Title of Invention

A PROCESS FOR PRODUCING CELLULOSE FIBERS OF FILAMENTS

Abstract

The present invention relates to a process for producing cellulose fibers or filaments from pulp by the dry-jet wet-extrusion process using aqueous amine oxides, by a) pulp and aqueous amine oxide being dispersed at elevated temperature in a mixingikneading reactor and converted by water removal and shearing into a homogeneous solution having a relaxation time in the range of 0.5 -80 seconds, b) the solution being fed to at least one spinning die and being shaped in the spinning capillary or capillaries at an elongation rate &#941;D, c) transporting the shaped solution through a noncoagulating medium with simultaneous further shaping at an elongation rate &#941;,<sub>a</sub> d) the cellulose filament or filament sheet being coagulated in a coagulation bath, separated from the coagulation bath by deflection over a godet, subjected in a multistage aftertreatment apparatus in fiber or filament form to washing, finishing, drying, and subsequently the filaments being individually wound up as a yarn or converged into a tow and cut to staple, which comprises producing a solution having a cellulose cuoxam DP &#8805; 450 in step a) and shaping this solution in steps b) and c) at an elongation rate.

Full Text

This invention relates to a process for producing cellulose fibers or cellulose filament yarns with improved properties from pulp by the dry-jet wet-extrusion process using aqueous amine oxides, especially N-methylmorpholine N-oxide, as solvents, by a) pulp and aqueous amine oxide being dispersed at elevated temperature in a reactor and converted by water removal and shearing into a homogeneous solution having a zero shear viscosity in the range of 1 000 - 8 000 Pas and a relaxation time in the range of 0.5 - 80 seconds at 85°C, b) the solution being fed to at least one spinning die and being shaped, c) transporting the solution jet through a noncoagulating medium with simultaneous further shaping, and d) the cellulose filament or filament sheet being coagulated in a coagulation bath, separated from the coagulation bath by a deflecting element and subjected in a multistage aftertreatment to washing, finishing, drying and optionally crosslinking. [Prior art] US patents 4 246 221 and 4 416 698 disclose dissolving cellulose in aqueous amine oxides, low-shear shaping in spinning capillaries, stretching the solution jets in a large air-gap, coagulating the cellulose by means of a spin bath containing aqueous amine oxide and withdrawing the cellulose filaments via a godet. US patent 5 417 909 describes a process whereby the solution is subjected to shaping in the spinning capillaries at medium to high shear, the solution jets are stretched in a short air-gap, the cellulose is precipitated and the filaments or sheet of filaments are collected via a spin funnel and transported cocurrently. EP 0 430 926, EP 0 494 852, EP 0 756 025 and WO 94/28 210 describe certain dies which vary in spinning capillary geometry and arrangement. WO 96/20 300 concerns the distance between two spinning capillaries and the path between spinning capillary and deflecting element in the coagulation bath. EP 0 584 318, EP 0 671 492, EP 0 795 052, WO 94/28 218 and WO 96/21 758 describe a wide variety of ways of treating the filament sheet in the gap between spinnerette and coagulation bath with air of varying water content. EP 0 659 219 describes the production of a cellulose fiber having a reduced tendency to fibrillate by keeping an empirical expression incorporating spinnerette hole diameter, dope flow, linear density, length of air-gap and moisture content of quench air to a value which does not exceed 10. EP 0731 856 proposes achieving a reduced tendency to fibrillate by including aliphatic alcohols in the quench air, while EP 0 853 146 proposes achieving a reduced tendency to fibrillate by performing the coagulation in two or more stages. It is further known to modify fiber structure and properties through certain aftertreatment processes, such as treatment with crosslinking agents EP 0 783 602, EP 0 796 358, with 10 - 18% caustic soda WO 97/45 574 or with alkanol, alkanediol, alkanetriol in at least one wash bath WO 97/25 462. The chemical crosslinking as part of the aftertreatment, as well as producing a desirable increase in the wet abrasion resistance, leads to a distinct embrittlement of the fibers in that loop strength and breaking extension of the fibers decrease significantly. In all the abovementioned processes the fiber-forming step in the lyocell process is not regarded as a unit, but rather predominantly statically and it is tried to influence fiber structure and fiber properties by modifying individual steps such as for example the spinnerette geometry, the atmosphere in the air-gap, the coagulation bath design and/or the aftertreatment. [Object of invention] It is an object of the present invention to provide a process having an improved fiber-forming operation which captures all parameters relevant to fiber formation in one equation and thus permits controlled adjustment of fiber/filament properties on the basis of a solution of defined cellulose concentration, molar mass and molar mass distribution. The fibers spun according to the present invention shall permit subsequent crosslinking without significant embrittlement. It was found that fiber formation from the extremely viscoelastic cellulose solutions in the lyocell process can be understood as a two-step elongational deformation where elongational deformation takes place in the first step under the influence of the pressure in the die channel and in the second step under the axial elongational stress in the air-gap (cf fig. 1). The pressure AP is given by Here, nD is the elongational viscosity in Pas, £ is the elongation rate in s-1 , T10 is the fineness in dtex of the fiber to be spun, va is the takeoff speed in m/min, pL is the density of the solution in g/cm . Ccell. is the cellulose concentration of the spinning solution in %, DE is the inlet diameter and DA the outlet diameter of the spinning capillary in cm, 1 is the length of the spinning capillary in cm, a is the length of the air-gap in cm and SV is the spin-stretch ratio in the air-gap, ie the ratio of takeoff speed to extrusion speed. The elongational viscosity is defined for any one spinning solution by the cellulose concentration, the molar mass and the molar mass distribution and changes only with the temperature and the elongation rate. The elongation rate of the overall operation is given by and contains all process-relevant parameters which capture the kinetics of fiber formation in particular. The zero shear viscosity and the zero strain viscosity are directly related by the Trouton equation: The zero shear viscosity of the cellulose solutions at 85°C is preferably 1 000 - 8 000 Pas when spinning into filaments and preferably 5 000 - 40 000 Pas when spinning into staple fibers. The width of the viscosity range results from the fact that the experimentally determinable zero shear viscosity of the cellulose solutions depends not only on the molar mass and concentration but also on their degree of solvation and will only attain a minimum end value when solvation is complete, ie after a long dissolving time. Commercially relevant spinning solutions frequently arrive at the spinning step in a state of incomplete solvation and so seem to possess a higher value for the zero shear viscosity or the molar mass, [cf Michels Ch. and Meister F. "Das Papier" 51 (1997) 4 p. 161 - 165 and Michels Ch. and Kosan B. "Chemical Fibers Intern." 50 (200) 12 p. 556 - 561] . It has now been found that there is a functional relationship between the elongation rate and the "quality of the fiber structure" as measured by the loop strength and the breaking extension of the fibers and filaments. Figures 2 and 3 show plots of respectively the loop strength and the breaking extension against the elongation rate for fiber samples obtained by spinning 3 cellulose solutions containing 11.2% of cellulose (cuoxam DP in range 507 - 527, polydispersity u^ = 5.9). The breaking strength of the 25 fiber samples was relatively constant at 41.1 ± 1.9 cN/tex and the variation of birefringence was low. In other words, the degree of orientation of the fiber samples was of the same order of magnitude, even though the spin-stretch ratio varied appreciably at values between 7 and 32. This also explains why there is probably a relationship between the work capacity of the fibers (product of breaking strength and breaking extension in J/g) and the elongation rate, although this is much less pronounced. In a preferred embodiment of the process according to the present invention, fibers are spun at an elongation rate in the range between 15 and 40 [1/s] and" the fibers are treated in the last stage prior to drying with a solution which simultaneously contains finish, a crosslinking agent and a crosslinking catalyst. The fiber obtained after drying and crosslinking possesses a distinctly enhanced wet abrasion resistance coupled with only minimal changes in the other fiber parameters. The finishing liquor also contains a bi- or polyfunctional crosslinking agent of the dialdehyde type, preferably glyoxal and/or derivatives thereof, and has a pH Another embodiment of the process according to the present invention comprises spinning filament yarns at an elongation rate in the range 60 - 100 [1/s], removing the amine oxide by multistage washing, drying over a first heated pair of rolls to a water content > 80%, using compressed air pad piston membrane pumps and spray nozzles to apply a defined amount of mixture of finish and crosslinking agent to the filament sheet, drying and crosslinking over a second heated pair of rolls. The filament yarn obtained possesses distinctly enhanced wet abrasion resistance. The method for determining the wet abrasion resistance is extensively described in the literature [Mieck K.P.; Langner H. ; Nechwatal A. "Melliand Textilberichte" 74 (1993) p. 945; "Lenzinger Berichte" 74 (1994) p. 61 - 68; and Mieck K.P.; Nicolai A; Nechwatal A.; "Lenzinger Berichte" 76 (1997) p. 103]. The wet abrasion resistance is measured in terms of the number of rubbing cycles required of a roll of defined geometry that is covered with a cellulose cloth until a moistened fiber under a defined tension is ruptured. Lyocell fiber gives a wet abrasion resistance in the range between 10 and 50 rubbing cycles, depending on their molar mass and orientation. The literature cited also reveals that wet abrasion resistance is sufficient when the fiber test gives ^ 340 rubbing cycles. The invention will now be more particularly described with reference to examples: [Examples] Example 1 465 g of activated and stabilized spruce sulfite pulp (water content 55% by mass; stabilizer 0.05% by mass; cuoxam DP 4 90; polydispersity Un, = 5.7) are dispersed in 2530 g of N-methylmorpholine N-oxide (NMMO) having a water content of 40% by mass and converted by heating, shearing and the evaporative removal of 995 g of water into a homogeneous solution having a zero shear viscosity of 5 950 Pas, a relaxation time of 4.2 s and a filter value of 56. The solution consists of 12.8% by mass of cellulose, 75.9% by mass of NMMO and 11.3% by mass of water. Spinning was carried out on a pilot plant which makes it possible to produce not only staple fibers but also filament yarns. In the present example, fibers were produced at the following settings: - fiber fineness 1.10 dtex - pump rate 1.11 ml of solution/min (density 1.18 g/cm3) - spinning temperature 85°C - spinnerette (56 spinning capillaries; DB = 228 µm; DA = 150 µm; 1 = 0.0 5 cm) - air-gap (a = 7.0 cm; linear quench with air - ca. 10 1/min 1.0 cm above point of entry of filaments into the coagulation bath at angle of ~ 80° to direction of movement of filaments.) - extrusion speed 1.12 m/min - takeoff speed 30.2 m/min - calculated elongation rate 6.02 s-1 The filament sheet was washed, cut into 50 mm staple, finished and dried. Testing revealed the following fiber parameters: 265 g of a pulp mixture of 98% eucalyptus and 2% cotton linters pulp were enzymatically pretreated, squeezed off to a water content of 50% by mass, dispersed in 2593 g of NMMO having a water content of 25% by mass and converted by heating, shearing and evaporative removal of 623 g of water into a homogeneous solution having a zero shear viscosity of 4108 Pas and a relaxation time of 4.9 s at 85°C. Particle analysis gave a filter value of 90. The composition of the solution was 10.6% by mass of cellulose, 77.8% by mass of NMMO and 11.6% by mass of water. The cellulose mixture of the solution had a cuoxam DP of 543 and a polydispersity of 6.05. The solution (density 1.16 g/cm^) was spun at a bulk temperature of 80°C through a die having 30 spinning capillaries (DE = 221 µm; DA = 140 µm; 1 = 0.05 cm) through an air-gap (a = 5 cm) with a spin-stretch ratio of 16.4 and a takeoff speed of 72.8 m/min into 1.12 dtex fiber. The resulting elongation rate was 19.2 s"^. The fiber was washed, finished and dried at 125°C (A) . Concurrently, in a second test series, the finishing liquor also contained 5 g/1 of glyoxal and 0.5 g/1 of magnesium chloride (pH 6.7). Application was first by spraying the fiber which had been predried to > 80% water (B) and secondly by dipping and squeezing off by means of a pair of rolls (C). Fiber testing revealed the following values: Rel. loop strength ratio % 44.2 35.0 26.6 Wet abrasion resistance cycles 22 373 625 Example 3 300 g of eucalyptus pulp, enzymatically pretreated, squeezed off to a water content of 45% by mass, are dispersed in 2 726 g of NMMO having a water content of 30% by mass and converted by heating, shearing and evaporative removal of 772 g of water into a homogeneous solution (density 1.178 g/cm3) having a zero shear viscosity of 5 081 Pas and a relaxation time of 6.0 s at 85°C. Particle analysis gave a filter value of 76. The composition of the solution was 12.0% by mass of cellulose (cuoxam DP 508, polydispersity 5.9), 76.3% by mass of NMMO and 11.7% by mass of water. The solution was spun at a bulk temperature of 85°C through a die having 330 spinning capillaries (DE = 225 µm; DA = 90 µm; 1 = 0.05 cm) through an air-gap (a = 2.0 cm) with a spin-stretch ratio of 10.3 and a takeoff speed of 32.2 m/min into 1.09 dtex fiber. The calculated elongation rate was 21.8 s-1. The fiber was washed, finished and dried at 125°C (A) . Concurrently, in a second test series, the finishing liquor also contained 7.5 g/1 of an adduct of glyoxal and sodium bisulfite (B). Parameter/Test (A) (B) Fineness dtex 1.09 1.10 Tenacity cond. cN/tex 39.1 38.8 Tenacity wet cN/tex 30.9 31.1 Rel. tenacity ratio % 79.0 80.1 Elongation cond. % 14.8 13.0 Elongation wet % 14.3 12.8 Loop strength cN/tex 17.9 13.3 Rel. loop strength ratio % 45.8 34.3 Wet abrasion resistance cycles 28 568 Example 4 The solution (10.6% of cellulose; density 1.16 q/cm at 85°C) is prepared similarly to example 2; it was spun at a bulk temperature of 84°C using the following parameters: - spinnerette DB = 221 µm; DA = 140 µm; 1 = 0.05 cm; 58 spinning capillaries - air-gap 6.0 cm (linear quenching of filament sheet with 11.5 1/min air perpendicularly to direction of movement of filaments about 1 cm prior to entry into the coagulation bath) - extrusion speed 18.5 m/min - takeoff speed 302 m/min - elongation rate 83.7 s"-"- The filaments were washed, predried, finished and dried before being wound up as a 75 dtex 58 filament yarn (A) . The finish was applied via a precision pump and "fingers". In a concurrent test, the finish also contained 10 g/1 of Arkofix (commercial product of Hoechst AG) and 1 g/1 of magnesium sulfate (B). Testing was carried out by the standard methods not only on the filament yarn (a, b) but also after cutting into staple as fiber A, B. Parameter/Test A B (a) (b) Fineness dtex 1.29 1.30 75.0 75.2 Tenacity cond. cN/tex 45.9 44.3 44.6 43.9 :B§nicity wet cN/tex WE CLAIM: 1. A process for producing cellulose fibers or filaments from pulp by the dry-jet wet- extrusion process using aqueous amine oxides, by a) pulp and aqueous amine oxide being dispersed at elevated temperature in a mixing/kneading reactor and converted by water removal and shearing into a homogeneous solution having a relaxation time in the range of 0.5 - 80 seconds, b) the solution being fed to at least one spinning die and being shaped in the spinning capillary or capillaries at an elongation rate £D , c) transporting the shaped solution through a noncoagulating medium with simultaneous further shaping at an elongation rate £a , d) the cellulose filament or filament sheet being coagulated in a coagulation bath, separated from the coagulation bath by deflection over a godet, subjected in a multistage aftertreatment apparatus in fiber or filament form to washing, finishing, drying, and subsequently the filaments being individually wound up as a yam or converged into a tow and cut to staple, which comprises producing a solution having a cellulose cuoxam DP > 450 in step a) and shaping this solution in steps b) and c) at an elongation rate 2. The process as claimed in claim 1, wherein in step d) prior to finishing, the filament or filament sheet is bleached prior to finishing step. 3. The process as claimed in claims 1 and 2, wherein in step d) prior to finishing, the filament or filament sheet is crosslinked after drying. 4. The process as claimed in claims 1 to 3, wherein the finishing liquor in step d) optionally also contains a crosslinking agent 5. The process as claimed in claims 1 to 4, wherein the aqueous amine oxide is N- methyl-morpholine N-oxide. 6. The process as claimed in claims 1 to 5, wherein the elongation rate in the die channel satisfies the relation where T10 is the fineness of the fiber/filament in dtex, Va is the takeoff speed in m/min, PL is the density of the spinning solution in g/cm3, Ccell. is the cellulose concentration of the solution in %, 1 is the length of the die channel in cm and DE and DA are respectively the diameters of the spirming capillary inlet and outlet. 7. The process as claimed in claims 1 to 6, wherein the elongation rate between spinning capillary outlet and coagulation bath inlet satisfies the relation where a is the length of the stretching path in cm and SV is the spin-stretch ratio, ie the ratio of takeoff speed to extrusion speed. 8. The process as claimed in any one of claims 1 to 7, wherein the elongation rate DAis preferably in the range 4 - 40 s" to spin fibers. 9. The process as claimed in any one of claims 1 to 7, wherein the elongation rate £ 1 0-1 is preferably in the range 40 - 120 s" to spin filament yams. 10. The process as claimed in any one of claims 1 to 9, wherein the finishing liquor also contains a bi- or polyfunctional crosslinking agent of the dialdehyde type, and has a pH 11. The process as claimed in claim 10, wherein the bi- or polyftinctional crosslinking agent of the dialdehyde type is glyoxal and/or a derivative thereof 12. The process as claimed in any one of claims 1 to 9, wherein the crosslinking agent is an adduct of glyoxal and sodium bisulfite. 13. The process as claimed in any one of claims 1 to 10, wherein the after treatment liquors pass through metering units consisting of nozzles and membrane piston pumps running at high frequency to be applied as a finely dispersed mist to the sheet of filaments and optionally any excess is squeezed off in defined fashion via a pair of rolls. 14. The process as claimed in any one of claims 1 to 10, wherein the crosslinking agent or the finish containing crosslinking agent is applied via a unit consisting of precision pump(s) and metering pin(s).

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