Patent Application
20080054516
Hereinbelow, the present invention will be described in detail with reference to the accompanying drawings in which:
The cellulose powder used in
In concentrated liquid-state NMMO, a small amount of the cellulose powder having a particle size of 5000 mm or less is first dissolved. The content of the cellulose powder is 0.01 to 5% by weight, and more specifically 0.1 to 3% by weight, with respect to the concentrated liquid-state NMMO. When the content of the cellulose powder is less than 0.01% by weight, the effect of the cellulose powder on the lowering of the solidification temperature of NMMO is negligible, thus not contributing to the swellability. On the other hand, when the content of the cellulose powder exceeds 5% by weight, the viscosity of the NMMO solution increases, thus the process of mixing and swelling in the kneader requiring a long time. Thereafter, the NMMO solution at a concentration of 20 to 30% by weight is concentrated by a conventional method to produce concentrated liquid-state NMMO having a water content of 10 to 18% by weight. When the NMMO solution is concentrated to have a water content of less than 10% by weight, it is economically disadvantageous because of increased costs. When the water content exceeds 18% by weight, the solubility of the cellulose powder may be deteriorated. Subsequently, the NMMO solution having a small amount of the cellulose powder dissolved is introduced into a kneader which has been maintained at 50 to 95° C. Then, the cellulose is mixed and swelled in the kneader without reducing pressure, to form a paste, and then the paste is fed to an extruder, where the paste is dissolved to a homogeneous state to form a homogeneous cellulose solution.
The NMMO solution having a small amount of the cellulose powder dissolved can be fed to the kneader by means of a gear pump or a screw type feeder, and is preferably introduced into the kneader by means of a screw type feeder.
The content of the cellulose powder in the cellulose solution mixed and swelled in the kneader is adjusted to 5 to 20% by weight, and more specifically 9 to 14% by weight, with respect to the total weight of the liquid-state NMMO solution in accordance with the degree of polymerization of the cellulose polymer.
When the content of the cellulose powder in the cellulose solution in the kneader is less than 5% by weight, the finally obtained fiber may not have the properties required from fiber. On the other hand, when the content of the cellulose powder exceeds 20% by weight, it is difficult to dissolve the cellulose powder in the liquid-state NMMO, and thus a homogeneous solution cannot be obtained.
According to the invention, after introducing the cellulose solution into the kneader in the step (B), cellulose is mixed and swelled in the kneader without a process of reducing pressure, to form a paste, and then the paste is fed to an extruder, where the paste is dissolved in a homogeneous state to produce a homogeneous solution. The extruder used for this purpose is preferably a twin-screw type extruder, and the twin-screw type extruder may have 3 to 16 barrels or may have the ratio L/D of the screw in the range of 12 to 64. When the number of barrels is less than 3, or when the ratio L/D of the screw is less than 12, the time taken by the cellulose solution to pass over the barrels is short, and thereby undissolved components are likely to be generated. On the other hand, when the number of barrels exceeds 16, or when the ratio LID of the screw exceeds 64, an excessive stress may be exerted on the screws, and thereby the screws may undergo deformation.
According to the invention, the cellulose powder at the step (A) or step (B) may be mixed with other polymer materials or additives. Especially, in the step (A), a polymer material such as polyvinyl alcohol, polyethylene, polyethylene glycol, polymethyl methacrylate or a cellulose derivative, or an additive such as titanium dioxide, silicon dioxide, carbon or ammonium chloride may be mixed into the cellulose solution, in order to impart stability or spinnability to the cellulose solution, or to impart functionality to the final molded product.
Here, the pulp sheet 1 is passed through a drying chamber 2 adjusted to a constant temperature and then is cooled by dry air 3 to be maintained at 25° C. Before passing the nip roller 5, the dry temperature of the drying chamber 2 is controlled by a contact-type moisture content measuring device so that the moisture content may not exceed 7%. Commonly supplied pulp has a moisture content of about 8 to 10%. However, the moisture content of the powdered cellulose stored in a storage tank 10 after pulverization may vary depending on the seasonal changes in humidity and temperature.
When the moisture content is high, aggregation of the pulp easily occurs, and it is difficult to obtain a homogeneous solution. In addition, there occurs variance in the composition of NMMO/cellulose/water, and there also occurs variance in the thickness of the fiber spun out through a nozzle 28, thus a uniform product not being obtained.
The particle size of the powdered cellulose can be adjusted according to the size of the screen sieve disposed inside the pulverizer 6 equipped with a knife, and a powder having a size of 5000 mm or less, and more specifically, 500 mm or less, can be favorably used. When the particle size of the powder is 5000 mm or greater, aggregation of the pulp may easily occur during the mixing with NMMO in the kneader, and such aggregated pulp may obstruct production of a homogeneous solution. The powdered cellulose passing through the screen sieve of the pulverizer 6 is supplied through a blower system 7 to a backfilter 8, while air is discharged out, with the powdered cellulose being fed to a powdered cellulose storage tank 10 through a rotary valve 9. The powdered cellulose is fed into a kneader 25 through a precise weight metering device 11.
The used NMMO that is generated during the process is controlled at a concentration of 20 to 35% by weight in control bath 15 and fed to a purification column 17, where ionic materials, carbide impurities and the like are removed, and the purified NMMO is stored in the supply tank 18 of a concentration column. The NMMO is supplied in definite amounts from the supply tank of the concentration column sequentially to three falling film concentration columns 19, and is produced into an aqueous solution of NMMO at a final concentration of 86 to 88% by weight. The concentrated NMMO is fed to a jacketed storage tank 20 which is maintained at 95° C., and the liquid-state NMMO 20 and the cellulose powder 21 are metered to a dissolution tank 22 equipped with a combination mixer for high viscosity dissolution, in order to be produced into an NMMO solution having a small amount of 0.01 to 5% by weight of cellulose powder dissolved. The produced solution is transported to a solution base tank 23, and is supplied in definite amounts together with the cellulose powder 11 into the kneader 25 through a gear pump 24.
The kneader 25 which is maintained at a desired temperature by heat medium jacketing can be adjusted to a temperature of about 50 to 95° C., and the suitable temperature may vary depending on the concentration of the cellulose dissolved in the introduced NMMO, the molecular weight of the cellulose powder used, and the final cellulose concentration.
When the low-temperature NMMO in which a small amount of cellulose is dissolved and the cellulose powder are mixed and kneaded in the kneader at 50 to 95° C., NMMO penetrates uniformly to the entire area of the cellulose, thereby forming a paste. As the paste is transported forward, the paste makes cellulose to swell and starts to partially dissolve the cellulose. The paste is supplied to a twin screw extruder 26 through a forced transporting device 12. The internal temperature of the twin-screw type extruder is adjusted in the range of 60° C. to 105° C., and the cellulose in the paste is completely dissolved under the effects of the temperature increase and the shear force. The obtained cellulose solution passes through a filter 27 and then is spun through a nozzle 28, and the spun cellulose is solidified in solidifying bath 13, washed in washing bath 14, and then finally dried to be produced into a cellulose fiber in dryer 29. A concentration of the used NMMO that is generated during the solidifying and washing process is controlled in control bath 15, and then the controlled NMMO is fed to the solidifying bath 13 by pump 16.
As shown in
The following Examples are provided for the readers' clear understanding of the present invention, but the scope of the invention is not intended to be limited by the Examples. In the Examples described below, the following evaluation methods and measuring methods were employed.
(a) Homogeneity of Cellulose Solution
A sample of the cellulose solution produced according to the invention was taken from the solution transport line immediately after passing through a kneader and being discharged from a twin-screw type extruder and was subjected to eye observation with a polarized microscope, and then the solubility of the cellulose solution was evaluated. The extent of the dissolved state was classified into 5 grades. The completely dissolved state was rated as Grade ‘1’, while an unspinnable state where a large quantity of undissolved components were present was rated as Grade '5′. The intermediate grades were classified into Grades 2, 3 and 4 in accordance with the amount of residual undissolved cellulose.
(b) Degree of Polymerization (DPw)
The intrinsic viscosity [IV] of the dissolved cellulose is measured as follows. 0.5M cupriethylenediamine hydroxide solution in the range of 0.1 to 0.6 g/dl concentration obtained according to ASTM D539-51T is measured by using an Uberod viscometer at 25±0.01° C. The intrinsic viscosity is calculated from the specific viscosity by using the calculation method of extrapolation and then Mark-Hauwink's equation to obtain the degree of polymerization.
[IV]=0.98×10−2DPw0.9
(c) The properties of the cellulose fiber produced according to the invention were measured as follows.
Dry strength: strength after drying at 107° C. for 2 hours (g/d)
Wet strength: strength measured after standing at 25° C. and 65% RH for 24 hours (g/d)
A cellulose sheet having a weight average degree of polymerization of 1,200 (V-81 available from Buckeye Technologies) was dried in a drying chamber to have a moisture content of 6.5 to 10%. A cellulose powder having a particle size of 500 mm or less and a moisture content of 3.5 to 7% by weight was produced using a pulverizer equipped with a screen sieve having a mesh size of 500 mm, and liquid-state NMMO concentrated to 87.5% by weight in a falling film concentration column and maintained at 90° C. was produced. During the process of concentrating the liquid-state NMMO, 0.001% by weight, with respect to the concentrated liquid-state NMMO, of an antioxidant was added and dissolved.
The liquid-state NMMO and the cellulose powder were metered into a dissolution tank equipped with a combination mixer for high viscosity dissolution, and a NMMO solution having cellulose powder dissolved to a small amount of 0.01 to 2.5% by weight was produced. The produced NMMO solution was introduced in definite amounts to a kneader whose internal temperature was maintained at 50 to 95° C., by means of a gear pump. The cellulose powder was metered by a precise weight metering device (K-tron feeder) and was introduced to the kneader, so that the final concentration of the cellulose paste was 11% by weight of the total solution. The kneader used herein had a volume of about 30 L, and the speed of the rotating blade was 20 to 30 rpm. The produced paste was transported by force to be fed into a co-rotating twin-screw type extruder. The twin-screw type extruder used had a screw with a diameter of 47 mm(I and the barrel temperature at the initial feeding section was maintained at 60 to 70° C., while the barrel temperature at the final discharge section was maintained at 95 to 105° C. The produced paste was swelled and dissolved, and was fed to a nozzle through a gear pump after passing through a filter. For the evaluation of solution homogeneity, sampling was done from the solution transport line immediately after discharge from the twin-screw type extruder.
The cellulose solution was discharged through a nozzle having 1,000 orifices, in which the orifice diameter was 150 mm, and the orifices's interval was 1.5 mm. The length of the air bed was maintained to be 90 mm, and the temperature and relative humidity of the cooling air blown from the air bed to the filament were 25° C. and 45% RH, respectively. The blowing speed was adjusted to 6.5 m/sec. The filament entering a solidifying bath from the air bed was washed, dried, oil-treated and then wound. The fineness of the finally obtained multi-filament was adjusted to 1500 deniers.
The results of Examples 1 through 12 are presented in Table 1.
A cellulose sheet having a weight average degree of polymerization of 850 (V-60 available from Buckeye Technologies) was dried in a drying chamber to have a moisture content of 6.5 to 10%. A cellulose powder having a particle size of 500 mm or less and a moisture content of 3.5 to 7% by weight was produced using a pulverizer equipped with a screen sieve having a mesh size of 500 mm, and liquid-state NMMO concentrated to 87.5% by weight in a falling film concentration column and maintained at 85° C. was produced. During the process of concentrating the liquid-state NMMO, 0.001% by weight, with respect to the concentrated liquid-state NMMO, of an antioxidant was added and dissolved.
The liquid-state NMMO and the cellulose powder were metered into a dissolution tank equipped with a combination mixer for high viscosity dissolution, and a NMMO solution having cellulose powder dissolved to a small amount of 0.1 to 5% by weight was produced. The produced NMMO solution was introduced in definite amounts to a kneader whose internal temperature was maintained at 50 to 95° C., by means of a gear pump. The cellulose powder was metered by a precise weight metering device and was introduced to the kneader, so that the final concentration of the cellulose paste was 13% by weight of the total solution. The kneader used herein had a volume of about 30 L, and the speed of the rotating blade was 20 to 30 rpm. The produced paste was transported by force to be fed into a co-rotating twin-screw type extruder. The twin-screw type extruder used had a screw with a diameter of 47 mm φ and the barrel temperature at the initial feeding section was maintained at 50 to 70° C., while the barrel temperature at the final discharge section was maintained at 95 to 105° C. The produced paste was swelled and dissolved, and was fed to a nozzle through a gear pump after passing through a filter. For the evaluation of solution homogeneity, sampling was done from the solution transport line immediately after discharge from the twin-screw type extruder.
The cellulose solution was discharged through a nozzle having 50 orifices, in which the orifice diameter was 150 mm, and the orifices's interval was 2.5 mm. The length of the air bed was maintained to be 60 mm, and the temperature and relative humidity of the cooling air blown from the air bed to the filament were 23° C. and 55% RH, respectively. The blowing speed was adjusted to 7 m/sec. The filament entering a solidifying bath from the air bed was washed, dried, oil-treated and then wound. The fineness of the finally obtained multi-filament was adjusted to 50 to 100 deniers.
In Example 22, a multi-filament was produced by the same method as that used in Examples 13 to 21, except that a cellulose sheet having an average weight degree of polymerization of 700 (Buckeye Technologies) was used.
The results of Examples 13 through 22 are presented in Table 2.
Unlike Examples 1 through 22, in Comparative Examples 1 through 5, the high-temperature, pure NMMO containing no dissolved pulp was introduced into a kneader and was mixed with cellulose powder and swelled in the kneader. The resulting product was dissolved in the extruder to produce a cellulose solution.
In Comparative Examples 6 through 8, unlike the Examples, only a twin-screw type extruder was used without using a kneader. Thus, liquid-state NMMO at a concentration 86.5% by weight, which was maintained at 95° C., was introduced into a first barrel, and cellulose powder was introduced to a third barrel through a lateral twin-screw type feeder. A cellulose solution was produced by mixing, swelling and dissolving the cellulose, while adjusting the temperature of the twin-screw type extruder. The other processing conditions are presented in Table 3, in comparison with those of Examples 1 through 22.
According to the present invention, cellulose is pulverized by controlling the moisture content of a pulp sheet, and a small amount of the cellulose powder is dissolved in concentrated liquid-state NMMO to lower the solidification temperature of the NMMO. By this, an NMMO solution can be fed to a kneader at a relatively low temperature, and the cellulose powder and the NMMO solution can be easily mixed and swelled in the kneader at low temperatures. When only a high-temperature NMMO solution is used, rapid swelling and dissolving at the surface of the cellulose powder or powder lumps may occur during the initial mixing and swelling process, and thus aggregation of the cellulose powder may occur. In addition, only the surface of the powder lumps is dissolved or swelled, while the powder at the inner side takes a long time to be dissolved, thus undissolved components possibly being generated. However, according to the method of the invention, when an NMMO solution having a small amount of the cellulose powder dissolved in concentrated liquid-state NMMO, the solidification temperature of the NMMO is lowered, and NMMO can be introduced and mixed in definite amounts at a low temperature, thereby rapid generation of film on the surface of the cellulose powder or powder lumps possibly being prevented. Further, a homogeneous cellulose solution can be produced even at a low temperature, and upon spinning, a low temperature homogeneous cellulose solution can be used to inhibit the property of cellulose undergoing decomposition at high temperatures in the extruder, thus allowing production of cellulose molded articles having excellent flexibility and strength.
In particular, pulp having low specific gravity can be easily introduced into a kneader having a high internal space as suggested in the present invention, and thus the output of the solution and the output of the cellulose molded articles can be increased. Also, direct introduction of concentrated NMMO at a concentration of about 86.5% by weight eliminates the need for a separate water evaporating unit utilizing reduced pressure, thus simplifying the structure of the apparatus. In addition, by controlling the particle size and the moisture content of the powdered cellulose, the swelling and dissolution of the surface film of the cellulose due to aggregation of the cellulose powder, and subsequent occurrence of undissolved cellulose particles can be prevented. Accordingly, the filter exchange interval is shortened. Furthermore, a cellulose paste which has been preliminarily swelled is produced in the kneader and fed to a twin-screw type extruder in a state having the minimum volume, and thus screw arrangement inside the twin-screw type extruder is less stressful. That is to say, insertion of reverse screw elements or kneading discs can be minimized, and thus the residence time distribution for the cellulose solution in the extruder may be made narrow, thus decomposition of the cellulose being prevented. The use of a twin-screw type extruder having high shear force efficiency immediately after the kneader, allows reduction of the dissolution time and dissolution temperature, and since reduction of the original degree of polymerization of pulp is minimized, the high molecular weight can be maintained. Thus, a cellulose fiber having excellent properties can be produced by the method according to the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0116907 | Dec 2004 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR05/04677 | 12/30/2005 | WO | 00 | 1/18/2006 |
