Note: Descriptions are shown in the official language in which they were submitted.
W092/0798t PCT/US90/~312
_ 1 _
PROCESS AND APPARATUS FOR CRIMPING FIBERS
The present invention is directed to a process
and an apparatus for producing nonlinear permanently
heat set polymeric fibers without imparting stress or
tension to the fibers.
More particularly, the invention relates to an
apparatus and a process for providing a loop, coil or
sinusoidal configuration to polymeric precursor fibers
by heat treating the fibers without subjecting the
fibers to stress or tension either before or during
0 crimping. The process and apparatus of the invention is
relatively inexpensive and simple and does not require
the prior formation of a knitted fabric. The apparatus
especially useful to produce crimped fibers utilizing
a multiplicity of precursor fibers of from 40,000 to
320,000 ibers (40K to 320K) which are assembled in the
form-of large size tows.~ The crimped fibers formed by
the present invention when dyed possess good dye
uniforml~ty~
The term "crimpi' as used herein can be defined
as~the nonlinearity or waviness of a fiber expressed as
crimps per~unit~length. For most of the man-made fibers
employed in~carpet manufacture, the crimp or bend in the
~25 f~ber i- iAduoed bl ther-dl/-~chanica1 techniques, e.g,
WO92/07981 2 0 7 1 9 ~ ~ PCT/US90/~312
a gear crimping mechanism or a stuffer box technique.
The crimping of fibers is important in the manufacture
of carpets because it provides bulk to the fibers by
preventing two or more fibers from lying parallel to one
another. As a result, the tufts of a carpet have
greater covering power, appear softer, and provide
greater resistance to wear and abrasion, among other
beneits.
Crimping is also useful in the processing of
staple fibers and in the processing of high modulus
fibers which are difficult to work with because of
slipperiness.
The crimp which is placed in most fibers, using
a ~tuffer box, is rarely uniform. The stuffer box
technique produces fibers having a wavy, random zigzag
type crimp which is V-shaped having sharp bends or
kinks. The randomness of the crimp which is obtained
causes the fibers to have a non-uniform crimp. However,
when several fibers are viewed, it can be seen that the
crimp produced by this method is regular or consistently
irregular.
Crimping of fibers in a stuffer box is achieved
by passing the fibers into a uniformly heated chamber
which is at the temperature required to heat set the
fibers in their crimped or nonlinear configuration. As
the fibers are forced into the chamber by feed rolls,
they are pushed against fibers which are already in the
chamber r thereby causing the fibers to bend and buckle
(crimp).
A weighted tube fitted into the top of the
stuffer box governs the flow and quantity of fibers into
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WO92/07981 PCT/US90/06312
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the stuffer box. The frequency (crimps per unit length)
and the crimp amplitude of the fibers are controlled by
regulating the speed of the feed rolls to that of the
take up rolls as well as the weight of the tube. Crimp
setting by this techniques can be done for single fibers
or tows having multiple fiber ends using a spunize
technique. The crimps are generally characterized by
numerous sharp bends in the fiber.
In order to obtain a crimp in the fiber by
present methods and apparatus, the fiber must undergo
severe bending stresses. During bending two types of
stress modes are simultaneously developed in the fiber.
A tensile stress is developed along the outer curvature
of the bent fiber, while a compressive stress is acting ;
on the inner portion of the bend.
A recent study of the effects of crimping on
polyester fibers showed that severe bending as in a
V-type crimp, can result in extensive fiber damage.
Even when the fibers had a more rounded V-type bend, the
fibers exhibited compression ridges on the underside of
the crimp. Severely crimped fibers (with sharp V-type
bends) therefore exhibit reduced mechanical properties
due to weakness in the fiber created by tensile and,
compressive forces operating within the fiber. Such
fibers usually failed by breaking due to tensile and
compressive forces operating within the fiber.
It has also been found that fibers that are
crimped in a stuffer box tend to take up dye
preferentially on the underside of the bend and can be
the cause for optical streaking. Such streaking occurs
because the knee of the bend projects toward the surface
of the fiber and hence is more visible to the eye.
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WO92/07981 PCT/US90/06312
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Since the underside of the fiber bend will contain more
dye the affect is a darker streak in the fiber. At the
same time, because the dye tends to concentrate at these
points, the remaining portion of the fiber tends to be
deficient in dye and therefore has a lighter colored
appearance.
It has been shown that crimp permanency after
loading can differ between fiber producers and even
among various types ~e.g., bright and semidull) made by
0 the same producer. Since the application of some
tension on fibers inevitably occurs during normal fiber
processing, it is to be expected that some loss in crimp
definition will occur. This loss must be near identical
from spindle to spindle, twister, to twister, etc.,
otherwise the fibers will appear to be different since -
crimped fibers differ in appearance from uncrimped
fibers as a result of the reduced bulking factor. At
the same time some fiber elongation is obtained during
crimp removal which would tend to order the fiber
microstructure. This could influence dyeing since a
more ordered microstructure will take up dye
differentially than fibers which have not undergone any
elon~ation.
European Publication No. 0199567, published
October 29, l990, of McCullough et al., discloses a
method for preparing nonlinear carbonaceous fibers
having physical characteristics resulting from heat
3 treating stabilized polymeric precursor fibers in the
form of a knitted fabric. There is described a process
wherein the knitted fabric is substantially irreversible -
heat set under conditions free of stress and tension.
In order to obtain individual fibers or tows, which are
nonlinear, it is necessary to knit and then deknit the
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W092t07981 2 0 7 ~ 9 ~ ~ PCT/US90/06312
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fabric. However, the knitting and deknitting of a
fabric to obtain nonlinear fibers substantially
increases the cost in producing the fibers.
U.S. Patent No. 2,245,874 to Robinson,
discloses a method for forming curled fibers by passing
the fibers over cold rollers under conditions to bend
and stretch the fibers beyond their elastic limits.
Such a process cannot be used to produce the stress
free, nonlinear fibers with the physical properties
produced by the present invention.
U.S. Patent No. 2,623,266 to Hemmi discloses
the mechanical preparation of sinusoidal or spirally ~
crimped fibers. The fibers are heated and passed -
through a series of bars which impart a meander-like
crimp. However, the fibers are formed in a crimped and
stretched state, i.e. a stress induced state.
More particularly, the invention resides in an
apparatus for crimping and heat setting at least one
polymeric precursor fiber, comprising a crimping
mechanism for providing said fiber with a temporary
nonlinear configuration which is free of sharp bends and
without the application of tension or stress on the
fiber, and conveyor means for transporting the nonlinear
fiber without the application of tension or stress
through a heating zone to provide said nonlinear fiber
with a permanent heat set.
~; The invention also resides in a process for
crimping and heat setting at least one polymeric fiber,
comprising the steps of supplying a polymeric precursor
fiber to a crimping mechanism operated at a temperature
sufficient to impart a temporary nonlinear configuration
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WO92/07981 ~0 7 1 9 8 ~ - PCT/US90/06312
to said fiber without applying stress or tension to the - .
fiber, transporting said nonlinear fiber without the
application of stress or tension through a heating zone
for heating said fiber to a temperature sufficient to . -
impart a permanent heat set to said fiber, and cooling
said fiber.
The invention further resides in a process for
producing a nonlinear carbonaceous fiber, comprising the
steps of supplying an oxidized polymeric precursor fiber
having a diameter to a pair of crimping members at least
one of which is a cylindrical gear member having ; -
apertures with rounded gear surfaces, heating at least
one of said crimping members and introducing said fiber ~ .
into the apertures of the gear member to provide the
fiber with a nonlinear temporary heat set without
applying stress or tension to the fiber, conveying the
nonlinear fiber with the temporary heat set through a
heating zone without applying stress or tension to the
20 fiber, heating the fiber in an inert atmosphere in said .
unstressed condition to a temperature sufficient to ~ :
impart a permanent set and to form a nonlinear ~ :.
carbonaceous fiber which is free of sharp bends or
de~ormations, wherein said carbonaceous fiber has a
diameter of from 4 to 20 micrometer, a reversible
deflection ratio of greater than 1.2:1, and a carbon
content of greater than 65 percent. -
The term "polymer" or "polymeric precursor : :
3 material~' used herein applies to organic polymers as
defined in Hawlev's Condensed Chemical DictionarY, -
: Eleventh Edition,-~published by Van Nostrand Rheinhold
Company. The organic polymers generally include: :
l) natural polymers, such as cellulose, and the like;
2) synthetic polymers such as thermoplastic or
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WO92/07981 PCT~US90/06312
thermosetting elastomers; and 3) Semisynthetic
cellulosics.
The term "fiber" used herein is intended to
include an assembly of a multiplicity of fibers such as
can be found in a fiber tow.
The term "oxidized" used herein applies to
fibers that have been oxidized at a temperature of
typically less than 250C for acrylic fibers. It will
be understood that, in some instances, the fibers can
also be oxidized by chemical oxidants at a lower
temperature.
The term "permanent heat set" used herein
applies to nonlinear carbonaceous fibers which have been
heat treated until they possess a degree of - ,
irreversibility where the nonlinear fibers, when
stretched to a substantially linear shape, without
exceeding their internal tensile strength, will revert
to their original nonlinear configuration once the
stress on the fiber is released. Accordingly, what is
meant by "permanently set" is that a fiber possesses a
degree of resiliency which manifests itself in a
"reversible deflection" of the fiber when it is placed
under stress such that the fiber is substantially linear
in shape. When the stress is relieved, the fiber will
return to its unstressed and nonlinear condition. The
term "reversible deflection" defines the minimum limit
of stretching the fiber which is expressed as a ratio of
l.2:l where the fiber in the stretched condition is at
least l.2 times the length of the fiber in its relaxed
or unstretched condition.
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WO92/07981 PCT/US90/06312
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The carbonaceous fibers are prepared from a
suitable polymeric precursor fiber, which is stabilized,
as for example by oxidation at a temperature which is
typically less than 250C for acrylic fibers. The
stabilized fiber is then heat treated, in a relaxed and
unstressed condition and in an inert atmosphere for a
period of time sufficient to produce a heat induced
thermoset reaction wherein additional cross-linking
and/or a cross-chain cyclization reactions occur between
the original polymer chains.
The carbonaceous fiber of the invention can be
classified into three groups depending upon the
particular use of the fiber and the environment in which
the fiber is used.
In a first group, the carbonaceous fiber is
partially carbonized and has a carbon content of greater
than 65 percent but less than 85 percent, is -
electrically nonconductive and does not possess any
electrostatic dissipating characteristics, i.e., the
fiber is not able to dissipate an electrostatic charge.
The term "electrically nonconductive" as
utilized in the present invention relates to a
resistance of greater than 4 x 106 ohms/cm when measured
on a 6K (6000 filaments) tow of fibers in which the
individual fibers each have a diameter of from 7 to 20
microns. The specific resistivity of the carbonaceous
~0 fiber is greater than about lo-l ohm-cm and is
calculated from measurements as described in WO
Publication No. 88/02695.
When the fiber is a stabilized and heat set
acrylic fiber it has been found that a nitrogen content
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WO92/07981 2 0 7 ~ 9 8 ~ PCT/US90/06312
_g_
of 18 percent or higher results in an electricallynonconductive fiber.
In a second group, the carbonaceous fiber is
classified as having a low electrical conductivity, i.e.
being partially electrically conductive, and having a
carbon content of greater than 65 percent but less than
85 percent. Low conductivity means that a 6K tow of -
fibers has a resistance of from 4 x 106 to 4 x 103
ohms/cm. Preferably, the carbonaceous fiber is derived
from a stabilized acrylic fiber and possesses a
percentage nitrogen content of from 16 to 22 percent,
preferably from 16 to 18.8 percent. Such a fiber finds
particular use in sound absorbing and thermal barrier
151 structures.
In a third group, the fiber has a carbon
content of at least 85 percent and a nitrogen content
of less than 10 percent. The fiber is characterized
as having a high electrical conductivity. That is,
the fiber is substantially graphitic and has an
electrical resistance is less than 4 x 103 ohms/cm.
Correspondingly, the electrical resistivity of the fiber
i5 less than lo-l ohm-cm. This fiber is useful as
furnace insulation or in applications where electrical
grounding or shielding is desired.
The carbonaceous fiber of the third group can
have imparted to it an electrically conductive property
on the order of that of a metallic conductor by heating
the fiber to a temperature above 1000~ in a non-
oxidizing atmosphere. The electroconductive property
can be obtained from selected starting materials such as
pitcA (petroleum or coal tar), polyacetylene, acrylic
materials, e.g., a polyacrylonitrile copolymer such as
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WO92/07981 2 0 7 1~ ~ ~ PCT/US90/06312
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PANOX~ (trademark of R.K. Textiles) or GRAFIL-01
(trademark of E.I. du Pont de ~emours & Co.),
polyphenylene, polyvinylidene chloride (SAR~N-~, a
trademark of The Dow Chemical Company), and the like.
Advantageously, the apparatus of the invention
is utilized to produce carbonaceous fibers from
polymeric precursor material fibers without subjecting
the fibers to a knit/deknit step. The apparatus
comprises a means for gear crimping the fiber, without
the application of compression forces, preferably at a
temperature of from 100C to 250C, to provide the fiber
with a nonlinear temporary set. A conveying means is
provided to receive the nonlinear set fiber and
transport it without tension or stress through a heating
zone comprising one or more heating units. One heating
unit may comprise a fiber oxidation or stabilization
zone. Another heating unit may comprise a heating means -
for substantially irreversibly heat setting the fiber in
an inert atmo~phere to produce a carbonaceous fiber
having a carbon content of greater than 65 percent.
Fibers that are derived from nitrogen containing
polymeric materials, such as acrylic based polymers,
generally have a nitrogen content of from 5 to 35
percent, preferably from 16 to 25 percent, and more
preferably from 18 to 20 percent.
In the preferred operation, the fiber is passed
through a rounded gear crimper wherein the temporary
- 3 crimp is imparted to the fiber. Preferably, the crimper
is heated so as to soften the fiber. The crimped fiber
is then placed in a relaxed and unstressed condition on
a conveyor where it ia transported through the heating
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W O 92t07981 2 ~ 71 9 8 ~ PC~r/US90/06312
zone at a temperature and speed sufficient to heat set
and/or carbonize the fiber.
Preferably, the polymeric precursor fibers
employed in the present invention are the high
performance fibers such as oxidizied acrylic fiber
(OPF), aramid fibers, PBI fibers, etc. Preferably, the
polymeric precursor fibers are acrylic fibers selected
from acrylonitrile homopolymers, acrylonitrile
copolymers and acrylonitrile terpolymers, wherein said
copolymers and terpolymers contain at least 85 mole
percent acrylic units and up to 15 mole percent of one
or more monovinyl units copolymerized with another
polymer. The apparatus is particularly suited to
prepare carbonaceous fibers as disclosed in the
aforementioned European Publication No. 0199567.
A more complete understanding of the invention
will be had by referring to the following description
and claims of a preferred embodiment, taken in
conjunction with the accompanying drawings, wherein like
reference members refer to similar parts throughout the
several views.
Figure l is a perspective view, partly in
section of a crimping apparatus of the invention;
Figure 2 is an elevational view showing a
section of the crimping unit of Figure l;
3a Figure 3 is a side elevation of the apparatus; -
and
Figure 4 illustrates a gear crimping apparatus
which can be utilized in the invention.
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WO92/07981 2 0 719 8 ~ PCT/US90/06312
12-
Although specific terms are used in the
following description for the sake of clarity, these
terms are intended to refer only to the particular
structure of the invention selected for illustration in
the drawings and are not intended to define or limit the
scope of the invention.
As seen in Figure l, the apparatus lO of the ;
invention comprises an endless conveying belt 11 which
travels around drive rolls 14, 14'. The conveyor belt
ll extends through a closure or housing 12 which
contains one or more compartments for heating and,
optionally, cooling. For example, two heating chambers
16A and 16B with heaters 17 and 17', respectively, are
provided through which the fiber 18 passes. The heating
chambers are preferably followed by a cooling chamber 20
having one or more cooling fans 21. The fiber 18 is
first passed through a crimper mechanism 13 which is ;
preferably heated. The crimper mechanism comprises a
pair of cylindrical crimping rolls or drums 13A and 13B
where the fiber 18 is made pliable and provided with a
temporary crimp or heat set while in an unstressed
condition, i.e., without subjected the fiber to tension
or compression such as occurs, for çxample, in gear
crimping mechanism employed in the industry. The
nonlinear fiber, provided with a temporary set, is then
placed in a relaxed condition on the conveyor belt ll so
as to be in an unstressed condition and without tension -
30 during the final heat setting procedure. The conveyor ~
belt is constructed of any suitable material that is '
unaffected by and resistant to the elevated temperature
in the heating chambers. After passage through the -
housing 12 the fiber 18 is taken up on take up roll 26. -
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W092t07981 2 0 719 8 4 PCT/US90/06312
-13-
As seen in Figure 2, the crimper mechanism 13
comprises a rotatable cylindrical drum 13A having a
plurality of spaced fingers 22 or longitudinally
extending peripheral ridges (not illustrated) with
rounded end surfaces 24. The fingers are mounted on an
outer surface of the drum. The cylindrical drum 13A is
mounted in an opposing relationship to a cylindrical
gear 13B which has a plurality of rounded gear teeth 15.
The cylindrical drum 13A is spaced from the cylindrical
gear at a distance sufficient to allow the fingers or
ridges to enter the spaces between the gears 15 thereby
pushing the fiber into the spaces between the gears and
holding them in such position without imparting a
compression or shearing force to the fiber. Optionally,
the finger like members 22 are slideably and
telescopically mounted in sockets 19 extending from the
peripheral surface of the cylindrical drum 13A. Thus,
the fingers can be adjusted in length by sliding them
into or out of the sockets and by securing them in any
20 desired position by means of the screws 23 to thereby -
adjust the spacing of the rounded surface of the finger
with respect to the rounded surface of the gear to allow
for different size fibers or fiber tows. Adjustment of
the fingers with respect to the rounded gear surfaces
therefor prevents tensile stress or compression of the
fiber between the surfaces as the fiber is being
provided with a temporary heat set by the heated drum or ~-
drums. The fiber is therefore provided with a temporary
heat set while it is being conveyed, in a unstressed
condition, to the conveyor. The fingers (or ribs) 22
can also be replaced with fingers of different length
and width depending on the size of the fiber or fiber
tow. It will be apparent that the invention can also be
practiced with a pair of opposing cylindrical gears in
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WO92/07981 20~ ~8~ PCT/US90/06312
-14-
:'
, .,
which the teeth of the gears are rounded and spaced from~ -
each other at a distance sufficient to accommodate a
fiber or fiber tow without subjecting the fiber or tow
to tension or compression forces, shown in Figure 4.
As seen in Figure 2, the fiber 18 is crimped by -
the crimping mechanism where it assumed a uniform
sinusoidal configuration. It will be apparent to
persons skilled in the art that the crimping mechanism
can be designed with fingers or elongated ribs of a
different length and width and matching gear to provide
a fiber or tow with a non-uniform crimp.
The operation of the apparatus is more clearly
shown in Figures 1 and 3. The fiber 18 is delivered
from a supply roll 28 to a heated crimper 13. After
applying a temporary set to the fiber 18, the nonlinear
fiber is deposited onto the conveyor 11 and then
transported into housing 12 without placing any stress
or tension on the fiber while maintaining its crimped
configuration. ~he housing 12 may contain one ore more
heating chambers 16A and 16B where a preoxidized or
stabilized fiber 18 is provided with a permanent heat
set. The heating chambers 16A, 16B are filled with an
inert gas.The heat setting of the fiber 18 can be
conducted by means of radiant heaters 17, 17' or by ~: -
irradiation with a high energy source such as, for
example, lasers. Suitable heating means are well known
in the art.
The fiber which is permanently heat set in
chambers 16~, 16B, has a carbon content of greater than
65 percent and is thus defined as a carbonaceous fiber.
The fiber is then cooled in chamber 20 by cooling means
21 such as, for example, a fan, and carried out of -
.
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WO92/07981 2 ~ ~ 1 9 8 4 PCT/US90/06312
-15-
housing to be taken up on roll 26. The conveyor 11 and
rolls 26, 28 are synchronized so that the fiber or tow
placed on the conveyor ll is not placed under stress or
tension in the heating chambers 16A, 16B. It will be
apparent that a plurality of fibers 18 can be processed
simultaneously by the apparatus 10 utilizing a plurality
of supply and take-up rolls 28, 26.
In th~ case where the fiber comprises a
stabilized or oxidized polyacrylonitrile fiber and heat
setting is to be effected, the oxidized fiber is heated
to a temperature of from 300C to 1400C in a non-
oxidizing atmosphere such as nitrogen, argon, helium or
hydrogen. The heating zone can contain a single or
multigradient furnace. The inert gas can be supplied
through any openings or conduits in the housing leading
to the heating zone, and it can be injected at any point
along the path of the fiber passing through the heating
zone.
The fiber residence time in the heating zone is -
dependent upon the particular fiber utilized, the degree
of carbonization desired, and the temperature(s)
utilized.
The following example is illustrative of the
present invention.
::
A 160K tow of oxidized polyacrylonitrile fiber
(OPF) manufactured under the trade name PANOX~ by R.K.
Textiles, Scotland, United Kingdom, was passed through a
rounded gear crimping mechanism having five gears per
inch (2 gears per cm) at a temperature of from 100C to
250C. This resulting nonlinear OPF tow, provided with
a temporary set, was allowed to fall in a relaxed state
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WO92/07981 2 0 7 ~ 9 8 4 PCT/US90/06312 ~- -
-16-
onto a moving belt conveyor which transported the fiber
tow through a graduated hot zone with a final
temperature of from 400C to 1000C to permanently heat
set the fiber tow to a carbonaceous nonlinear fiber tow.
Although the invention has been described with ~;
a certain degree of particularity, it is understood that
changes in construction and the arrangement of parts can
be resorted to without departing from the scope of the
invention.
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