FLAME RETARDANT LYOCELL FILAMENT

Description

[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

[0002] 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. 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 11, 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.

[0008] 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.

[0009] 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.

[0010] 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

[0011] 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.

[0012] As indicated above, the filaments of the present invention are FR filaments, i.e. filaments incorporating flame retardants. 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.

[0013] 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.

[0014] 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 pretreatments, 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.

[0015] 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

[0016] 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.

[0017] 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 processed depending on the intended use of the FR filaments.

[0018] 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.

[0019] 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.

[0020] The following examples do illustrate the present invention.

Examples

[0021] 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.

[0022] 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.

[0023] 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 11.6 % 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).

[0024] The spinning solution was filtered and extruded at 114°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.

[0025] After crossing the air gap, the cellulose precipitated in a spinning bath containing 10 % NMMO, the rest being water.

[0026] 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 %.

[0027] 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.

[0028] For other details of the manufacturing process, reference is made to US 4,246,221, WO 02/18682 A1 and WO 02/72929 A1.

[0029] 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.

[0030] The respective properties are reported below:

	Example 1
Material	Lyocell filament (FR)
Min dtex	1,36 dtex
Max dtex	2,31 dtex
FFk	33.2 cN/tex
FFn	19.5 cN/tex

	Comparative Example 1	Comparative Example 2	Comparative Example 3
material	Viscose (Non FR)	Cupro (Non FR)	Lyocell Filament (Non FR)
Min 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

[0031] 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

[0032] 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 retardancy. 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 11 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.

11. 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 11, satisfying the demands according to EN ISO 14 116 classification "limited flame spread index 3" when tested according to EN ISO 15025:2002 Process B - edge flaming.

13. Use or product according to any one of claims 9 to 12, being a multi filament yarn.

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