U.S. patent application number 10/565098 was filed with the patent office on 2008-03-06 for method for producing cellulose fiber.
Invention is credited to Soo-Myung Choi, Sung-Ryong Kim, Ik-Hyun Kwon, Tae-Jung Lee, Young-Soo Wang.
Application Number | 20080054516 10/565098 |
Document ID | / |
Family ID | 36615178 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080054516 |
Kind Code |
A1 |
Kwon; Ik-Hyun ; et
al. |
March 6, 2008 |
Method for Producing Cellulose Fiber
Abstract
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.
Inventors: |
Kwon; Ik-Hyun; (Kyonggi-do,
KR) ; Choi; Soo-Myung; (Kyonggi-do, KR) ;
Wang; Young-Soo; (Kyonggi-do, KR) ; Kim;
Sung-Ryong; (Kyonggi-do, KR) ; Lee; Tae-Jung;
(Kyonggi-do, KR) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Family ID: |
36615178 |
Appl. No.: |
10/565098 |
Filed: |
December 30, 2005 |
PCT Filed: |
December 30, 2005 |
PCT NO: |
PCT/KR05/04677 |
371 Date: |
January 18, 2006 |
Current U.S.
Class: |
264/211 |
Current CPC
Class: |
D01D 1/02 20130101; D01F
2/00 20130101 |
Class at
Publication: |
264/211 |
International
Class: |
D01F 1/10 20060101
D01F001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 2004 |
KR |
10-2004-0116907 |
Claims
1. A method for producing a cellulose fiber comprising the steps
of: (A) preparing an N-methylmorpholine-N-oxide solution by
dissolving a cellulose powder in concentrated liquid-state
N-methylmorpholine-N-oxide (NMMO) to a small amount of 0.01 to 5%
by weight; (B) introducing the N-methylmorpholine-N-oxide solution
having a small amount of the cellulose powder dissolved and
cellulose powder into a kneader, mixing, swelling and partially
dissolving the cellulose in the kneader without reducing the
pressure to produce a paste, and then feeding the paste to an
extruder to obtain a homogenized cellulose solution; (C) spinning
the cellulose solution by extrusion through a spinning nozzle, and
then solidifying the spun cellulose solution which has reached a
solidifying bath through an air bed to obtain a multi-filament; and
(D) washing, drying, oil-treating and winding the obtained
multi-filament.
2. The method for producing a cellulose fiber according to claim 1,
wherein the liquid-state N-methylmorpholine-N-oxide having a small
amount of cellulose dissolved is maintained at a temperature of
50.degree. C. to 95.degree. C. in the step (A).
3. The method for producing a cellulose fiber according to claim 1,
wherein the kneader into which the N-methylmorpholine-N-oxide
solution having a small amount of cellulose dissolved are
introduced is maintained at 50.degree. C. to 95.degree. C. in the
step (B).
4. The method for producing a cellulose fiber according to claim 1,
wherein the final cellulose solution prepared by dissolution in the
extruder in the step (B) contains cellulose at a concentration of 5
to 20% by weight with respect to the total weight of the
solution.
5. The method for producing a cellulose fiber according to claim 1,
wherein the N-methylmorpholine-N-oxide solution at the step (A)
contains moisture in an amount of 10 to 18% by weight with respect
to the total weight of the solution.
6. The method for producing a cellulose fiber according to claim 1,
wherein the liquid-state N-methylmorpholine-N-oxide having a small
amount of cellulose dissolved is supplied to the kneader while
being maintained at a temperature of 50.degree. C. to 95.degree. C.
in the step (B).
7. The method for producing a cellulose fiber according to claim 1,
wherein the cellulose powder at the step (A) or step (B) is mixed
with other polymer materials.
Description
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-state
N-methylmorpholine-N-oxide (NMMO) to lower the solidification
temperature of NMMO, introducing the low-temperature, concentrated
liquid-state 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.
[0005] U.S. Pat. No. 3,447,935 discloses the process for production
of cellulose fiber using the NMMO solvent.
[0006] U.S. Pat. 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. Pat. 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. Pat. 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.
[0009] 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.
[0010] U.S. Pat. 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 by-product
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. Pat. No. 5,921,675
discloses a horizontal cylinder-type mixer comprising a conveyor
screw at the outlet of the mixer.
[0011] U.S. Pat. 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 6.0 millimeter 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.
[0012] 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.degree. C.,
feeding cellulose powder into the third barrel of the extruder
maintaining an inner temperature of 75.degree. C., shifting and
mixing them, and obtaining the solution by rising the temperature
to 120.degree. 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 undissolved 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 undissolved 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.
[0013] 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.
[0014] 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 over-sizing 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.degree. C.(the
crystallization temperature of NMMO) or more that has too high
reaction activation.
[0015] 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 pre-determined 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 not-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.
DISCLOSURE OF INVENTION
Technical Problem
[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.
[0017] 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.
Technical Solution
[0018] 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.
[0019] It is an object of the invention to provide a cellulose
solution by dissolving a small amount of the cellulose powder in
concentrated liquid-state N-methyl-morpholine-N-oxide (NMMO) to
lower the solidification temperature of NMMO; subsequently
introducing the low-temperature, concentrated liquid-state 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.
[0020] 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.
[0021] According to a suitable embodiment of 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-state
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 multifilament; and
(D) washing, drying, oil-treating and winding the obtained
multifilament.
[0022] According to another suitable embodiment of the invention,
the liquid-state NMMO having a small amount of cellulose dissolved
may be maintained at a temperature of 50.degree. C. to 95.degree.
C. in the step (A).
[0023] 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.degree. C. to 95.degree. C. in the step (B).
[0024] According to another suitable embodiment of the invention,
the NMMO solution at the step (A) may contain moisture in an amount
of 10 to 18% by weight of the total weight of the NMMO
solution.
[0025] According to another suitable embodiment of the invention,
after the dissolution in the extruder in the step (B), the final
cellulose solution may contain cellulose at a concentration of 5 to
20% by weight of the total weight of the cellulose solution.
[0026] According to another suitable embodiment of the invention,
the liquid-state 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.degree. C. to 95.degree. C.
[0027] 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.
Advantageous Effects
[0028] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Hereinbelow, the present invention will be described in
detail with reference to the accompanying drawings in which:
[0030] 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;
[0031] FIG. 2 is a scheme illustrating the entire production
process for according to the invention; and
[0032] FIG. 3 is a diagram showing the change behavior of the
solidification temperature of NMMO in accordance with the cellulose
concentration.
BEST MODE FOR CARRYING OUT THE INVENTION
[0033] 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.
[0034] 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 mm or less, and more specifically 500
mm or less. When the size of the cellulose powder exceeds 5000 mm,
it is difficult to uniformly disperse the cellulose powder, and
thus there is a problem that the swelling process requires a long
time.
[0035] 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.degree. 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.degree. 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.
[0043] 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.
[0044] 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.
[0045] 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.degree. 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.
[0046] 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.degree. 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.
[0047] 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.degree. 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.degree. C. to
105.degree. 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.
[0048] 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.degree. C. to 30.degree. C.
[0049] As shown in FIG. 1, according to the invention, a small
amount of the cellulose powder is dissolved in concentrated
liquid-state 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.
[0050] 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.
[0051] (a) Homogeneity of Cellulose Solution
[0052] 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.
[0053] (b) Degree of Polymerization (DPw)
[0054] 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.degree. 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.times.10.sup.-2DP.sub.w.sup.0.9
[0055] (c) The properties of the cellulose fiber produced according
to the invention were measured as follows.
[0056] Dry strength: strength after drying at 107.degree. C. for 2
hours (g/d)
[0057] Wet strength: strength measured after standing at 25.degree.
C. and 65% RH for 24 hours (g/d)
MODE FOR THE INVENTION
Examples 1 Through 12
[0058] 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.degree. 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.
[0059] 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.degree. 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.degree. C., while the
barrel temperature at the final discharge section was maintained at
95 to 105.degree. 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.
[0060] 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.degree. 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.
[0061] The results of Examples 1 through 12 are presented in Table
1.
TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12
Concentration of cellulose 0.01 0.1 0.1 0.5 0.5 0.5 1.2 1.2 1.2 1.2
2.0 2.5 dissolved in NMMO solution (%) Temperature of NMMO solution
78 75 75 67 70 65 59 53 60 57 53 87 introduced into kneader
(.degree. C.) Temperature of kneader (.degree. 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
105 100 100 95 100 95 105 95 100 95 95 105 extruder (.degree. C.)
Amount of produced solution 110 140 130 180 170 180 220 170 230 170
160 235 (kg/hr) Moisture content of cellulose 4.3 3.9 4.1 3.9 4.0
4.0 4.2 4.8 4.4 4.9 4.0 7.5 powder (%) 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
Examples 13 Through 22
[0062] 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.degree. 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.
[0063] 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.degree. 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 .phi. and the
barrel temperature at the initial feeding section was maintained at
50 to 70.degree. C., while the barrel temperature at the final
discharge section was maintained at 95 to 105.degree. 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.
[0064] 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.degree. 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.
[0065] 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.
[0066] The results of Examples 13 through 22 are presented in Table
2.
TABLE-US-00002 TABLE 2 Example 13 14 15 16 17 18 19 20 21 22
Concentration of cellulose 0.1 0.1 0.5 0.5 1.2 1.2 1.2 2.0 3.0 5.0
dissolved in NMMO solution (%) Temperature of NMMO solution 75 75
67 70 63 65 65 61 55 52 introduced into kneader (.degree. C.)
Temperature of kneader (.degree. 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 100 95 95 100 95 100 105 95 105
100 extruder (.degree. C.) Amount of produced solution(kg/hr) 160
160 210 220 180 220 190 170 180 240 Moisture content of cellulose
4.9 4.3 3.7 4.5 4.9 4.2 5.3 4.9 4.5 4.7 powder(%) 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
[0067] 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.
[0068] 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.degree. 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-US-00003 TABLE 3 Comparative Example 1 2 3 4 5 6 7 8 DP 1200
1200 1200 1200 850 850 850 850 Concentration of cellulose dissolved
0 0 0 0 0 0 0 0 in NMMO solution (%) Temperature of NMMO solution
95 -- -- -- 95 -- -- -- introduced into kneader (.degree. C.)
Temperature of kneader(.degree. 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 105 95 95 95 105 100 95 105 extruder(.degree.
C.) Amount of produced solution(kg/hr) 105 55 65 80 120 65 70 80
Moisture content of Cellulose 5.1 4.1 4.1 3.9 5.1 4.3 4.5 3.9
Powder(%) 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
[0069] 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.
[0070] 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.
* * * * *