Note: Descriptions are shown in the official language in which they were submitted.
10467Z2
Tbe present invention is concerned with the manufacture of
synthetic fibres, including staple fibres and yarns, with textile arti-
cles including textile goods, rope and other cordage made therefrom, and
with machinery for the manufacture of such synthetic fibres. By the term
"synthetic fibres" is meant fibres formed from molecularly-orientable
organic polymers, particularly, though in no way exclusively, polyolefins
and olefin copolymers, for example, polypropylene and high density poly-
ethylene.
It is known that molecularly-orientable organic polymers in
the form of films which have been uniaxially oriented by stretching can
undergo fibrillating fracture (herein referred to as fibrillation) along
cleavage lines running in the direction of orientation but spaced apart
in a generally random fashion in the direction at right angles thereto.
Fibrillation can be induced for instance by subjecting the uniaxially
oriented film to a twisting treatment, a mechanical treatment, for ex-
ample brushing, or air blast treatment; such treatment is referred to
herein as "fibrillation treatment". If necessary the film can be slit
or scored in the direction of orientation prior to said mechanical
treatment with a view to promoting fibrillation and of reducing the
degree of randomness in the spacing apart of said cleavage lines. How-
ever, although the general concept of fibrillation has been known for
many years, considerable effort has been devoted, and continues to be
devoted, by those in the art to the many problems which arise when
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;72Z
applying this concept to the manufacture of "fine fibres", i.e.
fibres of extremely small cross-section, for example 5 to 90
denier fibres from molecularly-orientable organic polymers. In
order to compete with fibres produced by the conventional "spin-
neret method", the manufacture of fibres by fibrillation must be
capable of yielding fibres of acceptable and consistent quality at
comparable or lower cost and by reliable and practical techniques.
It has now been found, in accordance with the present
invention, that fine fibres can be manufactured from molecularly-
orientable organic polymers, for example polyolefins and olefin
copolymers (the term l'polymer" including a polymer composition) by the
controlled fibrillation of a film thereof which has been profiled in
cross-section in the manner described hereinafter. ~he profiling is
such as to provide longitudinally extending portions of the film, which
are the precursors of the required fibres, spaced apart by longi-
tudinally extending portions of lesser thickness, which are the
precursors of predetermined cleavage paths along which fibrillation
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~ 046722
will occur. The term "controlled fibril~ation" is used to indicate a fibril-
lating fracture along such predetermined cleavage paths to gi~e sharply de-
fined fibres substantially free from "whiskery" appendant fibrils; the term
is used herein to provide a contrast with random fibrillation occurring in a
longitudinal direction but not along predetermined cleavage paths since in
the latter case such fibrils tend to be formed even when the film is scored
or cut prior to fibrillation. The present invention is of particular interest
for the manufacture of polypropylene fine fibres for which appreciable poten-
tial outlets have become apparent in recent years in the textile industry, for
example for carpet manufacture, but it is not limited thereto.
According to the present invention there is provided a process for
the manufacture of synthetic fibres, which comprises passing a web of a mole-
cularly-orientable organic polymer at a temperature below its crystalline
melting point or a non-molten sheet-like mass of such polymer at a temperature
above its crystalline melting point, under pressure contact through the nip
formet between two contra-rotating rollers having non-yielding surfaces, at
least one of said rollers having a plurality of closely spaced and parallel
surface ridges extending circumferencially around the roller each having in-
wardly directed sides leading to a peak and the sides of adjacent ridges
forming troughs, to yield a grooved, profiled web; chilling, where required,
the profiled web during, after or both during and after contact with the rol-
lers to a temperature below the crystalline melting point of the polymer;
stretching the profiled web to effect orientation thereof; and subjecting it
during and~or after the stretching to conditions resulting in a controlled
fibrillation thereof to form the synthetic fibres. The present invention alsc
includes the resulting synthetic fibres which can be continuous fibres or
staple fibres formed by chopping or cutting such continuous fibres into short
lengths, and yarns, textile goods ant ropes ant cordage made therefrom. Such
fibres can have a denier of, for example 5 up to 90 and have excellent handle
and appearance, and good tenacity, for example up to 7 grams per denier.
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104672Z
In the above-defined process the profiled web has longitudinally-
extending thick portions, which are the precursors of the required synthetic
fibres, spaced apart by longitudinally-ex~ending thin por~ions, which provide
the precursors of regular sleavage paths along which controlled fibrillation
will take place~ The stretching operation causes molecular orientation and a
reduction in the cross-section of the web, and the fibrillation treatment
effects a controlled fibrillation as a result of the profile of the stretched
web.
The use of two hard-surfaced rollers, for example of steel is an
important feature of the present invention because considerable pressures are
generally involved in forming the necessary grooves in a web of an organic
polymer such, for example, as a nylon or a polyolefin or olefin copoly~er,
for example polypropylene. In order to form the required groo~es it is neces-
sary to apply a pressure which is depending on the polymer and on the forming
temperature employed. The requiret pressures are such that the use of a roller
having a yieldable surface as the backing roller for a ridged roller has been
found to result in corrugation of the web instead of the required grooving.
Consequently such a web behaves on fibrillation in a manner similar to a flat
web and the fibrillation which occurs is not a controlled fibrillation. Al-
though the pressure re~uired for grooving can be reduced by raising the webtemperature, there is a limit to pressure reduction achievable in this way.
It will be understood that the emplo~ment of rollers having non-yielding sur-
faces, for example steel rollers make it essential to effect grooving rather
than cutting of the web since if cutting takes place there is the danger of
wear or severe damage to the rollers due to the ridges of one roller con-
tacting the surface of the other roller. The above-defined process is pre-
ferably carried out continuously and said web can be profiled, i.e. impresset
with said grooves, on either one or both of its surfaces, although the pro-
vision of grooves on only one surface is preferred. However, when both sur-
3~ faces are to be grooved each of saîd rollers or the like are so mounted as to
10467ZZ
provide for accurate relative positioning of the ridges of one opposite thoseof the other. Preferably, the web is profiled over its entire width so that
all the web is converted into fibres. However, a partial profiling followed
by slitting, either before or after stretching, to remove the unprofiled por-
tion(s) of the web is not excluded, although such an operation would tend to
complicate the process and would normally be wasteful of material.
Machinery suitable for use in the manufacture of synthetic fibres
by the process of this invention comprises a web profiling unit, means for
stretching a profiled polymer web from said profiling unit and means for sub-
jecting a stretched web to a fibrillation treatment, said web profiling unitcomprising two contra-rotatable rollers having non-yieldable surfaces and at
least one of the rollers having a plurality of closely-spaced and parallel
surface ridges each having inwardly directed sides leading to a peak and the
sides of adjacent ridges forming troughs, and means for effecting pressure
contact between a moving web or sheet-like mass of polymer and the profiling
roller(s). Preferably said machinery includes means for subjecting a stretched
web to a fibrillation treatment which comprises an elongated passage of re-
stricted cross-section provided with means for passing a stretched web there-
through together with a co-current flow of air at a high velocity. Preferred
machinery also includes a slot-die or annular-die extruder for producing the
mass of polymer in the form of a web.
Reference should also be made to a web profiling unit per se useful
in the process of this invention; such a unit can be used in combination with
conventional in-line stretching equipment and any known or suitable fibril-
lating equipment. In a preferred web-profiling unit the ridged roller or
both ridged rollers is or are adapted to be driven and also comprise means
for biassing the rollers towards one another.
A web profiling unit preferably comprises an unridged backing rol-
ler which is movable with respect to a drivable, ridged roller mounted for
rotation about a fixed axis, and in which the biassing means comprises hy-
1 ~
~046722
draulic or pneumatic mechanism acting on said backing roller or the like and
proviting adjustable nip pressure between said rollcrs or the like. In a con-
venient arrangement the ridged roller, which is rotated by suitable driving
means, for example an electric motor, is disposed alongside the ~ac~ing rol-
ler, prorision being made for accurately positioning one roller with respect
to the other to ensure that their axes are truly parallel during operation of
the process. Such positioning can be achieved by means of hydraulic mechanism
which also provides the requiret pressure on the hot web during profiling.
Preferably one or both of the rollers is or are adapted for the cir-
culation of a heat-transfer ~ediu~ therethrough. In a particularly preferred
unit the profile of the ridges of the ridged roller(s) is such that the pitch
of the ridges is within the range 0.003 to 0.05 inches and the depth of the
troughs between adjacent ridges is within the range 0.002 to 0.02 inches.
The ridges will normally extend without interruption round the periphery of
the roller or the like, but it is also possible for each ridge to be divided
lengthwise into two or more sections by short plain, i.e. unridged, portions
of the roller surface, the plain portions being in staggered relationship
across the Nidth thereof; the latter arrange~ent may have advantages when it
is desired to form, for example a yarn for twisting into twine for use as
such or in the manufacture of rope or other cordage since the individual
fibres in the resulting yarn
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10467ZZ
will not be completely separated from one another thereby increasing the
strength of the twine.
Whilst in defining the process of the present invention the term
"roller" in the great majority of cases means cylinder or drum, the term
also comprises an endless belt having the requisite non-yielding properties.
In the process of the present invention the profiled web is
stretched, for example, tenfold using any known or suitable stretching equip-
ment, with the result that the polymer comprised therein is oriented and the
cross-sectional area of the web is reduced correspondingly. Consequently,
the stretched web breaks down on fibrillation to yield a large plurality of
fine fibres each of which is formed by a "hump" in the stretched profiled
web. Stretching can be carried out using, for example a pair of Godet roll
sets with a hot air oven disposed between them through which the web under
tension passes. The second Godet roll set is rotated faster than the first
to an extent which provides the desired degree of draw, i.e. the stretch ra-
tio. Typical ratios which can be employed for polypropylene are between
~ 5 : 1, and 12 : 1 or more; and the hot air oven can be operated at a
; temperature of the order of 140 to 150 C.
As a result of the profile of the stretched web a controlled
fibrillation thereof will occur under suitable conditions. In fact, it is
of particular advantage that in many instances such conditions may be pro-
vided by the mechanical handling of the web during the stretching operation.
In many cases, e.g. with polypropylene webs, the profiled web undergoes a
spontaneous breakdown into filaments during passage through the second Godet
unit, in fact some splitting can occur in the hot air oven. If necessary,
however, the conditions under which controlled fibrillation of the web takes
place are provided by sub~ecting the web, after stretching, to fibrillation
treatment, which can be carried out in any known or suitable manner. For
example, twisting can be utilized, using a conventional heavy duty twisting
machine such, for example, as the "Trawlmack" sisal type twisting machine.
Preferably, however, such fibrillation treatment when required is effected
by means of an air blast treatment effected by passing the stretched web
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1046722
through an elongated passage of restricted cross-section through which a
current of air flows at high velocity in the direction o~ movement of the
web. For example, good results have been obtained by feeding the stretched
web through an aspirator, for example the device commonly known as a "waste
collector" operated at about 80 pounds per square inch (gauge) pressure. In
this way one can avoid the need for reeling-up between stretching and fibril-
lation treatment since the air blast fibrillator can operate effectively at
throughput speeds equal to those at which the stretched film leaves the sec-
ond Godet roll set; such speeds can be, for example 200 to 400 feet or more
per minute.
Although the description herein refers mainly to continuous fibres
and yarns formed therefrom it will be understood that the present invention
can also be used for the manufacture of staple fibres, for example by chopp-
ing into short lengths the continuous fibres formed in the fibrillation
stage; theæe fibres can then be processed by conventional textile handling
techniques.
If desired, the web or sheet-like mass of polymer fed to the pro-
; filing unit can comprise a plurality of webs which are united during the
profiling operation. Por example, two such webs can be formed by slit-die
extrusion from polymers of different characteristics, for example different
molecular weight or different chemical nature; and the resulting hot webs
can be fed through the nip between the ridged roller and the backing roller
to become united into a single bi-component web and simultaneously profiled
in accordance with the present invention. Alternatively said individual
webs can be brought together to form a hot, bi-component web prior to con-
tacting the ridged drum or roller, for example by employing a multiple ori-
fice die or by bringing separate melts of the two polymers together in the
die-head in a region located ~ust before the extrusion orifice.
Preferably the ridges should have the sort of profile that can
best be described as sharp peak, but it is to be understood that the word
"sharp" is intended to include the case in which the peak is rounded off to
a small radius or in which the tip of the peak includes a small flat portion.
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1046722
The profile of the ridges should be such that the web is grooved, i.e. im-
pressed or embossed, to give a cross-sectional profile comprising a large
plurality of spaced apart "humps" each of suitable "fibre-forming" profile
joined together by narrow "troughs" having a thickness which preferably are
less than 1/10, often less than 1/20, of that of the original web. The
humps constitute the precursors of the ultimate fibres and the troughs con-
stitute the precursors of the predetermined cleavage paths along which the
stretched web will split during the controlled fibrillation thereof. As
previously indicated, such splitting can occur during the stretching stage
and in many cases a spontaneous breakdown into filaments takes place so that
a subsequent separate fibrillation treatment will not be necessary. A sep-
arate fibrillation treatment can be effected in those instances in which
splitting does not occur completely, or even does not occur to a significant
extent, during the stretching stage. The ultimate fine fibres can have a
denier of 5 up to 90, and such fibres have excellent handle and appearance,
and a good tenacity, for example, 7 grams per denier.
A preferred profile of the ridges is such that the pitch of the
ridges is lying within the range 0.003 to 0.05 inches and the depth of the
troughs between ad~acent ridges lies within the range 0.002 to 0.02 inches.
Preferably the ridges extend without interruption round the periphery of the
roller, but it is also possible for each ridge to be divided lengthwise into
two or more sections by plain i.e. un-ridged portions of the roller surface
which are staggered with respect to one another across the width of the rol-
ler, the latter arrangement may have advantages when, for example, it is
desired to form a yarn for twisting into twine for use as such or in the
manufacture of rope or other cordage since the individual fibres in the re-
sulting yarn will not be completely separated from one another thereby in-
creasing the strength of the twine.
As indicated above, there are two main embodiments of the present
process, depending on the physical state of the organic polymer. In the
first embodiment a web at a temperature below the crystalline melting point
is passed through the rollers, whereas in the second embodiment a sheet-like
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~04672Z
mass of at least partially fluid polymer is processed.
When, in carrying out the first embodiment, it is considered nec-
essary or desirable for the web to be at an elevated temperature during the
profiling operation it is ~ecessary to preheat the web at least partially
bèfore effecting profiling since if only a heated roller or rollers is or
are used the finite time required for such localised heating to be effective
places a severe limitation on the maximum throughput of the process; the
maximum throughput under such conditions may be less than one-tenth of that
achievable with the process of the present invention when preheating of the
web takes place. It will be appreciated that if the web is produced, for
example by the blown-film technique as a first stage of the process, it can
be arranged for the web to be at the required temperature as it contacts the
rollers. The web may be preheated, for example to 80 to 140 C in the case
of polypropylene prior to being passed through the nip formed between the
two rollers, the preheating being such that the temperature of the web does
not exceed that at which it can be handled under the necessary tensions in-
volved in pulling the web off a feed reel and through the preheating equip-
ment or in pulling the web from a first stage in the process of the present
invention in which the web is made, for example by the blown-film technique,
this first stage may be operated "in-line" with the remainder of the pro-
cess. Depending on the nature of the polymer from which the web is formed
and on the throughput rate at which the process is operated it may be advan-
tageous for the rollers or one of them to be heated. Alternatively, it may
be advantageous to remove heat from said rollers or the like or one of them,
and preferably provision is made for the circulation of a heat-transfer
fluid therethrough. There is also a need to provide for the accurate posi-
tioning of the axes of the rollers or the like with respect to one another.
In the latter respect it will be understood that the nip should impart an
even pressure on the web over the entire effective length of the rollers or
the like so as to form a consistent impression on the web. To this end ad-
justing means should be provided to enable the position of` one roller to be
adjusted with respect to the other in a direction normal to the axes thereof
_ g _
~0467ZZ
so that the necessary even pressure can be exerted on the web~
In the first embodiment of the present process the veb eOg. the
strip, band or tape fed to the profiling rollers should be of film or "thin
sheet" thickness and for polypropylene the thickness of the web may be of the
order of 25 to 200 microns. The web can be formed by any known or suitable
method, for example, by cutting or slitting tubular film and usually the
widest web that can be handled will be preferred. It may be advantageous to
use film made in the manner described in our United Kingdom specification No.
1,093,018 or in the specification of our Canadian Patent ApplicationsNosO
03q225 and 064842. If desired, a laminated film can be used to form bi-
component fibres or the lamination can be carried out, for the same purpose,
simultaneously with profiling by feeding two or more different webs to the
roller nip; such webs can be formed from different polymers or of different
physical forms of the same polymer. The possibility of forming a "cored"
synthetic fibre in this way by feeding to the nip three webs comprising a web
of the polymer, which will form the core and, on each side thereof, a web of
a polymer which will form the sheath of the fibre, is not excludedO When
lamination is carried out simultaneously with profiling the individual webs
may have a combined thickness of the order of that referred to previously in
connection with the use of single webs, and the possibility of applying heat
to the rollers in order to facilitate the uniting of the individual webs as
the composite structure passes through the nip is not excludedO
It is important that the ridges of the ridged roller(s) or the
like have the profile defined above, the peak iOe. the top of each ridge
preferably being rounded off to a small radius and the bottoms of the troughs
between the ridges being preferably concaveO The bottoms of the troughs may
have an appreciably greater radius of curvature than that of the peaks. It
is not essential that the bottom curvature be a regular curve, for example
a part of a circle. A preferred profile for the ridges is that generated by
the standard Whitworth screw thread form, for example at 40 turns per inch,
but other screw profiles can be used providing they conform to the profile
conditions defined aboveO Thus, for example, a square thread is unsuitable
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10467ZZ
When only one o~ the rollers is provided with surface ridges, this
roller can be mounted above or alongside the plain roller and it should be
the driven roller. In order to smooth out the web and to provide for better
tension control, the web may pass round part, for example, about 2/3 of the
surface of the lower, idler roller before entering the nip but this is not
essential, particularly if preheating with the aid of a band heater is em-
ployed.
In the second embodiment of the present process the sheet-like mass
of polymer will usually be of web form, but the simultaneous formation of
the required web ~orm during the profiling operation is not excluded. The
temperature of the polymer immediately prior to being brought into pressure
contact with the profiling element can be between the crystalline melting
point of the polymer and 150 C above it, for example between about 150 C and
300 C for polypropylene. Whilst the pressure contact referred to should not
be high enough to cause incision of the web during profiling, the pressure
should be sufficient to ensure that the grooved portions of the profiled web
are significantly thinner than the "humps" between the grooves thereof. ~he
humps are formed by polymer flowing into and filling the troughs between ad-
~acent ridges of the profiling element and the contact pressure should be
adequate to ensure that this takes place. To illustrate the order of pres-
sure required to effect the desired contact with the profiling element it
can be stated that good results have been obtained with contact pressures in
excess of 500 pounds per square inch.
The web to be profiled can be formed, for example by conventional
slot-die extrusion as a first step in the process of the present invention,
the disposition of the extrusion orifice with respect to the ridged roller
being, for example such that the hot, extruded web flows downwardly into the
nip formed between the ridged roller and the backing roller, although it
could also flow downwardly onto either roller. In this way the extruded
web, which at the temperatures involved has insufficient strength to with-
stand even the low tensions involved in pulling a web over rolls or off a
reel, can be handled without difficulty. It will be appreciated that pre-
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1046722
heating a preformed web of polymer to above its crystalline melting pointprior to contacting the ridged roller would be a difficult operation in
practice; carrying out the present process in this way, although not neces-
sarily excluded, is preferably avoided. At the temperature oP the web when
it contacts the ridged roller the selected groove profile can be accurately
reproduced in the impressed web provided the necessary contact pressure is
applied to the web as indicated above, accurate profiling is important from
the point of view of achieving uniformity in the resulting fine fibres. As
soon as the required grooves have been formed in the web the resulting groove
profile can be "set" and the web rendered handlable by the chilling opera-
tion. Consequently, rapid chilling of the hot web to below, for example,
appreciably below its crystalline melting point is preferably completed as
; soon as possible after the requisite grooves have been formed therein. The
required chilling can be obtained, for example, by the circulation of a
heat-transfer liquid, for example water through the ridged roller and/or
through the backing roller. In fact, both rollers preferably have provision
for the circulation of heat-transfer fluid therethrough so that the surfaces
of the rollçrs can be maintained at any desired temperature during operation
of the process. This opens up the possibility of effecting a differential
surface cooling of the profiled web which in some cases may be used to im-
part self-crimpine properties on the ultimate fibres.
The web can be profiled, i.e. impressed with said grooves, on
either one or both of its surfaces. In the latter case two ridged rollers
can be used, each of which is provided with the necessary surface ridges of
identical pitch and usually also identical profile, for example the hot web
can be passed through the nip formed between two ridged rollers which are
accurately positioned with respect to one another so that the peaks of the
respective ridges impress the web in exactly opposed positions. However, to
avoid unnecessary complication it is preferable to form grooves in only one
surface of the web unless fibres of particular cross-section which can only
be obtained by grooving both surfaces are required. Usually fibres of cir-
cular cross-section are required and these are readily obtainable by groov-
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:10467ZZ
ing only one surface of the web.
The web can be of any convenient width and in general the width ofthe web will be subject only to any limitations imposed thereon by the ex-
trusion process by means of which it is produced. It is a particular
advantage of the present invention that webs of quite large widths, for ex-
ample, up to 1 metre can be converted into a large number of fibres, for
example, up to 12,000 depending upon the web width and the denier of the
fibre. In this way a large fibre output can be achieved fro~ a single man-
ufacturing line comprising only one web-pro~iling unit. The hot web fed to
the profiling element can have a thickness of between 25 and 200 microns,
although webs of other thickness are not excluded.
The present invention will be further described with reference to
the accompanying drawings in which:
Figure I shows schematically the general arrangement of equipment
suitable for use in carrying out the first embodiment of the present pro-
cess;
Figure II illustrates a suitable ridge profile of the ridged rol-
ler used in the equipment of Figure I; and
Figure III illustrates machinery suitable for use in carrying out
the web-profiling stage.
Figure IV shows schematically the general arrangement of equipment
suitable for use in carrying out the second embodiment of the present pro-
cess;
Figure V illustrates a suitable ridge profile of the ridged roller
employed in the web-profiling unit of Figure IV;
Figure VI is a side elev~tion of one form of web-profiling unit in
accordance with the present invention; and
Figure VII is a plan view of the machine of Figure VI.
Referring to Figure I the process of the present invention is car-
ried out in three successive stages, namely web-profiling (A), stretching
(B) and fibrillation (C). In the first stage (a), a feed spool l provides
a web 2 of molecularly-orientable organic polymer which is pulled between
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1046722
the nip formed between a roller 3 having closely-spaced, parallel surface
ridges and a smooth-surfaced backing roller 4. Both rollers 3 and 4 are of
steel so as to provide the necessary non-yielding surfaces ~or impressing
the desired grooves into the surface of the web 2 without cutting through
the web, the latter being avoided by careful positioning o~ the backing rol-
ler 4 with respect to the ridged roller 3. The resulting grooved web 2'
passes over an idler roller 5 to the first roll of a standard Godet unit 6
which in operation provides the necessary tension in the web (2,2') to pull
it through the nip between rollers 3 and 4. ~he web 2' is pulled from the
first Godet unit 6 through a standard heating oven 7 by a second Godet unit
8 which runs at a higher speed than unit 6 so as to stretch the web 2'.
Such stretching effects molecular orientation of the web 2' and also results
in an appreciable draw-down of its cross-section to an extent depending on
the draw-down ratio employed; the profile of the stretched web 2" leaving
the last roll of the second Godet unit 8 is of the same form as that of the
web 2' before stretching since the stretching results in a uniform reduction
in the dimensions of the web cross-section. Providing the web is not cut
through at the profiling stage a degree of longitudinal splitting of the web
during stretching is not detrimental, although the complete division of the
web into individual fibres, each of drawn-down cross-section corresponding
to that of the "humps" of the impressed web, occurs during passage of the
stretched web 2" through an aspirator 9 in which fibrillatlon takes place to
form a yarn 2"' of individual fibres which is reeled-up on the spool 10.
Although the above process can be operated satisfactorily with the web 2 at
ambient temperature, it is preferable to preheat the web to a temperature
below the crystalline melting point of the polymer and this can be achieved
by means of a preheater (shown diagrammatically in broken lines at 11) of
any suitable type capable of imparting heat to the web at the throughput
speeds at which the process operates.
Figure II of the accompanying drawings shows on an enlarged scale
a preferred ridge profile of the roller 3. As will be seen from Figure II,
the characterising features of the profile are firstly the absence of sharp
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1046722
angles or flats at the peaks which are radiused; and secondly a dimension
"X" of the peaks which, whilst providing for adequate strength of the peaks
of the ridges of roller 3, results in the minimum "land" between ad~acent
"humps" of the grooved web 2, which land constitutes the predetermined lon-
gitudinal path along which the grooved web will split during the subsequent
fibrillation treatment. The thickness of the web 2 in this land portion can
be of the order of 1/20 of that of the web before grooving, and the depth of
the grooves in the ridged roller 3 (i.e. dimension Z in Figure II) should be
such that the material of the web ~lows into and fills the troughs of the
roller 3 during the grooving operation. In general, the denier of the re-
sulting fibres will be determined by the size of the humps of the web 2 and
the degree of draw-down which takes place during stretching; both can be
varied within sufficiently wide limits to enable fibres of an adeguately
wide range of denier to be manufactured.
Figure III of the accompanying drawings shows the essential oper-
ative parts of the machine used in carrying out Examples I C and II to be
described hereinafter. The machine is basically a horizontal milling ma-
chine carrying the ridged roller 3 on its driven spindle 12. The backing
roller 4 is mounted for rotation as an idler roller in a fra~e-work 13 car-
ried by the table 14 of the milling machine, and by this means the positionof the roller 4 can be ad~usted accurately with respect to roller 3. The
web 2 of polymeric material which is profiled by passage through the nip be-
tween the rollers 3 and 4 is obtained from a storage reel 1, and the result-
ing profiled web 2' is passed to standard stretching equipment (not shown)
such as known in the art. The web 2 from storage reel 1 can be preheated,
if desired, by passing the web 2 round a band-heater (not shown in Figure
III) prior to the web 2 entering the nip between rollers 3 and 4, the band-
heater having a heat transfer surface which is adequate having regard to the
speed of the web 2. Although good results were obtained using this machine,
it will be apparent that equipment designed specifically ~or use in carrying
out the present invention would be used in practice and reference is made in
this respect to the kind of machine depicted by Figures VI and VII. Advan-
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10467ZZ
tageousl~ the rollers are mounted one above the other as in the machineshown in Figure III.
Referring to Figure IV, the operat,ion is carried out in two suc-
cessive stages, namely web-profiling (A) and stretching and fibrillation
(B). In the first stage (A), a slot-die extruder 1 provides a web 2 of mo-
lecularly-orientable organic polymer at a temperature above its crystalline
melting point which is fea between the nip formed between a roller 3 having
closely-spaced, parallel surface ridges and a smooth-surfaced backing roller
4. Both rollers 3 and 4 are of steel so as to provide non-yielding surfaces
for impressing the desired grooves into the surface of the web 2 without
; cutting through the web, the latter being avoided by careful positioning of
the backing roller 4 with respect to the ridged roller 3. The resulting
grooved web 2' passes over an idler roller 5 to the first roll of a standard
Godet unit 6 which in operation provides the necessary tension in the web
(2,2') to pull it through the nip between rollers 3 and 4. The web 2' is
pulled from the first Godet unit 6 through a standard heating oven 7 by a
second Godet unit 8 which runs at a higher speed than unit 6 so as to stretch
the web 2'. Such stretching effects molecular orientation of the web 2' and
also results in an appreciable draw-down of its cross-section to an extent
depending on the draw-down ratio employed; somewhat surprisingly, in many
instances controlled fibrillation of the web 2" occurs during the mechanical
handling which occurs during its passage through the second Godet unit o; in
fact such fibrillation can start within the oven 7 in which stretching is
taking place. In this way a spontaneous and complete division of the web
into individual fibres, each of drawn-down cross-section corresponding to
that of the "humps" of the impressed web, occurs. However, if a complete
division is not achieved in this way the stretched web 2" is passed through
an aspirator shown in broken lines at 9, in which fibrillation takes place
or is completed. In either case the resulting yarn 2"' of individual fi-
bres is reeled-up on the spool 10.
Figure V of the accompanying drawings shows on an enlarged scale
the kind of ridge profile of the roller 3 which can be employed in carrying
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~0~6722
out the present invention, but which profile is particularly suitable foroperation of the second embodiment of the present process. The charac~er-
ising fe~tures of the profile are essentially the same as those mentioned in
the discussion of Figure II, and consequently the statements given herein-
before regarding the profile shown by Figure II also apply to the one now
under consideration. It will be noted, however, that the latter comprises
narrower troughs and somewhat sharper peaks, although still slightly radi-
used. Peaks of similarly preferred profiles may end in a small flat sur-
face.
Referring to Figures VI and VII of the accompanying drawings, the
profiling unit consists of a machine comprising a mainframe 11 carried on
legs 12 upstanding from a base 13, and a subframe 14 pivotally mounted on
the mainframe ll at pivot points 15. The mainframe 11 carries a steel ridged
roller 3 which is driven by an electric motor 16 through a belt drive 17, the
roller 3 being mounted in roller bearings 18. The subframe 14 carries a
steel backing roller 4 mounted in roller bearings l9, and both rollers 3 and
4 have provision for the circulation of a heat transfer medium therethrough,
the heat transfer medium entering through inlets 20, 21 and leaving through
outlets 22, 23. Movement of the subframe 14 about its pivot points 15 is
20 effected by two compressed air operated ~acking cylinders 24 and 25 which
are pivotally anchored to the base 13 at 26, 27 respectively and which are
pivotally attached to the subframe 14 at 28 and 29. Located above the pivot
points 28, 29 and ~panning between the two side plates 14' and 14" of the
subframe 14 is a torsion bar 30 which is fixed at one end to the side plate
14'. The other end of the torsion bar pro~ects with slight clearance through
a hole in the other side plate 14" to allow for minor differences in the
rate of lift between the ~acking cylinders 24, 25. The sideplates 14' and
14" of the subframe 14 are kept apart and in alignment by the backing roller
4. An idler roller 5 is provided in the mainframe 11 to assist in taking
off the profiled web to the stretching stage.
In operation of the machine shown in Figures VI and VII, the jack-
ing cylinders 24, 25 are operated to bring the backing roller 4 into the
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~04672Z
operative position in which it is slightly spaced from the ridged roller 3
to an extent depending on the desired web thickness. A hot polymer web is
then extruded downwardly into the nip between the rollers 3 and 4, whilst
the roller 3 is rotated by the motor 16. The frictional effect of the hot
web passing through the nip causes the roller 4 to turn in an opposite di-
rection to the roller 3. Air pressure is then applied to the jacking cyl-
inders 24, 25, for example a pressure of 80-90 p.s.i. in the case of the ma-
chine used in the following specific example to bias the backing roller
towards the ridged roller 3 so that the hot web is brought into pressure
contact with the ridges thereof and thereby impressed with the required pro-
file.
The process of the present invention has the advantages of sim-
plicity and reliability in operation, and it provides for accurate profiling
and in consequence little or no variation in denier between the individual
fibres produced. In general, and assuming substantially constant web dimen-
sions which can readily be achieved, individual fibres produced in accordance
with the present invention exhibit little or no variation in denier over
their lengths and no significant variation in denier is found between the
various fibres formed from a common web. Moreover, as a result of the con-
trolled fibrillation which occurs during their formation, such fibres may bemanufactured in a form in which they are substantially free from appendant
fibrils.
The fibres and yarns manufactured in accordance with the present
invention find application in many textile uses, for example, in the domes-
tic textile field including upholstery, curtaining, carpets and safety belts,
and in the rope and cordage industry.
The present invention is illustrated by the following Examples:
EXAMPLE I
The following comparative experiments were carried out:
A. A polypropylene having a melt index of 3.2 g/10 min. was extruded
through a slit using a mass temperature of 250C and a film extrusion rate
of 17 m/min. The extruded and still unset melt (temperature 195 C) was
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10467Z2
passed through a ~teel roller and a hard rubber backing roller pressedagainst each other. The steel roller was profiled with grooves (parallel
to the machine direction) having a depth of 200 microns and a width of 400
microns.
It appeared to be impossible to profile the viscous film suffi-
ciently. By longitudinal stretching (using a stretching ratio of 1 : 9
and an o~en temperature of 160 C) and fibrillation the obtained product is
insufficiently divided into regular continuous filaments.
Moreover, upon prolonged operation it appeared that the rubber
roller could not be cooled sufficiently. The gradually rising temperature
caused sticking of the film to the rubber roller, first noticeable by the
tendency of the film to become corrugated.
B. An equally unsatisfactory result was obtained by repeating the exper-
iment as described in A, except that the film was cooled to ambient temper-
ature (approx. 25 C) and the solidified film was passed through the rollers.
C. The experiments described in A and B were repeated under identical
condition~ using the same equipment, except that the rubber roller was re-
placed by an unprofiled steel roller.
In both cases the film appeared to have the desired rigid profila-
tion of thick and thin sections and by stretching and fibrillation to yielda satisfactory and regularly split product consisting of continuous fila-
ments. Substantial fibrillation occurred already during the stretching
stage.
EXAMPLE II
Polypropylene fibres of about 20 denier were made from a 3.5 Melt
Index polypropylene sold under the trade designation: Shell "Carlona" KZ61
at the output rate of 400 feet per minute using machinery comprising a web
profiling unit of the kind illustrated in Figure III of the accompanying
drawings, a stretching unit as known in the art, and a fibrillation unit
comprising a standard waste collector supplied with air under a pressure of
80 pounds per square inch (gauge). The web profiling unit comprised two
solid steel rollers 4 inches long and 2.5 inches in diameter one of which
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104672Z
was provided with parallel surface ridges formed by turning grooves 0.004
inches deep and 0.015 inches apart in the surface of the roller.
In operation a web of polypropylene 3 inches wide and 75 microns
thick was passed under slight tension through a preheater maintained at
110 C and then round the lower (idler) roller into the nip in such a manner
that the preheated web contacted about two-thirds of the surface of the low-
er roller. The profiled web leaving the nip travelled back over the upper
(ridged) roller to be taken off on the opposite side of the profiling unit
to that to which it was fed in, the profiled web then passed to the first
Godet set of the stretching unit. The latter was operated with a stretch
ratio of 10 : 1 and at an oven temperature of 150 C. The stretched web
was then passed through the waste collector to induce fibrillation thereof
to form the required yarn which was then reeled-up.
In a modification of the process ~ust described using a web 0.090
millimetres thick and a stretch ratio of 9 : l, the stretched web was
reeled-up and then fed, in a separate operation, to a "Trawlmack" machine,
i.e. a sisal type, heavy duty twisting machine operated at about 100 feet
per minute in which it was twisted at l twist per inch into a yarn. During
twisting, a controlled fibrillation occurred which broke down the stretched
web into individual fibres and the resulting yarn had a denier of 4,ô54
(g/9000 m), a tenacity of 5.2 grams per denier and an elongation of 13.5%;
the individual fibres had a denier of 31.
EXAMPLE III
Polypropylene fibres of an average denier of 30 were made from
polypropylene of melt index 3.5 sold under the trade designation "Carlona"
P, Grade KZ61 using machinery comprising a profiling unit as sho~n in Figure
V, and stretching equipment as known in the art. The profiling unit com-
prised a driven solid steel roller lO inches long and 4 inches in diameter
which was provided with 240 parallel, surface ridges extending over a 6 inch
length of its surface. The ridges were made by precision grinding to a 40
TPI ~threads per inch) Standard Whitworth form, the ridges having a pitch of
0.0125 inch, a depth of 0.0077 inch and an inclusive angle (see Figure V of
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' ~467æ
55). The ridged roller was provided with a shoulder on each side of its
ridged area, the shoulders standing Just slightly higher than the ridges to
provide a safeguard against accidental damage to the ridges as a result of
contact with the backing roller.
A hot web of polypropylene 6.5 inches wide and 0.003 inch thick
was extruded from a two-inch Shaw extruder located above the profiling unit,
the hot, extruded web falling vertically down into the nip between the
ridged roller and the backing roller at a speed of 30 feet per minute. Cool-
ing water was circulated through the ridged roller to maintain it at 15 C
during operation, but the backing roller was allowed to run at a higher tem-
perature, namely 90 C. The contact pressure exerted on the web as it passed
between the roller was about 1000 psi (as calculated on the basis of 80 psi
air pressure in the ~acking cylinders each of which has a 3 inch diameter
piston).
The resulting profiled web leaving the rollers was passed to the
first Godet set of the stretching unit. The latter was operated with a
stretch ratio of 8 : 1 and at an oven (i.e. stretching) temperature of
145 C. The stretched web was taken off at a speed of 240 feet per minute
and a complete breakdown into individual filaments had occurred as a result
of a controlled fibrillation of the web by the time it left the second Godet
set. The required yarn was then reeled-up in the form of a 10,000 denier
tow. The average denier of the fibres was 30.
The following additional data can be given in regard to the oper-
ation just described:
Extruder
Screw L/D = 22 : 1, compression ratio 3~ : 1
210/230/240/250/260/270C.
Barrel Die
Screw Speed 13 rpm
Die width 10 inches
Die lip separation 0.015 inch
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~)467;:Z
Physical Properties of Product
Tensile properties measured on the 10,000 denier tow
Tenacity 5.1 g/denier
Elongation at break 21%
Tensile properties of individual fibres:
Tenacity approx. 6 g/denier
Elongation at break 19%
In a modification of the operation ~ust described the stretched
web is reeled-up and then fed, in a separate operation, to a sisal type,
heavy duty twisting machine operated at about lOO feet per minute in which
it is twisted into a yarn.
