Technical Field
[0001] The present invention relates to a method for producing a cellulose solution which
is homogeneous at low temperatures, and to fiber produced by the method. More particularly,
the invention relates to a production of a cellulose solution which is homogeneous
at low temperatures, by dissolving a small amount of the cellulose powder in concentrated
liquid N-methylmorpholine-N-oxide (NMMO) to lower the solidification temperature of
NMMO, introducing the low-temperature, concentrated liquid NMMO solution having cellulose
dissolved and the cellulose powder into a kneader, mixing and swelling the cellulose
in the kneader without a process of reducing pressure to produce a paste, and then
supplying the paste into an extruder to dissolve the paste in a homogeneous solution.
Background Art
[0002] The fiber produced from the cellulose solution has excellent tenacity and dimensional
stability, and thus can be usefully used for making a single fiber or a filament for
clothing, as well as for making an industrial filament fiber or a reinforcing material
for rubber products such as a tire and a belt.
[0003] Cellulose has very high affinity for other materials, but cellulose is hardly soluble
in general solvents because of the crystalline structure formed from the molecular
chain or the strong hydrogen bonding between the chains. Among the solvents that are
capable of destroying such the crystalline structure and producing a solution, the
most widely used is N-methylmorpholine-N-oxide (NMMO).
[0004] The process for production of cellulose fiber using the NMMO solvent is frequently
used in the processes for production of cellulose-based products, from the perspectives
that the solvent can be all recovered, recycling of the solvent involves a pollution-free
process, and the fiber and film thus produced have high mechanical strength.
[0006] U.S. Patent Nos. 4,142,913,
4,144,080 disclose manufacturing methods for making cellulose solution by obtaining cellulose
solution by under reduced pressure distillation of cellulose that is swelled and dispersed
in NMMO hydrates, solidifying the cellulose solution to a precursor (solid-state)
by cooling the cellulose solution(a kind if 'making chips') and melting in an extruder.
These methods simplify the melting process by using an extruder, but require relatively
long time and a large amount of energy because of the preceding 'making chips'. And
also, the precursor is hard to protect from heat and humidity.
[0007] U.S. Patent No. 5,584,919 discloses a manufacturing method for making cellulose solution by preparing solid-state
NMMO comprising 5 to 17% by weight water, feeding the solid-state NMMO with cellulose
powder into a horizontal cylinder-type high speed mixer and mixing them to make a
granule type precursor, and melting the precursor using an extruder. This method,
however, has a disadvantage of a wide distribution of the obtained the precursor and
low yield. If the volume of the raw material is larger, the distribution of the obtained
precursor is more widened. And a complicated cooling apparatus is required to transfer
and store the precursor. And also, the solid-state NMMO is hard to manufacture and
store.
[0008] U.S. Patent Nos. 5,094,690,
5,534,113 and
5,603,883 disclose a manufacturing method for making cellulose solution by dispersing cellulose
in the NMMO comprising 40% by weight water to make slurry, removing the water from
the slurry by using a Force-drive type thin-layer distillation apparatus that can
form a thin, solution-layer, and obtaining the cellulose solution. These methods,
however, have disadvantages of a low efficiency to the volume of the raw material
because the slurry was distilled the water and melted by rotating of the rotor so
slurry was downstreamed. It caused a short dwelling time in the above apparatus. And
also, these methods require a relatively long time and relatively a large amount of
energy to produce cellulose solution, and the obtained fiber using the above cellulose
solution gets worse the tenacity by degradation of cellulose and change of color of
the NMMO.
[0009] U.S. Patent Nos. 5,421,525,
5,456,748,
5,534,113 and
5,888,288 disclose manufacturing methods cellulose solution by mixing pulp crashed into irregular
flat type with NMMO comprising 22% by weight water in a horizontal cylinder-type mixer
and swelling them, swelling again by stirring for hours in a storage hopper, removing
the water form the high viscid solution by using a Force-drive type thin-layer distillation
apparatus so as to obtain the melted cellulose solution. These methods, however, have
a disadvantage of extra handling and feeding of dust pulp produced as byproduct during
when crash the pulp into irregular flat type pulp. And also, it is hard to operate
the horizontal cylinder-type mixer to discharge the swelled solution. In
U.S. Patent No. 5,921,675 discloses a horizontal cylinder-type mixer comprising a conveyor screw at the outlet
of the mixer.
[0010] U.S. Patent No. 5,948,905 discloses a manufacturing method for making cellulose solution by distilling the
water from a mixture of cellulose and NMMO hydrates comprising about 23% by weight.
In this method, the mixture was distilled under reduced pressure during passing the
nozzle having 1.5 to 6.0millimeter diameter. It is composed of multi-stage chambers.
The first-stage chamber has a small number of nozzles having relatively large diameter.
As the chamber's stage is increased, the number of nozzle is increased and the diameter
of the hole of the nozzle is decreased so as to increase the cross-sectional area
in order to upgrade the efficiency of water vaporization. At the stage of eighth,
the last stage, an extruder is used. This method, however, has a disadvantage of needing
of a highly complicated apparatus that is composed of many chambers different each
other and comprised too many screws for shifting the chambers and distilling stages.
[0011] PCT WO 1997/47790 discloses a manufacturing method for making cellulose solution by solving cellulose
powder in the liquid-state NMMO directly in a twin-screw type extruder. The cellulose
solution is produced by feeding the liquid-state NMMO comprising 12% by weight water
into the first barrel of the extruder maintaining an inner temperature of 100°C, feeding
cellulose powder into the third barrel of the extruder maintaining an inner temperature
of 75°C, shifting and mixing them, and obtaining the solution by rising the temperature
to 120°C. In this method, however, three barrel of the extruder is used for feeding
the cellulose powder and NMMO, and another barrel is required for melting the cellulose.
In fact, there is a relatively short swelling zone so as to obtain cellulose solution
comprising un-dissolved cellulose particles. So, this method is effective to proceed
relatively small amount of raw material, however, it is not proper to adapt a. mass
production of cellulose solution because there are too many un-dissolved moiety. And
it is not proper economically because of requiring a lot of filter system. And also,
this method has a disadvantage of too short spinning cycle. If the swelling zone of
the extruder is increased by increasing the number of blocks and the L/D(length/diameter)
of the screw, it is hard to control the swelling condition and the melting condition
concurrently because the screws of the extruder are driven by single driving shaft.
[0012] Korean patent application laid-open publication No.
2002-24689 discloses a manufacturing method for making highly homogenized cellulose solution
by obtaining a mixture of swelled cellulose pulp powder and liquid-state NMMO by using
the liquid-state NMMO that is overcooled by cooling air and melting the mixture. This
method, however, is hard to control the temperature of the overcooled NMMO by using
the cooling air and to control the content of the NMMO because of exposing of the
moisture contained in the cooling air.
[0013] As described above, the prior arts provided manufacturing methods for making cellulose
solution by contacting cellulose with NMMO containing 20 to 40% by weight water firstly,
then, distilling the water by using a variety of distillation apparatus, followed
by swelling and melting the cellulose. There are, however, some disadvantages of shifting
high viscose solution, equipping an apparatus for dwelling the raw materials for the
time to distill the water from high viscose solution, an oversizing of an apparatus
for distilling water under reduced pressure and a large amount of energy consuming,
etc. And, there is an idea according to the prior arts to manufacture cellulose solution
by solving cellulose powder directly in the liquid-state NMMO comprising about 13%
by weight. This method, however, has a disadvantage of remaining undissolved moiety
that caused by melting the cellulose immediately without swelling when the cellulose
contacts with the NMMO maintaining at the temperature of 80°C(the crystallization
temperature of NMMO) or more that has too high reaction activation.
[0014] When observing the cellulose fiber of the pulp for solving morphologically, the holes
(hereinafter, referred to as 'pit') that penetrate water and the thickness of the
cell walls were distributed not uniformly. So, there are some areas that water can
penetrate easily and other areas that water can penetrate hardly. And this made some
differences to penetrate NMMO in the cellulose in a predetermined time. And, these
tendencies were showed in case of manufacturing pulp from wood fiber according to
the kinds of wood fiber and processes used for making pulp. Consequently, to obtain
fully homogenized cellulose solution, it is required that the solvent is fully penetrate
to the cellulose wholly and swelled the cellulose. Otherwise, there remains some un-dissolved
moiety by not fully melted that caused by regional differences of the solubility inter-
or intra-fibers of the cellulose fibers. Thus, controlling the packing state of cellulose
and the reaction activity of NMMO is a critical technique in the manufacture of cellulose
solutions.
[0015] Post-published documents
EP 1 500 724 A and
EP 1 493 753 A both relate to methods for preparing lyocell fibers comprising a first step of preparing
a NMMO solution containing low amounts of cellulose and a further step of mixing this
solution with cellulose powder in an extruder, but do not disclose all essential features
of the method of the present invention.
Disclosure of the Invention
[0016] Conventional methods for making cellulose solutions have problems such as complicated
processes which are disadvantageous in mass production, undesirable addition of purification
processes due to cellulose decomposition and NMMO discoloration occurring as the time
for production of solution is lengthened, cellulose decomposition due to high temperature,
and low homogeneity of the cellulose solution. In order to solve these problems and
thus to produce homogeneous cellulose solutions for lyocell, it is desired that the
NMMO solvent sufficiently penetrates into the macrostructure and the microstructure
of cellulose over the entire surface area within a short period of time at a low temperature
and a low shear force, thereby the NMMO solvent indefinitely swelling cellulose and
then dissolving the cellulose.
[0017] The present invention solves such conventional problems and, thus provides a homogeneous
cellulose solution even at low temperatures and a method for producing cellulose fiber
from the cellulose solution.
[0018] It is an object of the invention to provide a cellulose solution by dissolving a
small amount of the cellulose powder in concentrated liquid N-methylmorpholine-N-oxide
(NMMO) to lower the solidification temperature of NMMO; subsequently introducing the
low-temperature, concentrated liquid NMMO solution and the cellulose powder into a
kneader; making a paste by mixing and swelling the cellulose or by partially dissolving
the cellulose in the NMMO solution in the kneader without reducing pressure; and then
feeding the paste into an extruder to dissolve the cellulose to a homogeneous state;
and a fiber produced therefrom.
[0019] The invention is characterized in that when a kneader system is used, complete dissolution
does not occur in the kneader, and a paste prepared by mixing and swelling the cellulose
or by partially dissolving the cellulose is fed into an extruder, in which only the
step of dissolution is carried out. Therefore, according to the invention, a large
quantity of solution can be produced in a unit time, compared with the conventional
method of using an extruder only, which is constituted of respective compartments
for introducing raw materials employing NMMO of high concentration to dissolve cellulose,
mixing, swelling, and dissolving. In addition, the method of the present invention
is advantageous in that a simple mechanical apparatus is used, compared with the conventional
method of using a complicated apparatus in which NMMO of low concentration is used
to mix and swell cellulose, and then the cellulose is dissolved while the solvent
is concentrated by removing water.
[0020] According to the invention, the method for making a cellulose fiber from a homogeneous
cellulose solution comprises the steps of (A) preparing an NMMO solution by dissolving
a cellulose powder in concentrated liquid N-methylmorpholine-N-oxide (NMMO) to a small
amount of 0.01 to 5% by weight; (B) introducing the NMMO solution having a small amount
of the cellulose powder dissolved and the cellulose powder into a kneader, subsequently
making a paste by mixing and swelling the cellulose in the kneader without reducing
pressure, and then feeding the paste into an extruder; (C) spinning the cellulose
solution by extrusion through a spinning nozzle, and then solidifying the spun cellulose
solution which has passed through an air bed to reach a solidifying bath, to obtain
a multi-filament; and (D) washing, drying, oil-treating and winding the obtained multi-filament.
[0021] According to the invention, the NMMO solution at the step (A) contains moisture in
an amount of 10 to 18% by weight of the total weight of the NMMO solution.
[0022] According to the invention, after the dissolution in the extruder in the step (B),
the final cellulose solution contains cellulose at a concentration of 5 to 20% by
weight of the total weight of the cellulose solution.
[0023] According to another suitable embodiment of the invention, the liquid NMMO having
a small amount of cellulose dissolved may be maintained at a temperature of 50°C to
95°C in the step (A).
[0024] According to another suitable embodiment of the invention, the kneader into which
the NMMO solution having the small amount of cellulose dissolved and the cellulose
powder are introduced may be maintained at 50°C to 95°C in the step (B).
[0025] According to another suitable embodiment of the invention, the liquid NMMO having
a small amount of cellulose dissolved at the step (B) may be fed to the kneader while
being maintained at a temperature of 50°C to 95°C.
[0026] According to another suitable embodiment of the invention, the cellulose powder at
the step (A) or the step (B) may be mixed with other polymer materials.
Brief Description of the Drawings
[0027] Hereinbelow, the present invention will be described in detail with reference to
the accompanying drawings in which:
Fig. 1 is a scheme briefly illustrating the process for producing a homogeneous cellulose
solution by dissolving a small amount of the cellulose powder in NMMO of the invention;
Fig. 2 is a scheme illustrating the entire production process for according to the
invention; and
Fig. 3 is a diagram showing the change behavior of the solidification temperature
of NMMO in accordance with the pulp concentration.
Best Mode for Carrying Out the Invention
[0028] Fig. 1 is a scheme briefly illustrating the procedure of the process for producing
a homogeneous cellulose solution at a low temperature by dissolving a small amount
of cellulose in NMMO according to an embodiment of the present invention.
[0029] The cellulose powder used in Fig. 1 is obtained by pulverizing by means of a pulverizer
equipped with a knife bar, and has a particle size of 5000 µm or less, and more specifically
500 µm or less. When the size of the cellulose powder exceeds 5000 µm, it is difficult
to uniformly disperse the cellulose powder, and thus there is a problem that the swelling
process requires a long time.
[0030] In concentrated liquid NMMO, a small amount of the cellulose powder having a particle
size of 5000 µm 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 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
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.
[0031] 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.
[0032] 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 NMMO solution in accordance with the
degree of polymerization of the cellulose polymer.
[0033] 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 NMMO,
and thus a homogeneous solution cannot be obtained.
[0034] 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 L/D of
the screw exceeds 64, an excessive stress may be exerted on the screws, and thereby
the screws may undergo deformation.
[0035] 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.
[0036] Fig. 2 is a scheme briefly illustrating the process of the invention for producing
a highly homogeneous cellulose solution used for the production of lyocell, and the
fiber. Referring to Fig. 2, a pulp sheet 1 is conveyed by a nip roller 5 to a pulverizer
6. 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 µm or less, and more specifically,
500 µm or less, can be favorably used. When the particle size of the powder is 5000
µm 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.
[0037] 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 NMMO
and the cellulose powder 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 NMMO 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.
[0038] 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.
[0039] 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 fed to the solidifying bath 13 by pump 16.
[0040] Fig. 3 is a diagram illustrating the change behavior of the solidification temperature
of NMMO in accordance with the cellulose concentration. Referring to Fig. 3, it can
be seen that even if a small amount (about 0.01 to 6%) of cellulose is dissolved,
the solidification temperature of NMMO is remarkably lowered from 75°C to 30°C.
[0041] As shown in Fig. 1, according to the invention, a small amount of the cellulose powder
is dissolved in concentrated liquid NMMO in order to lower the solidification temperature
of the NMMO solution. By this, the NMMO solution can be fed to the kneader in the
liquid state at a relatively low temperature. Thus, the process can be carried out
in a wide range of temperature, and also, the cellulose powder and the NMMO solution
can be easily mixed and swelled at a low temperature. This prevents generation of
film on the surface of the cellulose powder, and eventually, a cellulose solution
which is homogeneous even at low temperatures can be produced.
[0042] 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
[0043] 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)
[0044] The intrinsic viscosity [IV] of the dissolved cellulose is measured as follows. 0.5M
cupriethylenediamine hydroxide solution in the range of 0.1 to 0.6g/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.
(c) The properties of the cellulose fiber produced according to the invention were
measured as follows.
[0045]
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)
EXAMPLES 1 THROUGH 12
[0046] 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 µm 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 µm, and liquid 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 NMMO, 0.001% by weight, with
respect to the concentrated liquid NMMO, of an antioxidant was added and dissolved.
[0047] The liquid NMMO and the cellulose powder were metered into a dissolution tank equipped
with a combination mixer for high viscosity dissolution, and an NMMO solution having
NMMO 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 mmΦ, 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.
[0048] The cellulose solution was discharged through a nozzle having 1,000 orifices, in
which the orifice diameter was 150 µm, and the orifice 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.
[0049] The results of Examples 1 through 12 are presented in Table 1.
Table 1
Example |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
Concentration of cellulose dissolved in NMMO solution (%) |
0.01 |
0.1 |
0.1 |
0.5 |
0.5 |
0.5 |
1.2 |
1.2 |
1.2 |
1.2 |
2.0 |
2.5 |
Temperature of NMMO solution introduced into kneader (°C) |
78 |
75 |
75 |
67 |
70 |
65 |
59 |
53 |
60 |
57 |
53 |
87 |
Temperature of kneader (°C) |
75 |
70 |
85 |
70 |
75 |
68 |
67 |
51 |
66 |
66 |
55 |
91 |
Rotating speed of kneader (rpm) |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
20 |
30 |
25 |
30 |
30 |
Rotating speed of extruder (rpm) |
200 |
200 |
200 |
180 |
200 |
230 |
200 |
180 |
250 |
200 |
150 |
250 |
Temperature of final barrel in extruder (°C) |
105 |
100 |
100 |
95 |
100 |
95 |
105 |
95 |
100 |
95 |
95 |
105 |
Amount of produced solution(kg/hr) |
110 |
140 |
130 |
180 |
170 |
180 |
220 |
170 |
230 |
170 |
160 |
235 |
Moisture content of cellulose powder (%) |
4.3 |
3.9 |
4.1 |
3.9 |
4.0 |
4.0 |
4.2 |
4.8 |
4.4 |
4.9 |
4.0 |
7.5 |
Homogeneity of solution (1∼5) |
2 |
2 |
2 |
1 |
1 |
2 |
1 |
1 |
1 |
3 |
2 |
2 |
DPw of filament |
1010 |
1030 |
960 |
990 |
1000 |
970 |
1040 |
1020 |
930 |
1020 |
1020 |
980 |
Strength of filament (g/d) |
7.0 |
7.3 |
6.7 |
7.1 |
7.0 |
6.5 |
7.0 |
7.5 |
6.9 |
6.9 |
7.3 |
7.2 |
Elongation of filament (%) |
5.9 |
6.1 |
5.4 |
6.2 |
6.7 |
6.4 |
5.7 |
5.9 |
5.4 |
5.0 |
5.5 |
6.5 |
[0050] 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 µm 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 µm, and liquid 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 NMMO, 0.001% by weight, with respect to the
concentrated liquid NMMO, of an antioxidant was added and dissolved.
[0051] The liquid NMMO and the cellulose powder were metered into a dissolution tank equipped
with a combination mixer for high viscosity dissolution, and an NMMO solution having
NMMO 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 mmΦ, 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.
[0052] The cellulose solution was discharged through a nozzle having 50 orifices, in which
the orifice diameter was 150 µm, and the orifice 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.
[0053] 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.
[0054] The results of Examples 13 through 22 are presented in Table 2.
Table 2
Example |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
concentration of cellulose dissolved in NMMO solution (%) |
0.1 |
0.1 |
0.5 |
0.5 |
1.2 |
1.2 |
1.2 |
2.0 |
3.0 |
5.0 |
Temperature of NMMO solution introduced into kneader (°C) |
75 |
75 |
67 |
70 |
63 |
65 |
65 |
61 |
55 |
52 |
Temperature of kneader (°C) |
70 |
80 |
75 |
75 |
67 |
70 |
75 |
65 |
57 |
54 |
Rotating speed of kneader (rpm) |
30 |
30 |
30 |
30 |
20 |
30 |
25 |
30 |
30 |
30 |
Rotating speed of extruder(rpm) |
180 |
180 |
180 |
230 |
180 |
250 |
200 |
150 |
250 |
250 |
Temperature of final barrel in extruder (°C) |
100 |
95 |
95 |
100 |
95 |
100 |
105 |
95 |
105 |
100 |
Amount of produced solution(kg/hr) |
160 |
160 |
210 |
220 |
180 |
220 |
190 |
170 |
180 |
240 |
Moisture content of cellulose powder (%) |
4.9 |
4.3 |
3.7 |
4.5 |
4.9 |
4.2 |
5.3 |
4.9 |
4.5 |
4.7 |
Homogeneity of solution (1 ∼ 5) |
1 |
2 |
1 |
1 |
1 |
1 |
2 |
2 |
2 |
1 |
DPw of filament |
750 |
730 |
750 |
700 |
720 |
690 |
710 |
760 |
745 |
630 |
Strength of filament (g/d) |
5.3 |
5.7 |
4.9 |
5.4 |
5.5 |
4.8 |
5.3 |
6.1 |
6.3 |
4.5 |
Elongation of filament (%) |
7.1 |
7.4 |
7.2 |
6.7 |
6.9 |
7.0 |
6.5 |
6.3 |
6.7 |
8.1 |
COMPARATIVE EXAMPLES 1 THROUGH 8
[0055] Unlike Examples 1 through 22, in Comparative Examples 1 through 5, the high-temperature,
pure NMMO containing no dissolved cellulose powder 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.
[0056] In Comparative Examples 6 through 8, unlike the Examples, only a twin-screw type
extruder was used without using a kneader. Thus, liquid 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.
Table 3
Comparative Example |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
D P |
1200 |
1200 |
1200 |
1200 |
850 |
850 |
850 |
850 |
Concentration of cellulose dissolved in NMMO solution (%) |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
Temperature of NMMO solution introduced into kneader (°C) |
95 |
- |
- |
- |
95 |
- |
- |
- |
Temperature of kneader(°C) |
90 |
- |
- |
- |
90 |
- |
- |
- |
Rotating speed of kneader (rpm) |
30 |
- |
- |
- |
25 |
- |
- |
- |
Rotating speed of extruder rpm) |
200 |
150 |
200 |
250 |
200 |
150 |
200 |
250 |
Temperature of final Barrel in extruder °C) |
105 |
95 |
95 |
95 |
105 |
100 |
95 |
105 |
Amount of produced solution kg/hr) |
105 |
55 |
65 |
80 |
120 |
65 |
70 |
80 |
Moisture content of Cellulose Powder %) |
5.1 |
4.1 |
4.1 |
3.9 |
5.1 |
4.3 |
4.5 |
3.9 |
Homogeneity of Solution (1 ∼ 5) |
3 |
3 |
2 |
4 |
3 |
4 |
2 |
2 |
DPw of filament |
1020 |
1050 |
990 |
900 |
690 |
740 |
700 |
680 |
Strength of filament (g/d) |
6.3 |
7.1 |
6.9 |
6.5 |
5.5 |
5.7 |
5.4 |
4.9 |
Elongation of filament %) |
5.5 |
5.2 |
4.8 |
4.0 |
6.5 |
7.0 |
6.7 |
6.5 |
Industrial Applicability
[0057] 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 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 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.
[0058] 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.