RU2789193C2 - Fire resistant lyocellic fiber - Google Patents

Abstract

FIELD: flame retardant lyocell filaments.

SUBSTANCE: present invention relates to flame retardant lyocell filaments, as well as to a method for the manufacture and use of flame retardant filaments. The flame retardant filament contains a fire retardant substance based on compounds containing nitrogen and phosphorus and cellulose, and is characterized in that the filament is a lyocell filament in which the amount of the flame retardant substance is in the range of 10 to 40 mass%, and in that the flame retardant filament has an average dry strength of at least 22 cN/tex and an average wet strength of at least 11 cN/tex. The method for manufacturing a flame retardant filament includes obtaining a composition containing wood pulp, NMMO, water and a flame retardant, and a spinning solution for making filaments, in which the amount of flame retardant and wood pulp in the spinning solution is in the range from 12 to 25 wt.% of the spinning solution, and the spinning speed is from 250 to 750 m/min.

EFFECT: flame retardant lyocell filament of the invention is used to make yarn, webs and textiles that meet high quality standards for strength and dimensional stability.

21 cl

Description

[0001] The present invention relates to flame retardant lyocell fibers, as well as to the method of manufacture and applications of flame retardant fibers.

State of the art of the present invention

[00002] Flame retardant fibers are used in a wide variety of applications from technical fabrics to outerwear. Although cellulosic fibers have long been used in these applications, cellulosic fibers, due to their known poor dimensional stability and low wet strength, have not yet achieved significant attention and application in this field. The term "fiber" as used herein defines, for example, in accordance with the terminology of the International Bureau for the Standardization of Man-made Fibers (BISFA) (other terms used in the present description and claims are in accordance with the definitions of the BISFA publication, also see below), fiber very long lengths are considered as continuous (endless), which distinguishes this fiber from fibers of shorter lengths, such as staple fibers and tow. For such shorter fibers, dimensional stability issues as well as strength issues are of less importance, and thus cellulose staple fibers and the like have gained wide acceptance and use, also in embodiments containing additives, including flame retardants. However, for continuous fibers, problems related to dimensional stability and strength properties, in particular wet strength, are of great importance. This is one of the reasons why cellulosic fibers, in particular flame retardant fibers, have not yet reached widespread use.

[0003] Viscose staple fibers made with flame retardants as additives are known from the prior art. US 2012/0156486 A1 and US 2013/0149932 A1 are examples of descriptions of such prior art staple fibers. However, cellulosic fibers such as viscose fibers, when made with flame retardant additives, have not shown the required properties such as dimensional stability as well as sufficient dry and wet strength. These properties are necessary to meet the requirements of textile processes such as weaving, dyeing and finishing, as well as to achieve proper textile performance in terms of wash shrinkage or tear testing.

OBJECT OF THE INVENTION

[0004] In view of the above problems, it is an object of the present invention to provide a flame retardant fiber that meets high quality standards in terms of strength and dimensional stability. The term "flame retardant fiber" as used herein defines a fiber that is not simply coated with a flame retardant, but that contains a flame retardant in a fiber matrix.

Brief summary of the present invention

[0005] This problem is solved by the fiber according to paragraph 1 of the claims of the present invention. Preferred embodiments are presented in paragraphs 2-5 of the claims. In addition, the present invention provides a method according to paragraph 6 of the claims, for which preferred embodiments are presented in paragraphs 7-9 of the claims. Finally, the present invention provides the use of claim 10 and the article of claim 11, for which preferred embodiments are defined in claims 12-15. Additional explanation is provided in the following description.

Detailed disclosure of the present invention

[0006] Surprisingly, flame retardant lyocell fibers have indeed been found to overcome the shortcomings of the prior art, as well as prejudices and concerns about flame retardant cellulosic fibers such as viscose fibers. Surprisingly, the lyocell fibers as described herein indeed exhibit a very satisfactory balance of properties and can be reliably produced in the form of flame retardant fibers. These flame retardant fibers have shown great promise in a variety of products including filament yarns as well as protective clothing webs or, for example, clothing webs or nonwovens made from the fibers and filaments of the present invention.

[0007] Lyocell fibers are well known in the art and a general technique for their manufacture is described, for example, in US 4,246,221 and in the International Bureau for the Standardization of Artificial Fibers (BISFA) Terminology of Artificial Fibers, 2009 Edition. incorporated herein by reference in their entirety.

Reference should also be made to documents WO 02/18682 A1 and WO 02/72929 A1, which relate to a process for making threads from cellulose fibers and are also incorporated herein in their entirety.

[0008] As mentioned above, the flame retardant fiber of the present invention is a lyocell fiber, i. fiber made by a method using the lyocell process. This method is well known to the person skilled in the art and thus will not be described in detail further herein. This document provides examples illustrating this method, as well as described patent documents. The fiber may have any desired linear density, with suitable values being in the range of 0.6 to 4 dtex and preferred values being in the range of 0.8 to 2 dtex. The cellulose starting material used to make the flame retardant fiber of the present invention is not critical, and any type of starting material suitable for the lyocell process can be used.

[0009] As stated above, the present invention is characterized in particular in that the new flame retardant fiber of the present invention does exhibit a very unexpected balance of properties such as dry and wet mechanical properties (stability/tensile strength) and also a very satisfactory dimensional stability. At the same time, the desired flame retardant properties of the fibers can be obtained even without excessive sacrifice of mechanical properties. The strength properties that can be obtained for fibers according to the present invention are generally determined in the conditioned state, and for flame retardant fibers according to the present invention, these properties are generally determined as follows:

The average dry strength (FFk) is at least 22 cN/tex, the average dry elongation at break (FDk) of the fibers is at least 6%, preferably 6% to 8%. These properties are evaluated using the following test devices and parameters:

Research device: USTER® Tensorapid 4 2.4.2 UTR4/500N:

Test sample length: 500 mm

Clamping speed: 60mm/min

Clamp pressure: 30%

Preload: 4.1 cN

[0010] Accordingly, the fibers of the present invention do indeed exhibit advantageous high dimensional stability and impart this advantage to yarns and webs made from them. Thus, high quality flame retardant articles can be made using the flame retardant fiber of the present invention.

[0011] As stated above, the fibers of the present invention are flame retardant fibers, i. e. fibers containing flame retardant substances. Since the fibers of the present invention are lyocell fibres, the incorporation of flame retardants can be achieved by including flame retardants in a suitable manner in the dope (or at least in the composition prior to spinning the fibres), as further illustrated in the example contained herein. The type of flame retardant is not critical, provided that it can in particular be present in the spinning solution or spinning composition, usually in the form of a solution, preferably an aqueous solution of the flame retardant. However, the flame retardant may also be present in the form of a finely divided powder or a dispersion of such a finely divided powder. If flame retardants are to be used in such solid forms, it is preferred that the average particle diameter of the flame retardant is not more than 50% of the fiber diameter, more preferably not more than 30%, even more preferably not more than 10% of the fiber diameter.

[0012] The amount of flame retardant in the final fiber, as a rule, is in the range from 2 to 50 wt. % fiber, preferably from 10 to 40 wt. %, more preferably from 15 to 30 wt. %. This amount can be adjusted as needed (eg depending on the degree of flame retardancy desired) and can be adjusted by changing the ratio of cellulose to flame retardant in the dope or spinning composition.

[0013] As indicated above, the type of flame retardant is not critical. However, flame retardants based on compounds containing nitrogen and phosphorus, such as those sold under the trademark Aflammit®, are preferred. Particularly preferred are organophosphorus compounds such as Aflammit KWB. Any flame retardants used can be subjected to pre-treatment, such as grinding, in order to obtain flame retardants having particle sizes (if they are not soluble in the spinning composition) that are suitable for the spinning process, which, as a rule, depends on the target diameter fibers. Such methods are known to the person skilled in the art.

[0014] According to one embodiment of the present invention, the flame retardant is an oxidized tetrakishydroxyalkylphosphonium salt condensate, and ammonia and/or nitrogenous compounds that contain one or more amino groups are excluded.

[0015] As noted above, the flame retardant fiber of the present invention is a lyocell fiber. Accordingly, the method for manufacturing a fiber according to the present invention includes making a spinning solution containing at least cellulose, water, N-methylmorpholine-N-oxide (NMMO) and a flame retardant, as well as spinning the solution and regenerating the fibers in a manner known to a person skilled in the art. technology. In accordance with the present invention, it has been determined that spinning speeds of about 250 to 750 m/min, for example 300 to 600 m/min, preferably 350 to 450 m/min, can be used. During the process, if required, any additional additives and stabilizers, such as dyes, pigments, etc., can be introduced.

[0016] Of course, after spinning, the fibers can be subjected to any conventional processing such as coating, sizing, etc. One skilled in the art will be able to select appropriate methods depending on the intended use of the flame retardant fibers. However, the following description presents preferred exemplary spinning processes, including details of the various process steps.

[0017] The present invention provides a method described herein for the manufacture of lyocell fibers, as well as, for example, lyocell multifilament yarns. This method will be described in detail with the introduction of individual process steps. It should be understood that these process steps and their respective preferred embodiments may be combined as appropriate, and that the present application extends to and describes these combinations even though they are not described in detail herein.

• Making a spinning solution

[0018] It has been found that it is preferable to use a cellulosic starting material that meets the following requirements.

[0019] The rheological properties of known lyocell spinning solutions are not compatible with the requirements of high speed fiber filament production. For example, an unacceptable number of fiber breaks has been observed with spinning solution compositions known for the manufacture of staple fibers. It has been found that this problem is overcome by the use of a cellulosic starting material having a broader molecular weight distribution than previously described materials, namely mixing from 5 to 30 wt. %, preferably from 10 to 25 wt. % cellulose, having a viscosity measured by SCAN in the range from 450 to 700 ml/g, and from 70 to 95 wt. %, preferably from 75 to 90 wt. % pulp having a SCAN viscosity in the range of 300 to 450 ml/g, the two fractions having a SCAN viscosity difference of 40 ml/g or more, preferably 100 ml/g or more. The SCAN-measured viscosity is determined according to the SCAN-CM 15:99 method, which uses an ethylenediamine copper complex solution, which is known to the person skilled in the art, and which can be carried out on commercially available devices, such as the Auto PulpIVA PSLRheotek device, supplied by PSL-Rheotek.

[0020] To obtain such cellulosic starting material (for example, from wood pulp) in order to achieve the desired molecular polydispersity, mixtures of various types of starting materials can be used. Optimum blend ratios will depend on the actual molecular weight of each component of the blend, fiber fabrication conditions, and the specific requirements of the fiber filament product. Alternatively, the desired polydispersity of the cellulose can also be obtained, for example, during the production of wood pulp by mixing before drying. This could eliminate the need for close supervision of the mixing of wood pulp raw materials during the manufacture of lyocell.

[0021] The total content of cellulose in the spinning solution is usually from 10 to 20 wt. %, preferably from 10 to 16 wt. %, for example, from 12 to 14 wt. %. Since the required components of spinning solutions for the lyocell process are known to the person skilled in the art, further detailed explanations of the components and the general method of manufacture are not deemed necessary here. In this regard, reference may be made to US 5,589,125, WO 96/18760, WO 02/18682 and WO 93/19230, which are incorporated herein by reference.

[0022] In order to further control the method in accordance with the present invention, it is preferable to use high levels of monitoring and control of the process to ensure uniformity of the dope composition. This may include real-time dope composition/pressure/temperature measurement, real-time solids content measurement, real-time dope dope temperature distribution in the jets/nozzles, and regular offline cross checks.

[0023] In addition, it is preferable to control and, if necessary, improve the quality of the lyocell spinning solution used according to the present invention, since the content of large particles can lead to unacceptable breaks in individual fibers during their manufacture. Examples of such particles are impurities such as sand, etc., as well as gel particles containing insufficiently dissolved cellulose. One option for minimizing such particulate matter is through filtration processes. Multi-stage spinning dope filtration is the best way to minimize solids content. One of ordinary skill in the art will appreciate that lower densities require filters with smaller apertures. As a rule, for example, depth filtration with an absolute retention of about 20 microns has been effective for fibers with a linear density of 1.3 decitex. An absolute retention of 15 microns is preferred for fibers with a lower linear density. Devices and technological parameters for the implementation of filtration are known to the person skilled in the art.

In addition, it has been found suitable to control the viscosity of the spinning dope in the range of 500 to 1350 Pa.s, which is measured at a shear rate of 1.2 s ^-1 and a temperature of 110°C.

[0024] the Temperature of the spinning solution during its manufacture, as a rule, is in the range from 105 to 120°C, preferably from 105 to 115°C. Prior to spinning/extrusion of the solution, optionally after filtration, the solution is heated to a higher temperature, typically 115 to 135°C, preferably 120 to 130°C, using methods and apparatus known to the person skilled in the art. . This process, together with a filtration step, increases the homogeneity of the dope after it has been initially made in order to obtain a dope (sometimes referred to as "spinning stock") suitable for extrusion through spinning nozzles. This dope is then, preferably before extrusion/spinning, brought to a temperature of 110°C to 135°C, preferably 115°C to 135°C, in a process which may include intermediate cooling and heating steps, as well as steps holding (stages in which the spinning solution is kept at a given temperature for a certain time). Such methods are known to the person skilled in the art.

• Fiber extrusion

[0025] It has been found that the uniformity and consistency of the dope flow through each spinning nozzle opening further improves the process and helps to meet the quality requirements of individual cellulosic fibers, and in turn the quality requirements of multifilament filaments. This is particularly relevant in view of the very high production speeds required to make fibers and filaments, in the range of 200 m/min and higher. According to the present invention, production speeds of 200 m/min or more, such as 400 m/min or more, preferably 700 m/min or more, and even up to 1000 m/min or more, can be achieved. Suitable ranges are 200 to 1500 m/min, eg 400 to 1000 m/min, or 700 to 1000 m/min, including ranges, eg 700 to 1500 m/min.

[0026] Each element of the spinning mechanism, which is used to extrude the lyocell dope, has a number of nozzle holes corresponding to the number of fibers required for a continuous fiber thread. A plurality of filaments can be extruded with a single jet by combining a plurality of spinning mechanism elements into a single spinning mechanism plate, for example as described in WO 03014429 A1, incorporated herein by reference.

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

[0028] The uniformity of the flow of the spinning solution can be improved by providing proper temperature control within the spinning mechanism and individual nozzles. It turns out to be preferable that during spinning the temperature variability within the nozzles (as well as between the nozzles) is as low as possible and preferably ±2° C. or less. This can be achieved by providing direct heating of the spinning mechanism and individual nozzles in succession in different zones in order to compensate for any local differences in the temperature of the spinning solution and to control precisely the temperature of the spinning solution during its extrusion from each nozzle of the spinning mechanism. Examples of such temperature control devices are disclosed in WO 02/072929 and WO 01/81662,

[0029] The profiles of the nozzles of the spinning mechanism are preferably designed to maximize the smooth acceleration of the flow of the spinning solution through the nozzle while minimizing the pressure drop. The main design features of a nozzle include, but are not limited to, a smooth inlet surface and sharp edges at the nozzle outlet.

• Initial cooling

[0030] After exiting the spinning nozzles, the individual fibers are typically subjected to a cooling process, typically using an air stream. Accordingly, it is preferred to cool the fibers at this stage by using forced airflow, preferably controlled crossflow in the air gap. The forced airflow must be humidity controlled in order to achieve the desired cooling effect without adversely affecting fiber quality. Suitable humidity values are known to the person skilled in the art. However, the direct application of known procedures for the manufacture of lyocell staple fibers at this stage does not work, because this would require, given the high speed of fiber production, a very long air gap (exceeding 200 mm). However, such an air gap cannot be realized, since the individual fibers will touch during the movement, which leads to the adhesion of the fibers and unsatisfactory product quality. For the same reason, it has been found that the high velocity of the described transverse air currents for the production of staple fibers can create problems. In addition, higher uniformity and tensile consistency is required for fiber products compared to staple fibers.

[0031] Thus, the present invention provides a new means for adjusting the method of manufacturing fibers in order to fulfill the quality requirements for manufacturing fiber filaments.

[0032] For example, WO 03014436 A1, incorporated herein by reference, discloses a suitable cross-airflow configuration. Homogeneous cooling of the fibers is preferred over the entire length of the air gap.

[0033] As noted above, longer air gaps that might be considered necessary in accordance with the general understanding of the spinning process, in particular, taking into account high manufacturing speeds, cannot be realized. However, it has been found that longer air gaps than those commonly used to make staple fibers can be successfully used, and this length is, for example, about 40 to 130 mm. Preferably the air gap is in the range of 40 to 120 mm, for example 50 to 100 mm. In embodiments, this can be combined with increased fiber spacing on the spinner surface (approximately twice the nozzle spacing used to make lyocell staple fibers). This configuration proved to be favorable for the manufacture of fibers. Thus, increasing the distance between the fibers reduces the possibility of contact between the fibers and ensures that the required uniform cooling of the fibers is achieved.

[0034] The transverse air flow rates are preferably significantly less than those used to make lyocell staple fibers. Suitable values are from 0.5 to 3 m/s, preferably from 1 to 2 m/s. Humidity values can range from 0.5 to 10 g of water per 1 kg of air, for example, from 2 to 5 g of water per 1 kg of air. The air temperature is preferably controlled below 25°C, for example below 20°C.

• Initial fiber coagulation

[0035] After leaving the nozzles of the spinning mechanism and cooling in the air gap, the produced fibers must be processed to further initiate coagulation. This is achieved by introducing the individual fibers into a coagulation bath, also referred to as a "spinning bath".

It has been found that in order to achieve a high degree of uniformity in product quality, this additional initial coagulation of the fibers should preferably take place within a narrow range, i.e. only with slight variability, preferably at the same point.

It has been found that traditional spin bath designs are often not suitable for this purpose because hydrodynamic forces due to high fiber production speeds (in excess of about 400 m/min) perturb the bath surface, resulting in a non-uniform initial coagulation (and variable air gap size) and also cause potential fiber bonding and other damage. In the event of such problems, it has been found to be preferable to use shallow spinning baths having a depth of less than 50 mm.

[0036] Such spinning baths are disclosed, for example, in WO 03014432 A1, which is incorporated herein by reference and describes shallow spinning baths with a depth in the range of 5 to 40 mm, preferably 5 to 30 mm, preferably 10 to 20 mm. The use of such shallow spinning baths makes it possible to adjust the point of contact of the spinning fibers with the coagulation solution in the spinning bath, and as a result, the problems that can occur with conventional depth spinning baths are avoided.

[0037] In addition, it has been found that the quality of the fibers can also be improved if the concentration of amine oxide in the spin bath is set to a level lower than the concentration commonly used in the manufacture of lyocell fibers. It has been found that fiber quality improves if the amine oxide concentration in the spinning bath is below 25% by weight. %, preferably below 20 wt. %, even more preferably below 15 wt. %. Preferred ranges for the concentration of amine oxide are from 5 to 25 wt. %, for example, from 8 to 20 wt. % or from 10 to 15 wt. %. This is well below the range described for the manufacture of lyocell staple fibers. To ensure that such a low concentration of amine oxide is maintained, continuous monitoring of the spinning bath composition is preferred, so that, for example, concentration adjustment can be carried out by adding water and/or by selectively removing excess amine oxide.

The temperature of this spinning bath, as a rule, is in the range from 5 to 30°C., preferably from 8 to 16°C.

[0038] Similar to the preferred spinning dope embodiments described above, highly precise filtration of the dope dope solution is possible in order to minimize potential damage to newly formed fine fibers by undesired solids in the spin dope. This is especially important at very high production speeds in excess of 700 m/min.

[0039] In the spin bath, the individual fibers of the target final filament are gathered together and spun into an initial multifilament tow by tapping from the spin bath, which typically has an annular outlet that collects the fibers together and also serves to control the amount of spin bath solution exiting from the spin bath. baths together with a fiber bundle. Suitable configurations are known to the person skilled in the art. The shape as well as the choice of material for the annular outlet affects the tension applied to the fiber tows, since at least some of the fibers are in contact with the annular outlet. The person skilled in the art will be aware of suitable materials and shapes for these spinning bath exits in order to minimize any adverse effect on the fiber tow.

[0040] Accordingly, according to a preferred embodiment of the method in accordance with the present invention, the method includes the steps of making a spinning solution suitable for the lyocell process and containing from 10 to 15 wt. %, preferably from 12 to 14 wt. % cellulose, and cellulose is a mixture of types of cellulose described above, having different values measured by the SCAN method of viscosity. In addition, this method includes the step of extruding the spinning solution through the extrusion nozzles while maintaining the temperature variability through the extrusion nozzles in the range of ±2° C. or less. The fibers produced in this way are subjected to an initial cooling as described above, after which the resulting fibers are initially coagulated in a coagulation bath (spinning bath) having a depth of less than 50 mm, preferably from 5 to 40 mm, preferably from 10 to 20 mm.

[0041] The composition of the coagulation solution used in this coagulation bath contains an amine oxide, the concentration of which is 23 wt. % or less, preferably below 20 wt. % and more preferably below 15 wt. %. Control of this amine oxide can be achieved by selectively removing the amine oxide and/or by adding fresh water to keep the concentration within the preferred ranges.

[0042] This method ensures that fibers of high quality and particularly high uniformity can be obtained, which in particular enter the coagulation bath in such a way as to ensure uniform coagulation and thus uniform fiber properties. In addition, according to embodiments of the method described above, it is preferable to control the distance between individual fibers during extrusion, for example, by using a larger distance between nozzles compared to standard methods for making lyocell staple fiber, as described in detail below. These preferred processing parameters and conditions allow, as described herein, the production of lyocell fibers having high uniformity while achieving the desired high production speeds (spinning speeds of 200 m/min or more, preferably 400 m/min or more and according to embodiments reaching high levels of 700 m/min or more). In this context, the present invention also provides continuous and long-term production of cellulosic lyocell fibers and related yarns, since the process parameters and conditions as explained above prevent fiber breakage and other disturbances that would require the suspension of the production of fibers and yarns.

• Stretching fibers

[0043] After exiting the spinning bath, the multifilament tows are received, typically by means of a guide roller, which guides the tow from which the final filament will be obtained, to subsequent processing steps such as washing, drying and winding. During this stage, preferably no stretching of the fiber tow occurs. The distance between the exit from the spinning bath and the contact with the guide roller can be chosen according to need, and distances of 40 to 750 mm, for example 100 to 400 mm, have proven to be suitable. It has been found that this process step may provide additional options for controlling and influencing product quality. In this process step, for example, the crystal structure of the fibers can be controlled and as a result, the desired properties of filaments of continuous lyocell fibers can be achieved. As indicated above, and can be deduced from the conditions of claim 1, the success of this process step has been found to be closely related to the rheology and consistency of the dope extruded from the nozzles as described above.

[0044] As mentioned above, a tool, such as a guide roller, receives the fibers, collects them to form the original filament, and directs the filament thus obtained to subsequent processing steps. In accordance with the present invention, it is preferred that the maximum tension applied to the fiber tow at the point of contact of the fiber tow (thread) with the guide roller is (4.2 × number of fibers / linear density of fibers) ^0.69 (cN) or less. This tension means the tension applied to the fibers/fiber tow from the exit point of the spinning nozzles to the first point of contact, for example with a guide roller present after the coagulation step. The above formula determines, by way of illustration, that the maximum tension for, for example, a tow of 60 fibers with a denier of 80 dtex (individual fibers have a denier of 1.33 dtex) is respectively (4.2×60:1, 33) ^0.69 \u003d 37.3 cN.

[0045] By maintaining such a certain maximum tension, the fibers can be prevented from breaking and thus high quality yarns can be obtained. In addition, it helps to ensure that the fiber manufacturing process can be carried out smoothly within the required time. One skilled in the art will appreciate that the tension referred to herein is the tension to be measured using samples taken throughout the process using a Schmidt ETB-100 three-roll strain gauge. The tension measured for fibers and fiber tows at a given point of contact specified in this document, using the technological parameters described therein in the context of the present invention, can be used to control product quality and process stability, in particular by controlling the composition of the spinning dope, the depth of the spinning bath and the composition of the solution in the spinning bath (coagulation bath), the speed of the cross-flow of air, as well as the design of the spinning mechanism, including the design of the nozzle and the distance between the nozzles, in order to control the tension values at the levels corresponding to the equation above.

• Fiber washing

[0046] Because the fibers still contain amine oxide after initial coagulation and cooling, the resulting fibers and/or filaments are typically washed. The newly made yarns can be washed free of amine oxide using a counter flow of demineralized water or other suitable liquid, typically at a temperature of 70 to 80°C. As with the prior process steps, it has been found that conventional washing techniques, such as trays, can be problematic given high production speeds in excess of about 400 m/min. In addition, uniform application of the wash solution to each individual fiber is advantageous in order to obtain a high quality product. At the same time, minimal contact between the fine fibers and the surfaces to be washed is preferred in order to maintain the integrity of the fibers and achieve the desired properties of the yarn. In addition, the individual fibers should be washed in close proximity to each other and the length of the line should be reduced to a minimum in order to make the process cost-effective. In view of the foregoing, it has been found that the preferred washing method includes the following conditions, present alone or in combination:

[0047] Washing is preferably carried out using a series of driven rollers, and each strand is individually subjected to a series of washing solution impregnation/solution removal steps.

[0048] It has proven to be advantageous to ensure uniform removal of spinning solution from each fiber strand without damaging the fine fibers after each step of soaking with the wash solution. This can be achieved, for example, by suitably designed and positioned guide rods. The guide rods can, for example, be matt chrome plated. The guide rods allow a short distance between the fibers (approximately 3 mm), proper contact with the fibers to ensure uniform removal of the solution, and low tension to minimize damage to the fibers.

[0049] An alkaline washing step may optionally be included to increase the efficiency of removing residual solvent from the fibers.

[0050] The wash solution used (after the first guide rod) typically has an amine oxide concentration of 10 to 30%, preferably 18 to 20%, before being returned to solvent recovery.

[0051] A soft finish may be applied to simplify post-processing. The types and methods of its application are known to those skilled in the art. For example, a lubrication roller that applies approximately 1% sizing to the fibres, followed by a pinch roller to control the tension of the yarn introduced into the dryer, has proved effective.

• Drying threads

[0052] Again, proper control of this stage contributes to the development of optimum yarn properties and minimization of potential fiber damage. Drying devices as well as drying parameters are known to the person skilled in the art. Preferred embodiments are defined as follows:

[0053] The dryer is composed of, for example, 12 to 30 heated drums having a diameter of about 1 m. Individual speed control is preferred to ensure that the tension of the fibers is kept low and constant, preferably below 10 cN, preferably below 6 cN. The distance between the threads during drying can be approximately 2 to 6 mm.

[0054] The initial temperature in the dryer is approximately 150°C. In the later stages of drying, process temperatures may be lower as drying progresses.

[0055] An antistatic agent and/or a soft sizing may be applied to the fiber filaments after drying using tools known to those skilled in the art.

[0056] Additional processing steps, such as bonding, texturing, or weaving the yarns, can be carried out after drying and before collection using methods known to a person skilled in the art. If desired, a soft sizing may be applied to the threads prior to the above steps.

• Collection of threads

[0057] The filaments can be collected using standard winding equipment. A suitable example is a set of winders. Winder speed control is used to fine-tune upstream process speeds to maintain low and constant yarn tension.

[0058] One skilled in the art will appreciate that a variety of builders such as dyes, antibacterial products, ion exchange products, active carbon, nanoparticles, lotions, flame retardants, superabsorbents, impregnating agents, sizing agents, crosslinking agents, grafting agents, binders substances and mixtures thereof may be added during the manufacture of the spinning dope or in the washing zone, provided that said additions do not interfere with the spinning process. This allows the fibers and yarns produced to be modified to meet individual product requirements. Those skilled in the art are well aware of methods for adding such aforementioned materials at a certain stage in the process of making a lyocell fiber filament. In this regard, it has been found that many of the desirable builders that are typically added during the washing step will not be effective in the processing of filaments due to the high line speed and therefore short residence time. In order to introduce these builders, an alternative approach is to collect fully washed but non-drying filaments and send them to subsequent processing in a batch mode, where residence time is not a limiting factor.

[0059] Flame retardant fibers according to the present invention can be used for the manufacture of subsequent products, such as threads, webs and nonwovens. The yarns may contain various numbers of fibers according to the present invention, suitable examples are from 10 to 200, for example from 15 to 150, and in embodiments from 25 to 100 fibers. The linear density of the thread can vary over a wide range depending on the intended application, and examples are linear density in the range from 30 to 150 denier, for example, from 50 to 120 denier. Due to the unique balance of properties such as high mechanical strength and relatively low elongation at break, high quality products with high dimensional stability can be made using the fibers of the present invention.

[0060] The flame retardant fibers of the present invention can be used in their pure form in the manufacture of subsequent (textile) products, however, these fibers can also be mixed with other types of fibers in order to obtain a mixture of fibers with a desired property profile. In particular, it may be possible to mix the flame retardant fibers according to the present invention with other fibers if a high degree of flame retardant properties is not required for given products. Another option is to blend flame retardant fibers with high tenacity fibers if high tenacity webs are desired. In any event, the flame retardant fiber of the present invention has been shown to provide the proper properties as explained above also when blended with other types of fibers.

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

The following examples demonstrate the superior properties of flame retardant lyocell fibers of the present invention compared to non-flame retardant viscose, copper ammonium and lyocell fibers.

Example 1 presents the properties of a flame retardant lyocell fiber in accordance with the present invention.

Comparative Examples 1-3 represent the properties of viscose fiber, copper ammonium fiber and lyocell fiber, respectively, all of which do not contain a flame retardant component.

The fibers according to example 1 of the present invention were made as follows:

Wood pulp (cellulose) was impregnated with an aqueous solution containing 78% N-methylmorpholine-N-oxide (NMMO) and small amounts of stabilizers. The resulting slurry contained 11.6% cellulose, 68% NMMO, 20.4% water and a gel polymer electrolyte (GPE) stabilizer. Wood pulp was a mixture of sulfite and sulfate cellulose. Flame retardant (Aflammit KWB, slurry of 20% milled Aflammit KWB in 50% NMMO aqueous solution) was added to form the final dope, excess water was removed from the slurry with stirring and heating to give a fiber free cellulose solution containing 12.7% cellulose , 73.8% NMMO, 10.7% water, and 2.8% flame retardant (all percentages are percentages based on the total weight of the composition).

The dope was filtered and extruded at 114° C. in a dry-wet process in which the dope was extruded through nozzles into an air gap. To stabilize the extrusion process, an air stream was introduced into the air gap. The spinning speed was 400 m/min.

After crossing the air gap, the pulp was deposited in a spinning bath containing 10% NMMO, with the rest of the mass being water.

The endless fibers produced in this way were washed with water, impregnated with a sizing, dried and wound on a reel. Washing took place using fully demineralized water in countercurrent mode. For drying, a contact dryer was used, which reduced the humidity to 10.5%.

Using these fibers, a multifilament fiber consisting of single fibers was produced. A non-twisted fiber thread was made from the multifilament fiber. The fibers can be used to make webs. The linear density of the yarn produced was 20 to 200 dtex, preferably 50 to 150 dtex.

Further details of the manufacturing method can be found in US 4,246,221, WO 02/18682 A1 and WO 02/72929 A1.

The fibers in Comparative Examples 1-3 were made using conventional methods, lyocell fibers were made using an experimental setup as described for Example 1, except for not using a flame retardant component.

Comparative Examples 1 and 2 show that, even without the addition of a flame retardant, the viscose and copper ammonium fibers do exhibit completely unsatisfactory properties. On the other hand, the flame retardant lyocell fibers do exhibit satisfactory properties even though their mechanical properties are somewhat inferior compared to the non-flame retardant lyocell fibers in Comparative Example 3. However, the properties of the flame retardant lyocell fiber according to the present invention are significantly better in compared to non-flame retardant viscose and copper ammonium fibers. Comparative examples using other types of cellulose fibers suffer from a significant imbalance of mechanical properties such that no dimensionally stable products can be made from said fibers. At the same time, the flame retardant fibers of the present invention, in addition to exhibiting very satisfactory flame retardant properties, also exhibit an excellent balance of mechanical properties.

Flame retardant lining

A multifilament yarn containing 40 fibers having a total linear density of 90 denier, which corresponded to 100 dtex, and obtained using a flame retardant lyocell fiber according to the present invention, was made into a backing web with a basis weight of 75 g/m ² . This backing web was used in a three-layer product containing a moisture barrier layer (laminate, 148 g/m ² , 50% meta-aramid/50% Lenzing flame retardant (flame retardant viscose staple fiber)/polyurethane membrane), outer web (260 g/m ² ; 50% flame retardant material Lenzing, 38% para-aramid, 12% polyamide) and the aforementioned backing fabric (100% flame retardant lyocell fiber) were evaluated with respect to flame retardant properties. The three-layer product passed the flame propagation test according to procedure A of EN ISO 15025: 2002 (flame test on the outer web and flame test on the backing web) and fully met all the requirements according to EN 469 (EN 533 index 3).

Claims (21)

1. A flame retardant filament containing a flame retardant based on compounds containing nitrogen and phosphorus and cellulose, and characterized in that the filament is a lyocell filament in which the amount of the flame retardant is in the range of 10 to 40 mass%, and that that the flame retardant filament has an average dry strength of at least 22 cN/tex and an average wet strength of at least 11 cN/tex. 2. The method of manufacturing a flame retardant filament according to claim 1, including obtaining a composition containing wood pulp, NMMO, water and a flame retardant, and a spinning solution for making filaments, in which the amount of flame retardant and wood pulp in the spinning solution is in the range from 12 to 25 wt.% spinning solution and the spinning speed is in the range of 250 to 750 m/min. 3. The method of claim 2, wherein the wood pulp contains sulfite and sulphate pulp. 4. The use of a fire-resistant filament according to claim 1 or a fiber made according to any one of paragraphs. 2, 3, for the manufacture of thread, fabrics and textiles. 5. Use according to claim 4, wherein the flame retardant filament is mixed with other types of fibers. 6. Application according to claim 4, meeting the requirements according to the classification of EN ISO 14 116 "limited flame spread index 3" when examined by method B according to EN ISO 15025:2002 - edge ignition. 7. Use according to claim 4, wherein the flame retardant filament contains a resin sizing. 8. Textile product containing a fire-resistant filament according to claim. 1 or a fiber made according to any one of paragraphs. 2, 3. 9. Textile product according to claim 8, in which the flame retardant filament is mixed with fibers of other types. 10. Textile item 8, meeting the requirements according to the classification of EN ISO 14 116 "limited flame spread index 3" when examined by method B according to EN ISO 15025:2002 - edge ignition. 11. Textile product according to claim 8, which is a multifilament thread. 12. Textile product according to claim 8, in which the flame retardant filament contains a resin sizing. 13. A thread containing a flame retardant filament according to claim 1 or a fiber made according to any one of paragraphs. 2, 3. 14. Thread according to claim 13, in which the flame retardant filament is mixed with fibers of other types. 15. Filament according to claim 13, meeting the requirements according to the classification of EN ISO 116 "limited flame spread index 3" when examined by method B according to EN ISO 15025:2002 - edge ignition. 16. The thread according to claim 13, which is a multifilament thread. 17. Thread according to claim 13, in which the flame retardant filament contains a resin sizing. 18. Cloth containing a fire-resistant filament under item 1 or a filament made according to any one of paragraphs. 2, 3. 19. A fabric according to claim 18, wherein the flame retardant filament is mixed with other types of fibers. 20. The blade according to claim 18, which meets the requirements according to the classification of EN ISO 14 116 "limited flame spread index 3" when examined by method B according to EN ISO 15025:2002 - edge ignition. 21. The fabric according to claim 18, wherein the flame retardant filament contains a resin sizing.