U.S. patent application number 10/258058 was filed with the patent office on 2003-08-21 for method for spinning a spinning solution and spinning head.
Invention is credited to Ecker, Friedrich, Zikeli, Stefan.
Application Number | 20030155673 10/258058 |
Document ID | / |
Family ID | 7639492 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155673 |
Kind Code |
A1 |
Zikeli, Stefan ; et
al. |
August 21, 2003 |
Method for spinning a spinning solution and spinning head
Abstract
The present invention relates to a spinning head (8) for
spinning a spinning dope, which is provided with a tubular,
thin-walled spinning capillary (7) having a discharge opening (94).
The spinning dope used is e.g. a mixture of cellulose, tertiary
amine oxide and water. In order to reduce the fibrillation tendency
of the fibres spun by means of the spinning head and in order to
increase the non-looping property, the present invention is so
conceived that the spinning capillary (7) is heated directly close
to the discharge cross-section (94). By means of this simple
measure, it is possible to reduce the fibrillation tendency and to
increase the non-looping property.
Inventors: |
Zikeli, Stefan; (Regau,
AT) ; Ecker, Friedrich; (Timelkam, AT) |
Correspondence
Address: |
MCDONNELL BOEHNEN HULBERT & BERGHOFF
300 SOUTH WACKER DRIVE
SUITE 3200
CHICAGO
IL
60606
US
|
Family ID: |
7639492 |
Appl. No.: |
10/258058 |
Filed: |
February 24, 2003 |
PCT Filed: |
April 19, 2001 |
PCT NO: |
PCT/EP01/04467 |
Current U.S.
Class: |
264/40.6 ;
264/187; 264/402; 425/144; 425/378.2; 425/382.2 |
Current CPC
Class: |
D01D 5/06 20130101; D01F
2/00 20130101; D01D 1/09 20130101; D01D 4/00 20130101 |
Class at
Publication: |
264/40.6 ;
264/187; 264/402; 425/378.2; 425/382.2; 425/144 |
International
Class: |
D01F 002/02; D01D
005/084 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2000 |
DE |
100 19 660.8 |
Claims
1. A method of spinning a spinning dope comprising a mixture of
cellulose, water and tertiary amine oxide, said method comprising
the steps of supplying the spinning dope to at least one spinning
head and conducting it in said spinning head through at least one
spinning capillary provided at its downstream end with a
spinning-dope discharge opening through which the spinning dope is
discharged from the spinning head, characterized in that, close to
said spinning-dope discharge opening (94), the wall of the spinning
capillary (7) is heated, at least sectionwise, to a temperature
which is higher than the core temperature of the spinning dope in
the spinning capillary.
2. A method according to claim 1, characterized in that the wall of
the spinning capillary is heated directly by a heating device (70,
72).
3. A method according to claim 1 or 2, characterized in that the
wall temperature of the spinning capillary (7) is controlled to an
adjustable value by means of a temperature controller.
4. A method according to one of the above-mentioned claims,
characterized in that the wall temperature of the spinning
capillary (7) is controlled in dependence upon the mass flow rate
of the spinning dope through the spinning capillary (7).
5. A method according to one of the above-mentioned claims,
characterized in that the wall temperature of the spinning
capillary (7) is controlled in dependence upon the spinning
pressure in the spinning dope, preferably in dependence upon the
spinning pressure of the spinning dope in the spinning capillary
(7).
6. A method according to one of the above-mentioned claims,
characterized in that, a predetermined temperature profile across
the flow cross-section of the spinning capillary (7) is adjusted by
heating the spinning-capillary wall when the spinning capillary is
in operation.
7. A method according to one of the above-mentioned claims,
characterized in that, a predetermined temperature profile of the
spinning-capillary wall is adjusted in the direction rection of
flow of the spinning dope by heating the spinning-capillary wall
when the spinning capilary is in operations.
8. A method according to one of the above-mentioned claims,
characterized in that the spinning-capillary wall is heated by a
heating fluid which flows around the wall of the spinning capillary
on the outside thereof.
9. A spinning head for spinning a spinning dope which consists of a
mixture of cellulose, water and tertiary amine oxide and which
flows through the spinning head, comprising at least one spinning
capillary having a spinning-dope discharge opening at its
downstream end, the spinning dope being discharged from the
spinning head through said spinning-dope discharge opening, and
further comprising a temperature-controlled heating device which
acts on said spinning dope, characterized in that, in an area close
to the spinning-dope discharge opening (94), the wall temperature
of the spinning capillary (7) produced by the heating device (70,
72) is higher than the core temperature of the spinning dope, when
the spinning head (8) is in operation.
10. A spinning head according to claim 9, characterized in that the
area of the spinning-capillary wall which is heated by said heating
device (70, 72) and the temperature of which is higher than the
core temperature of the spinning dope extends essentially up to the
spinning-dope discharge opening (94).
11. A spinning head according to claim 9 or 10, characterized in
that the area of the spinning-capillary wall which is heated by
said heating device (70, 72) and the temperature of which is higher
than the core temperature of the spinning dope extends essentially
over the whole length of the spinning capillary (7).
12. A spinning head according to one of the claims 9 to 11,
characterized in that the spinning capillary (7) is implemented as
a spinning-capillary tube in the form of a substantially
thin-walled tube, and that the heating device (70, 72) acts
directly on the wall area of said spinning-capillary tube close to
the spinning-dope discharge opening (94).
13. A spinning head according to one of the claims 9 to 12,
characterized in that a control unit is provided, which acts on the
heating device (70, 72) and by means of which the temperature of
the directly heated wall area of the spinning-capillary tube (7) is
adapted to be controlled, at least sectionwise.
14. A spinning head according to one of the claims 9 to 13,
characterized in that the heating device (70, 72) comprises a
heating fluid which surrounds the spinning-capillary tube (7), at
least sectionwise.
15. A spinning head according to claim 14, characterized in that
the heating fluid of the heating device (70, 72) surrounds the
spinning-capillary tube (7), at least sectionwise.
16. A spinning head according to one of the claims 9 to 15,
characterized in that the spinning-dope discharge opening (94) of
the spinning-capillary tube (7) is surrounded, at least
sectionwise, by a gap opening (74), a transport fluid flowing out
of said gap opening (74) essentially in the direction of the
spinning dope discharged from the spinning-dope discharge opening
(94) when the spinning head is in operation.
17. A spinning head according to claim 16, characterized in that
the velocity of the transport fluid flowing out of said gap opening
(74) when the spinning head is in operation corresponds
substantially at least to the velocity of the spinning dope
discharged from the spinning-dope discharge opening (94).
18. A spinning head according to one of the claims 9 to 17,
characterized in that, close to the spinning-dope discharge
opening, the spinning-capillary tube (7) is surrounded by a heating
chamber (70, 72) containing a heating fluid.
19. A spinning head according to one of the claims 16 to 18,
characterized in that the heating chamber (72) communicates with
the gap opening (74).
20. A spinning head according to one of the claims 16 to 19,
characterized in that the heating fluid serves as a transport fluid
and is conducted from the heating chamber (72) through the gap
opening (74).
21. A spinning head according to one of the claims 16 to 20,
characterized in that an annular space (102) extends between said
heating chamber (70) and said gap opening
14. A spinning head according to one of the claims 9 to 13,
characterized in that the heating device (70, 72) comprises a
heating fluid which surrounds the spinning-capillary tube (7), at
least sectionwise.
15. A spinning head according to claim 14, characterized in that
the heating fluid of the heating device (70, 72) surrounds the
spinning-capillary tube (7), at least sectionwise.
16. A spinning head according to one of the claims 9 to 15,
characterized in that the spinning-dope discharge opening (94) of
the spinning-capillary tube (7) is surrounded, at least
sectionwise, by a gap opening (74), a transport fluid flowing out
of said gap opening (74) essentially in the direction of the
spinning dope discharged from the spinning-dope discharge opening
(94) when the spinning head is in operation.
17. A spinning head according to claim 16, characterized in that
the velocity of the transport fluid flowing out of said gap opening
(74) when the spinning head is in operation corresponds
substantially to at least the velocity of the spinning dope
discharged from the spinning-dope discharge opening (94).
18. A spinning head according to one of the claims 9 to 17,
characterized in that, close to the spinning-dope discharge
opening, the spinning-capillary tube (7) is surrounded by a heating
chamber (70, 72) containing a heating fluid.
19. A spinning head according to one of the claims 16 to 18,
characterized in that the heating chamber (72) communicates with
the gap opening (74).
20. A spinning head according to one of the claims 16 to 19,
characterized in that the heating fluid serves as a transport fluid
and is conducted from the heating chamber (72) through the gap
opening (74).
21. A spinning head according to one of the claims 16 to 20,
characterized in that an annular space (102) extends between said
heating chamber (70) and said gap opening (74), said annular space
(102) surrounding the capillary tube (7) from outside essentially
along the whole length of said tube.
22. A spinning head according to claim 20, characterized in that
the annular space (102) has a substantially oval cross-section.
23. A spinning head according to one of the claims 9 to 21,
characterized in that the length of the spinning capillary (7) is
20 to 150 times as long as the diameter of said spinning
capillary.
24. A spinning head according to claim 23, characterized in that
said length is the length through which the spinning dope flows
and/or that said diameter is the internal diameter of the spinning
capillary (7).
25. A spinning head according to one of the claims 9 to 24,
characterized in that the discharge cross-section (94) is
circular.
26. A spinning head according to claim 25, characterized in that
the discharge cross-section (94) has a diameter of less than 500
.mu.m, preferably less than 250 .mu.m.
27. A spinning head according to one of the claims 9 to 26,
characterized in that the wall thickness of the spinning-capillary
tube (7) is less than 200 .mu.m, preferably less than 150
.mu.m.
28. A spinning head according to one of the claims 9 to 27,
characterized in that the temperature of the heating fluid in the
heating chamber (70, 72) is at least 100.degree. C., preferably
approximately 150.degree. C.
29. A spinning head according to one of the claims 9 to 27,
characterized in that the temperature of the heating fluid in the
heating chamber (70, 72) ranges from 50.degree. C. to 150.degree.
C.
30. A spinning head according to one of the claims 9 to 27,
characterized in that the temperature of the heating fluid in the
heating chamber (70, 72) ranges from 80.degree. C. to 150.degree.
C.
31. A spinning head according to one of the claims 9 to 27,
characterized in that the temperature of the heating fluid in the
heating chamber (70, 72) ranges from 100.degree. C. to 150.degree.
C.
32. A spinning head according to one of the claims 9 to 27,
characterized in that the temperature of the heating fluid in the
heating chamber (70, 72) ranges from 50.degree. C. to 180.degree.
C.
33. A spinning head according to one of the claims 9 to 32,
characterized in that at least one temperature sensor is provided
for detecting the temperature of the capillary wall and/or the
temperature of the spinning dope in the area of said capillary
wall, the capillary-wall temperature being adapted to be outputted
to the control device in the form of an electric signal by means of
said temperature sensor.
34. A spinning head according to claim 33, characterized in that
the temperature sensor is implemented as an electric resistance
element.
35. A spinning head according to one of the claims 9 to 34,
characterized in that at least one temperature sensor is provided
for detecting the temperature of the heating fluid, the temperature
of the heating fluid being adapted to be outputted to the control
device in the form of an electric signal by means of said
temperature sensor.
36. A spinning head according to one of the claims 9 to 35,
characterized in that the gap (74) is defined by a housing (100;
104a, 104b) which is movable transversely to the longitudinal axis
of the spinning capillary, at least sectionwise, and that the flow
cross-section of said gap (74) is variable.
37. A spinning head according to one of the claims 9 to 36,
characterized in that the spinning capillary is surrounded by at
least one electric heating element.
38. A spinning system with a pressure equalizing container
containing a spinning dope composed of cellulose, water and a
tertiary amine oxide and of one or a plurality of stabilizing
agents, said spinning system comprising a spinning head or a
plurality of spinning heads by means of which the spinning dope can
be spun so as to obtain formed bodies, and a spinning-dope conduit
by means of which the spinning dope is conducted from said pressure
equalizing container to said spinning head or said spinning heads,
characterized in that the, spinning head (8) is implemented
according to one of the claims 9 to 37 and/or that the spinning
system (1) is implemented for carrying out the method according to
one of the claims 1 to 8.
39. A spinning system according to claim 38, characterized in that
said spinning system includes an air gap (10) after said spinning
head (8) or said spinning heads (8), the spinning dope flowing into
and being drawn in said air gap (10) after having left the
spinning-dope discharge opening (94).
40. A spinning system according to claim 38 or 39, characterized in
that said spinning system (1) comprises a precipitation bath (11)
downstream of said air gap (10), the spinning dope discharged from
the spinning head (8) being immersed into said precipitation bath
after having passed through the air gap (10) and after having been
drawn so as to obtain a formed body.
41. A spinning system according to one of the claims 38 to 40,
characterized in that a drawing-off device (12) is provided by
means of which the spinning dope can be drawn off from the
precipitation bath in the form of a precipitated thread or formed
body.
Description
[0001] The present invention relates to a method of spinning a
spinning dope comprising a tertiary amine oxide, water and
cellulose, said method comprising the steps of supplying the
spinning dope from a spinning-dope storage reservoir to a spinning
head continuously or discontinuously and conducting it in said
spinning head through at least one spinning capillary provided at
its downstream end with a spinning-dope discharge opening through
which the spinning dope is discharged from the spinning head.
[0002] The present invention additionally relates to a spinning
head for spinning a spinning dope flowing through said spinning
head and containing tertiary amine oxide, said spinning head
comprising at least one spinning capillary having a spinning-dope
discharge opening at its downstream end, the spinning dope being
discharged from the spinning head through said spinning-dope
discharge opening, and further comprising a heating device which
acts on said spinning dope.
[0003] The term spinning capillary stands here for the last section
of the spinning head through which the spinning dope flows and
which defines the spinning-dope discharge opening. The spun thread
is formed by means of the spinning capillary.
[0004] Such a method and such a device are-known e.g. from WO
99/47733. In said reference a spinning capillary is described which
comprises a pre-capillary (referred to as capillary in said
reference) and a spinning capillary following said pre-capillary in
the direction of flow of the spinning dope (referred to as orifice
in said reference). The pre-capillary and the spinning capillary
are produced from a two-part metal block. The diameter of the
pre-capillary is 1.2 to 2.5 that of the spinning capillary.
[0005] The spinning head of WO 99/47733 is provided with openings
in the area of the pre-capillary, said openings being used for
accommodating a heating device. Said heating device serves to heat
the metal block of the spinning head in the area of the
pre-capillary.
[0006] The spinning block of WO 99/47733 is surrounded by a gas
chamber which contains a heated gas flowing out of the spinning
head substantially parallel to the spinning dope discharged from
the spinning-dope discharge opening and surrounding the discharged
spinning dope.
[0007] The operating temperature of the spinning head in the area
of the pre-capillary and of the spinning capillary ranges from
70.degree. C. to 140.degree. C. The temperature of the gas
discharged is preferably 70.degree. C., i.e. it is lower than the
temperature of the spinning head.
[0008] The spinning head according to WO 99/47733 is
disadvantageous insofar as, due to the structural design of the
spinning head described in said reference, the hole density that
can be realized is only low. An additional disadvantage is that the
temperature can only be influenced in the area of the
pre-capillary. Due to the high cellulose concentrations used when
NMO/water/cellulose solutions are spun and due to the high
structural viscosity, it is necessary to influence the spinning
temperature. In addition, attention should be paid to a good
uniformity of the temperature profile, a requirement which is not
fulfilled in the case of the spinning nozzle and the heating system
described in WO 99/47733.
[0009] It follows that, taking into account WO 99/47733, the object
to be achieved is to improve the spinning heads according to the
generic clause in such a way that the spun fibres have a lower
fibrillation tendency and a high non-looping property.
[0010] The fibrillation tendency is determined by a so-called
"shaking test". The shaking test is described in the periodical
"Chemiefaser Textilindustrie" 43/95 (1993), pp. 879 et seq., and in
WO 96/07779.
[0011] In said test, the fibres, which have a standard length, are
shaken in water in the presence of glass beads for a predetermined
period of time. The fibrillation degree of the fibre is determined
by examination under the microscope: if a large amount of split-off
fibrils is found under the microscope, this means that the
fibrillation value is high and consequently poor.
[0012] For the method mentioned at the start, this object is
achieved in accordance with the present invention by the feature
that, close to said spinning-dope discharge opening, the wall of
the spinning capillary is heated, at least sectionwise, to a
temperature which is higher than the core temperature of the
spinning dope in the spinning capillary.
[0013] Surprisingly enough, it has been found that, due to the
influence exerted on the temperature profile of the solution during
extrusion through the spinning capillaries, a largely
fibrillation-free cellulose fibre with good fibre characteristics,
e.g. good non-looping properties, can be produced on the basis of
the advantageous flow behaviour.
[0014] For the spinning head mentioned at the start, this object is
achieved in accordance with the present invention by the feature
that, in an area close to the spinning-dope discharge opening, the
wall temperature of the spinning capillary is higher than the core
temperature of the spinning dope, when the spinning head is in
operation.
[0015] By means of this simple measure cellulose fibres having a
lower fibrillation tendency and a higher non-looping property than
prior art fibres can be produced.
[0016] In the spinning head according to the most pertinent prior
art, WO 99/47733, the pre-capillary is heated, but the spinning
capillary extending up to the spinning-dope discharge opening is
not heated. The pre-capillary has a larger diameter than the
capillary. Due to the sudden change of cross-section between the
pre-capillary and the capillary, the temperature distribution in
the spinning dope, which has built up in the pre-capillary, is
disturbed so that a temperature distribution that is advantageous
for spinning the spinning dope can no longer develop over the short
length of the capillary.
[0017] In addition, the device according to WO 99/47733 does not
offer the possibility of heating the capillary wall to a
temperature which is higher than the core temperature of the
spinning dope. Due to the large travelling length of the
pre-capillary and the low flow rate of the spinning dope in the
pre-capillary, the spinning dope will heat in the pre-capillary to
the temperature of the pre-capillary wall. There are two reasons
for the fact that the wall temperature of the capillary of WO
99/47733 is lower than the temperature of the spinning dope:
firstly, the gas discharged from the gas chamber flows through the
annular gap along the outer wall of the capillary in the case of
the spinning head of WO 99/47733. The temperature of this gas is
lower than the temperature of the spinning dope. It follows that,
in the case of the device of WO 99/47733, the capillary area close
to the discharge opening is actually cooled by the gas to a
temperature below the core temperature of the spinning dope.
[0018] Secondly, the capillary wall close to the discharge opening
is heated only indirectly by the heating device of the spinning
head according to WO 99/47733: the heating device is arranged close
to the pre-capillary and acts primarily only on said pre-capillary.
The downstream capillary is heated only indirectly via the heating
of the capillary block. It follows that the wall temperature of the
capillary close to the discharge opening will always be lower than
the temperature of the pre-capillary in the case of the spinning
head according to WO 99147733.
[0019] In accordance with a particularly advantageous embodiment of
the present invention, the wall of the spinning capillary can be
heated directly by a heating device. In the case of direct heating,
the heating device acts directly on the spinning-capillary wall.
Such direct heating does not exist in the case of a conventional
spinning head of the type disclosed in WO 99/47733. In the case of
this spinning head, the spinning-capillary wall is heated
indirectly via the great mass of the spinning block. Direct heating
of the spinning-capillary wall has, however, the advantage that the
temperature of the wall can be controlled more exactly and with
faster response, since great inertial masses, which can react only
slowly to temperature variations, do not exist.
[0020] For adjusting the wall temperature of the spinning capillary
precisely and for controlling the process exactly, a temperature
controller by means of which the wall temperature of the spinning
capillary is controlled to an adjustable value can be provided in
accordance with a further advantageous embodiment. Such a
temperature controller permits the wall temperature to be adapted
automatically to variations in the spinning process, e.g. to
different spinning dopes or different spinning-head geometries.
[0021] According to one embodiment, the wall temperature of the
spinning capillary can be controlled in dependence upon the mass
flow rate of the spinning dope through the spinning capillary. The
heat transfer from the capillary wall increases in response to the
mass flow rate so that the heating of the capillary wall must be
adapted accordingly. In this connection, it will be advantageous
when variations in the mass flow rate through the spinning
capillary can be compensated for by controlling the wall
temperature.
[0022] According to a further advantageous embodiment, the wall
temperature of the spinning capillary can also be controlled in
dependence upon the spinning pressure in the spinning dope,
preferably in dependence upon the spinning pressure of the spinning
dope in the capillary. The flow velocity and, consequently, the
heat transfer in the spinning dope also depends on the spinning
pressure and thus on the flow velocity in the spinning dope: the
flow velocity of the spinning dope through the spinning capillary
increases as the spinning pressure increases. Also in this case, it
will be advantageous when variations in the spinning pressure can
be compensated for by controlling the wall temperature of the
spinning capillary.
[0023] The fibrillation tendency can especially be reduced, when,
in accordance with a further advantageous embodiment, the heating
of the spinning-capillary wall produces a predetermined temperature
profile across the flow cross-section of the spinning capillary
when the spinning head is in operation. By means of this
temperature profile, the velocity profile of the spinning dope in
the spinning capillary is purposefully influenced on the basis of
the temperature-dependent viscosity of the spinning dope.
Especially when the capillary wall is heated strongly, it will be
possible to reduce the viscosity of the spinning dope in the wall
area to a substantial extent. Such heating will lead to a reduced
wall friction in the spinning dope and to a fuller/wider flow
profile in the capillary: the distribution of the flow velocity
over the flow cross-section no longer has the strongly curved
profile of a pipe flow, but it has a broad maximum which extends in
an almost constant form up to the wall of the spinning capillary.
The fibrillation tendency can be improved in this way by
influencing the flow profile via the wall temperature.
[0024] This effect of the wall temperature on the flow profile of
the spinning dope in the spinning capillary can be increased still
further in accordance with an advantageous embodiment, when a
predetermined temperature profile of the spinning-capillary wall
can also be adjusted in the direction of flow of the spinning dope
by heating the spinning-capillary wall when the spinning head is in
operation. In the case of this embodiment the velocity profile in
the spinning capillary is influenced by purposefully changing the
temperature distribution in the direction of flow. The formation of
a pipe flow profile is reliably avoided and the flow profile can be
optimized still further by adapting the temperature distribution in
the direction of flow.
[0025] For this purpose, a plurality of independently operating
heating devices can be provided on the spinning capillary in the
direction of flow.
[0026] A particularly uniform heating of the spinning-capillary
wall can be achieved when a heated heating fluid flows around the
wall of the spinning capillary on the outside thereof. In contrast
to electric heating--of the type described e.g. in WO
99/47733--abrupt changes in the spatial temperature distribution
will not occur in the case of heating by means of a fluid. In
addition, local overheating can be avoided. The temperature of the
heating fluid is at least 100.degree. C., preferably approximately
150.degree. C. The temperature of the heating fluid can, in an
advantageous manner, also be in the range of 50.degree. C.,
80.degree. C. or 100.degree. C. and 150.degree. C. or 180.degree.
C. Due to the high flow velocities in the end capillary of the
spinning head, the wall temperature of the spinning capillary can
even exceed the decomposition temperature of the spinning dope. The
residence time of the spinning dope in the spinning capillary is
not long enough for the spinning dope to reach the decomposition
temperature.
[0027] In accordance with a further embodiment, at least one
temperature sensor can be provided for detecting the temperature of
the capillary wall and/or the temperature of the spinning dope in
the area of said capillary wall. The temperature sensor is adapted
to output an electric signal which is representative of the
capillary-wall temperature. With the aid of such a sensor, the
temperature of the capillary wall can be determined directly or
indirectly at any time. The signal can be supplied to a control
device by means of which the wall temperature can be controlled.
For this purpose, the temperature controller will change the
temperature of the heating fluid in a suitable manner.
[0028] When a heating fluid is used, at least one temperature
sensor can be provided in accordance with a further advantageous
embodiment, said temperature sensor being used for detecting the
temperature of the heating fluid and for outputting said
temperature of the heating fluid to the control device in the form
of an electric signal. In the case of this embodiment, the wall
temperature of the spinning capillary can be determined and
controlled via the detection of the heating fluid temperature.
[0029] As far as the spinning head is concerned, it may be
particularly advantageous when the area of the spinning-capillary
wall which is heated by the heating device and the temperature of
which is higher than the core temperature of the spinning dope
extends essentially up to the spinning-dope discharge opening. The
spinning-dope discharge opening is a particularly critical point at
which a high wall temperature will influence the fibrillation
tendency in a particularly advantageous manner. Especially, it
turned out that the jet expansion immediately after the discharge
of the spinning dope from the discharge opening, the so-called
strand expansion, can be suppressed by heating the discharge
opening. This will result in an improved surface structure of the
spun fibres and, consequently, the non-looping property will be
increased still further and the fibrillation tendency will be
reduced still further.
[0030] According to a further advantageous embodiment, the area of
the spinning-capillary wall which is heated by the heating device
and the temperature of which is higher than the core temperature of
the spinning dope can extend essentially over the whole length of
the spinning capillary. In the case of this embodiment, the whole
spinning capillary can be heated; due to the reduced viscosity of
the spinning dope in the vicinity of the wall and due to the
travelling length in the spinning capillary, this will lead to the
complete formation of a full velocity profile over the
cross-section of the spinning capillary.
[0031] In order to permit a rapid and purposeful control of the
wall temperature and thus of the temperature of the spinning dope
flowing close to the wall, the temperature of the
spinning-capillary wall should be rapidly adjustable by the heating
device and it should rapidly react to temperature variations. In
accordance with a further embodiment, this can be achieved by the
features that the spinning capillary is implemented as a
spinning-capillary tube in the form of a substantially thin-walled
tube, and that the heating device acts directly on the wall area of
said spinning-capillary tube close to the spinning-dope discharge
opening. Due to the thin-walled structural design of the spinning
capillary, the wall temperature will react rapidly in response to a
change of the temperature of the heating device, since there is
hardly any inertial mass. In view of the fact that the heating
device acts directly on the thin-walled spinning capillary, a rapid
response will additionally be guaranteed. It will be advantageous
when the wall thickness of the spinning-capillary tube is less than
200 .mu.m, preferably less than 150 .mu.m.
[0032] In accordance with a further embodiment the spinning-dope
discharge opening of the spinning-capillary tube can be surrounded,
at least sectionwise, by a gap opening, a transport fluid flowing
out of said gap opening essentially in the direction of the
spinning dope discharged from the spinning-dope discharge opening
when the spinning head is in operation. The transport fluid
surrounds the spinning-dope jet discharged from the discharge
opening of the spinning capillary and reduces the abrupt change of
velocity at the outer surface of the jet. This has the effect that
the jet is stabilized and that the flow on said outer surface calms
down. The velocity of the transport fluid flowing out of the gap
opening when the spinning head is in operation can correspond
substantially to the velocity of the spinning dope discharged from
the spinning-dope discharge opening.
[0033] One embodiment of the spinning head is so conceived that,
close to the spinning-dope discharge opening, the
spinning-capillary tube is surrounded by a heating chamber
containing a heating fluid. It will be particularly advantageous
when the heating chamber communicates with the gap opening. This
permits the heating fluid to flow through the gap opening and to
sweep over the area of the spinning-capillary wall which is located
in the vicinity of the discharge cross-section. The
spinning-capillary wall can be heated up to the discharge
cross-section in this way.
[0034] When the heating fluid is discharged from said gap opening
at a suitable velocity, it can simultaneously serve as transport
fluid. Hence, it will not be necessary to provide a separate
transport fluid for stabilizing the spinning-dope jet.
[0035] For the formation of a stabile and full flow profile, the
travelling length in the spinning capillary should be as long as
possible. The ratio of the spinning-capillary length to the
spinning-capillary diameter should therefore be as large as
possible. In accordance with an advantageous embodiment of the
spinning capillary, the length of the spinning capillary can be at
least 20 times to 150 times as long as the diameter of said
spinning capillary. The length taken into account in this ratio can
be the length through which the spinning dope flows and/or the
diameter can be the internal diameter of the spinning
capillary.
[0036] The flow cross-section of the gap through which the fluid is
discharged parallel to the spinning dope can be varied by means of
a displaceable housing, e.g. displaceable wings, in accordance with
a further advantageous embodiment. The velocity of the fluid
discharged from the gap can thus be varied depending on the
respective spinning operation and the respective spinning jet
velocity and thickness.
[0037] The spinning capillary can also be heated directly by means
of an electric heating element surrounding said spinning
capillary.
[0038] In accordance with a further advantageous embodiment, the
spinning capillary can be implemented as a precision steel tube. It
may also have a circular discharge opening. The diameter of the
discharge opening can be less than 500 .mu.m, preferably less than
250 .mu.m. For special cases of use, e.g. for spinning spinning
material so as to produce lyocell fibres, the diameter may also be
in the range of less than 100 .mu.m to 75 .mu.m.
[0039] The spinning head can be installed in a spinning system with
a pressure equalizing container containing a spinning dope with
tertiary amine oxide, said spinning system comprising a spinning
head by means of which the spinning dope can be spun so as to
produce a spinning filament, and further comprising a spinning-dope
conduit through which the spinning dope is conducted to a spinning
head. This spinning system then executes the method according to
the present invention.
[0040] The present invention also relates to the product produced
by the method according to the present invention, the spinning head
according to the present invention or the spinning system according
to the present invention; said product is characterized by an
improved non-looping property and by a lower fibrillation tendency
and it can have the form of a filament, a staple fibre, a
spunbonded fabric or a film/sheet.
[0041] In the following, the structural design and the mode of
operation of the method according to the present invention and of
the spinning head according to the present invention are explained
on the basis of embodiments.
[0042] FIG. 1 shows a schematic view of a spinning system;
[0043] FIG. 2 shows a first embodiment of the spinning head
according to the present invention in a cross-sectional view;
[0044] FIG. 3 shows a second embodiment of the spinning head
according to the present invention in a cross-sectional view;
[0045] FIG. 4 shows a third embodiment of the spinning head
according to the present invention in a cross-sectional view;
[0046] FIG. 5 shows a fourth embodiment of a spinning head
according to the present invention in a cross-sectional view.
[0047] A spinning system 1 by means of which the method according
to the present invention is carried out is schematically shown in
FIG. 1.
[0048] A spinning dope storage reservoir or reactor 2 contains a
highly viscous spinning dope 3 including a tertiary amine oxide,
e.g. a solution of cellulose, water and N-methylmorpholine-N-oxide
(NMMO).
[0049] The spinning dope is conveyed by means of a pump 4 from the
spinning dope reservoir 2 through a spinning dope conduit 4' and a
pressure equalizing container 5 to a manifold/distributor block 6.
The manifold block has connected thereto a large number of spinning
capillaries 7. The manifold block 6 and the spinning capillaries 7
are part of a spinning head 8.
[0050] The pressure equalizing container serves to equalize
possible pressure and/or volumetric flow rate variations in the
spinning dope conduit 4' and to guarantee a uniform supply of
spinning dope to the spinning head 8.
[0051] Highly viscous spinning dope jets 9 are discharged, each at
a high velocity, from the spinning head 8. After having been
discharged from the spinning head 8, these spinning dope jets 9
flow through an air gap 10 or a non-precipitative medium. In this
step, the spinning dope is accelerated and, consequently,
drawn.
[0052] The spinning dope jets then enter a precipitation bath 11 or
a bath comprising a non-solvent or an aqueous amine oxide solution.
From said precipitation bath 11, the spinning dope is drawn off in
the form of a fibre by means of a drawing-off device 12.
[0053] In the following, the structural design of a first
embodiment of the spinning head 8 according to the present
invention is described on the basis of FIG. 2.
[0054] The spinning head 8 is secured to a frame 50 and insulated
by a layer 52 of heat-insulating material so that no heat losses
will occur when the spinning head is heated.
[0055] The spinning head 8 has a modular structural design
comprising the manifold block 6, a substantially disk- or
plate-shaped pressure distributing plate 54, a substantially disk-
or plate-shaped spinning nozzle body 56 provided with a distributor
space 56a, at least one spinning capillary 7 and a holding device
60.
[0056] The pressure distributing plate 54 of the spinning nozzle
body 56 is held by means of said holding device 60 on the manifold
block 6 in the direction of a central axis M of the spinning head.
For this purpose, the holding device 60 defines an annular or
slot-shaped opening in which the pressure distributing plate 54 and
the spinning nozzle body 56 are accommodated. A shoulder 60a is
formed on one end of the annular opening, said shoulder engaging a
complementary opening 60b of the spinning nozzle body 56.
[0057] The spinning nozzle body 56 rests via one of its end faces
on the pressure distributing plate 54 essentially in full-area
contact therewith. A sealing element 62 is provided in the end face
of said nozzle body 56 so that no spinning dope can escape between
said pressure distributing plate 54 and said spinning nozzle body
56.
[0058] The end face of the pressure distributing plate 54 facing
away from the spinning nozzle body 56 abuts on the manifold block 6
essentially in full-area contact therewith. Also this end face has
a sealing element 62 provided therein so that no spinning dope can
escape between the manifold block 6 and the pressure distributing
plate.
[0059] By screw means 64 engaging the holding device 60, said
holding device 60 is drawn towards the manifold block 6. The
shoulder 60a of the holding device 60 thus applies a pressure to
the respective opening 60b of the nozzle body 56. The nozzle body
56 retransmits this pressure via the pressure distributing plate 54
to the manifold block 6. In this way, the pressure distributing
plate 54 and the nozzle body 56 are fixedly and sealingly held on
the manifold block 6 and can also be exchanged easily by releasing
the screw means 64 for the purpose of maintenance or for replacing
it by other geometries.
[0060] The spinning capillary 7 is secured to the spinning nozzle
body 56. The spinning capillary is implemented in the form of a
tube having a circular cross-section and an internal diameter of
less than 500 .mu.m.
[0061] The internal diameter of the spinning capillaries 7 is
constant over the whole length of said spinning capillaries.
[0062] The tubes used for the spinning capillaries 7 are precision
steel tubes originating from the field of medical engineering whose
internal diameter is less than 500 .mu.m, partly also less than 250
.mu.m. In particular for lyocell fibres, it would also be possible
to provide an internal diameter of less than 100 .mu.m down to less
than 50 .mu.m.
[0063] The spinning capillary 7 is thin-walled and has a maximum
wall thickness of 200 .mu.m. The length of the spinning capillary
is at least 20 times, preferably at least 150 times as long as the
internal diameter. Tests have shown that the fibrillation tendency
of the fibres decreases as the length/internal-diameter ratio of
the spinning capillaries increases.
[0064] Normally, a multitude of spinning capillaries 7 is arranged
on the spinning head 8 side by side or in a plurality of rows
displaced relative to one another. As can be seen in FIG. 1, a
plurality of the above-described spinning heads can be arranged in
an arbitrary mode of arrangement so as to define an economical
production unit. Each nozzle body 56 comprises a plurality of
spinning capillaries 7 arranged in one row or in several rows, in
an elongate or annular configuration.
[0065] In order to ensure a uniform onflow to the capillaries 7,
the distributor space 56a is implemented as a V-groove in an
elongate or annular shape, as a single groove or as a multi-row
V-groove. The pressure distributing plate 54 is located above the
distributor space 56a implemented as a V-groove.
[0066] The spinning capillary 7 is surrounded by an inner housing
66 and an outer housing 68. The inner housing 66 defines together
with the outer surface 7a of the spinning capillary a heating
chamber 70 which is closed towards the outside and through which a
heating fluid flows. The inner housing 66 and the nozzle body 56
define a unit. An outer housing 68 follows the unit consisting of
the nozzle body 56 and of the inner housing 66. The spinning
capillary 7 slightly projects beyond said inner housing 66 and said
outer housing 68.
[0067] The outer housing 68 surrounds the inner housing 66 and
defines a further heating chamber 72 with the outer surface of said
inner housing 66; in contrast to the heating chamber 70, said
heating chamber 72 is, however, open towards the outside. The
heating chamber 72 defines a gap 74 surrounding the end of the
spinning capillary 7 which is arranged opposite the spinning head.
A heating fluid flows through this heating chamber 72 as well, said
heating fluid flowing out through the gap and substantially
parallel to the central axis M.
[0068] In order to change the geometry of the gap 74, the outer
housing 68 is supported on the inner housing 66 such that it is
displaceable in the direction of the central axis M.
[0069] In the embodiment according to FIG. 2, the same kind of
heating fluid can be used for both chambers 70, 72. This heating
fluid is a gas which is inert with respect to the spinning dope and
which can be heated to 150.degree. C., e.g. via a heat exchanger
(not shown here). Alternatively, different kinds of heating fluids
can also be used for the chambers 70, 72. The heating chamber 70
defines the heating device for the spinning capillary 7.
[0070] The manifold block 6 and the holding device 60 are
implemented as substantially massive blocks of great mass and they
are provided with heating channels 76, 78, 80 for hot water, hot
air, heat-transfer oil, vapour or, optionally, with rod-shaped
heating elements. Due to the great mass of said manifold block 6
and of said holding device 60 and due to the thermal insulation,
only minor variations will occur in the operating temperatures of
said manifold block 6 and of said holding device 60.
[0071] In the following, the function of the spinning block
according to the present invention is described.
[0072] The spinning dope flows through the manifold block 6 via a
supply line 82, which is connected to the spinning dope supply via
sealing means 83, into a stabilizing chamber 84 provided with a
perforated disk or plate 86 having flow openings 88 formed therein.
The stabilizing chamber 84 and the perforated disk 86 are formed by
the pressure distributing plate 54. A filtration unit 90 is located
in front of the perforated disk 86 when seen in the direction of
flow. The stabilizing chamber 84, the perforated disk 86 and the
filtration unit 90 extend over all the spinning capillaries 7.
[0073] By means of the flow cross-section of the stabilizing
chamber 84, which is enlarged to a great extent in comparison with
the supply line 82, the flow velocity of the spinning dope is
reduced and the flow is rendered more uniform. The spinning dope
additionally flows through the filtration unit 90 and the openings
88 of the pressure distributing plate 54, whereby the flow and
pressure profile will be rendered still more uniform across the
flow cross-section and all capillaries 7 will be supplied
uniformly.
[0074] From the stabilizing chamber 84 the spinning dope flows in
the spinning head 8 through the pressure distributing plate 54 and
into the distributor space 56a defined by the spinning nozzle body
56. In the distributor space 56a the flow cross-section gradually
decreases in the direction of flow. This has the effect that the
spinning dope is accelerated and that the flow cross-section is
also gradually reduced to the flow cross-section of the spinning
capillaries 7.
[0075] The distributor space 56a is followed by the spinning
capillaries 7 when seen in the direction of flow, said spinning
capillaries 7 terminating in spinning-dope discharge openings 94 in
said direction of flow. The spinning dope is discharged from the
spinning head through said spinning-dope discharge openings 94 at a
high velocity and at a high mass flow rate, respectively. A typical
mass flow rate per spinning capillary is 0.03 to 0.5 g/min. Higher
flow rates up to 1.5 g/min are possible in the case of higher
heating temperatures of the spinning capillaries. The pressure of
the spinning dope can be up to 400 bar.
[0076] For operating the spinning head 8, it is important that the
spinning dope is maintained at the operating temperature when it
flows through said spinning head. For this purpose, the heating
channels 76, 78 and 80, which have already been mentioned briefly
hereinbefore, are provided in the manifold block 6 and in the
holding device 60.
[0077] The manifold-block heating channels 76 are arranged in the
vicinity of the supply line 82 and maintain the spinning dope in
said supply line 82 at operating temperature. A heating fluid, such
as hot water, a heat-transfer oil or vapour, flows through the
heating channels 76.
[0078] The heating channel 78 is arranged in the area of the
holding device 60 so far down that it will heat the distributor
space 56a already before the spinning material enters the capillary
7. A heating fluid, such as hot air, hot water, a heat-transfer oil
or vapour, also flows through the heating element 78.
[0079] Optionally, also a second manifold-block heating element 80
may be provided, which is attached to the spinning head section
located opposite the spinning-dope discharge opening 94. In the
embodiment according to FIG. 2, the manifold-block heating element
80 serves to heat the upstream part of the supply line 82.
[0080] The heating channels 76, 78, 80 may be connected to a common
heating circuit or they may define separate heating circuits. The
heating circuits of the heating channels 76, 78, 80 may also be
connected to the heating chamber.
[0081] In the first embodiment, cf. FIG. 2, the fibrillation
tendency is reduced by the fact that the spinning capillary 7 is
heated from outside in the area of the discharge opening 94. This
is achieved in that the heating fluid in the heating chamber 70
flows around the outer surface of the spinning capillary 7 thus
heating said spinning capillary 7 directly. Due to the fact that
the spinning capillary 7 has thin walls and a large outer surface
in view of its length, a high heat transfer takes place from the
heating fluid via the spinning-capillary wall to the spinning dope.
In order to achieve the best possible heating of the
spinning-capillary wall, the contact surface between the heating
fluid and the outer wall of the spinning capillary should be as
large as possible.
[0082] Since the spinning dope flows in the spinning capillary at a
high velocity, the temperature of the heating fluid may also safely
exceed the decomposition temperature of the spinning dope: due to
the high velocity at which the spinning dope flows along the heated
wall, the residence time of the spinning dope in the capillary will
not be long enough for the spinning dope to reach the wall
temperature of the capillary.
[0083] Surprisingly enough, it turned out that even at wall
temperatures of approx. 150.degree. C. it was possible to spin
fibres which have a very low fibrillation tendency. The
fibrillation tendency was even lower and the non-looping property
higher than in the case of a wall temperature of 105.degree. C.
[0084] Due to the great length of the spinning capillary, it is
guaranteed that the spinning-dope layer flowing close to the wall
will heat. Since, in the case of conventional spinning dopes, the
viscosity increases as the temperature decreases, the viscosity of
the spinning dope flowing through the spinning capillary 7 will be
reduced in the area close to the wall. It follows that a fuller
velocity profile can be obtained in the core flow over the great
travelling length of the spinning capillary 7 which is heated in
full length.
[0085] The formation of the velocity profile along the spinning
capillary 7 is schematically explained in FIG. 2 on the basis of
four velocity profiles A, B, C and D. Velocity profile A comes into
being a short distance behind the distributor space 56a and is
characterized by a narrow maximum in the area of the core flow
close to the centre line M. Said velocity profile A drops steeply
towards the walls of the spinning capillary 7.
[0086] Due to the fact that the spinning-capillary wall is heated,
the viscosity of the spinning dope decreases in the wall area, the
velocity profile becomes increasingly uniform and the velocity
maximum increases in width. This is schematically shown in velocity
profile B.
[0087] In the spinning-dope discharge opening 94, the velocity
distribution in the core flow is almost constant and drops steeply
towards the walls. This is shown by velocity profile C. The steep
drop in the wall area is possible due to the low viscosity and the
strong heating of the spinning-capillary wall up to the discharge
opening 94.
[0088] Velocity profile D shows schematically a velocity profile
after the discharge of the spinning dope from the discharge opening
94. The inert fluid from chamber 72 and the spinning dope from the
discharge opening 94 form together a broad jet.
[0089] It follows that, according to the present invention, the
capillary length, which is very long in comparison with the
capillary diameter, and the direct heating of said capillary
co-operate and result in an advantageous velocity profile. An
important aspect in this connection is that the temperature of the
spinning-capillary wall is higher than the temperature of the core
of the spinning-dope flow in the middle of the spinning capillary.
The temperature in the core of the spinning-dope flow through the
capillary 7 corresponds approximately to the operating temperature
of the manifold block 6 and of the holding device 60 with the
pressure distributing plate 54 and the nozzle body 56 accommodated
therein, said operating temperature being adjusted by the heating
channels 76, 78, 80. When flowing through the spinning capillary,
the core flow remains uninfluenced and does not change its
temperature.
[0090] Due to the small wall thickness of the capillary 7, the
temperature of the spinning-capillary wall 7 can, moreover, be
controlled precisely and with a fast response: due to the small
mass of the spinning-capillary wall, the wall temperature will
react immediately to temperature variations in the heating chamber
70.
[0091] For purposefully adjusting the wall temperature and for
purposefully influencing the flow through the capillaries 7 in this
way, a control device (not shown) may be provided. The control
device is connected to sensors (not shown), which detect the
temperature of the capillary wall and/or of the heating fluid in
the heating chamber 70, the flow velocity of the spinning dope
through the capillaries and the operating pressure of the spinning
dope. In this way, a closed-loop control circuit can be established
by means of which the temperature of the wall can be adapted to
varying operating conditions automatically or by control from
outside. Hence, variations of the operating parameters can be
compensated for without any deterioration of the spinning
quality.
[0092] Tests have shown that the fibrillation tendency can be
reduced to a decisive extent when the wall of the spinning
capillary 7 is heated also in the area of the discharge opening
94.
[0093] For this purpose, the heating fluid is conducted from the
heating chamber 72 through the gap 74 past the outer wall of the
spinning capillary 7 and out of the spinning head 8 in the
embodiment according to FIG. 2. This will guarantee that the
spinning capillary is actually heated over its whole length and
that the fuller flow profile developing over the length of the
spinning capillary 7 cannot recede due to a colder wall at the end
of the travelling length.
[0094] The fluid flows out of the gap 74 at a high velocity which
corresponds at least to the velocity at which the spinning dope is
discharged from the discharge opening 94. It follows that the fluid
also acts as a transport fluid which entrains and stabilizes the
spinning-dope jet.
[0095] If the discharge velocity of the fluid is higher than the
velocity of the spinning dope, a tensile stress will act on the
edge of the spinning-dope jet, which will stretch the highly
viscous jet.
[0096] Like the fluid in the heating chamber 70, also the fluid in
the heating chamber 72 may be part of a closed-loop control circuit
for the wall temperature of the spinning capillary 7. For this
purpose, a large number of sensors for detecting the operating
parameters of the spinning system as well as sensors for detecting
the, temperature of the spinning-capillary wall and of the heating
fluid may be provided, as has been described hereinbefore. The
signals of these sensors are supplied to a temperature controller
by means of which the temperature of the heating fluid in the
heating chamber 70 is controlled.
[0097] Due to the division into two heating chambers 70, 72, the
temperatures of the two heating fluids in these chambers can be
adjusted differently. In this connection, it proved to be
advantageous when the spinning-capillary wall close to the
discharge opening 94 is maintained at a higher temperature than the
middle area of the spinning capillary. This measure serves to
suppress the above-described strand expansion.
[0098] By subdividing the chamber 70 into further heating chambers
which are independent of one another, the temperature profile along
the spinning capillary can be controlled even more precisely in the
direction of flow of the spinning dope according to a further
embodiment, especially in cases in which said capillary is very
long. Each of these chambers can be provided with separate
sensors.
[0099] In the following, the structural design of the second
embodiment will be explained making reference to FIG. 3.
[0100] In so doing, only the differences existing in comparison
with the first embodiment will be explained. Identical components
or similar components having the same function as the components of
the first embodiment are provided with the same reference numerals
in FIG. 3.
[0101] The second embodiment according to FIG. 3 substantially
differs with respect to the structural design of the heating
chamber 70: the embodiment of FIG. 3 has in the area of the
spinning capillaries only a single heating chamber 70 which extends
up to the discharge opening 94 of the individual spinning capillary
7 and which defines the gap 74. Each spinning capillary 7 may have
a heating chamber 70 of its own, but a plurality of spinning
capillaries 7 may also be combined in one heating chamber 70.
Neither a second chamber 72 nor a second housing 68 is
provided.
[0102] In the embodiment according to FIG. 3, the heating chamber
70 is provided with a tube 100 having a circular or oval shape
which surrounds the outer surfaces of the spinning capillary and
which defines an annular space 102 between the spinning capillary 7
and the housing 66. The annular space 102 opens as an annular gap
74.
[0103] The heating fluid in the annular space 102 heats the whole
outer wall of the spinning capillary 7 up to the discharge opening
94. The heating fluid is therefore part of a heating device which
acts directly onto the spinning-capillary wall and which can be
used for purposefully controlling the wall temperature.
[0104] The tube 100 is produced from a precision steel tube.
[0105] The heating fluid flows out of the annular space 102
parallel and coaxially to the spinning-dope jet discharged from
spinning-dope discharge opening. This permits calm conducting of
the spinning-dope jet.
[0106] In the following, the third embodiment of the spinning head
according to the present invention will be explained making
reference to FIG. 4.
[0107] In so doing, only the differences existing in comparison
with the second embodiment will be discussed. Components of the
third embodiment which are equal to and/or which have the same
function as those of the second embodiment are provided in FIG. 4
with the same reference numerals which have been used in FIG.
1.
[0108] The embodiment of FIG. 4 differs from the second embodiment
insofar as the gap 74 defined by the housing 66 has not an annular
but an elongate shape. The housing 66 can be implemented in one
part or it may have two wings 104a, 104b which are adapted to be
displaced at right angles to the centre line M. The width of the
gap 74 can be adjusted by displacing the wings in the direction of
the arrows shown in FIG. 4.
[0109] In the following, the fourth embodiment of the spinning head
according to the present invention will be explained making
reference to FIG. 5.
[0110] In so doing, only the differences existing in comparison
with the second embodiment will be discussed. Components of the
fourth embodiment which are equal to and/or which have the same
function as those of the second embodiment are provided in FIG. 5
with the same reference numerals which have been used in FIG.
1.
[0111] In the case of the spinning head according to the fourth
embodiment, a heating chamber is no longer provided. The spinning
capillary is no longer heated via a heating fluid, but via an
electric heating jacket 110 which is part of the heating device of
the spinning head.
[0112] The heating jacket 110 may also be part of a closed-loop
control circuit for controlling the temperature of the
spinning-capillary wall; this type of closed-loop control circuit
has been described hereinbefore.
[0113] In order to achieve a precise control of the temperature
profile along the length of the spinning capillary, the heating
jacket may be subdivided into a plurality of independently
operating heating-jacket segments.
* * * * *