Note: Descriptions are shown in the official language in which they were submitted.
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MELTBLOWN PROCESS WITH MECHANICAL ATTENUATION
FIELD OF THE INVENTION
The present invention relates to a process for producing filaments employing a
modified meltblown process and more particularly to a process for producing
lyocell filaments
employing a modified meltblown process that mechanically attenuates the
filaments.
BACKGROUND OF THE INVENTION
In the past decade, major cellulose fiber producers have engaged in the
development of
processes for manufacturing shaped cellulose materials including filament and
fibers based on
the lyocell process. One process for producing lyocell filaments known as a
meltblown process
can be generally described as a one step process in which a fluid dope is
extruded through a
row of orifices to form a plurality
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of filaments while a stream of air or other gas stretches and attenuates the
hot
filaments. The latent filaments are treated to precipitate the cellulose. The
filaments
are collected as continuous filaments or discontinuous filaments. Such a
process is
described in International Publication No. WO 98/07911 assigned to
Weyerhaeuser
Company, the assignee of the present application.
Lyocell filaments produced by an existing meltblown process are
characterized by variability in diameter along their length, variability in
length and
diameter from filament to filament, a surface that is not smooth and a
naturally
imparted crimp. In addition it has been observed that lyocell filaments made
by a
meitblown process exhibit fibrillation at desirably low levels. These
properties of
lyocell filaments produced by known meltblown processes make them suitable for
applications where such properties are desirable; at the same time these
properties
make the meltblown lyocell filaments less suitable for other applications
where less
variability in filament diameter, less natural crimp and higher strength are
desired.
Another process for making lyocell filaments is known as dry-jet wet
spinning. An example of dry-jet wet processes is described in U.S. Patent
Nos. 4,246,221 and 4,416,698 to McCorsley III. A dry-jet wet process involves
the
extrusion of a fluid dope through a plurality of orifices to form continuous
filaments
in an air gap. Usually the air in this gap is stagnant, but sometimes air is
circulated in
a direction transverse to the direction that the filaments are traveling in
order to cool
aiid toughen the filaments. The formed continuous filaments are attenuated in
the air
gap by a mechanical tensioning device such as a winder. A tensioning device
has a
surface speed that is greater than the speed at which the dope emerges from
the
orifices.. This speed differential causes the filaments to be mechanically
stretched
resulting in a reduction in the diameter of the filaments and the
strengthening thereof.
The filaments are then taken up by a conveyer or other take up device after
they have
been treated with a non-solvent to precipitate the cellulose and form
continuous
filaments. These filaments can be gathered into a tow for transport and
washing.
Staple fibers can be made by cutting a tow of the filaments. Alternatively,
the
continuous filaments can be twisted to form a filament yarn.
Lyocell filaments formed by a dry-jet wet process are characterized by a
smooth surface and little variability in cross-sectional diameter along a
filament
length. In addition, diameter variability between dry-jet wet filaments is
low.
Further, lyocell filaments from the dry-jet wet process have little if any
crimp, unless
the filaments are post-treated to impart such crimp. It is believed that the
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susceptibility of lyocell filaments made by a dry -jet wet process to
fibrillate is greater than
the susceptibility of fibers made by known meltblown processes to fibrillate.
Therefore,
while lyocell filaments made by a dry-jet wet process or lyocell fibers made
from such
filaments may be preferred for applications where low natural crimp, smooth
surfaces, low
variability in cross sectional diameter along a fiber and low variability in
diameter from
fiber to fiber are desirable, they still may be more susceptible to
fibrillation compared to
lyocell fibers made using known meltblown processes.
As demand for lyocell fibers increases and broadens there is a need for
improved
methods of producing lyocell fibers that are capable of producing fibers with
desirable
properties and without those undesirable properties that are imparted to the
fibers by
existing processes for producing lyocell.
SUMMARY OF THE INVENTION
The present invention provides a process for forming lyocell fibers
comprising:
forming a dope from cellulose; extruding the dope through a plurality of
orifices into a
flowing gas stream; stretching the filaments with the flowing gas stream to
form
substantially continuous elongate filaments; attenuating the filaments by
applying an
external force to the filaments in a direction parallel to a length of the
filaments, the external
force being supplied by something other than the gas stream or gravity; and
regenerating the
filaments.
The present invention provides such an improved method of producing lyocell
filaments that includes the steps of extruding a dope through a plurality of
orifices into a
stream of gas to form substantially continuous elongate filaments. The gas
stream attenuates
and at times stabilizes the extruded filaments. In addition, in accordance
with the present
invention, the filaments are mechanically attenuated using a winder or other
type of take-up
device. The mechanical winder or other take-up device applies an external
force to the
filaments in a direction parallel to the length of the filaments. This force
is in addition to the
force applied by the gas stream or gravity. Lyocell filaments produced by a
process carried
out in accordance with the present invention and lyocell fibers cut from such
filaments
exhibit desirable properties such as low susceptibility to fibrillation,
smooth surfaces, low
variability in cross-sectional diameter along the filament or fiber length and
from fiber to
fiber and little natural crimp. In addition, the filaments and fibers possess
strength properties
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that make them suitable for many applications where lyocell filaments and
fibers are
presently used or contemplated.
A further advantage of the present invention is that it will enable higher
speed
spinning of lyocell filaments compared to the speed at which filaments are
spun using
conventional dry-jet wet or melt blowing processes. Higher speed spinning will
result in
increased production rates by increasing dope throughput. Alternatively, if
dope throughput
is not increased, fiber diameter can be decreased.
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The degree to which the extruded filament is attenuated by the gas and the
degree to which the filament is attenuated mechanically in accordance with the
present invention can vary. For example, in certain embodiments it may be
preferred
that the gas provides most of the attenuation with little mechanical
attenuation. In
other situations it may be preferred that little attenuation results from
introducing the
extruded filament into the gas stream and that most of the attenuation be
provided
mechanically.
Bicomponent cellulose filaments comprising cellulose and other polymers
and filaments comprising blends of cellulose and other materials can also be
produced using a process carried out in accordance with the present invention
by
forming dopes from combinations of cellulose with other polymers.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention
will become more readily appreciated as the same become better understood by
reference to 'the following detailed description, when taken in conjunction
with the
accompanying drawings, wherein:
FIGURE 1 is a block diagram of the steps of a presently preferred
embodiment of forming lyocell filaments in accordance with the present
invention;
FIGURE 2 illustrates one embodiment of an apparatus of carrying out a
process for forming filaments in accordance with the present invention;
FIGURE 3 is a cross-sectional view. of an extrusion head useful with the melt
blowing apparatus of FIGURE 2;
FIGURE 4 is a 1000X scanning electron micrograph of a lyocell filament
formed by a process carried out in accordance with one embodiment of the
present
invention after being subjected to a fibrillation test described in Example 1;
FIGURE 5 is a 1000X scanning electron micrograph of commercially
available Tencel lyocell fibers after being subjected to the same
fibrillation test as
the filaments of FIGURE 4; and
-FIGURE 6 is a graphical representation of the average fiber diameter and the
average coefficient of variability for the MBA filaments of Example 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIlVIENT
While the preferred embodiment of the invention has been illustrated and
described, it will be appreciated that various changes can be made therein
without
departing from the spirit and scope of the invention. For example in the
preferred
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embodiment air is described as the gas; however, it should be understood that
other gases
may function equally well. The plurality of orifices needed in accordance with
the present
invention are described below in the context of a meltblowing head. It should
be understood
that the description using a meltblowing head is exemplary and that other
types of devices
that include a plurality of orifices suitable for extruding a dope into
filaments would be
useful in the present invention.
The following description of an embodiment of the present invention makes
reference to the production of lyocell fibers; however it should be understood
that the
process described below could be carried out using other compositions to make
other types
of fibers, such as bicomponent fibers formed from a dope of a mixture of
cellulose and other
polymers.
In order to produce fibers using a method carried out in accordance with the
present
invention a dope is formed by dissolving cellulose, preferably in the form of
wood pulp in
an amine oxide, preferably a tertiary amine N-oxide containing a non- solvent
for cellulose
such as water. The wood pulp can be any of a number of commercially available
dissolving
or non-dissolving grade pulps from sources such as the Weyerhaeuser Company,
assignee of
the present application, International Paper Company, Sappi Saiccor sulfite
pulp, and
prehydrolyzed kraft pulp from International Paper Company. In addition, the
wood pulp can
be a high hemicellulose, low degree of polymerization pulp as described in
U.S. Patent Nos.
6,210,801 and 6,306,334 and International Publication No. WO 99/47733.
Representative examples of amine oxide solvents useful in the practice of the
present invention are set forth in U.S. Patent No. 5,409,532. The presently
preferred amine
oxide solvent is N-methyl-morpholine-N-oxide (NMMO). Other representative
examples of
solvents useful in the practice of the present invention include
dimethylsulfoxide (DMSO),
dimethylacetamide (DMAC), dimethylformamide (DMF) and caprolactan derivatives.
The
pulp can be dissolved in amine oxide solvent by any art-recognized means such
as are set
forth in U.S. Patent Nos. 5,534,113; 5,330,567 and 4,246,221.
FIGURE 1 shows a block diagram of the presently preferred process for forming
lyocell filaments from cellulose dopes. If necessary, the cellulose in the
form of pulp is
physically broken down, for example by a shredder, before being dissolved in
an amine
oxide-water mixture to form the dope. The pulps can be dissolved in an amine
solvent by
any known manner, e.g., as taught in McCorsley
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U.S. Patent No. 4,246,221. For example, the pulp can be wet in a nonsolvent
mixture
of about 40% NMMO and 60% water. The ratio of pulp to wet NIVIMO can be about
1:5.1 by weight. The mixture can be mixed in a double arm sigma blade mixer
for
about 1.3 hours under vacuum at about 120 C until sufficient water has been
distilled
off to leave about 12%-14% based on NMMO so that a cellulose solution is
formed.
Alternatively, NNIMO of appropriate water content may be used initially to
obviate
the need for the vacuum distillation. This is a convenient way to prepare
spinning
dopes in the laboratory where commercially available NMMO of about 40%-60%
concentration can be mixed with laboratory reagent NMMO having only about 3%
water to produce a cellulose solvent having 7%-15% water. Moisture normally
present in the pulp should be accounted for in adjusting necessary water
present in
the solvent. Reference might be made to articles by Chanzy, H. and A. Peguy,
Journal of Polymer Science, Polymer Physics Ed. 18:1137-1144 (1980), and
Navard,
P. and J.M. Haudin, British Polymer Journal, p. 174 (Dec. 1980) for laboratory
preparation of cellulose dopes in NMMO water solvents.
In accordance with an embodiment of the present invention, the< dope is
processed through a meltblown head which extrudes the dope through a plurality
of
orifices into a turbulent air stream moving generally parallel to the
direction the dope
exits the orifices, rather than directly into an air gap where there is no air
flow or an
air flow transverse to the direction that dope exits the orifices as in the
case of a dry-
jet wet process. Parallel air flow describes the flow of air downstream from
the point
where the dope exits the orifices. As described below in more detail,
depending
upon the particular configuration of the meltblown head, the air exiting the
meltblown head may not necessarily be traveling parallel to the direction that
the
filaments are traveling; however, at some point downstream from the point
where the
dope exits the orifices, in accordance with the present invention, the air
begins to
flow in a direction that is parallel to the direction that the filaments are
traveling.
The high-velocity air draws or stretches the filaments. This air attenuation
differs
from mechanical attenuation by providing more variable tension and may not
provide
a continuous tension due to the turbulence of the air flow. This non-
mechanical
stretching serves two purposes: it causes some degree of longitudinal
molecular
orientation and accelerates the filaments rapidly as they leave the nozzle
orifice, thus
reducing the ultimate fiber diameter. The air stream is also believed to
stabilize the
latent filament as described below in more detail.
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In accordance with the present invention, in addition to the attenuation of
the
filaments provided by the flowing air stream, additional attenuation of the
filaments
is accomplished by applying an external force to the filaments in a direction
parallel
to the length of the filaments where such external force is supplied by
something
other than the gas stream or gravity. In preferred embodiments, such external
force is
provided by a mechanical device such as a take-up device in the form of a
winder or
take-up roll. Such devices provide a mechanical attenuation that complements
and is
in addition to the attenuation provided by the air stream. In particular
embodiments,
the latent filaments can be regenerated before they are taken up by the device
providing the mechanical attenuation. The process carried out in accordance
with the
present invention produces substantially continuous elongate filaments which,
once
they are regenerated, are collected as substantially continuous elongate
filaments.
Such continuous elongate filaments are in contrast to shorter, staple
noncontinuous
fibers produced by prior meltblown processes, such as the one described in
International Publication No. W098/26122.
The dope is delivered at somewhat elevated temperature to the spinning
apparatus by a pump or extruder at temperatures from 70 C to up to about 140
C.
The temperature of the dope should not be so high that rapid decomposition of
the
solvent occurs or so low that the dope becomes brittle and unspinnable.
Regenerating solutions are nonsolvents such as water, a water-NMMO mixture,
lower aliphatic alcohols, or mixtures of these. The NMMO used as the solvent
can
then be recovered from the regenerating bath for reuse. Preferably the
regenerating
solution is applied as a fine spray at some predetermined distance below the
extrusion head.
FIGURE 2 shows details of a presently preferred embodiment of a modified
melt blowing process formed in accordance with the present invention. A supply
of
dope is directed through an extruder and positive displacement pump, not
shown,
through line 200 to an extrusion head 204 having a multiplicity of orifices.
Compressed air or another gas is supplied through line 206. Latent filaments
208 are
extruded from orifices 340 (seen in FIGURE 3) in the Z-direction. These thin
strands
of dope 208 are picked up by the high velocity gas stream traveling in the Z-
direction
created by air exiting intermittent slots 344 (FIGURE 3) in the extrusion
head. The
filaments are significantly stretched or elongated as they are carried
downward by the
air stream. At an appropriate point in their travel the now stretched latent
filaments
strands 208 pass between opposing spray pipes 210, 212 and are contacted with
a
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water spray or other regenerating liquid 214. The regenerated filaments 215
are
picked up by a rotating pickup rol1216 which serves as the source of the
external
force that causes the mechanical attenuations of the filaments. As the pickup
roll
begins to fill up, a new roll 216 is brought in to stretch and collect the
filaments
without slowing production, much as a new reel is used on a paper machine.
The surface speed of ro11216 is faster than the linear speed of the descending
filaments 215 so that the filaments are mechanically drawn. The mechanical
force
exerted on the filaments by the take up device is related to the surface speed
of the
rol1216, the rate that the filaments are carried by the gas stream, and the
speed the
dope is expelled from the orifices. Alternatively, a moving foraminiferous
belt may
be used in place of the roll to collect and mechanically stretch the filaments
and
direct them to any necessary downstream processing. In accordance with the
present
invention, the roller is operated above a minimum surface speed that imparts
at least
some mechanical attenuation to the filaments. The maximum speed at which the
roller can be operated will be determined by a number of factors including the
maximum speed at which a continuous filament can be formed. At the lower
winder
speeds, the filament will tend to be larger in diameter as opposed to
a'filament
formed when the roller is operated at a higher speed. Continuous filaments
have
been made using winder speeds ranging from abo,ut 200-1000 meters/minute. It
should be understood that the present invention is not limited to a specific
type of
take up device, other types of take up devices such as conveyers, belts,
rollers, and
the like can provide satisfactory results.
The regeneration solution containing diluted NMMO or other solvent drips
off the accumulated fiber 220 into container 222. From there it is sent to a
solvent
recovery unit where recovered NMMO can be concentrated and recycled back into
the process.
FIGURE 3 shows a cross section of a presently preferred extrusion head 300
useful, in the presently preferred process. A manifold or dope supply conduit
332
extends longitudinally through the nosepiece 340. Within the nosepiece a
capillary
or multiplicity of capillaries 336 descend from the manifold. These decrease
in
diameter in a transition zone 338 into the extrusion orifices 340. Gas
chambers 342
also extend longitudinally through the die. These exhaust through slits 344
located
adjacent the outlet end of the orifices. Slits or slots 344 are located
intermittently
along the length of head 300, centered on the orifices 340. The width and
length of
slots 344 can vary depending upon a number of factors, such as the volume of
air
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which is desired to flow through slots 334 as well as the desired velocity of
the gas
exiting slots 334. Generally, smaller slots will provide higher velocity gases
for a
given pressure within chamber 342, and larger slots will provide lower gas
velocities
at similar pressures in chamber 342. For the orifice diameters described
below, slots
having a width on the order of 0.01 inches and a length of 0.25 inches have
been
found to be suitable. Internal conduits 346 supply access for electrical
heating
elements or steam/oil heat. The gas supply in chambers 342 is normally
supplied
preheated but provisions may also be made for controlling its temperature
within the
extrusion head itself.
As discussed above, the dope is extruded into a flowing gas stream which
travels in a direction substantially parallel to the direction that the dope
is extruded
through orifice 340. Gas exiting slits 344 join at some predetermined angle to
form a
single jet which flows along the axis dividing the angle formed by the two
opposing
streams of gas. In the illustrated embodiment of FIGURE 3, the jets exiting
slits 344
join at an included angle of 60 and merge to form a single jet which flows
parallel to
the direction that the dope is extruded through slit 340. Accordingly, the
mean air
direction is provided in a direction that is substantially parallel to the
direction that
the dope is extruded from slot 340 and the direction that the latent filaments
travel.
While FIGURE 3 illustrates a preferred embodiment of an extrusion head
useful in accordance with the present invention, it should be understood that
other
types of extrusion heads are useful in accordance with the present invention.
For
example, the extrusion heads described in U.S. Patent No. 4,380,570 and U.S.
Patent
No. 5,476,616 are examples of useful extrusion heads. Another suitable
extrusion
head is described in GB 2337957A to Law.
The capillaries and nozzles in the extrusion head nosepiece of FIGURE 3 can
be formed in a unitary block of inetal by any appropriate means such as
drilling or
electrodischarge machining. Alternatively, due to the relatively large
diameter of the
orifices, the nosepiece may be machined as a split die with matched halves
348, 348"
(FIGURE 3). This presents a significant advantage in machining cost and in
ease of
cleaning.
Spinning orifice diameter may be in the 300-600 m range, preferably
about 400-500 m with a L/D ratio in the range of about 2.5-10. Most desirably
a
lead in capillary of greater diameter than the orifice is used. Capillaries
that are
about 1.2-2.5 times the diameter of the orifice and that have a L/D ratio of
about 10-250 are suitable. Larger orifice diameters utilized in the presently
preferred
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apparatus and method are advantageous in that they are one factor allowing
greater
throughput per unit of time, e.g., throughputs that equal or exceed about
1 g/min/orifice. Further, larger diameter orifices are not nearly as
susceptible to
plugging from small bits of foreign matter or undissolved material in the dope
as are
the smaller nozzles. The larger nozzles are much more easily cleaned if
plugging
should occur and construction of the extrusion heads is considerably
simplified, in
part due to lower pressures required. Operating temperature and temperature
profile
along the orifice and capillary preferably fall within the range of about 70 C
to
about 140 C to avoid a brittle dope or rapid solvent degradation. It appears
beneficial to have a rising temperature near the exit of the spinning
orifices. There
are many advantages to operation at as high a temperature as possible, up to
about 140 C where NMMO begins to rapidly decompose. Among these advantages,
throughput rate may generally be increased due to a reduction of viscosity at
higher
dope temperatures. By profiling orifice temperature, the decomposition
temperature.
may be safely approached at the exit point since the time the dope is held at
or near
this temperature is very minimal. Air temperature as it exits the melt blowing
head
can be in the 40 -140 C range, preferably about 70 C.
The minimum velocity of the gas stream is preferably greater than the
velocity of the dope exiting the orifices so that at least some attenuation of
the
fonned filament is caused by the gas stream. The gas maximum velocity will
depend
on the end result desired. At some maximum velocity staple (discontinuous)
fibers
will be formed, as opposed to continuous filaments which tend to be produced
at
lower gas velocities. The gas velocity can be adjusted in relation to the
surface speed
of the roller and dope flow rate to tailor the amount of non-mechanical
stretching
imparted by the gas stream compared to the mechanical stretching imparted by
the
take up device. For example, gas pressure at the entrance to 0.25 inch long
and
0.010 inch wide slots 344 ranging from about 0.60 to about 19.0 psi provide
gas
velocities of just greater than zero (0) up to sonic. As a specific example,
an air
pressure in chambers 342 of about 4.0 psi provides an air velocity at the exit
of
slots 344 of approximately 175 meters/second when the slots 344 are 0.25 inch
long
and 0.01 inch wide. This flowing air slows down dramatically upon exiting the
slots 344 as it entrains stagnant air from the sides into the expanding jet
created by
these flowing gas jets. In accordance with the present invention, the slow
down of
the air should not be so great that the air stream velocity falls below the
speed that
the filaments are extruded from the orifice.
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Varying the humidity of the gas can affect the properties of the produced
fibers, for example air with a higher humidity tends to produce fibers that
have
smaller diameters, as compared to fibers made using air with a lower humidity.
It has been observed that with mechanical attenuation being applied by the
take up device, there is an advantage to providing a minimum gas flow,
insufficient
to impart any non-mechanical (e.g., gas) attenuation, yet sufficient to
stabilize the
filaments for stretching by the winder. As described above, in conventional
dry-jet
wet process, no air flow or a transverse air flow is provided in the air gap
and it is
believed that the absence of an air flow in this air gap parallel to the
direction the
dope exits the orifices adversely affects the degree to which the dry-jet wet
process
can be controlled. For example, it is believed that the provision of a minimal
gas
flow (i.e., insufficient to attenuate the filaments) parallel to the direction
the dope
exits the die in a conventional dry-jet wet process will stabilize the formed
filaments
from lateral movements which otherwise may result in adjacent filaments
becoming
fused to each other. In addition, a minimal gas flow parallel to the direction
the dope
exits the die may avoid spring back of the latent filaments which can result
in the
formation of loops due to the elasticity of the latent filaments. An
additional benefit
of providing a gas flow parallel to the direction the dope exits the die
relates to the
ability to assist in guiding the filaments to the take up device after they
are initially
formed by the die.
Lyocell filaments having the following properties have been produced by a
process carried out in accordance with the present invention:
Fineness: about 2.2 to 0.5 dtex
Dry Tenacity: about 33 to 42 cN/tex
Wet Tenacity: about 22 to 28 cN/tex
Dry Elongation: about 11 % to 14%
Wet Elongation: about 12% to 15%
Loop Tenacity: about 13 to 18 cN/tex
Dry Modulus: about 670 to 780 cN/tex
Wet Modulus: about 170 to 190 cN/tex
Bundle Strength: about 33 to 47 cN/tex
Diameter variability along fiber about 6 to 17 CV%
Diameter variability between fibers about 10 to 22 CV%
Fibrillation index: about 0 to 1
Dyeability Good
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Smooth Surface texture which can be varied depending on degree of
stretch
Processes carried out in accordance with the present invention are believed to
provide unique opportunities to tailor the properties of lyocell fibers
produced using
such methods. By adjusting the orifice diameter, viscosity of the dope, rate
of
extrusion, gas velocity, and speed of the take-up device, lyocell filaments of
less than
one denier can be produced in accordance with the present invention. Specific
examples of properties of lyocell filaments produced by a process carried out
in
,
accordance with the present invention are described below.
COMPARATIVE EXAMPLE 1
DRY-JET WET
This comparative example illustrates the production of lyocell fibers using a
dry-jet wet process without air attenuation. Dope was prepared from an acid
treated
pulp described in International Publication No. W099/47733 having a
hemicellulose
content of 13.5% and an average cellulose degree of polymerization of about
600.
The treated pulp was dissolved in NN1MO to provide a cellulose concentration
of
about 12 weight percent and spun into filaments by a dry-jet wet process as
described
in U.S. Patent No. 5,417,909. The dry-jet wet spinning procedure was conducted
by
Thuringisches Instut fur Textil-und Kunststoff-Forschung. V., Breitscheidstr
97,
D-07407 Rudolstadt, Germany (TITK) and employed a stagnant air gap or an air
gap
where the air flow was transverse to the direction the filaments traveled. The
procedure produced filaments which were cut into staple fibers. The properties
of the
fibers prepared by the dry-jet wet process are summarized in Table 1 below as
DJW-
TITK.
COMPARATIVE EXAMPLE 2
MELT BLOWING WITHOUT MECHANICAL ATTENUATION
This comparative example illustrates the production of lyocell filaments using
a melt-blowing process without mechanical attenuation. A dope was prepared
from
an acid treated pulp described in Example 10 of International Publication
W099/47743 having a hemicellulose content of 13.5% and an average degree of
polymerization of about 600.
The acid treated pulp was dissolved in NMMO. Nine grams of the dried,
acid-treated pulp were dissolved in a mixture of 0.025 grams of propyl
gallate,
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61.7 grams of 97% NMMO and 21.3 grams of 50% NMMO producing a cellulose
concentration of about 9.8%. The flask containing the mixture was immersed in
an
oil bath at about 120 C, a stirrer was inserted, and stirring was continued
for about
0.5 hours until the pulp dissolved.
The resulting dope was maintained at about 120 C and fed to a single orifice
laboratory melt blowing head. Diameter at the orifice of the nozzle portion
was 483
m and its length about 2.4 mm, a L/D ratio of 5. A removable coaxial capillary
located immediately above the orifice was 685 m in diameter and 80 mm long, a
L/D ratio of 116. The included angle of the transition zone between the
orifice and
capillary was about 118 . The air delivery ports were parallel slots with the
orifice
opening located equidistant between them. Width of the air gap was 250 m and
overall width at the end of the nosepiece was 1.78 mm. The angle between the
air
slots and centerline of the capillary and nozzle was 30 . The dope was fed to
the
extrusion head by a screw-activated positive displacement piston pump. Air
velocity
was measured with a hot wire instrument as 3660m/min. The air was warmed
within
the electrically heated extrusion head to 60-70 C at the discharge point.
Temperature
within the capillary without dope present ranged from about 80 C at the inlet
end to
approximately 140 C just before the outlet of the nozzle portion. It was not
possible
to measure dope temperature in the capillary and nozzle under operating
conditions.
When equilibrium running conditions were established a continuous fiber was
formed from the dope. Throughput was greater than about 1 gram of dope per
minute.
A fine water spray was directed on the descending fiber at a point about
200 mm below the extrusion head and the fiber was taken up on a roll operating
with
a surface speed about 1/4 the linear speed of the descending fiber. The
properties of
the collected fibers are summarized in Table 1 below under the heading MB.
The following Examples 1-3 illustrate and describe embodiments of a process
for producing lyocell filaments in accordance with the present invention and
are
intended for illustrative purposes and not for purposes of limiting the scope
of the
present invention.
EXAMPLE 1
A dope for forming lyocell filaments was made by dissolving in N-methyl
morpholine N-oxide a kraft pulp having an average degree of polymerization of
about 600 as measured by ASTM D 1795-62, and a hemicellulose content of
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CA 02405091 2002-10-04
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about 13% as measured by a Weyerhaeuser Company Dionex sugar analysis method.
The cellulose concentration in the dope was 12% by weight. The dope was
extruded
from a meltblowing die that had 20 nozzles having an orifice diameter of
457 microns at a rate of 0.625 grams/holelminute. The orifices had a
length/diameter
ratio of 5. The die was maintained at a temperature ranging from 100 to 130
degrees
Celsius. The dope was extruded into an air gap 12.7 centimeters long before
coagulation with a water spray. Air at a temperature greater than 90 degrees
Celsius
and a pressure of 20 psi was supplied to the head. The air pressure in the air
cap
(chamber 342 in FIGURE 3) was about 4.0 psi and flowed at a rate of about
18 SCFM. This provided an air velocity at the exit to the air slots of about
175
meters/second. In this example, the slots were 0.25 inches long and 0.010
inches
wide.
Downstream of the air gap, the formed filaments were taken up by a winder
operating at a speed of 500 meter/minute which was greater than the linear
speed of
the filaments in the air gap. Water was used to precipitate the cellulose from
the
formed filaments. The water was applied by spraying it onto the filaments in
advance of the winder. Four different samples were made using the above
process.
The samples were designated MBA-1 through MBA-4.
The collected filaments were washed and dried and then subjected to the
following procedures to assess their fineness (TITK test using DIN EN ISO
1973),
dry tenacity (TITK tests using DIN EN ISO 5079), dry elongation (TITK test
using
DIN EN ISO 5079), wet tenacity (TITK test using DIN EN ISO 5079), wet
elongation (TITK test using DIN EN ISO 5079), relative wet tenacity (i.e., wet
tenacity/dry tenacity), loop tenacity (TITK test using DIN 53 843 T2), dry
modulus
(TITK test using DIN EN ISO 5079), wet modulus (TITK test using DIN EN
ISO 5079), diameter variability CV% (microscope measurement of 200 fibers for
among fiber CV% and 200 readings from a bundle strength (stelometer
measurement
by International Textile Center, Texas Tech University), and fibrillation
properties
(individualized fibers placed in a 25 milliliter test tube with 10 milliliters
of water
and shaken at low amplitude at a frequency of about 200 cycles per minute for
24 hours), evaluated on a scale of 0 to 10, with 0 being low or no
fibrillation as
exemplified in FIGURE 4 and 10 being high fibrillation as exemplified in
FIGURE 5. The abbreviation "TITK" referred to above identifies the German
company, Thutingisches Instut fur Textil und Kunststoff-Forschung eV, - that
performed the described tests.
2 25-03-2002
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The properties of the filaments MBA-1 through MSA-4 are summarized in
Table 1.
The fibrillation index was determined by viewing SEM photos of about 100
fiber segments about 10 microns in length. If 0 to 1 fibril/segment was
observed, the
fiber was rated 0. If each segment included 5-6 fibrils or the segments became
fragmented as in FIGURE 5, a rating of 10 was assigned.
TABLE 1
DJW-
Newcell DJW- DJW-
Sample filament MBA-1 MBA-2 MBA-3 MBA-4 TITK TENCEL MB
Pulp -- Kraft Kraft Kraft Kraft Kraft -- Kraft
Fineness 0.9-3.03 1.72 1.74 2.15 2.17 1.77 1.70 1.21
(dtex)
Tenacity dry 30-42 37.7 34.7 34.6 33.3 35.9 44.2 27.7
(cN/tex)
Tenacity wet 20-27 25.5 24.5 26.1 22.7 27.8 32.4 18.2
(cN/tex)
Relative -- 68 71 75 68 77 73 66
tenacity (%)
Elongation 6-10 12.3 12.1 13.4 11.1 13.0 13.8 11.4
dr (%)
Elongation 8-13 13.0 13.4 14.6 12.0 14.0 14.5 14.9
wet (%)
Loop tenacity 18-29 17.8 17.6 13.9 13.4 9.6 10.5 9.1
(cN/tex),
Modulus dry -- 752 672 701 777 519 829 666
(cN/tex)
Modulus wet -- 188 180 181 170 176 212 123
(cN/tex)
Diameter -- 21.58 10.12 11.01 13.88 7.3 5.2 29.5
variability
CV % (among
fibers)
Diameter -- 7.5 6.9 8.3 7.8 6.1 5.2 13.2
Variability
CV % (along
fibers)
Bundle -- 44.00 45.23 46.07 33.77 -- -- --
strength
(cN/tex)
Bundle -- 10.33 10.08 10.33 7.83 -- -- --
Elongation
(%)
Fibrillation -- 1 0 0 0.5 10 10 0
index
(estimated
from fibrils
in SEM)
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1 -16-
Average -- 12.4 13.1 14.2 13.40 13.5 13.5 11.2
diameter
(micron)
The resulting filaments MBA-1 through MBA-4 possess similar tenacity as
commercial lyocell filaments made by a dry-jet wet process available from
Newcell
GmbH & Co. KG, Kasino Str., 19-21 D-42103 Wuppertal as Newcell
(DJW-Newcell ), but have higher dry elongation than such commercial filaments.
The filaments of Example 1 also have higher loop strength compared to lyocell
staple
fibers prepared from similar dopes using the TITK dry-jet wet method described
in
comparative Example 1. The fibers of Example 1 also have higher dry modulus
compared to lyocell staple fibers prepared from similar dopes using the TITK
dry-jet
wet method of comparative Example 1. In addition, using the test described
above,
the fibers of Example 1 have lower tendency to fibrillate than commercial
lyocell
fibers produced by a dry-jet wet process available from Accordis Company under
the
trademark TENCEL@ (DJW-Tencel@) and the DJW-TITK fibers. Compared to
meltblown lyocell without mechanical stretching (Sample MB), the fibers of
Example 1(MBA-1 through MBA-4) have higher dry and wet tenacity, and lower
diameter variability both among and along the fibers. This example illustrates
properties of lyocell fibers having a fineness on the order of 1 denier
produced in
accordance with the present invention. Lyocell filaments having a denier less
than 1
can be produced by adjusting the dope viscosity, dope throughput in the
orifices, and
the winder speed as described below.
The procedure described above was repeated with dope samples prepared as-
described above. For Samples MBA-5 through MBA-17 set forth in Table 2, the
dopes were spun under the conditions described above except that the winder
speed
was set at either 220 meters/minute, 350 meters/minute, 400 meters/minute, or
600 meters/minute. The diameter and coefficient of variability for the
diameter is set
forth in Table 2 below for samples MBA-5 through MBA-17. For Samples MBA-18
and MBA-19, the dope throughput was reduced to 0.42 grams/hole/minute and
0.25 grams/hole/minute respectively, and the winder speed was 800
meters/minute.
The diameter and diameter variability for Samples MBA-18 and MBA-19 are set
forth in Table 2. The diameter and diameter variability of filaments MBA-1
through
MBA-4 are reported above in Table 1.
CA 02405091 2002-10-04
WO 01/81664 PCT/US01/12554
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Printed:11-04-2002 DESCTRAN EP01927152.7 - PCTUS 01 12554
CA 02405091 2002-10-04
-18-
The resulting filaments MBA-5 through MBA-20 generally had lower
diameters and lower diameter variability among the filaments compared to
meltblown fibers made without mechanical stretching as described above in
Comparative Example 1 and below in Comparative Example 2.
FIGURE 6 is a graph representing the average diameter and the average
coefficient of variability among the filaments for MBA-1 through MBA-16
produced
using the various winder speeds described in Example 1. From the graph, it is
observed that as the winder speed increases, the dry fiber diameter decreases
as well
as the coefficient of variation.
COMPARATIVE EXAMPLE 3
In order to produce filaments using a conventional meltblown process without
mechanical attenuation, the procedure of Example 1 was repeated using a dope
as
described in Example 1 with the exception that the winder speed was
0 meters/minute. Under these conditions, the formed filaments had an average
diameter of 26.1 microns and a coefficient of variation among fibers of 44%.
EXAMPLE 2
The procedure of Example 1 was repeated using a different air pressure. The
winder speed was 500 meters/minute. In this example the pressure of the air
supplied
to the meltblowing head was 1 psi which resulted in a pressure of about 0.6 in
the air
cap (chamber 342 in FIGURE 3). This low pressure provided a perceptible flow
of
air in the air gap traveling at a velocity greater than the linear velocity of
the
filaments exiting the orifices. The air flow was observed to attenuate the
extruded
filaments. The average diameter of the filaments produced was 14.74 microns.
The
filament diameter ranged from 64.12 to 7.10 microns.
COMPARATIVE EXAMPLE 4
DRY-JET WET
The procedure of Example 1 was repeated using a different air pressure and
winder speed. In this example the pressure of the air supplied to this
meltbiowing
head was 0 psi resulting in no flow of air in the air gap. Under these
conditions
filaments could not be produced at a winder speed of 500 meters/min. At such
winder speed with no air flow the extruded dope was observed to break up.
It was observed that in the absence of air flow in the air gap, at start-up of
the
process the frequency at which the extruded filament would not find its way to
the
3 25-03-2002
Printed:11-04-2002 DESCTRAN EP01927152.7 - PCTUS 01 12554
CA 02405091 2002-10-04
-19-
winder was greater compared to the start-up of the process described in
Examples 1
and 2 where air flow was provided in the air gap.
EXAMPLE 3
A dope for forming lyocell filaments was made by dissolving in N-methyl
morpholine N-oxide, a Kraft pulp having an average degree of polymerization of
about 750 as measured by ASTMD1795-62 and a hemicellulose content of
about 13% as measured by a Weyerhaeuser Company dionex sugar analysis method.
The cellulose concentration in the dope was about 12% by weight. The dope was
extruded from a melt blowing dye that had 20 nozzles having an orifice
diameter of
457 microns at a rate of 0.625 grams/hole/minute. The orifices had a
length/diameter
ratio of 5. The nozzle was maintained at a temperature ranging from 100 to
130 C.
The dope was extruded into an air gap 12.7 cm long before coagulation with a
water
spray. Air at a temperature greater than 90 C and a pressure of about 20psi
was
supplied to the head. The air pressure in the air cap (Chamber 342 in FIGURE
3)
was about 4.0 psi and flowed at a rate of about 18 SCFM. This provided an air
velocity at the exit to the air slots of about 175 meters/second.
Downstream of the air gap, the formed filaments were taken up by a winder
operating at a surface speed of about 900 meters/minute. Water was used to
precipitate the cellulose from the formed filaments. The water was applied by
spraying it onto the filaments in advance of the winder.
The collected filaments (MBA-20) were washed and dried and then subjected
to the tests described above in Example 1 to assess their fineness, dry
tenacity, dry
elongation, wet tenacity, wet elongation, loop tenacity, and fibrillation
properties.
The following values were observed:
Fineness (dtex) 1.12
Dry Tenacity (cN/tex) 42.10
Wet Tenacity (cN/tex) 28.10
Dry Elongation (%) 10.60
Wet Elongation (%) 13.10
Loop Tenacity (cN/tex) 16.40
Fibrillation Index 2.00
Average Diameter (microns) 9.40
Diameter Variability (CV%) 21.00
4 25-03-2002
