EP2664697B2 - Flame retardant cellulose regenerated fibers and process for their preparation - Google Patents

Description

The invention relates to a regenerated cellulose fiber, and a process for its preparation. WO 2011/026159 A1 discloses flame retarded cellulose regenerate fibers having increased strength properties.

The invention provides a flame-retarded cellulosic regenerate fiber having good dry strength properties according to claim 1. Further preferred embodiments and method aspects are specified in the following claims.

First, further explanations of the invention or the environment of the invention will be given. These include a process for the production of regenerated cellulose fiber, in particular a multifilament fiber, in which the viscose is still added a solid before wet-spinning, and in the after the at least partially coagulating the filaments in the spinning bath following the extrusion of the dope still a stretching in the secondary bath takes place, from which the filaments are withdrawn at a final take-off speed.

It has been found that multifilaments produced by this process from viscose either no longer meet the modern textile requirements with regard to their strengths or otherwise, if they meet the requirements with regard to the achievable strengths, difficulties arise in the further processing of the multifilament yarns into textile structures, especially if The multifilament is to be used as a warp material.

Fiber products currently being used are based primarily on staple fiber yarns using the Lenzing FR fiber, particularly due to market shortages. However, these staple fiber yarns are only of limited suitability for use as warp material.

A further aspect is to develop a method as mentioned above so that the further processability of the fiber products produced therewith improves, in particular with regard to use as a warp material, in particular for the production of high-quality textile products for use, for example, as protective clothing.

A refinement is preferably characterized in that a dimensionless first parameter formed from the quotient of the draft dimensioned in percent and the final take-off speed formed in meters per minute is less than 2.5, preferably less than 2.0, in particular less than 1, 67th

In this context, it has been recognized that on the one hand the addition of solids (for example, a flame retardant) and on the other hand by the drawing in the second bath (B-bath) using known process parameters there is a risk of increased brittleness of the fibers produced, which is directly negative the surface properties of the fibers and yarns produced. By contrast, with the choice of the first parameter according to the invention, improved surface properties of the fibers produced are achieved, in particular smoother fiber surfaces, despite solids addition and strength achieved by stretching.

In this way, it is no longer necessary, economically and ecologically unattractive countermeasures in the form of additional, the surface temporarily modifying operations such. To apply sizing and scouring oils.

Microscopically, fractures of individual capillaries as a result of spins are a major cause of a deteriorating surface quality, which is manifested in the form of thick spots on the yarn and commonly referred to as lint. In the course of the downstream textile operations, e.g. when twisting, weaving or knitting, they increase in size continuously. Due to the mechanical stress of the yarn due to friction at e.g. Pulleys, eyelets, pegs, etc. can defer these loose capillaries, whereby the lint gradually increase in size.

Quantitatively, the surface quality of the continuous fiber can thus be determined by the number of lint per unit of mass of the fiber, for example per 1000 meters of length (or per kilogram of yarn). In the present framework, the number of lint per 1000 meters means the number of detectable by a meter defects on the yarn per 1000 meters in length, a single broken single filament may already cause such a defect, however, two or more broken at the same point individual capillaries can not be counted twice or more times. A suitable measuring device is, for example, an Elkometer III from the company Textechno.

By the method preferred according to the invention, upper limits for an untwisted yarn of 4 lint / 1000 meters, but also 2 lintels / 1000 meters, even 1.5 lintels / 1000 meters can be achieved and maintained. This is also possible with spun-in pigments in an amount of more than 15%, in particular also in the range of 18% to 25%, these percentages referring to percentages by weight based on the α-cellulose. Furthermore, with the method preferred according to the invention, it is also possible to achieve twisted yarns with fluff values of 1 flute per 1000 meters or less, in particular 0.6 fluff per 1000 meters or less, even with a spun-on phosphorus-containing flame retardant with a phosphorus content based on cellulose from 3% to 4% and in industrial production.

To illustrate this dimensionless first parameter, the following short example can be used. For example, the second bath is stretched by 80% at a final take-off speed of 70 meters / minute. Then the first parameter is 80/70 = 1.14.

The first parameter is preferably greater than 0.75, in particular greater than 1.0. Also, the first parameter may be more preferably less than 1.5, preferably less than 1.33, in particular 1.25. This makes it possible to produce particularly good surface properties of the fibers.

Preferably, a dimensionless second parameter, which is not formed from the quotient but from the product of the two variables as the first parameter, is in the range from 3200 upwards, preferably greater than 3600, in particular greater than 4000, but preferably in the range of less than 8000 , preferably less than 7500, in particular less than 7000.

In this context, it is provided that at least a value of 40 m / min, preferably at least 50, more preferably at least 60 and in particular at least> 65 m / min is achieved as the absolute value for the final take-off speed. With regard to drawing, it is intended to draw by at least 60%, preferably by more than 70%, but preferably by not more than 120%, in particular not more than 100%.

In a further advantageous embodiment of the invention, the titer of the multifilament formed is specifically taken into account. It is provided that a dimensionless third parameter formed from the quotient of the second parameter and the root of the titer of the multifilament measured in dtex is not smaller than 300, preferably greater than 330, more preferably greater than 360, and in particular greater than 400. The titer specification refers to the total titer of the multifilament, this is 225, for example, and the second parameter is 6300, the third parameter is 420. However, these values of the third parameter relate primarily to multifibers with a total denier of 330 dtex or Less, but can also be used for slightly higher titers to about in the range of 600 dtex. In principle, however, for total titers of greater than 330 dtex, in particular of greater than 600 dtex or even greater than 900 dtex, a lower limit for the third parameter of 160, in particular 200, is preferred.

As the upper limit of the third parameter thus formed, the value 680 is preferable. More preferably, the third parameter should be 600 or smaller, more preferably less than 530 and in particular less than 500.

With regard to the amount of solids added, the total amount of such water-insoluble pigments, based on the percentage of α-cellulose, should preferably not exceed 25%. It is further preferred that the sized in meters per minute Endabzugsgeschwindigkeit under the curve 95 is - 0.016 x scroll ^{2 to} 0.025 x ^2, preferably under the curve 90th

With regard to applications which require fire resistance of the structures produced from the fiber, a phosphorus-containing flame retardant is preferably added as solid. The addition is preferably carried out by adding a dispersion of the particles. In particular, the addition may be made to the otherwise ready-to-spin mass. The above-mentioned dispersants can also find application here.

With regard to the total titer of the multifilament fiber, a fiber thickness of not less than 60 dtex is preferred. Further, it is preferable that the total titre of the fiber is not larger than 2500 dtex. With respect to the Kapillartiter a range of 1.8 to 2.6 dtex is considered to be preferred, in particular in the range of 2.2 to 2.6 dtex, the latter being particularly advantageous for Gesamtgarntiter of less than 330 dtex. As the average diameter of the single fiber, a range between 10 and 30 microns, preferably between 11 and 20 microns is considered advantageous.

Furthermore, it is preferably provided that the amount x _{FR of} the phosphorus-containing flame-retardant solid is metered in at a given total titer T of the multifilament in such a way that it relates in percent to the α-cellulose above 16.5 + (290-T) / 90, preferably above 17 + (290-T) / 90, and especially below 19 + (290-T) / 90, more preferably below 18.5 + (290-T) / 90. In particular, the flame retardant recited in claim 10 is intended. These quantities for x _FR are primarily for total titers in the range of 330 or less. For total titers in the range of 330 or greater, x _{FR should} preferably be in the range of 17.5 to 19.0%.

Furthermore, under this aspect, a viscose spun and twisted multifilament is proposed, which was produced in particular according to one of the method aspects described above, and in which a number of flakes of 2 flakes per 1000 meters in length is not exceeded, preferably a number of flutes of 1 flute per 1000 meters, in particular of 0.5 lint per 1000 meters, and on the other hand, a phosphorus content based on the α-cellulose of 2.8% or higher, preferably 3% or higher, in particular 3.2% or higher and 4.2% or less, preferably 4% or less, more preferably 3.8% or less. The twisting takes place on suitable twisting machines, for example and preferably on ring twisting machines of the brand Ratti on S500.

In particular, it is preferred that an upper limit for the product of fluff number per 1000 meters in length and in terms of α-cellulose in percent phosphorus content is not greater than 8, more preferably not greater than 6, even more preferably not greater than 4, and in particular not greater than 3.

Dry tensile strengths in the conditioned state in the range of over 25 cN / tex are achieved for the finished fiber. Furthermore, after the initial shrinkage (first to second washings), the fabric produced therefrom remains under 5% further shrinkage after another 50 washes.

The wet strength and thus also the wash resistance of the produced multifilament can be indicated, for example, by the Chord modulus, wet in the twisted state cN / tex with the extension points E1 = 4% and E2 = 3.5%, as in the BISFA, Testing Methods for Viscose, Cupro, Acetate, Triacetate, and Lyocell Filament Yarns, 2007 Edition, Chapter 7 (7.6.1.3). It is preferred that the product of the chord modulus thus measured in cN / tex be in the range of not less than 280, preferably not less than 320, more preferably not less than 360, with the square root of the denier of the fiber expressed in dtex Furthermore, this product should preferably not exceed 560, more preferably 520 and in particular 480 do not exceed. These product values apply in particular to fibers with a total titer of 330 dtex or less. In absolute terms, the chord modulus should preferably be at least 20 cN / tex for yarn titers ≥ 200 dtex, and at least 30 cN / tex for yarn titers of 120 dtex or less.

The roller temperature of the drying rollers is in this second aspect of the invention preferably in the range of 40 ° C or higher, preferably 45 ° C or higher, in particular 50 ° C or higher, and preferably 95 ° C or lower, preferably 80 ° C or lower, in particular 70 ° C or lower.

Particularly preferred pulp of the viscose is a pulp having an intrinsic viscosity of greater than 560 ml / g and an α-cellulose content of greater than 97.5%, in particular monomodal molecular weight distribution, in particular a kraft-softwood pulp. The intrinsic viscosity should be determined according to ISO / FDIS 5351: 2009 (Limiting Viscosity Number [η]).

It should be noted that regenerated cellulose fibers represent a thoroughly high-quality base material for flame-resistant fibers, since it can be equipped excellent flame-resistant per se known techniques. Because they are able to absorb large amounts of moisture as a hydrophilic, non-thermoplastic polymer.

In particular, they have advantages of naturally occurring cellulosic fibers such as cotton, with the added advantage that they are permanently flame resistant by the addition of flame retardants in the spinning solution, and not just on the surface, such as cotton.

For achieving desired strengths, preference is given to using pulps with very high purities; preference is given in particular to the use of a pulp having a monomodal molecular weight distribution.

In principle, the use of the lyocell method (direct dissolution method with NMMO as solvent) is possible, but very high strengths at a low fibrillation tendency are preferably achieved with the viscose method in its form as a filament spinning method, as described above. Thus, the inherent strength properties of cellulose can be utilized optimally.

On the one hand, a high degree of stretching can be advantageous here, but on the other hand drying in a non-relaxed state can also be advantageous. The resulting micro-morphology, degree of crystallization and degree of alignment of the elemental cellulose strands may be advantageous for high strength properties.

For the spinning of staple fibers, it is preferable to assume a certain roughness of the surface as well as sufficient crimping / bending / twisting of the staple fibers. In order to achieve these properties, staple fibers are formed by first producing endlessly produced fibers in a wet spinning process, then cutting them in a moist state and drying them later in a relaxed state.

In the context of the invention, however, it has been recognized that, on the one hand, spinning from staple fibers is still possible with sufficient reliability, even if these are produced from already dried filament yarn. This is surprising, since the fibers thus produced have a rather smooth and even surface and are at most slightly curled, so that staple fibers of this kind are considerably less suitable for further processing than the staple fibers usually cut in the moist state. However, it has been recognized that this disadvantage in spinnability is otherwise compensated for by surprisingly transferring strength properties of the filaments at least partially to the staple fibers as they are produced from already dried filaments. In particular, by stretch breaking of the filaments ("stretch-breaking") particularly good strength properties are produced. These become noticeable in particular by a significantly higher specific maximum tensile force (achievable 25% improvement) compared to conventional staple fibers, and in particular an improved specific maximum tensile force (40% higher values achievable).

In the stretch-drawing process, the filaments are re-stretched between rolls rotating at different speeds and finally torn. The length of the resulting staple fibers can be adjusted by adjusting the parameters of the stretch-breaking process.

Another preferred feature relates to the volume-to-surface ratio (or cross-sectional area to circumference, as determined by ImageJ Image Analysis Optical Software), which provides fewer targets for mechanical stress as well as heat exposure. In this regard, it has been found that even lower levels of phosphorus in the fiber generated by the incorporation of the flame retardant are conventionally sufficient, thereby creating an ecological as well as an economic advantage. In any case, phosphorus-containing, halogen-free agents such as the above-mentioned Sandoflam / Exolit are preferred.

As already stated, the staple fibers according to the invention are preferably produced by the viscose filament spinning process. This is a Viskosepinnmasse in an acidic spin bath or acidic spinning baths regenerated to cellulose and thereby stretched. The subsequent drying of the filaments thus produced can be done online or offline, wherein preferably the tension in the filaments is maintained. Subsequently, the stretch breakage of the fibers dried in the non-relaxed state can take place.

Preferred individual titers of the yarns according to the invention are in the range between 1.7 and 3.3 dtex, but in particular greater than 2.0 dtex and / or less than 2.7 dtex.

Also protected by the invention is a textile fabric which is produced by incorporation of a cellulose regenerated fiber, in particular a staple fiber or a multifilament, according to one of the properties described above.

Fig. 1

einen schematischen Aufbau für eine Anlage zur Herstellung von Celluloseregeneratfasern,

Fig. 2

eine REM-Aufnahme eines Multifilaments,

Fig. 3

eine Kraft-Dehnungs-Kurve trocken für aus einem Multifilement hergestellte Stapelfasern,

Fig. 4

eine Kraft-Dehnungs-Kurve naß für die Stapelfaser, und

Fig. 5

eine Umrißanalyse der erfindungsgemäßen Fasern im Vergleich zu herkömmlichen Stapelfasern.

In the following the invention will be explained by way of example with reference to the figures of the drawing. From this shows

Fig. 1

a schematic structure for a plant for the production of cellulose regenerated fibers,

Fig. 2

a SEM image of a multifilament,

Fig. 3

a force-elongation curve dry for staple fibers made from a multifilament,

Fig. 4

a force-strain curve wet for the staple fiber, and

Fig. 5

an outline analysis of the fibers of the invention compared to conventional staple fibers.

Based on FIGS. 1 and 2 describes a preparation of a flame-retardant fiber with the peculiarity of a direction of parallel preferred parallel direction preferred for the main particle axes of a flame-retardant entrained solid. However, this is not essential to the gist of the present invention. Rather, the invention shown in particular in the further embodiments is basically independent of the shape and the nature of the spinning of a flame-retardant solid.

From a stirred tank 1 is a dispersion of particles of a flame-retardant solid from a metering pump 2 via a check valve 5 a static

Mixer 6 supplied. In addition, the static mixer 6 is fed via a viscose pump 3 viscose. From the static mixer 6, the mixture of viscose and dispersion formed therein flows into another static mixer 7 and continues to be mixed there.

The flow leaving the static mixer 7 passes through a mass flow meter 8 to a spinning machine in which the cellulose regenerated fiber is spun. A control unit 10 generates in response to the measurement signals of the mass flow meter 8 and 9, a control signal for driving the metering pump 2, by the mass ratio of the two flow rates to a desired value is regulated.

Furthermore, the pressure of the conveyed to the spinning machine flow rate is detected by a pressure sensor 4 and regulated in response to the measurement signal, the delivery rate of the viscose pump 3.

Fig. 2 is an SEM image of a multifilament produced in any case according to the first aspect of this invention. It can be seen, indicated by the arrows, the orientation of the particle main axis in the parallel preferred direction of the fiber.

An example of the realization of preferred feature combinations is given without reference to figures as follows:
In the industrial process a multifilament with titre 200f76 with continuous spinning technology is produced. The spinning mass was added nor the phosphorus-containing flame retardant Viscofil Exolit 5060VP2988. At this point, and also generally for this application, an industrial process is understood to mean a process in which the machine used achieves an hourly production of at least 6 or preferably at least 8, in particular at least 10, kg per hour.

The temperature of the coagulation spinning bath is in the range of 58 to 63 ° C, that of the coagulation bath in the range of 90 to 94 ° C. The addition of the flame retardant is such that a solids content in the yarn (based on the α-cellulose) of 19.8% results.

In the drawing bath is stretched by 85%, the final deduction takes place at a speed of 80 m / min. This results in a first parameter of 1.06.

The dimensionless second parameter is 6800 and the dimensionless third parameter is 480.

The phosphorus content of the fiber relative to the α-cellulose is in the range of 3.5%. Nevertheless, in the conditioned state, the fiber retains a dry tensile strength in the range of 265 to 285 cN / 100dtex.

Despite its good flame retardancy and high strength, this multifilament yarn is twisted (S500) only 0.4 to 0.6 fluff per 1000 meters up. It is therefore ideal for further processing, especially as a warp material.

An embodiment of the invention is based on the Figures 3 and 4 explained. For this purpose, multifilament fibers were cut into staple fibers, for example, as in the example described above. The strength properties of these staple fibers result from the in the Figures 3 and 4 illustrated force-strain curves ( Fig. 3 : dry, Fig. 4 : wet). In these figures, the abscissa indicates the relative elongation in percent and the ordinate the force measured in cN / tex.

How out Fig. 3 shows that the zero slope of the measured values is higher than the slope after reaching an elongation force of about 10 cN / tex. In the following range, despite the decrease in pitch, excellent strength properties continue to exist, and an average slope here is 2 cN / tex /% in the range of 2 to 7% relative elongation. In terms of force, this range corresponds to values between about 10 and 20 cN / tex. In this regard, the strength properties are significantly better than comparable commercially available products such as the products already mentioned above.

Further goes out Fig. 4 show that the exemplary staple fiber also has advantageous wet strength properties, in particular a very high force required to rupture the fiber, which exceeds the conventional fibers by more than 40%.

The the Figures 3 and 4 underlying curves were carried out for 1.81 dtex titer fibers on a FAVIGRAPH with a gage length of 20.00 mm, a test speed of 20.0 mm / min, a pretensioning weight of 100.00 mg, a preload of 0.60 cN / tex for the given nominal fineness. Overall, the presentation includes the Figures 3 and 4 fifty attempts.

Finally, in Fig. 5 still shown that the staple fibers of this embodiment of conventional fibers also differ in their structure. In the Fig. 1 Fibers shown on the right have a more favorable surface area to volume ratio than conventional flame resistant staple fibers.

Further data for an exemplary embodiment of a fiber are: Titer / dtex cutting length Strength [cN / tex] Strain [%] Firmness wet [cN / tex] LOI% 1.8 50mm 30 14% 20 28

Another embodiment is a staple fiber yarn 200 dtex of 70% Viscont FR staple fiber and 30% m-aramid (Conex): Titer / dtex Firmness [cN / tex] Strain [%] Firmness wet [cN / tex] 200 17.4 9.2 13.9

The invention is not limited to the features shown individually in the embodiments. Rather, the features of the following claims and the foregoing description, alone or in combination, may be essential to the practice of the invention in its various embodiments.

Claims (15)

1. Flame-retardant regenerated cellulose fibres, in particular staple fibres, and in particular produced by the viscose process, with increased dry strength properties in the form of a force required in the range of between 2 and 7 % relative extension average percentage extension of 1.4 cN/tex or more, preferably at least 1.6 cN/tex or more, more preferably at least 1.8 cN/tex or more and in particular at least 2.0 cN/tex or more.
2. The regenerated cellulose fibres according to Claim 1 with a maximum tensile force (dry) of 26 cN/tex, preferably of at least 28 cN/tex, more preferably of at least 30 cN/tex.
3. The regenerated cellulose fibres according to Claim 1 or 2, with a maximum tensile force (wet) of at least 15 cN/tex, preferably at least cN/tex, in particular at least 20 cN/tex.
4. The regenerated cellulose fibres according to any of the preceding claims, wherein the flame-protection effect is provided by spinning in a flame protection means that is in particular phosphoric, a phosphorus content contained in the fibre in relation to the cellulose not exceeding 3.4 %, preferably not exceeding 3.2 %, in particular not exceeding 3.0 %.
5. The regenerated cellulose fibres according to any of the preceding claims, with a ratio of average cross-sectional area counted in pixels to average circumference counted in pixels of 16.6 or less, preferably 16.2 or less, in particular 15.8 or less.
6. The regenerated cellulose fibres according to any of the preceding claims, which are produced from dry filament yarn.
7. The regenerated cellulose fibres according to Claim 6, wherein the staple fibres are produced by cutting the filament yarn.
8. The regenerated cellulose fibres according to Claim 6, the staple fibres being produced by stretch breaking from the filament yarn.
9. The regenerated cellulose fibres according to any of Claims 6 to 8, wherein the length of the staple fibres comes within the range of between 30 and 150 mm.
10. The regenerated cellulose fibres according to any of the preceding claims, in the manufacture of which a quotient of the extension measured as a percentage in the second bath after precipitation in the spinning bath and the final removal speed from the second bath measured in metres per minute is less than 2.5, preferably less than 2.0, in particular less than 1.67.
11. A staple fibre yarn, comprising a regenerated cellulose fibre according to any of Claims 1 to 10 in the form of a staple fibre, and another mixture partner preferably made of aramid fibre, the proportion of regenerated cellulose fibre preferably being at least 20 % by weight (in relation to the yarn), more preferably at least 50 % by weight, particularly preferably at least 70 % by weight.
12. A textile fabric, produced by the incorporation of a regenerated cellulose fibre, in particular a fibre and/or a yarn according to any of Claims 1 to 11.
13. A process for the production of regenerated cellulose fibres according to claim 1, wherein filaments produced by the viscose filament spinning process are dried on-line or off-line, preferably by maintaining the tension in the filaments, and staple fibres are produced from the dry filaments.
14. The process according to Claim 13, wherein viscose is mixed in a specified proportion after the addition of a solid, and the mixture produced in this way is wet spun according to specific parameters and is extended in the spinning bath in a second bath after precipitation and is finally removed from the latter, a dimension-free first parameter formed form the quotient of the extension measured as a percentage and the final removal speed measured in metres per minute being less than 2.5, preferably less than 2.0, in particular less than 1.67.
15. The process according to Claim 13 or 14, wherein the staple fibres are produced from the multifilament in the dry state by cutting or stretch breaking.

Images