U.S. patent application number 09/909486 was filed with the patent office on 2003-01-30 for high-elongation apertured nonwoven web and method for making.
This patent application is currently assigned to The Procter & Gamble Company. Invention is credited to Benson, Douglas H., Curro, John J., Desai, Fred N., Nakahata, Hiroshi.
Application Number | 20030021951 09/909486 |
Document ID | / |
Family ID | 25427303 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030021951 |
Kind Code |
A1 |
Desai, Fred N. ; et
al. |
January 30, 2003 |
High-elongation apertured nonwoven web and method for making
Abstract
An extensible apertured nonwoven web, and a method for making
such an apertured nonwoven web. In one embodiment the method
comprises the steps of providing an apertured nonwoven web,
incrementally stretching it in a direction substantially parallel
to the cross machine direction, and applying tension in the machine
direction such that the web width after applying tension is less
than the web width after incremental stretching. In another
embodiment the method comprises the steps of providing a nonwoven
web; weakening the nonwoven web at a plurality of locations to
create a plurality of weakened, melt-stabilized locations; applying
a first tensioning force to the nonwoven web to cause the nonwoven
web to rupture at the plurality of weakened, melt-stabilized
locations creating a plurality of apertures in the nonwoven web
coincident with the weakened, melt-stabilized locations,
incrementally stretching the nonwoven web in a direction
substantially parallel to the cross machine direction, and applying
tension in the machine direction such that the web width after
applying machine direction tension is less than the web width after
incremental stretching. An apparatus for producing a web of the
present invention by this method is also disclosed. The extensible
apertured nonwoven web produced has a plurality of apertures each
having a hole size greater than 2 mm.sup.2, and a hole aspect ratio
less than 6, the nonwoven web having an open area greater than 15%
and being capable of at least 70% extension in the cross machine
direction at a loading of 10 g/cm.
Inventors: |
Desai, Fred N.; (Fairfield,
OH) ; Nakahata, Hiroshi; (Kobe, JP) ; Curro,
John J.; (Cincinnati, OH) ; Benson, Douglas H.;
(West Harrison, IN) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY
INTELLECTUAL PROPERTY DIVISION
WINTON HILL TECHNICAL CENTER - BOX 161
6110 CENTER HILL AVENUE
CINCINNATI
OH
45224
US
|
Assignee: |
The Procter & Gamble
Company
|
Family ID: |
25427303 |
Appl. No.: |
09/909486 |
Filed: |
July 20, 2001 |
Current U.S.
Class: |
428/131 ; 19/296;
428/137 |
Current CPC
Class: |
D04H 1/5412 20200501;
D04H 1/5418 20200501; A61F 2013/51322 20130101; Y10T 428/24273
20150115; Y10T 428/24322 20150115; A61F 13/512 20130101; D06C 3/00
20130101; D04H 1/559 20130101; D04H 1/56 20130101; B29C 55/146
20130101; D04H 1/5405 20130101 |
Class at
Publication: |
428/131 ;
428/137; 19/296 |
International
Class: |
B32B 003/10; D01G
025/00; D01G 027/00 |
Claims
What is claimed is:
1. A nonwoven web comprising a plurality of apertures each having a
hole size greater than 2 mm.sup.2, and a hole aspect ratio less
than 6, said nonwoven web having an open area greater than 15% and
being capable of at least 70% extension in the cross machine
direction at a loading of 10 g/cm.
2. The nonwoven web of claim 1, wherein said nonwoven web has a
basis weight between 15 and 70 gsm.
3. The nonwoven web of claim 1, wherein said nonwoven web has a
basis weight between 40 and 50 gsm.
4. The nonwoven web of claim 1 wherein said nonwoven web is a web
selected from the group consisting of a bonded carded web of
fibers, a web of spunbonded fibers, a web of meltblown fibers, and
a multilayer material including at least one of said webs.
5. The nonwoven web of claim 4 wherein said web of meltblown fibers
includes meltblown microfibers.
6. The nonwoven web of claim 1, wherein said nonwoven web is a
topsheet on a disposable absorbent article.
7. A nonwoven web comprising a plurality of apertures formed by
application of a tensioning force, said apertures coincident with a
plurality of weakened, melt-stabilized locations, said apertures
having a circumferential edge, a portion of said circumferential
edge being defined by a remnant of said melt-stabilized locations,
said nonwoven web capable of extension in the cross machine
direction of at least 70% at a loading of 10 g/cm.
8. The nonwoven web of claim 7, wherein said nonwoven web comprises
an open area greater than 15% and an average aperture size greater
than 2.0 mm.sup.2.
9. The nonwoven web of claim 7, wherein said nonwoven web has a
basis weight between 15 and 60 gsm.
10. The nonwoven web of claim 7, wherein said nonwoven web is a
topsheet on a disposable absorbent article.
11. A method for making a highly extensible apertured nonwoven web
comprising the steps of: a) providing a nonwoven web having a
length measured in a machine direction and a first width measured
in a cross machine direction; b) weakening said nonwoven web at a
plurality of locations to create a plurality of weakened,
melt-stabilized locations; c) applying a first tensioning force to
said nonwoven web to cause said nonwoven web to rupture at said
plurality of weakened, melt-stabilized locations creating a
plurality of apertures in said nonwoven web coincident with said
plurality of weakened, melt-stabilized locations, said first
tensioning force causing said nonwoven web to have a second width;
d) incrementally stretching said nonwoven web to locally extend
portions of said nonwoven web in a direction substantially parallel
to said cross machine direction to a third width that is greater
than the second width; e) applying tension to said nonwoven web in
the machine direction such that said nowoven web has a width less
than said -third width.
12. The method of claim 11 wherein said nonwoven web is a web
having a peak CD extensibility of at least 150%, and being selected
from the group consisting of a bonded carded web of fibers, a web
of spunbonded fibers, a web of meltblown fibers, and a multilayer
material including at least one of said webs.
13. The method of claim 12 wherein said meltblown web includes
meltblown microfibers.
14. The method of claim 11 wherein said nonwoven web comprises an
elastic nonwoven web.
15. The method of claim 11 wherein said nonwoven web comprises a
nonelastic nonwoven web.
16. The method of claim 11 wherein said second tensioning step
causes said nonwoven web to exhibit extension in the cross machine
direction of at least 70% at 10 g/cm loading.
17. A method for making a highly extensible apertured nonwoven web
comprising the steps of: a) providing an apertured nonwoven web
having a length measured in a machine direction and a first width
measured in a cross machine direction; b) incrementally stretching
said nonwoven web to locally extend portions of said nonwoven web
in a direction substantially parallel to said cross machine
direction to a second width that is greater than the first width;
e) applying tension to said nonwoven web in the machine direction
such that said nowoven web has a width less than said second
width.
18. The method of claim 17 wherein said nonwoven web is a web
having a peak CD extensibility of at least 150%, and being selected
from the group consisting of a bonded carded web of fibers, a web
of spunbonded fibers, a web of meltblown fibers, and a multilayer
material including at least one of said webs.
19. The method of claim 17 wherein said nonwoven web is a composite
material comprising a mixture of fibers and one or more other
materials selected from the group consisting of wood pulp, staple
fibers, particulates and superabsorbent materials.
20. The method of claim 17 wherein said tensioning step causes said
nonwoven web to exhibit extension in the cross machine direction of
at least 70% at 10 g/cm loading.
Description
FIELD OF INVENTION
[0001] The present invention relates to highly-extensible apertured
nonwoven webs and a method of making the same. Apertured nonwoven
webs are particularly well suited for use in disposable absorbent
articles such as diapers, incontinence briefs, training pants,
feminine hygiene garments, and the like.
BACKGROUND OF THE INVENTION
[0002] Nonwoven webs formed by nonwoven extrusion processes such
as, for example, meltblowing processes and spunbonding processes
may be manufactured into products and components of products so
inexpensively that the products could be viewed as disposable after
only one or a few uses. Representatives of such products include
disposable absorbent articles, such as diapers, incontinence
briefs, training pants, feminine hygiene garments, and the
like.
[0003] Infants and other incontinent individuals wear disposable
absorbent articles such as diapers to receive and contain urine and
other body exudates. Absorbent articles function both to contain
the discharged materials and to isolate these materials from the
body of the wearer and from the wearer's garments and bed clothing.
Disposable absorbent articles having many different basic designs
are known to the art.
[0004] A typical absorbent article includes a liquid pervious
topsheet, a liquid impervious backsheet joined to the topsheet, and
an absorbent core positioned between the topsheet and the
backsheet. Nonwoven webs are often used as the topsheet because
they are liquid pervious and provide a skin friendly surface.
However, in certain uses nonwoven webs do not function all that
well as a topsheet as body exudates sometimes hang-up or get caught
in the nonwoven web and thus become trapped against the wearer's
skin. One solution to the aforementioned problem is to provide
apertures in the nonwoven web so that body exudates may readily
penetrate through the nonwoven web and into the underlying
absorbent core. Unfortunately, certain techniques used to form
apertured nonwoven webs are either costly, create an undesirable
harsh feeling against the wearer's skin, or are subject to tearing,
particularly when the apertured nonwoven web is to be used as a
topsheet on a disposable absorbent article.
[0005] One economical method of forming apertures in a nonwoven to
solve the above-mentioned problems taught in U.S. Pat. Nos.
5,628,097, entitled Method For Selectively Aperturing a Nonwoven
Web, which issued May 13, 1997 to Curro et al.; and, 5,916,661,
entitled Selectively Apertured Nonwoven Web, which issued Jun. 29,
1999 to Curro et al., both of which are hereby incorporated herein
by reference. The nonwoven webs taught by both Curro et al. patents
have proven to be effective as topsheets in disposable absorbent
garments, including disposable diapers. The apertures formed by the
processes described are effective for management of higher
viscosity body wastes, for example.
[0006] Apertured nonwoven webs can be made by several other
processes as well, for example by i) slitting and stretching as
described in U.S. Pat. No. 5,714,107, entitled Perforated Nonwoven
Fabrics; ii) perforating with patterned rolls as in European Patent
No. EP-A-0 955 159, entitled Method for Forming Apertured Laminate
Web; iii) hydroentangling or hydroaperturing as described in U.S.
Pat. No. 5,414, 914, entitled Process for Producing Apertured
Nonwoven Fabric; and iv) hot needling as described in U.S. Pat. No.
4,469,734, entitled Microfibre Web Products.
[0007] The open area and hole size are two important properties of
apertured webs for use as a topsheet in a disposable absorbent
article. In order to effectively accept viscous body exudates, the
open area of each aperture needs to be greater than 1 mm2,
preferably greater than 2 mm.sup.2 and most preferably greater than
3 mm.sup.2. Also, the total open area of the entire topsheet is
preferably at least about 15%. Ideally, the apertures, or holes
should be circular, or almost circular. However, if the holes are
oval shaped, the hole aspect ratio, which is defined as the ratio
of the major axis to the minor axis of the oval, should be less
than 8, preferably less than 6 and most preferably less than 4.
[0008] While producing high quality, economical apertured nonwoven
webs, the webs taught by Curro et al., as well as webs made by the
other methods listed above suffer from the drawback that with known
technology, the webs exhibit a cross-machine direction
extensibility that limits their use in certain high-extensible
disposable garment products. For example, as disposable absorbent
garments are improved, extensibility of the various components
becomes more important. In disposable diapers, for example, it is
desirable to have extensible chassis components such as the
backsheet and the topsheet. Extensible components permit a wider
range of unrestricted movement of the wearer, such as a baby.
Higher extensibility results in easier application, less
restriction of the skin, and higher comfort levels for the
wearer.
[0009] Current apertured nonwovens typically have essentially the
same extensibility of the base, i.e., non-apertured nonwoven. That
is, the aperturing process does not improve the extensibility
characteristics. Even apertured nonwovens designed specifically for
disposable absorbent articles, such as those manufactured according
to the teachings of Curro et al., typically have cross-machine
direction extensibility of about 50% at a loading of 25 g/in. (25
g/2.54 cm, which is about 10 g/cm) tensile force. That is, an
apertured nonwoven web, such as for a diaper topsheet, having a
cross-machine direction dimension of 100 cm could elongate in that
direction up to about 150 cm under a tensile loading of about 10
g/cm (10 grams per linear centimeter applied to each opposing edge
being grasped to put the web in tensile loading) without
significant degradation in performance or material integrity.
[0010] Certain apertured nonwoven webs may exhibit sufficient
extensibility, but, nevertheless, fail to maintain adequate hole
size and shape upon extension. For example, apertured nonwoven webs
that are made by the slitting and stretching approach can
potentially be made extensible by consolidating the slit web, i.e.
stretching it in the machine direction to make it neck to a
narrower width in cross machine direction. This approach, however,
decreases the hole size substantially and will also increase the
hole aspect ratio. Another potential approach is to consolidate the
web and then slit and stretch it. However, when such a web is
stretched in cross machine direction, the web will tend to return
to its unnecked state prior to the holes opening up, thus losing
the benefit of consolidation. Yet another potential approach may be
to consolidate the web and punch holes in it via processes like hot
needling. These webs are unsuitable for diaper application as they
are not soft. This is because of the thick melt edges that are left
behind where the apertures are formed.
[0011] Accordingly, it would be desirable to have an apertured
nonwoven web that has hole size greater than 2 mm.sup.2, total open
area greater than 15% and hole aspect ratio less than 6 and that
can, in addition, exhibit cross-direction extensibility greater
than about 50% at about 10 g/cm tensile force.
[0012] Additionally, it would be desirable to have an apertured
nonwoven web suitable for use as a topsheet in a disposable diaper,
that can exhibit cross-direction extensibility greater than about
70% at 10 g/cm tensile force.
[0013] Further, it would be desirable to have an economical method
for making an apertured nonwoven web that can exhibit
cross-direction extensibility greater than about 70% at 10 g/cm
tensile force.
SUMMARY OF THE INVENTION
[0014] In accordance with the present invention there is provided
an extensible apertured nonwoven web, and a method for making such
an apertured nonwoven web. In one embodiment the method comprises
the steps of providing an apertured nonwoven web, incrementally
stretching it in a direction substantially parallel to the cross
machine direction, and applying tension in the machine direction
such that the web width after applying tension is less than the web
width after incremental stretching. In another embodiment the
method comprises the steps of providing a nonwoven web; weakening
the nonwoven web at a plurality of locations to create a plurality
of weakened, melt-stabilized locations; applying a first tensioning
force to the nonwoven web to cause the nonwoven web to rupture at
the plurality of weakened, melt-stabilized locations creating a
plurality of apertures in the nonwoven web coincident with the
weakened, melt-stabilized locations, incrementally stretching the
nonwoven web in a direction substantially parallel to the cross
machine direction, and applying tension in the machine direction
such that the web width after applying machine direction tension is
less than the web width after incremental stretching. An apparatus
for producing a web of the present invention by this method is also
disclosed.
[0015] The extensible apertured nonwoven web produced has a
plurality of apertures each having a hole size greater than 2
mm.sup.2, and a hole aspect ratio less than 6, the nonwoven web
having an open area greater than 15% and being capable of at least
70% extension in the cross machine direction at a loading of 10
g/cm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter which is
regarded as forming the present invention, it is believed that the
invention will be better understood from the following description
which is taken in conjunction with the accompanying drawings in
which like designations are used to designate substantially
identical elements, and in which:
[0017] FIG. 1 is a schematic representation of an exemplary process
for making a nonwoven web of the present invention;
[0018] FIG. 2 is an enlarged perspective illustration of a web
weakening arrangement of the present invention;
[0019] FIG. 3 is a schematic representation of a pattern for the
protuberances of weakening arrangement of the present
invention;
[0020] FIG. 4 is an enlarged plan view photograph of a nonwoven web
of the present invention after the nonwoven web has been weakened
at a plurality of locations;
[0021] FIG. 5 is a perspective view of an apparatus for stretching
a nonwoven web of the present invention;
[0022] FIG. 6 is an enlarged illustration showing details of the
incremental stretching system of the present invention; and
[0023] FIG. 7 is an enlarged plan view photograph of a nonwoven web
of the present invention after tension has been applied to rupture
the nonwoven web at the weakened locations to create apertures in
the nonwoven.
DETAILED DESCRIPTION OF THE INVENTION
[0024] As used herein, the term "nonwoven web" is used in its
normal sense, and specifically refers to a web that has a structure
of individual fibers or threads which are interlaid, but not in any
regular, repeating manner. Nonwoven webs can be formed by a variety
of known processes, such as, for example, meltblowing processes,
spunbonding processes and bonded carded web processes. The nonwoven
web, without apertures and prior to processing as disclosed herein,
is also referred to as the "precursor web."
[0025] As used herein, the term "nmicrofibers", refers to small
diameter fibers having an average diameter not greater than about
100 microns.
[0026] As used herein, the term "meltblown fibers", refers to
fibers formed by extruding a molten thermoplastic material through
a plurality of fine, usually circular, die capillaries as molten
threads or filaments into a high velocity gas (e.g., air) stream
which attenuates the filaments of molten thermoplastic material to
reduce their diameter, which may be to a microfiber diameter.
Thereafter, the meltblown fibers are carried by the high velocity
gas stream and are deposited on a collecting surface to form a web
of randomly dispersed meltblown fibers.
[0027] As used herein, the term "spunbonded fibers", refers to
small diameter fibers which are formed by extruding a molten
thermoplastic material as filaments from a plurality of fine,
usually circular, capillaries of a spinneret with the diameter of
the extruded filaments then being rapidly reduced as by, for
example, eductive drawing or other well-known spunbonding
mechanisms.
[0028] As used herein, the term "polymer" generally includes, but
is not limited to, homopolymers, copolymers, such as, for example,
block, graft, random and alternating copolymers, terpolymers, etc.,
and blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the material. These configurations
include, but are not limited to, isotactic, syndiaotactic and
random symmetries.
[0029] As used herein, the term "elastic" refers to any material
which, upon application of a biasing force, is stretchable, that
is, elongatable, at least about 60 percent (i.e., to a stretched,
biased length, which is at least about 160 percent of its relaxed
unbiased length), and which, will recover at least 55 percent of
its elongation upon release of the stretching, elongation force. A
hypothetical example would be a one (1.0) cm sample of a material
which is elongatable to at least 1.60 cm, and which, upon being
elongated to 1.60 cm and released, will recover to a length of not
more than 1.27 cm. Many elastic materials may be elongated by more
than 60 percent (i.e., much more than 160 percent of their relaxed
length), for example, elongated 100 percent or more, and many of
these materials will recover to substantially their initial relaxed
length, for example, to within 105 percent of their initial relaxed
length, upon release of the stretch force.
[0030] As used herein, the term "nonelastic" refers to any material
which does not fall within the definition of "elastic" above.
[0031] As used herein, the term "extensible" refers to any material
which, upon application of a biasing force, is elongatable, at
least about 50% without offering a significant resistance force
(less than 10 g/cm) or experiencing catastrophic failure.
Catastrophic failure includes substantial tearing, fracturing,
rupturing, or other failure in tension such that, if tested in a
standard tensile tester, the failure would result in a sudden
significant reduction in measured tensile force. As used herein,
the term "highly extensible" refers to any material which, upon
application of a biasing force, is elongatable, at least about 70%,
more preferably at least about 100%, and even more preferably about
120% without without offering a significant resistance force (less
than 10 g/cm) or experiencing catastrophic failure.
[0032] As used herein, the term "melt-stabilized" refers to
portions of a nonwoven web which have been subjected to localized
heating and/or localized pressure to substantially consolidate the
fibers of the nonwoven web into a stabilized film-like form.
[0033] As used herein, unless otherwise specified, all composition
percentages are weight percentages.
[0034] As used herein, the term "absorbent article" refers to
devices which absorb and contain body exudates, and, more
specifically, refers to devices which are placed against or in
proximity to the body of the wearer to absorb and contain the
various exudates discharged from the body. The term "disposable" is
used herein to describe absorbent articles which are not intended
to be laundered or otherwise restored or reused as an absorbent
article (i.e., they are intended to be discarded after a single use
and, preferably, to be recycled, composted or otherwise disposed of
in an environmentally compatible manner). A "unitary" absorbent
article refers to absorbent articles which are formed of separate
parts united together to form a coordinated entity so that they do
not require separate manipulative parts like a separate holder and
liner. As used herein, the term "diaper" refers to an absorbent
article generally worn by infants and incontinent persons that is
worn about the lower torso of the wearer. It should be understood,
however, that the present invention is also applicable to other
absorbent articles such as incontinence briefs, incontinence
undergarments, diaper holders and liners, feminine hygiene
garments, training pants, and the like.
[0035] As used herein the term "hole size" refers to the average
size of the open area of a single aperture, measured in units of
area, for example, square millimeters.
[0036] As used herein the term "open area" refers to the percentage
of the total area of a web that has apertures.
[0037] As used herein the term "hole aspect ratio" is the ratio of
the major axis to the minor axis of a single aperture that is
approximately oval shaped.
[0038] By "cross-machine direction" is meant the direction
corresponding to the cross-machine direction of the web during web
production, which is orthogonal to the "machine-direction". Thus,
during web production, the direction corresponding to the linear
direction of web production, i.e., the "length" of the web, is the
machine-direction. The direction transverse to the
machine-direction, i.e., the "width" of the web, is the
cross-machine direction as used herein.
[0039] For typical diapers produced on high speed diaper equipment,
the cross-machine direction of the component web materials
corresponds to a direction generally parallel to a transverse
centerline of the finished diaper, as described more fully herein.
It is this direction in which improvements in diaper extensibility
are desired.
[0040] A typical diaper comprises a containment assembly, commonly
referred to as a "chassis" comprising a liquid pervious topsheet
and a liquid impervious backsheet joined to the topsheet. An
absorbent core is positioned between the topsheet and the
backsheet. The diaper preferably further comprises other components
as known in the art, such as elasticized side panels; elasticized
leg cuffs; elasticized waistbands; and a fastening system
preferably comprising a pair of securement members (e.g., tape tabs
or mechanical fastener members) and a landing member.
[0041] A diaper also has two centerlines, a longitudinal centerline
and a transverse centerline. The term "longitudinal", as used
herein, refers to a line, axis, or direction in the plane of the
diaper that is generally aligned with (e.g. approximately parallel
with) a vertical plane which bisects a standing wearer into left
and right halves when the diaper is worn. The terms "transverse"
and "lateral", as used herein, are interchangeable and refer to a
line, axis or direction which lies within the plane of the diaper
that is generally perpendicular to the longitudinal direction
(which divides the wearer into front and back body halves).
[0042] While the topsheet, the backsheet, and the absorbent core
may be assembled in a variety of well known configurations,
exemplary containment assembly configurations are described
generally in U.S. Pat. No. 3,860,003 entitled "Contractible Side
Portions for Disposable Diaper" which issued to Kenneth B. Buell on
Jan. 14, 1975; and U.S. Pat. No. 5,151,092 entitled "Absorbent
Article With Dynamic Elastic Waist Feature Having A Predisposed
Resilient Flexural Hinge" which issued to Kenneth B. Buell et al.,
on Sep. 29, 1992; each of which is incorporated herein by
reference.
[0043] The topsheet can be made from a web of the present
invention, thereby being apertured so as to allow viscous body
fluids, like runny and pasty BM and menses, to go through and get
stored in the layers beneath. Key properties of the apertured
topsheet (ATS) are open area, hole size, and hole aspect ratio. In
a preferred embodiment, the open area is greater than about 15% and
the hole size is greater than about 2 mm.sup.2. In some instances
minimum and/or maximum hole size is important, but, unless noted
otherwise herein, hole size refers to average hole size. Ideally,
the holes should be circular in shape and relatively consistent in
size, such that the standard deviation of the average hole size is
very small. Non-round, for example oval shaped, holes would also be
functional provided the hole aspect ratio, which is defined as the
ratio of the major axis to the minor axis of the ellipse, is not
too large. For holes having a major axis within the ranges
disclosed herein, e.g., from 2-4 mm, the hole aspect ratio is
preferably less than about 6.
[0044] The topsheet made according to the the present invention
comprises a highly extensible apertured nonwoven web. By highly
extensible is meant that the apertured nonwoven web of the present
invention exhibits cross-direction extensibility at a load of about
10 g/cm of at least about 70%, more preferably at least about 100%,
and even more preferably about 120%. By way of comparison, webs
produced as taught by Curro et al. in the above-mentioned U.S.
patents exhibit cross-direction extensibility of about 50% at about
10 g/cm loading.
[0045] Referring to FIG. 1 there is schematically illustrated at
100 a process for producing a highly extensible apertured nonwoven
web suitable for use as a topsheet on a disposable absorbent
article.
[0046] According to the present invention, a precursor nonwoven web
102 is supplied as the starting material. The precursor nonwoven
web 102 can be supplied as discrete webs, e.g., sheets, patches,
etc., of material for batching processing. For commercial
processing, however, precursor nonwoven web is supplied as roll
stock, and, as such it can be considered as having a finite width
and an infinite length. In this context, the length is measured in
the machine direction (MD) which is the direction of web travel
during processing. Likewise, the width is measured in the cross
machine (CD) direction.
[0047] The nonwoven material 102 may be formed by known nonwoven
extrusion processes, such as, for example, known meltblowing
processes or known spunbonding processes, and passed directly
through the nip 106 without first being bonded and/or stored on a
supply roll.
[0048] The nonwoven web 102 may be extensible, elastic, or
nonelastic, as long as it can be processed by the methods described
herein and retain the properties described herein. That is, a great
many types of webs can be processed by the method of the present
invention, but not all nonwoven webs can be so processed. As shown
more fully below, a correlation has been found between the CD peak
tensile elongation properties of a precursor web and processibility
of such a web into a web of the present invention. In general, to
obtain a high-elongation apertured web of the present invention,
the precursor nonwoven web material should exhibit a peak CD
tensile elongation of at least about 150%, more preferably about
175%, and most preferably about 200%. "Peak CD tensile elongation"
refers to the highest force exhibited in a standard tensile test.
Tensile properties of the precursor webs of the present invention
are measured using Instron or MTS equipment, or the like, using
standard tensile test methodologies. In general, the sample width
tested was one inch (2.54 cm), gage length was two inches (5.08
cm), crosshead speed was two inches per minute (5.08 cm/min), and
the slack preload was one gram.
[0049] As long as it exhibits the above-described CD peak tensile
elongation properties, precursor nonwoven web 102 may be a
spunbonded web, a meltblown web, or a bonded carded web. If the
nonwoven web is a web of meltblown fibers, it may include meltblown
microfibers. The nonwoven web 102 may be made of fiber forming
polymers such as, for example, polyolefins. Exemplary polyolefins
include one or more of polypropylene, polyethylene, ethylene
copolymers, propylene copolymers, and butene copolymers. In a
preferred embodiment, the precursor nonwoven web 102 (prior to
processing by the method of the present invention), has a basis
weight of between 20 grams per square meter (gsm) and 70 gsm, more
preferably between about 30 gsm and 60 gsm. A currently preferred
basis weight for diaper topsheet applications is between about 40
and 50 gsm.
[0050] Likewise, in another embodiment, the precursor nonwoven web
102 may be a multilayer material having, for example, at least one
layer of a spunbonded web joined to at least one layer of a
meltblown web, a bonded carded web, or other suitable material. For
example, the precursor nonwoven web 102 may be a multilayer web
having two layers of spunbonded polypropylene, each having a basis
weight from about 20 to about 60 grams per square meter (gsm).
[0051] The precursor nonwoven web 102 may be joined to a polymeric
film to form a laminate. Suitable polymeric film materials include
but are not limited to polyolefins, such as polyethylenes,
polypropylene, ethylene copolymers, propylene copolymers, and
butene copolymers; nylon (polyamide); metallocene catalyst-based
polymers; cellulose esters; poly (methyl methacrylate);
polystyrene; poly (vinyl chloride); polyester; polyurethane;
compatible polymers; compatible copolymers; and blends, laminates
and/or combinations thereof.
[0052] The precursor nonwoven web 102 may also be a composite made
up of a mixture of two or more different fibers or a mixture of
fibers and particles. Such mixtures may be formed by adding fibers
and/or particulates to the gas stream in which the meltblown fibers
or spunbond fibers are carried so that an intimate entangled
co-mingling of fibers and other materials, e.g., wood pulp, staple
fibers and particles occurs prior to collection of the fibers.
[0053] The nonwoven web of fibers should be joined by bonding to
form a coherent web structure suitable for processing, such as from
rollstock. Suitable bonding techniques include, but are not limited
to, chemical bonding; thermobonding, such as point calendaring;
hydroentangling; and needling.
[0054] Precursor nonwoven web 102 is unwound from a supply roll 104
and travels in a direction indicated by the arrows (i.e., the
machine direction) associated therewith as the supply roll 104
rotates in the direction indicated by the arrows associated
therewith. The nonwoven material 102 passes through a nip 106 of
the web weakening roller arrangement 108 formed by rollers 110 and
112.
[0055] Referring to FIG. 2, the nonwoven web weakening roller
arrangement 108 comprises a patterned calendar roller 110 and a
smooth anvil roller 112. One or both of the patterned calendar
roller 110 and the smooth anvil roller 112 may be heated and the
pressure between the two rollers may be adjusted by well known
means to provide the desired temperature, if any, and pressure to
concurrently weaken and melt-stabilize the nonwoven web 102 at a
plurality of locations.
[0056] The patterned calendar roller 110 is configured to have a
circular cylindrical surface 114, and a plurality of protuberances
or pattern elements 116 which extend outwardly from surface 114.
The protuberances 116 are disposed in a predetermined pattern with
each protuberance 116 being configured and disposed to precipitate
a weakened, melt-stabilized location in the nonwoven web 102 to
effect a predetermined pattern of weakened, melt-stabilized
locations in the nonwoven web 102. As shown in FIG. 2, patterned
calendar roller 110 has a repeating pattern of protuberances 116
which extend about the entire circumference of surface 114.
Alternatively, the protuberances 116 may extend around a portion,
or portions of the circumference of surface 114.
[0057] A suitable pattern for patterned calendar roller 110 is
shown schematically in plan view in FIG. 3. Because the
protuberances 116 have a one-to-one correspondence to the pattern
of melt-stabilized locations, FIG. 3 can also be considered as
illustrating a typical pattern of melt-stabilized locations on a
calendared nonwoven web according to the present invention. As
shown, the protuberances can be in a regular pattern of staggered
rows or columns. The pattern shown is a regular repeating pattern
of staggered protuberances, generally in rows, each separated by a
row spacing, RS, of between about 0.030 inches ( 0.76 mm) and about
0.200 inches (5.08 mm). In a preferred embodiment, row spacing RS
is about 0.060 inches (1.52 mm). The protuberances can be spaced
apart within a column by a protuberance spacing, PS generally equal
to the protuberance length, LP, which in one embodiment is 0.150
inches (3.81 mm). But the spacing and pattern can be varied in
multiple ways depending on the end product desired.
[0058] The protuberances have a longitudinal centerline, C, that is
oriented generally parallel to the machine direction, MD, of the
web material. Likewise, each protuberance has a transverse
centerline, T, generally orthogonal to the longitudinal centerline.
The longitudinal dimension LP of each protuberance 116 corresponds
to the dimension measured parallel to the longitudinal centerline
C, and is much longer than the transverse dimension WP (likewise
corresponding to the dimension measured parallel to the transverse
centerline T), thereby resulting in the protuberances, and the
corresponding melt-stabilized locations, having a relatively high
aspect ratio (i.e., LP/WP). The aspect ratio is preferably greater
than 10, more preferably 15. The height of the protuberances, i.e.,
the distance the protuberances extend from the circular cylindrical
surface 114, should be selected according to the thickness of the
nonwoven web being melt-stabilized. In general, the height
dimension should be greater than the maximum thickness of the web
during the calendaring process, so that adequate melt-stabilizing
can be accomplished.
[0059] In general, it has been shown that by increasing the aspect
ratio of the protuberances, the corresponding aspect ratio of the
melt-stabilized locations contributes to the overall CD
extensibility of the finished highly extensible web of the present
invention. The increased aspect ratio contributes to a geometric
expansion advantage. However, it has been discovered that, for webs
having suitable open area and hole size for use as topsheets in
disposable diapers, the advantage only represents about 10-20%
extra elongation in the CD. While the parameter of aspect ratio of
the melt-stabilized locations alone could be sufficient to create
highly extensible apertured webs, it is believed that such webs
would result in an apertured web wherein the apertures have an
unacceptably high hole aspect ratio (major dimension/minor
dimension of the resulting apertures) for the applications of
interest, including use in disposable absorbent articles.
[0060] The protuberances 116 are preferably truncated conical
shapes which extend radially outwardly from surface 114 and which
can have somewhat elliptical distal end surfaces 117. Although it
is not intended to thereby limit the scope of the present invention
to protuberances of only this configuration. The roller 110 is
finished so that all of the end surfaces 117 lie in an imaginary
right circular cylinder which is coaxial with respect to the axis
of rotation of roller 110.
[0061] Although the protuberances 116 can be disposed in a regular
predetermined pattern of rows and columns as shown in FIG. 3, it is
not intended to thereby limit the scope of the present invention to
the pattern of protuberances of shown. The protuberances may be
disposed in any predetermined pattern about patterned calendar roll
110. In particular, it is believed that "fishbone" or "herringbone"
patterns would be useful for the present invention. Typically, the
longitudinal axis of the melt stabilized regions is at an angle of
45 degrees or less off of the machine direction of the nonwoven
web. These webs are incrementally stretched in the cross machine
direction in order to open up the apertures. If the longitudinal
axis of the melt stabilized regions is at an angle greater than 45
degres off of the machine direction, incremental stretching needs
to be done in the machine direction. Anvil roller 112, is
preferably a smooth surfaced, right circular cylinder of steel.
[0062] FIG. 4 is a photograph of the nonwoven web 102 after having
passed through the weakening roller arrangement 108, and prior to
passing through the nip 130 of the first incremental stretching
system 132. As can be seen in the photograph, the nonwoven web 102
includes a plurality of weakened, melt-stabilized locations 202.
Weakened, melt-stabilized locations 202 correspond to the pattern
of protuberances 116 extending from the surface 114 of patterned
calendar roller 110. As seen in FIG. 4, the nonwoven web 102 also
includes coherent web forming point calendered bonds 200 which
serve to maintain the structural integrity of the nonwoven web
102.
[0063] From the weakening roller arrangement 108, the nonwoven web
102 can be stretched in the CD direction by means of a tensioning
force to rupture the plurality of weakened, melt-stabilized
locations, thereby creating a plurality of apertures in the
nonwoven web coincident with the plurality of weakened,
melt-stabilized locations. Various tensioning means can be
utilized, such as tentoring, however in a preferred embodiment,
uniform tensioning throughout the web is achieved by passing the
nonwoven web through a nip 130 formed by a first incremental
stretching system 132 employing opposed pressure applicators having
three-dimensional surfaces which at least to a degree are
complementary to one another.
[0064] Referring now to FIG. 5, there is shown a perspective view
of the incremental stretching system 132 comprising incremental
stretching rollers 134 and 136. The incremental stretching roller
134 includes a plurality of teeth 160 and corresponding grooves 161
which extend about the entire circumference of roller 134.
Incremental stretching roller 136 includes a plurality of teeth 162
and a plurality of corresponding grooves 163. The teeth 160 on
roller 134 intermesh with or engage the grooves 163 on roller 136,
while the teeth 162 on roller 136 intermesh with or engage the
grooves 161 on roller 134. The teeth of each roller are generally
triangular-shaped, as shown in FIG. 6. The apex of the teeth may be
slightly rounded, if desired for certain effects in the finished
web.
[0065] With reference to FIG. 6, which shows a portion of the
intermeshing of the teeth 160 and 162 of rollers 134 and 136,
respectively, the term "pitch" refers to the distance between the
apexes of adjacent teeth. The pitch can be between about 0.02 to
about 0.30 inches (0.51-7.62 mm), and is preferably between about
0.05 and about 0.15 inches (1.27-3.81 mm). The height (or depth) of
the teeth is measured from the base of the tooth to the apex of the
tooth, and is preferably equal for all teeth. The height of the
teeth can be between about 0.10 inches (2.54 mm) and 0.90 inches
(22.9 mm), and is preferably about 0.25 inches (6.35 mm) and 0.50
inches (12.7 mm).
[0066] The teeth 160 in one roll can be offset by one-half the
pitch from the teeth 162 in the other roll, such that the teeth of
one roll (e.g., teeth 160) mesh in the valley (e.g., valley 163)
between teeth in the mating roll. The offset permits intermeshing
of the two rollers when the rollers are "engaged" or in an
intermeshing, operative position relative to one another. In a
preferred embodiment, the teeth of the respective rollers are only
partially intermeshing. The degree to which the teeth on the
opposing rolls intermesh is referred to herein as the "depth of
engagement" or "DOE" of the teeth. As shown in FIG. 6, the DOE, E,
is the distance between a position designated by plane P1 where the
apexes of the teeth on the respective rolls are in the same plane
(0% engagement) to a position designated by plane P2 where the
apexes of the teeth of one roll extend inward beyond the plane P1
toward the valley on the opposing roll. The optimum or effective
DOE for particular laminate webs is dependent upon the height and
the pitch of the teeth and the materials of the web.
[0067] In other embodiments the teeth of the mating rolls need not
be aligned with the valleys of the opposing rolls. That is, the
teeth may be out of phase with the valleys to some degree, ranging
from slightly offset to greatly offset.
[0068] As the nonwoven web 102 having weakened, melt-stabilized
locations 202 passes through the incremental stretching system 132
the nonwoven web 102 is subjected to tensioning in the CD direction
causing the nonwoven web 102 to be extended in the CD direction.
The tensioning force placed on the nonwoven web 102 can be adjusted
by varying the pitch, DOE, or teeth size, such that the incremental
stretching is sufficient to cause the weakened, melt-stabilized
locations 202 to rupture creating a plurality of apertures 204
coincident with the weakened melt-stabilized locations 202 in the
nonwoven web 102. However, the bonds 200 of the precursor nonwoven
web 102 do not rupture during tensioning, thereby maintaining the
nonwoven web in a coherent condition even as the weakened,
melt-stabilized locations rupture.
[0069] After passing through the first incremental stretching
system 132, the nonwoven web has width greater than the width of
the precursor web, apertures in the regions where the
melt-stabilized regions ruptured, and increased extensibility in
the cross-machine direction, CD. The actual width in the CD
direction depends on the amount of tension applied to the web when
it exits the incremental stretching system 132. As expected,
narrowing, and even necking of the web can be achieved by
increasing the tension in the MD sufficiently. The extension
properties described herein are for incrementally stretched webs
with little or no tension applied in the MD. At this stage, for
nonwovens of suitable basis weight and composition as typically
utilized as topsheets in disposable diapers, and having a hole size
greater than 2 mm.sup.2, and an open area of at least 15%, the
elongation at 10 g/cm loading is only about 40-50%. After extension
of about 40-50%, the nonwoven web at this stage of processing
offers substantial resistance to further tensile loading and, in
some cases, begins to tear, shred, or otherwise lose structural
integrity.
[0070] Referring now to FIG. 7 there is shown a photograph of the
nonwoven web 102 after having been subjected to the tensioning
force applied by the incremental stretching system 132. As can be
seen in the photograph, the nonwoven web 102 now includes a
plurality of apertures 204 which are coincident with the weakened,
melt-stabilized locations 202 of the nonwoven web shown in FIG. 4.
A portion of the circumferential edges of apertures 204 include
remnants 205 of the melt-stabilized locations 202. It is believed
that the remnants 205 help to resist further tearing of the
nonwoven web particularly when the nonwoven web is used as a
topsheet on a disposable absorbent article.
[0071] Other exemplary structures of incremental stretching
mechanisms suitable for incrementally stretching or tensioning the
nonwoven web are described in U.S. Pat. No. 5,518,801 issued to
Chappell et al. on May 21, 1996, and hereby incorporated herein by
reference.
[0072] Newer diaper designs that require higher extensibility of
components to facilitate better fit and comfort require that the
material for use as the topsheet have at least 70% extension at
about 10 g/cm loading. It is important to distinguish between pure
extension, and extension under a specified loading, especially a
relatively low loading such as about 10 g/cm. For disposable
absorbent articles, including diapers, it is important that the
extension be available for body movements under low tension and
also for ease of application. Low force extension contributes to a
feeling of comfort, fit, and softness. For example, when fit about
a baby's buttocks regions, it is important that the diaper
components substantially freely extend upon movements such as
sitting, bending, or twisting. Thus, the diaper does not chaff,
rub, or pull on the baby's skin, causing discomfort and skin
irritation. The same considerations apply to adult garments,
including catamenials, incontinence garments, and the like.
[0073] Therefore, to make a highly extensible topsheet, after
passing through the first incremental stretching system 132, the
nonwoven web is passed through an additional, second incremental
stretching system 132'. During the second incremental stretching,
the web width is substantially increased. By applying tension in
the machine direction, the web width is decreased to about the same
level as it was prior to the second incremental stretching. In this
process, it is this second incremental stretching step followed by
application of MD tension that produces the apertured nonwovens
having the requisite extensibility characteristics of the claimed
invention. The processing parameters, equipment set up, and related
methodologies for the second incremental stretching system 132' can
be, and preferably are, substantially identical to first
incremental stretching system 132, and therefore, a description for
each "prime number" counterpart of first incremental stretching
system 132 will not be repeated here. In a preferred embodiment,
the nonwoven web of the present invention is processed in the
second incremental stretching system 132' in the same manner, and
with respect to the same methodologies as described above with
respect to incremental stretching system 132. However, for certain
other embodiments second incremental stretching system 132' can
differ significantly in certain respects, for example, in the pitch
and depth of engagement of the mating rollers.
[0074] The purpose of the second incremental stretching system 132'
is to put further extension potential into the nonwoven web in the
form of additional incremental stretching of the previously
incrementally-stretched web. By "extension potential" is meant that
after incrementally stretching and necking according to the process
described herein, the nonwoven web can be, and preferably is,
essentially the same width in the cross machine direction as before
the second stretching step, yet it is able to extend substantially
beyond its original width in the cross machine direction. This is
believed to be partly due to the accordian-like, or fan-folded,
pleating induced in the web during incremental stretching. It is
believed that this additional incremental stretching can only be
achieved, as stated above, when the precursor web exhibits a
certain minimum extensibility. Otherwise, the second incremental
stretching step simply shreds the nonwoven web. By controlling the
tensions of the web as it exits the incremental stretching
apparatus, the width of the finished nonwoven web can be maintained
at a predetermined dimension, with a corresponding extension
potential of over 100% at low extension forces.
[0075] As noted above, the additional incremental stretching of the
nonwoven web by the method of the present invention may stretch the
nonwoven beyond the limit of which the constituent fibers and bonds
are able to withstand structural integrity. Therefore, the
precurser nonwoven web for the present invention must have
sufficient structural properties to withstand such additional
incremental stretching. Such precursers nonwoven webs have been
developed for the present invention, embodiments of which are
described herein, including in Table 1 of the Examples section
below.
[0076] Incremental stretching via the apparatus described herein is
preferred due to its ability to uniformly stretch the web across
its width. However, the second stretching step could be achieved by
other stretching means, such as tentoring, with a subsequent
"consolidation" step that would put the post-tentored web in
machine direction tension thereby necking the web down to the
pre-tentoring width.
[0077] Additionally, if desired, the incremental stretching steps
described herein can be performed at elevated temperatures. For
example, one or both of the incremental stretching rollers could be
heated. Utilizing heat in the stretching step serves to soften the
nonwoven web, and aids in extending the fibers without
breaking.
[0078] The nonwoven web 102 is preferably taken up on wind-up roll
180 and stored. Alternatively, the nonwoven web 102 may be fed
directly to a production line where it is used to form a topsheet
on a disposable absorbent article.
[0079] Both the first and second incremental stretching can either
be done off-line or on-line. Furthermore, the incremental
stretching can either be done over the entire area of the web or
only in certain regions. For example, the second incremental
stretching can be done only in a region corresponding to the back
portion of a diaper where high extensibility is desired.
[0080] With certain highly extensible precursor nonwoven webs, it
may be possible to achieve a highly extensible apertured nonwoven
web with just one incremental stretching step instead of two,
followed by limited spreading and MD tensioning. In this approach,
the web having the above-mentioned melt weakened regions can be
incrementally stretched to at a relatively high depth of engagement
(DOE), after which MD tension is applied to achieve the desired
open area, hole size, aspect ratio, and CD extensibility.
[0081] In another embodiment, an extensible apertured nonwoven web
can be made by first aperturing a nonwoven web by other known
methods, such as by slitting and stretching, perforating with
patterned rolls, hydroentangling or hydroaperturing, or hot
needling, subjecting the apertured nonwoven material to at least
one incremental stretching step as described above, and then
applying tension in the machine direction to reduce the web width
(i.e., consolidate the web) as described above. In this manner, the
requisite extensiblility can be imparted to an apertured nonwoven
web to make it a highy extensible nonwoven web, the web having at
least 70% extension at about 10 g/cm loading. In an alternative
process for forming a highly-extensible nonwoven web of the present
invention, the nonwoven web weakening arrangement can comprise an
ultrasonic transducer and an anvil cylinder instead of thermal
point bonding protuberances. As the nonwoven material is forwarded
between the ultrasonic transducer and the anvil cylinder it is
subjected to ultrasonic vibrational energy whereupon predetermined
pattern locations of the nonwoven web are weakened and
melt-stabilized. A suitable transducer is described in the
aforementioned U.S. Pat. No. 5,628,097 patent. As disclosed above,
in this process, after passing through the first incremental
stretching system the nonwoven web is passed through an additional,
second incremental stretching system that produces the apertured
nonwovens having the requisite extensibility characteristics of the
claimed invention.
EXAMPLES
[0082] Table 1 lists mechanical properties of several nonwoven webs
processed by the method of the present invention. As shown, certain
precursor nonwoven materials are not suitable for such processing.
The samples disclosed in these Examples which can be processed into
highly-extensible apertured nonwovens are shown are meant to be
illustrative of possible structures, and are not meant to be
limiting to any particular material or structure.
[0083] All the samples shown in Table 1 were processed as described
below. For samples 1, 2, 3, 5 and 6 web weakening was achieved by
thermal bonding of rollstock precursor nonwovens using web
weakening roller arrangement 108 in a continusous process. For
sample 4 web weakening was achieved ultrasonically on handsheets of
the precursor nonwovens. For the samples that were thermally
bonded, the line speed through the web weakening roller arrangement
108 was about 250 feet per minute (about 75 meters per minute), but
the line speed is not considered critical to the operation of the
method. The patterned calendaring pressure, i.e., nip pressure, was
about 700 psig (4823 kPa) for all the samples, but the pressure can
be varied as desired as long as sufficient melt stabilization is
achieved. Line speed and nip pressures are considered to be
variable, depending on the materials being processed, and suitable
variations are within the abilities of one skilled in the art
without undue experimentation. The patterned calendar roller 110
was configured with pattern elements 116 having a row spacing RS
(or pitch) of 0.060 inches (1.52 mm), a protuberance width, WP, of
0.010 inches (0.25 mm), and a protuberance length, LP, of either
0.100 inches (2.54 mm) (Samples 1 and 2) or 0.150 inches (3.81 mm)
(Samples 3-6).
[0084] To form the extensible apertured nonwoven webs shown in
Table 1 below (except for ultrasonically-bonded sample 4), after
the patterned calendar roller, the thermally bonded laminate was
processed by the first and second incremental stretching processes
as described above with reference to FIG. 1. For these samples the
incremental stretching roller pitch was 0.060" (1.52 mm) and the
line speed was 250 fpm (about 75 meters per minute). Depth of
engagement ("DOE") was varied as shown to achieve the requisite
extensibility without destroying the web. Sample 4 was processed
using mating flat plate variants of incremental stretching rollers,
with similar pitches, DOE, as shown.
[0085] Samples 1a and 1b, described in the Table as "50/50 PE/PP
bico SB Lurgi process", are spunbond webs comprising 50%
polyethylene sheath/50% polypropylene core bicomponent fibers
having a fiber denier from about 3-5. The nonwovens are available
from BBA, Simpsonville, S.C., USA, and are made via a standard
Lurgi process, as known in the art. Peak elongations are typically
lower than 150% measured by standard tensile testing methods (e.g.,
Instron, MTS, etc.) with a one inch sample width, one inch gage
length, 10 inches/minute crosshead speed, and a slack preload of
one gram.
[0086] Samples 2a and 2b described in the Table as "50/50 PE/PP
bico SB Slot-draw Process" are spunbond webs comprising 50%
polyethylene sheath/50% polypropylene core bicomponent fibers
having a fiber denier from about 4-6. These precursor nonwovens are
available from BBA, Simpsonville, S.C., USA, and are made via a BBA
slot drawing process to have relatively high CD peak tensile
elongation. Peak elongations are typically greater than 250%,
measured by standard tensile testing methods (e.g., Instron, MTS,
etc.) with a one inch sample width, one inch gage length, 10
inches/minute crosshead speed, and a slack preload of one gram.
These precursor webs are believed to be made according to one or
more of the following US Pat. Nos. : 5,292,239, 5,470,639, and/or
5,397,413. Samples 3a and 3b were also made using the same slot
draw process. However, it is believed that, due to variations in
the slot drawing parameters, as set by BBA during manufacture, the
CD peak elongation of this precursor nonwoven was lower.
[0087] Samples 4a and 4b were made with two layers of precursor
nonwovens: the top layer was an 80/20% PE/PP bico spunbond and the
lower layer was a 50/50% PE/PP bico spunbond. Both of these
precursor nonwovens were made using the slot draw process described
above and exhibited CD peak elongations of about 150 and 325%
respectively.
[0088] Samples 5a and 5b were made from a spunbond nonwoven made
with a polypropylene copolymer. This nonwoven, obtained from BBA
under the name Softspan 200 exhibited a CD peak elongation of
190%
[0089] The 50/50% PE/PP bico SB Lurgi process spunbond that was
used for making samples 6a and 6b was similar in chemistry to the
precursor web that was used to make samples 1a and 1b, but was
processed by BBA so as to have higher CD peak elongation. The
higher CD peak elongation enabled this web to be processed into an
extensible apertured topsheet with the added variation of using
longer bond pattern length (bond length=3.81 mm). Without being
bound by theory, it is believed that this bond length is near the
limit for effective webs of the present invention for use as
topsheets in absorbent garments, due to the resulting aperture
size.
[0090] The open area, hole size, and hole aspect ratio are
indications of the usefulness of the webs for use as topsheets in
absorbent garments. In particular, it is desired that hole size and
open area are sufficient to permit viscous bodily waste to pass
through. However, to function as an effective topsheet, it should
also be effective as a barrier between the wearer's skin and the
absorbent core of the garment. Thus, the webs of the present
invention for use as a topsheet exhibit an acceptable balance of
sufficient open area, hole size and hole aspect ratio for use as a
topsheet in a disposable absorbent article.
[0091] The open area, hole size, and hole aspect ratio are are
measured using an optical microscope equipped with a digital camera
and an image analysis system. The microscope is a Zeiss SV8
stereoscope (Zeiss Inc., New York, N.Y.) with a 0.5.times.condenser
lens. Since the apertures are fairly large, the magnification needs
to be low. Typically, the magnification is low enough to get at
least 15 apertures in the field of view. For samples with smaller
apertures, there could even be as many as 50 apertures in the field
of view. The sample is illuininated from the sides and bottom.
[0092] The image is captured by a Sony DKC-ST5 digital camera (Sony
Corp., Japan) and the image analysis is done using Image-Pro Plus
software (version 4.1.0.2 from Media Cybernetics. The threshold for
aperture size is set at 0.4 mm.sup.2. When measuring hole size and
hole aspect ratio, all partial holes, i.e. holes that are only
partially in the area of interest, need to be excluded. On the
other hand, these partial holes have to be included for open area
measurements. The Image-Pro Plus software gives average hole size
and hole aspect ratio. Sometimes, the image analysis software may
pick up small holes in areas where the nonwoven basis weight is low
and/or if the lighting is less than optimal. These holes need to be
excluded from all measurments as they would significantly lower the
average hole size.
[0093] Tensile properties of the apertured webs of the present
invention are measured using Instron or MTS equipment using
standard tensile test methodologies. For the results shown in Table
1, the sample width was one inch (2.54 cm), gage length was two
inches (5.08 cm), crosshead speed was two inches per minute (5.08
cm/min), and the slack preload was zero gram. It is necessary to
set the slack preload to zero grains for the apertured webs, since
a large part of the extension in these extensible webs occurs at
low force that is close to zero grams. Since the
incrementally-stretched webs of the present invention have a fluted
or mildly corrugated shape, it is important to mark the two-inch
gage length on the nonwoven when it is still on the roll, or
otherwise in its finished, consolidated width. Once off the roll,
some the samples may stretch somewhat in the cross direction, even
before applying any tension.
1TABLE 1 Samples of processed materials Process Precursor Nonwoven
Conditions Apertured Nonwoven Sam- Incremental Basis CD peak Bond
Strain at Open Hole Hole Basis ple Stretching, weight elongation
length DOE 10 g/cm area size aspect weight Web no. First/second
Description (gsm) (%) (mm) (mm) load (%) (%) (mm.sup.2) ratio (gsm)
integrity 1a First 50/50 PE/PP bico SB, 26 .times. 2 142 2.54 2.03
56 23.3 3.3 2.4 18 Good Lurgi Process (BBA) 1b Second 50/50 PE/PP
bico SB, " " -- >1.52 Web has no integrity Poor Lurgi Process
(BBA) (shreds) 2a First 50/50 PE/PP bico SB, Slot- 50 353 2.54 2.54
35 16.5 2.2 2.6 27.2 Good draw Process (BBA) 2b Second 50/50 PE/PP
bico SB, Slot- " " -- 2.41 141 16.9 2.1 2.6 30.9 Good draw Process
(BBA) 3a First 50/50 PE/coPP bico SB, 45 212 3.81 2.41 59 22.0 4.1
4.2 29.9 Good Slot-draw Process (BBA) 3b Second 50/50 PE/coPP bico
SB, " " -- 2.29 115 23.6 3.8 3.1 30 Good Slot-draw Process (BBA) 4a
First 80/20 + 50/50 PE/PP bico 29 .times. 2 80/20: 148; 3.81 1.78
64 19.5 2.8 3.7 41.2 Good SB, Slot-draw process 50/50: 325 (BBA) 4b
Second 80/20 + 50/50 PE/PP bico " 80/20: 148; -- 1.78 142 -- -- --
-- Good SB, Slot-draw process 50/50: 325 (BBA) 5a First Softspan
200, SB 2 .times. 25 190 3.81 2.54 31 23.3 4.6 3.5 28.6 Good
nonwoven made with a PP copolymer (BBA) 5b Second Softspan 200, SB
" " -- 2.03 111 23.6 4.7 3.5 30.8 Borderline nonwoven made with a
PP OK copolymer (BBA) 6a First 50/50 PE/PP bico SB, 26 .times. 2
157 3.81 2.41 57 21.0 3.6 2.4 35.0 Good Lurgi Process (BBA) 6b
Second 50/50 PE/PP bico SB, " " -- 2.79 102 23.0 4.2 3.2 35.2 OK
Lurgi Process (BBA)
[0094] As shown in Table 1 above, highly extensible apertured
nonwoven webs can be produced by the method disclosed herein. CD
peak elongation of the precursor web is an important processing
limitation, with bond length of the melt stabilized regions being
an important parameter as well.
[0095] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other combinations and
modifications can be made without departing from the scope of the
invention. It is therefore intended to cover in the appended claims
all such combinations and modifications that are within the scope
of this invention.
* * * * *