KR100416212B1 - Process for producing crimped cellulose fiber by forming melt fracture - Google Patents

Abstract

The present invention relates to a method of continuously producing cellulose fibers using N-methylmorpholine-N-oxide (hereinafter referred to as "NMMO") as a solvent, without expressing a crimping process, while maintaining high productivity. It relates to a method of imparting excellent and flexible crimp. More specifically, as a method of imparting melt fracture to the flow of cellulose extrudates extruded through the spinning nozzle during spinning of the NMMO solution of cellulose to impart crimp to the extruded fibers, without a separate crimping process. Crimp is effectively given to cellulose fibers. The present invention relates to a method of fixing a crimp imparted by melt fracture formation in a post-processing process consisting of coagulation in a void and a coagulation bath, washing with water, and wet heat drying.

Description

Process for producing cellulose crimp fibers by melt fracture formation {PROCESS FOR PRODUCING CRIMPED CELLULOSE FIBER BY FORMING MELT FRACTURE}

The present invention relates to a method for producing cellulose crimp fibers. More specifically, in the continuous production of cellulose fibers using an NMMO solution of cellulose as the spinning solution, when the spinning solution is extruded through a spinning nozzle, melt fracture formation is induced on the flow of the extruded cellulose extrudate on the fibers. It relates to a method of applying a crimp and fixing the crimp in a subsequent step.

The conventional method for producing cellulose fibers by a process using NMMO as a solvent is to extrude the cellulose solution through a spinning nozzle, to cool and solidify in an air gap, to solidify in a coagulation bath, and to wash in a washing bath. It is. This method is followed by a drying process after washing with water, and then cutting into fibers having a constant length, or after washing with water after wet washing, and then drying to obtain staple fibers having a final length. Consists of At this time, the spinning and abrasion properties are imparted so as to be suitable for use in woven fabrics, knitted fabrics, and nonwoven fabrics. In addition, in order to give a bulky feeling and a soft feeling, the fibers are given a crimp, and a crimping process is generally performed before or after drying.

U.S. Pat.Nos. 5,591,388 and 5,601,765, International Publication Nos. 94/28220 and 94/27903 disclose methods using conventional crimping processes, i.e., mechanically imparting lyocell fibers to a crimp. It is. According to this method, continuous cellulose filament bundles (tow, tow) prepared by solution spinning are washed with water for solvent removal, tanned, dried to about 165 ° C. in a drying process, and then dried tow is removed under appropriate conditions. A nip roller is used to feed into a stuffer box that imparts crimp in a mechanical manner. The tow is folded in the stuffer box and treated with hot water vapor to have a crimp effect. The tow passing through the stuffer box is finally cut to the length of the staple yarn in the cutting process. This method is a general method that separates the crimping process through the stuffer box after the primary drying process, and has a disadvantage in that the device is complicated and energy consumption is large due to the separate crimping process. The above method of imparting a crimp in a mechanical manner also presents a problem that the crimp is not fixed in the tow and disappears during subsequent processing steps.

U.S. Patent No. 6,117,378 discloses that the solution extruded through the spinning nozzle is passed through the voids and the coagulation bath to a swollen cellulose tow containing water, and then the tow is 4 cm, the length of the staple yarn. Cut. The chopped fibers are mixed with water to form a slurry, which is then squeezed at a pressure of 10 ⁶ Pascals per 0.1 second on a first squeezing roll, and the pressed tow is washed with water The method of passing through a pressing roll and finally drying is disclosed. This method compresses the swelled fibers prior to drying, which contains water, to produce release cross-section lyocell fibers instead of circular cross sections, thereby increasing cohesion between the fibers during carding and crimping after drying. It has been reported to have the advantage of not disappearing. However, this method requires a separate mixing process such as mixing a fiber cut to a staple yarn length with water to make a slurry in order to compress it in the swollen state and passing the pressing roller twice. There is this. That is, this method also requires such an additional process to impart crimp to the lyocell fibers, and as a result, the manufacturing apparatus is complicated, which is disadvantageous in terms of energy efficiency.

As described above, the conventional methods for imparting crimp to NMMO solvent-based cellulose fibers require a crimping process separate from the fiber manufacturing process, and thus, the manufacturing apparatus is complicated, energy consumption is large, and energy efficiency is disadvantageous. Crimps imparted by the process have a disadvantage of not being fixed in the post-processing process after the crimping process and disappearing.

SUMMARY OF THE INVENTION An object of the present invention is to continuously manufacture cellulose fibers using NMMO as a solvent, and to maintain high productivity, cellulose crimped staple fibers having excellent flexibility and crimp expression properties, using a conventional crimping process. It is to provide a method for producing easily while omitted.

1 is a schematic diagram of a cellulose crimp fiber manufacturing process according to the present invention.

FIG. 2 is a photograph of cellulose crimp fibers produced by the process of FIG. 1. FIG.

The inventors of the present invention continuously produce cellulose fibers using NMMO as a solvent, and when the cellulose solution is extruded through the spinning nozzle, the cellulose tow is extruded by inducing melt formation in the flow of the cellulose extrudates extruded from the spinning nozzle. The object of the present invention was achieved by imparting a crimping effect and producing cellulose staple fibers having excellent flexibility and crimp expression, without a separate crimping process.

When spinning the polymer melt, the distorted extrudates caused by radiation instability such as the formation of melt fractures in the spinning nozzle are more than a critical-die-wall shear stress at the die wall. In a wide range of polymer melts. This spinning instability is associated with the sliding of the exit region of the die or the wall inside the die, and the deformation extrudate is due to the flow instability of the die exit. Extruded materials with large and rough deformations are mainly formed by high extrusion speeds, which are due to the breakage of the melt flow, and the mechanism is fracture of melts and wall slipping depending on the melted material. slippage phenomena, hydrodynamic instabilities associated with viscoelasticity.

The present invention relates to the elasticity of melt fracture resulting from spinning shear extrusion in the case of increasing the shear rate at the spinning nozzle within the region of the appropriate size, i.e., increasing the spinning extrusion speed. Instability of the melt flow, known as the elastic turbulance of melt fracture, results in the formation of a deformed extrudate, i.e., an extrudate with folded bends, and the crimp in the cellulose tow from which the bend of the extrudate is extruded. It is a method of using the effect to provide. Thus, there is no need for a separate crimping process for imparting crimp on the fibers.

In order to fix the crimp of the cellulose tow extruded using melt fracture formation, and to give a high degree of flexibility, as shown in Figure 1, the primary coagulation in the air gap (2) through the solidification bath of NMMO aqueous solution as shown in FIG. The next solidification, washing and wet heat drying processes are carried out in sequence.

The hot tow extruded from the spinning nozzle is drawn to the tow by a certain draw ratio in the void where the first solidification occurs, and is cooled by the blowing air to cool the first to solidify. .

On the other hand, it is also possible to solidify the tow extruded by circulating humid carbon dioxide gas at room temperature instead of using cooling air in the first solidification process. This is a pseudo-neutralization reaction between the weakly alkaline NMMO solvent and the weakly acidic wet carbon dioxide, which results in a decrease in the solubility of cellulose in the NMMO solvent, resulting in primary coagulation.

The cellulose crimp tow, which is drawn and first solidified while passing through the pores, is mostly solidified while passing through a solidification bath of a 20% NMMO aqueous solution, which is a second solidification process, and the crimp formed during extrusion is fixed to have morphological stability as a cellulose crimp fiber. do. Therefore, the crimp does not disappear even during the subsequent washing process and the process of wet heat drying by hot steam and air, and the cellulose staple fibers have good spinning properties because of excellent flexibility and crimp expression.

Next, specific conditions for carrying out the manufacturing method of the cellulose crimp fiber according to the present invention will be described.

In continuously producing cellulose crimp fibers using NMMO as a solvent, the weight average degree of polymerization (DPw) of cellulose that can be used is 600-1100, and the concentration of NMMO aqueous solution used as a solvent is 86-92% by weight. The content of cellulose in the spinning cellulose solution prepared using the NMMO aqueous solution as a solvent is 6-20 wt%, and the spinning temperature is in the range of 90-135 ° C.

When extruding a cellulose solution from a die or nozzle, the shear rate at the spinning nozzle is increased within the range of 13,000-30,000 sec ^-1 in order to induce a phenomenon in which melt fracture occurs when the melt is spun. In the prior art, spinning at 12,000 sec ⁻¹ or less is common, and spinning is impossible if the shear rate is 30,000 sec ⁻¹ or more. The shear rate at the spinneret is expressed from Poiseuille's equation as shown in the following equation (1).

γ _w = (8V ₀ ) / (60 × d _c ) (1)

Where γ _w is the apparent wall shear rate (sec ⁻¹ ) at the spinning nozzle wall, V ₀ is the linear velocity (m / min), d _c is the diameter of the spinning nozzle (capillary diameter, m Linear velocity is the discharge volume (Q, g / min) from the nozzle divided by the density of the discharge (d, 10 ⁶ g / m ³ ) (John M. Dearly, Kurt F. Wissbrun, Melt Rheology and Its) Role in Plastics Processing , Van Nostrand Reinhold, New York, 1989). As the spinning nozzles, those having an odd number of 36 to 60,000 and holes having a diameter of 0.08 to 0.50 mm are usually used.

The cellulose tow extruded from the nozzle has a turbulence at the exit of the spinning nozzle due to the high shear rate at the nozzle, i.e., the high extrusion rate, and observes that the extruded tow is folded, such as oscillating. do. This is a form of deformed extrudate by melt fracture, which has the effect of imparting crimp to the tow being extruded. This phenomenon is due to the formation of melt fracture caused by the high shear rate during extrusion, which is different from the steady flow spinning conditions of conventional cellulose tow. In other words, by intentionally forming melt fracture within the shear rate range of 13,000-30,000 sec ^-1 to extrude the cellulose solution, the cellulose tow radiated from the nozzle has a crimp. The number of crimps per unit length formed in the tow is determined by the shear rate during extrusion and the resulting spin draw ratio, usually about 7-13 points / 2.54 cm.

The cellulose crimp tow extruded through a die or nozzle under high shear rate is made of cellulose fibers through subsequent solidification, washing, and wet heat drying processes (see FIG. 1). Does not disappear and is further fixed.

Solidification of the cellulose crimp tow consists of primary solidification in the pores and secondary solidification in the solidification bath of a 20% NMMO aqueous solution. Primary solidification in the voids is generally accomplished by cooling with cooling air in the temperature range of -5 to 20 ° C supplied at a constant angle to the hot cellulose tow extruded from the spinning nozzle at about 90 ° C or higher. Cellulose tow passing through the pores of a certain length is the primary solidification by drawing and cooling air according to the draw ratio in this area. The length of the void is the distance from the spinning nozzle to the coagulation bath, usually 1-30 cm.

In the first solidification process in the air gap, in the case of solidifying by circulating and supplying wet carbon dioxide at room temperature instead of solidification by cooling air, a transparent box surrounding the spinning pack, the air gap, and the primary solidification bath and By supplementary facilities. It is preferable that the moisture content in the humid carbon dioxide supplied to the circulation is 8 g or less per 1 kg of dry carbon dioxide. The pressure of the wet carbon dioxide gas supplied is 15-100 psi, and the temperature is in the range of 15-20 ° C.

The cellulose crimp tow, which has been stretched and firstly solidified while passing through the pores of a certain length, removes the NMMO solvent while passing through a solidification bath of a 20% NMMO aqueous solution at room temperature, and the second solidification is performed. The tow after this process has morphological stability as cellulose crimp fibers, and the crimps expressed during extrusion are fixed.

Crimped cellulose crimp tow is transferred and fed to a subsequent continuous washing and wet heat drying process by means of a traveling screen or roller. When supplied to the washing process by the mobile screen, the crimp tow on the moving screen is washed by the washing liquid evenly sprayed, and when supplied by the roller by the roller, the crimp tow passes through the washing tub to remove water and solvent. You will go through the process. The water content in the cellulose crimp toe after the washing process is about 190%. Subsequently, an oiling process of the oil ring is performed, followed by drying in a wet heat drying method using steam at 120 ° C. and air at 150 ° C. When supplied to a mobile screen, the cellulose crimp tow on the mobile screen is dried, and when supplied by a roller, it is wet-heated with hot steam and air in a drum dryer. The moisture content in the crimp tow after the drying process is about 11-25%. The crimp of the tow expressed by the melt fracture formation during extrusion is solidified and heat-set during the above-described series of processes so that it does not disappear in the post-processing process, thereby obtaining cellulose crimp fibers having excellent expression.

To give the cellulose crimp tow, which has been finished up to the drying process, or to fix the formed crimp, optionally a continuous tow can be optionally supplied with a circular conical barrel with a compressed air nozzle of 3 to 6 atm. Pass through the (conic circle tube). Compressed air nozzles are installed inside the circular cone cylinders so that compressed air is supplied from the wall surface of the cylinders toward the outlets with smaller diameters, and the compressed air is gradually narrowed while the crimp toe supplied into the circular cone cylinders is folded. It is designed to come out by the pressure of. The pressure received by the tow is adjusted according to the exit diameter of the circular conical barrel and the amount of tow passing, so that the tow can be further crimped. Also, in this process, the hot tow supplied through the wet heat drying process is quenched and dried due to cold compressed air and fixed with crimp tow having excellent flexibility. The circular cone cylinder is an additional crimping device, and this additional process can be selectively applied if necessary in the entire manufacturing process, but it can be omitted. If the addition crimping process is omitted, the moisture content in the cellulose crimp tow after drying is adjusted to about 11%.

After all of the above process, depending on the application through a cutting process finally to obtain a staple fiber of a constant length.

Hereinafter, the manufacturing method of the cellulose crimp fiber according to the present invention through the examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited thereto.

Example 1

A cellulose NMMO solution having a cellulose content of 13% by weight was prepared using a cellulose of DPw 850 and an NMMO aqueous solution of 88% by weight, and used as a spinning solution.The spinning nozzle having an odd number of holes of 0.21 holes / mm 2 and a hole diameter of 0.10 mm Cellulose crimp fiber was prepared using. In order to crimp the cellulose tow due to melt fracture at the time of manufacture, it was wound at a speed of about 104 m / min while varying the shear rate during spinning nozzle extrusion from about 15,000 sec ⁻¹ to 22,000 sec ⁻¹ . The fabric preparation followed the process diagram of FIG. 1, spinning temperature was 110 ° C., and cooling air at 7 ° C. was used for primary solidification in the pores. Shear rate, linear velocity, spinning traction ratio, diameter of wound fiber and presence or absence of crimp formation at the time of extrusion are shown in Table 1.

sample Shear rate (sec ^-1 ) Linear velocity of spinning solution (m / min) Radiation towing cost Fiber diameter (㎛) Crimp Formation B1 15,160 11.37 9.20 10.66 formation B2 16.244 12.18 8.58 11.03 formation B3 17,327 12.99 8.05 11.40 formation B4 18,409 13.81 7.57 11.75 formation B5 19,492 14.62 7.15 12.09 formation B6 20,575 15.43 6.78 12.42 formation B7 21,658 16.24 6.44 12.74 formation

As shown in Table 1, melt fracture occurred at the spinning nozzle during extrusion in the shear rate range of about 15,000-22,000 sec ⁻¹ , thereby forming a crimp on the tow.

Example 2

Cellulose crimp fibers were prepared under the same conditions as in Example 1, except that cooling air was not used in the pores and humid carbon gas at room temperature was used instead, and the results are shown in Table 2. As in Example 1, melt fracture was formed in the range where the shear rate at the spinning nozzle was about 15,000-22,000 sec ⁻¹ , thereby forming a crimp on the tow.

sample Shear rate (sec ^-1 ) Linear velocity of spinning solution (m / min) Radiation towing cost Fiber diameter (㎛) Crimp Formation C1 15,052 11.29 9.26 10.62 formation C2 16.135 12.10 8.64 11.00 formation C3 17,218 12.91 8.10 11.36 formation C4 18,301 13.73 7.62 11.71 formation C5 19,384 14.54 7.19 12.05 formation C6 20,466 15.35 6.81 12.39 formation C7 21,549 16.16 6.47 12.71 formation

Example 3

A cellulose NMMO solution having a cellulose content of 12% by weight was prepared using a cellulose having DPw 1,000 and an aqueous NMMO solution of 87% by weight, and used as a spinning solution. The odd number was 0.21 holes / mm 2, the diameter was 0.15mm, and the hole L was used. Cellulose crimp fibers were made using a spinning nozzle with a / D of 2.0. For the formation of the crimped tow of cellulose due to the melt fracture formed during the production, the shear forces during extrusion spinneret was changed from ^-1 to 15,000sec 20,000sec ^-1. The fabrication procedure followed the process diagram of FIG. 1 and the spinning temperature was 110 ° C. The number of crimps per unit length of the extrusion tow according to the shear rate and the spin pull ratio during extrusion is shown in Table 3.

Radial Towing Ratio (sec ^-1 ) 13.0 16.0 19.0 22.0 20,000 11 10 9 8 17,500 10 9 8 7 15,000 9 8 7 7

As shown in Table 3, the higher the shear rate within a certain range during extrusion, the greater the number of crimps formed per unit length, and the higher the traction ratio, the greater the elongation ratio for the extrusion rate, so the number of crimps per unit length after winding Appeared to decrease.

Example 4

A cellulose NMMO solution having a cellulose content of 12% by weight was prepared using a cellulose having DPw 1,000 and an aqueous NMMO solution of 87% by weight, and used as a spinning solution. The number of holes was 0.21 holes / mm 2, the diameter of holes was 0.15 mm, and the hole L was used. Cellulose crimp fibers were made using a spinning nozzle with a / D of 2.0. At the time of manufacture, the shear rate of the spinning nozzle was 20,428 sec ⁻¹ (linear speed 22.98 m / min), the spinning temperature was 110 ° C., and the fabrication procedure followed the process diagram of FIG. 1. The number and basic physical properties of the crimp per unit length of the produced cellulose tow fibers are shown in Table 4.

sample Radiation towing cost Crimp Number (points / 2.54cm) Fiber diameter (μm) Strength (g / d) Elongation (%) D1 10.31 11 15.1 3.2 12.1 D2 13.35 10 13.3 3.6 11.3 D3 16.38 9 11.9 3.75 9.9 D4 19.41 8 11.0 3.9 8.4

As shown in Table 4, it was shown that as the spinning traction ratio increases, the number of crimps formed per unit length of the tow after winding decreases, and the fineness and elongation of the extruded tow decrease due to the elongation ratio. The intensity tended to increase as the radial traction ratio increased.

Example 5

Cellulose crimp fibers were prepared under the same conditions as in Example 4 except that the shear rate at extrusion in the spinning nozzle was 17,347 sec ⁻¹ (linear speed 19.52 m / min), and the results are shown in Table 5. .

sample Radiation towing cost Crimp Number (points / 2.54cm) Fiber diameter (μm) Strength (g / d) Elongation (%) E1 8.75 11 16.4 3.11 13.1 E2 12.32 10 13.8 3.24 12.3 E3 15.89 9 12.2 3.58 11.7 E4 19.47 8 10.9 3.78 9.4

As shown in Table 5, the larger the traction ratio, the greater the elongation ratio, the smaller the number of crimps formed per unit length of the tow after winding, and the smaller the fineness and elongation of the extruded tow. The intensity tended to increase as the radial traction ratio increased.

Example 6

Cellulose crimp fibers were prepared under the same conditions as in Example 4 except that the shear rate during extrusion at the spinning nozzle was 14,385 sec ⁻¹ (linear speed 16.18 m / min), and the results are shown in Table 6. .

sample Radiation towing cost Crimp Number (points / 2.54cm) Fiber diameter (μm) Strength (g / d) Elongation (%) F1 6.63 11 18.8 2.89 14.2 F2 10.94 10 14.7 3.18 13.0 F3 15.25 9 12.4 3.33 12.1 F4 19.56 8 10.9 3.66 10.8

As shown in Table 6, due to the increased elongation ratio, the number of crimps formed per unit length of the tow after winding decreased and the fineness and elongation of the extruded tow decreased. The intensity tended to increase as the radial traction ratio increased.

Comparative example

In the case of extrusion under normal steady-state conditions, it was observed that melt fracture was formed in the spinning nozzle while changing the shear rate in the range of 15,000 sec ^-1 or less, and the results are shown in Table 7. A cellulose solution having a cellulose content of 13% by weight was prepared using a cellulose having a DPw of 850 and an NMMO aqueous solution having a concentration of 88% by weight, and used as a spinning solution. The number of holes was 0.21 holes / mm 2 and the diameter of the holes was 0.10 mm. A nozzle was used and the spinning temperature was 110 ° C.

sample Shear rate (sec ^-1 ) Linear velocity of spinning solution (m / min) Melt fracture formation A1 7,700 5.81 Do not form A2 9,300 6.97 Do not form A3 10,000 7.55 Do not form A4 10,800 8.13 Do not form A5 11,600 8.71 Do not form

As shown in Table 7, melt fracture was not formed in the shear rate range of 7,700-11,600sec- ¹ during extrusion.

Cellulose crimp fiber manufacturing method of the present invention using the melt fracture formation during spinning does not require a separate crimping process, the process is simpler than the conventional crimping method, high shear rate at the spinning nozzle during extrusion, that is, high extrusion The use of speed can greatly increase production in the same time, which is advantageous in terms of productivity and energy efficiency. Since the cellulose fibers imparted with the melt fracture formation are fixed with crimps and have increased flexibility during the processing of FIG. 1, the cellulose crimp fibers prepared according to the present invention have a crimp expression property (see FIG. 2) and flexibility. This is excellent.

Claims (9)

When extruding a cellulose spinning solution using an aqueous solution of N-methylmorpholine-N-oxide as a solvent through a spinning nozzle, the flow of the extruded cellulose extrudate induces melt fracture formation to impart a crimp onto the fiber, A method for producing cellulose crimp fibers by fixing crimps. The method according to claim 1, wherein the shear rate at the spinning nozzle is adjusted in the range of 13,000 to 30,000 sec ⁻¹ to induce the formation of melt fracture at the spinning nozzle. The manufacturing method of Claim 1 whose ranges of the weight average polymerization degree of the cellulose contained in the said cellulose spinning solution are 600-1,100. The method according to claim 1, wherein the concentration of the aqueous N-methylmorpholine-N-oxide solution used as a solvent in the cellulose spinning solution is 86-92 wt%. The method according to claim 1, wherein the cellulose content in the cellulose spinning solution is 6-20% by weight. The method according to claim 1, wherein the spinning temperature for forming melt fracture in the cellulose extrudate is in the range of 90-130 ° C. The method according to claim 1, wherein in the step of forming and fixing the crimp fibers by melt rupture, a primary solidification process is performed using a wet carbon dioxide gas at room temperature containing 8 g or less of moisture per kg of dry carbon dioxide. The method according to claim 1, wherein the solidified and washed fibers are wet-heat-dried in a step of fixing the crimp formed on the fibers with steam at 120 ° C and hot air at 150 ° C. A cellulose crimp fiber produced by the method according to any one of claims 1 to 8.