclosed, i.e., by blending 5 to 30 wt%, preferably 10 to 25 wt% of cellulose having a scanning viscosity in the range of 450 to 700 ml/g with 70 to 95 wt%, preferably 75 to 90 wt% of cellulose having a scanning viscosity in the range of 300 to 450 ml/g, these two fractions are reduced to 40 ml/g or more, preferably 100 It has been found that this problem is overcome when having a scan viscosity difference greater than or equal to ml/g. Scanning viscosity is determined in capriethylenediamine solutions according to SCAN-CM 15:99 and is a technique known to those skilled in the art and can be performed on commercially available equipment such as the equipment Auto PulpIVA PSLRheotek manufactured by psl-rheotek.

Blends of different types of starting materials may be used to obtain such cellulosic feedstocks (eg, from wood pulp) to achieve the required molecular polydispersity. The optimum blend ratio will depend on the actual molecular weight of each blend component, filament manufacturing conditions, and specific product requirements for the filament yarn. Alternatively, the required cellulose polydispersity can be obtained by blending prior to drying, for example during the manufacture of wood pulp. This eliminates the need to carefully monitor and blend pulp stocks during lyocell manufacturing.

The total content of cellulose in said spinning solution is typically 10-20 wt%, preferably 10-16 wt%, such as 12-14 wt%. Since those skilled in the art are aware of the components required in the spinning solution for the lyocell process, further detailed description of said components and general method of preparation is not believed necessary here. See US Pat. No. 5,589,125, WO 96/18760, WO 02/18682, and WO 93/19230, all of which are hereby incorporated by reference.

To further control the process according to the present invention, a high level of process monitoring and control is preferably used to ensure compositional uniformity of the spinning solution. This may include in-line measurement of spinning solution composition/pressure/temperature, in-line measurement of particle content, in-line measurement of spinning solution temperature distribution in the jet/nozzle, and periodic off-line cross-checks.

It is further preferable to control and, if necessary, improve the quality of the lyocell spinning solution used in the present invention, because the inclusion of large particles can result in unacceptable breakage of individual filaments during the forming process. Examples of such particles are impurities, such as sand, and gel particles containing poorly dissolved cellulose. One option for minimizing the content of such solid impurities is a filtration process. Multistage filtration of the spinning solution is the optimum method to minimize solid impurities. Those skilled in the art will appreciate that higher filtration stringency is required for finer filament fineness. Typically, for example, depth filtration, which has an absolute stopping power of about 20 microns, has been found effective for 1.3 decitex filaments. An absolute stopping power of 15 microns is preferred for finer filament decitex. Equipment and process parameters for performing filtration are known to those skilled in the art.
In addition, it was found suitable to adjust the viscosity of the spinning solution in the range of 500-1350 Pa·s, measured at 110° C. and a shear rate of 1.2 (1/s).

The temperature of the spinning solution during its production is typically in the range 105-120°C, preferably 105-115°C. Before the actual spinning/extrusion, the solution, optionally after filtration, is heated to a higher temperature, typically 115-135°C, preferably 120-130°C, using processes and equipment known to those skilled in the art. This process, along with a filtration step, enhances the homogeneity of the spinning solution after its initial preparation to provide the spinning solution (sometimes referred to as a spin product) suitable for extrusion through a spinning nozzle. The spinning solution is then preferably brought to a temperature of 110° C. to 135° C., preferably 115° C. to 135° C., prior to extrusion/spinning, a process that may include intermediate cooling and heating stages, as well as tempering stages (stages in which the spinning solution is maintained at a given temperature for a certain period of time). Such processes are known to those skilled in the art.

Filament Extrusion It has been found that a uniform and constant flow rate of the spinning solution through each spinneret nozzle hole further improves the process and helps meet the quality requirements for individual cellulose filaments and consequently for multifilament yarns. This is particularly suitable in view of the very high production speeds required for filament and filament yarn production, in the range of 200 m/min or more. According to the invention, production speeds of 200 m/min or more 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 200-1500 m/min, such as 400-1000 m/min or 700-1000 m/min, including ranges such as 700-1500 m/min.

Each spinneret section used to extrude the lyocell spinning solution has a number of nozzle holes corresponding to the number of filaments required for the continuous filament yarn. Multiple threads can be extruded from a single jet by combining multiple spinneret sections into a single spinneret plate, for example as disclosed in WO 03014429 A1, which is incorporated herein by reference.

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

Spinning solution flow uniformity can be improved by providing good temperature control within the spinneret and the individual nozzles. Temperature fluctuations within and between the nozzles during spinning are preferably as small as possible, preferably within ±2°C. This can be achieved by means of direct heating of the spinneret and the individual nozzles in a series of different zones to allow any local differences in spin solution temperature to be compensated and to precisely control the temperature of the spin 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.

The spinneret nozzle profile is preferably designed to maximize smooth acceleration of the spinning solution through said nozzle while minimizing pressure drop. Important design features of the nozzle include, but are not limited to, smooth inlet surfaces and sharp edges at the nozzle outlet.

- Initial cooling After exiting the spinning nozzle, the individual filaments are typically subjected to a cooling process, typically using a stream of air. Cooling of the filaments in this step is therefore preferably carried out by using drafts, preferably controlled cross drafts in an air gap. The draft should have a controlled humidity to obtain the desired cooling effect without detrimentally affecting the quality of the fibers. Suitable humidity values are known to those skilled in the art. However, direct application of the known lyocell staple fiber procedure to this process does not work well, as it requires very long air gaps (greater than 200 mm) to allow for high filament production rates. However, such air gaps are impractical because the individual filaments move and touch, leading to fusion of the filaments and poor product quality. For the same reason, it has been found that the high velocity cross draft disclosed for staple fiber production can also present problems. In addition, more uniformity and consistency of drawing is required for filament products compared to staple fibers.

Accordingly, the present invention provides a novel means of adjusting the filament manufacturing process to meet filament yarn manufacturing quality requirements.

For example, WO 03014436 A1, incorporated herein by reference, discloses a suitable cross-ventilation mechanism. Uniform filament cooling over the length of the air gap is preferred.

As outlined above, said long air gaps, which are deemed necessary according to common spinning process understandings, especially when considering high production rates, are not feasible. However, it has been found that longer air gap lengths than typically used in staple fiber production, such as about 40-130 mm, can be successfully used. Preferably, said air gap is in the range of 40-120 mm, such as 50-100 mm. In embodiments, this can be combined with increasing the filament spacing at the spinneret face (approximately twice the nozzle spacing used in Lyocell staple fiber production). Such a mechanism has been found to be beneficial in filament production. By increasing the filament spacing in this manner, the possibility of filament contact is reduced and the required uniform filament cooling can be achieved.

Cross draft speeds are preferably much lower than those used in lyocell staple fiber production. Suitable values are 0.5-3 m/s, preferably 1-2 m/s. Humidity values may be in the range of 0.5-10 g water/kg air, such as 2-5 g water/kg air. The temperature of the wind is preferably controlled to a value below 25°C, such as below 20°C.

Initial Solidification of Filaments After exiting the spinneret nozzle and being cooled in the air gap, the filaments produced need to be further processed for initial solidification. This is achieved by placing the individual filaments in a coagulation bath, also called spinning bath. In order to achieve a high degree of product quality uniformity, it has been found that this further initial solidification of the filaments preferably takes place within narrow tolerances, i.e. with only slight variations, preferably at exactly the same position.
It has been found that conventional spin bath designs are often unsuitable for this purpose as fluid forces due to high filament velocities (greater than about 400 m/min) disturb the bath surface resulting in uneven initial solidification (and inconsistent air gap sizes), as well as the possibility of filament fusion and other damage. For such problems, it has been determined that it is preferable to use shallow spinning baths having a depth of less than 50 mm.

Such spin baths are disclosed, for example, in WO 03014432 A1, incorporated herein by reference, which discloses shallow spin bath depths in the range of 5-40 m, preferably 5-30 mm, more preferably 10-20 mm. The use of such shallow spin baths makes it possible to control the contact position between the spun filaments and the coagulation solution in the spin bath, thereby avoiding the aforementioned problems that can occur when using conventional spin bath depths.

In addition, it has been found that filament quality can also be improved if the concentration of amine oxide in the spinning bath is controlled to values lower than those typically used for lyocell fiber production. It has been found that spin bath concentrations of less than 25 wt%, more preferably less than 20 wt%, and even more preferably less than 15 wt% amine oxide improve filament quality. A preferred range for the amine oxide concentration is 5 to 25 wt%, such as 8 to 20 wt% or 10 to 15 wt%. This is significantly lower than the ranges disclosed for lyocell staple fiber production. To be able to maintain such low amine oxide concentrations, continuous monitoring of the spin bath composition is preferred, so that, for example, adjustments to the concentration can be made by water replenishment and/or by selective removal of excess amine oxide.
The temperature of this spinning bath is typically in the range 5-30°C, preferably 8-16°C.

Similar to the preferred embodiment disclosed above for the spin solution, high stringency spin bath solution filtration is contemplated to minimize the likelihood of newly formed vulnerable filaments being damaged by unwanted solid impurities in the spin bath. This is particularly important for very high production speeds above 700 m/min.

Within the spin bath, an outlet from the spin bath causes the individual filaments of the final yarn of interest to be brought together and grouped into an initial multifilament bundle, the outlet typically being a ring-shaped outlet that holds the filaments together and also serves to control the amount of spin bath solution that exits the bath with the filament bundle. Suitable mechanisms are known to those skilled in the art. Since at least a portion of the filaments are in contact with the ring-shaped outlet, the shape of the ring-shaped outlet as well as the choice of material will affect the tension applied to the filament bundle. Those skilled in the art will know suitable materials and shapes for these outlets from the spinning bath to minimize any negative impact on the filament bundle.

Thus, in a preferred embodiment of the process according to the invention, said process comprises producing a spinning solution suitable for the Lyocell process comprising 10-15% by weight, preferably 12-14% by weight of cellulose, said cellulose being the aforementioned blend of celluloses with different scan viscosity values. The process further includes extruding the spinning solution through the extrusion nozzle while maintaining a temperature variation of ±2° C. or less through the extrusion nozzle. The filaments thus produced are subjected to initial cooling as described above, followed by said initial solidification of the filaments thus obtained in a coagulation bath (spinning bath) having a depth of less than 50 mm, preferably 5 to 40 mm, more preferably 10 to 20 mm.

The composition of said coagulating liquid used in this coagulating bath exhibits a concentration of amine oxide of 23 wt% or less, more preferably less than 20 wt%, even more preferably less than 15 wt%. This adjustment of amine oxide content can be accomplished by adjusting the concentration to the preferred range by selective removal of amine oxide and/or replenishment of fresh water.

Such a process makes it possible to reliably obtain filaments of high quality and particularly high homogeneity, said filaments being introduced into said coagulation bath in a manner which in particular ensures uniform coagulation and thus uniform filament properties. In addition, in the process embodiments described above, it is preferable to control the distance between the individual filaments during extrusion, for example by using wider nozzle spacing, as compared to standard lyocell staple fiber manufacturing processes, as further described below. These preferred process parameters and conditions enable the production of highly uniform lyocell filaments, as described herein, while also enabling the desired high process speeds (spinning speeds as high as 200 m/min or higher, more preferably 400 m/min or higher, and in embodiments as high as 700 m/min or higher). In this regard, the present invention further enables continuous long-term production of cellulose lyocell filaments and corresponding yarns, as the process parameters and conditions described above avoid filament breakage, etc., which would require the production of filaments and yarns to be stopped.

Filament drawing After exiting the spinning bath, the multifilament bundle is typically taken up by guide rollers that direct the bundle to the next processing stages such as washing, drying, and winding, which will result in the final yarn. During this step, preferably no drawing of the filament bundles takes place. The distance from the outlet of the spinning bath to the contact with the guide roller may be chosen according to need, and a distance of 40-750 mm has been shown to be suitable, such as 100-400 mm. It has been found that this process step can provide additional options for controlling and influencing product quality. This process step allows, for example, the adjustment of the crystal structure of the filaments, thereby achieving the desired properties of the lyocell continuous filament yarn. As noted above, and as can be derived from the language of aspect <1> below, it has been found that success at this process step is closely related to the rheology of the spinning solution and the consistency of extrusion through the nozzle, as noted above.

As mentioned above, means such as guide rollers take up the filaments and collect them to form the initial yarn and guide said yarn thus obtained towards further processing steps. According to the present invention, the maximum tension applied to the filament bundle (yarn) at the contact position between the filament bundle (yarn) and the guide roller is preferably (4.2×number of filaments/filament fineness) ^0.69 (cN) or less. This tension means the tension applied to the filament/filament bundle from the point of exiting the spinning nozzle to the point of first contact, e.g. to the point of first contact with the guide roller provided after the coagulation step. From the formula provided above, by way of example, said maximum tension for a filament bundle of, for example, 60 filaments and a yarn fineness of 80 dtex (each filament has a fineness of 1.33 dtex) is determined, said maximum tension being (4.2×60:1.33) ^0.69 , thus 37.3 cN.

By maintaining such a specific maximum tension, filament breakage can be reliably prevented so that a high quality yarn can be obtained. Additionally, this helps ensure that the filament manufacturing process can continue for the required time without failure. Those skilled in the art will understand that the tensions referred to herein are tensions measured with samples taken from the overall process by using a three roll testing apparatus Schmidt-Zugspan-nungsmessgerat ETB-100. Said tension measured for filaments and filament bundles at the designated contact positions referred to herein can be used to control product quality and process stability using the process parameters disclosed herein with respect to the present invention, in particular by adjusting the composition of said spinning solution, said spinning bath depth and said spinning bath solution (coagulation bath) composition, said cross draft, and spinneret design such as nozzle design and nozzle spacing, for the purpose of adjusting said tension values to values according to the formulas provided above.

• Washing of filaments Since the filaments after initial solidification and cooling still contain amine oxides, the resulting filaments and/or yarns are typically subjected to washing. Amine oxides can be removed from the newly formed threads via a countercurrent flow of demineralized water or other suitable liquid, typically at 70-80°C. As with the previous process steps, it has been found that conventional cleaning methods, such as the use of troughs, can present problems in view of high production speeds in excess of about 400 m/min. Additionally, a uniform application of the wash solution to each individual filament is preferred in order to obtain a high quality product. At the same time, it is also preferred that there is minimal contact between the sensitive filaments and cleaning surfaces in order to maintain the integrity of the filaments to achieve the desired yarn properties. Additionally, individual filament yarns need to be washed in close proximity to each other and line lengths should be minimized to make the process economically viable. In view of the above, preferred cleaning processes have been found to include, alone or in combination:

Washing is preferably carried out using a series of driven rollers and each yarn is individually subjected to a series of wash impregnation/wash removal steps.

It has been found beneficial to provide a means of uniformly removing or draining liquid from each yarn filament after each washing impregnation step without damaging said sensitive filaments. This can be achieved, for example, through appropriately designed and arranged pin guides. The pin guide may for example be constructed with a matt chrome treatment. The guides allow for close spacing of the filament threads (approximately 3 mm), good contact with the filaments, uniform liquid removal and low tension to minimize filament damage.

If desired, an alkaline wash step may be included to increase the efficiency of removing residual solvent from the filaments.

The spent cleaning fluid (after the first pin guide) typically has a concentration of 10-30%, preferably 18-20% amine oxide before returning to solvent recovery.

A "softener" may be applied to aid further processing. The types and methods of application are known to those skilled in the art. For example, it has been found effective to apply about 1% finish onto the filaments with a "lick-roller" mechanism, followed by nip rollers to control the tension of the yarn going to the dryer.

Yarn Drying Again, good control of this process aids in developing optimum yarn properties and minimizing the potential for filament damage. Drying means as well as drying parameters are known to those skilled in the art. Preferred embodiments are defined below.

The dryer consists, for example, of 12 to 30 heated drums with a diameter of about 1 m. It is preferred to control the individual speeds to ensure that the filament tension remains low and constant, preferably below 10 cN, preferably below 6 cN. The spacing of the threads through drying may be about 2-6 mm.

The initial temperature of the dryer is about 150°C. Later stages of the drying process may have lower temperatures as drying progresses.

After drying, antistatic agents and/or fabric softeners may be applied to the filament yarns by means known to those skilled in the art.

Further process steps such as yarn blending, bulking, union weaving may be applied after drying and before recovery using processes known to those skilled in the art. If desired, a softener may be applied to the yarn prior to the steps indicated above.

Yarn recovery Yarn may be recovered using standard winding equipment. A good example is a single row winder. The winder speed is used to fine tune the upstream process speed to maintain a low and constant yarn tension.

Those skilled in the art will appreciate that various modifiers such as dyes, antimicrobial products, ion exchange products, activated carbon, nanoparticles, lotions, flame retardant products, superabsorbents, impregnating agents, dyes, finishes, crosslinkers, grafting agents, binders, and mixtures thereof may be added during manufacture of the spinning solution or in the washing zone, provided that these additions do not interfere with the spinning process. This allows the filaments and yarns produced to be modified to meet individual product requirements. Those skilled in the art are well aware of how to add such above-mentioned substances during the steps of the lyocell filament yarn manufacturing process. In this regard, it has been found that many desirable modifiers that would normally be added in the washing stage are not effective in the filament yarn path due to high line speeds and thus short residence times. Another alternative approach to introducing these modifiers is to collect well-washed but "never dried" filament yarns and subject them to batchwise further processing where residence time is not a limiting factor.

FR filaments according to the present invention can be used to produce additional products such as yarns, fabrics and nonwovens. Yarns may comprise varying numbers of filaments of the present invention, suitable examples being 10-200 filaments, such as 15-150, in embodiments 25-100. The fineness of the yarn may encompass a wide range depending on the intended field of use, for example a fineness within the range of 30-150 denier, such as 50-120 denier. Due to the unique balance of properties such as high mechanical strength and slightly lower elongation at break, the filaments of the present invention can be used to produce high quality products with high dimensional stability.

The FR filaments of the present invention may be used alone when making further (textile) products, but they may also be blended with other types of fibers to create filament mixtures with desired property profiles. In particular, blending the FR filaments of the present invention with other fibers can be an option when 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 a high strength fabric is desired. in any case. Thus, the FR filaments in the present invention have been shown to provide good properties even when blended with other types of fibers, as explained above.

The following examples illustrate the invention.

The following examples demonstrate the superior properties of the FR lyocell filaments of the present invention compared to non-flame retardant viscose, cupro, and lyocell filaments.
Example 1 demonstrates the properties of FR lyocell filaments according to the invention.
Comparative Examples 1-3 demonstrate the properties of viscose filaments, cupra filaments, and lyocell filaments, respectively, all of which do not contain flame retardant components.

A filament according to the invention in Example 1 was made as follows.
Pulp (cellulose) was impregnated with 78% N-methylmorpholine N-oxide (NMMO) aqueous solution and a small amount of stabilizer. The resulting suspension contained 11.6% cellulose, 68% NMMO, 20.4% water and stabilizer GPE. The pulp consisted of a mixture of cellulose sulfite and cellulose sulfate. Flame retardant (Aflammit KWB, suspension of 20% ground Aflammit KWB in 50% aqueous NMMO solution) was added to prepare the final spinning solution and excess water was removed from the slurry under shear and heat to yield a fiber-free spinning solution containing 12.7% cellulose, 73.8% NMMO, 10.7% water, and 2.8% flame retardant (all percentages are total composition weight basis for goods).
The spinning solution was filtered and extruded through a nozzle into an air gap at 114° C. by a dry-wet process. An air flow was provided in the air gap to stabilize the extrusion process. The spinning speed was 400 m/min.
After passing through the air gap, the cellulose was precipitated in a spinning bath containing 10% NMMO and the balance water.
The endless filaments thus obtained were washed with water, impregnated with a finish, dried and wound onto bobbins. Washing was carried out in countercurrent with completely demineralized water. For drying, a contact dryer was used and the humidity was reduced to 10.5%.
These filaments were used to prepare multifilaments consisting of single filaments. A non-twisted filament yarn was produced from the multifilament. Textiles can be produced from the filament yarns. The linear density of said yarns 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 Pat. No. 4,246,221, WO 02/18682 A1, and WO 02/72929 A1.

Filament Comparative Examples 1-3 were produced using a conventional process, the lyocell filaments were produced using the experimental set-up described in Example 1, but without the flame retardant component.
The properties of each are reported below.

Comparative Examples 1 and 2 show that viscose and cupra filaments exhibit quite unsatisfactory properties even without the addition of flame retardants. On the other hand, the FR lyocell filaments exhibit very satisfactory mechanical properties, albeit slightly lower than those of Comparative Example 3, ie the non-FR lyocell filaments. However, said properties of FR lyocell filaments according to the invention are greatly improved compared to said non-FR viscose and cupra filaments. Said comparative examples with other types of cellulose filaments suffer from a large and unbalanced mechanical properties, so dimensionally stable products cannot be produced from these filaments. At the same time, the flame retardant filaments of the present invention, in addition to exhibiting very satisfactory flame retardancy, also exhibit an excellent balance of mechanical properties.

Flame Retardant Lining A lining of 75 g/m ² was produced from the yarn obtained using the FR lyocell filaments of the invention (den 90/40 (90 total denier multifilament with 40 filaments), yarn fineness dtex 100f40). This lining was used as a 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 ; evaluated. Said three-layer assembly passed the flame spread test according to method EN ISO 15025:2002 A (outer fabric ignition test as well as lining ignition test) and fulfilled all the requirements according to EN469 (EN533 index 3).
The present invention includes the following aspects.
<1> A flame-retardant filament (FR filament) containing a flame retardant and cellulose, wherein the filament is a lyocell filament.
<2> The FR filament according to <1>, having an average dry tensile strength of 22 cN/tex or more.
<3> The FR filament according to <1> or <2>, having an average wet tensile strength of 11 cN/tex or more.
<4> The FR filament according to any one of <1> to <4>, wherein the amount of flame retardant is 2 to 50% by weight.
<5> The method for producing FR filaments according to any one of <1> to <4>, comprising providing a composition comprising pulp, N-methylmorpholine N-oxide, water, and a flame retardant, and spinning the solution to produce filaments.
<6> The method of <5>, wherein the amount of flame retardant and pulp in the spinning solution is in the range of 12-25% of the spinning solution.
<7> The method according to <5> or <6>, wherein the spinning speed is in the range of 250 to 750 m/min.
<8> The method according to any one of <5> to <7>, wherein the pulp contains cellulose sulfite and cellulose sulfate.
<9> Use of the FR filament according to any one of <1> to <4> or the FR filament manufactured according to any one of <5> to <8> for manufacturing yarns, fabrics, and textile products.
<10> A yarn, fabric, or textile product comprising the FR filament according to any one of <1> to <4> or the FR filament produced according to any one of <5> to <8>.
<11> The use or product of <9> or <10>, wherein the FR filaments are blended with other types of fibers.
<12> The use or product according to any one of <9> to <11>, which, when tested in accordance with EN ISO 15025:2002 B method-bottom ignition, satisfies the requirements according to EN ISO 14 116 classification "flame spread index 3".
<13> The use or product according to any one of <9> to <12>, which is a multifilament yarn.
<14> The use or product according to any one of <9> to <13>, wherein the FR filament contains a resin finish.

Claims (14)

A flame-retardant filament (FR filament) comprising a flame retardant and cellulose, characterized in that said filament is a lyocell filament. 3. The FR filament of claim 1, having an average dry tensile strength of 22 cN/tex or greater. 3. The FR filament of claim 1 or claim 2, having an average wet tensile strength of 11 cN/tex or greater. FR filament according to any one of claims 1 to 3, wherein the amount of flame retardant is 2-50% by weight. A method for making FR filaments according to any one of claims 1 to 4, comprising providing a composition comprising pulp, N-methylmorpholine N-oxide, water, and a flame retardant, and spinning said solution to make filaments. 6. The method of claim 5, wherein the amount of flame retardant and pulp in said spinning solution is in the range of 12-25% of said spinning solution. A method according to claim 5 or claim 6, wherein the spinning speed is within the range of 250-750 m/min. A method according to any one of claims 5 to 7, wherein the pulp comprises cellulose sulfite and cellulose sulfate. Use of the FR filament according to any one of claims 1 to 4 or the FR filament produced according to any one of claims 5 to 8 for the production of yarns, fabrics and textile products. A yarn, fabric or textile product comprising the FR filament according to any one of claims 1-4 or the FR filament produced according to any one of claims 5-8. 11. Use or product according to claim 9 or claim 10, wherein the FR filaments are blended with other types of fibers. 12. Use or product according to any one of claims 9 to 11, which, when tested according to EN ISO 15025:2002 Method B - Bottom ignition, meets the requirements according to EN ISO 14 116 classification "Flame spread index 3". Use or product according to any one of claims 9 to 12, which is a multifilament yarn. Use or product according to any one of claims 9 to 13, wherein said FR filaments comprise a resin finish.