U.S. patent application number 10/715315 was filed with the patent office on 2005-05-19 for nonwoven elastic fibrous webs and methods for making them.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Berrigan, Michael R., De Rovere, Anne N., Eaton, Bradley W., Ista, Troy K., Lindquist, Timothy J., Nolan, Brandy S..
Application Number | 20050106982 10/715315 |
Document ID | / |
Family ID | 34574197 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050106982 |
Kind Code |
A1 |
Berrigan, Michael R. ; et
al. |
May 19, 2005 |
Nonwoven elastic fibrous webs and methods for making them
Abstract
A coherent nonwoven fibrous web comprises directly formed
elastic fibers that have a molecular orientation sufficient to
provide a birefringence number of at least 1.times.10.sup.-5 and
preferably at least 1.times.10.sup.-2. The web can be made by a
method that comprises a) extruding filaments of
elastic-fiber-forming material; b) directing the filaments through
a processing chamber in which gaseous currents apply a longitudinal
stress to the filaments that attenuates and draws the filaments; c)
maintaining the filaments at their orienting temperature while the
filaments are under attenuating and drawing stress for a sufficient
time for molecules within the filaments to become oriented along
the length of the filaments; d) cooling the filaments to their
orientation-locking temperature while the filaments are under
attenuating and drawing stress and further cooling the filaments to
a solidified fiber form; and e) collecting the solidified fibers as
a fibrous nonwoven web. In a preferred aspect, the method includes
the further step of annealing the collected fibers by exposing them
to a temperature that is above their shrinking temperature but less
than their relaxation temperature, and preferably bonding the
fibers after (or before) the annealing step. Dimensionally stable
webs comprising elastic oriented fibers are obtained.
Inventors: |
Berrigan, Michael R.;
(Oakdale, MN) ; De Rovere, Anne N.; (Woodbury,
MN) ; Eaton, Bradley W.; (Woodbury, MN) ;
Nolan, Brandy S.; (Woodbury, MN) ; Ista, Troy K.;
(River Falls, WI) ; Lindquist, Timothy J.;
(Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
34574197 |
Appl. No.: |
10/715315 |
Filed: |
November 17, 2003 |
Current U.S.
Class: |
442/415 ;
442/328; 442/400; 442/401; 442/408; 442/409 |
Current CPC
Class: |
Y10T 442/681 20150401;
Y10T 442/69 20150401; D01F 6/06 20130101; Y10T 442/602 20150401;
D01D 5/0985 20130101; Y10T 442/697 20150401; D01F 6/04 20130101;
D04H 3/08 20130101; D01F 6/42 20130101; D04H 3/14 20130101; D04H
3/00 20130101; D01F 6/60 20130101; Y10T 442/68 20150401; D01F 6/70
20130101; Y10T 442/689 20150401; Y10T 442/601 20150401; D01F 6/62
20130101 |
Class at
Publication: |
442/415 ;
442/328; 442/408; 442/409; 442/400; 442/401 |
International
Class: |
D04H 003/16; D04H
003/00; D04H 001/56; D04H 005/02 |
Claims
What is claimed is:
1. A coherent nonwoven dimensionally stable fibrous web comprising
directly formed elastic fibers that have a molecular orientation
sufficient to provide a birefringence number of at least
1.times.10.sup.-5.
2. A web of claim 1 in which said directly formed elastic fibers
have a molecular orientation sufficient to provide a birefringence
number of at least 1.times.10.sup.-2.
3. A web of claim 1 in which the elastic fibers comprise
ethylene-based polymer and the fibers exhibit a birefringence
number of at least 1.times.10.sup.-2.
4. A web of claim 1 in which the elastic fibers comprise
propylene-based polymer and the fibers exhibit a birefringence
number of at least 1.times.10.sup.-2.
5. A web of claim 1 in which the elastic fibers comprise
urethane-based polymer and the fibers exhibit a birefringence
number of at least 1.times.10.sup.-2.
6. A web of claim 1 in which the elastic fibers comprise a styrenic
block copolymer.
7. A web of claim 1 in which the elastic fibers comprise aliphatic
polyester or aliphatic polyamide.
8. A web of claim 1 that has been annealed by heating the elastic
fibers above their shrinking temperature while retaining said
molecular orientation sufficient to provide a birefringence number
of at least 1.times.10.sup.-5.
9. A web of claim 1 that exhibits a shrinkage in width of no more
than 10% when heated to 70.degree. C.
10. A web of claim 1 in which the elastic fibers exhibit an
elongation to break of at least 200%.
11. A web of claim 10 in which the elastic fibers have sufficient
elastic recovery that when released from tension stretching them to
twice their original length they will retract to no more than
one-and-one-fourth their original length.
12. A web of claim 11 in which the elastic fibers exhibit a
birefringence number of at least 1.times.10.sup.-2.
13. A web of claim 1 in which the elastic fibers have been
thermally bonded.
14. A web of claim 13 in which the bonds comprise autogenous
bonds.
15. A web of claim 1 in which the fibers of the web have been
hydroentangled to mechanically bond the fibers.
16. A web of claim 1 in which the elastic fibers exhibit
strain-induced crystallization.
17. A coherent nonwoven dimensionally stable fibrous web comprising
directly formed elastomeric fibers that have a molecular
orientation sufficient to provide a birefringence number of at
least 1.times.10.sup.-2.
18. A web of claim 17 in which the elastomeric fibers comprise an
ethylene-based or propylene-based polymer.
19. A web of claim 17 in which the elastomeric fibers have been
annealed and subsequently bonded while retaining said molecular
orientation sufficient to provide a birefringence number of at
least 1.times.10.sup.-2.
20. A web of claim 17 in which the elastomeric fibers exhibit
strain-induced crystallization.
21. A fiber-forming method comprising a) extruding filaments of
elastic-fiber-forming material; b) directing the filaments through
a processing chamber in which a longitudinal stress is applied to
the filaments that attenuates and draws the filaments; c)
maintaining the filaments at their orienting temperature while the
filaments are under attenuating and drawing stress for a sufficient
time for molecules within the filaments to become oriented along
the length of the filaments; d) cooling the filaments to their
orientation-locking temperature while the filaments are under
attenuating and drawing stress and further cooling the filaments to
solidified elastic fibers; and e) collecting the solidified elastic
fibers as a fibrous nonwoven web.
22. A method of claim 21 in which the filaments enter the
processing chamber at a temperature higher than the glass
transition temperature or melting point of the filaments.
23. A method of claim 21 in which the largest longitudinal stress
is applied to the filaments after they leave the processing
chamber.
24. A method of claim 22 in which the largest longitudinal stress
is applied to the filaments after they leave the processing
chamber.
25. A method of claim 21 in which the filaments pass through the
processing chamber at a rate of at least 2800 meters/minute.
26. A method of claim 22 in which the filaments pass through the
processing chamber at a rate of at least 2800 meters/minute.
27. A method of claim 24 in which the filaments pass through the
processing chamber at a rate of at least 2800 meters/minute.
28. A method of claim 21 in which the filaments pass through the
processing chamber at a rate of at least 4000 meters/minute.
29. A method of claim 21 including the further step of annealing
the collected fibers by exposing them to a temperature that is
above their shrinkage temperature but less than the relaxation
temperature of the fibers.
30. A method of claim 21 including the further step of thermally
bonding the fibers after they have been annealed.
31. A method of claim 21 in which the collected fibers of the
nonwoven web exhibit an elongation to break of at least 200
percent.
32. A method of claim 21 in which the filaments comprise an
ethylene-based polymer or a propylene-based polymer.
33. A method of claim 21 in which the filaments comprise a
urethane-based polymer.
34. A method of claim 21 in which the filaments comprise a styrenic
block copolymer.
35. A method of claim 21 in which the filaments comprise an
aliphatic polyester or an aliphatic polyamide.
36. A method for preparing a fibrous web comprising 1) preparing
extruded filaments from an elastic-fiber-forming liquid, 2)
processing and attenuating the extruded filaments to solid
collectible fibers having molecular orientation, 3) collecting the
fibers as a nonwoven web, 4) annealing the collected fibers by
exposing them to a temperature that is above their shrinking
temperature but less than their relaxation temperature to make the
web dimensionally stable while retaining sufficient molecular
orientation that the fibers exhibit a birefringence of at least
1.times.10.sup.-5, and 5) bonding the web to give it increased
coherency.
37. A method of claim 36 in which step (4) is performed after step
(5).
38. A method of claim 37 in which bonding of the web in step (5)
comprises hydroentangling the web.
39. A method of claim 36 including the further step of thermally
bonding the fibers after they have been annealed.
40. A method of claim 36 in which the filaments are processed and
attenuated by passing the filaments through a processing chamber at
a rate of at least 2800 meters/minute.
Description
FIELD OF THE INVENTION
[0001] This invention relates to nonwoven fibrous webs that
comprise elastic fibers, whereby the web as a whole can have
elastic properties.
BACKGROUND
[0002] Important commercial opportunities await nonwoven fibrous
webs that are suitably stretchable, elastic and strong. Such webs
could be useful to make a garment form-fitting, or to make a cuff,
neck-line or other portion of a garment elastically retain its
shape. Or such webs could provide breathable, soft, lightweight,
cloth-like fabrics. Also, such webs tend to be of high friction,
which can be useful in a number of applications.
[0003] Recognizing the opportunities, many prior workers have
sought to produce elastic nonwoven fibrous webs. Their prior work
is represented in the patent literature, which includes U.S. Pat.
Nos. 3,686,385; 4,707,398; 4,820,572; 4,891,957; 5,322,728;
5,366,793; 5,470,639; and 5,997,989.
[0004] While the prior work may have met some needs, many
opportunities remain unsatisfied. In general, the prior efforts
have not produced a fibrous web having an adequate combination of
stretchability, elasticity, bondability and strength to fulfill
many of the visualized opportunities.
SUMMARY
[0005] The present invention provides a fibrous elastic nonwoven
web that comprises directly collected elastic fibers that are
oriented, thereby providing the fibers and the web with beneficial
and superior strength properties.
[0006] By "directly formed fibers" it is meant fibers formed and
collected as a fibrous nonwoven web in essentially one operation,
e.g., by extruding filaments from a fiber-forming liquid,
processing the extruded filaments to a solidified fiber form as
they travel to a collector, and collecting the processed fibers as
a web within seconds after the fibers left the liquid form. Such a
method is in contrast with methods in which, for example, extruded
fibers are chopped into staple fibers before they are assembled
into a web. Meltblown fibers and meltspun fibers, including
spunbond fibers and fibers prepared and collected in webs in the
manner described in U.S. Pat. No. 6,607,624, are examples of
directly formed fibers useful for the present invention.
[0007] By "oriented" it is meant that portions of polymer molecules
within the fibers are aligned lengthwise of the fibers, and are
locked in, i.e., are thermally fixed or trapped in, that alignment.
In other words, for the molecules to move out of their orienting
alignment would require the fibers to be heated above the
relaxation temperature for the fibers for sufficient time that the
molecules would be free to move and rearrange themselves
sufficiently to lose their orientation ["relaxation temperature" is
defined herein as a temperature that is within plus or minus
5.degree. C. of the glass transition temperature (for amorphous
noncrystalline materials) or melting temperature (for crystalline
or semicrystalline materials)]. The aligned molecules can improve
strength properties of the fibers.
[0008] Whether molecules are oriented within a fiber can generally
be indicated by measuring whether the fibers exhibit birefringence.
If fibers exhibit a birefringence number of at least about
1.times.1.sup.-5 by the test described herein, they are regarded as
oriented. The higher the birefringence number, the higher the
degree of orientation, and preferably fibers in webs of the
invention exhibit a birefringence number of at least
1.times.10.sup.-4 or at least 1.times.10.sup.-3; and with certain
polymers we have successfully prepared fibers with birefringence
numbers of 1.times.10.sup.-2 or more. Fibers of different polymer
classes may show different degrees of orientation and different
levels of birefringence number.
[0009] The directly formed oriented fibers can have varying degrees
of elasticity, but preferably they are "elastomeric" fibers. The
term "elastomeric fibers" is regarded herein as meaning fibers that
may be stretched to at least twice their original length and, when
released from tension stretching them to twice their original
length, will promptly retract to no more than one-and-one-fourth
times their original length. Elastomeric fibers are especially
needed for certain uses, and oriented elastomeric fibers make
distinct contributions that elastic fibers of less stretchability
or less elastic recovery cannot make. The term "elastic fibers" is
regarded herein as describing a larger category of fibers,
including fibers of a lesser stretchability, but which elastically
recover at least partially from their stretched dimensions. An
elastic fiber generally is regarded herein as one that may be
stretched to at least 125 percent of its original length before
breaking, and upon release of tension from such a degree of stretch
will retract at least 50% of the amount of elongation.
[0010] Though having oriented fibers, webs of the invention can be,
and preferably are, dimensionally stable. By "dimensionally stable"
it is meant that the web will shrink in its width dimension
(transverse to the machine direction, i.e., the direction of
movement of a collector on which the web was collected) by no more
than about 10 percent when heated to a temperature of 70.degree. C.
We have found that webs can be annealed to release strains that
would otherwise cause the web to shrink upon heating, and despite
the annealing the fibers can have a retained orientation that
provides improved properties.
[0011] The present invention also provides a new method for making
elastic fibers and webs of the invention, which in brief summary,
comprises a) extruding filaments of elastic-fiber-forming material;
b) directing the filaments through a processing chamber in which a
longitudinal stress is applied to the filaments that attenuates and
draws the filaments; c) maintaining the filaments at their
orienting temperature while the filaments are under attenuating and
drawing stress for a sufficient time for molecules within the
filaments to become oriented and aligned along the length of the
filaments; d) cooling the filaments to their orientation-locking
temperature while the filaments are under the attenuating and
drawing stress; and e) collecting the processed filaments.
[0012] By "orienting temperature" is meant a temperature at which
molecules within the extruded filaments can move into alignment
lengthwise of the filaments under attenuation or drawing stress;
such a temperature is generally at least about or greater than the
glass transition (T.sub.g) or melting point (T.sub.m) for the
filaments. By "orientation-locking temperature" is meant a
temperature at which the molecules of the filaments become
thermally fixed or trapped into an orientation they may have
attained within the filament. Such a temperature is generally at
least about 30.degree. C. less than the relaxation temperature for
the filaments.
[0013] In another aspect of the invention, a method as described
includes the further step of annealing the prepared fibers by
exposing them to a temperature that is at or above the shrinking
temperature of the fibers but at least 10.degree. C. less than the
relaxation temperature of the fibers. ("Shrinking temperature"
means herein a temperature at which fibers release strain by
shrinking more than 10%, but which is less than the melting or
softening temperature of the fibers.) We have found that during
such a step preferred fibers prepared according to the invention
can undergo shrinkage while maintaining some useful molecular
orientation. And the elastic properties of the fibers and webs,
especially the amount of their stretchability, can be increased by
annealing and by shrinkage that occurs with annealing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic overall diagram of apparatus useful
for forming a nonwoven fibrous web of the invention.
[0015] FIG. 2 is an enlarged side view of a processing chamber
useful for forming a nonwoven fibrous web of the invention, with
mounting means for the chamber not shown.
[0016] FIG. 3 is a top view, partially schematic, of the processing
chamber shown in FIG. 2 together with mounting and other associated
apparatus.
[0017] FIGS. 4a, 4b, and 4c are schematic diagrams through
illustrative fiber bonds in webs of the invention.
[0018] FIG. 5 is a schematic diagram of a portion of a web of the
invention, showing fibers crossing over and bonded to one
another.
[0019] FIGS. 6 and 7 are schematic diagrams showing an illustrative
extruded filament extending from extrusion head to collector, with
accompanying illustrative apparatus and descriptive
information.
DETAILED DESCRIPTION
[0020] FIG. 1 shows an illustrative apparatus that can be used to
prepare nonwoven fibrous webs of the invention. Fiber-forming
material is brought to an extrusion head 10--in this particular
illustrative apparatus, by introducing a fiber-forming material
into hoppers 11, melting the material in an extruder 12, and
pumping the molten material into the extrusion head 10 through a
pump 13. Although solid polymeric material in pellet or other
particulate form is most commonly used and melted to a liquid,
pumpable state, other fiber-forming liquids such as polymer
solutions could also be used.
[0021] The extrusion head 10 may be a conventional spinnerette or
spin pack, generally including multiple orifices arranged in a
regular pattern, e.g., straightline rows. Filaments 15 of
fiber-forming liquid are extruded from the extrusion head and
conveyed to a processing chamber or attenuator 16. Typically, some
quenching streams of air or other gas 18 are presented to the
extruded filaments by conventional methods and apparatus to reduce
the temperature of the extruded filaments 15. Sometimes the
quenching streams may be heated to obtain a desired temperature of
the extruded filaments and/or to facilitate drawing of the
filaments. There may be one or more streams of air (or other
fluid)--e.g., a first stream 18a blown transversely to the filament
stream, which may remove undesired gaseous materials or fumes
released during extrusion; and a second quenching stream 18b that
achieves a major desired temperature reduction. Depending on the
process being used or the form of finished product desired, the
quenching stream may be sufficient to solidify some of the extruded
filaments 15 before they reach the attenuator 16. But in general,
in a method of the invention extruded filamentary components are
still in a softened or molten condition when they enter the
attenuator. Alternatively, no quenching streams are used; in such a
case ambient air or other fluid between the extrusion head 10 and
the attenuator 16 may be a medium for any temperature change in the
extruded filamentary components before they enter the
attenuator.
[0022] The filaments 15 pass through the attenuator 16, as
discussed in more detail below, and then exit. Most often, as
pictured in FIG. 1, they exit onto a collector 19 where they are
collected as a mass of fibers 20 that may or may not be coherent
and take the form of a handleable web. The collector 19 is
generally porous and a gas-withdrawal device 14 can be positioned
below the collector to assist deposition of fibers onto the
collector.
[0023] Depending on the chemical composition of the filaments,
different kinds of morphology can be obtained in a fiber. As
discussed below, the possible morphological forms within a fiber
include amorphous, ordered or rigid amorphous, oriented amorphous,
crystalline, oriented or shaped crystalline, and extended-chain
crystallization (sometimes called strain-induced crystallization).
Fibers in webs of the invention can exhibit more than one of these
different kinds of morphology. Also, in some embodiments the
different kinds of morphology can exist within the same fiber,
e.g., can exist along the length of a single fiber, or can exist in
different amounts or at different degrees of order or orientation.
And these differences can exist to the extent that longitudinal
segments along the length of the fiber differ in softening
characteristics during a bonding operation.
[0024] After passing through a processing chamber, but prior to
collection, extruded filaments or fibers may be subjected to a
number of additional processing steps not illustrated in FIG. 1,
e.g., further drawing, spraying, etc. Upon collection, the whole
mass 20 of collected fibers may be conveyed to other apparatus such
as a bonding oven, through-air bonder, calenders, hydroentangling
mechanical bonder, embossing stations, laminators, cutters and the
like; or it may be passed through drive rolls 22 and wound into a
storage roll 23.
[0025] In one preferred practice of the invention the collected
fibers are exposed to heat, e.g., by passage through an oven or
past a "through-air" oven, or hot-air knife, to anneal the fibers.
That is, tensions or other stresses within the fibers are reduced
or removed, whereupon the fibers have improved stability under
certain environmental conditions. As discussed above, it has been
found that when elastic fibers oriented according to the invention
are heated to a temperature above the shrinking temperature but
less than the relaxation temperature the fibers undergo shrinking
and lose some orientation, but not all their orientation. Preferred
fibers of the invention generally retain some orientation after
annealing, which improves the physical properties of the fibers.
The amount of orientation retained generally can be controlled at
least partially by the length of heat exposure and the temperature
to which the fibers are exposed.
[0026] The described step of annealing can be beneficial as
preparation for bonding of the collected fibers, if bonding has not
already been achieved during collection. If certain collected
masses of fibers of the invention are thermally bonded without
first annealing, the collected mass may shrink during the bonding
operation to form a distorted web shrunk in an uncontrolled manner.
But it has been found in preferred embodiments that, after a
controlled annealing as discussed above, bonding can be achieved
while leaving the web in a usefully undistorted state, and with the
fibers retaining a beneficial, fiber-strengthening orientation.
[0027] When annealing and bonding are used, the bonding can be
performed immediately following annealing. For example, thermal
bonding can be performed in the same oven where annealing was
performed, or in an adjacent oven, heated to a higher temperature
than used in the annealing operation. Or bonding can be performed
by conveying the web to a through-air bonder, or a calendering or
point-bonding apparatus. Bonding need not be performed immediately
after annealing, and it may be desirable to wait a period of time
such as 36-48 hours after annealing for the fibers, during which
time the fibers may further relax. Preferably thermal bonds are
autogenous bonds, meaning formed without pressure such as applied
by a calender or point-bonder. Bonding also can be achieved by
inclusion of bonding fibers or resins in a web, or by application
of solvents to the web, or to points or portions of the web.
[0028] The apparatus pictured in FIG. 1 is of advantage in
practicing the invention because it allows control over the
temperature of filaments passing through the attenuator, allows
filaments to pass through the chamber at fast rates, and can apply
stresses on the filaments that introduce desired degrees of
orientation on the filaments. (Apparatus as shown in the drawings
has also been described in U.S. Pat. No. 6,607,624, issued Aug. 19,
2003, which is incorporated by reference in the present
application.) As part of a desired control of the process, the
distance 17 the extruded filaments 15 travel before reaching the
attenuator 16 can be adjusted, as can the conditions to which the
filaments are exposed. For example, the processing chamber can be
moved closer to the extrusion head to cause the extruded filaments
to be higher in temperature when they enter the processing chamber
than they otherwise would be. When such higher-temperature
filaments are subjected to tension in the processing chamber, they
may more easily stretch, and molecules within the filaments may
become aligned or oriented.
[0029] In general, the temperature of the filaments entering the
processing chamber, and the tension applied to the filaments in the
processing chamber are chosen to achieve desired and effective
(i.e., non-rupturing) degrees of stretch in the extruded filaments
as they travel through the processing chamber. In contrast to
typical prior art spunbond processes and equipment, the present
invention provides new methods that can include, among other
things, application of drawing/attenuating stress while the
extruded filament is still sufficiently elevated in temperature to
be at orienting temperature as defined herein; application of
drawing/attenuating stress for relatively longer times (i.e., for a
greater proportion of their time in the threadline); and
application of drawing/attenuating stress until the extruded
filament has cooled below its orientation-locking temperature. In
the present invention the threadline stress can be held to a lower
level than typically used in the spunbond process so as to avoid
rupturing even of filaments that are above their glass transition
temperature or melting point. In fact, the intentional application
of attenuating stress while filaments are above their glass
transition or melting point contributes to the ability to use low
stress. And filaments can be moved through the processing chamber
at fast rates that minimize the opportunity for oriented molecules
within a filament to retract to a nonoriented condition (i.e., not
aligned lengthwise of the filament) before the filament cools to
the orientation-locking temperature.
[0030] As stated above, the filaments should generally be above
their orienting temperature during at least part of the time they
are under longitudinal stress. The useful orienting temperature
varies depending on the polymer family, but in general it is a
temperature at least 20.degree. C. and preferably at least
40.degree. C. above the relaxation temperature for the
filaments.
[0031] As the filaments proceed through the processing chamber and
to the collector they cool, and eventually they reach the
orientation-locking temperature. Again, this temperature will vary
for different polymer families, but typically it is a temperature
at least 30.degree. C. less, and preferably at least 80.degree. C.
less than the relaxation temperature. When the filaments reach the
orientation-locking temperature they are under longitudinal stress,
which in general has been applied long enough that molecules within
the filaments have become aligned lengthwise of the filaments.
Lower stresses than would be applied to filaments that have cooled
and are undergoing cold-draw can be applied to the still-hot
filaments of a method of the invention, and those stresses can be
applied for longer times than is typical in the prior art
processes. As a corollary, a larger extent of orientation can be
introduced into the filaments before the filaments reach the
orientation-locking temperature.
[0032] Because the filaments have orientation and are under
longitudinal tension when they cool to the orientation-locking
temperature, the orientation is retained at least in part in the
collected fibers. Sufficient of such retained orientation is
present that, even though later annealing may cause some loss of
orientation, orientation can remain after annealing to enhance
strength and stability of the fibers.
[0033] Other useful controls of the process can generally be
achieved by controlling the length of the processing
chamber/attenuator, the velocity and temperature of the filaments
as they move through the attenuator, and the distance of the
attenuator from the collector 19. By causing some or all of the
filaments and segments thereof to cool to a solid condition while
under tension and in a stretched condition, the orientation of the
filaments, and the consequent morphology of the fibers, can become
frozen in; i.e., molecules or portions thereof in the filaments or
fibers can be thermally fixed or trapped in their aligned position,
as discussed above.
[0034] Some advantageous features of the apparatus are further
shown in FIG. 2, which is an enlarged side view of a representative
processing device or attenuator, and FIG. 3, which is a top view,
partially schematic, of the processing apparatus shown in FIG. 2
together with mounting and other associated apparatus. The
illustrative attenuator 16 comprises two movable halves or sides
16a and 16b separated so as to define between them the processing
chamber 24: the facing surfaces of the sides 16a and 16b form the
walls of the chamber. As seen from the top view in FIG. 3, the
processing or attenuation chamber 24 is generally an elongated
slot, having a transverse length 25 (transverse to the path of
travel of filaments through the attenuator), which can vary
depending on the number of filaments being processed.
[0035] Although existing as two halves or sides, the attenuator
functions as one unitary device and will be first discussed in its
combined form. (The structure shown in FIGS. 2 and 3 is
representative only, and a variety of different constructions may
be used.) The representative attenuator 16 includes slanted entry
walls 27, which define an entrance space or throat 24a of the
attenuation chamber 24. The entry walls 27 preferably are curved at
the entry edge or surface 27a to smooth the entry of air streams
carrying the extruded filaments 15. The walls 27 are attached to a
main body portion 28, and may be provided with a recessed area 29
to establish a gap 30 between the body portion 28 and wall 27. Air
may be introduced into the gaps 30 through conduits 31, creating
air knives (represented by the arrows 32) that increase the
velocity of the filaments traveling through the attenuator, and
that also have a further quenching affect on the filaments. The
attenuator body 28 is preferably curved at 28a to smooth the
passage of air from the air knife 32 into the passage 24. The angle
(.alpha.) of the surface 28b of the attenuator body can be selected
to determine the desired angle at which the air knife impacts a
stream of filaments passing through the attenuator. Instead of
being near the entry to the chamber, the air knives may be disposed
further within the chamber.
[0036] The attenuation chamber 24 may have a uniform gap width (the
horizontal distance 33 on the page of FIG. 2 between the two
attenuator sides is herein called the gap width) over its
longitudinal length through the attenuator (the dimension along a
longitudinal axis 26 through the attenuation chamber is called the
axial length). Alternatively, as illustrated in FIG. 2, the gap
width may vary along the length of the attenuator chamber. When the
attenuation chamber is defined by straight or flat walls, the
spacing between the walls may be constant over their length, or
alternatively the walls may slightly diverge or converge over the
axial length of the attenuation chamber. In all these cases, the
walls defining the attenuation chamber are regarded as parallel
herein, because the deviation from exact parallelism is relatively
slight. As illustrated in FIG. 2, the walls defining the main
portion of the longitudinal length of the passage 24 may take the
form of plates 36 that are separate from, and attached to, the main
body portion 28.
[0037] The length of the attenuation chamber 24 can be varied to
achieve different effects; variation is especially useful with the
portion between the air knives 32 and the exit opening 34,
sometimes called herein the chute length 35. The angle between the
chamber walls and the axis 26 may be wider near the exit 34 to
change the distribution of fibers onto the collector as well as to
change the turbulence and patterns of the current field at the exit
of the attenuator. Structure such as deflector surfaces, Coanda
curved surfaces, and uneven wall lengths also may be used at the
exit to achieve a desired current force-field as well as spreading
or other distribution of fibers. In general, the gap width, chute
length, attenuation chamber shape, etc. are chosen in conjunction
with the material being processed and the mode of treatment desired
to achieve desired effects. For example, longer chute lengths may
be useful to increase the crystallinity of prepared fibers.
Conditions are chosen and can be widely varied to process the
extruded filaments into a desired fiber form.
[0038] As illustrated in FIG. 3, the two sides 16a and 16b of the
representative attenuator 16 are each supported through mounting
blocks 37 attached to linear bearings 38 that slide on rods 39. The
bearing 38 has a low-friction travel on the rod through means such
as axially extending rows of ball-bearings disposed radially around
the rod, whereby the sides 16a and 16b can readily move toward and
away from one another. The mounting blocks 37 are attached to the
attenuator body 28 and a housing 40 through which air from a supply
pipe 41 is distributed to the conduits 31 and air knives 32.
[0039] In this illustrative embodiment, air cylinders 43a and 43b
are connected, respectively, to the attenuator sides 16a and 16b
through connecting rods 44 and apply a clamping force pressing the
attenuator sides 16a and 16b toward one another. The clamping force
is chosen in conjunction with the other operating parameters so as
to balance the pressure existing within the attenuation chamber 24.
In other words, under preferred operating conditions the clamping
force is in balance or equilibrium with the force acting internally
within the attenuation chamber to press the attenuator sides apart,
e.g., the force created by the gaseous pressure within the
attenuator. Filamentary material can be extruded, passed through
the attenuator and collected as finished fibers while the
attenuator parts remain in their established equilibrium or
steady-state position and the attenuation chamber or passage 24
remains at its established equilibrium or steady-state gap
width.
[0040] During operation of the representative apparatus illustrated
in FIGS. 1-3, movement of the attenuator sides or chamber walls
generally occurs only when there is a perturbation of the system.
Such a perturbation may occur when a filament being processed
breaks or tangles with another filament or fiber. Such breaks or
tangles are often accompanied by an increase in pressure within the
attenuation chamber 24, e.g., because the forward end of the
filament coming from the extrusion head or the tangle is enlarged
and creates a localized blockage of the chamber 24. The increased
pressure can be sufficient to force the attenuator sides or chamber
walls 16a and 16b to move away from one another. Upon this movement
of the chamber walls the end of the incoming filament or the tangle
can pass through the attenuator, whereupon the pressure in the
attenuation chamber 24 returns to its steady-state value before the
perturbation, and the clamping pressure exerted by the air
cylinders 43 returns the attenuator sides to their steady-state
position. Other perturbations causing an increase in pressure in
the attenuation chamber include "drips," i.e., globular liquid
pieces of fiber-forming material falling from the exit of the
extrusion head upon interruption of an extruded filament, or
accumulations of extruded filamentary material that may engage and
stick to the walls of the attenuation chamber or to previously
deposited fiber-forming material.
[0041] In effect, one or both of the attenuator sides 16a and 16b
"float," i.e., are not held in place by any structure but instead
are mounted for a free and easy movement laterally in the direction
of the arrows 50 in FIG. 1. In a preferred arrangement, the only
forces acting on the attenuator sides other than friction and
gravity are the biasing force applied by the air cylinders and the
internal pressure developed within the attenuation chamber 24.
Other clamping means than the air cylinder may be used, such as a
spring(s), deformation of an elastic material, or cams; but the air
cylinder offers a desired control and variability.
[0042] Many alternatives are available to cause or allow a desired
movement of the processing chamber wall(s). For example, instead of
relying on fluid pressure to force the wall(s) of the processing
chamber apart, a sensor within the chamber (e.g., a laser or
thermal sensor detecting buildup on the walls or plugging of the
chamber) may be used to activate a servomechanical mechanism that
separates the wall(s) and then returns them to their steady-state
position. In another useful apparatus of the invention, one or both
of the attenuator sides or chamber walls is driven in an
oscillating pattern, e.g., by a servomechanical, vibratory or
ultrasonic driving device. The rate of oscillation can vary within
wide ranges, including, for example, at least rates of 5,000 cycles
per minute to 60,000 cycles per second.
[0043] In still another variation, the movement means for both
separating the walls and returning them to their steady-state
position takes the form simply of a difference between the fluid
pressure within the processing chamber and the ambient pressure
acting on the exterior of the chamber walls. More specifically,
during steady-state operation, the pressure within the processing
chamber (a summation of the various forces acting within the
processing chamber established, for example, by the internal shape
of the processing chamber, the presence, location and design of air
knives, the velocity of a fluid stream entering the chamber, etc.)
is in balance with the ambient pressure acting on the outside of
the chamber walls. If the pressure within the chamber increases
because of a perturbation of the fiber-forming process, one or both
of the chamber walls moves away from the other wall until the
perturbation ends, whereupon pressure within the processing chamber
is reduced to a level less than the steady-state pressure (because
the gap width between the chamber walls is greater than at the
steady-state operation). Thereupon, the ambient pressure acting on
the outside of the chamber walls forces the chamber wall(s) back
until the pressure within the chamber is in balance with the
ambient pressure, and steady-state operation occurs. Lack of
control over the apparatus and processing parameters can make sole
reliance on pressure differences a less desired option.
[0044] In sum, besides being instantaneously movable and in some
cases "floating," the wall(s) of the processing chamber are also
generally subject to means for causing them to move in a desired
way. The walls can be thought of as generally connected, e.g.,
physically or operationally, to means for causing a desired
movement of the walls. The movement means may be any feature of the
processing chamber or associated apparatus, or an operating
condition, or a combination thereof that causes the intended
movement of the movable chamber walls--movement apart, e.g., to
prevent or alleviate a perturbation in the fiber-forming process,
and movement together, e.g., to establish or return the chamber to
steady-state operation.
[0045] In the embodiment illustrated in FIGS. 1-3, the gap width 33
of the attenuation chamber 24 is interrelated with the pressure
existing within the chamber, or with the fluid flow rate through
the chamber and the fluid temperature. The clamping force matches
the pressure within the attenuation chamber and varies depending on
the gap width of the attenuation chamber: for a given fluid flow
rate, the narrower the gap width, the higher the pressure within
the attenuation chamber, and the higher must be the clamping force.
Lower clamping forces allow a wider gap width. Mechanical stops,
e.g., abutting structure on one or both of the attenuator sides 16a
and 16b may be used to assure that minimum or maximum gap widths
are maintained.
[0046] In one useful arrangement, the air cylinder 43a applies a
larger clamping force than the cylinder 43b, e.g., by use in
cylinder 43a of a piston of larger diameter than used in cylinder
43b. This difference in force establishes the attenuator side 16b
as the side that tends to move most readily when a perturbation
occurs during operation. The difference in force is about equal to
and compensates for the frictional forces resisting movement of the
bearings 38 on the rods 39. Limiting means can be attached to the
larger air cylinder 43a to limit movement of the attenuator side
16a toward the attenuator side 16b. One illustrative limiting
means, as shown in FIG. 3, uses as the air cylinder 43a a
double-rod air cylinder, in which the second rod 46 is threaded,
extends through a mounting plate 47, and carries a nut 48 which may
be adjusted to adjust the position of the air cylinder. Adjustment
of the limiting means, e.g., by turning the nut 48, positions the
attenuation chamber 24 into alignment with the extrusion head
10.
[0047] Because of the described instantaneous separation and
reclosing of the attenuator sides 16a and 16b, the operating
parameters for a fiber-forming operation are expanded. Some
conditions that would previously make the process inoperable--e.g.,
because they would lead to filament breakage requiring shutdown for
rethreading--become acceptable; upon filament breakage, rethreading
of the incoming filament end generally occurs automatically. For
example, higher velocities that lead to frequent filament breakage
may be used. Similarly, narrow gap widths, which cause the air
knives to be more focused and to impart more force and greater
velocity on filaments passing through the attenuator, may be used.
Or filaments may be introduced into the attenuation chamber in a
more molten condition, thereby allowing greater control over fiber
properties, because the danger of plugging the attenuation chamber
is reduced. The attenuator may be moved closer to or further from
the extrusion head to control among other things the temperature of
the filaments when they enter the attenuation chamber.
[0048] Although the chamber walls of the attenuator 16 are shown as
generally monolithic structures, they can also take the form of an
assemblage of individual parts each mounted for the described
instantaneous or floating movement. The individual parts comprising
one wall engage one another through sealing means so as to maintain
the internal pressure within the processing chamber 24. In a
different arrangement, flexible sheets of a material such as rubber
or plastic form the walls of the processing chamber 24, whereby the
chamber can deform locally upon a localized increase in pressure
(e.g., because of a plugging caused by breaking of a single
filament or group of filaments). A series or grid of biasing means
may engage the segmented or flexible wall; sufficient biasing means
are used to respond to localized deformations and to bias a
deformed portion of the wall back to its undeformed position.
Alternatively, a series or grid of oscillating means may engage the
flexible wall and oscillate local areas of the wall. Or, in the
manner discussed above, a difference between the fluid pressure
within the processing chamber and the ambient pressure acting on
the wall or localized portion of the wall may be used to cause
opening of a portion of the wall(s), e.g., during a process
perturbation, and to return the wall(s) to the undeformed or
steady-state position, e.g., when the perturbation ends. Fluid
pressure may also be controlled to cause a continuing state of
oscillation of a flexible or segmented wall.
[0049] As will be seen, in the preferred embodiment of processing
chamber illustrated in FIGS. 2 and 3, there are no sidewalls at the
ends of the transverse length of the chamber. The result is that
fibers passing through the chamber can spread outwardly outside the
chamber as they approach the exit of the chamber. Such a spreading
can be desirable to widen the mass of fibers collected on the
collector. In other embodiments, the processing chamber does
include side walls, though a single side wall at one transverse end
of the chamber is not attached to both chamber sides 16a and 16b,
because attachment to both chamber sides would prevent separation
of the sides as discussed above. Instead, a sidewall(s) may be
attached to one chamber side and move with that side when and if it
moves in response to changes of pressure within the passage. In
other embodiments, the side walls are divided, with one portion
attached to one chamber side, and the other portion attached to the
other chamber side, with the sidewall portions preferably
overlapping if it is desired to confine the stream of processed
fibers within the processing chamber.
[0050] While apparatus as shown, in which the walls are
instantaneously movable, are much preferred, the invention can also
be run--generally with less convenience and efficiency--with
apparatus such as shown except that the walls defining the
processing chamber are fixed in position.
[0051] A wide variety of elastic-fiber-forming materials,
preferably elastomeric-fiber-forming materials, may be used to make
fibrous webs of the invention. Organic polymeric materials that can
satisfy the definitions of elastic and elastomeric fibers stated
above, in at least some forms (e.g., in at least some molecular
structures or molecular weights, or with appropriate co-monomers or
other additives) include urethane-based polymers, ethylene-based
polymers and propylene-based polymers, ethylene-styrene copolymers,
ultra-low-density polyethylene or ultra-low-density polypropylene,
ethylene-propylene copolymers and ethylene-propylene block
copolymers, styrenic block copolymers, aliphatic polyesters and
aliphatic polyamides. Some polymers or materials that are more
difficult to form into fibers by spunbond or meltblown techniques
can be used.
[0052] In the case of semicrystalline polymeric materials,
preferred embodiments of the invention provide nonwoven fibrous
webs comprising chain-extended crystalline structure (also called
strain-induced crystallization) in the fibers, thereby increasing
strength and stability of the web (chain-extended crystallization,
as well as other kinds of crystallization, typically can be
detected by X-ray analysis). Combination of that structure with
autogenous bonds, sometimes circumference-penetrating bonds, is a
further advantage. The fibers of the web can be rather uniform in
diameter over most of their length and independent from other
fibers to obtain webs having desired loft properties. Lofts of 90
percent (the inverse of solidity and comprising the ratio of the
volume of the air in a web to the total volume of the web
multiplied by 100) or more can be obtained and are useful for many
purposes such as filtration or insulation. Even the less-oriented
fiber segments preferably have undergone some orientation that
enhances fiber strength along the full length of the fiber. Other
fiber-forming materials that are not crystalline, e.g., styrenic
block copolymers, can still benefit from orientation.
[0053] While the invention is particularly useful with
fiber-forming materials in molten form, other fiber-forming liquids
such as solutions or suspensions may also be used. The specific
polymers listed above are examples only, and a wide variety of
other polymeric or fiber-forming materials are useful.
Interestingly, fiber-forming processes of the invention using
molten polymers can often be performed at lower temperatures than
traditional direct extrusion techniques, which offers a number of
advantages.
[0054] Fibers also may be formed from blends of materials,
including materials into which certain additives have been blended,
such as pigments or dyes. The term "fiber" is used herein to mean a
monocomponent fiber; a bicomponent or conjugate fiber (for
convenience, the term "bicomponent" will often be used to mean
fibers that consist of two components as well as fibers that
consist of more than two components); and a fiber section of a
bicomponent fiber, i.e., a section occupying part of the
cross-section of and extending over the length of the bicomponent
fiber. Core-sheath or side-by-side bicomponent fibers, may be
prepared. In bicomponent fibers of the invention, at least one of
the components satisfies the description of an elastic or
elastomeric fiber stated above; preferably all components of the
fiber satisfy those descriptions.
[0055] In addition, different fiber-forming materials may be
extruded through different orifices of the extrusion head so as to
prepare webs that comprise a mixture of fibers. In other
embodiments of the invention other materials are introduced into a
stream of fibers prepared according to the invention before or as
the fibers are collected so as to prepare a blended web. For
example, other staple fibers may be blended in the manner taught in
U.S. Pat. No. 4,118,531; or particulate material may be introduced
and captured within the web in the manner taught in U.S. Pat. No.
3,971,373; or microwebs as taught in U.S. Pat. No. 4,813,948 may be
blended into the webs. Alternatively, fibers prepared according to
the present invention may be introduced into a stream of other
fibers to prepare a blend of fibers.
[0056] Besides the retained orientation of elastic fibers discussed
above, webs and fibers of the invention can exhibit other unique
characteristics. As one example, a new web of the invention
preferably comprises fibers that vary in morphology over their
length so as to provide longitudinal segments that differ from one
another in softening characteristics during a selected bonding
operation (this characteristic is also described in earlier-filed
related applications, U.S. Ser. Nos. 10/151,782 and 10/151,780,
both filed May 20, 2002, which are incorporated herein by
reference). Some of these longitudinal segments soften under the
conditions of the bonding operation, i.e., are active during the
selected bonding operation and become bonded to other fibers of the
web; and others of the segments are passive during the bonding
operation. Preferably, the active longitudinal segments soften
sufficiently under useful bonding conditions, e.g., at a
temperature low enough, that the web can be autogenously bonded.
Preferably, also, adjacent longitudinal segments differ in diameter
by no more than about 10 percent. Thus, the fibers can have a
"uniform diameter," by which it is meant herein that the fibers
have essentially the same diameter (varying by 10 percent or less)
over a significant length (i.e., 5 centimeters or more)).
[0057] With respect to block copolymers, it may be noted that the
individual blocks of the copolymers may vary in morphology, as when
one block is crystalline or semicrystalline and the other block is
amorphous; the variation in morphology often exhibited by fibers of
the invention is not such a variation, but instead is a more macro
property in which several molecules participate in forming a
generally physically identifiable portion of a fiber.
[0058] While adjacent longitudinal segments may not differ greatly
in diameter in webs of the invention, there may be significant
variation in diameter from fiber to fiber.
[0059] As another unique characteristic of fibers and webs of the
invention, in some collected webs fibers are found that are
interrupted, i.e., are broken, or entangled with themselves or
other fibers, or otherwise deformed as by engaging a wall of the
processing chamber. The fiber segments at the location of the
interruption--i.e., the fiber segments at the point of a fiber
break, and the fiber segments in which an entanglement or
deformation occurs--are all termed an interrupting fiber segment
herein, or more commonly for shorthand purposes, are often simply
termed "fiber ends": these interrupting fiber segments form the
terminus or end of an unaffected length of fiber, even though in
the case of entanglements or deformations there often is no actual
break or severing of the fiber. Such interrupting fiber segments
are described in greater detail in issued U.S. Pat. No. 6,607,624,
which is incorporated herein by reference.
[0060] The fiber ends have a fiber form (as opposed to a globular
shape as sometimes obtained in meltblowing or other previous
methods) but are usually enlarged in diameter over the medial or
intermediate portions of the fiber; usually they are less than 300
micrometers in diameter. Often, the fiber ends, especially broken
ends, have a curly or spiral shape, which causes the ends to
entangle with themselves or other fibers. And the fiber ends may be
bonded side-by-side with other fibers, e.g., by autogenous
coalescing of material of the fiber end with material of an
adjacent fiber.
[0061] Webs of the invention may be coherent upon collection, or
steps may be taken after collection to make them coherent or
increase their coherency. Such steps include bonding between
fibers, including thermal bonding, adhesive bonding with added
adhesive or bonding fibers, or mechanical bonding such as achieved
by entanglement such as hydroentangling. The basic operating
procedure of hydroenetangling is described in, for example, U.S.
Pat. No. 5,389,202, issued Feb. 14, 1995, to Everhart et al. (see
for example columns 8 and 9), the contents of which are
incorporated herein by reference.
[0062] Considering the bonding aspects of the invention, the
invention can be understood as a method for preparing a fibrous web
comprising 1) preparing extruded filaments from an
elastic-fiber-forming liquid, 2) processing and attenuating the
extruded filaments to solid collectible fibers having molecular
orientation, 3) collecting the fibers as a nonwoven web, 4)
annealing the collected fibers by exposing them to a temperature
that is above their shrinking temperature but less than their
relaxation temperature to make the web dimensionally stable while
retaining sufficient molecular orientation that the fibers exhibit
a birefringence of at least 1.times.10.sup.-5, and 5) bonding the
fibers (thermally, mechanically, or otherwise) to give the web
increased coherency. The steps need not be in the order listed; for
example, step (4) could follow step (5).
[0063] In thermal bonding, the best bonds are obtained when the
bonding portion of a fiber flows sufficiently to form a
circumference-penetrating type of bond as illustrated in the
schematic diagrams FIGS. 4a and 4b. Such bonds develop more
extensive contact between bonded fibers, and the increased area of
contact increases the strength of the bond. FIG. 4a illustrates a
bond in which one fiber or segment 52 deforms while another fiber
or segment 53 essentially retains its cross-sectional shape. FIG.
4b illustrates a bond in which two fibers 55 and 56 are bonded and
each deforms in cross-sectional shape. In both FIGS. 4a and 4b,
circumference-penetrating bonds are shown: the dotted line 54 in
FIG. 4a shows the shape the fiber 52 would have except for the
deformation caused by penetration of the fiber 53; and the dotted
lines 57 and 58 in FIG. 4b show the shapes the fibers 56 and 55,
respectively, would have except for the bond. FIG. 4c schematically
illustrates two fibers bonded together in a bond that may be
different from a circumference-penetrating bond, in which material
from exterior portions (e.g., a concentric portion or portions) of
one or more of the fibers has coalesced to join the two fibers
together without actually penetrating the circumference of either
of the fibers.
[0064] The bonds pictured in FIGS. 4a-4c can be autogenous bonds,
e.g., obtained by heating a web of the invention without
application of calendering pressure. Such bonds allow softer hand
to the web and greater retention of loft under pressure. However,
pressure bonds as in point-bonding or area-wide calendering are
also useful. Bonds can also be formed by application of infrared,
laser, ultrasonic or other energy forms that thermally or otherwise
activate bonding between fibers. Solvent application may also be
used. Webs can exhibit both autogenous bonds and pressure-formed
bonds, as when the web is subjected only to limited pressure that
is instrumental in only some of the bonds. Webs having autogenous
bonds are regarded as autogenously bonded herein, even if other
kinds of pressure-formed bonds are also present in limited amounts.
In general, in practicing the invention a bonding operation is
desirably selected that allows some longitudinal segments to soften
and be active in bonding to an adjacent fiber or portion of a
fiber, while other longitudinal segments remain passive or inactive
in achieving bonds.
[0065] The invention is particularly useful as a
direct-web-formation process in which a fiber-forming polymeric
material is converted into a web in one essentially direct
operation (including extrusion of filaments, processing and
solidifying of the filaments, collection of the processed
filaments, and, if needed, further processing to transform the
collected mass into a web). Nonwoven fibrous webs of the invention
preferably comprise directly collected fibers or directly collected
masses of fibers, meaning that the fibers are collected as a
web-like mass as they leave the fiber-forming apparatus. Other
components such as staple fibers or particles or other directly
formed fibers can be collected together with the mass of directly
formed fibers of the invention.
[0066] The average diameter of fibers prepared according to the
invention may range widely. Microfiber sizes (about 10 micrometers
or less in diameter) may be obtained and offer several benefits;
but fibers of larger diameter can also be prepared and are useful
for certain applications; often the fibers are 20 micrometers or
less in diameter. Fibers of circular cross-section are most often
prepared, but other cross-sectional shapes may also be used.
Depending on the operating parameters chosen, the collected fibers
may be rather continuous or essentially discontinuous.
[0067] As indicated above, according to the invention filaments are
processed at fast velocities. For example, polypropylene is not
known to have been processed at apparent filament speeds of 8000
meters per minute through a processing chamber, but such apparent
filament speeds are possible with apparatus as shown in FIGS. 1-3
(the term apparent filament speed is used, because the speeds are
calculated, e.g., from polymer flow rate, polymer density, and
average fiber diameter). A filament speed of 2800 meters/minute or
higher has been found to provide advantages in the present
invention; generally we prefer to operate at a filament speed of at
least 4000 or 5000 meters per minute. Even faster apparent filament
speeds have been achieved on apparatus as shown in FIGS. 1-3, e.g.,
10,000 meters per minute, or even 14,000 or 18,000 meters per
minute, and these speeds can be obtained with a wide range of
polymers.
[0068] In addition, large volumes of polymer can be processed per
orifice in the extrusion head, and these large volumes can be
processed while at the same time moving extruded filaments at high
velocity. This combination gives rise to a high productivity
index--the rate of polymer throughput (e.g., in grams per orifice
per minute) multiplied by the apparent velocity of extruded
filaments (e.g., in meters per minute). The process of the
invention can be readily practiced with a productivity index of
9000 or higher, even while producing filaments that average 20
micrometers or less in diameter.
[0069] FIGS. 6 and 7 illustrate some of the terminology and
concepts involved in the invention. FIG. 6 is a schematic diagram
of a typical extruded filament 80 prepared from a molten
fiber-forming material and processed into a fiber according to the
invention; the figure shows the filament as it is processed and
changes dimensions, but does not show the filament actually passing
through attenuating or other apparatus. Dimensions in the schematic
diagram are greatly enlarged and not intended to accurately
represent true dimensions.
[0070] As shown in FIG. 6, the filament is extruded from an
extrusion head 81 and travels to a collector 82. The filament
passes through a processing chamber, but for purposes of
illustration, the processing chamber 83 is drawn at extremely small
scale in comparison to the filament and placed at the side of the
threadline (rather than in its normal position on the
threadline).
[0071] When the molten filament 80 leaves the extrusion head 81, it
typically swells in size because of its release from the confines
of the extrusion orifice. Then it narrows in diameter because of
drawing forces applied to it, e.g., the pull of air blown threw the
processing chamber. The extruded filament continues to narrow in
diameter as it moves further away from the extrusion head and
toward the collector, during which time the filament is
cooling--e.g., because cooler air such as ambient or quenching
streams of air or other gas typically surrounds the fiber.
Narrowing in diameter continues essentially until the filament
reaches the solidification/melting temperature of the filamentary
material (for crystalline or semicrystalline materials) or the
glass transition temperature (for amorphous materials); the
location where the filament reaches the solidification/melting
temperature or the glass transition temperature is marked on the
threadline as a region 85, as well as by a bar marked
T.sub.m/T.sub.g to represent that this region need not be a precise
point but typically will extend for a distance along the
threadline. From the region 85 onward toward the collector the
filament can essentially retain its diameter; some narrowing can
continue if the drawing forces applied to the filament are large
enough.
[0072] According to the invention the relative positions of the
region 85 and the processing chamber 83 can be varied. One
illustrative position for the processing chamber is shown in solid
lines, but the processing chamber can also occupy different
positions within a range suggested by dotted lines; the dotted
lines are not intended to fully describe or exhaust the possible
positions of the processing chamber. In other words, the extruded
filament 80 can reach a temperature corresponding to T.sub.m or
T.sub.g before it reaches the processing chamber, while it is in
the processing chamber, or after it leaves the processing
chamber.
[0073] After the extruded filament leaves the processing chamber it
generally travels through a region of turbulence. Turbulence occurs
as the currents passing through the processing chamber reach the
unconfined space at the end of the chamber, where the pressure that
existed within the chamber is released. The current stream widens
as it exits the chamber, and eddies develop within the widened
stream. These eddies--whirlpools of currents running in different
directions from the main stream--subject the filament to forces
different from the straight-line forces the filament is subjected
to within the chamber and before reaching the chamber. For example,
the filament can undergo a to-and-fro flapping, illustrated at 87,
and be subjected to forces that have a vector component transverse
to the length of the filament. The forces applied in a turbulent
field past the processing chamber may be the strongest experienced
by an extruded filament during travel from an extrusion head to a
collector.
[0074] FIG. 6 also schematically shows typical ranges of positions
along the threadline where the filament may be at its orientation
temperature or orientation-locking temperature assuming T.sub.m or
T.sub.g is in the position shown. As shown in FIG. 6 the filament
can generally be at orienting temperature within the range of
positions represented by the line 88, when T.sub.m or T.sub.g is in
the position shown. And the filament can generally achieve the
orientation-locking temperature within the range of positions
represented by the line 89, when T.sub.m or T.sub.g is in the
position shown.
[0075] FIG. 7 is another schematic diagram, showing filament 80
without identifying a particular region where the filament reaches
T.sub.m or T.sub.g. The intention of this diagram is to show that
an extruded filament can be at the orienting temperature or the
orientation-locking temperature at a variety of distances from the
extruder. As shown in FIG. 7 the range of positions at which the
filament remains at the orienting temperature, shown by the line
88', can extend from the extrusion head 81 (where the
filament-forming material is at a temperature (T.sub.E) that is
typically 30-40.degree. C. above T.sub.m or T.sub.g) to a position
near the collector. And conversely, the range of positions at which
the filament reaches the orientation-locking temperature,
represented by the line 89', can extend from a position near the
collector 82 to a position before (upstream of) the processing
chamber 83.
[0076] Various processes conventionally used as adjuncts to
fiber-forming processes may be used in connection with filaments as
they enter or exit from the attenuator, such as spraying of
finishes or other materials onto the filaments, application of an
electrostatic charge to the filaments, application of water mists,
etc. In addition, various materials may be added to a collected
web, including bonding agents, adhesives, finishes, and other webs
or films.
[0077] Although there typically is no reason to do so, filaments
may be blown from the extrusion head by a primary gaseous stream in
the manner of that used in conventional meltblowing operations.
Such primary gaseous streams cause an initial attenuation and
drawing of the filaments.
EXAMPLES 1-4
[0078] Apparatus as shown in FIGS. 1-3 was used to prepare four
different fibrous webs. Two of the webs, Examples 1 and 2, were
formed from a polyurethane resin (PS440-200 supplied by Huntsman
Polyurethanes of Salt Lake City, Utah, having a melt flow rate of
25 g/10 min.). The polyurethane was heated to 221.degree. C. in the
extruder (temperature measured in the extruder 12 near the exit to
the pump 13), and the die was heated to a temperature as listed in
Table 1 below.
[0079] The other two webs, Examples 3 and 4, were formed from an
ultra-low-density polyethylene resin (Engage 8411 available from
Dupont-Dow Elastomers, Wilmington Del., which includes 33% octene
as a co-monomer (percentages are weight percents unless otherwise
indicated) and has a melt index of 18 g/10 minute). The
polyethylene was heated to 271.degree. C. in the extruder
(temperature measured in the extruder 12 near the exit to the pump
13), and the die was heated to a temperature as listed in Table 1
below.
[0080] In all four examples the extrusion head or die had 16 rows
of orifices; in Examples 1 and 2 each row had 32 orifices, making a
total of 512 orifices; in Examples 3 and 4 each row had 16
orifices, making a total of 256 orifices. The die had a transverse
length of 7.875 inches (200 millimeters). The hole diameter was
0.040 inch (0.889 mm) and the L/D ratio was 6. The polymer flow
rate was 0.89 g/hole/minute and 0.98 g/hole/minute in Examples 3
and 4.
[0081] The distance between the die and attenuator (dimension 17 in
FIG. 1) was 37 inches (about 94 centimeters), and the distance from
the attenuator to the collector (dimension 21 in FIG. 1) was 26.75
inches (68 centimeters). The air knife gap (the dimension 30 in
FIG. 2) was 0.030 inch (0.76 millimeter); the attenuator body angle
(.alpha. in FIG. 2) was 30.degree.; room temperature air was passed
through the attenuator; and the length of the attenuator chute
(dimension 35 in FIG. 2) was 6 inches (152 millimeters). The air
knife had a transverse length (the direction of the length 25 of
the slot in FIG. 3) of about 251 millimeters; and the attenuator
body 28 in which the recess for the air knife was formed had a
transverse length of about 330 millimeters. The transverse length
of the wall 36 attached to the attenuator body was 14 inches (406
millimeters).
[0082] Other attenuator parameters were as described in Table 1
(below at the end of the examples), including the gaps at the top
and bottom of the attenuator (the dimensions 33 and 34,
respectively, in FIG. 2); the total volume of air passed through
the attenuator (given in actual cubic meters per minute, or ACMM;
about half of the listed volume was passed through each air knife
32); and filament speed (apparent). Clamping pressure on the walls
of the attenuator was about 500 kilopascals in Examples 1 and 2 and
about 550 kilopascals in Examples 3 and 4, both of which pressures
tended to hold the walls against movement during the process.
[0083] The webs of Examples 1 and 2 were subjected to annealing by
passing them under a hot air knife set at 95 degrees C. for an
exposure time of 0.11 second with a face velocity of 21 meters per
second with a slot width (the machine-direction dimension) of 1.5
inches (3.8 centimeters).
[0084] The webs of Examples 3 and 4 were subjected to annealing by
passing them under a hot air knife set at 90 degrees C. for an
exposure time of 0.19 second with a face velocity of 19 meters per
second and a slot width of 1.5 inches (3.8 centimeters).
[0085] Optical examinations including birefringence studies using a
polarized microscope were performed on the prepared webs (after
annealing) to examine the degree of orientation within the fibers
of the webs, and the results are reported in Table 2 (at the end of
the examples). The birefringence of the fibers was measured using a
Nikon Eclipse E600 polarized microscope manufactured by Nikon
Instruments Inc, 1300 Walt Whitman Road, Melville, N.Y. The Berek
compensator technique outlined by Berek Compensator Instructions,
Nichika Corporation, Japan, Revision Aug. 10, 2001, was used in
making the measurements. A protocol for the measurement is as
follows: Carefully align the microscope to center objectives,
optics, condenser and light source. Place the fiber to be measured
in the center of the view field. Rotate the stage to the extinction
position closest to North-South alignment in the view field. Rotate
the sample 45 degrees counterclockwise. Using the Berek compensator
turn the drum clockwise until the black band appears in the center
of the fiber. Note the reading in degrees. Using the Berek
compensator, turn the drum counterclockwise until the black band
appears in the center of the fiber. Note the reading in degrees.
The inclination is the difference between the readings divided by
two.
[0086] The retardation value may be obtained from a table provided
by the manufacturer or by calculation knowing the machine constant;
for Examples 1-4, the calculation equation is R=10000 F(.sub.i)
multiplied by C/10000, where F(.sub.i) is obtained from a table
provided by the manufacturer and C/10000 is 1.009. The diameter of
the fiber is then measured at the point where the birefringence was
measured and birefringence is calculated from retardation divided
by diameter. Values were reported as an average of a minimum of ten
readings of representative single fibers.
[0087] In a subsequent bonding step, the webs of Examples 3 and 4
were heat sealed using a two-roll calender. The calender settings
were as follows:
[0088] Top Roll--
[0089] Point Bond Diamond pattern with a 20% bond area
[0090] Points have a 1 mm.times.1 mm land area.
[0091] 22 inches (56 cm) wide (along the axis of the drum) with an
outer diameter of 10 inches (25.4 cm)
[0092] Temperature of oil in roll=155.degree. F. (68 degrees
C.)
[0093] Speed of web 5 feet per minute (1.52 meters per minute)
[0094] Bottom Roll--
[0095] Smooth Steel
[0096] 22 inches (56 cm) wide (along the axis of the drum) with an
outer diameter of 10 inches (25.4 cm)
[0097] Temperature of oil in roll=155.degree. F. (68.degree.
C.)
[0098] Speed of web 5 feet per minute (1.52 meters per minute)
[0099] Nip Pressure--100 psi (689 kPa)
[0100] Tensile tests were performed on samples of the webs with an
Instron Model 5544 tensile testing machine. Three machine-direction
samples (sample cut from the web in the same direction that the
fibers were made) and three cross-direction samples were tested
using a 10-inch (25.4 centimeter)/minute crosshead speed, a 2-inch
(5.08-centimeter) jaw gap, and sample strips cut to 1.times.4
inches (2.54 by 5.08 centimeter). When similar samples are
stretched to 200% their original length and released, they quickly
(within seconds) recover to less than 125% their original
length.
1 Tensile Strength Average Tensile Strain Example (Newtons)
(Percent) 1 4.4 680 2 4.73 780 3 4.9 350 4 5.8 368
EXAMPLES 5 AND 6
[0101] Apparatus as shown in FIGS. 1-3 was used to prepare two
different fibrous webs from blends of diblock polymers and other
components. Example 5 used a blend of 60% of a styrenic block
copolymer (Kraton.RTM. D1119P available from Kraton.RTM. Polymers
Houston Tex., consisting of about 34% STS copolymer and about 66%
SI diblock with about 22% styrene content) and 40% mineral oil
(Chevron Superla.RTM. White Oil 31 available from Chevron Texaco
Corporation Midland Tex.). The blend was heated to 253 degrees C.
in the extruder (temperature measured in the extruder 12 near the
exit to the pump 13), and the die was heated to a temperature as
listed in Table 1 below.
[0102] Example 6 used a blend consisting of 90% of a different
styrenic block copolymer (Kraton.RTM. RP 6936 available from
Kraton.RTM. Polymers Houston Tex.) and 10% of a paraffin oil
("Paraffin Prills Purified," available from J. T. Baker,
Phillipsburg, N.J.). The blend was heated to 241 degrees C. in the
extruder (temperature measured in the extruder 12 near the exit to
the pump 13), and the die was heated to a temperature as listed in
Table 1 below.
[0103] The extrusion head or die had two rows of orifices, and each
row had 16 orifices, making a total of 32 orifices. The die had a
transverse length of 4.125 inches (104.8 millimeters). The hole
diameter was 0.040 inch (0.889 mm) and the L/D ratio was 6. The
polymer flow rate was 0.87 g/hole/minute for both examples.
[0104] The distance between the die and attenuator (dimension 17 in
FIG. 1) was 2.7 inches (about 6.8 centimeters), and the distance
from the attenuator to the collector (dimension 21 in FIG. 1) was
22 inches (59 centimeters). The air knife gap (the dimension 30 in
FIG. 2) was 0.050 inch (0.1.3 millimeter); the attenuator body
angle (.alpha. in FIG. 2) was 30.degree.; room temperature air was
passed through the attenuator; and the length of the attenuator
chute (dimension 35 in FIG. 2) was 3 inches (76 millimeters). The
air knife had a transverse length (the direction of the length 25
of the slot in FIG. 3) of about 121 millimeters; and the attenuator
body 28 in which the recess for the air knife was formed had a
transverse length of about 156 millimeters. The transverse length
of the wall 36 attached to the attenuator body was 10 inches (254
millimeters).
[0105] Other attenuator parameters were also varied as described in
Table 1 including the gaps at the top and bottom of the attenuator
(the dimensions 33 and 34, respectively, in FIG. 2); and the total
volume of air passed through the attenuator (given in actual cubic
meters per minute, or ACMM; about half of the listed volume was
passed through each air knife 32). No clamping pressure was applied
to the walls of the attenuator, so the walls were free to move
under the force of air pressure.
[0106] For Examples 5 and 6, samples were held in a constant
temperature oven for 5 minutes at 70 degrees C. and returned to
room temperature before measurements were taken.
[0107] Optical examinations including birefringence studies using a
polarized microscope were performed on the prepared webs (after
annealing) to examine the degree of orientation within the fibers
of the webs, and the results are reported in Table 2 (at the end of
the examples).
EXAMPLE 7
[0108] Apparatus as shown in FIGS. 1-3 was used to prepare webs
from an elastomeric polyethylene-based resin (Engage 8402 (22%
octene comonomer content) available from Dupont-Dow Elastomers
Wilmington Del.). The resin was heated to 240.degree. C. in the
extruder (temperature measured in the extruder 12 near the exit to
the pump 13), and the die was heated to a temperature as listed in
Table 1 below. The extrusion head or die had 16 rows of orifices,
and each row had 32 orifices, making a total of 512 orifices. The
die had a transverse length of 8.0 inches (20.3 millimeters). The
hole diameter was 0.040 inch (0.889 mm) and the L/D ratio was 6.
The polymer flow rate was 0.5 g/hole/minute.
[0109] The distance between the die and attenuator (dimension 17 in
FIG. 1) was 44 inches (about 112 centimeters), and the distance
from the attenuator to the collector (dimension 21 in FIG. 1) was
37.5 inches (92 centimeters). The air knife gap (the dimension 30
in FIG. 2) was 0.050 inch (0.1.27 millimeter); the attenuator body
angle (.alpha. in FIG. 2) was 30.degree.; room temperature air was
passed through the attenuator; and the length of the attenuator
chute (dimension 35 in FIG. 2) was 6 inches (152 millimeters). The
air knife had a transverse length (the direction of the length 25
of the slot in FIG. 3) of about 251 millimeters; and the attenuator
body 28 in which the recess for the air knife was formed had a
transverse length of about 330 millimeters. The transverse length
of the wall 36 attached to the attenuator body was 14 inches (406
millimeters). The clamping pressure on the walls of the processing
chamber was 900 kilopascal, which held the walls against movement
during the process.
[0110] Other attenuator parameters were also varied as described in
Table 1, including the gaps at the top and bottom of the attenuator
(the dimensions 33 and 34, respectively, in FIG. 2); and the total
volume of air passed through the attenuator (given in actual cubic
meters per minute, or ACMM; about half of the listed volume was
passed through each air knife 32).
[0111] The collected batt of Example 7 was hydroentangled with a
conventional hydraulic entangling system consisting of 6
manifolds/jets (three above and three below the web). The basic
operating procedure is described in, for example, U.S. Pat. No.
5,389,202, issued Feb. 14, 1995, to Everhart et al. (see for
example columns 8 and 9), the contents of which are incorporated
herein by reference. Each manifold had an orifice size of 120
microns diameter. Orifices were positioned in a single row at a
spacing of about 16 orifices per linear centimeter of manifold.
Manifold water pressure was successively ramped up to 10,000 kPa
which generated high energy fine columnar jets. The hydraulic
entangling surface was a single layer 100 stainless steel twill
wire backing manufactured by Albany International, Portland, Term.
The hydraulic entangling surface was a single-layer standard-weave
14.times.13 polyester netting with 28 percent open-area
manufactured by Albany International, Portland, Term. The material
of Example 7 was passed under the manifolds at a line speed of
about 5 meters per minute where they were washed and consolidated
by the pressurized jets of water. The resulting composite web was
dried utilizing a conventional laboratory handsheet dryer at 80
degrees C. to dry and anneal the sample. Though shrinking of fibers
occurred during the annealing step, the web remained as an integral
well-formed sheet material, and was an elastic, soft and
dimensionally stable material after annealing was completed.
[0112] Optical examinations including birefringence studies using a
polarized microscope were performed on the prepared webs (after
annealing) to examine the degree of orientation within the fibers
of the webs, and the results are reported in Table 2 (at the end of
the examples).
2TABLE 1 Die Tem- Attenuator Attenuator Filament Ex- per- Gap Gap
Attenuator Air Speed ample ature Top Bottom Air Flow Pressure
(meters/ No. (.degree. C.) (mm) (mm) (ACMM) kPa minute) 1 220 5.1
5.0 3.8 120 3600 2 220 5.1 5.0 3.1 81 7000 3 270 5.1 5.0 3.1 81
4500 4 270 5.1 5.0 4.8 136 9000 5 254 8 8 2.5 141 6800 6 260 10 10
0.8 35 5200 7 250 7.5 7.1 8.9 136 5300
[0113]
3TABLE 2 Fiber's Color Seen Fiber Diameter Through Polarized
Example (.mu.m) Birefringence Microscope 1 13.25 0.050
Peach-Red-Blue 2 17 0.040 Orange-Blue 3 16 0.031 Gray-Amber 4 11
0.040 Gray-Amber 5 32.3 0.0052 Gray 6 21.5 0.0016 Gray 7 11.6 0.037
Gray-Amber
* * * * *