HIGH STRENGTH CELLULOSIC FILAMENT ITS USE, AND METHOD FOR THE PRODUCTION THEREOF

Abstract

The present invention relates to high-strength, possibly pigment-containing—for example flame-retardant—regenerated cellulosic filaments having improved textile properties, in particular as regards strength and uniformity, to their use for the production of fabrics, and to a method for the production of these filaments.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to high-strength regenerated cellulosic filaments having improved textile properties, in particular as regards strength and uniformity, to their use for the production of fabrics, as well as to a method for the production of these filaments. These high-strength filaments may also contain pigments such as flame-retardant pigments.

Regenerated cellulosic filaments have been known for a long time. They are used particularly for textiles, but in a high-strength form also for technical applications such as tire cords. For the purposes of this invention, the term “regenerated cellulosic fibers” denotes such fibers that are made of a cellulose-containing spinning solution by spinning into a spinning bath (often also referred to as a precipitation bath), the cellulose in the spinning solution being present in the form of a cellulose derivative, in particular as cellulose xanthogenate, while in the precipitation bath a regeneration back into pure cellulose takes place. The regenerated fibers and filaments produced via the xanthogenate are usually referred to as “viscose” or “rayon”. Also the cellulose-containing spinning solution is referred to as “viscose” or also as “viscose spinning solution”. Therefore, the manufacturing method itself is referred to as viscose method.

In principle, viscose processes for staple fibers and continuous filaments have been known for many years and are, for instance, described in detail in K. Götze, Chemiefasern nach dem Viskoseverfahren, 1967. However, the textile properties of the fibers and filaments obtained thereby are influenced significantly by many parameters. In addition, the size of the existing production facilities imposes limits on many influencing variables, which cannot be exceeded for technical or economic reasons, so that arbitrary variations of the parameters are often not even possible and would therefore not occur to those skilled in the art.

In the course of time, different variants of the viscose method were developed and, to some extent, have found industrial use to the present day. The different variants differ mainly in the composition of the spinning solution and of the precipitation bath, which may strongly influence the mechanical properties of the products. Examples thereof are the Modal and the Polynosic fibers which, however, on a commercial scale, are only manufactured in the form of staple fibers. The fundamentals of the Modal method for the production of staple fibers are described in AT 287905. With respect to filaments, it has meanwhile become possible, through technical improvements of machinery, to spin continuously by means of the so-called Continue method, instead of the former discontinuous centrifugal methods.

Today, standard viscose filaments are widely used in the textile and clothing industries, particularly for lining materials. Nevertheless, the usability of viscose filaments for textiles is limited by their low strength, especially in the wet state, by their high elongation, and by their high area shrinkage. More specifically, they do not permit the production of lightweight, i.e., thin, yet strong textiles that can also be washed without problems. In addition, they are not suited for more heavily stressed textiles, e.g. work clothing and uniforms, either. While, in this case, there exist some possible solutions with synthetic filaments, for example filaments made of polyester or polyamide, these are, especially when it comes to wearing comfort, significantly inferior to cellulosic materials. Therefore, there continues to exist a need for high-strength cellulosic filaments for textile applications, which cannot be produced cost-effectively using the known methods.

A known, commercially available, regenerated high-strength filament is CORDENKA®, for example, which is produced by a modified viscose method. It is produced with single-fiber titers of approx. 1.8 dtex and strengths (conditioned) of approx. 45 to approx. 52 cN/tex. It is used in the technical field to reinforce rubber goods, particularly high-quality vehicle tires. For textile applications, such a filament is too coarse and also too expensive to produce. In this case, especially the compositions of the spinning solution and of the precipitation bath were changed, as compared to standard viscose.

Generally, it has also been known for a long time to spin various pigments into regenerated cellulosic fibers, especially into fibers obtained using the viscose method. In that case, the pigments may be flame-retardant pigments, especially phosphorus-based pigments, or also colorants and matting agents, respectively. Such pigment-containing viscose fibers are produced worldwide with a single-fiber titer between 0.8 and 16 dtex for standard applications in the textile and nonwovens sectors. In this context, the pigments are added to the cellulose-containing spinning solution using suitable dosing devices. Then, this pigment-containing spinning solution is extruded through spinnerets and precipitated and subjected to further treatment according to the known methods. The pigments introduced into the fibers in this way are very firmly embedded and can for example not be washed out using conventional washing processes.

The relevant literature describes various chemicals that can be used to provide viscose fibers with a flame-retardant finish. It is mainly flame retardants based on halogens, silicon, and phosphorus that are used for this purpose.

Patents DE4128638A1 or DE102004059221A1 describe flame retardant dispersions based on a 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide, using various dispersing agent systems, and they also mention the use of these dispersions for providing viscose fibers with a flame-retardant finish.

EP1882760 also describes the production of flame-retardant viscose fibers by using flame retardant dispersions based on a 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide. It is described therein that an important feature of the invention is that the particle size must not be greater than 10 μm and that, prior to spinning, the spinning dope must therefore be cleaned using filters having a maximum mesh width of 10 μm. However, it has been found that this criterion is not enough to manufacture fibers that satisfy the requirements described herein. The maximum particle size of 10 μm described in EP1882760 may perhaps be sufficient for continuous viscose filaments or monofilaments having a large titer, however, it does not nearly satisfy the demands of a modern staple fiber production involving fiber fineness levels of approx. 1 to 4 dtex; a 1.3 dtex fiber has a diameter of approx. 10 μm.

The fibers that are described in prior art documents or are commercially available are all produced by means of standard viscose methods. In fact, they feature comparatively good mechanical fiber properties for flame-retardant viscose fibers, as the phosphorus contents are very low. However, studies with various phosphorus-based flame retardants have shown that a sufficient flame-retardant activity is only achieved starting from phosphorus contents greater than 2.8%. In this case, the flame-retardant capacity correlates well with the content of retardant agent, converted into pure phosphorus.

It was found, however, that for example the incorporation of large quantities (15-25%) of a flame-retardant pigment caused a further deterioration of the textile parameters of the viscose fiber. Therefore, the limitations of usability already mentioned in connection with standard viscose fibers apply even more so to flame-retardant viscose fibers.

This is all the more regrettable, as flame-retardant fibers could be used to particular advantage in products that are also exposed to high mechanical stresses, for example, in the work clothing used for particularly dangerous activities such as in fire brigades, foundries, in the military, and in the petroleum and chemical industries. For such products, usually synthetic high-performance fibers such as (aromatic) polyamides, aramides, polyimides, and the like are already being employed. These fibers, however, offer a low wearing comfort, as they are unable to absorb moisture to a sufficient extent. It would therefore be desirable to have a mixture of these fibers with cellulosic fibers that add enhanced wearing comfort to the spectrum of properties without causing the remaining properties to deteriorate significantly.

It has also been known to spin color pigments or matting agents, particularly titanium oxide, into regenerated cellulosic fibers. In this case, the same problems will generally emerge because of the solids content. The problems described here caused by spinning in of larger quantities of solids apply to viscose staple fibers, however, even more so to viscose filaments.

WO 2011/026159 A1 discloses a method for the production of flame-retardant cellulosic staple fibers, which is supposed to solve these problems. The fiber described therein contains a spun-in particulate phosphorus compound serving as a flame-retardant substance, preferably an organophosphorus compound, and has a so-called use value between 6 and 35, preferably between 8 and 35, and more preferably between 10 and 35. Such a fiber was produced for the first time by means of a modified viscose process.

For the production of the fibers described in WO 2011/026159 A1, a cellulose concentration of 4-7%, when using a pulp having an R-18 content of 93-98%, and an alkali ratio (=cellulose concentration/sodium hydroxide concentration, each in g/l) from 0.7 to 1.5 have been found to constitute the ideal conditions. However, because of the addition of the flame-retardant FR pigment, the spinning parameters must be adapted accordingly.

Therefore, WO 2011/026159 A1 also describes a method for the production of a flame-retardant regenerated cellulose fiber for textile applications by spinning a viscose containing 4 to 7% cellulose, 5 to 10% NaOH, 36 to 42% (related to cellulose) carbon disulfide as well as 1 to 5% (related to cellulose) of a modifier into a precipitation bath, withdrawing the coagulated threads, a viscose being used whose spinning gamma value is 50 to 68, preferably 55 to 58, and whose spinning viscosity is 50 to 120 falling ball seconds; and that the temperature of the precipitation bath is 34 to 48° C., where

a. the alkali ratio (=cellulose concentration/alkali content) of the ready-to-spin viscose is 0.7 to 1.5;

b. the following precipitation bath concentrations are used:

• • H₂SO₄ 68-90 g/1
  • Na₂SO₄ 90-160 g/1
  • ZnSO₄ 30-65 g/1

c. the final withdrawal from the precipitation bath takes place at a velocity between 15 and 60 m/min; and

d. a pigment-type organophosphorus compound in the form of a pigment dispersion is spun in as a flame-retardant substance.

Conveniently, a viscose is used to which the modifier has been added only shortly before the viscose is spun.

Together, the measures proposed in WO 2011/026159 A1, that is, to comply with a certain spinning ripeness represented by the spinning gamma value, to comply with a certain viscosity represented by the falling ball values, and to comply with certain conditions in the precipitation bath, bring about the envisaged fiber properties. The spinning gamma value denotes the proportion of carbon disulfide molecules bonded to 100 cellulose molecules. The spinning gamma value is determined according to the Zellcheming Draft Leaflet by R. Stahn [1958] and to Leaflet III/F 2, respectively. The falling ball is used in the falling ball method to determine viscosity; it is expressed in falling ball seconds. The determination is described in K. Götze, Chemiefasern [1951], p. 175.

The flame-retardant phosphorus compound that is produced as a pigment is, according to WO 2011/026159 A1, added to the viscose spinning solution in the form of a pigment dispersion. In this case, so much of the flame-retardant substance is spun in that the finished fiber contains at least 2.6%, preferably between 3.2% and 6.0%, more preferably between 3.5% and 6.0% phosphorus, related to cellulose.

As has already been explained hereinabove, a flame-retardant organophosphorus compound that is particularly well suited for the purposes of the present invention is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide.

The quality of the pigment dispersion, in particular, also has a significant influence on fiber properties. This quality depends on the average and maximum particle sizes of the pigments, on the concentration of the dispersion in use, i.e., when adding it to the viscose spinning solution, as well as on the type and the quantity of the dispersing agents.

Contrary to the possible upper particle size of 10 μm described in the patent EP1882760, it has been found that an average particle size (x₅₀) of less than 1 μm and a maximum particle size (x₉₉) of less than 5 μm, preferably of less than 3 μm, are necessary. FIG. 3 shows a size distribution of a pigment dispersion that is still suitable.

Preferably, according to WO 2011/026159 A1, the pigment dispersion should contain between 10 and 50% of the flame-retardant substance.

Most prior art documents do not describe the influence of the dispersing agent in such detail as would be appropriate. Many chemicals, even though they provide an excellently stabilized flame retardant dispersion, have a negative impact on the spinning process because they, while also causing a modifying effect in the viscose thread, do not positively influence the fiber strength as opposed to the modifiers used. Dispersing agents that have been found to be ideal for the flame retardant dispersion used to produce the inventive fibers and do not adversely influence the fiber strength are especially those that were selected from the group comprising modified polycarboxylates, water-soluble polyesters, alkyl ether phosphates, end-group-capped nonyl phenol ethoxylates, castor oil alkoxyl esters, and carboxymethylated alcohol polyglycol ethers. Preferably, the pigment dispersion should contain between 1.5 and 13% of the dispersing agent.

WO 2011/026159 A1 relates expressly to the production of staple fibers. Since they usually have a cutting length between approx. 25 and 90 mm and are mixed thoroughly several times prior to their final use in textiles, minor differences in the uniformity of the individual fibers as well as small spinning faults do not play a significant role in their production. The situation is entirely different in the production of (continuous) filaments for textile or technical applications. They are usually spun out in thin filament bundles of approx. 10 to 2000 individual filaments and reeled up directly. It takes approx. 48 hours until a reel is full. Even if due to a spinning fault only one individual filament ruptures during these 48 hours, this will have a significant impact on product quality and thus on the obtainable price. In addition, the filaments are naturally no longer mixed during their use so that any irregularities of the filaments become clearly visible, for example in textiles. This also affects the product quality and thus the obtainable price.

Summing up, regenerated cellulose filaments that have high strength but excessively coarse titers are known in the state of the art, as are textile filaments that, even though they are so fine that they offer a textile wearing comfort, provide only low strength. In particular, no textile regenerated cellulose filaments are known that, while featuring high strength, also contain such a high proportion of pigment such as flame-retardant pigment that they actually exhibit good flame-retardant properties.

SUMMARY OF THE INVENTION

Surprisingly, it was possible to solve this problem by using regenerated cellulose filaments that have a pigment content of more than 20 wt % as well as a strength (conditioned) greater than 22 cN/tex.

These pigments are used to incorporate desired additional functionalities into the filaments. This may be, for example, flame retardation, a durable coloration, or a matting effect. Yet, for special products, other additives can be used that, for example, provide for extremely good visibility or an extremely good warning effect, electrical conductivity, the absorption of pollutants, or radiographic visibility (e.g. for surgical suture yarns). Generally, all such solids are suited for use as pigments that, under the conditions in the viscose spinning solution, i.e., strongly alkaline and CS₂-containing, and in the strongly acidic precipitation bath, will not undergo any undesired changes, especially that they will not go into solution, either partly or entirely. Substances that, in a strongly alkaline environment, are present in a dissolved form and that, only in the acidic precipitation bath, pass into the form of a solid aggregate constitute a conceivable exception. In particular, in this case, the pigment is selected from the group comprising flame-retardant, colored, fluorescent (“high-vis” colorants), and radiographically detectable pigments. The present invention shall also expressly encompass mixtures of these pigments for a combination of several properties in the same filament, for example the combination of color pigments, high-vis color pigments, and flame-retardant pigments for use in light-fast, warning-colored, flame-retardant clothing for fire brigades and rescue services.

The described advantageous mechanical properties of the inventive pigment-containing regenerated cellulose filaments are achieved with particular reliability if the pigment has a particle size distribution with x₅₀ at less than 1.0 lam and x₉₉ at less than 5.0 μm, preferably at less than 3.0 μm.

The object resulting from the state of the art can be achieved particularly well and in a surprising manner if the inventive regenerated cellulose filaments have a fine single-fiber titer of between 0.4 and 4 dtex, preferably of between 0.8 and 3.0 dtex. So far, it had not been possible to produce such fine regenerated cellulose filaments with the above described strengths, especially if they contained sufficient quantities of pigment.

Preferably, the spun-in pigments have a particle size distribution with x_so at less than 1.0 μm and x₉₉ at less than 5.0 μm, preferably at less than 3.0 μm.

The preferred organophosphorus compound used is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide (Formula I). This substance is available in sufficient quantities, for example, under the trade names Exolit and Sandoflam, and it is not washed out of the fibers during the manufacturing process and also during their subsequent use:

In a preferred embodiment, the inventive filament contains at least 2.8%, preferably between 3.2% and 6.0%, more preferably between 3.5% and 6.0% phosphorus, in each case related to cellulose. Lower phosphorus contents than 2.8% do not yield a sufficient flame-retardant effect. Higher phosphorus contents than 6% cause the mechanical properties of the filaments to deteriorate and are also no longer cost-effective.

Most prior art documents do not describe the influence of the dispersing agent in such detail as would be appropriate. Many chemicals, even though they provide an excellently stabilized flame retardant dispersion, have a negative impact on the spinning process because they, while also causing a modifying effect in the viscose thread, do not positively influence the fiber strength as opposed to the modifiers used. Dispersing agents that have been found to be ideal for the flame retardant dispersion used to produce the inventive regenerated cellulose filaments that do not adversely influence the fiber strength are especially those that were selected from the group comprising modified polycarboxylates, water-soluble polyesters, alkyl ether phosphates, end-group-capped nonyl phenol ethoxylates, castor oil alkoxyl esters, and carboxymethylated alcohol polyglycol ethers. Preferably, the pigment dispersion should contain between 1.5 and 13% of the dispersing agent.

Another object of the present invention is a non-pigmented regenerated cellulose filament that has a strength in the conditioned state of greater than 36 cN/tex. Preferably, also the inventive regenerated cellulose filaments have a fine single-fiber titer of between 0.4 and 4 dtex, more preferably of between 0.8 and 3.0 dtex.

A regenerated cellulose filament having such high strength and fineness is well suited for processing into woven fabrics and other textile fabrics that—compared to standard viscose filament which has a strength of approx. 20 cN/tex—have extraordinarily high abrasion resistance. Hence, it is particularly well suited for use in sports, for example for motorcycle garments, karting garments, and sportswear. In this context, abrasion resistance particularly refers to the property measured in the Martindale abrasion test. Due to the greater temperature resistance as compared to synthetic filaments such as polyester and nylon, the high-strength filament is also used in many technical applications, e.g., for turbocharger hoses in passenger cars and trucks.

For the purposes of the present invention, both (non-pigmented) filaments having a strength in the conditioned state of greater than 36 cN/tex and pigment-containing filaments having a pigment content of more than 20 wt % and a strength (conditioned) of more than 22 cN/tex shall be referred to as “high-strength”.

When being used, the inventive filaments are not used one by one, but in the form of the filament bundles—also referred to as filament yarn—that are obtained in the spinning process from each of the spinnerets. In the textile sector, a filament yarn usually contains about 30-200 individual filaments. In technical applications, for example for reinforcing car tires, conveyor belts, or other rubber goods, yarns usually contain approx. 700 to 2000 individual filaments.

Another object of the present invention is the use of the inventive filaments for the production of a textile fabric. In addition to the inventive fibers, this fabric may also contain other fiber yarns or filament yarns, for example and in particular, wool, flame-retardant wool, para-aramides (Kevlar®, Twaron®) and meta-aramides (Nomex®), polybenzimidazole (PBI), p-phenyl-2,6-bezobisoxazole (PBO), polyimide (P84®), Polyamidimide (Kermel®), modacrylics, polyamides, flame-retardant polyamides, flame-retardant acrylic fibers, melamine fibers, polyesters, flame-retardant polyesters, polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), glass fibers, cotton, silk, carbon fibers, oxidized, thermally stabilized polyacrylonitrile fibers (PANOX®), elastanes, and electrically conductive fibers, as well as mixtures of these fibers.

Preferably, the fabric is a woven fabric, a knitted fabric, or a crocheted fabric. In the case of a woven or knitted fabric, mixing of the inventive filaments with the further fiber or filament yarns is possible either by mixing prior to the production of the yarn, so-called intimate blending, or by the combined use of pure yarns of the various filament and fiber types for weaving, knitting, or crocheting.

The inventive regenerated cellulosic filaments can be produced using a viscose process modified according to the invention. Therefore, it is also an object of the present invention to provide a continuous method for the production of a high-strength regenerated cellulose filament by spinning of a viscose containing 4 to 8% cellulose, 5 to 10% NaOH, 36 to 42% (related to cellulose) carbon disulfide, as well as 1 to 5% (related to cellulose) of a modifier into a precipitation bath, withdrawing the coagulated filaments, a viscose being used whose spinning gamma value is 50 to 68 and whose spinning viscosity is 50 to 150 falling ball seconds; and that the temperature of the precipitation bath is 34 to 65° C.,

Aa. the alkali ratio (=cellulose concentration/alkali content) of the ready-to-spin viscose being 0.7 to 1.5;

b. the following precipitation bath concentrations being used:

• • H₂SO₄ 68-95 g/1
  • Na₂SO₄ 90-160 g/1
  • ZnSO₄ 30-65 g/1

c. the final withdrawal from the precipitation bath and reeling up taking place at a velocity between 15 and 180 m/min, wherein

d. the filaments coagulated in the precipitation bath are subsequently passed through a second bath, the second bath containing aqueous sulfuric acid, 3-7 wt %, at a temperature of 80-98° C.

By spinning such a spinning solution followed by stretching and fixing in the second bath, one obtains high-strength regenerated cellulosic filaments that, even after the incorporation of flame-retardant or coloring pigments, have filament and/or yarn strengths that are markedly above those of comparable regenerated cellulosic filaments spun from a textile viscose spinning solution according to the state of the art.

Conveniently, a viscose is used to which the modifier has been added only shortly before the viscose is spun.

In the context of the inventive method, “continuous” shall mean that spinning the viscose into the precipitation bath, stretching, washing, drying, and reeling up take place continuously in the same processing step. This is contrasted by the widely used centrifugal spinning methods in the course of which the moist filaments are wound up in centrifuges and these so-called spinning cakes are then washed and dried discontinuously.

Together, the measures proposed according to the invention, that is, to comply with a certain spinning ripeness represented by the spinning gamma value, to comply with a certain viscosity represented by the falling ball values, and to comply with certain conditions in the precipitation bath, bring about the envisaged fiber properties. The spinning gamma value denotes the proportion of carbon disulfide molecules bonded to 100 cellulose molecules. The spinning gamma value is determined according to the Zellcheming Draft Leaflet by R. Stahn [1958] and to Leaflet III/F 2, respectively. The falling ball is used in the falling ball method to determine viscosity; it is expressed in falling ball seconds. The determination is described in K. Götze, Chemiefasern [1951], p. 175.

In order to reliably achieve the high strength of the filaments, it has proven advantageous to use pulp having an α-content of 93-99% as cellulosic raw material. Such pulp has only a small content of low-molecular minor constituents that reduce the strength in the finished filament, on the one hand, and may get into the precipitation bath circuits, on the other, where they may interfere in various ways as contaminants.

An important feature of the inventive method is that the filaments are stretched by 70% to 105% in the second bath. In the state of the art, no second bath is used that contains only aqueous sulfuric acid and has a temperature of 80-98° C., on the one hand, while, on the other hand, upon exit from the precipitation bath, stretching is carried out by only approx. 5% in the Continue spinning method and by approx. 10-20% in discontinuous methods for textile filaments.

This method renders it possible to produce non-pigmented high-strength regenerated cellulose filaments as well as such regenerated cellulose filaments that have a pigment content of more than 20 wt % and a strength (conditioned) of more than 22 cN/tex.

In this context, a surprising connection was discovered between the strength of a non-pigmented regenerated cellulose filament and that of a pigment-containing regenerated cellulose filament if only the pigment content in the filament is changed and the other process parameters are maintained constant:

FFK_P=FFK_R×c_Cell²

wherein FFK_P is the fineness-related strength of the pigment-containing regenerated cellulose filament, FFK_R the fineness-related strength of the non-pigmented regenerated cellulose filament, and c_Cell the cellulose content of the pigment-containing regenerated cellulose filament, related to the dry content of the filament and expressed as a fraction.

For example, in inventive process conditions, in which non-pigmented regenerated cellulose filaments having a strength of 35 cN/tex can be produced, one also obtains pigment-containing regenerated cellulose filaments having a strength of 22 cN/tex and a pigment content of 0.21 (i.e., a cellulose content of 0.79).

Preferably, the pigments are spun in in the form of a pigment dispersion. More preferably, the pigment dosing ratio is controlled and/or adapted automatically based on the spinning solution flow rate and is adjusted by means of a controlled dosing pump. Accurate dosing is extremely important, for example, in order to achieve a consistent filament quality. In the textile sector, any deviation from such consistency will, in the final application, be clearly visible on the fabric. In technical applications, irregularities may cause failure of the final product.

Therefore, the selection of a suitable controlled dosing pump is of importance for the success of the inventive method. Eccentric screw pumps, for example, have proven to be particularly well suited. Piston pumps, in turn, are typically used for large streams of liquid, however, they are not accurate enough for the small streams of liquid encountered in this case, as they do not function continuously, but in pulses, thereby causing a constantly changing pigment concentration. The gear pumps widely used in the synthetic fiber sector are not suitable for use in the present method, either, because, on the one hand, the pigments used, especially TiO₂, would lead to very high abrasion on the gear pumps. On the other hand, there exists the risk of the pigment being deposited between the teeth of the pump gears, clogging them up so that the output is decreasing and the dispersion enters the viscose spinning solution with a lower pigment content.

According to the invention, all such solids are generally suited for use as pigments that, under the conditions in the viscose spinning solution, i.e., strongly alkaline and CS₂-containing, will not undergo any undesired changes. In particular, in this case, the pigment is selected from the group comprising flame-retardant, colored, fluorescent (“high-vis” colorants) and radiographically detectable pigments. The present invention shall expressly also encompass mixtures of these pigments for a combination of several properties in the same filament. In a preferred embodiment of the invention the pigment-type substance is therefore at least partly a flame-retardant substance.

In order to achieve an effective flame-retardant action, in the inventive method such a quantity of the flame-retardant substance is spun in that the finished fiber contains at least 2.8%, preferably between 3.2% and 6.0%, more preferably between 3.5% and 6.0% phosphorus, related to cellulose. Preferably, phosphorus is present in the form of the organophosphorus compound 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide (I).

The described advantageous mechanical properties of the regenerated cellulose filaments obtained according to the inventive method are achieved with particular reliability if the pigment dispersion contains between 10 and 50% of the flame-retardant substance with an average particle size (x₅₀) of less than 1.0 lam and a maximum particle size (x₉₉) of less than 5.0 μm, preferably smaller than 3.0 μm, as well as between 5 and 20% of a dispersing agent.

Preferably, this dispersing agent for the flame retardant dispersion is selected from the group comprising modified polycarboxylates, water-soluble polyesters, alkyl ether phosphates, end-group-capped nonyl phenol ethoxylates, castor oil alkoxyl esters, and carboxymethylated alcohol polyglycol ethers.

According to the invention, the flame-retardant phosphorus compound that is produced as a pigment is added to the viscose spinning solution in the form of a pigment dispersion. In this process, so much of the flame-retardant substance is spun in that the finished fiber contains at least 2.6%, preferably between 3.2% and 6.0%, more preferably between 3.5% and 6.0% phosphorus, related to cellulose.

As has already been mentioned hereinabove, a flame-retardant organophosphorus compound that is particularly well suited for the purposes of the present invention is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide.

The quality of the pigment dispersion, in particular, also has a significant influence on fiber properties. This quality depends on the average and maximum particle sizes of the pigments, on the concentration of the dispersion in use, i.e., when adding it to the viscose spinning solution, as well as on the type and the quantity of the dispersing agents.

Contrary to the possible upper particle size of 10 μm described in the patent EP1882760, it has been found that an average particle size (x₅₀) of less than 1 μm and a maximum particle size (x₉₉) of less than 5.0 μm, preferably of less than 3 μm, are necessary. FIG. 3 shows a size distribution of a pigment dispersion that is still suitable.

Preferably, the pigment dispersion should contain between 10 and 50% of the flame-retardant substance.

The inventive method will now be described based on a feasible and well suited embodiment, without intending to limit the invention to such embodiment. The invention expressly encompasses functionally equivalent solutions, as well.

FIG. 1 shows in principle the spinning machine that is used to carry out the method: The viscose or the viscose dispersion mixture is fed via the pipe line system 1. Dosing of the titer-dependent viscose quantity is carried out by means of precision gear pumps 2. In the filters 3, the dosed viscose is filtered. In the variant described herein, typical spinnerets 4 are installed as submerged in the precipitation bath 5 on so-called spinning pipes for the production of the required filament. Preferably, in a precipitation bath, two filament yarns from discrete spinnerets 4 are spun side by side and are then guided parallel to one another across the entire spinning machine. These spinnerets 4 contain the number of holes that corresponds to the desired number of individual filaments in one filament yarn. The precipitation bath 5 is supplied with precipitation bath liquid of the inventive composition via a level-controlled inlet. Via a pipe line, the coagulated filaments, together with the precipitation bath liquid, first arrive at a trough 7 that serves as drain for the precipitation bath. Such a method is usually also referred to as a tube spinning method. Above the trough 7, the filaments are guided onto the first godet 8 of the stretching station where excess precipitation bath is collected by the trough 7. From the godet 8, the filaments run on to the second bath 9 where they are stretched and fixed at the same time. This second bath has an inlet 10 and a drain 11 for the above described bath liquid. From the deflection device arranged in the second bath, which may be a movable (not driven) pair of rollers or also a rigid glass rod or the like, the filaments are guided to a interlocked pair of rollers equipped with a washing water feeder 12 and a washing water drain 13, where they are first washed and then dried in a drying zone 14. Subsequently, they are finished in a finishing station 15 and finally reeled up on a twin reel station 16. The pair of rollers can additionally be equipped with an aspirator 17 for the generated steam and other gaseous secondary products.

The tube spinning method described herein achieves an approx. 10% greater strength as well as faster to approx. three times faster spinning than the conventional immersion spinning method. Without the addition of a pigment dispersion, spinning velocities of up to 180 m/min are possible, with the addition of a pigment dispersion, spinning velocities of up to 85 m/min are still possible.

Particularly regular admixing of the pigments can for example be achieved with a dosing apparatus as shown in FIG. 2: It comprises an agitator vessel 18 used to prepare the pigment dispersion, a dispersion dosing pump 19 used to deliver the dispersion, an appropriate flow measurement 20 as well as two static mixers 21, 22 used to mix the dispersion with the main stream of the viscose spinning solution which, via a conduit 23, a pressure booster pump 24, and a flow measurement 25, arrives at the static mixers 21, 22. Following another flow measurement 27, the viscose pigment dispersion is guided to the spinning machine via another pipe line 28. In addition, a temperature control circuit 27 can be provided for controlling the temperature of the main viscose stream.

The invention will now be explained based on examples. These examples shall be construed as possible embodiments of the invention. By no means is the invention limited to the scope of these examples.

EXAMPLE 1

6 parts by weight of 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphoriane]2,2′disulfide, 6 parts by weight of water, and 0.55 parts by weight of alkyl polyglycol ether phosphoric acid ester are homogenized using a dissolver and ground in an agitator bead mill (Drain, type Perl Mill PML-V/H) with zirconium oxide grinding beads at a temperature of 40-55° C. until the finished dispersion has an x₉₉<1.50 μm. Beech pulp (R18=97.5%) was alkalized with mashing lye that contained 240 g/1 of NaOH at 35° C., while being stirred, and pressed into an alkali cellulose nonwoven. The alkali cellulose nonwoven was defibered, ripened, and sulfidized. Using diluted caustic soda, the xanthogenate was dissolved into a viscose with 5.6% cellulose, 6.8% NaOH, and 39% CS₂, related to cellulose. The viscose was filtered 4 times and vented. 1 hour prior to spinning, 3% (related to cellulose) of ethoxylated amine, a modifier causing a sheath structure, was added to the viscose. The viscose was post-ripened to a spinning gamma value of 57. The viscosity during spinning was 80 falling ball seconds. The finished flame retardant dispersion is added to this ready-to-spin viscose.

The spinnerets used have a spinneret hole diameter of 60 μm. The precipitation bath contains 75 g/1 of sulfuric acid, 113 g/1 of sodium sulfate, and 53 g/1 of zinc sulfate. The precipitation bath temperature was 39° C.

The coagulated and partly regenerated plastic thread strand of a pale yellow color was guided via a godet G1 into a second bath whose temperature was 95° C. and that contained 4.8 wt % of sulfuric acid, where it was stretched by 100% between G1 and a second godet G2. The final withdrawal was carried out at a velocity of 30 m/min. The filament was then washed acid-free with hot water, dried, and subsequently reeled up.

TABLE 1
Fiber data
					BISFA
		Individual			wet
	Titer	filaments	FFk	FDk	modulus	P content
Fiber	[dtex]	[number]	[cN/tex]	[%]	[cN/tex]	[%]
Example 1	200	76	23.5	6.1	5.2	3.5

Claims

1. A regenerated cellulose filament, wherein the filament has a pigment content of more than 20 wt % and a strength in the conditioned state of more than 22 cN/tex.

2. The regenerated cellulose filament according to claim 1, wherein the pigment is selected from the group consisting of flame-retardant, colored, fluorescent and radiographically detectable pigments.

3. The regenerated cellulose filament according to claim 2, wherein the pigment has a particle size distribution with x50 at less than 1.0 μm and x99 at less than 5.0 μm.

4. The regenerated cellulose filament according to claim 2, wherein the filament has a single-fiber titer of between 0.4 and 4.0 dtex.

5. The regenerated cellulose filament according to claim 2, which comprises at least 2.8%, phosphorus related to cellulose.

6. The regenerated cellulose filament according to claim 2, wherein the phosphorus is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide (I).

7. The regenerated cellulose filament according to claim 2, wherein the filament comprises a dispersing agent selected from the group consisting of modified polycarboxylates, water-soluble polyesters, alkyl ether phosphates, end-group-capped nonyl phenol ethoxylates, castor oil alkoxyl esters, and carboxymethylated alcohol polyglycol ethers.

8. A regenerated cellulose filament having a strength in the conditioned state of greater than 36 cN/tex.

9. A textile fabric comprising the regenerated cellulose filament according to claims 1 or 2.

10. A continuous method for the production of a high-strength regenerated cellulose filament comprising:

1) spinning a viscose containing 4 to 8% cellulose, 5 to 10% NaOH, 36 to 42% (related to cellulose) carbon disulfide and 1 to 5% (related to cellulose) of a modifier into a precipitation bath to form coagulated filaments,

2) withdrawing and reeling up the coagulated filaments, wherein: a viscose is used whose spinning gamma value is 50 to 68 and whose spinning viscosity is 50 to 150 falling ball seconds; the temperature of the precipitation bath is 34 to 65° C.; the alkali ratio (=cellulose concentration/alkali content) of the ready-to-spin viscose is 0.7 to 1.5; the bath concentrations are: H2SO4 68-95 g/1 Na2SO4 90-160 g/1 ZnSO4 30-65 g/1; and the withdrawing and reeling up take place at a velocity between 15 and 180 m/min; and

3) passing the coagulated filaments in the precipitation bath through a second bath, wherein the second bath comprises aqueous sulfuric acid, 3-7 wt %, at a temperature of 80-98° C. to form the regenerated cellulosic filaments.

11. The method according to claim 10, wherein pulp having an α-content of 93-99% is used as cellulosic raw material.

12. The method as according to claim 10, wherein the coagulated filaments are stretched by 70% to 105% in the second bath.

13. The method according to claim 10, wherein a pigment-type substance in the form of a pigment dispersion is spun into the filaments.

14. The method according to claim 13, wherein the pigment dosing ratio is controlled and/or adapted automatically based on the spinning solution flow rate and adjusted by means of a controlled dosing pump.

15. The method according to claim 14, wherein the controlled dosing pump is an eccentric screw pump.

16. The method according to claim 13, wherein the pigment-type substance is selected from the group consisting of flame-retardant, colored, fluorescent, and radiographically detectable pigments.

17. The method according to claim 16, wherein the pigment-type substance is at least partly a flame-retardant substance.

18. The method according to claim 17, wherein the high-strength regenerated cellulose filament comprises at least 2.8% phosphorus related to cellulose.

19. The method according to claim 18, wherein the phosphorus is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′disulfide (I).

20. The method according to claim 17, wherein the pigment dispersion contains between 10 and 50% of the flame-retardant substance with an average particle size (x50) of less than 1.0 μm and a maximum particle size (x99) of less than 5.0 μm and between 1.5 and 20% of a dispersing agent.

21. The method according to claim 17, wherein a dispersing agent is used to disperse the flame retardant substance, wherein the dispersing agent is selected from the group consisting of modified polycarboxylates, water-soluble polyesters, alkyl ether phosphates, end-group-capped nonyl phenol ethoxylates, castor oil alkoxyl esters, and carboxymethylated alcohol polyglycol ethers.

22. The method according to claim 10, wherein the spinning of the viscose into the precipitation path takes place in the form of a tube spinning method.

23. The flame-retardant regenerated cellulose filament according to claim 5, which comprises between 3.2% and 6.0% phosphorus related to cellulose.

24. The flame-retardant regenerated cellulose filament according to claim 5, which comprises between 3.5% and 6.0% phosphorus related to cellulose.

25. The method according to claim 17, wherein the high-strength regenerated cellulose filament comprises between 3.2% and 6.0% phosphorus related to cellulose.

26. The method according to claim 17, wherein the high-strength regenerated cellulose filament comprises between 3.5% and 6.0% phosphorus related to cellulose.