Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
t 376~ 2~
Description:
Spinning process and device for its performance
The present invention relates to a process and apparatus for
producing synthetic fibers of particularly high uniformity
and high dynamic efficiency wherein the freshly spun
filaments are cooled by central gas quenching.
DE-C-1,278,684 and US-A-3,259,681 already disclose melt
spinning processes where the filaments are immediately
cooled after emerging from the spinneret by central gas
quenching. In these known processes, the filaments are spun
from a spinning nozzle whose spinning holes are arranged in
one or more concentric circles, the diameter of the smallest
hole circle being sufficiently large for installation of a
quench stick just below the center of the spinning nozzle.
This quench stick consists of a tubular hollow body, made of
a porous gas-permeable material, is sealed at one end and
supplied at the other end with cooling air. In action, the
quench stick produces a radially outward stream of cooling
air which penetrates the few "layers" (corresponding to the
number of concentric spinning hole circles) of the
downward-moving filament curtain surrounding the quench
stick. This arrangement is supposed to give an appreciably
more powerful cooling effect, and it is also expected that
the cooling of the individual filament layers will become
more uniform. However, in practice it was found that central
gas quenching does not give sufficiently uniform filaments
and that there are frequent process disruptions due to
filament breakage.
US-A-4,414,169 discloses a process for producing high-
strength polyester multifilament yarns. In this process, the
filaments are cooled by gas quenching directly beneath the
spinning nozzle and drawn off under relatively high tension.
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The filaments are then drawn in two stages. In this process,
the gas quenching of the filaments just below the spinning
nozzle can also be performed by an outward directed gas
stream supplied in the center of the filament bundle. In
this process too, however, the uniformity of the filaments
cooled by central gas quenching leaves a lot to be desired,
and there are frequent filament breakages in the course of
production.
DE-A-3,629,731, EP-A-40,482 and EP-A-50,483 disclose melt
spinning processes where the filaments are likewise cooled
by central gas quenching immediately following their
emergence from the die plate and where the gas quenching is
followed immediately by a likewise central impingement of
the filaments with a spin finish. This spin finish is
applied by a central contact body which is wetted with the
spin finish and over which the circular filament bundle
glides, or by a centrally positioned radial spray nozzle.
These known processes and apparatuses likewise have the
disadvantage that the filaments obtained are not
sufficiently uniform for many applications and that there
are an excessive number of production disruptions due to
filament breakage.
A proposal to improve the uniformity of polyester filaments
is known from US-A-3,858,386. Therein polyester filaments
are melt spun, then guided through a heating zone underneath
the nozzle surface and then cooled by central gas quenching.
The object of this process is a polyester yarn of improved
uniformity in its physical properties, in particular the
Uster values and strength measured across the cross-section
of a filament bundle. The heating zone through which the
filaments pass immediately after emerging from the spinning
plate is 15 to 60 cm in length and at a temperature of 260
to 460C.
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However, the polyester yarns thus obtained have high thermal
shrinkage values, which presents problems for some
applications such as, for example, the production of tire
cords.
The present invention therefore provides a spinning
apparatus with which a stable and highly reproducible
process for producing very uniform high-strength synthetic
fibers of low shrinkage and low elongation and hence of high
dynamic efficiency can be carried out.
The spinning apparatus according to the invention comprises
a ring spinning nozzle, a quench stick arranged centrally
beneath the spinning plate at a distance therefrom, and a
circular slotted diaphragm arranged between the spinning
plate and the upper edge of the quench stick.
In what follows, reference is made to Figures 1 to 5.
Figure 1 is a schematic plan view of the spinning plate (1)
of a ring spinning nozzel having an approximately square
ring area (2) with the spinning bores (3).
Figure 2 is a schematic plan view of the spinning plate (1)
of a referred ring spinning nozzle with 3 concentric circles
(2a) of spinning bores (3).
Figure 3 is a schematic plan view of a circular slotted
diaphragm (4) enclosing between the inner part (5) and the
outer part (6) the circular slot (7).
Figure 4 is a schematic perpendicular section through a
spinning apparatus according to the invention, comprising
the spinning nozzle (8), the spinning bores (3), the
filaments (9) extruded therefrom, and the circular slotted
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diaphragm (4) whose inner part (5) is attached by means of a
spacer piece (10) to the quench stick (11). The shell (12) of
the quench stick is made of a porous, gas-permeable
material; the cooling air is supplied through the flat
tube (13).
Figure 5 is a cross-section through the flat tube (13).
For the purposes of the present invention a ring spinning
nozzle is a spinning nozzle whose spinning plate has a
central zone which is free of bores. The zone which does
contain bores hence surrounds the bore-free zone in the
shape of a frame, i.e. a closed, not necessarily circular,
ring area.
Figure 1 is a schematic view of the spinning plate of a ring
spinning nozzle comprising an approximately square ring area
(2) with bores (3).
The area with bores can be for example square, rectangular,
polygonal or oval and have at its center a correspondingly
smaller bore-free zone with a respectively square,
rectangular, polygonal or oval shape.
Advantageously, the width of the ring area which contains
the bores is approximately the same in any direction,
measured radially from the center. Such dimensioning ensures
a particularly uniform cooling of all spun filaments.
Uniform cooling of all filaments is also promoted by a very
high central symmetry of the ring area. Particular reference
is therefore given to a circular ring area.
Within the ring area the spinning bores can be uniformly
distributed in a conventional manner. In a particularly
advantageous arrangement, the spinning bores are arranged in
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closed lines, in the case of a circular ring area
accordingly in circle lines.
A preferred ring spinning nozzle therefore has from 1 to 10,
preferably 1 - 4, die hole circles. Particular preference is
given to a spinning nozzle having 2 or 3 hole circles where
the nozzle holes making up the individual hole circles are
positioned opposite gaps.
Figure 2 is a schematic view from below of a ring spinning
nozzle preferred for the construction of the spinning
apparatus according to the invention. The nozzle holes (3)
are arranged in concentric circles (2a), the smallest of
which has the diameter di and the largest the diameter da.
The following observations are for simplicity directed at
the use of such a ring spinning nozzle having a circular,
bore-containing ring area, but the person skilled in the art
will have no problem applying them to non-circular ring
spinning nozzles:
The quench stick used in the process according to the
invention is of a conventional design. It comprises a
tubular hollow body made of a gas-permeable material, for
example a sinter metal, which is sealed at one end and which
is supplied at the other end with a stream of cooling air.
The diameter of the quench stick does of course depend on
the diameter di of the smallest nozzle hole circle. In
general, the diameter D of the quench stick is
D = (0.5 - 1.0) x di, preferably (0.7 - 0.8) x di,
and ranges from 45 to 180 mm. The length of the quench stick
is in general from 500 to 1,500 mm, preferably from 800 to
1,300 mm.
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The distance between the spinning plate and the top edge of
the quench stick is advantageously between 50 and 500 mm,
preferably 100 to 200 mm.
The ring slot diaphragm arranged between the spinning plate
and the top edge of the quench stick is a plate with a
closed-shape slot. Again, the slot of the ring slotted diaphragm
need not necessarily be circular. Rather its shape is
similar to the shape of the spinning bore ring area of the
ring spinning nozzle.
If a preferred ring spinning nozzle is used, where the
spinning bores are arranged within a circular ring area
(corresponding to Figure 2), the circular slotted diaphragm used
does of course also have a circular ring slot. Similarly,
the subsequent statements concerning such a preferred circular
slotted diaphragm are readily applied to other embodiments
featuring non-circular ring slots.
Figure 3 is a schematic plan view of such a preferred circular
slotted diaphragm with a circular slot. The inner edge of the
ring slot (7) is formed by the inner part (5) of the circular
slotted diaphragm, which comprises a circular plate of diameter
dp. The outer part (6) of the circular slotted diaphragm, which
forms the outer edge of the ring slot, consists of a plate
with a circular cutout of diameter dr~ dr being greater than
dp and the slot width s being accordingly (dr-dp)/2. The
dimensions of the circular slotted diaphragm of course also
depend on the arrangement of the spinning nozzle holes, i.e.
on the diameters di and da of the smallest and the largest
circle of holes in the spinning plate. Advantageously, dp -
(0.5 to 1.0) x di, preferably (0.7 to 0.8) x di.
The slot width s is accordingly given by the following
relation:
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s = (1.0 to 4.5) x (da-di), preferably (3.0 to 4.0) x (da-di).
In general the following dimensions are selected for di and
da in practice:
di = 50 to 200 mm, preferably 50 - 180;
da = 55 to 205 mm.
The distance Ab of the circular slotted diaphragm from the
spinning plate relates to the distance Ak of the spinning
plate from the top edge of the quench stick. Advantageously,
the circular slotted diaphragm is arranged at a distance
Ab = (0.3 to 0,8) x Ak, preferably (0.4 to 0.7) x Ak,
beneath the spinning plate.
In general, the circular slotted diaphragm should be
dimensioned in such a way as to provide an as narrow as
possible ring slot (i.e. a ring slot with the smallest
possible s) which is just wide enough for all the spun
filaments to pass through without problems.
The inner part of the circular slotted diaphragm is
separated from the outer part by the slot. It is possible in
principle to join inner part and outer part together with
very narrow webs in such a way that the inner part is in the
plane of the outer part. Preference, however, is given to
installing inner part and outer part separately in the
spinning apparatus. The outer part of the circular slotted
diaphragm can be attached for example in a conventional
manner by means of a flange at the desired distance beneath
the spinning nozzle, while the inner part is secured by
means of a spacer either at the center of the spinning
nozzle or alternatively at the quench stick in such a way
that the inner part is in the plane of the outer part of the
circular slotted diaphragm. A suitable material for the
circular slotted diaphragm is any
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.
sufficiently temperature resistant material, for example a
metal, a ceramic or even a high temperature resistant
plastic. Preference is given to a circular slotted diaphragm
made of a heat-insulating material or coated with such a
material. For instance, a circular slotted diaphragm can be
made of a metal and for heat insulation be coated
(laminated) with a layer of a bonded mineral fiber web.
In a constructionally particularly favourable design of the
spinning apparatus according to the invention, the cooling
air is supplied in a conventional manner from the side at
the lower end of the quench stick. The air supply ducts
employed here advantageously take the form of a flat tube;
that is, they do not have a round cross-section but an
extremely elliptical or rectangular croos-section with a
long axis which is 5 to 10 times the length of the short
axis. These air supply ducts are installed with the long
cross-sectional axis in the yarn transport direction. The
advantage of this design is that, despite the air supply
from the side, the filament bundle does not need to be split
as in US-A-3,858,386. The strong cooling of the filaments in
the region of the quench stick leads to trouble-free running
of the filaments. Preferably, the air supply ducts are
provided with a surface of low friction, for example with a
matt chrome finish or with a coating of fluoropolymer.
Particular preference is given to those spinning apparatuses
according to the invention having more than one preferred
feature.
The spinning apparatus according to the invention shows its
particular advantages at spinning speeds of above 2,000 m/min.
The present invention therefore also provides a spinning
process for producing very uniform high-strength yarns of
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low shrinkage and low elongation, which comprises using the
above-described spinning apparatus and operating at spinning
takeoff speeds of more than 2,000 m/min, preferably at
2,500 to 4,000 m/min.
The filaments spun according to the invention can be further
processed in a conventional manner immediately thereafter or
in a separate step, and in particular can be drawn in a
conventional manner in one or more stages at ambient or
elevated temperatures.
Particularly advantageous results are obtained on using
polyesters whose I.V., measured in 50/50 o-chlorophenol/
phenol at 25C, is above 0.7 dl/g, in particular above
0.8 dl/g.
The process according to the invention gives filament yarns
where the filaments across the diameter of the bundle are
more uniform than with yarns hitherto produced. The heat is
carried off uniformly and rapidly, thereby in addition
permitting short spinning columns. An additional heating
means to delay the cooling of the spun filaments is not
necessary and not desired in the process according to the
invention. Such means would destroy the high preorientation
of the filaments which is desirable here.
A further surprising advantage is that cylinder-symmetrical
quenching from the inside to the outside gives in
conjunction with the circular slotted diaphragm the same
preorientation of the filaments at as low a spinning takeoff
speed as 2,600 m/min as is obtainable with transverse
quenching only at a spinning takeoff speed of 3,000 m/min.
The subsequent drawing of the filaments spun according to
the invention gives high-strength filament yarns or fibers
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having a low total of elongation and shrinkage and a high
dynamic efficiency.
Illustrative embodiment
The illustrative embodiment described hereinafter utilizes a
spinning apparatus according to the invention (Figure 4).
This apparatus possesses as features essential to the
invention a ring spinning nozzle (8) with two concentric
circles of a total of 200 spinning bores (3) each situated
opposite a gap. The smaller circle of bores has a diameter
di of 166 mm and the larger circle of bores has a diameter
of 177 mm.
At the center beneath the nozzle there is an 800 mm long
quench stick (11) 105 mm in diameter comprising a shell
(12) made of sintered metal, the top edge of which is at a
distance of 100 mm from the nozzle plate.
At a distance of 70 mm below the nozzle plate there is a
circular slotted diaphragm (4) made of a 2 mm thick sheet of
VA metal and bearing a 5 mm thick bonded rock wool web. The
inner edge of the circular slot has a diameter of 120 mm,
and the slot width is 40 mm. The inner part (5) of the
diaphragm is attached with a spacer (10) 30 mm in length to
the quench stick.
The cooling air is supplied from the side through a flat
tube (13) 600 mm in height and 60 mm at its widest point
which is tapered towards its upper edge and has been
installed on end (see cross-section in Figure 5).
This spinning apparatus is used to spin a polyethylene
terephthalate of I.V. 0.90 dl/g, measured in 50/50 o-
chlorophenol/phenol at 25C, at a nozzle temperature of
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315C into filaments taken off at 2,600 m/min. The spun
filaments are gathered together, have a low level of
protective twist applied to them and are wound up.
The yarn obtained is then drawn in a ratio of 3.11:1 at a
temperature of 265C. The filament yarn thus obtained can be
further processed in a conventional manner, for example by
plying and texturing or, collected into tow form, by cutting
into staple fibers. The filament yarns obtained have the
following data:
Titer: 1,440 dtex f 200
Breaking strength: 72 cN/tex
Elongation at break: 8.7
Elongation under a load
of 54 cN/tex: 6.2
Hot air shrinkage at 200C: 6.4 ~
The filament yarns differ from conventionally produced yarns
by excellent, appreciable improved uniformity of the
textile data across the yarn.
