U.S. patent application number 11/295285 was filed with the patent office on 2006-04-20 for elastomeric multicomponent fibers, nonwoven webs and nonwoven fabrics.
This patent application is currently assigned to BBA Nonwovens Simpsonville. Invention is credited to Jared A. Austin, Ruediger Kesselmeier.
Application Number | 20060084342 11/295285 |
Document ID | / |
Family ID | 32176654 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060084342 |
Kind Code |
A1 |
Austin; Jared A. ; et
al. |
April 20, 2006 |
Elastomeric multicomponent fibers, nonwoven webs and nonwoven
fabrics
Abstract
A bonded web of multi-component strands that include a first
polymeric component and a second polymeric component is capable of
overcoming a number of problems associated with nonwoven webs
including both stickiness and blocking. The first polymeric
component and second polymeric component are arranged in
substantially distinct zones extending longitudinally along at
least a portion of a length of the strands which make up the web
with the second component containing a zone constituting at least a
portion of the peripheral surface of the strand. The first
polymeric component also has an elasticity which is greater than
that of the second polymer component. A process producing
elastomeric spunbonded nonwoven fabrics which utilizes the
activation by incremental stretching of the strands is also
provided.
Inventors: |
Austin; Jared A.; (Greer,
SC) ; Kesselmeier; Ruediger; (Naiiheim, DE) |
Correspondence
Address: |
Robert M. O'Keefe;O'KEEFE, EGAN & PETERMAN, LLP
Building C, Suite 200
1101 Capital of Texas Highway South
Austin
TX
78746
US
|
Assignee: |
BBA Nonwovens Simpsonville,
The Dow Chemical Company
Corovin GMBH
|
Family ID: |
32176654 |
Appl. No.: |
11/295285 |
Filed: |
December 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10692313 |
Oct 23, 2003 |
6994763 |
|
|
11295285 |
Dec 6, 2005 |
|
|
|
60420949 |
Oct 24, 2002 |
|
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|
Current U.S.
Class: |
442/361 ;
442/364 |
Current CPC
Class: |
Y10T 442/637 20150401;
Y10T 442/627 20150401; D01F 8/16 20130101; D04H 3/14 20130101; Y10T
442/602 20150401; Y10T 442/601 20150401; Y10T 442/69 20150401; D01F
8/06 20130101; Y10T 442/641 20150401; D06C 3/00 20130101; D04H 3/00
20130101 |
Class at
Publication: |
442/361 ;
442/364 |
International
Class: |
D04H 13/00 20060101
D04H013/00 |
Claims
1-17. (canceled)
18. An elastic nonwoven fabric comprising: a plurality of
multicomponent strands randomly arranged to form a nonwoven web; a
multiplicity of bond sites or substantially randomly intertwined
strands bonding the strands together to form a coherent bonded
nonwoven web; the strands of the web including first and second
polymer components, the first polymer component comprising an
elastomeric polymer, and the second polymer component comprising a
non-elastomeric polymer; and wherein first portions of the
multicomponent strands of the web are stretch-activated and
elastic.
19. The fabric according to claim 18, wherein other portions of the
multicomponent strands of the web are not stretch-activated and
less elastic than the first portions.
20. The fabric according to claim 19, including narrow, spaced
apart longitudinally extending stretch-activated elastic zones in
the fabric, separated by intervening longitudinally extending
non-activated, substantially less elastic zones.
21. The fabric according to claim 20, wherein the first polymer
component comprises an elastomeric polyurethane, elastomeric
polyethylene, elastomeric polypropylene, styrene block copolymers
or blends thereof and the second polymer component comprises a
polyolefin.
22. The fabric according to claim 18 wherein the second polymer
component is polypropylene, polyethylene, or blend thereof.
23. The fabric according to claim 18, wherein the first and second
polymer components are arranged in a sheath core configuration, and
the stretch-activated portions of the stands have corrugations in
the sheath and in the core of the strands.
24-25. (canceled)
26. A multicomponent fiber comprising an elastomeric component and
a component have less elasticity than the elastomeric component,
said multicomponent fiber exhibiting an overall helical
configuration which includes the components having less elasticity
bulked around the elastomeric component.
27. The fiber according to claim 26, wherein the fiber has been
subjected to incremental stretching.
28-30. (canceled)
Description
[0001] This application claims priority to provisional application
Ser. No. 60/420,949, filed Oct. 24, 2002, incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The invention relates to nonwoven fabrics produced from
multi-component strands, processes for producing nonwoven webs and
products using the nonwoven webs. The nonwoven webs of the
invention can be produced from multi-component strands including at
least two components, a first, elastic polymeric component and a
second, extensible but less elastic polymeric component.
BACKGROUND OF THE INVENTION
[0003] In recent years there has been a dramatic growth in the use
of nonwovens, particularly elastomeric nonwovens, in disposable
hygiene products. For example, elastic nonwoven fabrics have been
incorporated into bandaging materials, garments, diapers, support
clothing, and feminine hygiene products. The incorporation of
elastomeric components into these products provides improved fit,
comfort and leakage control.
[0004] However, many laminates composed of an elastic film bonded
to one or two non-elastic nonwoven layer or layers must be
"activated" to provide suitable tensile and recovery properties. In
particular, many of these elastic film/non-elastic nonwoven
laminates must be subjected to an initial drawing or stretching
process to develop their ultimate properties. Traditional
stretching equipment associated with wide web products include
conventional draw rolls and tenter frames. Unfortunately, draw
rolls can impart non-uniform stretching when used in conjunction
with elastomeric fabrics. Tenter frames are expensive and require a
significant amount of space within manufacturing facilities.
[0005] The present inventors have recognized that there remains a
need in the art for elastomeric nonwoven fabrics exhibiting
improved drape and which further may be produced economically.
SUMMARY OF THE INVENTION
[0006] The present invention is based, at least in part, on the
surprising discovery that bonded webs made from a plurality of
strands comprising at least two polymeric components where one
component is elastic and another component is less elastic but
extensible wherein the bonded nonwoven web has been subjected to
incremental stretching, can overcome a variety of problems in the
field.
[0007] The present invention is generally directed to methods for
producing elastic nonwoven webs and fabrics that may include melt
spinning a plurality of multicomponent strands having first and
second polymer components longitudinally coextensive along the
length of the filament. The first component is formed from an
elastomeric polymer and the second component is formed from a
non-elastomeric polymer. The melt spun strands are formed into a
nonwoven web which is subsequently bonded and incrementally
stretched in at least one direction to activate the elastic
properties of the nonwoven web. Incremental stretching is
accomplished by supporting a web at closely spaced apart locations
and then stretching the unsupported segments of the web between
these closely spaced apart locations. This is most easily
accomplished by passing the web through a nip formed between a pair
of meshing corrugated rolls, which have an axis of rotation
perpendicular to the direction of web travel. Incremental
stretching apparatuses designed for machine direction, cross
direction, and diagonal stretching are described in U.S. Pat. No.
5,861,074, incorporated herein by reference. The incremental
stretching step may include stretching the web so that portions of
the multicomponent strands are stretch-activated and become
elastic, while other portions of the strands are not stretch
activated and are substantially less elastic. In advantageous
embodiments, the web is incrementally stretched so that
substantially all of the multicomponent strands are uniformly
stretch-activated and become elastic.
[0008] In further beneficial aspects, the incremental stretching
step includes incrementally stretching the web in both the machine
direction and the cross-machine direction. In one embodiment, the
incremental stretching may be accomplished by directing the web
through at least one pair of interdigitating stretching rollers at
a temperature less than about 35.degree. C. In one aspect of such
embodiments, the interdigitating stretching rollers give rise to
narrow, spaced apart longitudinally extending stretch-activated
elastic zones within the fabric, separated by intervening
longitudinally extending non-activated zones that are substantially
less elastic. In beneficial aspects of the invention, the
incremental stretching may be accomplished by directing an
incrementally stretched web through a second pair of
interdigitating stretching rollers at a temperature less than about
35.degree. C. to stretch activate a second portion of the
non-activated strands within the web. In further advantageous
aspects, mechanical incremental stretching may be performed in
conjunction with an impinging fluid directed onto the surface of
the web. Advantageously, the impinging fluid is air or water.
[0009] With respect to the multicomponent strands, the first and
second components can be derived from any of a wide variety of
polymers. In one embodiment of the invention, the first polymer
component is formed from an elastomeric polyurethane, elastomeric
styrene block copolymer, or an elastomeric polyolefin and the
second polymer component is formed from a polyolefin that is less
elastic than the first component.
[0010] Aspects of the invention are directed to the production of
strands having a sheath/core configuration in which the step of
incremental stretching forms corrugations within both the sheath
and the core of the strands. Individual strands are lengthy,
generally extruded continuously and are infinite in length. The
strands are not broken into smaller lengths after the activation by
incremental stretching; rather, the strands have generally been
formed in structures that have a corrugated, bellows-like
configuration throughout substantially the entire length of the
nonwoven web that has been subjected to the incremental stretching.
This corrugated appearance and structure can be observed using
standard microscopy techniques, and are difficult if not impossible
to detect using the unaided eye. The thickness of the individual
folds in the incrementally stretched and corrugated portions of the
nonwoven web are essentially the width of the sheath component of
the strand, and as such are typically on the order of 0.1 to 2
microns in thickness. Alternative aspects of the invention involve
melt spinning strands having either segmented pie-wedge or tipped
multilobal configurations and using incremental stretching to split
the components apart from one another or form corrugations,
serpentines, or other forms of texture down the length of the
strands.
[0011] The present invention further includes elastic nonwoven
fabrics produced by the methods of the invention, as well as
multicomponent elastic fibers. In one advantageous embodiment,
multicomponent elastomeric fibers exhibiting an overall helical
configuration (similar to the appearance of a candy cane or barber
pole) are provided. In beneficial aspects of these embodiments, the
helical fibers may further be split to produce helically wrapped
fibers of the non-elastomeric components around one or more
elastomeric components.
[0012] In one broad respect, this invention is a method for
producing an elastic nonwoven fabric, comprising: incrementally
stretching a nonwoven web in at least one direction to activate the
elastic properties of the nonwoven web and to form the elastic
nonwoven fabric, wherein the nonwoven web comprises a plurality of
multicomponent strands having first and second polymer components
longitudinally coextensive along the length of the strands, said
first component comprising an elastomeric polymer, and said second
polymer component comprising a polymer less elastic than the first
polymer component. In one embodiment, the nonwoven web can be
formed by: melt spinning a plurality of multicomponent strands
having first and second polymer components longitudinally
coextensive along the length of the strands, said first component
comprising an elastomeric polymer, and said second polymer
component comprising a non-elastomeric polymer; forming the
multicomponent strands into a nonwoven web; and bonding or
intertwining the strands to form a coherent bonded nonwoven web. In
one embodiment, the incremental stretching of the web may comprise
stretching the fabric so that portions of the multicomponent
strands are stretch-activated and become elastic, while other
portions of the strands are not stretch-activated and are
substantially less elastic. In one embodiment, the incrementally
stretching the web may comprises stretching the fabric so that
substantially all of the multicomponent strands are
stretch-activated and become elastic. In one embodiment, the
incrementally stretching the web comprises incrementally stretching
the web in both the machine direction and in the cross-machine
direction. In one embodiment, the incrementally stretching the web
comprises directing the web through at least one pair of
interdigitating stretching rollers at a temperature less than 35
degrees Centigrade. In one embodiment, directing the web through
interdigitating stretching rollers includes forming narrow, spaced
apart longitudinally extending stretch-activated elastic zones in
the fabric, separated by intervening longitudinally extending
non-activated zones that are substantially less elastic. In one
embodiment, the incrementally stretching the web comprises
directing the web through a first pair of interdigitating
stretching rollers to stretch activate at a first portion of the
web and subsequently directing the web through a second pair of
interdigitating stretching rollers to stretch activate a second
portion of the non-activated strands within the web. In one
embodiment, the incrementally stretching the web further comprises
impinging fluid onto the surface of the web. In one embodiment, the
fluid is either water or air. In one embodiment, the first polymer
component comprises an elastomeric polyurethane, and the second
polymer component comprises a polyolefin that is less elastic than
the elastomeric polyurethane, and in another embodiment the second
polymer component is polypropylene, polyethylene, or a blend
thereof. In one embodiment, the melt spinning comprises arranging
the first and second polymer components in the strand cross-section
to form a sheath/core configuration, and wherein the step of
incrementally stretching includes forming corrugations in both the
sheath and the core of the strands. In one embodiment, the melt
spinning comprises arranging the first and second polymer
components in the strand cross-section to form the polymer
components in a segmented pie configuration, and wherein the step
of incrementally stretching includes splitting the first and second
polymer components apart from one another. In one embodiment, the
melt spinning comprises arranging the first and second polymer
components in the strand cross-section to form polymer components
in a tipped multilobal configuration, and wherein the step of
incrementally stretching includes either splitting the first and
second polymer components apart from one another or forming crimps
or forming serpentines or other non-linear, random textures down
the length of the strand. In one embodiment, at least a portion of
the multicomponent strands has a sheath/core configuration. In one
embodiment, at least a portion of the multicomponent strands have a
trilobal or tipped trilobal configuration. Any combination of these
embodiments or other embodiments described herein can be employed
in the practice of this invention.
[0013] In another broad respect, this invention is an elastic
nonwoven fabric comprising: a plurality of multicomponent strands
randomly arranged to form a nonwoven web; a multiplicity of bond
sites or substantially randomly intertwined strands bonding the
strands together to form a coherent bonded nonwoven web; the
strands of the web including first and second polymer components,
the first polymer component comprising an elastomeric polymer, and
the second polymer component comprising a non-elastomeric polymer;
and wherein first portions of the multicomponent strands of the web
are stretch-activated and elastic. In one embodiment, other
portions of the multicomponent strands of the web are not
stretch-activated and less elastic than the first portions. In one
embodiment, the fabric includes narrow, spaced apart longitudinally
extending stretch-activated elastic zones in the fabric, separated
by intervening longitudinally extending non-activated,
substantially less elastic zones. In one embodiment, the first
polymer component comprises an elastomeric polyurethane, and the
second polymer component comprises a polyolefin. In one embodiment,
the second polymer component is polypropylene, polyethylene, or
blend thereof. In one embodiment, the first and second polymer
components are arranged in a sheath core configuration, and the
stretch-activated portions of the stands have corrugations in the
sheath and in the core of the strands. In one embodiment, the first
and second polymer components are arranged in a segmented pie
configuration, and the stretch-activated portions of the strands
have either the first and second polymer components split apart
from one another or the components both exhibit crimps down their
length. In one embodiment, the first and second polymer components
are arranged in a tipped multilobal configuration, and the
stretch-activated portions of the strands have either the first and
second polymer components split apart from one another or the
components both exhibit crimps down their length.
[0014] In another broad respect, this invention is a multicomponent
fiber comprising an elastomeric component and a component having
less elasticity than the elastomeric component, said multicomponent
fiber exhibiting an overall helical configuration which includes
the components having less elasticity bulked around the elastomeric
component. In one embodiment, the fiber has been subjected to
incremental stretching.
[0015] In another broad respect, this invention is a garment
comprising a plurality of layers, wherein at least one of said
layers comprises the nonwoven fabric described above. The garment
can be, for example, a training pant, a diaper, an absorbent
underpant, underwear, an incontinence product, a feminine hygiene
item, an industrial apparel, a coverall, a head covering, a pant, a
shirt, a glove, a sock, wipes, a surgical gown, wound dressings,
bandages, a surgical drape, a face mask, a surgical cap, a surgical
hood, a shoe covering, or a boot slipper.
[0016] In another broad respect, this invention is an incrementally
stretch activated nonwoven web, made from the multicomponent
strands.
[0017] The fibers and articles of the present invention have
utility in a variety of applications. Suitable applications
include, for example, but are not limited to, disposable personal
hygiene products (e.g. training pants, diapers, absorbent
underpants, incontinence products, feminine hygiene items and the
like); disposable garments (e.g. industrial apparel, coveralls,
head coverings, underpants, pants, shirts, gloves, socks and the
like); infection control/clean room products (e.g. surgical gowns
and drapes, face masks, head coverings, surgical caps and hood,
shoe coverings, boot slippers, wound dressings, bandages,
sterilization wraps, wipers, lab coats, coverall, pants, aprons,
jackets), and durable and semi-durable applications such as bedding
items and sheets, furniture dust covers, apparel interliners, car
covers, and sports or general wear apparel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. ("FIGS.") 1A-1M illustrate cross sectional views of
strands made in accordance with the present invention.
[0019] FIG. 2 illustrates a cross direction incremental stretching
system in accordance with one aspect of the present invention.
[0020] FIG. 3 illustrates a machine direction incremental
stretching system in accordance with another aspect of the present
invention.
[0021] FIG. 4 illustrates one example of a processing line for
producing nonwoven fabrics according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention will be described more fully
hereinafter in connection with illustrative embodiments of the
invention which are given so that the present disclosure will be
thorough and complete and will fully convey the scope of the
invention to those skilled in the art. However, it is to be
understood that this invention may be embodied in many different
forms and should not be construed as being limited to the specific
embodiments described and illustrated herein. Although specific
terms are used in the following description, these terms are merely
for purposes of illustration and are not intended to define or
limit the scope of the invention. As an additional note, like
numbers refer to like elements throughout.
[0023] As discussed above, the present invention generally relates
to the production and use of webs produced from multicomponent
strands. It should be understood that the scope of the invention is
meant to include strands with two or more components. Further, in
this invention, "strand" is being used as a term generic to refer
to strands, fibers, and filaments. Thus, the terms "strand" or
"fiber" or "filament" as used herein are synonymous.
[0024] Referring now to FIGS. 1A-1M, cross sectional views of
exemplary multicomponent strands of the present invention are
provided. As shown, the multicomponent strands generally include a
first polymeric component 1 and a second polymeric component 2.
[0025] The first polymeric component is formed from one or more
"elastomeric" polymers. The term "elastomeric" generally refers to
polymers that, when subjected to an elongation, deform or stretch
within their elastic limit. For example, spunbonded fabrics formed
from elastomeric filaments typically have a root mean square
average recoverable elongation of at least about 75% based on
machine direction and cross direction recoverable elongation values
of the fabric after 30% elongation of the fabric and one pull.
Advantageously, spunbonded fabrics formed from elastomeric
filaments typically have a root mean square average recoverable
elongation of at least about 65% based on machine direction and
cross direction recoverable elongation values of the fabric after
50% elongation of the fabric and one pull.
[0026] The second component is formed from one or more extensible
polymers, e.g. one or more non-elastomeric polymers. The second
component polymer may have elastic recovery and may stretch within
its elastic limit as the multicomponent strand is stretched.
However, the second component is selected to provide poorer elastic
recovery, e.g. be less elastic, than the first component polymer.
As such, the second component is beneficially a polymer which can
be stretched beyond its elastic limit and permanently elongated by
the application of tensile stress.
[0027] The first and second components are generally present in
longitudinally extending "zones" of the strand. The arrangement of
the longitudinally extending zones in the strand can be seen from
the cross-sectional views set forth in FIGS. 1A-1M. As can be seen
in each of these figures, the first polymeric component, 1, and
second polymeric component, 2, are present in substantially
distinct zones in the strand.
[0028] In advantageous embodiments of the invention, the zone of
the second component constitutes substantially the entire
peripheral surface of the strand, as illustrated by FIGS. 1A
through 1E. Beneficially, the second component constitutes at least
about 50% of the peripheral surface of the strand. Exemplary
configurations of such embodiments include concentric and eccentric
sheath/core configurations (FIGS. 1A and 1B, respectively). Further
exemplary sheath/core cross sections include trilobal (FIG. 1C) and
round with a quadrilobal core (FIG. 1D). Further aspects including
a peripheral second component include the "islands in a sea" cross
section (FIG. 1E). In the "islands in a sea" configuration, the
first component is distributed into a number of fine continuous
strands. In advantageous embodiments of the invention, the strands
of the invention are configured in either the symmetric sheath/core
arrangement of FIG. 1A or the asymmetrical sheath/core arrangement
of FIG. 1B. Asymmetrical configurations advantageously induce a
helical (coil) shape or other means of bulking the conjugate
strands, resulting in increased loft in fabrics produced
therefrom.
[0029] Alternatively, the strand may be configured so that the
first and second components may be split or separated to form finer
denier microfilaments. For example, the strand may include first
and second components arranged so as to form distinct unocclusive
cross-sectional segments extending along the length of the fiber
such that the segments are dissociable. As used herein, the terms
"split" and "dissociable" include strands exhibiting any amount of
separation within any portion of the components within the strands.
In advantageous embodiments, at least 50% of the original total
interface between the components is no longer joined following
splitting.
[0030] Exemplary strand configurations for the splittable
embodiments include side-by-side configurations (FIG. 1F),
pie-wedge configurations (FIG. 1G), hollow pie-wedge configurations
(FIG. 1H) and sectional configurations (FIG. 1I). In one
advantageous embodiment, a splittable strand having a tipped
trilobal construction (FIG. 1M) is provided. In such advantageous
embodiments, the tips 2 may beneficially be formed from
non-elastomeric polymer while the innermost section 1 may be formed
from elastomeric polymer.
[0031] It is to be noted that suitable splittable configurations
need not have a symmetrical geometry provided that they are not
occlusive or interlocking to such an extent that splitting is
precluded. Consequently, suitable splittable configurations also
include asymmetrical configurations, such as those shown in FIGS.
1J and 1K. FIG. 1J illustrates a conjugate strand of a sectional
configuration that has an unevenly large end segment. FIG. 1K
illustrates a conjugate strand having a pie-wedge configuration
that has one unevenly large segment. These asymmetrical
configurations are suitable for imparting a helical or spiral shape
to the conjugate fibers and, thus, for increasing the loft of the
fabric produced therefrom.
[0032] The splittable strands need not be conventional round
fibers. Other useful shapes include rectangular, oval and
multilobal shapes and the like. Particularly suitable strand shapes
for the present invention are rectangular or oval shapes. FIG. 1L
illustrates the cross-section of an exemplary rectangular conjugate
strand.
[0033] Each of the components within the multicomponent strands may
further be separated into any number of segments, particularly in
splittable configurations. For example, each component within the
multicomponent strand may be separated into about 2 to 20 segments.
For example, in one advantageous embodiment, a multicomponent
strand having 4 segments is provided. The multicomponent strands of
the invention may further be produced in a wide range of denier.
Exemplary deniers for the multicomponent strands range from about
1.5 to 15. In one advantageous embodiment, the multicomponent
strand is about a 2 denier strand.
[0034] The first and second components may be present within the
multicomponent strands in any suitable amounts, depending on the
specific shape of the fiber. In advantageous embodiments, the first
component forms the majority of the fiber, i.e., greater than about
50 percent by weight, based on the weight of the strand ("bos").
For example, the first component may beneficially be present in the
multicomponent strand in an amount ranging from about 80 to 99
weight percent bos, such as in an amount ranging from about 85 to
95 weight percent bos. In such advantageous embodiments, the
non-elastomeric component would be present in an amount less than
about 50 weight percent bos, such as in an amount of between about
1 and about 20 weight percent bos. In beneficial aspects of such
advantageous embodiments, the second component may be present in an
amount ranging from about 5 to 15 weight percent bos, depending on
the exact polymer(s) employed as the second component. In one
advantageous embodiment, a sheath/core configuration having a core
to sheath weight ratio of greater than or equal to about 85:15 is
provided, such as a ratio of 95:5. Alternatively, the first
component may be present in amounts as low as about 30 weight
percent or less, particularly in applications in which fiber
economics are the primary concern.
[0035] Applicants have found that unexpected properties are
provided by multicomponent strands having particular configurations
which further contain an effective amount of particular components.
More specifically, Applicants have determined that in embodiments
in which the zone of the second component constitutes substantially
the entire peripheral surface of the strand, such as the
embodiments illustrated in FIGS. 1A through 1E, intermittent
corrugations may be made to arise within both the first and second
components upon sufficient stretch activation if the second
component is present in amounts of less than about 20 weight
percent bos. The corrugations give the resulting fabrics a
microfiber tactility.
[0036] The corrugations, present in both the sheath and core, are
in the form of a plurality of ribs formed in the circumferential
direction perpendicular to the fiber axis which extend along the
direction of the fiber axis. These corrugations impart a
bellows-like outer surface shape to the fiber periphery.
Beneficially, the height of the ribs (peak to valley) is at least
about 1/20 of the fiber diameter. Advantageously, the ribs each
have widths (peak to peak) of up to several microns. The
corrugations, triggered by a stretch activation step, are present
within the fibers as they rest in a relaxed state. The shape and
dimension of the corrugations can be readily changed. For example,
the axial-direction pitch, height and width can be changed by
altering the type of polymer, component ratio, the amount of
drawing occurring during spinning and/or stretch activation, or the
fiber cooling rate.
[0037] The splittable strands of the invention may also exhibit
advantageous fiber geometries. More specifically, splittable
strands of the invention can form self-bulked constructions when
the non-elastomeric components within stretch activated strands
bulk up, or bunch up, around the more centrally located elastomeric
components(s) following splitting. This bulking produces
"self-textured" strands that are characterized by a softer touch or
feel in comparison to comparable non-bulked strands. Dissociated
splittable configurations may further exhibit kinks or crimps down
their length upon splitting. Such kinking or crimping would also be
expected to contribute to a softer touch or feel within the split
fibers.
[0038] In advantageous embodiments the elastomeric component is
present within the interior region of or otherwise recessed within
the splittable configuration to further optimize the resulting
softness of the split fiber and to minimize contact between
elastomeric components of adjacent strands during spinning and
quenching. For example, a tipped trilobal fiber may be provided
with an elastomeric interior and non-elastomeric tips. To further
diminish the aesthetic impact of the elastomeric polymer and to
decrease the amount of interstrand elastomeric contact during
extrusion, the amount of the elastomeric component may be minimized
within the non-fully encompassing multicomponent configurations.
For example, it may be advantageous to include 70 weight percent or
less of the elastomeric component within splittable
configurations.
[0039] As briefly noted above, spiral or helical fibers may further
be formed in accordance with the invention. Spiral or helically
configured strands can provide numerous benefits to fabric
structures, including increased loft. Asymmetrical configuration
such as FIGS. 1B, 1J or 1K may be utilized to impart a spiral
structure to the multicomponent strand, as noted above. A modified
spinneret design may also be used to impart a spiral or helical
structure to the strand. More specifically, the exit surface of the
spinneret holes (or slots) may be cut at an angle, such as an
oblique angle, relative to the normal plane of the spin line. This
oblique angle is believed to impart angular momentum into the
composite fiber strand, causing it to twist or rotate on axis. This
design does not rely on differential polymer properties, draw, nor
heat to create the spiral configuration. In the case of undrawn
filaments, it is anticipated that the shape of the filament will be
like that of a screw, where at least part of the threads of the
screw consist of the second, non-elastomeric component and the
shaft consists mainly of the elastomer. This is different that what
occurs in many drawn or heated multiconstituent fibers where the
filaments look more like springs (known as helical crimp). The
inventive fibers may form both helical twist (screw) and helical
crimp (coil spring) due to processing.
[0040] Helical or spiral strands in accordance with the invention
are beneficial because they further minimize any potential
elastomer-elastomer contact between adjacent fibers. Further, in
splittable helical constructions the non-elastomeric component can
become better wrapped around the elastomeric component after
splitting. This enhanced wrapping in helical splittable
configurations improves the shielding properties of the second
component, decreasing the rubbery feel of the resulting fabric and
imparting a softer touch due to the enhanced bulking. These
advantages are present in both the split and non-split fiber
cases.
[0041] Materials for use as the first and second components can
vary widely. Typically the materials are selected based on the
desired function for the strand. In one embodiment, the polymers
used in the components of the invention have melt flows ranging
from about 5 to about 1000. Generally, the meltblowing process will
employ polymers of a higher melt flow than the spunbonded
process.
[0042] The first component may be formed from any combination of
one or more elastomeric polymers known in the art. For example, the
first component may be formed from polyurethane (including both
polyester polyurethane and polyether polyurethane), polyetherester,
polyetheramides, low crystalline (<0.90 g/cm.sup.3 density)
polyolefins (such as elastomeric polypropylene, elastomeric
polyethylene, and copolymers and interpolymers based on propylene
and/or ethylene), interpolymers (random copolymers of
crystallizable and noncrystallizable components such as
ethylene/styrene pseudo-random compolymers), elastomeric fiber
forming block copolymers, and mixtures thereof. Elastomeric
polypropylene is described, for example, in U.S. Pat. No.
6,525,157, WO 2003040201 (US Patent Application 20030088037
corresponds to WO 2003040201), all of which are incorporated by
reference. Exemplary elastomeric fiber forming block copolymers
include co-polyesters, co-polyamides, diblock and triblock
copolymers based on polystyrene (S) and unsaturated or fully
hydrogenated rubber blocks. The rubber blocks for use in
conjunction with polystyrene include butadiene (B), isoprene (I),
or the hydrogenated version, ethylene-butylene (EB). Thus, S-B,
S-I, S-EB, as well as S-B-S, S-I-S, and S-EB-S block copolymers can
be used. In advantageous embodiments, the first component is formed
from a polyurethane, such as polyester polyurethane, or a polyester
elastomer.
[0043] Suitable polyurethanes for inclusion in the first component
are not particularly restricted if they have fiber formability, but
thermoplastic, low hardness (Shore A.ltoreq.80) polyurethanes are
considered beneficial. A thermoplastic polyurethane is a polymer
which is obtained by reacting a high molecular weight diol, an
organic diisocyanate, and a chain extender and can be melt spun.
Advantageously, the molecular weight of the polyurethane elastomer
is at least 100,000 Daltons.
[0044] The high molecular weight diol has hydroxyl groups at both
ends and may have an average molecular weight of 500-5,000.
Examples of high molecular weight diols are the either type
polyols, e.g., polytetramethylene glycol, polypropylene glycol,
etc., the ester type polyols, e.g., polyhexamethylene adipate,
polybutylene adipate, polycarbonate diol, polycaprolactone diol,
etc. or mixtures thereof.
[0045] As the chain extender, there is 1,4-butanediol, ethylene
glycol, propylene glycol, bis(2-hydroxyethoxy)benzene having a
molecular weight of 500 or less. Of these, 1,4 butanediol and
bishydroxyethoxybenzene are common and may advantageously be
employed. Chain extenders with 1 or more amine terminations, for
example ethanol amine or ethylene diamine, may be considered, but
normally used as mixtures with diol chain extenders and at
relatively low percentages (<10% by weight of the chain
extender).
[0046] Exemplary organic diisocyanates include tolylene
diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI),
non-yellowing diisocyanates such as 1,6-hexanediisocyanate, etc.,
and mixtures thereof. Of those, MDI is particularly
advantageous.
[0047] The weight percent hard segment (% HS), which is an index of
the MDI and chain extender content in polyurethanes and relates to
the hardness of polyurethanes, generally ranges from about 55
weight percent to 15 weight percent. In advantageous embodiments,
polyurethane includes from about 40 weight percent to 20 weight
percent hard segments.
[0048] Further, known modifiers or miscibilizing agents, such as
titanium dioxide, dyes and pigments, UV stabilizer, UV absorbent,
bactericide, etc. can be added to the polyurethane.
[0049] In addition to the above mentioned high molecular weight
diols, organic isocyanates, and chain extenders, small percentages
of comparable components having higher functionality, i.e. having
more than 2 hydroxyl or isocyanate groups, may be blended into the
polyurethane to impart some cross-linking. Generally it is
beneficial to keep the total cross-linking below 10 equivalence %,
such as below 5 equivalence %.
[0050] As noted above, polyester elastomers may also be employed as
the elastomeric component. Generally, polyester elastomers include
a short chain ester section as the hard segment and a long chain
polyether section and/or a long chain polyester section as the soft
segment. The short chain ester typically consists of an aromatic
dicarboxylic acid and a low-molecular weight diol having a
molecular weight of 250 or less. Suitable aromatic dicarboxylic
acids for the hard segment include terephthalic acid, isophthalic
acid, bibenzoic acid, substituted dicarboxylic compounds having two
benzene nuclei, e.g., bis(p-carboxyphenyl)methane,
p-oxy(p-carboxyphenyl) benzoic acid, ethylene-bis(p-oxybenzoic
acid), 1,5-naphthalenedicarboxylic acid, and the like.
Phenylenedicarboxylic acids, namely terephthalic acid and
isophthalic acid, are especially beneficial. Exemplary
low-molecular weight diols include any diol having a molecular
weight of about 250 or less, such as ethylene glycol, propylene
glycol, tetramethylene glycol, hexamethylene glycol, cyclohexane
dimethanol, resorcinol, hydroquinone, and the like. Advantageously,
the aliphatic diols contain 2-3 carbon atoms.
[0051] Exemplary long chain polyether sections for use in the
polyester elastomers include poly(1,2- and 1,3-propylene oxide)
glycol, poly(tetramethylene oxide) glycol, ethylene
oxide-1,2-propylene oxide random or block copolymer, and the like.
Poly(tetramethylene oxide) glycol can be advantageously employed as
the long chain polyether. Exemplary long chain polyester sections
for use in the polyester elastomers include poly(aliphatic lactone
diol), such as polycaprolactone diol, polyvalerolactone diol, and
the like. Polycaprolactone diol is particularly advantageous. As
the other long chain polyester part, there are aliphatic polyester
diols such as reaction products of dibasic acids, e.g., adipic
acid, sebacic acid, 1,3-cyclohexane dicarboxylic acid, glutaric
acid, succinic acid, oxalic acid, azelaic acid, and the like, with
low-molecular weight diols, e.g., 1,4-butanediol, ethylene glycol,
propylene glycol, hexamethylene glycol and the like. Polybutylene
adipate is particularly advantageous as a long chain polyester.
[0052] As examples in the above-exemplified elastomers, articles on
the markets such as HYTREL.RTM. elastomers (Du Pont-Toray Co.),
PELPRENE.RTM. elastomers (Toyobo Co.), GRILUX.RTM. elastomers
(Dainippon Ink and Chemicals Inc.), ARNITEL.RTM. elastomers (AKZO
Co.) can be used.
[0053] Polyamide elastomers also comprise a hard segment and a soft
segment. As the hard segment, a polyamide block such as nylon 66,
610, 612, or nylon 6, 11, 12 may be used while as the soft segment,
a polyether block such as polyethylene glycol, polypropylene
glycol, polytetramethylene glycol and the like or an aliphatic
polyester diol may be used. The properties of the resulting
polyamide elastomer varies with the polyamide raw material for the
hard segment, polyether or polyester raw material for the soft
segment, and the hard segment/soft segment ratio. For instance,
when the hard segment is increased, the mechanical strength, heat
resistance, and chemical resistance are improved, but the rubber
elasticity is lowered. Conversely, when the hard segment is
decreased, the cold resistance, and softness are improved.
[0054] As examples for the above-exemplified polyamide elastomers,
articles on the market such as DIAMIDE.RTM. elastomers (Daicel Huls
Co.), PEBAX.RTM. elastomers (Toray Corp.) and GRILUX.RTM.
elastomers (Dainippon Ink and Chemicals Inc.) can be used.
[0055] Polystyrene based block copolymer elastomers similarly
comprise a hard segment and a soft segment. The hard segment can be
formed from polystyrene. The soft segment can be derived from
polybutadiene, polyisoprene, or polyethylene butylene that has been
block copolymerized. Elastomers obtained from the above ingredients
can be expressed by SBS, SIS, and SEBS. Random copolymers of
styrene and, for example, ethylene, typified by polyethylene runs
with occasional insertions of a single styrene molecule, may also
be used. Further, if the styrene section is increased the
mechanical strength increases, but it tends to raise the hardness
and lose the rubber elasticity. Conversely, if the styrene section
is decreased, the opposite occurs.
[0056] As the above-exemplified polystyrene elastomers, articles on
the market such as KRATON G.RTM. elastomers (Kraton Corp.), VECTOR
elastomers (Dexco), CARIFLEX.RTM. elastomers (Shell Kagaku K.K.),
RABALON.RTM. elastomers (Mitsubishi Petroleum Co.), TUFPRENE.RTM.
elastomers (Asahi Chemical Industry Co.), ARON.RTM. elastomers
(Aron Co.) can be used.
[0057] Further commercially available elastomers for use in the
present invention include PELLETHANE.TM. polyurethane by Dow
Chemical, the KRATON polymers sold by Kraton Corp., and the VECTOR
polymers sold by DEXCO. Other elastomeric thermoplastic polymers
include polyurethane elastomeric materials such as ELASTOLLAN sold
by BASF, ESTANE sold by B.F. Goodrich Company, polyester
elastomeric materials such as ARNITEL sold by Akzo Plastics; and
polyetheramide materials such as PEBAX sold by Elf Atochem Company.
Heterophasic block copolymers, such as those sold by Montel under
the trade name CATALLOY are also advantageously employed in the
invention. Also suitable for the invention are polypropylene
polymers and copolymers described in U.S. Pat. No. 5,594,080.
Elastomeric polyethylene, such as 58200.02 PE elastomer, available
from Dow Chemical, and EXACT 4023, available from the Exxon
Chemical Company, may also be used as the first component. Polymer
blends of elastomers, such as those listed above, with one another
and with non-elastomeric thermoplastic polymers, such as
polyethylene, polypropylene, polyester, nylon, and the like, may
also be used in the invention. Those skilled in the art will
recognize the elastomer properties can be adjusted by polymer
chemistry and/or blending elastomers with non-elastomeric polymers
to provide elastic properties ranging from full elastic stretch and
recovery properties to relatively low stretch and recovery
properties.
[0058] Where the first component is to be a blend of one of more
elastomers, the materials are first combined in appropriate amounts
and blended. Among the commercially well suited mixers that can be
used include the Barmag 3DD three-dimensional dynamic mixer
supplied by Barmag AG of Germany and the RAPRA CTM cavity-transfer
mixer supplied by the Rubber and Plastic Research Association of
Great Britain.
[0059] The second component may be formed from any polymer or
polymer composition exhibiting inferior elastic properties (less
elasticity) in comparison to the polymer or polymer composition
used to form the first component. Exemplary non-elastomeric,
fiber-forming thermoplastic polymers include polyolefins, e.g.
polyethylene, polypropylene, and polybutene, polyester, polyamide,
polystyrene, and blends thereof. It should be appreciated that
these polymers may be homopolymers or may include relatively small
amount of comonomers.
[0060] One specific example of a suitable second component polymer
composition is a polyethylene/polypropylene blend. Typically in
this blend, polyethylene and polypropylene are blended in
proportions such that the material comprises between 2 and 98
percent by weight polypropylene, with the balance being
polyethylene. Strands made from these polymer blends have a soft
hand with a very little "stickiness" or surface friction.
[0061] Various types of polyethylene may be employed in the second
component with the most preferred being linear, low density
polyethylenes. LLDPE can be produced such that various density and
melt index properties are obtained which make the polymer well
suited for melt-spinning with polypropylene. Linear low density
polyethylene (LLDPE) also performs well in filament extrusion.
Preferred density values range from 0.87 to 0.96 g/cc with 0.90 to
0.96 being more preferred, and preferred melt index values usually
range from 0.2 to about 150 g/10 min. (ASTM D1238-89, 190.degree.
C.).
[0062] The propylene included within the second component can be an
isotactic or syndiotactic polypropylene homopolymer, copolymer, or
terpolymer with the most preferred being in the form of a
homopolymer. Modified, low-viscosity or high melt flow (MF)
polypropylene (PP) may be employed. Exemplary melt flows include
35, 25, and 17. Examples of commercially available polypropylene
polymers which can be used in the present invention include ARCO
40-7956X, BP 50-7657X, Basell PH805, and Exxonmobil 3155E2.
[0063] Exemplary polyesters suitable for use in the second
component include copolymerized polyesters which are obtained by
copolymerizing polyethylene terephthalate as the principal
ingredient with up to 50 mole % of another dicarboxylic acid
component, such as isophthalic acid and/or up to 35 mole % of
another diol component, such as diethyelene glycol, triethylene
glycol, neopentyl glycol, butanediol, and the like.
[0064] As was the case with the first component, where the second
component is a blend, the polymer materials, e.g., polyethylene and
polypropylene, are combined in appropriate proportional amounts and
intimately blended before producing the fibers.
[0065] While the principal components of the multi-component
strands of the present invention have been described above, the
first and/or second polymeric components can also include other
materials which do not adversely affect the multi-component
strands. For example, the first and second polymeric components can
also include, without limitation, dyes, pigments, antioxidants, UV
stabilizers and absorbents, surfactants, waxes, flow promoters,
matting agents, conducting agents, bactericides, miscibilizing
agents, solid solvents, particulates and material added to enhance
the processability or splittability of the components of the
composition, radical scavengers, amines, U.V. inhibitors,
colorants, fillers, antiblock agents, slip agents, luster
modifiers, and the like, and combinations thereof. Typically, if
present, each additive is used in an amount less than about 5
percent by weight.
[0066] The strands according to the present invention can be used
in the formation of fabrics, and, in particular, nonwoven fabrics.
The strands may also be used to form yarn and threads which may
subsequently be incorporated into knit or woven fabrics.
[0067] Multicomponent elastomeric strands in accordance with the
invention can be melt spun by any means known in the art of
composite fibers. Subsequent to spinning, the multicomponent
strands of the invention generally require an activation step, such
as a stretch activation step, to develop their full range of
elastic properties. For example, the as spun sheath/core strands of
the invention are characterized by a relatively smooth surface and
stiff feel until an activation process introduces corrugation and
improved elasticity into the fiber. The corrugations give rise to
suppleness within the strand, as well as a soft hand. The improved
elastic behavior imparted by the activation step is indicated by a
reduced initial modulus.
[0068] Similarly, the as spun splittable strands of the invention
are characterized by a relatively smooth surface and stiff feel
until an activation process fully or partially splits the strands
into their component parts. Following activation by incremental
stretching, the resulting split strand exhibits a softer,
self-textured surface, with the non-elastomeric components bulking
or bunching up around the elastomeric component(s). A reduced
initial modulus is similarly noted within activated splittable
strands of the invention.
[0069] The activation process using incremental stretching is
generally performed after the strands have been formed into a
nonwoven web or fabric, although it may be done before. The
activation process generally incrementally stretches the nonwoven
web or fabric about 1.1 to 10.0 fold. In advantageous embodiments,
the web or fabric is stretched or drawn to about 2.5 times its
initial length. Incremental stretching in accordance with the
present invention may be accomplished by any means known in the
art.
[0070] A number of different stretchers and techniques may be
employed to stretch the starting or original laminate of a nonwoven
fibrous web and elastomeric film. Incremental stretching can be
accomplished using, for example, a diagonal intermeshing stretcher,
cross direction ("CD") intermeshing stretching equipment, machine
direction ("MD") intermeshing stretching equipment. The diagonal
intermeshing stretcher includes a pair of left hand and right hand
helical gear-like elements on parallel shafts. The shafts are
disposed between two machine side plates, the lower shaft being
located in fixed bearings and the upper shaft being located in
bearings in vertically slidable members. The slidable members are
adjustable in the vertical direction by wedge shaped elements
operable by adjusting screws. Screwing the wedges out or in will
move the vertically slidable member respectively down or up to
further engage or disengage the gear-like teeth of the upper
intermeshing roll with the lower intermeshing roll. Micrometers
mounted to the side frames are operable to indicate the depth of
engagement of the teeth of the intermeshing roll. Air cylinders are
employed to hold the slidable members in their lower engaged
position firmly against the adjusting wedges to oppose the upward
force exerted by the material being stretched. These cylinders may
also be retracted to disengage the upper and lower intermeshing
rolls from each other for purposes of threading material through
the intermeshing equipment or in conjunction with a safety circuit
which would open all the machine nip points when activated. A drive
means is typically utilized to drive the stationery intermeshing
roll. If the upper intermeshing roll is to be disengageable for
purposes of machine threading or safety, it is preferable to use an
antibacklash gearing arrangement between the upper and lower
intermeshing rolls to assure that upon reengagement the teeth of
one intermeshing roll always fall between the teeth of the other
intermeshing roll and potentially damaging physical contact between
addendums of intermeshing teeth is avoided. If the intermeshing
rolls are to remain in constant engagement, the upper intermeshing
roll typically need not be driven. Drive may be accomplished by the
driven intermeshing roll through the material being stretched. The
intermeshing rolls can resemble fine pitch helical gears. In one
embodiment, the rolls have 5.935'' diameter, 45.degree. helix
angle, a 0.100'' normal pitch, 30 diametral pitch, 141/2.degree.
pressure angle, and are basically a long addendum topped gear. This
produces a narrow, deep tooth profile which allows up to about
0.090'' of intermeshing engagement and about 0.005'' clearance on
the sides of the tooth for material thickness. The teeth are not
designed to transmit rotational torque and do not contact
metal-to-metal in normal intermeshing stretching operation. The CD
intermeshing stretching equipment is identical to the diagonal
intermeshing stretcher with differences in the design of the
intermeshing rolls and other minor areas noted below. Since the CD
intermeshing elements are capable of large engagement depths, it is
important that the equipment incorporate a means of causing the
shafts of the two intermeshing rolls to remain parallel when the
top shaft is raising or lowering. This is necessary to assure that
the teeth of one intermeshing roll always fall between the teeth of
the other intermeshing roll and potentially damaging physical
contact between intermeshing teeth is avoided. This parallel motion
is assured by a rack and gear arrangement wherein a stationary gear
rack is attached to each side frame in juxtaposition to the
vertically slidable members. A shaft traverses the side frames and
operates in a bearing in each of the vertically slidable members. A
gear resides on each end of this shaft and operates in engagement
with the racks to produce the desired parallel motion. The drive
for the CD intermeshing stretcher must operate both upper and lower
intermeshing rolls except in the case of intermeshing stretching of
materials with a relatively high coefficient of friction. The drive
need not be antibacklash. The CD intermeshing elements are machined
from solid material but can best be described as an alternating
stack of two different diameter disks. In one embodiment, the
intermeshing disks would be 6'' in diameter, 0.031'' thick, and
have a full radius on their edge. The spacer disks separating the
intermeshing disks would be 51/2'' in diameter and 0.069'' in
thickness. Two rolls of this configuration would be able to be
intermeshed up to 0.231'' leaving 0.019'' clearance for material on
all sides. As with the diagonal intermeshing stretcher, this CD
intermeshing element configuration would have a 0.100'' pitch. The
MD intermeshing stretching equipment can be identical to the
diagonal intermeshing stretch except for the design of the
intermeshing rolls. The MD intermeshing rolls closely resemble fine
pitch spur gears. In one embodiment, the rolls have a 5.933''
diameter, 0.100'' pitch, 30 Diametral pitch, 141/2.degree. pressure
angle, and are basically a long addendum, topped gear. A second
pass can be taken on these rolls with the gear hob offset 0.010''
to provide a narrowed tooth with more clearance. With about 0.090''
of engagement, this configuration will have about 0.010'' clearance
on the sides for material thickness. The above described diagonal,
CD or MD intermeshing stretchers may be employed to produce the
incrementally stretched nonwoven webs of this invention.
[0071] An exemplary configuration of one suitable incremental
stretching system is shown in FIG. 2. The incremental stretching
system 10 generally includes a pair of first 12 (e.g. top) and
second 14 (e.g. bottom) stretching rollers positioned so as to form
a nip. The first incremental stretching roller 12 generally
includes a plurality of protrusions, such as raised rings, and
corresponding grooves, both of which extend about the entire
circumference of the first incremental stretching roller 12. The
second incremental stretching roller 14 similarly includes a
plurality of protrusions, such as raised rings, and corresponding
grooves which also both extend about the entire circumference of
the second incremental stretching roller 14. The protrusions on the
first incremental stretching roller 12 intermesh with or engage the
grooves on the second incremental stretching roller 14, while the
protrusions on the second incremental stretching roller 14
intermesh with or engage the grooves on the first incremental
stretching roller 12. As the web passes through the incremental
stretching system 10 it is subjected to incremental drawing or
stretching in the cross machine ("CD") direction. In advantageous
embodiments the protrusions are formed by rings, and the
incremental stretching system is referred to as a "ring
roller."
[0072] Alternatively or additionally, the web may be incrementally
drawn or stretched in the machine direction ("MD") using one or
more incremental stretching systems, such as provided in FIG. 3. As
shown in FIG. 3, MD incremental stretching systems 16 similarly
include a pair of incremental stretching rollers with intermeshing
protrusions and grooves. However, the protrusions and grooves
within MD incremental stretching systems generally extend across
the width of the roller, rather than around its circumference.
[0073] Alternatively, incremental stretching may be performed in
conjunction with an impinging fluid. For example, heated fluid may
be directed onto the surface of the web. Exemplary fluids include
water or air. Suitable temperatures for the heated fluid include
temperatures less than 35.degree. C.
[0074] Due to the nature of incremental stretching processes, only
a portion of the web is subjected to stretch activation within a
single pass. Stated differently, following a single pass through an
incremental stretching system portions of the web (and hence the
multicomponent strands) will be stretch activated and more elastic,
while other portions of the web (and hence the multicomponent
strands) will not be stretch-activated and are substantially less
elastic. Therefore, fabrics which are partially activated, e.g.
webs that have been subjected to a single pass of incremental
stretching, include narrow, spaced apart longitudinally extending
stretch-activated elastic zones separated by intervening
longitudinally extending non-activated, substantially less elastic
zones.
[0075] Consequently, webs formed in accordance with the invention
may be passed through one or more activation steps to fully develop
the elastic properties of the web. For example, webs formed in
accordance with the invention may be directed through a series of
incremental stretching systems. In beneficial aspects of the
invention, webs formed in accordance with the invention are passed
through a series of incremental stretching systems that are off-set
so that the protrusions of the top roller of the first incremental
stretching system are aligned with the grooves of the top roller of
a second incremental stretching system. The off-set incremental
stretching systems in such embodiments are arranged so as to
stretch activate substantially all of the multicomponent within the
web. The increasing amount of stretch activated strands within the
web following each incremental stretching may be reflected in a
number of elastic properties, including a lowering of the webs
initial modulus.
[0076] Nonwoven webs can be produced from the multicomponent
strands of the invention by any technique known in the art. A class
of processes, known as spunbonding is one common method for forming
nonwoven webs. Examples of the various types of spunbonded
processes are described in U.S. Pat. No. 3,338,992 to Kinney, U.S.
Pat. No. 3,692,613 to Dorschner, U.S. Pat. No. 3,802,817 to
Matsuki, U.S. Pat. No. 4,405,297 to Appel, U.S. Pat. No. 4,812,112
to Balk, and U.S. Pat. No. 5,665,300 to Brignola et al. In general,
traditional spunbonded processes include:
[0077] a) extruding the strands from a spinneret;
[0078] b) quenching the strands with a flow of air which is
generally cooled in order to hasten the solidification of the
molten strands;
[0079] c) attenuating the filaments by advancing them through the
quench zone with a draw tension that can be applied by either
pneumatically entraining the filaments in an air stream or by
wrapping them around mechanical draw rolls of the type commonly
used in the textile fibers industry;
[0080] d) collecting the drawn strands into a web on a foraminous
surface; and
[0081] e) bonding the web of loose strands into a fabric.
[0082] This bonding can use any thermal, chemical or mechanical
bonding treatment known in the art to impart coherent web
structures. Thermal point bonding may advantageously be employed.
Various thermal point bonding techniques are known, with the most
preferred utilizing calender rolls with a point bonding pattern.
Any pattern known in the art may be used with typical embodiments
employing continuous or discontinuous patterns. Preferably, the
bonds cover between 6 and 30 percent, and most preferably, 12
percent of the layer is covered. By bonding the web in accordance
with these percentage ranges, the filaments are allowed to elongate
throughout the full extent of stretching while the strength and
integrity of the fabric can be maintained. In alternative aspects
of the invention, bonding processes that entangle or intertwine the
strands within the web may be employed. An exemplary bonding
process which relies upon entanglement or intertwining is
hydroentanglement.
[0083] All of the spunbonded processes of this type can be used to
make the elastic fabric of this invention if they are outfitted
with a spinneret and extrusion system capable of producing
multicomponent strands. However, one preferred method involves
providing a drawing tension from a vacuum located under the forming
surface. This method provides for a continually increasing strand
velocity to the forming surface, and so provides little opportunity
for the elastic strands to snap back.
[0084] Another class of process, known as meltblowing, can also be
used to produce the nonwoven fabrics of this invention. This
approach to web formation is described in NRL Report 4364
"Manufacture of Superfine Organic Fibers" by V. A. Wendt, E. L.
Boone, and C. D. Fluharty and in U.S. Pat. No. 3,849,241 to Buntin
et al. Conventional meltblowing process generally involve:
[0085] a.) Extruding the strands from a spinneret.
[0086] b.) Simultaneously quenching and attenuating the polymer
stream immediately below the spinneret using streams of high
velocity heated air. Generally, the strands are drawn to very small
diameters by this means. However, by reducing the air volume and
velocity, it is possible to produce strand with deniers similar to
common textile fibers.
[0087] c.) Collecting the drawn strands into a web on a foraminous
surface. Meltblown webs can be bonded by a variety of means, but
often the entanglement of the filaments in the web or the
autogeneous bonding in the case of elastomers provides sufficient
tensile strength so that it can be wound onto a roll.
[0088] Any meltblowing process which provides for the extrusion of
multicomponent strands such as that set forth in U.S. Pat. No.
5,290,626 can be used to practice this invention.
[0089] For the sake of completeness, one example of a suitable
processing line for producing nonwovens from multi-component
strands is illustrated by FIG. 4. In this figure, a process line is
arranged to produce bi-component continuous strands, but it should
be understood that the present invention comprehends nonwoven
fabrics made with multi-component filaments having more than two
components. For example, the fabric of the present invention can be
made with filaments having three or four components. Alternatively,
nonwoven fabrics including single component strands, in addition to
the multi-component strands can be provided. In such an embodiment,
single component and multi-component strands may be combined to
form a single, integral web.
[0090] The process line 18 includes a pair of extruders 20 and 20a
for separately extruding the first and second components. The first
and second polymeric materials A, B, respectively, are fed from the
extruders 20 and 20a through respective melt pumps 22 and 24 to
spinneret 26. Spinnerets for extruding bi-component filaments are
well known to those of ordinary skill in the art and thus are not
described here in detail. A spinneret design especially suitable
for practicing this invention is described in U.S. Pat. No.
5,162,074. The spinneret 26 generally includes a housing containing
a spin pack which includes a plurality of plates stacked on top of
the other with a pattern of openings arranged to create flow paths
for directing polymeric materials A and B separately through the
spinneret. The spinneret 26 has openings arranged in one or more
rows. The spinneret openings form a downwardly extending curtain of
strands S when the polymers are extruded through the spinneret. For
example, the spinneret 26 may be arranged to form tipped trilobal
multicomponent filaments. Alternatively, the spinneret 26 may be
arranged to form concentric sheath/core bi-component filaments.
[0091] The process line 18 also includes a quench air blower 28
positioned adjacent the curtain of filaments extending from the
spinneret 26. Air from the quench air blower 28 quenches the
filaments extending from the spinneret 26. The quench air can be
directed from one side of the filament curtain as shown in FIG. 4,
or both sides of the filament curtain.
[0092] A fiber draw unit or aspirator 30 is positioned below the
spinneret 26 and receives the quenched filaments. Fiber draw units
or aspirators for use in melt spinning polymers are well known.
Suitable fiber draw units for use in the process of the present
invention include a slot attenuator, linear fiber aspirator and
eductive guns. In advantageous embodiments a low draw slot is used
to attenuate the fibers of the invention.
[0093] Generally described, the fiber draw unit 30 includes an
elongated vertical passage through which the filaments are drawn by
aspirating air entering from the sides of the passage and flowing
downwardly through the passage. The aspirating air draws the
filaments and ambient air through the fiber draw unit.
[0094] An endless foraminous forming surface 32 is positioned below
the fiber draw unit 30 and receives the continuous strands S from
the outlet opening of the fiber draw unit 30 to form a web W. The
forming surface 32 travels around guide rollers 34. A vacuum 36
positioned below the forming surface 32 where the filaments are
deposited draws the filaments against the forming surface 32.
[0095] The process line 18 further includes a compression roller 38
which, along with the forward most of the guide rollers 34, receive
the web W as the web is drawn off of the forming surface 32. In
addition, the process line includes a pair of thermal point bonding
calender rolls 40 for bonding the bi-component filaments together
and integrating the web to form a finished fabric.
[0096] In the beneficial embodiment illustrated in FIG. 4, the
bonded web on the traveling forming surface 32 is subsequently
transported through a stretch activation process in the form of an
incremental stretching system 42 that includes a pair of
interdigitating stretching rollers 44, 46 that draw the web in
either the CD or MD.
[0097] Although a single incremental stretching system is
illustrated in FIG. 4, in beneficial embodiments a series of such
incremental stretching systems may be used to draw the web. For
example, two incremental stretching systems may be used to stretch
activate the fabric in the CD. Advantageously, the stretching
rollers within the two systems may be offset to impart a higher
degree of stretch activation to the web. Either alternatively or
additionally, one or more incremental stretching systems may be
used to stretch activate the web in the MD. In alternative
embodiments, the web may be initially stretch activated and then
bonded.
[0098] Lastly, the process line 18 includes a winding roll 48 for
taking up the bonded fabric.
[0099] To operate the process line, the hoppers 50 and 52 are
filled with the respective first and second polymer components
which are melted and extruded by the respective extruders 20 and
20a through melt pumps 22 and 24 and the spinneret 26. Although the
temperatures of the molten polymers vary depending on the polymers
used, when, for example, PELLETHANE.TM. 2103-70A polyurethane and
ARCO 40-7956X polypropylene are used as the first and second
components, the preferred temperatures of the polymers at the
spinneret range from about 200 to 225.degree. C.
[0100] As the extruded strands extend below the spinneret 26, a
stream of air from the quench blower 28 at least partially quenches
the strands. After quenching, the strands are drawn into the
vertical passage of the draw unit 30 by a flow of air through the
draw unit 30. It should be understood that the temperatures of the
aspirating air in unit 30 will depend on factors such as the type
of polymers in the strands and the denier of the strands and would
be known by those skilled in the art.
[0101] The drawn filaments are deposited through the outer opening
of the fiber draw unit 30 onto the traveling forming surface 32.
The vacuum 36 draws the strands against the forming surface 32 to
form an unbonded, nonwoven web of continuous strands. The web is
then lightly compressed by the compression roller 38 and thermal
point bonded by bonding rollers 40. Thermal point bonding
techniques are well known to those skilled in the art and are not
discussed here in detail.
[0102] However, it is noted that the type of bond pattern may vary
based on the degree of fabric strength desired. The bonding
temperature also may vary depending on factors such as the polymers
in the filaments.
[0103] Although the method of bonding shown in FIG. 4 is thermal
point bonding, it should be understood that the fabric of the
present invention may be bonded by other means such as oven
bonding, ultrasonic bonding, hydroentangling or combinations
thereof to make cloth-like fabric. Such bonding techniques such as
through air bonding, are well known to those of ordinary skill in
the art and are not discussed here in detail.
[0104] The bonded web is subsequently subjected to incremental
stretching. Although the method of incremental stretching shown in
FIG. 4 is a roller based system, any incremental stretching system
known in the art may be used. The incremental stretching process is
generally performed at elevated temperatures, depending on the
polymers employed within the multicomponent strands. In
advantageous embodiments, the incremental stretching is performed
at a temperature less than 35.degree. C. The incremental stretching
process is further generally operated at a depth of roller
engagement ranging from about 0.025 to 0.250 inches.
[0105] Lastly, the stretch activated web is wound onto the winding
roller 48 and is ready for further treatment or use.
[0106] The invention is capable of solving the stickiness and
blocking problem associated with previous processes while at the
same time providing improved properties. The web can be employed in
non-limiting exemplary products such as disposable diaper
coverstock, adult incontinence bodies, sanitary napkin supports,
waistbands, cuffs, side panels for training pants, bandages,
durables such as apparel interliners, components for disposable or
semi-durable items, such as medical gowns and the like. To this
end, the fabric may be treated with conventional surface treatments
by methods recognized in the art. For example, conventional polymer
additives can be used to enhance the wettability of the fabric.
Such surface treatment enhances the wettability of the fabric and
thus, facilitates its use as a liner or surge management material
for feminine care, infant care, child care, and adult incontinence
products.
[0107] The fabric of the invention may also be treated with other
treatments such as antistatic agents, alcohol repellents and the
like, by techniques that would be recognized by those skilled in
the art.
[0108] The present invention will be further illustrated by the
following non-limiting examples. The foregoing examples are
illustrative of the present invention and are not to be construed
as limiting the scope of the invention or claims appended
hereto.
EXAMPLE 1
[0109] A web of 10/90 sheath/core bicomponent filaments was
prepared on a spunbond apparatus similar to that described in FIG.
4. The core was prepared from PELLETHANE2103-70A polyurethane and
the sheath was prepared from Dow ASPUN 6811A polyethylene. The
filaments were spun through a die having 144 holes of 0.35 mm
diameter. The filaments were drawn at a speed of approximately 600
m/min through an air attenuation device and distributed on a
foraminous belt as a web of 68 gsm basis weight. The denier of the
filaments was approximately 5. The web was thermally point bonded
at a temperature of 111.degree. C. and passed through mechanical
incremental stretching devices so that it was stretched in both the
machine direction and the cross machine direction. The mechanical
properties of the fabric are given in Table 1.
EXAMPLE 2
[0110] A web of 9/91 sheath/core bicomponent filaments was prepared
in the apparatus used for Example 1. The core was prepared from
PELLETHANE2102-75A polyurethane and the sheath was prepared from
Arco 40-7956X polypropylene. The web was thermal point bonded at
136.degree. C. and mechanically incrementally stretched in both the
machine direction and the cross machine direction. The mechanical
properties of this fabric are given in Table 1.
EXAMPLE 3
[0111] A web of 10/90 sheath/core bicomponent filaments was
prepared on an apparatus similar to that described in FIG. 4. The
core was prepared from PELLETHANE2102-75A polyurethane and the
sheath was prepared from Arco 40-7956X polypropylene. The filaments
were spun through a die having 4000 holes of 0.35 mm diameter
across a width of 1.2 meters. The filaments were drawn at a speed
of approximately 1200 m/min through an air attenuation device and
distributed on a foraminous belt to form a web of 50 gsm basis
weight. The denier of the filaments was approximately 5. The web
was thermal point bonded at a temperature of 138.degree. C. and
mechanically incrementally stretched in both the machine and cross
machine direction. The mechanical properties of this fabric are
given in Table 1.
EXAMPLE 4
[0112] A web of 20/80 sheath core bicomponent filaments was
prepared on an apparatus similar to that described in FIG. 4. The
core was prepared from PELLETHANE2102-75A polyurethane and the
sheath was prepared from Dow ASPUN 6811A polyethylene. The web was
thermal point bonded at 118.degree. C. and mechanically
incrementally stretched in both the machine direction and the cross
machine direction. The mechanical properties of this fabric are
given in Table 1. TABLE-US-00001 TABLE 1 PROPERTIES OF ELASTIC
BICOMPONENT FABRICS Example 1 2 3 4 Basis Weight 68 62 50 50 Grams
per square meter MD Tensile g/in 867 2428 4263 3577 CD Tensile
Strength g/in 1470 4620 1771 2329 MD Elongation - % 268 187 233 289
CD Elongation - % 390 234 336 330 MD Stress Relaxation - % 31 41 37
43 CD Stress Relaxation - % 33 39 43 48
Stress relaxation was measured by extending the fabric to 50% gauge
length and holding the sample for 5 min. while observing the stress
decay. The percent stress relaxation is (1-final stress/initial
stress).times.100%. An Instron Tensile testing device was used to
measure stress vs. strain for elastomeric nonwoven spunlaid
fabrics. Basis weight of the fabric was determined from the weight
of the actual punched-out sample or an average weight of many large
pieces taken from a production roll.
EXAMPLE 5
[0113] Three elastic bicomponent spunbonded fabrics were prepared
using extrusion methods similar to those of Example 1. All three
fabrics were formed from 4.0 denier sheath/core bicomponent
filaments of composition 5/95 Arco 40-7956X
polypropylene/PELLETHANE 2103-70A polyurethane. The fabrics were
thermal point bonded at 110 degrees Centigrade. Specimen 1 was
tested without any stretch activation. Specimen 2 was stretch
activated by passing it once through a ring roller. Specimen 3 was
stretch activated by passing it twice in the same direction though
a ring roller. The ring roller was equipped with 17 parallel rings
per inch with a depth of roller engagement of 0.16''. The effect of
stretch activation was to decrease the force required to elongate
the specimen. The force required to elongate Specimen 1 to 100% was
2.4 kgf/in (kilograms force per inch). The force required to
elongate Specimen 2 to 100% was 1.8 kgf/in. The force required to
elongate Specimen 3 to 100% was 1.6 kgf/in. The decrease in initial
modulus with successive stretch activation steps is indicative of
the stretch activation of previously unactivated strands within the
various webs during each successive ring rolling.
EXAMPLE 6
[0114] Two elastic bicomponent spunbonded fabrics were prepared
using extrusion methods similar to those of Example 1. Both fabrics
were formed from 7 denier tipped trilobal filaments similar to
those described in FIG. 1C. The polymer in the central portion of
the filament was Vector 4111. The polymer located on the tips was
Dow ASPUN 6811A LLDPE. The fabrics were thermal point bonded at 69
degrees Centigrade. Specimen 1 was tested without stretch
activation. Specimen 2 was stretch activated by passing it through
a ring roller twice. The ring roller was equipped with 17 parallel
rings per inch with a depth of roller engagement of 0.16''. The
effect of stretch activation was different from the effect observed
in Example 5. The force required to elongate Specimens 1 and 2 to
100% was 1.4 kgf/in. However, the force to elongate Specimen 3 to
100% was 0.1 kgf/in. In this case, two passes through the ring
roller were required to stretch the relatively thick outer layer of
polyethylene. The effect of stretching on filament geometry was
evident from scanning electron micrographs. In particular, the
filaments in Specimen 1 were relatively straight whereas filaments
in Specimen 3 were highly kinked and crenulated. The highly
crenulated shape of the filaments contributes to the elasticity of
the fabric. The recovery of Specimen 1 from 100% elongation was
60%. The recovery of Specimen 2 from 100% elongation was 90%.
EXAMPLE 7
[0115] Three elastic bicomponent spunbonded fabrics were prepared
using extrusion methods similar to those of Example 1. All three
fabrics were formed from 8 denier sheath/core bicomponent
filaments. The core polymer, which constituted 95% of the filament,
was Dow 58200.02 PE elastomer. The sheath polymer, which
constituted 5% of the filament, was a 85/15 blend of Dow 6811A
LLDPE/PP homopolymer. The filament webs were bonded at 110.degree.
C. Specimen 1 was tested without any stretch activation. Specimen 2
was stretch activated by passing it through a ring roller. Specimen
3 was stretch activated by passing it twice in the same direction
through a ring roller. The ring roller was equipped with 17
parallel ring per inch with a depth of roller engagement of 0.16''.
The effect of stretch activation was to decrease the force required
to elongate the specimen. The force required to elongate Specimen 1
to 100% was 1.0 kgf/in. The force required to elongate Specimen 2
to 100% was 0.6 kgf/in. The force required to elongate Specimen 3
to 100% was 0.4 kgf/in.
* * * * *