Note: Descriptions are shown in the official language in which they were submitted.
~i~3~21
SPINNING DEVICE
The invention is concerned with a spinning device for
carrying out the amine-oxide process according to the
dry/wet-spinning process, wherein a spinneret is used
comprising spinning holes for extruding filaments, a
container containing spinning bath liquid, a bundling means
provided in the spinning bath liquid for bundling the
extruded filaments and an air gap defined as the distance of
the spinneret to the surface of the spinning bath liquid.
In general terms, the technique of the dry/wet-spinning
process consists in that dope is extruded through a forming
tool, such as a spinneret, into a medium which is non-
precipitating for the dope, such as air or an inert gas,
whereby, when a spinneret is used, filaments are produced
which are stretched in this medium and subsequently conducted
into a spinning bath liquid (precipitation bath), wherein the
filaments coagulate.
In general terms, amine-oxide process refers to the
production of cellulose moulded bodies using tertiary amine-
oxides. In this process, cellulose is dissolved in a mixture
of a tertiary amine-oxide and water, the solution is moulded
by means of a forming tool and conducted through an aqueous
precipitation bath wherein the cellulose is precipitated. As
the amine-oxide, primarily N-methylmorpholine-N-oxide (NMMO)
is used. Other amine-oxides are described e.g. in EP-A - 0
553 070. A process for the production of mouldable cellulose
solutions is known i.e. from EP-A - 0 356 419.
The operation of the amine-oxide process according to the
dry/wet-spinning process is known e.g. from DE-A - 29 13 589.
From WO 93/19230 and WO 95/04173 of the applicant, an advantageous embodiment
of the amine-oxide process and a device for the production of
cellulose fibres are known, whereby a solution of cellulose
in a tertiary amine-oxide is moulded in hot state, and the
moulded solution is introduced through a gaseous medium (air)
~~33~~~
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into the precipitation bath to precipitate the cellulose
therein contained, the hot, moulded solution being cooled
before introducing it into the precipitation bath. Cooling is
carried out immediately after moulding, consisting preferably
in that air is blown horizontally to the cellulose moulded
body. By means of the process according to that.invention the
cellulose solution can be spun with a high filament density,
preventing the adhesion between individual filaments after
being extruded from the spinneret.
DD-A - 218 121 is also concerned with a dry/wet-spinning
process for the production of cellulose fibres from cellulose
solutions in tertiary amine-oxides. Also according to this
process, the cellulose solution is spun into an air gap, i.e.
the space between the spinneret and the surface of the
spinning bath liquid, stretched and conducted into an aqueous
precipitation bath. In DD-A - 218 121 it is mentioned that
the air gap may be reduced without any negative effects on
the spinning safety, when before spinning a polyalkylene
ether is added to the cellulose solution. A small air gap is
advantageous, since the risk of an adhesion between the
individual fresh extruded filaments is reduced.
In EP-A - 0 574 870, a dry/wet-spinning process for
processing solutions of cellulose in tertiary amine-oxides is
described, pointing out the advantage of a small air gap.
According to the specification of this patent application,
this spinning process can be carried out employing a small
air gap and a high number of spinning holes per area unit. It
is maintained that inspite of these conditions, the adhesion
between the individual filaments during the spinning
operation can be prevented. It is recommended to carry out
the contacting of the spun filaments with the spinning bath
liquid in a-spinning funnel. Spinning bath liquid is
conducted through this spinning funnel in parallel flow to
the filaments. The axis of the spinning funnel is
substantially vertical to the plane of the spinneret, and the
flow of the spinning bath liquid is directed downwards from
~~~~o~~
-3-
above, the flow originating generally from the gravitational
fall of the spinning bath liquid.
According to EP-A - 0 574 870, the drawing or stretching of
the fresh extruded filaments is attained in that the
filaments are accelerated substantially to their drawing rate
by the spinning bath liquid flowing through the spinning
funnel .
This known spinning device has the disadvantage that the
funnel pipe of the spinning funnel sets an upper limit to the
filament bundles to be conducted therethrough with regard to
its total section, due to its relatively small diameter.
Additionally, this limit is set at an unsatisfactorily low
level for an industrial-scale realization of the process.
Thus, according to the experience of the present applicant,
when employing a diameter of 6 mm, as exemplified in EP-A - 0
574 870, it is only possible to conduct a filament bundle
consisting of not more than 100 filaments through the funnel,
since spinning bath liquid also has to be transported through
the funnel. This means that when such a spinning funnel is
used, only a spinneret comprising not more than 100 spinning
holes may be employed.
On the other hand, when a wide spinneret having thousands of
spinning holes is used, such as described for instance in the
Austrian Patent AT-B 397.392 of the applicant, the
funnel pipe has to be appropiately wider and thus a lot more
spinning bath liquid is discharged and has to be circulated.
This high throughput of spinning bath liquid causes turbulent
flows in the spinning bath, interfering with the dry/wet-
spinning process.
In GB-A - 1,017,855, a device for dry/wet-spinning of
synthetic polymers is described, recommending also the use of
a spinning funnel, wherethrough spinning bath liquid is
allowed to flow in parallel flow to the extruded fibres. The
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spinneret is located approximately 0,5 cm above the spinning
bath surface.
It is the object of the invention to provide a spinning
device whereby it is possible to carry out the amine-oxide
process according to the dry/wet-spinning process without
complex equipment and achieving a good spinnability (high
spinning safety). A good spinnability means attaining a
maximum final drawing as high as possible (minimum titer)
before the fibre breaks. Another indicator for spinnability
is the period of time during which spinning is possible
without the occurrence of spinning deficiencies which require
technical assistance. Moreover, even when using spinnerets
having high hole densities, the adhesion of the fresh
extruded filaments in the air gap is to be prevented, and a
titer as constant as possible (low titer variations) is to be
attained.
The spinning device according to the invention for carrying
out the amine-oxide process according to the dry/wet-spinning
process comprising
- a spinneret having spinning holes for extruding
filaments,
- a blowing device whereby the extruded filaments may be
cooled immediately after being delivered from the
spinning holes,
- a container containing spinning bath liquid,
- a bundling means provided in the spinning bath liquid
for bundling the extruded filaments, and
- an air gap defined as distance of the spinneret to the
surface of the spinning bath liquid,
is characterized in that
- the bundling means is located at such a distance from
the spinneret that the angle (a) formed by the filaments
with respect to the vertical to the surface of the
spinning bath liquid does not exceed 45° and
- that the relation
CA 02183627 2005-O1-26
-5-
~h - 1~
0,1 + 0,0051 <- 0,7.do .
h
is fulfilled, wherein do is the distance (mm) between a
spinning hole and its neighbouring spinning hole on the
spinneret, h is the distance (mm) of the bundling means to the
spinneret and 1 is the air gap (mm), and wherein
0,4 mm <- d o <- 2 mm and
0 mm < 1 < 60 mm.
According to an aspect of the present invention, there is
provided a spinning device for carrying out a wet/dry-spinning
process for a solution of cellulose in an aqueous tertiary
amine-oxide, the process comprising
- a spinneret having spinning holes for extruding
filaments,
- a blowing device whereby said extruded filaments
may be cooled immediately after being delivered
from the spinning holes,
- a container containing spinning bath liquid,
- a bundling means provided in said spinning bath
liquid for bundling said extruded filaments, and
- an air gap defined as distance of said spinneret
to the surface of said spinning bath liquid,
wherein
- said bundling means is located at such a distance from
said spinneret that the angle (a) formed by the
filaments with respect to the vertical to the surface
of said spinning bath liquid does not exceed 45° and
- that the relation
~h - 1~
0,1 + 0,0051 <- 0,7.do .
h
is fulfilled, wherein do is the distance (mm) between
a spinning hole and its neighbouring spinning hole on
said spinneret, h is the distance (mm) of said
bundling means to said spinneret and 1 is said air gap
(mm) , and wherein
CA 02183627 2005-06-10
-5a-
0, 4 mm <_ d o S 2 mm and
0 mm < 1 < 60 mm.
It has been shown that the object of the invention is attained
by designing the employed spinning device such that the two
criteria mentioned above (angle a does not exceed 45°;
inequations mentioned above are fulfilled) are met. When using
spinnerets having a high hole density it is necessary to cool
the freshly extruded filaments immediately after being
delivered by the spinning holes. This cooling is known to the
skilled person from the state of the art (see e.g. WO 95/04173
of the applicant).
A preferred embodiment of the spinning device according to the
invention is characterized in that the bundling means is
designed as a diverting means whereon the filaments are not
only bundled but also diverted.
It has proven advantageous to provide the diverting means such
that it will not rotate when diverting the filaments. Thus,
according to this embodiment, no rotat<~ble roll or cylinder is
provided. This serves to prevent torn-off filaments from
wrapping around the diverting means, gnus facilitating the
operation of the amine-oxide process.
Another preferred embodiment of the spinning device according
to the invention is.characterized in that the angle a does not
exceed 20°. It has been shown that it is of vital importance
for the spinning safety in the dry/wet-spir._ning process that
the drawing angle a in the air gap is as small
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as possible and preferably does not exceed 20°. Thus the risk
of an adhesion between individual filaments in the space
between the spinneret and the surface of the spinning bath
can be minimized and the spinning safety can be increased.
The invention is also concerned with a spinning device for
carrying out the amine-oxide process according to the
dry/wet-spinning process comprising
- a spinneret having spinning holes for extruding
filaments,
- a blowing device whereby the extruded filaments may be
cooled immediately after being delivered from the
spinning holes,
- a container containing spinning bath liquid,
- a diverting means provided in the spinning bath liquid
for bundling and diverting the extruded filaments, and
- an air gap defined as the distance of the spinneret to
the spinning bath liquid,
which is characterized in that the diverting means is
designed such that it will not rotate when diverting the
filaments.
Another appropiate embodiment of the spinning device
according to the invention consists in that the spinneret
comprises
- a substantially rotationally symmetrical nozzle body
having in its center a feeding for cooling gas,
- a feeding for the cellulose solution,
- an annular spinning insert having spinning holes and
- a baffle plate for diverting the cooling gas flow
towards the filaments which are extruded from the
spinning holes, so that the cooling gas stream hits the
filaments essentially at right angles.
That embodiment enables spinning with a still higher hole
density while at the same time effectively preventing the
adhesion of the fresh extruded filaments in the air gap.
"'~30~7
L
Cooling of an annular filament bundle by means of blowing
cooling air at it is known from WO 95/04173 of the applicant.
Another preferred embodiment of the spinning device according
to the invention consists in that the container containing
the spinning bath liquid is connected to a lifting device
whereby the container can be moved towards and away from the
spinneret in vertical direction, distance 1 thus being
varied, and that the bundling means is arranged such that the
distance h remains constant inspite of this movement.
By means of the drawing consisting of Figures 1, 2 and 3, an
embodiment of the invention will be illustrated. The drawing
shows a general illustration of the dry/wet-spinning process
including the relevant parameters for the relation according
to the invention.
In Figure 1, 1 denotes a container for the spinning bath
liquid, the surface of the spinning bath liquid being
indicated by la. During spinning operation, dope is extruded
through spinneret 3, and extruded filaments 4, 5 are drawn
across the air gap 1 into the spinning bath liquid, wherein
they coagulate. At diverting means 2, which is a non-
rotatable cylindrical bar, the coagulated filaments are
bundled, diverted and drawn diagonally upwards. As the air
gap 1, the distance of the bottom of spinneret 3 to the
surface la of the spinning bath liquid is defined. The angle
defined above formed by the filaments vertically to the
surface of the spinning bath liquid is indicated by a.
Reference number 4 denotes a filament delivered from a
spinning hole located at the outermost edge of an annular
ring formed by the spinning holes in spinneret 3. dl is the
radius (mm) of the circle limiting the annular ring formed by
the spinning holes towards the outside, dp indicates the
distance of this spinning hole to its neighbouring spinning
hole 5, denoting in each case the distance between each of
the centers of the two neighbouring spinning holes. h is the
CA 02183627 2005-O1-26
distance of diverting means 2 to spinneret 3 and 1 is the air
gap.
According to the embodiment described in Figure 1, container 1
is located on a lifting device (not shown) whereby container 1
can be moved vertically, thus varying in a simple way the size
of air gap 1.
It has proven particularly advantageous not to fix diverting
means 2 to container l, but provide that container 1 can be
moved while at the same time distance h remains constant. In
this simple way, air gap 1 can be varied while keeping
distance h constant. This represents an essential
simplification when adjusting the spinning device according to
the invention. Figures 2 and 3 show such embodiments of the
spinning device according to the invention.
Figure 2 substantially shows the spinning device of Figure 1,
the same means being denoted by the same reference numbers.
The non-rotatable diverting means 2 is connected to a fixed
means 7 by means of a rigid arm 6 not connected to container
1, so that when lifting or lowering container 1 means 7 will
not be moved simultaneously. Means 7 may be for instance a
wall. In Figure 2, two positions of container 1 are indicated,
the lower position being indicated by a dotted line. The
device for lifting and lowering container 1 is not shown. From
Figure 2 it is evident that by means of lifting and lowering
container 1, the air gap can be shortened or lengthened, while
distance h remains constant.
Figure 3 illustrates another embodiment of the spinning device
according to the invention. In this embodiment, diverting
means 2 is anchored to the ground by means of a rigid arm 9.
Arm 9 rises to an appropriate outlet 11 provided in container
1. To prevent liquid from being lost from said container 1, a
jacket 10 for sealing is provided, which simply is folded when
container 1 is lowered by means of a device not shown.
CA 02183627 2005-O1-26
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By means of the following Examples 1, 2, 3 and 4, the
invention will be described in still more detail, Examples 1
and 2 revealing the effect of angle a on the spinnability of
cellulose solutions. Example 4 demonstrates the advantageous
effect of a non-rotatable diverting means on spinnability.
Example 1
A spinning device corresponding substantially to Figure 1 was
used, although as the bundling means a spinning funnel
according to EP-A - 0 574 879 was used. As the spinneret, the
one described in WO 95/04173 was used.
This known spinneret (number of holes: 3960; hole diameter:
100 Vim; external diameter of the nozzle (outermost row of
holes) d1: 145 mm) exhibits a substantially rotationally
symmetrical nozzle body having in its center a feeding for
cooling gas, a feeding for cellulose solutions (13,50 of
cellulose; temp.. 120°C), an annular, deep-drawn spinning
insert of precious metal having spinning holes, said spinning
insert having a tub-shaped section, and a baffle plate to
direct a cooling gas stream to cellulose filaments which are
extruded from the spinning holes (output: 0,025 g/min), so
that the cooling gas stream (24 m3/h) strikes the extruded
cellulose filaments substantially essentially at right angles.
The spinning holes in the spinning insert are spaced
substantially at identical distances from each other
(hole/hole-distance d0: 1000 um).
The air gap 1 had a length of 15 mm. The air in the air gap
had a temperature of 24,5°C and a water content of 4,5 g of
water/kg of air.
Several spinning tests were carried out, varying distance h of
the bundling point of the funnel (boundary between the
cylindrical pipe to the funnel itself) to the spinneret
surface in such a way that the relation
zl~3~zl
-lo-
(h-1)
0,l+0,0051 _< o,7.do~ h
(1 = 15 and dp = 1000) was fulfilled, while air gap 1
remained unchanged. In each test, the highest achievable
final drawing, i.e. the maximum drawing rate of the filaments
at breaking of the fibre, was measured. The results are shown
in Table 1:
TABLE 1
h (mm) Angle a final drawing
(m/min)
240 16,8 43
190 20,9 42
140 27,4 42
90 38,8 41
70 46,0 29
40 61,1 0
From Table 1 it can be seen that up to an angle of about 40°
no reduction of the final drawing rate and thus no
deterioration of spinnability can be observed. From an angle
of 45° onwards however, the maximum final drawing rate is
significantly reduced. At an angle of about 61°, the solution
is no more spinnable.
Example 2
A spinning device corresponding to Figure 2 was used, and
again as the spinneret the one described schematically in WO
95/04173 (number of holes: 28 392; hole diameter: 100 Vim;
external diameter of the nozzle (outermost row of holes) dl:
155 mm; hole/hole-distance d0: 500 Vim) was used.
The cellulose solution used contained 13,5 of cellulose and
had a temperature of 120°C. The output was 0,025 g/min. The
air gap 1 had a length of 20 mm. The air in the air gap had a
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temperature of 12°C and a water content of 5 g of water/kg of
air.
The filaments were diverted at a cylindrical, non-rotatable
bar 2 and drawn diagonally upwards from the spinning bath.
While air gap 1 remained unchanged, distance h again was
varied, and the maximum final drawing rate and angle a were
determined. The results are given in Table 2.
TABLE 2
h (mm) Angle a final drawing
(m/min)
345 13° 18
165 25° 18
115 34° 18
75 46° 4
As can be seen from Table 2, when changing the angle a in a
range of from 13° to 34°, the maximum final drawing rate will
not be reduced. However, when increasing the angle a to 46°,
the final drawing rate, i.e. the spinnability, is drastically
reduced. When distance h is further reduced (and thus the
angle a increased), the solution is no more spinnable.
Example 3
The same spinning device as described in Example 2 was used,
the air gap 1 however was held constant at 30 mm. Distance h
was again varied. The spinning safety of the solution under
the given conditions was determined according to the
occurrence of spinning deficiencies (filament break, extreme
adhesion of the filaments among each other).
The spinning safety is high when in a period of time of more
than 15 minutes practically no spinning deficiencies will
occur. When spinning deficiencies abound within a period of
15 minutes or even before, spinning at an industrial scale is
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only possible when continuous technical assistance is
provided.
Subsequently, the spinning safety is defined by a time
indication. In the following Table 3, the indication "> 15
min" means that spinnability was good (practically no
spinning deficiencies within 15 minutes). An indication of
e.g. "< 10 min" means that already in less than 10 minutes
after spinning start, massive spinning deficiencies which
require an interruption of spinning will occur.
TABLE 3
h (mm) Angle a Spinning
safety
345 13° > 15 min
165 25° > 15 min
115 34° > 15 min
100 38° 10-15 min
85 42° < 10 min
From Table 3 it can be seen that up to a distance h of 115
mm, the spinnability is good. However, when h is chosen still
smaller, the relation defined according to the invention is
no more fulfilled and spinnability will deteriorate
drastically. This is the case for the last two tests. This
deterioration of the spinning behaviour occurs in the present
Example already at an angle a clearly below 45°.
Example 4
In a pilot plant for the production of cellulose fibres
according to the amine-oxide process, the way the filaments
are diverted in the spinning bath in the spinning device
according to the invention was examined in numerous
individual tests.
Rotationally symmetrical rotatable diverting means of many
designs (rolls including glass sticks having a smooth or
ribbed surface) were tested. In these tests, it was
CA 02183627 2005-O1-26
- 13 -
repeatedly found out that, as soon as the diverting means
rotates around its own axis, filaments will wrap around the
diverting roll within a short period of time. The reason for
this wrapping around evidently is that in the spinning bath,
fibres sometimes will break, are collected by the rotating
diverting roll, dragged along by the diverting roll, and will
lead to an increased wrapping around by dragging along other
filaments. In this process, the spun filaments are
deteriorated, since the filaments wrapped around the diverting
means have to be removed by means of a mechanical intervention
that implies a deterioration of the final product.
It has been shown that when using a rotatable diverting roll,
the spinning process has to be interrupted in a period of time
of less than 30 minutes to remove the fibres wrapped around
the diverting means.
When rotation of the diverting means is impeded by e.g.
designing it as a rigid means while maintaining the other
parameters, practically no wrapping around will occur. It has
been shown that in this way, a continuous spinning process can
be maintained for several hours. Thus the use of rotatable
diverting means has to be avoided. To guarantee a satisfactory
operation, it is necessary to design, if possible, all
diverting means as non-rotatable means.
