Method of producing polypropylene yarns

Continuous polypropylene multifilament yarns are made by melt spinning and stretching in an integral process; a sufficient number of filaments for forming at least 8 continuous filament yarns each consisting of at least 10 filaments are melt spun through a spinneret (11) at a speed of at least 400 m/min into a vertical air quenching zone or shaft (12) for solidification; the filaments are arranged to form a substantially planar array of parallel and mutually distanced yarn strands; then, the filaments are stretched to achieve substantial orientation by passing the yarn strands, while maintaining them in the array, over peripheral surface portions of a sequence of rotating cylinders (141, 142, 143, 144) having parallel axes of rotation, each strand (S) passing over said surface portions along a discrete path which is substantially defined by a plane intersecting perpendicularly with the parallel axes of the cylinders; each strand is in frictional contact with the peripheral surface portions for a total contact path length of from 1000 to 6500 mm and at least 50%, preferably 75-100%, of the path length of frictional contact are provided on a total number of from 2 to 6 and preferably 4 large diameter cylinders; the yarn strands are wound as a product at a speed of at least 1000 m/min, e.g. at about 2000 m/min.

BACKGROUND OF THE INVENTION 
The invention generally relates to the production of polypropylene yarns 
and specifically to a method of making such yarns by melt spinning. 
Melt spun polypropylene has been in commercial use for monofilaments, such 
as fishing lines, and staple fibers, such as carpet yarns. However, 
attempts to introduce polypropylene filament yarns into the apparel market 
have met with problems to the extent that quality fine denier yarns made 
of nylon or polyester are the rule while those made of propylene, if 
available at all, are the exception. Considering the lower costs of 
polypropylene as well as its unique properties, such as mechanical 
strength combined with thermal and chemical stability as well as its 
favorable ability to transfer moisture in the vapor phase, this is 
surprising since polypropylene would seem to provide for very desirable 
textile yarns. 
The crucial problem, however, is that the processing technologies developed 
for polyesters and polyamides, notably the preoriented yarn (POY) methods, 
are not suitable at all for commercial polypropylene processing. This 
lacking transferability of established method and apparatus means for 
production of continuous yarns is believed to be due essentially to the 
fact that molten polypropylene behaves as a non-Newtonian liquid 
exhibiting structural viscosity phenomena that cause what is termed "draw 
resonance" or "spinning resonance" as illustrated, for example, in FIGS. 4 
and 5 of EP - A -0 025 812 or US - A - 4,347,206 incorporated herein by 
way of reference. 
Briefly and in exaggeration, polypropylene not only exhibits dye-swelling 
upon extrusion but upon drawing-down from the swellings formed at the 
underside of the spinneret produces a filament with a non-uniform 
thickness in the manner of a string of linked sausages. Various prior art 
methods have been aimed either at modifying the polypropylene material or 
at specific methods (e.g. FR Pat. No. 1,276,575, EP - A -0 028 844, DE - A 
- 33 23 202) and it appears that acceptable results can be achieved best 
when semi-finished filament yarns are made in a first process by yarn 
producers and then textured and/or drawn to substantial orientation as 
required for most commercial uses of the yarns in a second separate 
process, e.g. by the yarn users. 
However, integral methods, i.e. those starting from the unspun polymer and 
producing final polypropylene yarns composed of a plurality of continuous 
and substantially oriented filaments by melt spinning and stretching on a 
single production unit, have suffered either from low processing speeds of 
typically below 500 meters per minute or -- when operable at acceptable 
production speeds of above 1000 meters per minute from severe limitations 
as to the number of yarns that can be obtained per stretching installation 
unit. Consequently, production output per investment unit has not been 
satisfactory, or a multiplicity of stretching installation units had to be 
used and maintained. 
Accordingly, it is a main object of the invention to provide for an 
integral method where a multitude of yarns, say 8 to 16 or more, can be 
obtained on a single stretching unit at speeds of above 1000 m/min 
yielding final product yarns that could either be in the form of fully 
oriented continuous yarns (FOY) and/or in the form of bulked continuous 
yarns (BCY) with yarn and filament deniers both for apparel use or any 
other yarn application where the unique properties of polypropylene 
provide an improved product. 
A further object of the invention is an apparatus specially adapted for 
carrying out the novel method. 
SUMMARY OF THE INVENTION 
These and further objects apparent from the following description will be 
achieved according to the present invention by a method of producing 
polypropylene yarns composed of a plurality of continuous and 
substantially oriented individual filaments by melt spinning and 
stretching them in an integral process, characterized by 
(A) simultaneously extruding a sufficient number of said individual 
filaments for forming at least 8, preferably at least 10 and typically 
from 12 to 16 continuous multifilament yarns, each consisting of at least 
10 individual filaments, e.g. of about 30, 60 or more, at an extrusion 
speed of at least 400 meters per minute, preferably at least 600 m/min, 
into an essentially vertical air quenching zone for solidification of said 
filaments; 
(B) arranging the filaments to form a substantially planar array of 
parallel and mutually distanced (e.g. 5 to 50 mm distances) yarn strands 
in a number corresponding to step (A); 
(C) together stretching the strands to achieve the required substantial 
orientation, e.g. at typical draw ratios of 1.div.1 to 1.div.3, by passing 
said yarn strands, while maintaining them in said planar array, over 
peripheral surface portions of a sequence of rotating cylinders having 
parallel axes of rotation; each strand passing over said surface portions 
along a discrete path which is substantially defined by a plane 
intersecting perpendicularly with said parallel axes of said cylinders; 
each strand being in frictional contact with said peripheral surface 
portions for a contact path length of from 1000 to 6500 mm, preferably 
from 1000 to 4000 mm and most preferably from 1500 to 3000 mm; at least 
50% and preferably 75 to 100% of said contact path length being provided 
on a total number of from 2 to 6, preferably from 3 to 5 and most 
preferably 4 cylinders; 
(D) optionally providing a texturizing and/or entangling step after said 
drawing step (C); 
(E) preferably providing a first and a second group of rupture control 
means for each of said yarn strands at mutually distanced positions of 
said discrete path; 
(F) and finally winding said yarn strand obtained as product, e.g. FOY or 
BCY, e.g. with a typical yarn denier range of from 40 to about 800 and 1.5 
to 15 den per filament, at a speed of at least 1000 m per minute, e.g. 
2000 m/min or more. 
The apparatus for use in this method comprises a number of conventional 
elements i.e. 
(a) a spinneret means, e.g. a conventional spinning plate or 
multi-spinneret frame connected with an extruder and pumps; the spinning 
plate or the spinnerets have a plurality of openings for melt spinning of 
a molten polypropylene composition; 
(b) vertical shaft or chute means for cooling or quenching and solidifying 
the molten polypropylene after emergence from the spinneret means to form 
a plurality of filaments; 
(c) means to combine the monofilaments to form at least one multifilament 
yarn strand; 
(d) stretching means to substantially orient said filaments of said at 
least one yarn strand; 
(e) winding means; 
the apparatus being characterized in that the spinneret means (a) has a 
sufficient number of openings to form at least 8 yarns, e.g. 10, 12, 14, 
16 or more yarns, each comprising at least 10 filaments and typically 
comprising about 30, 60 or more continuous filaments; the vertical shaft 
means have a length sufficient to provide for a free path length of the 
filaments after emergence from the spinneret means and prior to first 
contact with a mechanical filament-contacting means of at least 2.5 
meters, e.g. 3-5 meters or more, while a free path length of above 7.5 m 
is feasible but not generally preferred; the stretching means are formed 
by a sequence of rotating cylinders having parallel axes of rotation (i.e. 
with parallel cylinder surfaces for engagement with the strands) arranged 
to provide for a path length of frictional contact with the yarn strands 
of from 1000 to 6500 mm, preferably of from 1000 to 4000 m and most 
preferably from 1500 to 3000 mm, and wherein at least 50% and preferably 
75 to 100% of the length of frictional contact are provided on a total 
number of from 2 to 6, preferably from 3 to 5 and most preferably 4 
cylinders. 
Thus, the invention combines the element of rapid spinning of a sufficient 
number of filaments for a large number of yarns with the element of 
stretching the resulting yarn-forming groups of filaments together, i.e. 
in common, on a small number of large cylinders along parallel and 
discrete or individual pathways in which the length of frictional contact 
is within specified limits and provided, at least predominantly, by the 
large cylinders. 
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
When operating the inventive method, the cylinders will generally be 
maintained at a predetermined and generally elevated temperature as is 
conventional per se; also, in a manner known per se, the cylinders provide 
for incrementation of speed as needed for a particular draw ratio. 
It has been observed that the occurrence of yarn breaks tends to be very 
low when using the inventive method and apparatus; While not wishing to be 
bound by any specific theory, it is believed that prolonged interfacial 
contact between cylinders and filaments tends to improve uniformity of 
frictional interaction and/or heat transfer. For practical purposes, it is 
preferred that most or all cylinders used for stretching according to the 
invention will have equal diameters; cylinder diameters should be at least 
300 mm and preferably at least 400 mm; diameters of more than 1000 mm 
would be operable but are not generally preferred for practical purposes. 
Length (= width) requirements of the cylinders depend upon the number of 
yarn strands that are commonly stretched on a given cylinder, and the 
minimum distance required or desired between parallel strands. Typical 
strand distances are in the general range of from 5 to 50 mm, e.g. 8-15 
mm, and a typical cylinder length for simultaneous stretching of 16 
strands will be in the range of from 200 to 500 mm. 
An additional advantage of the large-cylinder-stretching approach with a 
plurality of yarn strands is that if yarn rupture does occur its control, 
removal and repair can be achieved in a relatively simple manner as long 
as reasonable distances are provided between adjacent cylinders. 
Surface materials and surface conditions do not seem to be overly critical; 
stainless steel surfaces, chromium platings and the like structural metals 
are suitable. 
A total number of 4 cylinders for stretching according to the invention is 
preferred for reasons of simplicity of construction and operation. For 
example, when providing a preferred contact path length of from 1500 to 
3000 m on a total of 4 stretching cylinders having equal diameters in the 
range of from 400 to 500 mm, the first cylinder "upstream" (i.e. closest 
to the spinneret) and the subsequent or second cylinder will be rotated by 
a conventional drive at a relatively "low" peripheral speed which depends, 
of course, upon the extrusion speed but may typically be within the range 
of from 600 to 1000 m/min; while the first two cylinders have a common 
speed, this does not necessarily imply identical speeds; for example, it 
may be advantageous to operate the second cylinder of the low-speed first 
group at a peripheral speed that is somewhat higher than that of the first 
cylinder, e.g. by 5 to 15%. 
The second cylinder group in the preferred arrangement just mentioned 
operates at a common "high" peripheral speed, e.g. 1200 to 2200 m/min 
depending upon the peripheral speed of the first cylinder group and the 
desired draw ratio that, typically, may be in the range of from 1.div.1 to 
1.div.3. Again, a "common" speed of the second cylinder group does not 
mean identical speeds, and the second cylinder of the second group (i.e. 
the last cylinder of the preferred stretching embodiment just mentioned) 
may have a somewhat higher peripheral speed than the immediately preceding 
first cylinder of the second group. 
Depending upon the desired product, a texturizing and/or entangling stage 
may be provided and conventional methods or devices for use in processing 
of polypropylene filament yarns can be used; in this embodiment additional 
cylinders will generally be required before and after the texturizing 
and/or entangling step, notably for bringing the textured and/or entangled 
yarn from a holding position, such as in the groove of a perforated 
suction drum, to the speed of the winders. 
Generally, the winding speed will be at least 1200 m/min but higher winding 
speeds, say 2000 m/min or more, will be used for many purposes of the 
invention. 
Since both the texturizing and/or entangling step as well as winding of the 
product yarns are conventional per se and can be carried out with 
commercially available elements, this aspect need not be discussed in more 
detail. 
While yarn rupture control methods and apparatus means are known as well, 
the invention provides a new aspect thereof as regards stretching of a 
large number of yarns on a single stretching device at speeds of 
substantially above 500 m/min. Specifically, since yarn ruptures can never 
be totally exluded, simple and effective rupture control and repair is an 
important additional aspect of the invention. 
First, as mentioned above, the inventive concept of 
largecylinder-stretching of a yarn array, i.e. 8 or more yarns, along 
discrete pathways that are parallel with each other and perpendicular 
relative to the rotation axes of all stretching cylinders is based upon 
large cylinder surfaces provided essentially on but a few large cylinders. 
With sufficient distances between adjacent cylinders, e.g. typical 
distances of at least half the mean cylinder diameter of any two adjacent 
cylinders of the stretching means, the stretching device is easily 
accessible to the operator in charge of yarn rupture control so that 
repair and re-feeding of a broken strand presents no problems. 
Further, according to a preferred embodiment, first and second rupture 
control means are provided near the start (e.g. between the first large 
diameter cylinder, i.e. that next to the spinneret, and the second large 
diameter cylinder), as well as near the end (e.g. after the last large 
diameter cylinder of the stretching means) of said path length of 
frictional contact for each of said yarn strands. Additional smaller 
cylinders may be provided for the stretching stage, e.g. between the large 
diameter cylinders, but this is not preferred; in general, the large 
diameter cylinders alone are sufficient for yarn path deflection within 
the stretching stage. 
Few and large diameter cylinders for together stretching the filaments 
combined with rupture control near the start and near the end of the 
stretching means provide for a particularly effective rupture control and 
repair even when simultaneously stretching 10, 12 or 16 parallel yarns on 
a single stretching unit at speeds of 1000 m/min or more in a single 
stretching stage according to the invention and effected on a sequence of 
but a few large cylinders. 
According to the invention, the second rupture control, typically a yarn 
detector, would sense a discontinuity or absence of yarn passage and 
activate a small cutter provided for this and any strand in the first 
rupture control means. A suction opening associated with each yarn cutter 
would now receive the freshly cut leading edge of the broken strand. A 
signal means coordinated with the second and/or the first rupture control 
means will be triggered upon rupture of any given strand, of course, to 
inform the operator of a strand rupture and of the position of the strand. 
Then, the operator will activate a mobile aspirator, direct it to the 
suction opening into which the broken strand passes after operation of the 
cutter, and manually cut the strand so that the new leading edge of the 
broken strand will be sucked into the mobile aspirator. Then, without 
stopping production of the unbroken strands, the operator can easily 
re-insert the line of the previously broken strand into the corresponding 
pathway which is recognizable because of the incompleteness of the array 
and is accessible on the large cylinder surfaces. 
After re-insertion of the broken strand into and through the optional 
texturizing and/or entangling stage is completed, the re-fed yarn is 
passed from the mobile aspirator to the winder and/or a yarn-mending 
device cooperating therewith. 
Yarn rupture control of this type including various forms of yarn 
aspirators, yarn detectors etc. are commercially available and need no 
further explanation except as regards the number of strands. Since at 
least 8 and typically 16 strands per stretching device may require 
individual control in the inventive method, combinations of a sufficient 
number of modular units, e.g. one cutter/aspirator and yarn detector 
module for each yarn, are required. Further, in order to facilitate yarn 
feeding upon start-up or upon yarn rupture repair, a preferred embodiment 
of the first and/or second rupture control means provides for automatic 
strand feeding and includes a number of yarn guide slots substantially 
corresponding with the array of strands and arranged in an elongated bar 
extending over the width of the yarn array. An elongated and displacable 
slide bar is provided for guiding some or all strands of the array along a 
path portion that does not pass through the slots but beyond them. The 
slide bar will be in this position only for start-up or yarn repair and is 
withdrawn when the complete array passes on top of the slide bar so that 
all strands will again be put into the slots of the slide bar.

Polypropylene suitable for use inthe present method is obtainable 
commercially for melt spinning of continuous multifilament yarns, e.g. the 
products sold by Himont, Italy, under the registered trademark MOPLEN; 
commercial spinning grade pellet products containing or not the usual 
additives are preferred or, in other words, neither particularly critical 
substance parameters nor special formulations are generally required for 
practicing the inventive method; typical examples are polypropylene 
homopolymers having a melt index (cf. ASTM D 1238/L) of at least about 10 
dg/min, e.g. from 10 to 12 dg/min or more, e.g. up to 18 dg/min at 
230.degree. C. and 21.6N; a flexural modulus of elasticity (ASTM D 790) of 
at least about 1500 N/mm.sup.2, e.g. about 1700 N/mm.sup.2 ; a tensile 
strength at yield (ASTM D 638) of 35 to 40, e.g. 38 N/mm.sup.2 ; an 
elongation at yield (ASTM D 638) of about 10%, e.g. 11%; and a Vicat 
softening point (ASTM D 1525) of 150.degree.- 160.degree. C., e.g. 
155.degree. C. Molecular weight distribution values (i.e. the ratio of the 
weight average molecular weight to the number average weight) of from 
about 5 to 6 have been found to be suitable for the subject method. 
Colored master batch materials can be used and/or pigments and other 
additives can be added prior to use herein. 
Generally, polypropylenes for use in the present invention should be 
capable of being melt spun with commercially available extruders and 
spinning pumps at extrusion speeds of at least 400 m/min through the holes 
of a spinning plate or spinneret having diameters required for spinning 
multifilaments in the typical denier range of from 1 to 15 den per 
filament, typical yarn deniers being in the range of from 40 to 800 den. 
Hence, suitable polypropylenes must be capable of "substantial 
orientation" in the sense that filaments obtained by extrusion and 
drawing-down are able to achieve molecular orientation by stretching to 
near the limit of plastic flow. Generally, filaments that have been 
substantially oriented will show a substantially reduced or "low" 
elongation if compared with the "drawn-down" filaments obtained after 
solidification of the melt spun filaments prior to the application of 
substantial stretching. Typically, substantially oriented filaments will 
have an individual elongation at room temperature of less than about 250%; 
frequently, the final yarn obtained according to the inventive method will 
have even less elongation, depending, however, whether FOY or BCY products 
are made, i.e. whether or not a texturizing and/or entangling step is 
applied to the yarns after stretching. 
Thus, the term "substantial orientation" includes "substantially full 
orientation" as well as an approximation thereto that is sufficient for 
normal end uses of the yarns. 
A first essential feature of the inventive method relates to the number of 
yarns being produced simultaneously with a single stretching means, or the 
number of "yarn strands" that are being processed according to the 
invention; in this context, a "filament" is a "fiber" of infinite length, 
and "individual filament" refers to one of a plurality of filaments 
forming a yarn or "yarn strand" which latter term refers to a group of 
individual filaments which are stretched as a single group or unit; such 
strands may be identified when practicing the invention by a consecutive 
number of from 1 to 8, 10, 12, 14 or 16 depending upon the actual number 
of strands or yarns actually run in the inventive method per each 
stretching unit. 
As is conventional, each yarn or strand of a multifilament yarn will 
include a multiplicity of typically about 30, 60 or even about 120 
individual filaments per yarn and it is assumed herein that when referring 
to a multifilament yarn, at least 10 filaments are assumed to be present 
in the yarn. This is a matter of practice rather than theory since normal 
yarns will contain substantially more than 10 filaments. 
Hence, the first essential portion of an apparatus for carrying out the 
inventive method such as depicted in FIG. 1 will comprise a spinneret 
means 11 that may be a fixed spinning plate or, preferably (cf. FIG. 1A), 
is formed by one or more frame plates 113, 114 each comprising a number of 
exchangeable, e.g. circular spinneret inserts 111, 112 in line with the 
filament denier and/or the number of filaments per yarn and/or the 
cross-section of the filaments desired for the final yarn. 
While it is important for the inventive method that a sufficient number of 
filaments are melt spun to permit formation of at least 8 yarns or yarn 
strands per stretching means or unit, it is not believed to be of 
importance whether these strands pass through a common shaft means 12 or 
whether the shaft means is composed of more than one chamber (two chambers 
121, 122 being illustrated in FIGS. 1 and 1A); also, it is not believed to 
be essential whether or not the extrusion openings or holes of the 
spinning means are already grouped in accordance with the yarn strands to 
be formed or whether they have no group orientation during solidification. 
Strand collecting means 131, 132 formed by a line of hooks or ears will 
normally be used for collecting the required number of filaments into each 
strand. 
The "extrusion speed" is another essential feature of the invention insofar 
as it determines the minimum production speed which, according to the 
invention, is at least 1000 meters per minute. The term "extrusion speed" 
is used synonymously with "melt spinning speed" and does not necessarily 
refer to the speed of the molten mass upon emergence from the spinneret 
but rather to the speed of formation of solidified but essentially 
non-oriented filaments. Generally, the inventive method operates with an 
extrusion speed of at least about 400 m/min. 
The shaft means 12 or the shaft portions 121, 122 together form the 
essentially vertical "air quenching zone" in the sense that the heat 
exchange medium is gaseous rather than liquid, and that the temperature of 
the gaseous quenching medium is substantially lower than the temperature 
of the molten mass that emerges from the spinning holes of the spinneret; 
hence, the term "air" is intended to include any practical gas or gaseous 
mixture that can be maintained without undue problems at a quenching 
temperature of typically in the range of from about 0.degree. to about 
50.degree. C. with a preferred temperature in the range of from about 10 
.degree. to about 30.degree. C. Forced, i.e. accelerated yet essentially 
laminar, passage of air through shaft 12 or its portions is generally 
preferred, as is temperature control. Whether or not artificial cooling is 
needed may depend upon the ambient climate. 
In order to feed a suitable supply of molten polypropylene to the spinneret 
means 11 according to the invention, conventional extruder means 10 can be 
used. For example, an extruder 100 of 1.times.75 mm screw diameter can be 
used for production of yarns of 40 to 250 den while a screw diameter of 
1.times.90 mm would be suitable for yarns in the 150 to 800 den range when 
a total of 16 to 32 yarns is produced from the output of extruder 100. As 
is conventional, a spinning pump 101 and a heating means 102 are generally 
used to ascertain a sufficient and suitably heat controlled supply of 
molten polypropylene to the spinneret means 11. 
FIG. 1A is a semi-diagrammatic plane view of the spinneret end as viewed 
from a shaft 12 which in its upper part is formed by a pair of parallel 
cooling chambers 121, 122 encompassed by air-permeable inner and outer 
wall pairs 123, 125 and 124, 126, respectively, and supplied with a 
substantially laminar stream of cold or cooled air via conduit 129. Side 
walls 127, 128 need not be permeable to air but it is preferred that the 
front walls 125, 126 can be removed easily for access to the spinneret 
ends 111, 112. The intensity of cooling or quenching of the at least 8 
strands to be formed at the spinneret or, in any case, when forming the 
strand array on the first cylinder 141 as explained in more detail below 
will depend upon the passage of molten polypropylene mass per time unit 
into and through the air quenching zone formed by or in shaft means 12. 
However, it is generally preferred according to the invention that the 
vertical length or "height" H of the shaft means as measured from the 
lower end of the spinnerets 111, 112 to the first point of contact with a 
mechanical yarn contacting means should be at least 2.5 meters, e.g. about 
3 to 6 meters, but essentially for practical reasons not substantially 
above about 7.5 meters. 
A next essential step of the inventive method is formation of a "planar 
array" A of the yarn strands S; to this effect, filaments F are collected 
or assembled to form strands which, normally, are formed by filaments in 
equal numbers, e.g. each strand containing 64 filaments; such groups may 
be preformed by the spinneret openings 111, 112 but "hooks" or "ears" 
arranged in the form of transverse guide bars 131, 132 for the strands 
from each shaft portion 121, 122 are preferred. The collected strands in 
which the filaments are densely packed close to each other are now 
directed onto the surface of the first cylinder 141 of stretching means 14 
according to the invention to form the "strand array". Such an array is 
characterized by common parallel alignment of all strands that are to be 
stretched in a stretching unit according to the invention; each strand 
runs along an individual path since the strands are distanced from each 
other, e.g. by distances of from 0.5 to 50 mm or more depending upon the 
number of strands and the axial length of the cylinders; a generally 
equidistanced array may be preferable but equidistance is not a critical 
requirement as long as all paths are parallel and substantially maintained 
in this array during the stretching operation, i.e. until substantial 
orientation of the filaments has been achieved. This requires that the 
stretching cylinders have substantially parallel axes of rotatation such 
that each strand will pass through the stretching stage in a plane that 
intersects perpendicularly with the rotation axis of any cylinder. This is 
illustrated diagrammatically in FIG. 1B in which the frictional path 
length FPL of strand S on cylinder C is defined essentially by a plane P 
which intersects perpendicularly with the rotation axis A of cylinder C, 
and the length of contact between strand S and cylinder C. 
As briefly mentioned above, it is believed to be essential for the 
inventive method that the length of frictional contact of each strand with 
the parallel stretching cylinders, e.g. the sum of a, b, c and d in FIG. 1 
is within the range of from 1000-6500 mm, preferably 1500 to 4000 mm and 
notably between 2000 and 3000 mm, but that this frictional contact length 
also should be provided at least predominantly (i.e. more than 50%) and 
preferably essentially (i.e. from 75 to 100%) on a small total number of 
cylinders which number is between 2 and 6; a total of 3 to 5 cylinders may 
be used but an even number of cylinders is preferred. While 2 cylinders 
could be sufficient, the cylinder diameters required might not be 
practical; a total number of 4 cylinders is suitable and preferred as 
shown in FIG. 1 where the cylinders 141, 142, 154, 144 contribute 
substantially equal portions a, b, c and d of the total frictional contact 
length. 
Generally, the first cylinder 141 will rotate at a lower peripheral speed 
than the last cylinder 144 and the difference of peripheral speeds will be 
commensurate with the required or desired draw ratio; each of the 
cylinders is connected with a drive (not shown) and provided with heat 
control or heating means such that a predetermined and substantially 
constant surface temperature in the range of from 80.degree. to 
130.degree. C. can be maintained on each cylinder. 
Peripheral speeds of the first cylinder 141 or the first cylinder pair 141, 
142 of from 600 to 1000 m/min are typical while peripheral speeds of from 
1200 to 2000 m/min or more would be typical for cylinders 143, 144. Small 
differences of peripheral speeds, say about 10% between cylinders 141 and 
142, on the one hand, and between 143 and 144, on the other hand, may be 
advantageous. In general, "frictional contact" is assumed to exist if the 
amount of "slippage" (i.e. yarn speed is smaller than the speed of the 
contacting cylinder) should be lower than 20%, preferably not 
substantially more than 10%. While special coatings or surfaces of the 
stretching cylinders, e.g. ceramic or glass surfaces are not excluded if 
frictional contact can be maintained, conventional cylinder surfaces of 
stainless steel, chromium (e.g. as electroplating) are satisfactory for 
many purposes of the invention. 
Preferably, a first yarn rupture control means 151 is provided between the 
first and the second cylinder, i.e. near the start of the stretching 
stage, while a second rupture control means 152 is provided near the end 
of the stretching stage, e.g. down-stream of cylinder 144. A sliding rod 
or bar 153 may be used on either or both yarn rupture control(s) as shown 
diagrammatically in FIG. 1C. Slot bar 153 is shown for simplicity with but 
three slots 156, 157, 158 for passage of three strands S-1, S-2 and S-3. 
When in normal operation, each strand passes through its proper slot 
provided, for example, with conventional yarn detecting means (not shown). 
For startup of the apparatus or for re-feeding a broken strand, slide bar 
153 is moved from below into the position shown in full lines in 153b. 
After placement of all strands in accordance with the array used in a 
given apparatus and with a given strand number so that the strands pass 
above the slots as indicated by S-1b, S-2b and S-3b, the slide bar is now 
withdrawn or moved into position 153a (broken lines) and all strands will 
then be guided into and through their corresponding slots automatically 
along the normal pathways S-1a, S-2a, S-3a. 
When the apparatus shown in FIG. 1 is to produce bulked and/or texturized 
yarns the strands are passed through a texturizing and/or entangling 
device 16, e.g. a number of hot air texturizing jets 164, onto a collector 
drum 163 from which they are drawn off via auxiliary rollers 17. Further 
auxiliary rollers 160 and 161 may be used to guide the strands into device 
164. 
FIG. 2 illustrates a prior art integral production apparatus for melt 
spinning and drawing polypropylene multifilament yarns. As are apparent, a 
large number of shafts 22a to 22d is needed since prior art stretching 
devices 24 of the spiral path type consisting of two rollers with small 
diameters and an angular arrangement of the axes of rotation of the two 
rollers relative to each other were believed to be the best for high speed 
integral operation. Generally, at least two such or similar stretching 
devices with small diameter cylinders of typically 200 mm or less were 
needed for each shaft, and parallel pathways of a multiplicity of yarn 
strands were impossible to achieve on such prior art machines. An enlarged 
view of a spiral-path stretching device is shown in FIG. 2A. 
As is clearly seen from the comparison with FIG. 3 showing a large diameter 
cylinder C with an array A of 11 strands S in parallel alignment as taught 
according to the invention, the use of few but large diameter cylinders, 
in addition to the other advantages discussed above, provides for 
simultaneous passage of a multiplicity of yarns through a stretching unit 
while prior art requires one group of stretching devices per each shaft or 
module while generating but one or only very few strands per shaft and 
stretching unit. 
FIGS. 4 and 4A show a semi-diagrammatic presentation of an apparatus 
according to the invention in side view and top view. The side view shows 
essentially the same elements as FIG. 1, namely a pair of shaft portions 
421, 422 supplied from an extruder 40 via spinneret 41 to produce 
filaments F that are collected to form strands S and are stretched in the 
form of a planar array A by means of a stretching unit 44 composed of 4 
substantially equal stretching cylinders of at least about 400 mm diameter 
as explained above; the oriented yarn strands are then passed through a 
texturizing and entangling device 46 and via auxiliary rollers 47 fed into 
a winding apparatus 49. 
However, as seen from the top view of FIG. 4A, the apparatus shown in FIG. 
4 actually is "twinned" in that a single extruder 40 supplies a pair of 
spinnerets 41, 41a, a pair of double shafts 421, 422, 421a, 422a, a pair 
of stretching units 44, 44a, a pair of auxiliary rollers 47, 47a and also 
a pair 49, 49a so as to produce typically 30 continuous filament yarns or 
more at speeds of typically at least about 2000 m/min as a continuous 
product stream in an integral operation from the common extruder 40. 
Yarn rupture control means as explained above in connection with FIG. 1 
have been omitted in FIG. 4 but for simplicity of presentation and will, 
of course, be used in practice to provide optimum yarn rupture control at 
high speed multistrand production of polypropylene yarns according to the 
invention. 
In sum, the invention provides for extremely effective and compact means 
for economic production of high quality polypropylene continuous filament 
yarn products including those suitable for garment use. 
Suitable modifications can be made to the method and apparatus described 
herein. While preferred embodiments have been explained in some detail, 
the invention is not limited to these embodiments but may be practiced 
within the scope of the following claims.