Note: Descriptions are shown in the official language in which they were submitted.
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Background of the_Invention
Polypropylene yarns, particularly continuous filament
textile face yarns, are usually produced with conventional
'down-the-stack' air quench extrusion apparatus. These
are housed in a building several stories high with an
extruder on an upper floor, air quench cabinets on the
floor below, and inter-floor tubes extending down to a
lower floor where the yarn is taken up onto packages.
Cooled air Ls blown throuyh the quench cabinets to solidify
L0 and cool the yarn.
One disadvantage ~hat occurs i~ resonance in the
~ formation of the filaments of the yarn. As the polypropy-
; lene melt is extruded through a capillary in a spinnerette,
it swells out on the underside of the spinnerette and then
the filament is drawn-down from such swelling. However,
this drawing-down occurs non-uniformly and, in exaggeration,
the filament forms like a string of sausage links: this ls
resonance. Subsequently, when the filaments are being fully
drawn, this resonance tend~ to cause draw breaks in the
fiLaments. The more pronounced the resonance~ the greater
the frequenoy of draw breaks.
Also, the point at which a filament completes its
drawing-down, ln the quench cabinet, to its undrawn denler
varies. This can~be seen~as~a~ raln drop effect when looking
into the quench cabinet. This contributes to further non-
.
uniformity.
The temperature at whLch~the polypropylene melt is
e~truded is usually o~ the order of 500F, although lower
temperatures have been tried. It is known~that, in general,
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as the temperature is lowered, the swell on the underside
of the spinnerette yets greater with an increase in
resonance, and even the occurance of spin breaks at or
near the spinnerette face.
The problem of resonance and subsequent draw breaks
gets more acute with finer denier per filament yarns, for
example yarns having an undrawn denier per filamen~ less
than 30, say less than 10 denier per filame~t in the finally
drawn yarn. Also, with finer denier yarns the problem of
denier variation from filament to filament, as well as
along the length of the filament, becomes more noticable.
Summary of the Invention
The invention is based upon the realization that if
the filaments are extruded into a relatively short hot
zone, at or slightly below the temperature of extxusion,
before they are contacted by the cooling air, then the
extrusion temperature can be decreased without the usual
increase ln the volume of swell at the splnnerette face.
It has been found that as the extrusion temperature decreases
~ 20 the resonance in the filaments decreases; an optimum point
:~ is reach d around 400F. When the temperature goes much
~ ;~ lower th n this optimum poi.nt, resonance starts increasing
:
again and then spin breaks occur. The precise optimum
point is~ believed t~ be influenced by the swell value of the
polypropylene and its melt flow. It is theoriæed that as
the temperature of the melt decreases, the melt becomes more
Newtonian in its behavlor; this is~beL.ieved to be further
helped as the swell value of the polypropylene is decreased,
for example to below 2.5.
According to one aspect of the invention there is
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provided a method of producing po1ypropylene filaments com-
prising heating polypropylene having a narrow molecular
weight distribution wi-th a swell value of less than 3 to
a temperature at which it is molten, extruding the mol-ten
polypropylene at a temperature less than 425F. into a
plurality of filaments, passing the filaments through a
first zone having a temperature sufficiently high to re-
tard cooling of the filaments therein, drawing down the
filaments to their undrawn denier in said first zone, then
passing the filaments through a second zone, and directing
cooling gas over the filaments in said second zone to cool
them, the combination of the swell value of the polypropylene,
-the temperature of extrusion, and the temperature of said
first zone interacting to substantialIy eliminate the occur-
rence of resonance in the filaments as they are drawn down
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in said first zone.
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The extrusion temperature may be less than 420F, such
as in the range 415F to 350F or in the range 410F to 360F.
The polypropylene may have a swell value of less than
3, preferably less than 2.5. The melt flow may he greater
than 20, and is preferably greater than 30.
The temperature of said first zone may be less than
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70F below the temperature oE extrusion; it may be a~ove
350F. Preferably it is withln 60F of the extrusion tem-
perature.
Said first zone preferably contains air, or gas, in
a quiescent state. ~
The yarn may have filaments which are drawn down in
,
said first zone to a denier per f1lament of less than 40,
for example less th.an 3C.
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In the quenching zone coolin~ air may be blown trans-
versely over the yarn to cool it.
A specific embodiment of the invention wil]. now be
described in greater detail with reference to the accom-
panying drawings.
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Brief description of the drawings
Figure 1 is a schemmatic vertical section of an
apparatus for carrying out the method of the invention;
Figure 2 is a diagrammatic section, on a larger
scale, on the line 2-2 of Figure l;
Figure 3 is a diagrammatic sectional view on the
line 3-3 of Figure 1 but on the same scale as Figure 2;
Figure 4 is an illustration, on an enlarged scale,
of a filament being produced; and
Figure S is an illustration, on an enlarged scale,
of another filament being produced uni~ormly.
Description of a specific embodiment
In Figure 1 an extruder 10 has an infe~d hopper 11,
a screw 12, and band heaters 13a~ 13b, 13c and 13d~ A
transfer tube 14 connects the discharge end o the extruder
10 to a metering pump 15. The transfer tube 14 and the
metering p~mp 15 are surrounded by band heaters 16 and 17,
respectively. The discharge side of the metering pump 15
is connected by a tube 18 to a spin pack 19 mounted in a
spin block 20 which is surrounded by a band heater 21. The
spin pack 19 has a cover plate 22, ~a body 23, a breaker
plate 24,~and~a splnnerette 25. For simplLcity~ the usual
heat insulation that covers the band~heaters and other parts
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of the apparatus is not shown. A shroud 26 is attached by
bolts 27 (see Figure 2) to the underside of the spin block
20. Below the shroud 26 is mounted an air quench cabinet
28 at the bottom of which are ~finish applying guides 29.
Just below the guides 29 is a denier control roll 30.
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The shroud 26 defines a rectangle in horizontal
section, see Figures 3. At its upper end is a flange 31
through which the bolts 27 pass. At the lower end of the
- shroud 26 is an inwardly directed collecting trough 32.
The spinnerette 25 has capillaries 33 arranged in
three groups 34, 35, and 36, respectively, to produce three
multi-filament yarns 37, 38, and 39, respectively. To
produce yarns having various filament counts, different
spinnerettes can be used having a different: number of
capillaries.
The quench cabinet 28 has a top cover 40 which fits
closely around the outside of the trough 32. One wall of
.
the quench cabinet 28 is formed of wire mesh 41 supported
in a rame~ 42.~ The opposite wall is formed o slotted
sheet metal 43 supported in a frame 44. A cooling air
plenum 45 registers with the wire mesh 41. In cross-section
the quench cabinet is rectangular, similar to the shroud 26
and the face of the spinnerette 25 with the groups of
capillaries 34, 35 and 36 spaced apart in a direction
parallel to the longer sides of these rectangles.
The shroud 26 is relatively short and fits closely
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~ ~ around the groups 34, 35 an~ 36 of capillaries but with
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sufficient clearance so that the yarns 37, 38 and 39, if
they sway, do not come in contact with the inner edge of
the trough 32. As~seen in Figure 3, the longer side of the
shroud 26 is 12 inches and the shorter side 7 inches; the
length of the face~of the spinnerette 25 is 8 inches and
the width 4 inches. The height of the shroud 26, as seen
in Figure 2, is 9 inches.
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With the method according to the invention~ pellets
of polypropylene resin and pellets of color concentrate
are ed via the hopper 11 into the extruder 10. The poly-
propylene has a melt flow of 30 and has a narrow molecular
weight distribution with a die swell or swell value below
2, in this instance 1.9. The resin and color are melted
and heated by the extruder heaters to a temperature of
400F and mixed by the screw 12. The heaters 13a, 13b,
13c and 13d are set to control their zones at 300F, 350F,
375~F and 400F, respectively. The downstream heaters 16,
17, 21 are set to control their zones at 400F. The melt
is fed by the screw 12 throu~h the~trans~er tube 14 to the
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metering pump 15 which~delivers~ a metered stream o~ mel~
through the tube 18 to the spin pack 19. Inside the spin
pack this~metered stream 15 hydraulically split ar.d extrud-
ed downwards through the capillaries 33 into the multitude
of filaments forming the three spaced apart yaxns 37, 38,
and 39. The number of capillarles in the spinnere-tte is
chosen to determine the number of filaments in each yarn,
in this~instance 70 filaments. ~These yaxns pass through
the shroud 26,~which defines a~hot zone, and are then
cooled as they pass through the quench cabinet 28. The
cooling o~ the yarns is effected~by ~lowing;air transversely
across them, the aLr ~rom~the plenum~45 entering the quench
cabinet through the wire mesh 41 and being exhaus~ed ~o
atmosphere thxough the slots in the sheet metal 43. The
cooled~yarns then pass through th guides 29 which apply
spin finlsh to them be~ore they are brought toge~h~r around
the denler control roll 30, after which the three yarns are
separated and wound onto separate packages 47, 48 and 49.
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The denier control roll pulls the yarns down from the capil-
laries 33 at a controlled rate~ in this instance 600 meters
per minute, to determine their undrawn denier, in this
instance 900 denier.
The air inside the shroud 26 is trapped there and
remains quiescent. This air is heated by the metal above
it, nameIy the face of the spinnerette 25, the lower end
of the pack body 23 and part of the spin block 20, these
bein~ heated by the spin block heater 21. The molten
filaments leaving the capillaries 33 also heat this air.
In this way, the air inside the shroud 26 remains hot at
a temperature close to or just below, the temperature of
the melt being extruded and prevents substantial cooling
of the fllaments as they pass therethrough. The temperature
in the lower portion of the shroud 26 may be at a lower
temperature than in the upper portion, but is suf~iciently
high to retard cooling o~ the filaments.
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Flgure 4 shows in an exsggerated msnner a poLypropy-
lene filament being extruded from a caplllary S0 directly
into an air quenching zone 51 by a conventional air quench
process. The molten polypropylene swells out at 5~ under
the face of the spinnerette and then forms a series of dim-
inishing swellings 53, 54 before the draw-down to the size
of the filament is completed.~ Thls series o~ swellings
is not completely drawn out and results in the filament
exibiting resonanc~ to som~ degree.
Figure 5 illustrates the way in which the swell
draws down in the present invention. An initial swell S5
~:
occurs under the face of the spinnerette, but then due to
the combination o the low temperature of extrusion and the
extrusion o~ the filament into a hot quiescent ~one S6,
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the draw down occurs quicker over a shoxter distance to
a uni~orm filament 57. As can be seen, the total volume
of the swell 55 is less than the volume of the ~longated
swell 52, 53, 54 shown in Figure 4.
The 900 undrawn denier 70 filament yarn produced by
the method of the invention, when subseg~en~ly draw~ at
a draw ratio of 3:1 to a continuous fi}ament 300 denier
70 fllament yarn, produces a uniform yarn with substantially
no resonance symptoms and improved uniformly of denier
from flIament to filament. The yarn also draws with a
high efficiency with substantially no draw breaks. This
further makes possible multi-end drawing, for example
drawing eight yarns together on the same drawframe.
For the production of finer denier per ~ilament
yarns it is preferable to use narrow molecular weight
distributlon polypropylene with a higher mel~ flow, for
example in the range 35 to 45, and with a lower swell value,
or example in the range 1.2 to 1.7.
Narrow molecular weight distribution polypropylene
; 20 is usually made by thermal degradation of reactor resin,
although th~s can be done chemically. The object is to
; degrade ~he~hLgh molecular welght materialO The swell
value is the ratio of the di~ameter of the extrudate just
below the face of the spinnerette divided by the diameter
of the capillary through which it is bein~ extruded4 This
should be measured using a~ capillary with basically zero
land (length to radius ratio not greater than 0.221~ at
a temperature of 190C and at a shear rate of one thousandth
of a second. Shear rate equals ~our times the volumetric
flow rate ~q in cubic centimeters per second) divided by
g
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~ times the third power of the capillary radius (in
centimeters~ i e. Shear rate = 4~
7~ X radius 3
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