U.S. patent application number 10/500917 was filed with the patent office on 2005-10-06 for spinning device and method having turbulent cooling by blowing.
Invention is credited to Ecker, Friedrich, Zikeli, Stefan.
Application Number | 20050220916 10/500917 |
Document ID | / |
Family ID | 7711657 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050220916 |
Kind Code |
A1 |
Zikeli, Stefan ; et
al. |
October 6, 2005 |
Spinning device and method having turbulent cooling by blowing
Abstract
The present invention relates to an apparatus for producing
continuously molded bodies from a molding material, such as a
spinning solution containing cellulose, water and tertiary amine
oxide. The apparatus (1) comprises a die plate (3) including
extrusion orifices (4) through which the molding material is
extruded into substantially filament-like continuously molded
bodies (5). The continuously molded bodies (5) are passed through
an air gap (6) and guided in a precipitation bath (9) by a
deflector (10) to a bundling means (12) where they are united into
a bundle of fibers. In the air gap, a blowing means (14) is
provided for directing a cooling gas stream (15) onto the
continuously molded bodies (5) in a direction transverse to the
direction of passage (7). To improve the spinning stability and
mechanical properties of the continuously molded bodies, it is
intended according to the invention that the cooling gas stream
(15) is turbulent when exiting from the blowing means (14).
Inventors: |
Zikeli, Stefan; (Regau,
AT) ; Ecker, Friedrich; (Timelkam, AT) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH, LLP
100 E WISCONSIN AVENUE
MILWAUKEE
WI
53202
US
|
Family ID: |
7711657 |
Appl. No.: |
10/500917 |
Filed: |
March 28, 2005 |
PCT Filed: |
November 11, 2002 |
PCT NO: |
PCT/EP02/12592 |
Current U.S.
Class: |
425/71 ;
425/378.1; 425/382.2; 425/464; 425/72.2 |
Current CPC
Class: |
D01F 2/00 20130101; D01D
5/06 20130101; D01D 5/088 20130101; B60R 11/0241 20130101 |
Class at
Publication: |
425/071 ;
425/072.2; 425/378.1; 425/382.2; 425/464 |
International
Class: |
D01D 005/088 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 2002 |
DE |
102 00 406.4 |
Claims
1. Apparatus for producing continuously molded bodies from a
molding material, such as a spinning solution containing cellulose,
water and tertiary amine oxide, comprising a multitude of extrusion
orifices through which during operation the molding material can be
extruded into continuously molded bodies, a precipitation bath and
an air gap arranged between the extrusion orifices and the
precipitation bath, and a blowing means for producing a cooling gas
streams, the continuously molded bodies being passed during
operation in successive order through the air gap and the
precipitation bath, and the cooling gas stream being directed in
the area of the air gap to the continuously molded bodies, the
cooling gas stream being turbulent at least at the exit from the
blowing means.
2. The apparatus according to claim 1, wherein the cooling gas
stream has a Reynolds number (Re) of at least 2,500 based on its
width (B), measured substantially in the direction of passage of
the continuously molded bodies through the air gap, and on its
velocity in the direction of flow, and the viscosity (v) of the
cooling flow medium.
3. The apparatus according to claim 2, wherein the Reynolds number
is at least 3,000.
4. The apparatus according to claim 1, wherein the velocity of the
cooling stream is at least 30 m/s.
5. The apparatus according to claim 4, wherein the velocity of the
cooling gas stream is at least 40 m/s.
6. The apparatus according to claim 5, wherein the velocity of the
cooling stream is at least 50 m/s.
7. The apparatus according to claim 1, wherein the width of the
cooling stream at the exit is not more than 2 mm.
8. The apparatus according to claim 7, wherein the width of the
cooling gas stream at the exit is not more than 1 mm.
9. The apparatus according to claim 1, wherein the specific blowing
force of the cooling gas stream is at least 5 mN/mm.
10. The apparatus according to claim 9, wherein the specific
blowing force of the cooling gas stream is at least 10 mN/mm.
11. The apparatus according to claim 1, wherein the cooling gas
stream His turbulent in the area of the first row of continuously
molded bodies on which it impinges.
12. The apparatus according to claim 1, wherein the air gap
comprises a first shielding zone by which the cooling gas stream is
separated from the extrusion orifices.
13. The apparatus according to claim 12, further comprising apart
from the first shielding zone, a second shielding zone through
which the cooling area is separated from the precipitation bath
surface.
14. The apparatus according to claim 1, wherein the boundary area
facing the extrusion orifices and located between the cooling area
and the first shielding zone extends substantially in parallel with
a plane in which the extrusion orifices are positioned on
average.
15. The apparatus according claim 1, wherein the extrusion orifices
are arranged on a substantially rectangular base in rows in a
direction transverse to the direction of the cooling gas
stream.
16. The apparatus according to claim 4, wherein the number of the
extrusion orifices in row direction is greater than in the cooling
gas stream direction.
17. The apparatus according to claim 1, wherein the precipitation
bath has disposed therein a deflector by which during operation the
continuously molded bodies are deflected as a substantially planar
curtain to the precipitation bath surface, and that outside of the
precipitation bath there is provided a bundling means by which
during operation the continuously molded bodies are united to form
a fiber bundle.
18. The apparatus according to claim 1, wherein the width (D) of
the cooling gas stream in a direction transverse to the direction
of the passage of the continuously molded bodies through the air
gap is larger that the height (B) of the cooling gas stream in the
direction of passage.
19. The apparatus according to claim 1, wherein the cooling gas
stream (is composed of a plurality of individual cooling gas
streams.
20. The apparatus according to claim 8, wherein the individual
cooling gas streams are arranged side by side in row direction.
21. The apparatus according to claim 1, wherein the cooling gas
stream is designed as a turbulent air flow in the area where the
continuously molded bodies Fare passed through the air gap.
22. The apparatus according to claim 1, wherein the cooling gas
stream a velocity component oriented into the direction of
passages.
23. The apparatus according to claim 1, wherein the molding
material prior to its extrusion has a zero shear viscosity of at
least 10000 Pas, at 85.degree. C.
24. The apparatus according claim 1, wherein the distance of the
cooling area from extrusion orifice in the direction of passage is
at least 2 mm each time.
25. The apparatus according to claim 1, wherein the distance I of
the cooling area in the direction of passage from each extrusion
orifice in millimeters satisfies the following inequality:
I>H+A.multidot.[tan(.b- eta.)-0.14]where H is the distance of
the upper edge of the cooling gas stream in the direction of
passage from the plane of the extrusion orifices at the exit from
the blowing means in millimeters, A is the distance in a direction
transverse to the direction of passage between the exit of the
cooling gas stream of the blowing means in millimeters and the row
of the continuously molded bodies that is the last one in flow
direction, in millimeters, and .beta. is the angle in degrees
between the cooling gas stream direction and the direction
transverse to the direction of passage.
26. The apparatus according to claim 1, wherein the height L of the
air gap in the direction of passage in millimeters satisfies the
following inequality: L>I+0.28.multidot.A+B where I is the
distance of the cooling area from the extrusion orifices in the
area where the continuously molded bodies are passed through the
air gap, A is the distance in a direction transverse to the
direction passage between the exit of the cooling gas stream from
the blowing means and the row of the continuously molded bodies
that is the last one in flow direction, in millimeters, and B is
the height of the cooling gas stream in a direction transverse to
the cooling gas stream direction 1 in the direction of passage at
the exit of the cooling gas stream from the blowing means.
27. A method for producing continuously molded bodies from a
molding material, such as a spinning solution containing water,
cellulose and tertiary amine oxide, the molding material being
first extruded to obtain continuously molded bodies, the
continuously molded bodies being then passed through and air gap
and stretched in said air gap and exposed to a cooling gas stream
from a blowing means, and the continuously molded bodies being then
guided through a precipitation bath, wherein the cooling gas stream
(is put into a turbulent flow state by the blowing means at least
at the exit from the blowing means.
Description
[0001] The present invention relates to an apparatus for producing
continuously molded bodies from a molding material, such as a
spinning solution containing cellulose, water and tertiary amine
oxide, the apparatus comprising a multitude of extrusion orifices
through which during operation the molding material can be extruded
into continuously molded bodies, a precipitation bath, an air gap
arranged between the extrusion orifices and the precipitation bath,
and a blowing means for producing a cooling gas stream, the
continuously molded bodies being guided in successive order through
the air gap and the precipitation bath during operation, and the
cooling gas stream being directed in the area of the air gap onto
the continuously molded bodies.
[0002] The fundamentals of the production of continuously molded
bodies, such as lyocell fibers, from a spinning solution containing
cellulose, water and tertiary amine oxide, preferably
N-methylmorpholine-N-oxide (NMMNO) are described in U.S. Pat. No.
4,246,221. Thus, continuously molded bodies are substantially
produced in three steps: First the spinning solution, is extruded
through a multitude of extrusion orifices to obtain continuously
molded bodies. The continuously molded bodies are then stretched in
an air gap--whereby the desired fiber strength is set--and are
subsequently guided through a precipitation bath where they
coagulate.
[0003] The advantage of lyocell fibers or corresponding
continuously molded bodies lies, on the one hand, in a particularly
environmentally friendly production process which permits an almost
complete recovery of the amine oxide and, on the other hand, in the
excellent textile properties of the lyocell fibers.
[0004] The process, however, poses problems insofar as the freshly
extruded continuously molded bodies show a strong surface
tackiness, which will only be reduced upon contact with a
precipitant. Therefore, when the continuously molded bodies are
passed through the air gap, there is the risk that the continuously
molded bodies will contact one another and immediately stick
together or conglutinate. The risk of conglutinations can be
reduced by adjusting the operation and process parameters, such as
tensile stress in the air gap, air gap height, filament density,
viscosity, temperature and spinning velocity. However, when such
conglutinations occur, the manufacturing process and fiber quality
will be affected in a negative way because the conglutinations may
lead to breaks and thickened portions in the continuously molded
bodies. In the most adverse case the manufacturing method must be
interrupted and the spinning process must be started once again,
which entails high costs.
[0005] Nowadays, a spinning process without conglutinations is
demanded from the manufacturers of continuously molded bodies, for
instance from the yarn manufacturers as part of the textile
processing chain, i.e. the individual filament stacks must not
stick together because otherwise there will be irregularities e.g.
in the yarn thickness.
[0006] A high profitability in the production of lyocell fibers,
mainly staple fibers and filaments, however, can only be achieved
when the spinneret orifices are arranged at a small distance from
one another. A small distance, however, increases the risk of
conglutinations in the air gap due to an incidental contact of the
continuously molded bodies.
[0007] For improving the mechanical and textile properties of
lyocell fibers, it is of advantage if the air gap is as large as
possible because in the case of a large air gap the stretching of
the filaments is distributed over a greater running length and
stresses arising in the continuously molded bodies that are just
being extruded can be reduced more easily. However, the larger the
air gap, the lower is the spinning stability or the greater is the
risk that the manufacturing process must be interrupted because of
the conglutinations of the spun filaments.
[0008] Starting from the principles of U.S. Pat. No. 4,246,221,
there are some solutions in the prior art in which the attempt is
made to improve both the economic efficiency and the spinning
stability in the production of continuously molded bodies from a
spinning solution containing cellulose and tertiary amine
oxide.
[0009] For instance, U.S. Pat. No. 4,261,941 and U.S. Pat. No.
4,416,698 describe a method in which the continuously molded bodies
are brought into contact with a nonsolvent immediately after
extrusion to reduce surface tackiness. Subsequently, the
continuously molded bodies are guided through a precipitation bath.
The additional wetting of the continuously molded bodies by the
nonsolvent prior to their passage through the precipitation bath is
however too complicated and expensive for commercial use.
[0010] Another approach of increasing the spinning-density, i.e.
the number of extrusion orifices per unit area, is taken in WO
93/19230: In the method described therein the continuously molded
bodies are cooled immediately after their extrusion by horizontal
blowing in a direction transverse to the extrusion direction with a
cooling gas stream. This measure reduces the surface tackiness of
the continuously molded bodies, and the air gap can be
extended.
[0011] This solution, however, has the inherent problem that the
cooling gas stream interacts with the extrusion process at the
extrusion orifices and may affect it in a negative way. In,
particular, it has been found in the method of WO 93/19230 that the
spun filaments have no uniform quality because not all of the
filaments have been subjected to the cooling gas stream in the same
way. The risk of sticking together is at any rate not
satisfactorily reduced in the method of WO 98/19230.
[0012] To permit a uniform blowing of the continuously molded
bodies immediately after their delivery from the extrusion
orifices, the apparatus of WO 95/01470 employs a ring nozzle in
which the extrusion orifices are distributed over a substantially
circular surface. Blowing with a cooling gas stream takes place
through the center of the ring nozzle and through the circular ring
of the continuously molded bodies in radial direction horizontally
to the outside. The air flow is here kept in a laminar state when
exiting from the blowing means. The configuration of a laminar air
flow is obviously considerably enhanced by the air guiding means
indicated in the patent specification.
[0013] WO 95/04173 refers to a constructional development of the
ring nozzle and the blowing means that is substantially based on
the apparatus of WO 95/01470.
[0014] Although the solutions of WO 95/01470 and WO 95/05173
actually bring about a more uniform blowing operation, the ring
arrangement of the continuously molded bodies leads to problems
when the continuously molded bodies are passed through the
precipitation bath: since the continuously molded bodies immerse as
a circular ring into the precipitation bath and entrain the
precipitation liquid in the precipitation bath, a region having
insufficient supply of precipitation liquid is created in the area
between the continuously molded bodies, which results in a
compensating flow through the ring of the continuously molded
bodies and in an agitated precipitation bath surface, which in turn
entails the conglutination of the fibers. Moreover, it is also
found with the solutions of WO 95/01470 and WO 95/04173 that it is
very difficult to control the extrusion conditions that are
essential to the mechanical and textile product characteristics and
that prevail at the extrusion orifices.
[0015] As an alternative to the ring nozzle arrangements, segmented
rectangular nozzle arrangements have been developed in the prior
art, i.e. nozzles having the extrusion orifices arranged
substantially in rows on a substantially rectangular base area.
Such a segmented rectangular nozzle arrangement is outlined in WO
94/28218. In this apparatus, blowing is carried out with a cooling
gas stream in a direction transverse to the extrusion direction,
the cooling gas stream extending along the longer side of the
rectangular nozzle arrangement. After passage through the
continuously molded bodies the cooling gas stream is again sucked
off in the apparatus of WO 94/28218. The suction is necessary so
that the air current can be passed through the whole cross-section
of the air gap.
[0016] The concept of rectangular nozzles with extrusion orifices
arranged in rows has been developed further in WO 98/18983. It is
the objective of WO 98/18983 that the extrusion orifices in one row
are spaced apart differently than the rows of the extrusion
orifices among one another.
[0017] Finally, WO 01/68958 describes a blowing operation in a
direction substantially transverse to the direction of passage of
the continuously molded bodies through the air gap with a different
goal. Blowing by means of an air flow is not meant for cooling the
continuously molded bodies, but for calming the precipitation bath
surface of the precipitation bath in the area where the
continuously molded bodies immerse into the precipitation bath and
the spinning funnel, respectively: According to the teachings of WO
01/68985, the length of the air gap can be increased considerably
when the blowing process becomes effective at the immersion points
of the capillary bundles into the precipitation bath so as to calm
the movement of the spinning bath surface. It is assumed that the
strong bath turbulence that is typical of spinning funnels is
reduced by performing a calming blowing operation on the spinning
bath surface in that a liquid transport through the spun filaments
is induced by the blowing process on the precipitation bath
surface. To this end just a weak air flow is provided according to
the teachings of WO 01/68958. It is essential in the teachings of
WO 01/68958 that the blowing operation is performed shortly before
the entry of the continuously molded bodies into the spinning bath
surface. However, at the velocities of the air flow indicated in WO
01/68958 and at the location where the air flow is used for calming
the spinning bath, no cooling effects can be achieved any more in
the continuously molded bodies.
[0018] Thus, in the apparatus of WO 01/68958, in addition to the
blowing operation described therein, which is performed shortly
before the entry of the continuously molded bodies into the
spinning bath surface, a cooling of the spun filaments near the
extrusion orifices is also needed, as is known from the prior art.
The additionally required and necessary cooling, however, results
in a very expensive system.
[0019] In the light of the drawbacks of the solutions known from
the prior art, it is the object of the present invention to provide
an apparatus and a method which allow, at only a small
constructional effort, a combination of large air gap lengths and a
high spinning density at a high spinning stability.
[0020] According to the invention this object is achieved for a
spinning apparatus as indicated at the outset by a cooling gas
stream that is at least turbulent at the exit from the blowing
means.
[0021] So far it has probably been assumed in the prior art that
cooling of lyocell type spun filaments can only be performed by way
of a laminar cooling air flow because a laminar cooling gas stream
produces a smaller surface friction on the continuously molded
bodies than a turbulent flow and the continuously molded bodies are
thus subjected to a reduced mechanical load.
[0022] Surprisingly, it has now been found that, in the case of a
cooling gas stream exiting in a turbulent state and at a high
velocity from the blowing device and having the same cooling
capacity as a laminar cooling gas stream, considerably smaller
amounts of blowing air seem to be needed than has been initially
assumed. Due to the reduced amount of blowing gas, which is
preferably achieved by virtue of small cross-sections of the gas
stream, the surface friction on the continuously molded bodies can
be kept small despite a turbulent blowing, so that the spinning
process is not negatively affected.
[0023] The positive effect of the turbulent cooling gas stream is
all the more astonishing as according to general fluid mechanics an
improved cooling effect in the case of a turbulent flow would have
had to be expected only at a small number of rows. To operate the
spinning process in a economically efficient way at a high hole
density, a multitude of rows must be provided so that according to
fluid mechanics only a fraction of the continuously molded bodies
should actually profit from the improved heat exchange conditions.
Nevertheless, the use of a turbulent cooling gas stream yielded
improved spinning characteristics also in the last rows most
distant from the cooling gas stream.
[0024] Furthermore, one would have expected in the case of a
blowing process performed with a turbulent cooling gas stream at a
high velocity that due to the high velocities the spun filaments
would be blown off and would thus stick together. Surprisingly,
however, it has been found that the spun filaments are not
impaired, but quite to the contrary the gas demand can be reduced
drastically when small turbulent gas streams are used, and the risk
of sticking is very small. Fiber titers of less than 0.6 dtex can
be spun without any problems with turbulent cooling gas streams.
The aspect of the turbulent gas stream cooling operation is
advantageous per se, i.e. independently of the remaining
developments according to the invention.
[0025] A Reynolds number formed with the width of the cooling g as
stream in the direction of passage and the rate of the cooling gas
stream can be at least 2,500, preferably at least 3,000, according
to one development of the invention.
[0026] The velocity of the cooling gas stream is at least 30 m/s,
and excellent results were achieved in first tests at flow rates of
at least 40 m/s, and even better results at flow rates of more than
50 m/s.
[0027] To penetrate a multitude of filament rows, it is very
important that the cooling stream be guided to and through the
filament bundles in an energy intensive way. To meet this
requirement, a blowing means must be designed for producing the
cooling gas stream such that the specific blow force is high on the
one hand and that the distribution of the individual cooling flows
produced by the blowing means meets the demands made on the
filament bundles to be cooled on the other hand.
[0028] According to another advantageous development, the
distribution of the individual cooling flows is meant to yield a
substantially planar jet pattern (flat jet), the width of the
substantially planar jet being required to have at least the width
of the filament curtain to be cooled. Preferably, the planar jet
pattern distribution can also be formed by adjacently arranged
individual round, oval, rectangular or other polygonal jets;
several rows arranged one on top of the other are also possible
according to the invention for forming a planar jet pattern
distribution.
[0029] The specific blowing force is determined as follows: A
nozzle for producing the cooling gas stream with a rectangular
(flat) jet pattern distribution and a maximum width of 250 mm is
mounted in the blowing direction perpendicular to a baffle plate
mounted on a weighing device with an area of 400.times.500 mm. The
nozzle exit forming the exit of the cooling gas stream from the
blowing means is spaced apart from the baffle plate at 50 mm. The
nozzle is acted upon by compressed air having an overpressure of 1
bar and the force acting on the baffle plate is measured and
divided by the width of the nozzle in millimeters. The resulting
value is the specific blowing force of the nozzle with the unit
[mN/mm].
[0030] In an advantageous development a nozzle has a specific
blowing force of at least 5 to 10 mN/mm. With a blowing force of at
least 10 mN/mm enhanced cooling effects can be achieved.
[0031] The rectangular nozzle may comprise several extrusion
orifices arranged in rows, the rows being possibly staggered in the
direction of the cooling gas stream. To achieve a considerable
action of the cooling gas stream also in the rearmost row of the
continuously molded bodies in the direction of the cooling gas
stream, the number of the extrusion orifices in the rectangular
nozzle may be greater in the row direction than in the direction of
the cooling gas stream.
[0032] If rectangular nozzles are used the continuously molded
bodies may in particular be deflected as a substantially planar
curtain within the precipitation bath in the direction towards the
precipitation bath surface, so that the continuously molded bodies
can be bundled, i.e. the continuously molded bodies can be
converged towards an imaginary point, outside the precipitation
bath.
[0033] According to a further advantageous configuration the air
gap comprises a shielding zone immediately after extrusion and a
cooling area separated from the extrusion orifices by the shielding
zone, the cooling area being defined by the gas stream acting as
the cooling gas stream. Thus, the cooling area is that area in
which the cooling gas stream impinges on the continuously molded
bodies and cools the same.
[0034] Surprisingly, in particular in combination with the
turbulent cooling gas stream, this configuration results in a
higher spinning density and in a longer air gap than in
conventional apparatus in which the cooling area directly reaches
the extrusion orifices and a shielding zone does not exist.
[0035] It seems as if the shielding zone, i.e. the spacing of the
cooling gas stream boundary from the extrusion orifices, prevents a
cooling of the extrusion orifices and thus a negative effect on the
extrusion process at the extrusion orifices, which process is
extremely important for the development of the mechanical and
textile properties. Hence, with the design according to the
invention, the extrusion process can be carried out with parameters
which can be exactly defined and exactly observed, in particular
with an exact temperature control of the molding material up to the
extrusion orifices.
[0036] One reason for the surprising effect of the solution
according to the invention could be that the continuously molded
bodies expand in an area-immediately following extrusion. The
tensile force which effects the stretching of the continuously
molded bodies only begins to become effective behind said expansion
zone. In the expansion zone itself, the continuously molded bodies
have no orientation yet and are largely anisotropic. The shielding
zone obviously avoids an action of the cooling gas stream in the
anisotropic expansion zone, which action is detrimental to the
characteristics of the fibers. In the case of the solution
according to the invention the cooling action seems to take place
when the tensile force acts on the continuously molded bodies and
effects a gradual molecular alignment of the continuously molded
bodies.
[0037] To prevent the surface of the precipitation bath from being
agitated by the cooling gas stream, it is provided according to one
particularly advantageous configuration of the apparatus that, in
addition to the first shielding zone, the air gap comprises a
second shielding zone by which the cooling area is separated from
the surface of the precipitation bath. The second shielding zone
prevents the cooling gas stream from contacting the precipitation
bath surface in the immersion area of the filament bundles contacts
and from producing waves that could mechanically stress the
continuously molded bodies upon their entry into the precipitation
bath surface. The second shielding zone is particularly useful when
the cooling gas stream has a high velocity.
[0038] The quality of the continuously molded bodies produced can
surprisingly be improved according to a further advantageous
configuration if the inclination of the cooling gas stream in the
direction passage or extrusion is greater than the expansion of the
cooling gas stream in the flow direction. In this embodiment, the
cooling gas stream at each point in the area of the continuously
molded bodies has a flow component which is oriented in the
direction of passage and supports the stretching operation in the
air gap.
[0039] A particularly, good shielding or insulation of the
extrusion process against the effect of the cooling gas stream is
achieved when the distance of the cooling area from each extrusion
orifice is at least 10 mm. At this distance even strong cooling gas
streams can no longer act on the extrusion process in the extrusion
orifices.
[0040] In particular the distance I of the cooling area from each
extrusion orifice in millimeters according to a further
advantageous embodiment satisfies the following (dimensionless)
inequality:
I>H+A.multidot.[tan(.beta.)-0.14]
[0041] where H is the distance of the upper edge of the cooling gas
stream from the plane of the extrusion orifices to the exit of the
cooling gas stream in millimeters. A is the distance between the
exit of the cooling gas stream and the row of the continuously
molded bodies that is the last one in the direction of flow, in
millimeters, in a direction transverse to the direction of passage,
in which the continuously molded bodies are passed through the air
gap, normally the horizontal direction. The angle in degrees
between the cooling jet direction and the direction transverse to
the direction of passage is designated as .beta.. The cooling gas
stream direction is substantially defined by the central axis or,
in the case of planar cooling streams, by the central plane of the
cooling gas stream. When this dimensioning formula is observed, the
spinning quality and the spinning stability can surprisingly be
improved to a considerable degree.
[0042] The angle .beta. may assume a value of up to 40.degree..
Independently of the angle .beta. the value H should be greater
than 0 at any rate to avoid any influence on the extrusion process.
The distance A may correspond at least to a thickness E of the
curtain of the continuously molded bodies in a direction transverse
to the direction of passage. The thickness E of the filament
curtain is 40 mm at the most, preferably 30 mm at the most, even
more preferably 25 mm at the most. The distance A may in particular
be greater by 5 mm or, preferably by 10 mm, than the thickness E of
the filament curtain.
[0043] Likewise, it has surprisingly been found that the spinning
quality and the spinning stability are both increased if between
the height L of the air gap in the direction of passage in
millimeters, the distance I of the cooling area from the
continuously molded bodies in the direction of passage in
millimeters, the distance A between the exit of the cooling gas
stream and the row of the continuously molded bodies that is the
last one in the direction of flow, transversely to the direction of
passage in millimeters, and the height B of the cooling gas stream
in the direction of passage in millimeters, the following
(dimensionless) relation is satisfied in the area of the air gap
taken up by the continuously molded bodies:
L>I+0.28.multidot.A+B
[0044] The apparatus according to the invention is in particular
suited for producing continuously molded bodies from a spinning
solution which prior to its extrusion has a zero shear viscosity of
at least 10000 Pas, preferably of at least 15000 Pas, at 85.degree.
C. measuring temperature. Owing to the adaptation of the viscosity
of the molding material, which is generally carried out by
selecting the pulp type and the concentration of cellulose and
water in the spinning solution, a certain inherent or basic
strength is imparted to the extrudate, so that stretching into
molded bodies can be carried out. At the same time, the necessary
viscosity range can be set by adding stabilizers and by guiding the
reaction in the preparation of the solution.
[0045] The above-mentioned object underlying the invention is also
achieved by a method for producing continuously molded bodies from
a molding material, such as a spinning solution containing water,
cellulose and tertiary amine oxide, the molding material being
first extruded into continuously molded bodies, the continuously
molded bodies being then guided through an air gap and stretched in
the air gap and subjected to a cooling gas stream from a blowing
means, and the continuously molded bodies being subsequently passed
through a precipitation bath when the cooling gas stream is put
into a turbulent flow state by the blowing means at least at the
exit from the blowing means.
[0046] FIG. 1 is a perspective illustration of an apparatus
according to the invention in a schematic overall view;
[0047] FIG. 2 shows a first embodiment of the apparatus illustrated
in FIG. 1, in a schematic section taken along plane II-II of FIG.
1;
[0048] FIG. 3 is a schematic illustration of the apparatus of FIG.
1 for explaining geometrical parameters;
[0049] FIG. 4 is a schematic illustration for explaining the
processes in a continuously molded body directly after
extrusion.
[0050] First of all, the construction of an apparatus according to
the invention shall be described with reference to FIG. 1.
[0051] FIG. 1 shows an apparatus 1 for producing continuously
molded bodies from a molding material (not shown). The molding
material may, in particular, be a spinning solution containing
cellulose, water and tertiary amine oxide.
N-methylmorpholine-N-oxide may be used as the tertiary aminoxide.
The zero shear viscosity of the molding material at about
85.degree. C. is between 10000 and about 30000 Pas.
[0052] The apparatus 1 comprises an extrusion head 2 which is
provided at its lower end with a substantially rectangular, fully
drilled die plate 3 as the base. The die plate 3 has provided
therein a multitude of extrusion orifices 4 that are arranged in
rows. The number of rows shown in the figures is for illustration
purposes only.
[0053] The molding material is heated and passed through the
preferably heated extrusion orifices where a continuously molded
body 5 is extruded through each extrusion orifice. As schematically
shown in FIG. 1, each continuously molded body 5 is substantially
in the form of a filament.
[0054] The continuously molded bodies 5 are extruded into an air
gap 6 which is traversed by the bodies in a direction 7 of passage
or extrusion. According to FIG. 1 the extrusion direction 7 may be
oriented in the direction of gravity.
[0055] After having passed through the air gap 6, the continuously
molded bodies 5 immerse as a substantially planar curtain into a
precipitation bath 9 consisting of a precipitant, such as water. In
the precipitation bath 9, there is a deflector 10 by which the
planar curtain 8 is deflected from the extrusion direction into the
direction of the precipitation bath surface as a curtain 11 and is
guided to a bundling means 12 in this process. The planar curtain
is combined or assembled by the bundling means 12 into a bundle of
filaments 13. The bundling means 12 is arranged outside the
precipitation bath 9.
[0056] As an alternative to the deflector 10, the continuously
molded bodies may also be passed in the direction of passage 7
through the precipitation bath and exit through a spinning funnel
(not shown) at the side opposite the precipitation bath surface 11,
i.e., on the bottom side of the precipitation bath. This
embodiment, however, is disadvantageous insofar as the consumption
of precipitation bath liquid is high, turbulent flows are created
in the spinning funnel and the separation of precipitation bath and
fiber cable at the funnel exit poses problems.
[0057] In the area of the air gap 6 there is disposed a blowing
means 14 from which a-cooling gas stream 15 exits having an axis 16
extending in a direction transverse to the direction of passage 7,
or which comprises at least one main flow component in said
direction. In the embodiment of FIG. 1 the cooling gas stream 15 is
substantially planar.
[0058] The designation "planar gas flow" means a cooling gas stream
whose height B in a direction transverse to the direction 16 of the
gas flow is smaller, preferably much smaller, than width D of the
gas flow in the direction of rows, and which is spaced apart from
solid walls. As can be seen in FIG. 1, the direction of width D of
the gas flow extends along the long edge 17 of the rectangular
nozzle 3.
[0059] The two boundary areas 18a and 18b of the cooling gas stream
15, of which 18a designates the upper boundary area facing the die
plate 3 and 18b designates the lower boundary area facing the
precipitation bath surface 11, define a cooling area 19. Since the
temperature of the planar gas stream 15 is lower than the
temperature of the continuously molded bodies 5, which are still
heated up by the extrusion process, an interaction between the
planar gas stream 15 and the continuously molded bodies 5 and thus
a cooling and solidification of the continuously molded bodies
takes place in the cooling area.
[0060] The cooling area 19 is separated from the extrusion orifices
4 by a first shielding or insulation zone 20 in which there is no
cooling of the continuously molded bodies 5. The cooling area 19 is
separated from the precipitation bath surface 11 by a second
shielding zone 21 in which there is also no cooling and/or no air
movement.
[0061] The first shielding zone 20 has the function that the
extrusion conditions directly prevailing at the extrusion orifices
are as little affected as possible by the subsequent cooling
operation by means of the cooling gas stream in the cooling area
19. By contrast, the second shielding zone 21 has the function to
shield the precipitation bath surface 11 from the cooling gas
stream and to keep it as calm as possible. One possibility of
keeping the precipitation bath surface 11 calm consists in the
feature that the air is kept as motionless as possible in the
second shielding zone 21.
[0062] The blowing means 14 for producing the cooling gas stream 15
comprises a multi-duct nozzle with one or several rows, as is e.g.
offered by the company Lechler GmbH in Metzingen, Germany. In this
multi-duct nozzle, the cooling gas stream 15 is formed by a
multitude of circular individual streams having a diameter between
0.5 mm and 5 mm, preferably around 0.8 mm, which after a running
path depending on their diameter and flow velocity are united to
form a planar gas stream. The individual streams exit at a rate of
at least 20 m/s, preferably at least 30 m/s. In particular, rates
of more than 50 m/s are suited for producing turbulent cooling gas
streams with a good spinning stability. The specific blowing force
of a multi-duct nozzle of such a type should be at least 5 mN/mm,
preferably at least 10 mN/mm. The Reynolds number is at least
2,500, and at least 3,500 at very high rates.
[0063] The thickness E of the curtain of continuously molded bodies
5, which is to be penetrated by the cooling gas stream, measured in
a direction transverse to the direction of passage 7, is less than
40 mm in the embodiment of FIG. 1. Said thickness is substantially
determined by a sufficient cooling effect being produced by the
cooling gas stream in the cooling area 16 in the row 22 of the
continuously molded bodies 5 that is the last one in gas flow
direction 16. Depending on the temperature and velocity of the
cooling gas stream and on the temperature and velocity of the
extrusion process in the area of the extrusion orifices-4,
thicknesses E of less than 30 mm or less than 25 mm are also
possible.
[0064] FIG. 2 depicts a special embodiment of the spinning
apparatus 1 shown in FIG. 1. The same reference numerals are used
in Fig. 2 for the elements of the apparatus 1 already described in
FIG. 1. The embodiment is shown in a schematic section along plane
II of FIG. 1, which forms the plane of symmetry in the direction of
width D of the flow 15.
[0065] The dimensionless relation:
L>I+0.28.multidot.A+B
[0066] is applicable between the height I of the shielding zone 20
measured in the direction of flow 7 in millimeters, the height L of
the air gap 6 measured in the direction of flow 7, the distance A
from the exit of the cooling gas stream 15 from the blowing
means-14 to the last row 22 of the continuously molded bodies 5 in
millimeters, and the width B of the cooling gas stream 15 in a
direction transverse to the cooling gas stream direction 16.
[0067] The distance A can here correspond at least to the thickness
E of the curtain from continuously molded bodies 5, but may
preferably be 5 mm or 10 mm greater than E. The sizes L, I, A, B
are shown in FIG. 3.
[0068] When use is made of a cooling gas stream 15 having a round
cross section, the diameter thereof can be taken instead of the
width B of the cooling gas stream 15.
[0069] FIG. 2 shows an embodiment in which the direction 16 of the
cooling gas stream 15 is inclined by an angle .beta. relative to
the vertical 23 towards the direction of inclination 7. The cooling
gas stream 15 thereby has a velocity component which is oriented
into the direction of passage 7.
[0070] In the embodiment of FIG. 2 the angle .beta. is greater than
the angle of propagation y of the cooling gas stream. Due to this
dimensioning rule the boundary area 18a between the gas flow 15 and
the first shielding zone 20 extends in inclined fashion in the
direction of passage 7. The angle .beta. as shown in FIG. 2 may be
up to 40.degree.. At every location in the cooling area 19 the
cooling gas stream 15 has a component oriented in the direction of
passage 7.
[0071] In the embodiment of FIG. 2, apart from the already
indicated inequality for the air gap height L, the following
inequality is always satisfied, by which the height I of the first
shielding zone 20 in the direction of passage 7 is determined. The
following inequality is applicable:
I>H+A.multidot.[tan(.beta.)0.14]
[0072] where the size H represents the distance in the direction of
passage 7 between the extrusion orifices 4 and the upper edge of
the cooling gas stream 15 directly at the exit from the blowing
means 14.
[0073] In particular, the height of the first shielding zone 20
should nowhere be smaller than 10 mm in the area of the extrusion
orifices.
[0074] The height I of the shielding zone can be explained as
follows with reference to FIG. 4, which describes one embodiment.
FIG. 4 shows detail VI of FIG. 3, where a single continuously
molded body 5 is just shown by way of example directly after having
exited from an extrusion orifice 4 into the air gap 6.
[0075] As can be seen in FIG. 4, the continuously molded body 5 is
expanded directly after extrusion in an expansion zone 24 before
being narrowed again under the action of the tensile force to about
the diameter of the extrusion orifice 4. The diameter of the
continuously molded body in a direction transverse to the direction
of passage 7 may be up to three times the diameter of the extrusion
orifice.
[0076] In the expansion zone 24, the continuously molded body still
shows a relatively strong anisotropy which is gradually reduced in
the direction of passage 7 under the action of the tensile force
acting on the continuously molded body.
[0077] In contrast to the blowing methods and apparatuses known
from the prior art, the shielding zone 20 extends in the solution
of the invention according to FIG. 4 at least over the expansion
zone 24. This prevents the cooling gas stream 15 from acting on the
expansion zone.
[0078] According to the invention it is intended that the
first-shielding or protection zone 20 extends up to an area 25 in
which the expansion of the continuously molded body 5 is either
small or does not exist any more. As shown in FIG. 4, the area 25
in the direction of passage 7 is positioned behind the largest
diameter of the expansion zone. Preferably, cooling area 19 and
expansion zone 25 do not overlap, but directly follow one
another.
[0079] The function of the spinning apparatus according to the
invention and of the method according to the invention shall now be
explained with reference to comparative examples.
[0080] In the illustrated examples and in the general table 1 there
are indicated the spinning density, i.e. the number of extrusion
orifices per square millimeter, the take-off rate at which the
bundle of filaments 12 is withdrawn, in meter/second, the molding
material temperature in degree Celsius, the heating temperature of
the extrusion orifices in degree Celsius, the air gap height in
millimeter, the Reynolds number, the velocity of the cooling gas
stream directly at the exit from the blowing means in meter/second,
the distance H in millimeters, the angle .beta. in degrees, the
spun fiber titer in dtex, the coefficient of variation in percent,
the subjectively evaluated spinning behavior with marks between 1
and 5, the width of the cooling gas stream or--in the case of a
round cooling gas stream the diameter thereof, as well as the
amount of air standardized by the width of the cooling gas stream
in liter/hour per mm nozzle width. With mark 1, the spinning
behavior is rated to be good, with mark 5 to be poor.
[0081] The coefficient of variation was determined according to DIN
EN 1973 with the test device Lenzing Instruments Vibroskop 300.
[0082] The Reynolds number as a measure of the turbulence of a gas
stream was determined in accordance with the formula
Re=w.sub.0*B/v, where w.sub.0 is the exiting velocity of the gas
from the nozzle in m/s, B is the blow gap width or the hole
diameter of the blowing apparatus, in mm, and v is the kinematic
viscosity of the gas. The kinematic viscosity v was assumed to be
153.5.times.10.sup.-7 m.sup.2/s for air at a temperature of
20.degree. C. When other gases or gas mixtures are produced for
generating a cooling gas stream, the value of v can be adapted
accordingly.
[0083] The general table 1 is a summary of the test results.
COMPARATIVE EXAMPLE 1
[0084] An NMMNO spinning material consisting of 13% cellulose type
MoDo Crown Dissolving-DP 510-550, 76% NMMNO and 11% water, was
supplied at a temperature of 78.degree. C., stabilized with gallic
acid propylester, to an annular spinning nozzle having a ring
diameter of about 200 mm. The spinning nozzle consisted of several
drilled individual segments, each containing the extrusion orifices
in the form of capillary bores. The extrusion orifices were heated
to a temperature of 85.degree. C.
[0085] The space between the precipitation bath surface and the
extrusion orifices was formed by an air gap of about 5 mm height.
The continuously molded bodies pass through the air gap-without
being blown at. The continuously molded bodies coagulated in the
spinning bath in which a spinning funnel was arranged below the
extrusion orifices.
[0086] The ring-like bundle of continuously molded bodies was
bundled in the spinning funnel by the exit surface thereof and
guided out of the spinning funnel. The length of the spinning
funnel in the direction of passage was about 500 mm.
[0087] The spinning behavior turned out to be very problematic
because the spun fiber material was sticking together at many
points. The poor conditions also became obvious from a strong
variation of the fiber fineness, the variance of which was at more
than 30% in this comparative example.
[0088] COMPARATIVE EXAMPLE 2
[0089] In Comparative Example 2 a blowing operation directed from
the outside to the inside was additionally carried out directly
after extrusion without a first shielding zone under otherwise
identical conditions. The blowing operation took place at a
relatively low rate of about 6 m/s.
[0090] The blowing operation could increase the height of the air
gap only insignificantly; the spinning quality and the spinning
stability remained substantially unchanged in comparison with
Comparative Example 1.
COMPARATIVE EXAMPLE 3
[0091] The molding material used in Comparative Examples 1 and 2
was supplied in the Comparative Example 3 at a temperature of also
78.degree. C. to a rectangular nozzle, which was composed of
several drilled individual segments. The rectangular nozzle had
three rows of extrusion orifices kept at a temperature of about
90.degree. C.
[0092] Underneath the extrusion orifices there was a precipitation
bath in which a deflector was mounted. An air gap of about 6 mm
through which the continuously molded bodies passed as a curtain
was formed between the precipitation bath surface and the extrusion
orifices. A cooling blowing in parallel with the spinning bath
surface was used for supporting the spinning operation.
[0093] The continuously molded bodies were coagulated in the
precipitation bath where the curtain consisting of continuously
molded bodies was deflected by the deflector and supplied obliquely
upwards to a bundling means arranged outside the precipitation
bath. The curtain of the continuously, molded bodies was united by
the bundling means into a bundle of filaments and then passed on to
further processing steps.
[0094] Comparative example 3 showed a slightly improved spinning
behavior, but spinning flaws were observed time and again. The
continuously molded bodies were sticking together in part; the
fiber fineness varied considerably.
COMPARATIVE EXAMPLE 4
[0095] In Comparative Example 4, a blowing means having a width B
of 8 mm was mounted under otherwise identical conditions with
respect to Comparative. Example 3 on a long side of the rectangular
nozzle in such a way that the cooling area extended up to the
extrusion orifices, i.e. there was no first shielding zone.
[0096] The cooling gas stream had a velocity of about 10 m/s when
exiting from the blowing means.
[0097] In comparison with Comparative Example 3, the air gap could
only be increased insignificantly in the arrangement of Comparative
Example 4, the achieved spinning stability as well as the fiber
data remained unchanged in comparison with the values of
Comparative Example 3.
COMPARATIVE EXAMPLE 5
[0098] Like in Comparative Example 4, a blowing means with a
cooling gas stream width of 6 mm upon exit from the blowing means
was mounted in this comparative example on a long side of the
rectangular nozzle in such a way that the cooling area extended
without an interposed shielding zone up to the extrusion orifices.
In contrast to Comparative Example 4 a rectangular nozzle drilled
all over its surface was used instead of a segmented rectangular
nozzle.
[0099] The velocity of the cooling gas stream at the exit on the
blowing means was about 12 m/s.
[0100] In Comparative Example 5 the air gap could be increased to
about 20 mm and the spinning stability was improved considerably.
As for the fiber data, however, no improvements were observed,
especially since sticking occurred time and again.
[0101] In the following Comparative Examples 6 to 8, a cooling gas
stream was produced by means of several multi-duct compressed-air
nozzles arranged side by side in a row. The diameter of each
compressed-air nozzle was about 0.8 mm. The exit velocity of the
individual cooling gas streams from the blowing means was more than
50 m/s in Comparative. Examples 6 to 8. The individual cooling
streams were turbulent. The gas supply of the nozzle was carried
out with compressed-air of 1 bar overpressure; the gas stream was
throttled by means of a valve for adapting the blowing
velocity.
[0102] The spinning head comprised a rectangular nozzle of special
steel that was drilled all over its surface. Otherwise, the
spinning system of Comparative Examples 3 to 5 was used.
COMPARATIVE EXAMPLE 6
[0103] Like in Comparative Example 5, the multi-duct compressed-air
nozzle was mounted in Comparative Example 6 in such a way that the
cooling area extended directly to the extrusion orifices, i.e.,
there was no first shielding zone.
[0104] In this arrangement no improved results were observed; the
spinning characteristics could not be rated as satisfactory.
COMPARATIVE EXAMPLE 7
[0105] In this test the cooling gas stream was directed obliquely
upwards in the direction of the nozzle and therefore had a
component opposite to the direction of passage.
[0106] In Comparative Example 8 the spinning characteristics were
not as good as in Comparative Example 7.
COMPARATIVE EXAMPLE 8
[0107] In comparison with Comparative Example 7 the cooling gas
stream had a flow direction obliquely downwards towards the
spinning bath surface. Thus the cooling gas stream had a velocity
component in the direction of passage.
[0108] In the arrangement according to Comparative Example 8 the
best results could be achieved. The coefficient of variation of the
continuously molded bodies was clearly below 10%. The spinning
characteristics were highly satisfactory and left some room for
finer titers or higher take-off rates.
[0109] It should here be noted that in Comparative Examples 6, 7 to
9 the cooling area and the precipitation bath surface had arranged
thereinbetween a second shielding zone in which the air was
substantially stationary.
1 GENERAL TABLE 1 Example 1 2 3 4 5 6 7 8 Hole density 1.86 1.96
1.86 0.99 2.81 3.18 3.18 3.18 Take-off rate 40 30 30 32 34 31 35 40
Spinning material temperature 78 78 78 83 81 83 83 84 Nozzle heat
temperature 85 85 80 100 98 100 100 102 Air gap L 5 6 6 16 20 18 16
22 Reynolds number 782 5,211 4,690 3,388 3,648 3,908 Velocity at
the cooling gas stream -- -- 6 10 12 65 70 75 exit Distance between
exit from blow- A -- -- 35 23 22 32 32 32 ing means and last row of
the continuously molded bodies Distance between the extrusion H --
-- 0 0 0 0 10 10 orifices and the upper edge of the cooling gas
stream exit in the direction of passage Blowing angle .beta. -- --
0 0 0 0 -10 20 Titer 1.72 1.66 1.74 1.55 1.4 1.47 1.35 1.33
Coefficient of variation of the titer 30.3 23.5 25.8 18.5 24.3 18.6
21.1 7.6 Spinning behavior 4-5 4 4-5 4 3 3-4 4 1-2 Cooling stream
width/individual B 2 8 6 0.8 0.8 0.8 bore diameter Gas quantity per
mm width 43 288 259 39 42 45
[0110] As for the values of the General Table 1, it must be assumed
in the case of the indicated flow velocities that there was a
turbulent cooling gas stream at the high flow velocities of
Comparative Examples 6 to 8.
* * * * *