CA1145909A - Method of extruding polypropylene - Google Patents

Method of extruding polypropylene

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Publication number
CA1145909A
CA1145909A CA000335965A CA335965A CA1145909A CA 1145909 A CA1145909 A CA 1145909A CA 000335965 A CA000335965 A CA 000335965A CA 335965 A CA335965 A CA 335965A CA 1145909 A CA1145909 A CA 1145909A
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CA
Canada
Prior art keywords
zone
filaments
temperature
polypropylene
less
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000335965A
Other languages
French (fr)
Inventor
John S. Roberts
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kling-Tecs Inc
Original Assignee
Kling-Tecs Inc
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Filing date
Publication date
Application filed by Kling-Tecs Inc filed Critical Kling-Tecs Inc
Priority to CA000335965A priority Critical patent/CA1145909A/en
Application granted granted Critical
Publication of CA1145909A publication Critical patent/CA1145909A/en
Expired legal-status Critical Current

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Abstract

Title of the Invention METHOD OF EXTRUDING
POLYPROPYLENE YARN

Abstract A method of extruding multi-filament polypropylene yarn in which the polypropylene is extruded at a tempera-ture below 425°F, such as in the range 415°F to 350°F, particularly about 400°F, into a hot zone having a tempera-ture sufficiently high to retard cooling of the extruded polypropylene yarn. The temperature of the hot zone can be within 60°F of the temperature of extrusion. The yarn is then passed through a quenching zone across which air is blown to cool the yarn. The swell value of the polypropylene can be less than 3 and its melt flow may be greater than 30.
The yarn is drawn down in the hot zone and the filaments may be drawn down to an undrawn denier of less than 40.

Description

~s~

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,
-2-'~.,~

~$9~g 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
-3 5~

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 ` :
in said first zone.

:
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 :: :
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.

- 4a -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.

~59~

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 ~ . , 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.

~s~

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 :
~ ~ around the groups 34, 35 an~ 36 of capillaries but with : ~ : :
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.

5~

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 :
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.

~5~

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.

' 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, ~ ~59~)~

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 S9~

~ times the third power of the capillary radius (in centimeters~ i e. Shear rate = 4~
7~ X radius 3 ,~1

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-
1. A method of producing polypropylene filaments com-prising heating polypropylene having a narrow molecular weight distribution with a swell value of less than 3 to a temperature at which it is molten, extruding the molten polypropylene at a temperature less than 425 F. 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 substantially eliminate the oc-curence of resonance in the filaments as they are drawn down in said first zone.
2. A method as claimed in claim 1 in which the first zone contains gas at a temperature less than 75°F. below the temperature at which the molten polypropylene is extruded.
3. A method as claimed in claim 1 in which the first zone contains gas at a temperature above 350°F.
4. A method as claimed in Claim 1 in which the tempera-ture of said first zone is within 60°F. of the temperature at which said molten polypropylene is extruded.
5. A method as claimed in claim 1 in which said cooling gas is passed through said second zone transversely to the filaments.
6. A method as claimed in claim 5 in which the tempera-ture of said cooling gas as it enters said second zone is less than 90°F.
7. A method as claimed in claim 5, in which said first zone is short relative to said second zone and contains gas in a quiescent state.
8. A method as claimed in claim 1 in which the filaments are drawn down in said first zone to a denier per filament less than 40.
9. A method as claimed in claim 8 in which said denier is less than 30.
10. A method as claimed in claim 1 in which a metered stream of said molten polypropylene is extruded through a spinnerette having at least two groups of orifices to produce from said metered stream at least two yarns each having a plurality of filaments.
11. A method of producing polypropylene filaments com-prising heating polypropylene having a narrow molecular weight distribution with a swell value of less than 2.5 and a melt flow greater than 30 to a temperature at which it is molten, metering a stream of said molten polypropylene, extruding said metered stream at a temperature in the range 360°F. to 420°F. downwards through a spinnerette having at least two groups of orifices to produce at least two groups of filaments therefrom, passing said two groups of filaments downwards through a first zone containing quiescent air at a tempera-ture sufficiently high to retard cooling of the filaments therein, passing the filaments through a second zone, direct-ing cooling air transversely over the filaments in said second zone to cool them, pulling the two groups of filaments out of said second zone at a controlled rate so that said filaments while in said first zone are drawn down to an un-drawn denier per filament of less than 40, the combination of the swell value of the polypropylene, the temperature of extrusion, and the temperature of said first zone interacting to substantially eliminate the occurrence of resonance in the filaments as they are drawn down in said first zone.
12. A method of producing polypropylene filaments, com-prising heating polypropylene having a narrow molecular weight distribution with a swell value of less than 2.5 and a melt flow greater than 20 to a temperature at which it is molten, extruding the molten polypropylene at a tem-perature in the range 415°F. to 350°F. into a plurality of filaments, passing the filaments through a first zone having a temperature sufficiently high to retard cooling of the filaments therein, drawing down the filaments to their un-drawn 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 substantially eliminate the occurrence of resonance in the filaments as they are drawn down in said first zone.
13. The method recited in claim 12, in which said molten polypropylene is extruded at a temperature in the range 410°F. to 360°F.
14. The method recited in claim 13, in which said extru-sion temperature is 400°F.
15. The method recited in claim 12, in which said swell value is less than 2Ø
16. The method recited in claim 15, in which said swell value is in the range 1.2 to 1.7.
17. The method recited in Claim 16, in which said melt flow is in the range 35 to 45.
18. The method recited in claim 12, in which said cooling gas comprises air and isiblown transversely across saicl fil-aments and exhausted to atmosphere.
19. The method recited in Claim 18, in which the tempera-ture of said air as it enters said second zone is less than 90°F.
20. The method of producing filaments recited in claim 12, in which said filaments are produced as multifilament yarns, and further comprising the steps of winding said yarns into separate packages, and subsequently multi-end drawing said yarns.
21. The method recited in Claim 20, in which said multi-end drawing comprises drawing eight yarns together.
22. A method of producing a uniform polypropylene filament comprising extruding the filament at a temperature less than 425°F. into a relatively short hot zone contain-ing gas at a temperature less than 70°F. below the temper-ature of extrusion, drawing down said filament to its undrawn denier, and thereafter passing the filament through a quenching zone to cool it, the low temperature of extrusion and the closeness to it of the temperature of the gas in said hot zone interacting in relation to the drawing down of the filament to substantially eliminate the occurence of resonance in the filament.
23. A method of producing a uniform polypropylene filament as claimed in claim 22 in which the temperature of the gas in said hot zone is greater than 350°F.
CA000335965A 1979-09-19 1979-09-19 Method of extruding polypropylene Expired CA1145909A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA000335965A CA1145909A (en) 1979-09-19 1979-09-19 Method of extruding polypropylene

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA000335965A CA1145909A (en) 1979-09-19 1979-09-19 Method of extruding polypropylene

Publications (1)

Publication Number Publication Date
CA1145909A true CA1145909A (en) 1983-05-10

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Family Applications (1)

Application Number Title Priority Date Filing Date
CA000335965A Expired CA1145909A (en) 1979-09-19 1979-09-19 Method of extruding polypropylene

Country Status (1)

Country Link
CA (1) CA1145909A (en)

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