U.S. patent application number 09/948751 was filed with the patent office on 2002-02-21 for elastic composite fabric from unidirectionally cold stretched nonwoven webs of multipolymer fibers.
This patent application is currently assigned to BBA Nonwovens Simpsonville, Inc.. Invention is credited to Meece, Barry DeWayne, Quantrille, Thomas Edward.
Application Number | 20020022424 09/948751 |
Document ID | / |
Family ID | 22689991 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020022424 |
Kind Code |
A1 |
Meece, Barry DeWayne ; et
al. |
February 21, 2002 |
Elastic composite fabric from unidirectionally cold stretched
nonwoven webs of multipolymer fibers
Abstract
A nonwoven web of multipolymer fibers is described that is
unidirectionally stretched and permanently elongated at ambient
conditions and exhibits a substantial increase in tensile strength
in the stretch direction. The ratio of tensile strength of the web
in the direction of fiber orientation to the tensile strength in
the other direction is at least about 10:1. The ratio of elongation
at peak load in a direction transverse to the direction of fiber
orientation is at least about 6:1. The multipolymer fibers normally
are a blend of polyethylene and a polypropylene homopolymer or
copolymer, one of which is a dominant phase and one of which is a
dispersed phase. A third component having elastomeric properties
that is at least partially miscible with one or both of the other
components is included in some blends. The nonwoven webs are
stretchable well beyond their initial dimensions in the direction
perpendicular to the stretch direction and are especially useful in
laminates with elastomeric members for use in disposable absorbent
articles to impart elasticity thereto.
Inventors: |
Meece, Barry DeWayne;
(Pelzer, SC) ; Quantrille, Thomas Edward;
(Simpsonville, SC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
BBA Nonwovens Simpsonville,
Inc.
Simpsonville
SC
|
Family ID: |
22689991 |
Appl. No.: |
09/948751 |
Filed: |
September 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09948751 |
Sep 6, 2001 |
|
|
|
09187677 |
Nov 6, 1998 |
|
|
|
Current U.S.
Class: |
442/328 ;
428/103; 442/361; 442/366; 442/382; 442/394 |
Current CPC
Class: |
Y10T 428/24041 20150115;
Y10T 442/643 20150401; Y10T 442/66 20150401; Y10T 442/69 20150401;
D04H 1/544 20130101; Y10T 442/602 20150401; Y10T 442/674 20150401;
D04H 1/4291 20130101; Y10T 442/601 20150401; Y10T 442/692 20150401;
D04H 1/54 20130101; D04H 1/43828 20200501; D04H 1/56 20130101; D04H
1/43832 20200501; D04H 1/4383 20200501; D04H 3/14 20130101; Y10T
442/637 20150401; A61F 13/49012 20130101; D04H 3/147 20130101; Y10T
428/24802 20150115; Y10T 428/24826 20150115 |
Class at
Publication: |
442/328 ;
442/361; 442/366; 442/394; 442/382; 428/103 |
International
Class: |
B32B 003/06; B32B
009/00; D04H 001/00 |
Claims
What is claimed is:
1. A composite fabric comprising at least one layer of an
elastomeric component bonded to at least one layer comprising a
nonwoven web of multipolymer fibers, said fibers of said nonwoven
web being substantially oriented in one direction, and said web
having a plurality of discrete bond sites throughout the web
bonding the fibers together, and wherein the ratio of the tensile
strength of the web in the direction of orientation of the fibers
to the tensile strength of the web in the other direction is at
least about 10:1.
2. The composite fabric of claim 1 wherein the ratio of the tensile
strength of the web in the direction of orientation of the fibers
to the tensile strength of the web in the other direction is at
least about 16:1.
3. The composite fabric of claim 1 wherein the ratio of the
elongation at peak load of the web in the direction transverse to
the direction of orientation of the fibers to the elongation at
peak load in the direction of elongation is at least about 6:1.
4. The composite fabric of claim 1 wherein the ratio of the
elongation at peak load of the web in the direction transverse to
the direction of orientation of the fibers to the elongation at
peak load in the direction of elongation is at least about 8:1.
5. The composite fabric of claim 1 wherein said discrete bond sites
comprise areas where the fibers have been fusion bonded
together.
6. The composite fabric of claim 5, wherein said bond sites are
embedded within the web between opposite surfaces of the web and
are of a distorted, non-planar configuration extending generally in
the z-axis direction of the web.
7. The composite fabric of claim 6 additionally including a
plurality of bond sites that are generally planar and extend
parallel to the surface of the web.
8. The composite fabric of claim 1 wherein said multipolymer fibers
comprise a blend of polypropylene and polyethylene.
9. The composite fabric of claim 1 wherein said multipolymer fibers
comprise a blend of two immiscible polymer phases and a third
component which is at least partially miscible with the two
immiscible polymer phases.
10. The composite fabric of claim 1 wherein said multipolymer
fibers are formed from a blend comprising: a) isotactic
polypropylene present in an amount of from about 65 to 80 percent
by weight based upon the weight of said blend; b) linear low
density polyethylene present in an amount of from about 1 to 5
percent by weight based upon the weight of said blend; and c) a
block or grafted polyolefin copolymer or terpolymer having at least
a portion of the chain thereof miscible with said isotactic
polypropylene and wherein said block or grafted polyolefin
copolymer or terpolymer is present in an amount of from about 15 to
30 percent by weight based upon the weight of said blend.
11. The composite fabric of claim 10 wherein the multicomponent
fibers are selected from the group consisting of spunbond
continuous filaments, carded discontinuous staple fibers, and
meltblown fibers.
12. A composite fabric comprising at least one layer of an
elastomeric component bonded to at least one layer comprising a
nonwoven web of multipolymer fibers, said fibers of said nonwoven
web being substantially oriented in one direction, and said
multipolymer fibers comprising a blend of two immiscible polymer
phases and a third component which is at least partially miscible
with the two immiscible polymer phases, said web having a plurality
of discrete point bond sites throughout the web bonding the fibers
together, said point bond sites comprising areas where the fibers
have been fusion bonded together to form bond sites, said bond
sites being of a distorted, non-planar configuration extending
generally in the z-axis direction of the web.
13. The composite fabric of claim 12 wherein said elastomeric
component is selected from the group consisting of elastic strands,
elastic film, and scrim comprising elastomeric strands.
14. The composite fabric of claim 13 wherein said elastic film is
breathable.
15. A disposable absorbent article comprising as a component
thereof, the composite fabric of claim 12.
16. A disposable absorbent article of claim 15 wherein said
composite fabric is a component of an elastic side panel for a
disposable absorbent garment.
17. A composite fabric comprising at least one layer of an
elastomeric component bonded to at least one layer comprising a
bonded nonwoven web of multipolymer fibers, said nonwoven web
having a plurality of discrete bond sites throughout the web
bonding the fibers together, said bond sites comprising areas where
the fibers have been fusion bonded together, said bond sites being
of a distorted, non-planar configuration extending generally in the
z-axis direction of the web, and said web additionally including a
plurality of bond sites that are generally planar and extend
parallel to the surface of the web.
18. A composite fabric comprising at least one layer of an
elastomeric component bonded to at least one layer comprising a
bonded nonwoven web of multipolymer fibers having an elongation at
peak load in one or the other of the machine or cross machine
directions of at least about 400% and a ratio of elongation at peak
load in said one direction to the elongation at peak load in said
other direction of at least about 6:1.
19. The composite fabric of claim 18 wherein said elongation at
peak load is at least about 500%
20. The composite fabric of claim 18 wherein said ratio of
elongation at peak load in said one direction to the elongation at
peak load in said other direction is at least about 8:1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of application No. 09/187,677
filed Nov. 6, 1998.
FIELD OF THE INVENTION
[0002] The invention relates to elasticized composite fabrics for
use in disposable absorbent articles and to the components of these
fabrics.
BACKGROUND OF THE INVENTION
[0003] Disposable diapers are composite absorbent articles that are
designed to be worn about the lower torso as undergarments by
incontinent persons and by infants and young children prior to
toilet training. Disposable diapers typically include a liquid
impervious back sheet as the outer surface of the diaper, a liquid
pervious topsheet as the inner surface of the diaper for placing
adjacent the skin of the wearer, and an absorbent core placed
between the topsheet and the back sheet for absorbing urine and
other liquids. The absorbent core is normally contained in a
central, longitudinally extending region of the diaper and the
topsheet and back sheet are normally bonded about the periphery of
the diaper.
[0004] The diaper is placed between the legs with the topsheet next
to the skin and the ends are fastened at the waist to hold the
diaper in place for the collection and retention of urine and
feces. One area of concern in the development and construction of
the modern disposable diaper has been maintaining the wearer's
comfort and the fit of the diaper throughout the period of use of
the diaper, especially on active infants and young children.
[0005] Disposable diapers have front and back waist regions that
are usually characterized by side panels or ear flaps that extend
in the lateral direction on each end of the diaper so as to
encircle the waist and hold the diaper in place. The front waist
region normally includes a landing member upon which decorative
indicia may be placed. The back waist region normally includes a
securing tab on each side for attaching to the landing member. The
securing tab and landing member can be attached by hook and prong
fastening means similar to Velcro, by a pressure-sensitive adhesive
on a securing tab tape, or by other suitable means.
[0006] Disposable diapers may also include elasticized waist bands,
leg cuffs and side panels. The elasticized components improve the
fit of the diaper and can assist in precluding leakage from the
diaper.
[0007] U.S. Pat. No. 5,242,436 is directed to a disposable diaper
that has an elasticized waist band with a dual tensioning fastening
system to improve the dynamic fit of the elasticized waist band and
the containment characteristics of the absorbent article. A pair of
elasticized side panels that are elastically extensible in the
lateral direction are disposed in the back waist region between the
topsheet and the back sheet in the ear flaps of the diaper on
either side of the absorbent core.
[0008] The topsheet and the backsheet are extensible, but
inelastic. The webs can be stretched, but are permanently elongated
and do not have significant recovery of their prestretched
dimension. It is necessary to activate the topsheet and back sheet
in the region of the elastic side panels so that the topsheet and
back sheet can stretch and recover with the side panels. The
topsheet and back sheet are activated by incremental mechanical
stretching in the cross-machine direction. A laminate of the
topsheet, back sheet, and elastic side panel is passed in an
untensioned condition through at least one set of meshing
corrugated rolls. The laminate is rendered elastically extensible
in the cross direction up to the limit of incremental
stretching.
[0009] U.S. Pat. Nos. 4,981,747 and 5,114,781 are directed to the
preparation of composite elastic laminates for use in disposable
absorbent articles, including diapers. The laminates are of elastic
materials and extendable but nonelastic nonwoven webs. The webs are
described as "reversibly necked," which is to say that the webs are
permanently elongated in one direction and necked down in a
direction generally perpendicular to the direction of elongation of
the web. The web is heat treated while necked. The heat treatment
is said to impart memory to the nonelastic webs so that the webs
can then be stretched and recover in a direction generally parallel
to the direction of neckdown and perpendicular to the direction of
elongation. Extension of the reversibly necked material is
described as limited to the pre-necked dimensions.
[0010] A composite elastic laminate can be prepared by laminating
the reversibly necked material to an elastic material. The laminate
is said to be elastic in a direction generally parallel to the
direction of neckdown of the reversibly necked material. A laminate
that is elastic in two directions can be prepared if the reversibly
necked material is laminated to an elastic material elongated in
the direction of extension of the web and then relaxed. The
reversibly necked material is gathered between points of attachment
to the elastic material and is said to have stretch and recovery to
the extent the gathers allow the elastic material to elongate.
[0011] Hassenboehler, Jr. et al. U.S. Pat. No. 5,244,482 describes
another method for drawing a web of nonelastic nonwoven fibers in
the machine direction. The stretched web is said to be useful as a
filter material and to have reduced pore size, improved uniformity
in pore size, and high lateral elasticity characteristic of stretch
fabric having approximately 120% elongation to break. The web is
said to be useful in preparing laminates with webs of elastomeric
polymers, among others.
[0012] The precursor web has substantial bonding and relatively low
processing extensibility and is heated to its softening temperature
and drawn in the machine direction. Elastomeric polymer webs and
webs having 50% standardized elongation before break are said to be
totally unsatisfactory for use in the practice of method.
[0013] It would be desirable to provide alternative composite
elastic laminates that have improved properties, are more
versatile, or require less effort to prepare. It would be desirable
to develop nonwoven webs for composite elastic laminates that are
strong enough to withstand the rigors of incremental mechanical
stretching in diaper construction where it is desirable to use
elastomeric strands or scrim for breathability, rather than
films.
SUMMARY OF THE INVENTION
[0014] The invention provides a nonwoven web of multipolymer
fibers, a method for making the web, a composite elastic laminate
that includes the web and an elastic component, and a disposable
absorbent article that includes the composite elastic laminate of
the invention. The laminate is suitable for use in disposable
absorbent articles, including use as elasticized side panels in
diapers that are subjected to incremental mechanical stretching to
activate the topsheet and the back sheet. The laminate is also
suitable for use as a discrete stretchable member that is attached
to the side edges of the main body of a garment, including a
diaper, and has exceptional cloth like hand.
[0015] The nonwoven web is made from multipolymer fibers that are
substantially oriented in one direction. A plurality of discrete
bond sites throughout the web bond the fibers together. The ratio
of the tensile strength of the web in the direction of orientation
of the fibers to the tensile strength of the web in the other
direction is at least about 10:1.
[0016] The multipolymer fibers are highly elongatable. The web can
be stretched to orient the fibers in one or the other of the
machine direction or the cross machine direction to substantially
increase the elongation of the web at peak load in a direction
perpendicular to the elongation of the web and to also increase the
tensile strength in the web in the direction of elongation. The web
can be stretched in the absence of heat treatment, which is to say
that the web can be stretched at a temperature from about 35 to 150
degrees Fahrenheit. Normally, the web will be stretched at an
ambient temperature from about 65 to 110 degrees Fahrenheit.
[0017] Prior to stretching, the web will typically have an
elongation at peak load in at least one of the machine direction or
the cross machine direction of at least 70 percent. Mechanical
stretching permanently elongates the web and develops a high degree
of stretchability in the direction perpendicular to the elongation
of the web. The elongation at peak load in the direction
perpendicular to the direction of stretch is increased by a factor
of at least about 2:1, and in a more specific aspect of the
invention, by a factor of more than 4:1. Composite elastic fabrics
made with the nonwoven web of the invention can typically be
stretched to the elastic limit of the elastic component since the
web is usually capable of stretching farther. The web is
substantially strengthened and does not undergo thinning and damage
during incremental mechanical stretching.
[0018] The multipolymer fibers can be formed with the different
polymers in discrete structural domains or from a blend of polymers
that are miscible, immiscible, or a blend of miscible and
immiscible polymers. A blend can also be used as one component in a
multipolymer fiber formed of discrete structural domains. In one
embodiment, the polymers are immiscible and are blended to form a
dominant continuous phase and at least one dispersed phase.
Exemplary immiscible polymers include polyethylene, including
linear low density polyethylene and polypropylene. These polymers
are normally considered to be inelastic. Either polymer can be the
dominant continuous phase. The blend can also include an elastic
component. The preferred blend includes a third component that is
at least partially miscible with the two phases and gives the blend
highly elongatable characteristics.
[0019] An example of a suitable blend for forming multipolymer
fibers is:
[0020] isotactic polypropylene present in an amount of about 65 to
80 percent by weight based upon the weight of the blend;
[0021] linear low density polyethylene present in an amount from
about 1 to 5 percent by weight based upon the weight of the blend;
and
[0022] a block or grafted polyolefin copolymer or terpolymer having
at least a portion of the chain thereof miscible with the isotactic
polypropylene and wherein the block or grafted polyolefin copolymer
or terpolymer is present in an amount from about 15 to 30 percent
by weight based upon the weight of the blend.
[0023] Examples of such a block or grafted polyolefin copolymer are
the commercially available Catalloy.TM. copolymers available from
Montell.
[0024] The multipolymer fibers can be spunbond continuous
filaments, carded discontinuous staple fibers and meltblown fibers.
Normally, the web will be prepared from continuous spunbond
filaments.
[0025] In another embodiment, the invention comprises a composite
fabric that has at least one layer of an elastomeric component
bonded to at least one layer of the nonwoven web described above.
The elastomeric component can be selected from elastic strands,
scrim, elastic films, and breathable elastic films. The fabric can
be gathered in the direction in which the nonwoven web component
previously was permanently elongated by mounting the web to the
stretched elastic component and then relaxing the elastic component
in the manner taught in U.S. Pat. No. 5,114,781.
[0026] In yet another embodiment, the invention comprises a method
for substantially increasing the elongation at peak load of a
bonded nonwoven web wherein a web of multipolymer fibers is
prepared and then stretched in one of the machine or cross machine
directions at a temperature from about 35 to 150 degrees Fahrenheit
to permanently elongate the web. The elongation at peak load of the
web in the direction perpendicular to the stretch direction is
substantially increased. The method can include the additional
step, if desired, of stabilizing the web against retraction of the
fibers by lightly bonding the stretched web, normally through the
application of heat and pressure.
[0027] Thus, the invention provides a composite elastic fabric with
cloth like hand and good cover characteristics that is suitable for
use in disposable absorbent articles, especially as elastic side
panels in diapers, either as discrete members attached to the main
body of the garment or in laminates mounted between the topsheet
and back sheet. The nonwoven web component of the composite fabric
has the strength to perform well in incremental stretching. The web
can be permanently elongated in one direction to impart substantial
ability to stretch in a direction perpendicular to the direction of
elongation, all in the absence of heat treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Some of the objects and advantages of the invention have
been stated. Others will appear when taken in connection with the
accompanying drawings and photomicrographs, in which:
[0029] FIG. 1 is a perspective view of a portion of a bonded
nonwoven web of multipolymer fibers prior to stretching in
accordance with the invention;
[0030] FIG. 2 is a perspective view of the nonwoven web of FIG. 1
after the nonwoven web has been permanently elongated in accordance
with the invention and stabilized by application of light
bonding;
[0031] FIG. 3 is a schematic of an exemplary process for
permanently elongating in the machine direction a bonded nonwoven
web of multipolymer fibers;
[0032] FIG. 4 is a partially broken away top perspective view of a
portion of the schematic of FIG. 3 taken along line 4-4 and showing
the reduction in the cross direction of the width of the web as the
web is stretched;
[0033] FIG. 5 is an exploded perspective view of a laminate of two
nonwoven webs of the invention as shown in FIG. 2 with elastomeric
strands placed between the two webs;
[0034] FIG. 6 is a plan view of the relevant structure of a
disposable diaper of the invention having the outer surface back
sheet facing the viewer;
[0035] FIG. 7 is an exploded perspective view of a broken away
portion of the diaper of FIG. 6, showing the placement within the
diaper of a composite fabric of the invention;
[0036] FIG. 8 is a photomicrograph at 5.times. magnification of a
pointbonded spunbond nonwoven web of multipolymer continuous
filaments prior to stretching in accordance with the invention;
[0037] FIG. 9 is a photomicrograph showing the web of FIG. 8 at
20.times. magnification;
[0038] FIG. 10 is a photomicrograph at 5.times. magnification
showing a point bonded spunbond nonwoven web of multipolymer
continuous filaments after stretching in the machine direction
followed by light bonding to stabilize the stretched web against
retraction;
[0039] FIG. 11 is a photomicrograph showing the web of FIG. 10 at
20.times. magnification;
[0040] FIG. 12 is a photomicrograph at 20.times. magnification of a
section through a pointbonded spunbond nonwoven web of multipolymer
continuous filaments prior to stretching in accordance with the
invention and showing a pointbond horizontally oriented in the body
of the fabric; and
[0041] FIG. 13 is a photomicrograph at 20.times. magnification of a
section through a pointbonded spunbond nonwoven web of multipolymer
continuous filaments after the web has been stretched in accordance
with the invention and showing a pointbond that has become
vertically orientated in the fabric as a result of the
stretching.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The invention will be described with particular reference to
the drawings, in which illustrative embodiments of the invention
are set forth. It should be understood that persons skilled in the
art to which this invention pertains may modify the specific
details described while still continuing to use the invention. The
description should be understood as a broad teaching of the
invention that is directed to the persons of skill in the
applicable arts.
[0043] FIG. 1 is a perspective view of a portion of a bonded
nonwoven web 20 prepared from multipolymer fibers. The nonwoven
fibrous web represented in FIG. 1 should be considered in a generic
sense to include generally planar structures that are relatively
flat, flexible and porous and are comprised of multipolymer staple
fibers or continuous filaments. The nonwovens may be carded,
spunbonded, wet laid, air laid or meltblown. Normally, prior to
stretching, the web will have an elongation at peak load in at
least one of the machine direction or the cross machine direction
of at least 70 percent. In the embodiment illustrated, the nonwoven
fibrous web is a spunbonded nonwoven comprising multipolymer
spunbond continuous filaments. The filaments are bonded together at
discrete bond sites 22 distributed throughout the fabric to form a
unitary, coherent nonwoven web.
[0044] FIG. 8 is a photomicrograph at 5.times. magnification
showing a point bonded nonwoven fabric of spunbond continuous
multipolymer filaments. This same web is shown in FIG. 9 at a
magnification of 20 times. The individual filaments and the
consolidated areas of the point bonds are evident. As is evident
from the photomicrographs, the point bonds are planar and lie in
the plane of the web. The point bond sites 22 comprise discrete
areas where the filaments have been fusion bonded by the
application of heat and pressure. In the embodiment illustrated,
the bond sites 22 are point bonds, but other known configurations
or shapes could be employed, including lines or other patterns.
[0045] The multipolymer fibers of the invention are predominantly
formed from polymers that normally are considered nonelastic.
Useful polymer combinations for use in the practice of the
invention are taught in published PCT International Patent
Application WO 96/16216 entitled Extensible Composite Nonwoven
Fabrics. The contents of this application and the teachings
contained therein are hereby incorporated by reference in their
entirety. The term "multipolymer fibers" includes staple and
continuous filaments prepared from blends of two or more polymers
and from two or more polymers present in discrete structural
domains in the fiber. For the purposes of the invention, the term
"polymer" is used in a general sense, and is intended to include
homopolymers, copolymers, grafted copolymers, and terpolymers. The
term blend is also used generally herein, and is intended to
include immiscible and miscible polymer blends. The polymers are
considered to be "immiscible" if they exist in separate, distinct
phases in the molten state; all other blends are considered to be
"miscible." It is understood that varying levels of miscibility can
exist, and are also intended to be within the scope of this
invention.
[0046] Blends with more than two polymers may also be utilized,
including those with three or more polymer components. Both
immiscible and miscible polymers may be added to a two component
blend to impart additional properties or benefits with respect to
blend compatibility, viscosity, polymer crystallinity or phase
domain size.
[0047] Since the polymers employed in the invention will undergo
extrusion, stabilizers and antioxidants are conventionally added to
the polymer. Other additives may also be added in accordance with
the present invention. For example inorganic additives such as
titanium dioxide, talc, fumed silica or carbon black. The polymer
resin may also contain other additives, such as other polymers,
diluents, compatibilizers, antiblocking agents, impact modifiers,
plasticizers, UV stabilizers, pigments, delusterants, lubricants,
wetting agents, antistatic agents, nucleating agents, rheology
modifiers, water and alcohol repellents, and the like. It is also
anticipated that additive materials which have an affect on
processing or product properties, such as extrusion, quenching,
drawing, laydown, static and/or electrical properties, bonding,
wetting properties or repellency properties may also be used in
combination with the blend. In particular, polymeric additives may
also be used that impart specific benefits to either processing
and/or end use.
[0048] The multipolymer fibers are normally formed of a polymer
blend composed of two or more polymers. The polymers of the blend
can be miscible, immiscible, or a combination of miscible and
immiscible polymers. In one embodiment in accordance with the
invention, the polymers may exist as a dominant continuous phase
and at least one substantially discontinuous dispersed phase. In
the case where the blend exists as a dominant continuous phase and
at least one discontinuous phase, other polymers may also be
present which are either miscible in one, or the other, or both
polymer phases.
[0049] According to a further aspect of the invention, the
multipolymer fibers are formed of a polymer blend including a
relatively low modulus polymer and at least one higher modulus
polymer. It is believed that this combination is particularly
valuable when the low modulus polymer is the dominant phase and the
higher modulus polymer is dispersed therein. It is theorized that
the higher modulus polymer acts to "reinforce" the low modulus
dominant phase, lending stability to spinning, and stiffening the
web just enough to allow for higher bond temperatures while
reducing the risk of the web sticking to and wrapping the calender.
In the case of multipolymer fibers formed of an immiscible polymer
blend it is believed that the small amount of the dispersed polymer
may have the effect of wind up speed suppression (WUSS) on the
dominant polymer phase as described by Brody in U.S. Pat. No.
4,518,744. Wind up speed suppression occurs when a small amount of
an immiscible additive effectively reduces the degree of molecular
orientation within the fiber at a given filament spinning velocity.
The result is a filament with generally higher elongation and lower
tenacity.
[0050] In yet another aspect of the invention, the multipolymer
fibers are formed of a polymer blend composed of a dominant
continuous phase, and at least one polymer, having low mutual
affinity with the dominant phase, dispersed therein, and at least
one additional polymer which is at least partially miscible in one
or the other or both continuous and dispersed polymer phases. If
the one additional polymer is miscible in the dominant phase, and
effectively reduces its crystallinity, it is believed that the
improved extensibility observed in the resulting composites may be
due to an "impact-modifying" effect. If the one additional polymer
has an affinity for both polymers, or serves to lower the surface
energies between the two phases, it is believed that the
improvement observed in the composite extensibility is due to a
compatibilization effect. Independent of theory, the blend must
ultimately form filaments or fibers, which when formed into webs
and composite structures exhibit the properties described by the
invention, meaning low fuzz and good elongation.
[0051] In one embodiment, the multipolymer fibers may comprise from
1 to 50 percent by weight polyethylene and from 99 to 50 percent by
weight polypropylene. Fabrics formed from such blends exhibit low
fuzz and good elongation.
[0052] In applications where tensile strength is particularly
important and high elasticity is of lesser concern, the composite
fabric may include a coherent, extensible nonwoven web formed of
fibers of a polyethylene and polypropylene blend where the
polyethylene is present in the range of 1% to 10% and the
polypropylene is present in the range of 90% to 99% by weight. In
still another embodiment, very substantial and surprising increases
in elongation can be achieved by blending a third polymer component
into the blend. For example, the multipolymer fibers may include a
dominant amount of a polypropylene, such as isotactic
polypropylene, a small amount of a polymer having low mutual
affinity with the dominant polymer, such as polyethylene, and an
additional third polymer which either reduces crystallinity and/or
compatibilizes the blend. What results is a softer web, with
extremely high extensibility. Preferred multipolymer fibers
according to this embodiment may comprise greater than 50 percent
by weight polypropylene, 1 to 10 percent polyethylene, and 10 to 40
percent of the third polymer. Suitable additional third polymers
include polypropylene copolymers and terpolymers such as the
commercially available Catalloy.TM. copolymers available from
Montell. These resins are characterized by having the comonomer(s)
exist to some degree in blocks, and wherein at least some portion
of the polymer chain is miscible with one or the other, or both,
dominant and dispersed polymer phases. Other suitable polymers are
the Reflex.TM. flexible polyolefins from Rexene. These
crystallinity reducing resins are characterized as having atactic
segments present in the polymer chain, such that the "tacticity" of
the polymer is affected.
[0053] Especially preferred multipolymer fibers according to this
embodiment comprise 65 to 80 percent isotactic polypropylene, 1 to
5 percent polyethylene, and 15 to 30 percent of a polyolefin
copolymer wherein at least a portion of the chain is miscible with
isotactic polypropylene.
[0054] Another class of useful and advantageous products according
to this aspect of the invention employ multipolymer fibers formed
of a polymer blend comprised of a soft, extensible polymer phase,
and at least one additional polymer having low mutual affinity with
the soft, extensible phase, such that it modifies either the
rheological, mechanical, and/or thermal properties of the fibers in
a way that improves processability (e.g. melt spinning), bonding
and/or abrasion resistance while maintaining high extensibility. In
a preferred embodiment the soft, extensible phase is present as a
dominant, continuous phase. For example, polyethylene can be used
as the soft, extensible dominant phase and a polypropylene as the
additional modifying polymer. In a preferred embodiment the
additional polymer is added in a small proportion relative to the
dominant phase. In another preferred embodiment, the additional
polymer exhibits higher viscosity relative to the dominant phase.
Blending a relatively small proportion of the higher viscosity
polypropylene with the soft, extensible polyethylene imparts
greatly increased abrasion resistance to a nonwoven fabric formed
from the polymer blend, without significant adverse effect upon
other important fabric properties, such as extensibility, softness,
tensile strength, etc. The spinnability of the polyethylene is also
improved by the presence of the additional polypropylene. According
to this embodiment, the fibers preferably comprise between 2 to 50
percent by weight of the propylene polymer, e.g. 3%
ethylene-propylene copolymer, and 98 to 50 percent by weight of the
soft, extensible polymer, e.g. polyethylene. In one particularly
preferred embodiment, the fiber composition may range from 5 to 40
percent by weight propylene polymer, and most desirably between 5
to 25 percent by weight propylene polymer and 75 to 95 percent by
weight polyethylene. Especially suited for applications requiring
good extensibility, tensile strength and abrasion resistance are
fiber compositions of from 5 to 25 percent by weight propylene
polymer. A most preferred embodiment contains 5 to 25 percent by
weight of ethylene-propylene copolymer or terpolymer and 75 to 95
percent by weight linear low density polyethylene. In these
embodiments, the lower melting polyethylene is present as a
substantially continuous phase in the blend and the higher melting
propylene polymer is present as a discontinuous phase dispersed in
the polyethylene phase.
[0055] In producing the fibers, the polyethylene and polypropylene
components are combined in appropriate proportional amounts and
intimately blended before being melt-spun. In some cases sufficient
mixing of the polymer components may be achieved in the extruder as
the polymers are converted to the molten state. In other cases,
more dynamic mixing may be required.
[0056] Various types of polyethylene may be employed. As an
example, a branched (i.e., non-linear) low density polyethylene or
a linear low density polyethylene (LLDPE) can be utilized and
produced from any of the well known processes, including
metallocene and Ziegler-Natta catalyst systems. LLDPE is typically
produced by a catalytic solution or fluid bed process under
conditions established in the art. The resulting polymers are
characterized by an essentially linear backbone. Density is
controlled by the level of comonomer incorporated into the
otherwise linear polymer backbone. Various alpha-olefins are
typically copolymerized with ethylene in producing LLDPE. The
alpha-olefins which preferably have four to eight carbon atoms, are
present in the polymer in an amount up to about 10 percent by
weight. The most typical comonomers are butene, hexene,
4-methyl-1-pentene, and octene. In general, 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. In particular, preferred density values range from
0.87 to 0.95 g/cc (ASTM D-792) and melt index values usually range
from 0.1 to about 150 g/10 min. (ASTM D1238-89, 190EC). Preferably,
the LLDPE should have a melt index of greater than 10, and more
preferably 15 or greater for spunbonded filaments. Particularly
preferred are LLDPE polymers having a density of 0.90 to 0.945 g/cc
and a melt index of greater than 25. Examples of suitable
commercially available linear low density polyethylene polymers
include those available from Dow Chemical Company, such as ASPUN
Type 6811 (27 MI, density 0.923), Dow LLDPE 2500 (55 MI, 0.923
density), Dow LLDPE Type 6808A (36 MI, 0.940 density), and the
Exact series of linear low density polyethylene polymers from Exxon
Chemical Company, such as Exact 2003 (31 MI, density 0.921).
[0057] Various polypropylenes made by processes known to the
skilled artisan may also be employed. In general, the polypropylene
component can be an isotactic or syndiotactic propylene
homopolymer, copolymer, or terpolymer. Examples of commercially
available propylene homopolymers which can be used in the present
invention include SOLTEX Type 3907 (35 MFR, CR grade), HIMONT Grade
X10054-12-1 (65 MFR), Exxon Type 3445 (35 MFR), Exxon Type 3635 (35
MFR) AMOCO Type 10-7956F (35 MFR), and Aristech CP 350 J (melt flow
rate approximately 35). Examples of commercially available
copolymers of propylene include Exxon 9355 which is a random
propylene copolymer with 3% ethylene, 35 melt flow rate; Rexene
13S10A, a 10 melt flow rate random propylene copolymer with 3%
ethylene; Fina 7525MZ, an 11 melt flow rate 3% ethylene random
propylene copolymer, Montel EPIX 30F, a 1.7% ethylene, 8 melt flow
rate random copolymer of propylene. When the propylene polymer is
the dominant continuous phase of the blend, the preferred melt flow
rate is greater than 20. When the propylene polymer exists as the
dispersed phase of the blend, the preferred melt flow rate is less
than 15 and most preferably less than 10.
[0058] In still another embodiment, the multipolymer fibers of the
web may be bicomponent or multicomponent fibers or filaments. The
term bicomponent or multicomponent refers to the existence of the
polymer phases in discrete structured domains, as opposed to blends
where the domains tend to be dispersed, random or unstructured. The
polymer components can be configured into any number of
configurations including sheath-core, side-by-side, segmented pie,
islands-in-the-sea, or tipped multilobal. A coherent extensible
nonwoven web can be made, for example, from a sheath-core
bicomponent fiber having a polyester core and a polyethylene
sheath, or the sheath or core can comprise a blend as discussed
above. Alternatively, the extensible web can comprise a single web
containing a combination of spunbonded filament and meltblown
fibers or a combination of carded staple fibers and meltblown
fibers.
[0059] The extensible nonwoven web, in all embodiments in
accordance with the present invention, is characterized by having
high surface abrasion resistance and high elongation. The surface
abrasion resistance of the web may be conveniently measured
objectively by physical tests which are standard in the industry,
such as the Taber abrasion test as defined by ASTM Test Method
D-3884-80. Extensible webs useful in the composite fabrics of the
present invention are characterized by having a Taber abrasion
value (rubber wheel) of greater than 10 cycles. The webs are
further characterized by having an elongation at peak load (ASTM
D-1682), prior to stretching, in either the machine direction (MD)
or in the cross-machine direction (CD) or both of at least 70
percent, more preferably at least 100 percent, and most desirably
at least 150 percent. The multipolymer fibers of the web are of
relatively fine diameter, typically 10 denier or less.
[0060] The web shown in FIG. 1 has been bonded so that it can be
stretched, but has not yet been stretched. The web shown in FIG. 1
has been point bonded by passing the web through a calender nip in
which one of the calender rolls is smooth and one of the calender
rolls has a patterned surface for applying the bonding pattern.
Intermittent point bond regions 22 are formed wherein the web is
bonded. The discrete bond sites comprise areas where the fibers
have been fusion bonded together. It should still be possible to
trace an individual filament through the bond site if the bond site
is not overbonded. Preferably, the fused regions cover between 6
and 30 percent of the area of the web, more preferably 8 to 20
percent, and most preferably 12 to 18 percent of the web 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
is maintained.
[0061] The skilled artisan should recognize that there are myriad
other ways to bond a web sufficiently to enable the web to be
stretched. While thermal point bonding is most preferred for
spunbond, carded, and other webs, any thermal, chemical, or
mechanical bonding treatment may be used to form a coherent web
structure.
[0062] Turning now to a discussion of the properties of the web
after stretching, FIG. 2 represents the nonwoven web 20 of FIG. 1
that has been permanently elongated by mechanical stretching in
either the machine direction or the cross direction. It should be
understood that the web can be subjected to stretching in either of
the cross machine or machine direction to achieve the benefits of
the invention, but not both. Normally, the web is stretched in a
direction having an elongation at peak load of at least 70 percent.
It should be recognized that this property could be met in one of
or both the machine and cross machine directions.
[0063] The web has been stretched and permanently elongated by the
stretching at a temperature of between about 35 to 150 degrees
Fahrenheit. The web normally is elongated in the absence of heat
treatment at an ambient temperature, which typically varies from
about 65 degrees on a relatively cold day to about 110 degrees on a
hot summer day, and most typically is on the order of about 65 to
85 degrees.
[0064] As a result of the "cold" stretching, the nonwoven web
develops extraordinary elongation at peak load in the direction
perpendicular to the direction of stretch. Elongation at peak load
can be at least about 400 to 500% and values above 700% have been
achieved. Typically, the ratio of elongation at peak load in the
direction perpendicular to the direction of stretch to the
elongation at peak load in the stretch direction is increased at
least about 2:1 to more than 10:1. Increase by a factor of at least
about 6:1 to 8:1 is typical. Thereafter, the fabric is capable of
stretch well beyond the original dimension of the fabric in the
direction perpendicular to the stretch direction. The tensile
strength of the webs in the direction of orientation of the
filaments, which is normally the stretch direction, is greatly
increased. The ratio of tensile strength of the web in the
direction of orientation of the fibers to the tensile strength of
the web in the other direction is at least about 10:1 and can be
increased to at least about 16:1.
[0065] A further characteristic of the web is high extensibility at
low force. The nonwoven web has an elongation in one direction,
which is the direction perpendicular to the stretch direction, of
at least 70% when a load is applied to the web in that direction
that is less than or equal to about 300 grams force per inch. A
force of about 300 grams force per inch or less is about the force
that the consumer feels on the wrist when using a fabric in
accordance with the invention. The web can be prepared wherein the
elongation of the web in the direction perpendicular to the stretch
direction is at least 100% to 350% at a load of less than 300 grams
force per inch. Table 2, below, shows examples at 100%, 200%, and
350% elongation at loads of less than 300 grams force per inch.
[0066] While not wishing to be bound by theory, it is believed that
the filaments that are not oriented in the stretch direction prior
to stretching become oriented in the stretch direction as a result
of the stretching, but are either not elongated or are only
partially elongated. This feature is graphically illustrated in the
photomicrographs shown in FIGS. 10 and 11, which are at 5 and
10.times. magnification, respectively, and show a multipolymer
continuous filament pointbonded spunbond nonwoven web that has been
stretched in the machine direction. A substantial number of the
filaments can be seen to be oriented in the machine direction,
which is the direction of stretch. In any event, the fabric becomes
stretchable in the direction perpendicular to the stretch direction
to an extent beyond the prestretched dimension in that
direction.
[0067] The fabric also develops a z-direction axis and becomes
thicker as the fabric is stretched and the dimension in the
direction perpendicular to the stretch direction becomes smaller.
The point bonds 22, which initially are flat and lie in the plane
of the web, become strained, and become oriented generally in the
z-axis direction within the thickness dimension of the fabric and
disposed between the opposing fabric surfaces. This detail is
graphically illustrated in FIG. 13, which shows in a
photomicrograph at 20.times. magnification the distorted, deformed
point bonds of a non-planar configuration embedded in the web
between opposite surfaces of the web. These bond sites have been
pulled into the body of the spunbond nonwoven web and extend in the
Z-direction axis. Prior to stretching, the pointbond was
horizontally oriented as shown in the photomicrograph of FIG. 12,
which is also at 20.times. magnification. Increase in the thickness
of the nonwoven web due to stretching can also be seen by comparing
FIGS. 12 and 13.
[0068] As shown in FIG. 2, the fabric has been lightly bonded after
stretching with a plurality of point bond sites 24 in a pattern
reminiscent of cross laid bricks. The point bond sites 24 include
film-like fused regions that are generally planar and are parallel
to the surface of the web and lie at the web surface. The stretched
fabric was bonded by passing through a calender nip at light
pressure and low heat to stabilize the web and to substantially
preclude retraction, since a small about of elastomeric polymer is
used in the fibers of which the fabric is made. The bonding is
graphically illustrated in the photomicrographs of FIGS. 10 and 11.
It should be recognized that a wide variety of suitable bonding
patterns are available and should provide equivalent performance in
the practice of the invention. The bonding should be enough to
stabilize the web against retraction of the fibers after elongation
to the desired extent, but not so great as to preclude stretching
in the direction perpendicular to the stretch direction, for which
the fabric is designed.
[0069] It is usually advisable to lightly bond the web after
stretching when the web will be rolled rather than supplied
directly to a laminator for lamination with an elastomeric
component. The elastomeric component of the web can cause the web
to retract in the roll if the web is not lightly bonded.
[0070] The fabric illustrated in FIG. 2 can be stretched in any of
several ways known to the skilled artisan. The fibers normally are
extruded, collected on a web forming surface, bonded, and stretched
in line. Alternatively, for certain processes, the nonwoven web is
rolled prior to stretching and stretching is accomplished as a
separate operation.
[0071] Stretching in the cross machine direction normally is
accomplished using a standard tenter frame. It should be recognized
that other methods and apparatus can be used to stretch the
nonwoven web in the cross direction, although not necessarily with
equivalent results. For example, the web can be incrementally
stretched in the cross direction using intermeshing or
interdigitating rollers.
[0072] Typically, the web is stretched in the machine direction.
One method of machine direction stretching is schematically
represented in FIGS. 3 and 4. It should be recognized that other
methods and apparatus can be used to stretch the nonwoven web in
the machine direction, although not necessarily with equivalent
results. For example, the web can be incrementally stretched in the
machine direction using intermeshing or interdigitating
rollers.
[0073] As shown in FIG. 3, a nonwoven web of multipolymer fibers 20
prepared from the polymer combinations discussed above is supplied
from a roll 26 called the unwinder. The web passes around three
rolls 28, including a load cell and two idler rolls, arranged at
the corners of a triangle for sensing and adjustment of web tension
prior to stretching the web. The web is stretched by passing
through a series of rolls in three successive S-wrap stations 30,
32, and 34. In each of the S-wrap stations shown, the bottom roller
36, 38, 40 is driven and the top roller and bottom roller form a
nip 42, 44, 46 that applies light pressure to the web that does not
bond the web, but provides sufficient grip that the web can be
stretched between the subsequent sets of S-wrap rollers. Subsequent
S-wrap roll stations are driven at increasing speeds to apply
increasing tension to the web between each set of rollers in the
S-wrap station sufficient to stretch the web.
[0074] FIG. 4 represents a partially broken away top perspective
view of a portion of the schematic of FIG. 3 taken along line 4-4.
The reduction in the cross direction of the width of the web is
shown as the web is stretched in the machine direction, first as
the web passes between the first and second S-wrap stations 30, 32,
and second as the web passes between the second and third S-wrap
stations 32, 34. The width of the web is the cross machine
direction is considerably reduced between the first S-wrap station
and the third. The web is permanently elongated.
[0075] It should be recognized that the filaments in the outer
portions of the web tend to be elongated faster than the filaments
located in the center of the web. For this reason, the distance
between the first S-wrap station and the second should be
sufficient to provide that the filaments in the center of the web
are also permanently elongated to the desired extent.
[0076] It should be recognized that other configurations of rollers
can be used to stretch the web in the machine direction. Rollers
can be used in the omega configuration to apply sufficient tension
to the web to permanently elongate the web.
[0077] After stretching, the now permanently elongated web is
treated in a manner believed to be known to the skilled artisan to
improve its uniformity by passing over first and second bow rolls
48, 50 to flatten the web and take out wrinkles. The web is then
lightly bonded to stabilize the web against retraction prior to
tension adjustment 57 and rolling the web on a winder 58 for supply
to a line for making disposable absorbent articles. The web can be
bonded by passing through a calender nip 52 formed between two
rollers 54, 56. The calender nip should be operated at light
pressure and low heat.
[0078] The calender preferably is operated so as to take up the web
at a lower speed than it is supplied by the third S-wrap station
34. Operating the calender at a lower speed than the third S-wrap
station gives the filaments, which have been overstretched to some
extent, an opportunity to retract slightly so that they do not
retract against the light bond that is later applied.
Alternatively, the lamination line could be in line, in which case
bonding the web may no longer be necessary.
[0079] Table 1 below shows two examples of nonwoven webs prepared
in accordance with the invention and compares these webs with a the
nonwoven web prior to stretching. The unstretched web is labelled
"Control" in Table 1. The nonwoven control web and the two examples
were all prepared from spunbond continuous filaments prepared from
a blend of a dominant phase of isotactic polypropylene, a dispersed
phase of linear low density polyethylene, and Catalloy.TM.
polymer.
1TABLE 1 CD MD Elonga- Elonga- tion tion CD at MD at Basis tensile
peak tensile peak MD/CD MD/CD CD/MD CD/MD Wt. strength load
strength load Tensile Elongation Tensile Elongation Example
g/m.sup.2 (g/in) (%) (g/in) (%) Ratio Ratio Ratio Ratio Control
Avg. 25.063 908 184.2 2562 191.5 2.82 1.04 0.35 0.96 S.D. 0.875
132.5719 25.8 351.4531 15.1 Ex. 1 Avg. 62.07 498.67 750.70 8135.83
70.01 16.32 0.09 0.06 10.72 S.D. 3.22 77.71 98.26 1250.15 27.02 %
Change 148% -45% 308% 218% -63% 478% -91% -83% 1015% Ex. 2 Avg.
64.61 517.53 707.35 8512.37 77.25 16.45 0.11 0.06 9.16 S.D. 3.51
69.23 83.60 1075.78 29.67 % Change 158% -43% 284% 232% -60% 483%
-89% -83% 852%
[0080] Examples 1 and 2 are were both prepared from the same
control fabric at different line conditions. The relatively slight
differences in the values obtained for the physical characteristics
of these webs is due primarily to differences in line
conditions.
[0081] The control fabric had similar physical characteristics in
the machine direction as in the cross machine direction, as is
reflected by the ratio of the tensile strength in the machine
direction to the tensile strength in the cross direction of 2.82. A
value of 2.82 means that the nonwoven control web was relatively
square in its properties. The balance of properties is also
reflected by the MD/CD elongation ratio, which reflects that the
fabric is stretchable and permanently elongatable in either the
cross direction or the machine direction.
[0082] Permanent elongation of the control fabric in the machine
direction produced nonwoven webs having the characteristics recited
in Table 1 for Examples 1 and 2. The basis weight more than doubled
from about 25 g/m.sup.2 to over 60 g/m.sup.2. The increase in basis
weight reflects that the dimension of the fabric in the cross
direction is greatly reduce by stretching in the machine
direction.
[0083] Tensile strength in the cross direction, CD, in g/in, which
is grams per one inch strip of material, is reduced by nearly half.
Elongation at peak load in the cross direction, as a percentage
based on the original width of the web, quadruples, indicating the
high degree to which the web can be stretched in the cross
direction, far exceeding the cross machine width of the web prior
to stretching. Stretchability in the cross direction is also
reflected by the increase in the ratio of the cross direction
elongation at peak load to that of the machine direction of about
10 times.
[0084] Similar, but opposite, values are obtained in the machine
direction. Tensile strength in the machine direction quadruples and
elongation at peak load is reduced by about half, indicating that
the web is permanently elongated in the machine direction. The
properties of the fabric are no longer square.
[0085] Table 2, below, compares the extensibility of the control
fabric of Table 1 with that of Example 1, Table 1. The force
required to extend the web is determined at three different
elongations. The control fabric requires a force of 420 grams per
inch to elongate the fabric 100%. At 200 and 350% elongation, the
control web breaks. In contrast, the web of Example 1 requires a
force of only 260 grams per inch to elongate the web by 350%.
2TABLE 2 Load at 100% el. Load at 200% el. Load at 350% el. Example
(g/in) (g/in) (g/in) Control 420 Breaks Breaks Example 1 52 109
260
[0086] A nonwoven web stretched as shown in FIGS. 3 and 4 is
illustrated in FIG. 5 in an exploded view of an elastic fabric
laminate of the invention 62. Elastomeric strands 60 are placed
between two nonwoven webs 20 (FIG. 2) and the laminate is bonded,
normally by application of a hot melt or other suitable adhesive.
It should be recognized that the laminate can be prepared with a
single nonwoven web on one side to produce a two layer laminate
rather than a three layer laminate, if desired. The fabric of the
invention has sufficient cover provided by Z axis development to
preclude substantial glue bleed-through. The elastomeric strands
are oriented to stretch in a direction perpendicular to the
direction in which the nonwoven webs were permanently elongated.
The webs were stretched in the machine direction as shown in FIGS.
3 and 4, and so the elastomeric fibers are oriented to stretch in
the cross machine direction.
[0087] The fabric laminate is elastic in the cross machine
direction and recovers substantially all of the distance it is
stretched when stretched below the elastic limit of the elastomeric
strands. The nonwoven webs of the invention can stretch in the
cross machine direction to many times the distance of the initial
width of the nonwoven web prior to elongation. Typically, the
strands are bonded to the web directly, without being placed under
tension or elongated.
[0088] If it is desired that the fabric laminate stretch in two
directions, then the elastic component that is sandwiched between
the nonwoven webs of the invention should provide for stretch in
two directions. The nonwoven web can then be applied to the elastic
component so as to form gathers when the elastic component is
relaxed that can allow stretch in the direction in which the web
was permanently elongated. For example, the web can be applied to
tensioned elastomeric strands so that the gathers form when the
strands are relaxed. The laminate can then be stretched and will
exhibit recovery to the extent allowed by the gathers.
[0089] A wide variety of elastic components are suitable for use in
the practice of the invention. Elastomeric strands, scrim, or
elastomeric film, including perforated and nonperforated films and
barrier or moisture vapor transmitting films, are all suitable for
use, depending on the results desired. Elastomeric strands and
scrim tend to produce fabrics with enhanced breathability as
compared to films and are preferred in countries of high heat and
humidity. Films are preferred in more arid climates since they are
cheaper.
[0090] The elastic laminate of the invention is suitable for use as
an elastic fabric having highly desirable cloth like
characteristics. The laminate is suitable for use in a variety of
disposable absorbent articles. The laminate is useful as a stretch
side panel in diaper construction.
[0091] A disposable diaper 64 is represented in FIG. 6 that
incorporates a pair of elastic side panels 62 made from fabric
laminate of the invention. The diaper is shown in plan view having
the outer surface back sheet 66 facing the viewer. Internal
structure is shown in outline by the dashed lines. The diaper
includes a water pervious topsheet 65 (FIG. 7), a water impervious
back sheet 66, and an absorbent core 68 that typically comprises
wood pulp or other absorbent material and typically includes
superabsorbent polymer powder. A surge layer, not shown, may be
used to provide a holding area for urine in the front waist region
for the time required for the superabsorbent polymer to take up the
urine after strikethrough.
[0092] The diaper includes front and rear waist bands 70, 72, which
typically are elasticized. Securing tabs 74 are provided on the
back waist region on opposite sides of the waistband for securing
the diaper back waist region to the front waist region about the
waist of the wearer. The securing tabs typically are secured to a
landing panel on the front waist region that includes decorative
indicia. The tabs can be secured by pressure sensitive adhesive or
a hook and loop fastening system similar to Velcro.
[0093] The front and rear waist regions are shown to flare
outwardly from the body of the diaper to provide sufficient
material to encircle the waist and to provide for secure attachment
of the back waist region to the front about the waist of the
wearer. These outwardly flared portions are often referred to as
ears. The securing tabs extend outwardly from and are anchored to
the ears 76 of the back waist region.
[0094] The elastic side panels of the invention 62 are laminated
into the diaper structure between the back sheet and the topsheet.
As shown, the anchored ends of the securing tabs overlap somewhat
the elastic side panels. The side panels are oriented in the diaper
to provide transverse stretch, which is in the direction of tension
on the securing tab, to improve the fit of the diaper, even under
conditions where the wearer is active. When made with elastic scrim
or elastomeric fibers, the composite typically has good
breathability, but also contributes to fluid barrier outside the
strikethrough and absorbent region. Elastic film can also be used
as described in Weil et al. U.S. Pat. No. 5,242,436, which
illustrates a diaper construction having an elastic side panel
therein.
[0095] Placement of the elastic side panel of the invention into
the diaper is represented in FIG. 7. As shown, the laminate is
placed between the top sheet and the back sheet so as to provide
some elasticity to the ear region in the direction of pull of the
securing tab.
[0096] One of the advantages of the invention is that the fabric of
the invention provides a soft, cloth like hand and excellent cover,
and yet is exceptionally strong. In the diaper construction
illustrated, the topsheet and the back sheet typically are
constructed of inelastic materials that do not exhibit stretch and
recovery and it normally is necessary to treat the diaper
construction in the region of the elastic side panel so that the
topsheet and back sheet will be activated to move with the elastic
side panel. A suitable method for mechanically incrementally
stretching in the cross direction the composite of the top sheet,
elastic stretch laminate of the invention, and the back sheet is
described in Weil et al. U.S. Pat. No. 5,242,436.
[0097] The description of the method of U.S. Pat. No. 5,242,436 is
incorporated herein by reference in its entirety. The composite
passes through meshing corrugated rolls as described. Incremental
stretching in the cross direction permanently elongates the
topsheet and back sheet components and destroys any light bonding
of the elastomeric nonwoven web composite. The topsheet and the
back sheet can now be stretched to provide for stretching of the
elasticized side panel. The fabric of the invention from which the
elasticized side panel is made is sufficiently strong by virtue of
having been already stretched in the machine direction to withstand
the rigors of incremental stretching in the composite and to
provide a desirable provide cover.
[0098] It should be recognized that the nonwoven fabric laminate of
the invention can be used in the manner described in U.S. Pat. Nos.
4,981,747 and 5,114,781 as a fabric that is secured to the securing
tab and mounted onto the diaper back sheet rather than laminated
within the diaper between the topsheet and the back sheet.
[0099] Particular embodiments of the invention have been described
in detail in the drawings, photomicrographs, and specification and
specific terms have been used. These should be understood in a
generic and descriptive sense and not for purposes of limitation.
The scope of the invention is defined by the claims.
* * * * *