U.S. patent application number 10/679835 was filed with the patent office on 2004-04-08 for methods for forming a fluted composite.
This patent application is currently assigned to Weyerhaeuser Company. Invention is credited to Bolstad, Clifford R., Bunker, Daniel T., Graef, Peter A., Howard, Fred B., Miller, Charles E..
Application Number | 20040065420 10/679835 |
Document ID | / |
Family ID | 28679137 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065420 |
Kind Code |
A1 |
Graef, Peter A. ; et
al. |
April 8, 2004 |
Methods for forming a fluted composite
Abstract
Methods for forming an absorbent fibrous composite containing
absorbent material dispersed in bands through the composite and
along the composite's length are disclosed. The methods generally
include depositing a fibrous slurry on a foraminous support to form
a web and depositing or injecting absorbent material into the web
across its width to provide a web having absorbent material in
bands along the composite's length. Drying the web provides a
fluted absorbent composite. In one embodiment, the method is a
wetlaid method and in another embodiment, the method is a
foam-forming method. Preferably, the methods are twin-wire forming
methods.
Inventors: |
Graef, Peter A.; (Puyallup,
WA) ; Bolstad, Clifford R.; (Federal Way, WA)
; Howard, Fred B.; (Gig Harbor, WA) ; Miller,
Charles E.; (Tacoma, WA) ; Bunker, Daniel T.;
(Karhula, FI) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Company
|
Family ID: |
28679137 |
Appl. No.: |
10/679835 |
Filed: |
October 6, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10679835 |
Oct 6, 2003 |
|
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09664576 |
Sep 18, 2000 |
|
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6630054 |
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09664576 |
Sep 18, 2000 |
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PCT/US99/05997 |
Mar 18, 1999 |
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60078779 |
Mar 19, 1998 |
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60082771 |
Apr 23, 1998 |
|
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|
60082790 |
Apr 23, 1998 |
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60111845 |
Dec 11, 1998 |
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Current U.S.
Class: |
162/9 ; 162/101;
162/146; 162/157.6; 241/28 |
Current CPC
Class: |
D21C 9/002 20130101;
D21H 11/20 20130101; A61F 13/15699 20130101; A61F 13/15617
20130101; D21F 11/006 20130101; A61F 2013/4581 20130101; A61F
2013/530481 20130101; A61F 13/15658 20130101; A61F 13/536 20130101;
D21F 9/006 20130101; D21F 11/04 20130101; A61F 2013/1539 20130101;
D21F 11/002 20130101; A61F 13/534 20130101; D21F 11/14 20130101;
A61F 2013/530386 20130101 |
Class at
Publication: |
162/009 ;
162/157.6; 162/146; 162/101; 241/028 |
International
Class: |
D21C 009/00; D21F
011/00 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for making a fibrous layer, comprising: refining
cellulosic fibers to provide refined fibers, wherein the cellulosic
fibers comprise crosslinked cellulosic fibers; combining the
refined fibers with a dispersion medium to provide a fibrous
slurry; depositing the fibrous slurry on a foraminous support to
provide a wet composite; drying the wet composite to provide a
fibrous layer.
2. The method of claim 1, wherein the cellulosic fibers comprise a
blend of crosslinked cellulosic fibers and noncrosslinked
cellulosic fibers.
3. The method of claim 2, wherein the noncrosslinked fibers are at
least one of softwood fibers or hardwood fibers.
4. The method of claim 2, wherein the noncrosslinked fibers
comprise southern pine fibers.
5. The method of claim 1, wherein the cellulosic fibers comprise a
blend of crosslinked cellulosic fibers and southern pine
fibers.
6. The method of claim 1, wherein the cellulosic fibers comprise a
refined blend of crosslinked cellulosic fibers and southern pine
fibers.
7. The method of claim 1, wherein the cellulosic fibers comprise a
blend of crosslinked cellulosic fibers and refined southern pine
fibers.
8. The method of claim 1, wherein the cellulosic fibers comprise a
refined blend of crosslinked cellulosic fibers and refined southern
pine fibers.
9. The method of claim 1, wherein the method is carried out on at
least one of a Fourdrinier or a twin-wire papermaking machine.
10. The method of claim 1, wherein the method is at least one of a
wetlaid method and a foam-forming method.
11. A method for making a fibrous layer, comprising: refining
cellulosic fibers to provide refined fibers, wherein the cellulosic
fibers comprise crosslinked cellulosic fibers; combining the
refined fibers with a dispersion medium to provide a fibrous
slurry; moving a first foraminous element in a first path; moving a
second foraminous element in a second path; passing a first portion
of the fibrous slurry into contact with the first foraminous
element; passing a second portion of the fibrous slurry into
contact with the second foraminous element; forming a fibrous web
from the slurry by withdrawing liquid from the slurry through the
first and second foraminous elements; and drying the web provide a
fibrous layer.
12. The method of claim 11, wherein the cellulosic fibers comprise
a blend of crosslinked cellulosic fibers and noncrosslinked
cellulosic fibers.
13. The method of claim 12, wherein the noncrosslinked fibers are
at least one of softwood fibers or hardwood fibers.
14. The method of claim 12, wherein the noncrosslinked fibers
comprise southern pine fibers.
15. The method of claim 11, wherein the cellulosic fibers comprise
a blend of crosslinked cellulosic fibers and southern pine
fibers.
16. The method of claim 11, wherein the cellulosic fibers comprise
a refined blend of crosslinked cellulosic fibers and southern pine
fibers.
17. The method of claim 11, wherein the cellulosic fibers comprise
a blend of crosslinked cellulosic fibers and refined southern pine
fibers.
18. The method of claim 11, wherein the cellulosic fibers comprise
a refined blend of crosslinked cellulosic fibers and refined
southern pine fibers.
19. The method of claim 11, wherein the method is at least one of a
wetlaid method or a foam-forming method.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/664,576, filed Sep. 18, 2000, which is a
continuation of International Application No. PCT/US99/05997, filed
Mar. 18, 1999, which claims the benefit of U.S. Provisional
Application No. 60/078,779, filed Mar. 19, 1998, U.S. Provisional
Application No. 60/082,771, filed Apr. 23, 1998, U.S. Provisional
Application No. 60/082,790, filed Apr. 23, 1998, and U.S.
Provisional Application No. 60/111,845, filed Dec. 11, 1998, the
benefit of the priority of the filing dates of which are hereby
claimed under 35 U.S.C. .sctn..sctn. 120 and 119, respectively.
Each of these applications is incorporated herein by reference in
its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to methods for forming an
absorbent composite and, more particularly, to methods for forming
a fluted absorbent composite that includes superabsorbent
material.
BACKGROUND OF THE INVENTION
[0003] Cellulose fibers derived from wood pulp are used in a
variety of absorbent articles, for example, diapers, incontinence
products, and feminine hygiene products. It is desirable for the
absorbent articles to have a high absorbent capacity for liquid,
rapid liquid acquisition, low rewet, as well as to have good dry
and wet strength characteristics for durability in use and
effective fluid management. The absorbent capacity of articles made
from cellulose fibers is often enhanced by the addition of
absorbent materials, such as superabsorbent polymers.
Superabsorbent polymers known in the art have the capability to
absorb liquids in quantities from 5 to 100 times or more their
weight. Thus, the presence of superabsorbent polymers greatly
increases the liquid holding capacity of absorbent articles made
from cellulose.
[0004] Because superabsorbent polymers absorb liquid and swell upon
contact with liquid, superabsorbent polymers have heretofore been
incorporated primarily in cellulose mats that are produced by the
conventional dry, air-laid methods. Wet-laid processes for forming
cellulose mats have not been used commercially because
superabsorbent polymers tend to absorb liquid and swell during
formation of the absorbent mats, thus requiring significant energy
for their complete drying.
[0005] Cellulose structures formed by the wet-laid process
typically exhibit certain properties that are superior to those of
an air-laid structure. The integrity, fluid distribution, and the
wicking characteristics of wet-laid cellulosic structures are
typically superior to those of air-laid structures. Attempts to
combine the advantages of wet-laid composites with the high
absorbent capacity of superabsorbent materials has led to the
formation of various wet-laid absorbent composites that include
superabsorbent polymers. These structures can be generally
characterized as structures that either have superabsorbent
polymers distributed on the surface of a wet-laid composite,
laminates, or, alternatively, structures that have superabsorbent
material distributed relatively uniformly throughout the
composite.
[0006] However, absorbent composites that contain superabsorbent
materials commonly suffer from gel blocking. Upon liquid
absorption, superabsorbent materials tend to coalesce and form a
gelatinous mass which prevents the wicking of liquid to unwetted
portions of the composite. By preventing distribution of acquired
liquid from a composite's unwetted portions, gel blocking precludes
the effective and efficient use of superabsorbent materials in
fibrous composites. The wicking capacity of conventional fibrous
composites that include relatively homogeneous distributions of
superabsorbent material is generally significantly restricted after
initial liquid insult. The diminished capacity of such fibrous
composites results from narrowing of capillary acquisition and
distribution channels that accompanies superabsorbent material
swelling. The diminution of absorbent capacity and concomitant loss
of capillary distribution channels for conventional absorbent cores
that include superabsorbent material is manifested by decreased
liquid acquisition rates and far from ideal liquid distribution on
successive liquid insults.
[0007] Accordingly, there exists a need for methods for forming an
absorbent composite that includes superabsorbent material and that
effectively acquires and wicks liquid throughout the composite and
distributes the acquired liquid to absorbent material where the
liquid is efficiently absorbed and retained without gel blocking.
The present invention seeks to fulfill these needs and provides
further related advantages.
SUMMARY OF THE INVENTION
[0008] The present invention provides methods for forming an
absorbent fibrous composite containing absorbent material dispersed
in bands through the composite and along the composite's length.
The methods generally include depositing a fibrous slurry on a
foraminous support to form a web and depositing or injecting
absorbent material to the web across the its width to provide a web
having absorbent material in bands along the composite's length.
Drying the web provides a fluted absorbent composite. In one
embodiment, the method is a wet-laid method and in another
embodiment, the method is a foam-forming method. Preferably, the
methods are twin-wire forming methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0010] FIG. 1 is a top view of a representative composite formed in
accordance with the present invention;
[0011] FIG. 2A is a cross-sectional view of a representative
composite of the present invention in a dry state;
[0012] FIG. 2B is a cross-sectional view of a representative
composite of the present invention in a wetted state;
[0013] FIG. 2C is a perspective view of the wetted composite shown
in FIG. 2B;
[0014] FIG. 3 is a cross-sectional view of a representative
composite formed in accordance with the present invention;
[0015] FIG. 4A is a perspective view of the upper surface of a
representative composite formed in accordance with the present
invention;
[0016] FIG. 4B is a perspective view of the lower surface of a
representative composite formed in accordance with the present
invention;
[0017] FIG. 5 is a perspective view of a representative absorbent
material banding pattern formed in accordance with the present
invention;
[0018] FIG. 6 is a perspective view of another representative
absorbent material banding pattern formed in accordance with the
present invention;
[0019] FIG. 7 is a perspective view of another representative
absorbent material banding pattern formed in accordance with the
present invention;
[0020] FIG. 8 is a photomicrograph (15 X magnification) of a
portion of a representative composite formed in accordance with the
present invention, the photomicrograph shows a machine direction
view of a cross-machine direction cut through a region enriched
with absorbent material;
[0021] FIG. 9 is a photomicrograph (15 X magnification) of a
portion of a representative composite formed in accordance with the
present invention, the photomicrograph shows a machine direction
view of a cross-machine direction cut through a liquid distribution
zone;
[0022] FIG. 10 is a photomicrograph (15 X magnification) of a
portion of a representative composite formed in accordance with the
present invention, the photomicrograph shows a machine direction
view of a cross-machine direction cut through an interface region
of the composite between a liquid distribution zone and a region
enriched with absorbent material;
[0023] FIG. 11A is a perspective view of another representative
composite formed in accordance with the present invention;
[0024] FIG. 11B is a perspective view of an absorbent construct
composed of the composite shown in FIG. 11A and an acquisition
layer;
[0025] FIG. 12A is a diagrammatic view illustrating a device and
method for forming the composite of the present invention;
[0026] FIG. 12B is a top plan view of a portion of a device for
forming the composite of the present invention;
[0027] FIG. 13 is a diagrammatic view illustrating a twin-wire
device and method for forming the composite of the present
invention;
[0028] FIGS. 14A-14H are cross-sectional views of representative
composites formed in accordance with the present invention;
[0029] FIG. 15 is a diagrammatic view illustrating a representative
headbox assembly and method for forming the composite of the
present invention;
[0030] FIG. 16 is a diagrammatic view illustrating a representative
headbox assembly and method for forming the composite of the
present invention;
[0031] FIG. 17 is a view illustrating representative conduits for
introducing absorbent material into a fibrous web in accordance
with the present invention;
[0032] FIG. 18 is a cross-sectional view of a portion of a
component of an absorbent article incorporating a representative
composite formed in accordance with the present invention;
[0033] FIG. 19 is a cross-sectional view of a portion of a
component of an absorbent article incorporating a representative
composite formed in accordance with the present invention;
[0034] FIG. 20 is a cross-sectional view of a portion of an
absorbent construct incorporating a storage layer and a
representative composite formed in accordance with the present
invention;
[0035] FIG. 21 is a cross-sectional view of a portion of an
absorbent construct incorporating a storage layer and a
representative composite formed in accordance with the present
invention;
[0036] FIG. 22 is a cross-sectional view of a portion of an
absorbent construct incorporating a storage layer, an acquisition
layer, and a representative composite formed in accordance with the
present invention;
[0037] FIG. 23 is a cross-sectional view of a portion of an
absorbent construct incorporating a storage layer, an acquisition
layer, and a representative composite formed in accordance with the
present invention;
[0038] FIGS. 24A-24D are cross-sectional views of a portion of
absorbent constructs incorporating a representative composite
formed in accordance with the present invention;
[0039] FIGS. 25A-25H are cross-sectional views of a portion of
absorbent articles incorporating a representative composite formed
in accordance with the present invention;
[0040] FIG. 26A is a cross-sectional view of a portion of an
absorbent article incorporating a representative composite formed
in accordance with the present invention;
[0041] FIG. 26B is a cross-sectional view of a preferred embodiment
of an absorbent article incorporating a liquid pervious facing
sheet, a liquid impervious backing sheet, and a representative
composite formed in accordance with the present invention;
[0042] FIG. 27 is a cross-sectional view of a portion of an
absorbent article incorporating a representative composite formed
in accordance with the present invention;
[0043] FIG. 28 is a cross-sectional view of a portion of an
absorbent article incorporating a representative composite formed
in accordance with the present invention; and
[0044] FIG. 29 is a cross-sectional view of a portion of an
absorbent article incorporating a representative composite formed
in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0045] The present invention provides methods for forming an
absorbent composite that is a fibrous composite that includes
absorbent material. The absorbent composite includes a fibrous
matrix having absorbent material dispersed in bands along the
composite's length. Between the composite's bands of absorbent
material lie distribution zones composed primarily of fibers.
Generally, the absorbent material serves to absorb and retain
liquid acquired by the composite. The composite's fibrous
distribution zones serve to acquire liquid contacting the composite
and to distribute the acquired liquid throughout the composite and,
ultimately, to the absorbent material.
[0046] The absorbent composite can be advantageously incorporated
into a variety of absorbent articles such as diapers including
disposable diapers and training pants; feminine care products
including sanitary napkins, and pant liners; adult incontinence
products; toweling; surgical and dental sponges; bandages; food
tray pads; and the like. Because the composite is highly absorbent,
the composite can be included into an absorbent article as a liquid
storage core. In such a construct, the composite can be combined
with one or more other composites or layers including, for example,
an acquisition and/or a distribution layer. Alternatively, because
the composite can rapidly acquire, distribute, and store liquid,
the composite can be effectively incorporated into an absorbent
article as the sole absorbent component without including other
individual layers such as acquisition and/or distribution layers.
An absorbent article, such as a diaper, can be formed from a fluted
absorbent composite having a liquid pervious facing sheet and a
liquid impervious backing sheet. In addition, because of the
composite's capacity to rapidly acquire and distribute liquid, the
composite can serve as a liquid management layer that acquires and
transfers a portion of the acquired liquid to an underlying storage
core. Thus, the absorbent composite can be combined with a storage
core to provide an absorbent core that is useful in absorbent
articles.
[0047] The absorbent composite is a fluted composite. As used
herein, the term "fluted" refers to the nature of the composite,
which on wetting, develops ridges or flutes as a result of
absorbent material expansion. As noted above, absorbent material is
located in bands or stripes positioned across the composite's width
and extending in bands along the composite's length. On contact
with liquid acquired by the fibrous composite, absorbent material
swelling occurs and produces a wetted composite having ridges or
flutes that include swollen absorbent material separated by
distribution zones or channels, regions of the composite that are
generally substantially free of absorbent material.
[0048] The fluted composite is a fibrous structure prepared from
cellulosic fibers that have been wetted during the formation
process and, as a result, provide a fibrous composite in which the
fibers are bonded. As used in this context, the term "bonded"
refers to hydrogen bonding that occurs between fibers that have
been wetted and then formed into a mat or web. The bonding that
occurs between wetted fibers subsequently formed into a fibrous web
results in a web that has increased strength and structural
integrity, when both wet and dry, compared to air-laid webs.
Fibrous webs formed from wetted fibers have strength and integrity
significantly greater than air-laid fibrous webs formed from dry
fibers, which are incapable of any significant interfiber bonding.
The mere proximity of dry fibers in a fibrous web is insufficient
to provide any significant bonding between fibers. Consequently, as
is well know, air-laid fibrous webs generally lack wet or dry
strength. In addition to standard wet-laid processes, wetted fibers
can be produced and formed into fibrous webs by foam-forming
processes.
[0049] The banded nature of the fluted absorbent composite is
illustrated in FIGS. 1-3. Referring to FIG. 1, a representative
fluted absorbent composite indicated generally by reference 10
formed in accordance with the present invention includes regions 12
enriched with absorbent material (i.e., liquid storage zones) and
fibrous regions 14 that are substantially free of absorbent
material (i.e., liquid distribution zones). Regions 12 enriched
with absorbent material are generally fibrous regions to which have
been added absorbent material.
[0050] When the absorbent composite is contacted with liquid,
liquid is rapidly acquired by the predominantly fibrous regions of
the composite. The fibrous regions are relatively open and porous
in nature and promote rapid liquid acquisition, wicking, and
distribution. Liquid acquired by the composite generally travels
rapidly longitudinally through the fibrous composite along the
composite's length via the distribution zones (i.e., regions 14)
and is absorbed by regions of the composite enriched with absorbent
material (i.e., regions 12). The acquired liquid is generally
wicked laterally into the absorbent material as the liquid is
distributed along the composite's length.
[0051] For the fluted composite, successive liquid insults are
absorbed at a rate greater than the rate for initial insult through
the establishment of flutes and channels on initial liquid insult.
On wetting, the composite of the present invention becomes on a
fluted structure having channels for rapidly acquiring additional
liquid and distributing the liquid to sites that are remote to
insult. Uptake of liquid by superabsorbent leads to expansion and
enhancement of voids in the fibrous structure. For the fluted
composite, acquisition times for subsequent liquid insult are
generally less than that for the initial acquisition Reduced
acquisition times for successive liquid insults is not generally
observed for conventional absorbent constructs. Because
conventional absorbent structures cannot form a fluted structure
and therefore lack channels for distributing additional liquid,
acquisition times for these structures generally increase for
successive liquid insults. Increased acquisition time is
attributable to the fact that liquid is only slowly acquired and
distributed through a composite's saturated regions to more remote
regions of the composite that are capable of absorbing liquid.
Thus, the fluted absorbent composite provides for initial liquid
acquisition rates that are generally comparable or greater than for
conventional absorbent structures and have significantly increased
rates of liquid acquisition for successive liquid acquisition
relative to conventional composites.
[0052] The dry and wet structures of the fluted composite are
illustrated in FIGS. 2A and 2B, which are lateral cross-sectional
views of a representative fluted absorbent composite. FIG. 2A is a
cross-sectional view of the dry composite shown in FIG. 1
indicating regions 12 and 14 and the relatively uniform thickness
of the unwetted composite. FIG. 2B is a cross-sectional view of the
composite shown in FIG. 1 in a wetted state, for example, after
liquid insult and liquid absorption and swelling and expansion of
the absorbent material. Referring to FIG. 2B, absorbent material
enriched regions 12 (i.e., liquid storage regions) are shown as
ridges or flutes separated by fibrous regions 14 (i.e., liquid
distribution zones) that form a valley floor or channel between the
flutes. Due at least in part to the fluted structure of the wetted
fibrous composite, subsequent liquid insults are rapidly absorbed
by the fluted composite compared to composites containing absorbent
material in other configurations, for example, composites in which
the absorbent material is distributed substantially uniformly
throughout the composite and that are particularly susceptible to
gel blocking, low acquisition rates, and liquid leakage.
[0053] Liquid acquisition rates and times for a representative
fluted absorbent composite are compared to those of storage cores
having relatively uniform distributions of absorbent material in
Example 1. Acquisition rates for the fluted absorbent composite
were significantly greater than for commercially available cores
which showed acquisition rates that decreased substantially with
successive insults. In contrast, the composite of the invention
maintained high rates for three insults. The fluted composite also
exhibited rates greater than for a similarly composed wet composite
having a relatively uniform distribution of absorbent material
throughout the composite.
[0054] Example 2 compares the wicking characteristics of a
representative fluted absorbent composite to a commercially
available diaper core and a wet-laid fibrous core that contains
superabsorbent material distributed substantially uniformly
throughout the composite. The horizontal and vertical wicking
results indicate that the air-laid commercial core has the poorest
wicking characteristics, while the fluted composite having bands of
absorbent material exhibits significantly enhanced wicking compared
to a similarly composed composite that includes relatively
uniformly distributed absorbent material.
[0055] Distribution of liquid from the site of insult throughout
the composite demonstrates the composite's wicking capacity and
efficiency of material utilization. The liquid distribution of a
representative fluted composite is compared to two commercially
available diaper cores in Example 3. The results indicate that, in
contrast to the commercial cores which suffer from liquid
accumulation at the site of insult, the fluted composite has nearly
ideal distribution, distributing liquid throughout the entire
composite and fully utilizing the composite's materials.
[0056] Because liquid insults are absorbed in a conventional
storage core at a rate less than the average infant's urination
rate, liquid can leak from the diaper at its edges. To prevent such
leakage, diaper manufacturers have developed elaborate and
expensive leg cuff gasketing systems that fit tightly about an
infant's leg and is generally uncomfortable and leaves marks. When
incorporated into a diaper as a storage core, the fluted composite
of this invention overcome the problems of edge leaking associated
with conventional storage cores. Accordingly, in one preferred
embodiment, the fluted absorbent composite includes outermost bands
of absorbent material that include relatively greater amounts of
absorbent than the inner bands. Referring to FIG. 3, outermost
absorbent material enriched regions 12 have a greater amount of
absorbent material relative to the inner regions 12 and, as a
consequence, have a greater absorbent capacity and therefore can
swell and expand to greater size that those flutes containing
relatively lesser amount of absorbent material. The fluted
absorbent core having relatively greater amount of absorbent
material in the outermost regions 12 can assist in the prevention
of liquid leaking from the edge of the composite. In another
preferred embodiment, outermost absorbent materials enriched
regions 12 contain absorbent material having a higher absorptive
and/or liquid retention capacity than the absorbent material
contained in inner regions 12.
[0057] An infant's skin is always susceptible to irritation and
rash resulting from moisture associated with retained liquid from a
diaper's storage core. The amount of liquid released from an
absorbent article that has acquired liquid is referred to as
"rewet". While a storage core's surface is generally necessarily
hydrophilic to effectively absorb liquid, such hydrophilic surfaces
also promote rewet. In contrast to conventional absorbent articles
that are in continuous contact with a wearer's skin, the fluted
composite's surface contacts the wearer only at the flute's
ridgetops thereby minimizing contact with the wearer's skin and
rewet. Because of the minimized contact between an infant's skin
and the wetted surface of the fluted absorbent composite compared
to the wetted surface of a conventional storage core, the fluted
absorbent composite offers advantages relating to skin health and
comfort to the wearer. It is contemplated that the composite's
fluted structure also provides skin health advantages related to
cooling and air flow through an absorbent article that contains the
fluted composite. The rewet performance of a representative fluted
absorbent composite is compared to a commercially available diaper
core in Example 1. Generally, for successive insults, rewet
increases for the commercial core. In contrast, rewet remains low
and substantially unchanged for the fluted composite.
[0058] The structure of fluted composite offers the possibility of
further reduction in rewet. Liquid insult generally occurs across
the width of the composite which includes bands of fibrous regions
and regions enriched with absorbent material. Liquid is generally
rapidly acquired and distributed through the composite's fibrous
regions (i.e., regions 14) and generally stored in the composite's
regions enriched with absorbent material (i.e., regions 12).
Ultimately, the acquired liquid resides in the bands of absorbent
material in the fluted structure. To further reduce rewet, the
fluted absorbent composite can include a hydrophobic barrier
coincident with the top surface of the composite's flutes (i.e.,
coatings for the surfaces of regions 12). Suitable hydrophobic
barriers generally include latex and other hydrophobic films and
coatings known in the art. Because the distribution zones between
the coated flutes (i.e., regions 14) are physically removed from
the wearer and because the wearer is protected from the flutes
containing the absorbent material and acquired liquid by a
hydrophobic barrier, such a coated fluted composite provides for
increased skin health through a reduction of skin wetness.
Optionally, a hydrophobic barrier can also be affixed to the
outward facing surface of the absorbent composite. Such a
construction allows for a reduction in the thickness of the
polyethylene moisture barrier (i.e., liquid impervious backing
sheet) traditionally employed in a diaper. The application of a
hydrophobic barrier to the outward surface of the composite would
reduce total cost and material usage in an absorbent article
incorporating the fluted absorbent composite.
[0059] A representative fluted absorbent composite having a
hydrophobic barrier coincident with the composite's bands of
absorbent material and affixed to inward surface of the composite
is illustrated in FIG. 4A. Referring to FIG. 4A, coated composite
20 includes regions 12 and 14, as described above, and hydrophobic
barriers 16 substantially coincident with and covering regions 12
enriched with absorbent material. A representative fluted absorbent
composite having a hydrophobic barrier affixed to the outward
facing surface of a fluted absorbent composite is illustrated in
FIG. 4B.
[0060] Fibers are a principal component of the fluted absorbent
composite. Fibers suitable for use in the present invention are
known to those skilled in the art and include any fiber from which
an absorbent composite can be formed. Suitable fibers include
natural and synthetic fibers. Combinations of fibers including
combinations of synthetic and natural fibers, and treated and
untreated fibers, can also be suitably used in the composite.
[0061] Generally, fibers are present in the composite in an amount
from about 20 to about 90 weight percent, preferably from about 50
to about 70 weight percent, based on the total weight of the
composite. In a preferred embodiment, the composite includes about
60 percent by weight fibers.
[0062] The composite includes resilient fibers. As used herein, the
term "resilient fiber" refers to a fiber present in the composite
that imparts reticulation to the composite. Generally, resilient
fibers provide the composite with bulk and resiliency. The
incorporation of resilient fibers into the composite allows the
composite to expand on absorption of liquid without structural
integrity loss. Resilient fibers also impart softness to the
composite. In addition, resilient fibers offer advantages in the
composite's formation processes. Because of the porous and open
structure resulting from wet composites that include resilient
fibers, these composites drain water relatively easily and are
therefore dewatered and dried more readily than wet composites that
do not include resilient fibers. Preferably, the composite includes
resilient fibers in an amount from about 10 to about 60 percent by
weight, more preferably from about 20 to 50 percent by weight,
based on the total weight of the composite.
[0063] Resilient fibers include cellulosic and synthetic fibers.
Preferred resilient fibers include chemically stiffened fibers,
anfractuous fibers, chemithermomechanical pulp (CTMP), and
prehydrolyzed kraft pulp (PHKP).
[0064] The term "chemically stiffened fiber" refers to a fiber that
has been stiffened by chemical means to increase fiber stiffness
under dry and wet conditions. Fibers can be stiffened by the
addition of chemical stiffening agents that can coat and/or
impregnate the fibers. Stiffening agents include the polymeric wet
strength agents including resinous agents such as, for example,
polyamide-epichlorohydrin and polyacrylamide resins described
below. Fibers can also be stiffened by modifying fiber structure
by, for example, chemical crosslinking. Preferably, the chemically
stiffened fibers are intrafiber crosslinked cellulosic fibers.
[0065] Resilient fibers can include noncellulosic fibers including,
for example, synthetic fibers such as polyolefin, polyamide, and
polyester fibers. In a preferred embodiment, the resilient fibers
include crosslinked cellulosic fibers.
[0066] As used herein, the term "anfractuous fiber" refers to a
cellulosic fiber that has been chemically treated. Anfractuous
fibers include, for example, fibers that have been treated with
ammonia.
[0067] In addition to resilient fibers, the composite includes
matrix fibers. As used herein, the term "matrix fiber" refers to a
fiber that is capable of forming hydrogen bonds with other fibers.
Matrix fibers are included in the composite to impart strength to
the composite. Matrix fibers include cellulosic fibers such as wood
pulp fibers, highly refined cellulosic fibers, and high surface
area fibers such as expanded cellulose fibers. Other suitable
cellulosic fibers include cotton linters, cotton fibers, and hemp
fibers, among others. Preferably, the composite includes matrix
fibers in an amount from about 10 to about 50 percent by weight,
more preferably from about 15 to about 30 percent by weight, based
on the total weight of the composite.
[0068] The composite preferably includes a combination of resilient
and matrix fibers. In one preferred embodiment, the composite
includes resilient fibers in an amount from about 25 to about 50
percent by weight and matrix fibers in an amount from about 10 to
about 40 percent by weight based on the total weight of the
composite. In a more preferred embodiment, the composite includes
from about 30 to about 45 percent by weight resilient fibers,
preferably crosslinked cellulosic fibers, and from about 15 to
about 30 percent by weight matrix fibers, preferably wood pulp
fibers, based on the total weight of fibers in the composite. For
representative composites formed by wet-laid and foam processes,
the composite preferably includes about 45 percent by weight
resilient fibers (e.g., crosslinked cellulosic fibers) and about 15
percent by weight matrix fibers.
[0069] Cellulosic fibers can be a basic component of the fluted
absorbent composite. Although available from other sources,
cellulosic fibers are derived primarily from wood pulp. Suitable
wood pulp fibers for use in the invention can be obtained from
well-known chemical processes such as the kraft and sulfite
processes, with or without subsequent bleaching. Pulp fibers can
also be processed by thermomechanical, chemithermomechanical
methods, or combinations thereof. The preferred pulp fiber is
produced by chemical methods. Ground wood fibers, recycled or
secondary wood pulp fibers, and bleached and unbleached wood pulp
fibers can be used. Softwoods and hardwoods can be used. Details of
the selection of wood pulp fibers are well-known to those skilled
in the art. These fibers are commercially available from a number
of companies, including Weyerhaeuser Company, the assignee of the
present invention. For example, suitable cellulose fibers produced
from southern pine that are usable in the present invention are
available from Weyerhaeuser Company under the designations CF416,
NF405, PL416, FR516, and NB416.
[0070] The wood pulp fibers can also be pretreated prior to use in
the present invention. This pretreatment may include physical
treatment, such as subjecting the fibers to steam, or chemical
treatment, for example, crosslinking the cellulose fibers using any
one of a variety of crosslinking agents. Crosslinking increases
fiber bulk and resiliency, and thereby can improve the fibers'
absorbency. Generally, crosslinked fibers are twisted or crimped.
The use of crosslinked fibers allows the composite to be more
resilient, softer, bulkier, and to have enhanced wicking. Suitable
crosslinked cellulose fibers produced from southern pine are
available from Weyerhaeuser Company under the designation NBH416.
Crosslinked cellulose fibers and methods for their preparation are
disclosed in U.S. Pat. Nos. 5,437,418 and 5,225,047 issued to Graef
et al., expressly incorporated herein by reference.
[0071] Crosslinked fibers can be prepared by treating fibers with a
crosslinking agent. Suitable cellulose crosslinking agents include
aldehyde and urea-based formaldehyde addition products. See, for
example, U.S. Pat. Nos. 3,224,926; 3,241,533; 3,932,209; 4,035,147;
3,756,913; 4,689,118; 4,822,453; U.S. Pat. No. 3,440,135, issued to
Chung; U.S. Pat. No. 4,935,022, issued to Lash et al.; U.S. Pat.
No. 4,889,595, issued to Herron et al.; U.S. Pat. No. 3,819,470,
issued to Shaw et al.; U.S. Pat. No. 3,658,613, issued to Steiger
et al.; and U.S. Pat. No. 4,853,086, issued to Graef et al., all of
which are expressly incorporated herein by reference in their
entirety. Cellulose fibers have also been crosslinked by carboxylic
acid crosslinking agents including polycarboxylic acids. U.S. Pat.
Nos. 5,137,537; 5,183,707; and 5,190,563, describe the use of C2-C9
polycarboxylic acids that contain at least three carboxyl groups
(e.g., citric acid and oxydisuccinic acid) as crosslinking
agents.
[0072] Suitable urea-based crosslinking agents include methylolated
ureas, methylolated cyclic ureas, methylolated lower alkyl
substituted cyclic ureas, methylolated dihydroxy cyclic ureas,
dihydroxy cyclic ureas, and lower alkyl substituted cyclic ureas.
Specific preferred urea-based crosslinking agents include
dimethylol urea (DMU, bis[N-hydroxymethyl]ure- a),
dimethylolethylene urea (DMEU,
1,3-dihydroxymethyl-2-imidazolidinone), dimethyloldihydroxyethylene
urea (DMDHEU, 1,3-dihydroxymethyl-4,5-dihydro-
xy-2-imidazolidinone), dimethyldihydroxy urea (DMDHU),
dihydroxyethylene urea (DHEU, 4,5-dihydroxy-2-imidazolidinone), and
dimethyldihydroxyethyle- ne urea (DMeDHEU,
4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone).
[0073] Suitable polycarboxylic acid crosslinking agents include
citric acid, tartaric acid, malic acid, succinic acid, glutaric
acid, citraconic acid, itaconic acid, tartrate monosuccinic acid,
and maleic acid. Other polycarboxylic acids crosslinking agents
include polymeric polycarboxylic acids such as poly(acrylic acid),
poly(methacrylic acid), poly(maleic acid),
poly(methylvinylether-co-maleate) copolymer,
poly(methylvinylether-co-itaconate) copolymer, copolymers of
acrylic acid, and copolymers of maleic acid. The use of polymeric
polycarboxylic acid crosslinking agents such as polyacrylic acid
polymers, polymaleic acid polymers, copolymers of acrylic acid, and
copolymers of maleic acid is described in U.S. patent application
Ser. No. 08/989,697, filed Dec. 12, 1997, and assigned to
Weyerhaeuser Company. Mixtures or blends of crosslinking agents may
also be used.
[0074] The crosslinking agent can include a catalyst to accelerate
the bonding reaction between the crosslinking agent and cellulose
fiber. Suitable catalysts include acidic salts, such as ammonium
chloride, ammonium sulfate, aluminum chloride, magnesium chloride,
and alkali metal salts of phosphorous-containing acids.
[0075] Although not to be construed as a limitation, examples of
pretreating fibers include the application of surfactants or other
liquids which modify the surface chemistry of the fibers. Other
pretreatments include incorporation of antimicrobials, pigments,
dyes and densification or softening agents. Fibers pretreated with
other chemicals, such as thermoplastic and thermosetting resins
also may be used. Combinations of pretreatments also may be
employed. Similar treatments can also be applied after the
composite formation in post-treatment processes.
[0076] Cellulosic fibers treated with particle binders and/or
densification/softness aids known in the art can also be employed
in accordance with the present invention. The particle binders
serve to attach other materials, such as cellulosic fiber
superabsorbent polymers, as well as others, to the cellulosic
fibers. Cellulosic fibers treated with suitable particle binders
and/or densification/softness aids and the process for combining
them with cellulose fibers are disclosed in the following U.S.
patents: (1) U.S. Pat. No. 5,543,215, entitled "Polymeric Binders
for Binding Particles to Fibers"; (2) U.S. Pat. No. 5,538,783,
entitled "Non-Polymeric Organic Binders for Binding Particles to
Fibers"; (3) U.S. Pat. No. 5,300,192, entitled "Wet Laid Fiber
Sheet Manufacturing With Reactivatable Binders for Binding
Particles to Binders"; (4) U.S. Pat. No. 5,352,480, entitled
"Method for Binding Particles to Fibers Using Reactivatable
Binders"; (5) U.S. Pat. No. 5,308,896, entitled "Particle Binders
for High-Bulk Fibers"; (6) U.S. Pat. No. 5,589,256, entitled
"Particle Binders that Enhance Fiber Densification"; (7) U.S. Pat.
No. 5,672,418, entitled "Particle Binders"; (8) U.S. Pat. No.
5,607,759, entitled "Particle Binding to Fibers"; (9) U.S. Pat. No.
5,693,411, entitled "Binders for Binding Water Soluble Particles to
Fibers"; (10) U.S. Pat. No. 5,547,745, entitled "Particle Binders";
(11) U.S. Pat. No. 5,641,561, entitled "Particle Binding to
Fibers"; (12) U.S. Pat. No. 5,308,896, entitled "Particle Binders
for High-Bulk Fibers"; (13) U.S. Pat. No. 5,498,478, entitled
"Polyethylene Glycol as a Binder Material for Fibers"; (14) U.S.
Pat. No. 5,609,727, entitled "Fibrous Product for Binding
Particles"; (15) U.S. Pat. No. 5,571,618, entitled "Reactivatable
Binders for Binding Particles to Fibers"; (16) U.S. Pat. No.
5,447,977, entitled "Particle Binders for High Bulk Fibers"; (17)
U.S. Pat. No. 5,614, 570, entitled "Absorbent Articles Containing
Binder Carrying High Bulk Fibers; (18) U.S. Pat. No. 5,789,326,
entitled "Binder Treated Fibers"; and (19) U.S. Pat. No. 5,611,885,
entitled "Particle Binders"; all expressly incorporated herein by
reference.
[0077] In addition to natural fibers, synthetic fibers including
polymeric fibers, such as polyolefin, polyamide, polyester,
polyvinyl alcohol, polyvinyl acetate fibers, and can also be used
in the absorbent composite. Suitable synthetic fibers include, for
example, polyethylene terephthalate, polyethylene, polypropylene,
nylon, and rayon fibers. Other suitable synthetic fibers include
those made from thermoplastic polymers, cellulosic and other fibers
coated with thermoplastic polymers, and multicomponent fibers in
which at least one of the components includes a thermoplastic
polymer. Single and multicomponent fibers can be manufactured from
polyester, polyethylene, polypropylene, and other conventional
thermoplastic fibrous materials. Single and multicomponent fibers
are commercially available. Suitable bicomponent fibers include
Celbond.RTM. fibers available from Hoechst-Celanese Company. The
absorbent composite can also include combinations of natural and
synthetic fibers. Synthetic fibers, including blends of natural and
synthetic fibers, can be utilized in the composite's flutes and/or
distribution zones.
[0078] In one preferred embodiment, the absorbent composite
includes a combination of pulp fibers (e.g., Weyerhaeuser
designation NB416) and crosslinked cellulosic fibers (e.g.,
Weyerhaeuser designation NHB416). In a preferred embodiment, the
absorbent composite includes a combination of pulp fibers present
in the composite in about 50 weight percent and crosslinked
cellulosic fibers present in the composite in about 50 weight
percent based on the total weight of fibers.
[0079] In a preferred embodiment, the wet-laid or foam-formed
fluted composite is formed from a fiber furnish that includes a
blend of refined southern pine fibers and crosslinked fibers.
Composites formed from such a blend have increased sheet integrity
and enhanced bulk compared to composites formed from a mixture of
southern pine and crosslinked fibers that has been refined.
Optionally, the blend of refined southern pine fibers and
crosslinked fibers can be further lightly refined.
[0080] The fluted absorbent composite can serve as a storage layer
for acquired liquids when incorporated into an absorbent article.
To effectively retain acquired liquids, the composite includes
absorbent material.
[0081] As described above, absorbent material is located in bands
incorporated into the fibrous composite. Basically, bands of
absorbent material can be configured in virtually any shape, size,
and composite location. Suitable configurations of the composite's
bands include any configuration that does not impede liquid
acquisition or promote gel blocking. The bands of absorbent
material can include straight and parallel bands, curved or wavy
bands, and zigzag bands, among others. A representative banded
absorbent composite having wavy bands is illustrated in FIG. 5. The
composite's bands can also include pulsed bands of absorbent
material. As used herein the term "pulsed band" refers to a band
that extends along the composite's length that is not a continuous
band, but rather is a band that is interrupted by regions
containing substantially no absorbent material. A function of the
pulsed bands is to provide the composite with enhanced liquid
distribution capacity across the composite's width (i.e., the
cross-machine direction). A representative banded absorbent
composite having pulsed bands is illustrated in FIG. 6. As
illustrated in FIG. 6, in one embodiment, the pulsed bands have an
offset configuration to further enhance cross-machine direction
liquid distribution. Such an offset configuration of absorbent
material can be formed by injecting absorbent material into the
composite through nozzles delivering nonsynchronous pulses of
absorbent material (i.e., pulses from one nozzle that is not
synchronized with pulses from another nozzle). The length of the
pulsed band can vary greatly and can, for example, be a dot or spot
of absorbent material having a length equal to about its width. A
representative banded absorbent composite having pulsed bands
resembling dots or spots is illustrated in FIG. 7.
[0082] The composite's bands or flutes are regions of the composite
that are enriched with absorbent material. The composite's
distribution zones can include some absorbent material. It will be
appreciated that while absorbent material is incorporated into the
composite in bands, the formation of absorbent material bands in
the composite can lead to the introduction of some absorbent
material into the composite's fibrous distribution zones. The
incorporation of absorbent material into the composite can result
in some mixing between the absorbent material and fibers present in
the fibrous base. The result is a transition zone between the
primarily fibrous distribution zones and the absorbent material
bands. Such a transition zone includes both fibers and absorbent
material. The composite's fibrous matrix can also be formed to
include some absorbent materials thereby resulting in distribution
zones containing absorbent material. In embodiments having
absorbent material in the distribution zones, the amount of
absorbent material present is not so great as to diminish the
effectiveness of these zones in distributing acquired liquid.
[0083] Cross-sectional views of a representative composite formed
by a wet-laid method are shown in the photomicrographs in FIGS.
8-10. FIG. 8 is a machine direction view of a cross-machine
direction cut through the composite's absorbent material band
(i.e., region 12 of the composite enriched with absorbent
material). FIG. 9 is a machine direction view of a cross-machine
direction cut through a distribution zone (i.e., region 14 of the
composite substantially free of absorbent material). FIG. 10 is a
machine direction view of a cross-machine direction cut
intermediate an absorbent material band and a distribution zone
(i.e., through a transition zone as described above).
[0084] As use herein, the term "absorbent material" refers to a
material that absorbs liquid and that generally has an absorbent
capacity greater than the cellulosic fibrous component of the
composite. Preferably, the absorbent material is a water swellable,
generally water insoluble polymeric material capable of absorbing
at least about 5, desirably about 20, and preferably about 100
times or more its weight in saline (e.g., 0.9 percent saline). The
absorbent material can be swellable in the dispersion medium
utilized in the method for forming the composite. In one
embodiment, the absorbent material is untreated and swellable in
the dispersion medium. In another embodiment, the absorbent
material is an absorbent material that is resistant to absorbing
water during the composite formation process. Such absorbent
materials that are resistant to absorption include coated and
chemically modified absorbent materials.
[0085] The amount of absorbent material present in the composite
can vary greatly depending on the composite's intended use. When
the absorbent composite is used as a stand alone absorbent
composite as in, for example, an absorbent toweling, the amount of
absorbent material in the composite is comparative low (e.g., about
0.1 weight percent). The amount of absorbent material present in an
absorbent article such as an absorbent core for an infant's diaper
is considerably greater. In such a construct, the absorbent
material is suitably present in the composite in an amount from
about 10 to about 80 weight percent, preferably from about 30 to
about 50 weight percent, based on the total weight of the
composite. In preferred embodiments, the composite includes about
40 percent by weight absorbent material based on the total weight
of the composite.
[0086] The absorbent material may include natural materials such as
agar, pectin, and guar gum, and synthetic materials, such as
synthetic hydrogel polymers. Synthetic hydrogel polymers include,
for example, carboxymethyl cellulose, alkaline metal salts of
polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene
maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl
cellulose, polyvinyl morpholinone, polymers and copolymers of vinyl
sulphonic acid, polyacrylates, polyacrylamides, and polyvinyl
pyridine among others. In a preferred embodiment, the absorbent
material is a superabsorbent material. As used herein, a
"superabsorbent material" refers to a polymeric material that is
capable of absorbing large quantities of fluid by swelling and
forming a hydrated gel (i.e., a hydrogel). In addition to absorbing
large quantities of fluids, superabsorbent polymers can also retain
significant amounts of bodily fluids under moderate pressure.
[0087] Superabsorbent polymers generally fall into three classes:
starch graft copolymers, crosslinked carboxymethylcellulose
derivatives, and modified hydrophilic polyacrylates. Examples of
such absorbent polymers include hydrolyzed starch-acrylonitrile
graft copolymers, neutralized starch-acrylic acid graft copolymers,
saponified acrylic acid ester-vinyl acetate copolymers, hydrolyzed
acrylonitrile copolymers or acrylamide copolymers, modified
crosslinked polyvinyl alcohol, neutralized self-crosslinking
polyacrylic acids, crosslinked polyacrylate salts, carboxylated
cellulose, and neutralized crosslinked isobutylene-maleic anhydride
copolymers.
[0088] Superabsorbent polymers are available commercially, for
example, polyacrylates from Clariant of Portsmouth, Va. These
superabsorbent polymers come in a variety of sizes, morphologies
and absorbent properties (available from Clariant under trade
designations such as IM 3500 and IM 3900). Other superabsorbent
particles are marketed under the trademarks SANWET (supplied by
Sanyo Kasei Kogyo Kabushiki Kaisha), and SXM77 (supplied by
Stockhausen of Greensboro, N.C.). Other superabsorbent polymers are
described in U.S. Pat. No. 4,160,059; U.S. Pat. No. 4,676,784; U.S.
Pat. No. 4,673,402; U.S. Pat. No. 5,002,814; U.S. Pat. No.
5,057,166; U.S. Pat. No. 4,102,340; and U.S. Pat. No. 4,818,598,
all expressly incorporated herein by reference. Products such as
diapers that incorporate superabsorbent polymers are described in
U.S. Pat. No. 3,699,103 and U.S. Pat. No. 3,670,731.
[0089] Suitable superabsorbent polymers useful in the absorbent
composite include superabsorbent polymer particles and
superabsorbent polymer fibers.
[0090] In a preferred embodiment, the absorbent composite includes
a superabsorbent material that that swells relatively slowly for
the purposes of composite manufacturing and yet swells at an
acceptable rate so as not to adversely affect the absorbent
characteristics of the composite or any construct containing the
composite.
[0091] In one embodiment, the present invention provides a
composite having absorbent material present in the composite in a
concentration gradient. As used herein, the term "concentration
gradient" refers to a gradient in the concentration of absorbent
material in the fibrous composite with respect to a particular
dimension (i.e., thickness, width, and length) of the composite. An
absorbent material concentration gradient is formed through
selective distribution of the material into the composite. For
example, as described below, introduction of the absorbent material
into the composite can be accomplished with significant fiber
mixing and an accompanying loss of an absorbent material
concentration gradient. Alternatively, the absorbent material can
be introduced into the composite without significant fiber mixing
resulting in the formation of a relatively greater concentration
gradient. The composite's concentration gradient can be present in
either the z-direction (i.e., the thickness of the composite), the
x-direction (i.e., across the width of the composite, the
cross-machine direction), the y-direction (i.e., along the length
of the composite, the machine direction) or combinations of the x-,
y- and z-directions. Concentration gradients of absorbent material
are contemplated to increase liquid wicking and further to reduce
the potential for gel blocking.
[0092] In another embodiment, the present invention provides a
banded composite having absorbent material relatively uniformly
distributed across its width and extending along its length
throughout its thickness in addition to absorbent material present
in the bands. The absorbent material is distributed into the
fibrous composite as described below and preferably is present in
the composite in a concentration gradient. Preferably the
concentration gradient is present in at least the z-direction
(i.e., the composite's thickness), although gradients in the x- and
y-directions are also contemplated to provide useful composites.
Composites include those having concentration gradients in one or
more of the x-, y-, and z-directions. For embodiments having a
z-direction gradient, the high concentration surface is preferably
positioned in an absorbent article away from liquid insult. In one
embodiment having a concentration gradient in the x-direction
(i.e., the composite's width), the concentration is preferably
maximal at center of the composite's width and decreases outwardly
from the center toward the composite's edges. In another
embodiment, the concentration is preferably maximal at the
composite's edges. Gradients in the y-direction generally provide
regions of absorbent material along the composite's length.
[0093] The absorbent composite optionally includes a wet strength
agent. The wet strength agent provides increased strength to the
absorbent composite and enhances the composites wet integrity. In
addition to increasing the composites wet strength, the wet
strength agent can assist in binding the absorbent material, for
example, superabsorbent material, in the composite's fibrous
matrix.
[0094] Suitable wet strength agents include cationic modified
starch having nitrogen-containing groups (e.g., amino groups) such
as those available from National Starch and Chemical Corp.,
Bridgewater, N.J.; latex; wet strength resins such as
polyamide-epichlorohydrin resin (e.g., Kymene.RTM. 557LX, Hercules,
Inc., Wilmington, Del.), polyacrylamide resin (described, for
example, in U.S. Pat. No. 3,556,932 issued Jan. 19, 1971 to Coscia
et al.; also, for example, the commercially available
polyacrylamide marketed by American Cyanamid Co., Stanford, Conn.,
under the trade name Parez.TM. 631 NC); urea formaldehyde and
melamine formaldehyde resins, and polyethylenimine resins. A
general discussion on wet strength resins utilized in the paper
field, and generally applicable in the present invention, can be
found in TAPPI monograph series No. 29, "Wet Strength in Paper and
Paperboard", Technical Association of the Pulp and Paper Industry
(New York, 1965).
[0095] Generally, the wet strength agent is present in the
composition in an amount from about 0.01 to about 2 weight percent,
preferably from about 0.1 to about 1 weight percent, and more
preferably from about 0.3 to about 0.7 weight percent, based on the
total weight of the composite. In a preferred embodiment, the wet
strength agent useful in the composite is a
polyamide-epichlorohydrin resin such as commercially available from
Hercules, Inc. under the designation Kymene.RTM.. The wet and dry
tensile strength of an absorbent composite formed in accordance
with the present invention will generally increase with an
increasing the amount of wet strength agent.
[0096] It has been observed that after successive liquid insults,
the composites formed in accordance with the present invention
maintain their structural integrity and remain substantially intact
on removal from a diaper construct. In contrast, conventional
storage cores that contain superabsorbent material lose structural
integrity in a wetted diaper. Thus, the wet tensile strength of the
fluted absorbent cores significantly exceeds that of conventional
storage cores.
[0097] The absorbent composite generally has a basis weight from
about 50 to about 1000 g/m.sup.2, and preferably from about 200 to
about 800 g/m.sup.2. In a more preferred embodiment, the absorbent
composite has a basis weight from about 300 to about 600 g/m.sup.2.
The basis weight of the fluted composite can be varied and will
depend on its intended use. When the fluted composite's intended
use is as a storage layer, the composite preferably has a basis
weight greater than about 300 g/m.sup.2. For use as a liquid
management layer, the composite preferably has a basis weight from
about 100 to about 400 g/m.sup.2. The absorbent composite generally
has an average density (in the cross-machine direction) of from
about 0.03 to about 0.8 g/cm.sup.3, preferably from about 0.04 to
about 0.3 g/cm.sup.3. In a more preferred embodiment, the absorbent
composite has an average density of about 0.15 g/cm.sup.3.
[0098] In one embodiment, the absorbent composite is a densified
composite. Densification methods useful in producing the densified
composites are well known to those in the art. See, for example,
U.S. Pat. No. 5,547,541 and patent application Ser. No. 08/859,743,
filed May 21, 1997, entitled "Softened Fibers and Methods of
Softening Fibers," assigned to Weyerhaeuser Company, both expressly
incorporated herein by reference. Post dryer densified absorbent
composites generally have a density from about 0.1 to about 0.5
g/cm.sup.3, and preferably about 0.15 g/cm.sup.3. Predryer
densification can also be employed. Preferably, the absorbent
composite is densified by either a heated or room temperature
calender roll method. See, for example, U.S. Pat. Nos. 5,252,275
and 5,324,575, both expressly incorporated herein by reference.
[0099] The composition of the absorbent composite can be varied to
suit the intended use of the end product in which the composite is
incorporated. In one preferred embodiment, the absorbent composite
includes about 60 weight percent cellulosic fibers, about 40
percent by weight absorbent material (e.g., superabsorbent
polymeric particles), and about 0.25 percent by weight wet strength
agent (e.g., polyamide-epichlorohydrin resin, Kymene.RTM., about
2-20 pounds resin per ton fiber) based on the total weight of the
composite.
[0100] The dimensions of the fluted absorbent composite can be
varied greatly depending on the desired characteristics of the
composite and its intended use. Typically, for a child's diaper,
the composite includes from about 2 to about 6 bands of absorbent
material across the composite's width, the outward edges of the
composite preferably including bands of absorbent material. For a
typical adult incontinence product, the composite can include 10 or
more bands. Although the configuration and widths of the bands are
not particularly critical, the bands of absorbent material are
generally evenly spaced across the composite's width and have
widths of from about 0.10 to about 0.75 inch. The bands are
typically separated by distribution zones having widths from about
0.10 to about 1.0 inch. Feminine care products contain a relatively
low amount of absorbent material and fluted composites useful in
such products have relatively narrow bands of absorbent
material.
[0101] The present invention provides methods for forming a fluted
absorbent composite. The fluted structure of the composite can be
formed in any one of variety of methods known to those in the art,
all of which are within the scope of this invention. For example, a
fluted structure can be formed by attaching one of more bands of
absorbent material or acquisition/distribution material to a
fibrous base; depositing, injecting, applying, impregnating, or
infusing absorbent material into a fibrous base; or by wet-laid and
foam-forming processes as described below.
[0102] For embodiments that are formed by attaching bands of
absorbent or acquisition/distribution materials to a fibrous base,
the bands can further include other materials such as fibers. For
these embodiments, the absorbent material-containing bands and the
fibrous base can be independently formed by methods known to those
in the art including air-laid, wet-laid, and foam-forming methods,
as described below. The fluted composite can be formed by affixing
or attaching the bands to a fibrous base by any method that permits
fluid communication between these components of the composite.
Suitable means for affixing or attaching include, for example,
gluing, thermobonding, and entangling. Generally, these embodiments
have improved absorbent properties due to enhanced fluid
communication between the composite's components compared to the
composites that have absorbent material in mere proximity to the
composite's fibrous component.
[0103] Referring to FIG. 11A, fluted absorbent composite 22
includes distribution zones 26 that serve to rapidly acquire and
distribute liquid to storage zones 24 and storage core 28. As noted
above, distribution zones 26 are composed primarily of fibrous
materials, and storage zones 24 and core 28 are generally fibrous
layers that include absorbent material. As described above,
composite 22 can be formed by attaching bands of fibrous materials
and absorbent materials to a storage core to form distribution
zones 26 and storage zones 24, respectively. Alternatively, storage
zones 24 can be formed integrally with storage core 28 and,
similarly, distribution zones 26 can also be integrally formed with
storage zones 24 and core 28. Although the distributions zones are
generally prepared from wet-laid composites, the absorbent material
containing storage zones can be made from air-laid composites. In
one preferred embodiment, the distribution zones are formed from
wet-laid fibrous composite that include fibrous materials suitable
for liquid acquisition and distribution, and the storage zones and
core are formed from air-laid fibrous composites that include
absorbent material suitable for liquid storage. In another
preferred embodiment, the storage zones and core are formed from a
wet-laid composite. Generally, an absorbent composite having such a
structure has enhanced liquid acquisition compared to conventional
storage cores and those having relatively poor fluid communication
between composite components.
[0104] Multilayered absorbent constructs can also include the
fluted absorbent composite. One such construct is illustrated in
FIG. 11B. Referring to FIG. 11B, absorbent construct 23 includes
fibrous composite 22 and an acquisition layer 32 (e.g., formed
primarily from fibrous materials). As noted above composite 22
includes distribution zones 26, storage zones 24, and storage core
28.
[0105] Fluted composites having a unitary structure are generally
preferred because of the intimate fluid communication between
components (i.e., regions of the composite) and for reasons
relating to manufacturability. Accordingly, in a preferred
embodiment, the fluted absorbent composite is an integrally formed
unitary structure.
[0106] The fluted absorbent composite can be formed by wet-laid and
foam-forming processes. These general methodologies are known to
those of skill in the pulp processing art.
[0107] Preferably, the fluted absorbent composite is prepared from
a wet-laid or a foam-forming process. A representative example of a
wet-laid process is described in U.S. Pat. No. 5,300,192, issued
Apr. 5, 1994, entitled "Wet-Laid Fiber Sheet Manufacturing with
Reactivatable Binders for Binding Particles to Fibers", expressly
incorporated herein by reference. Wet-laid processes are also
described in standard texts, such as Casey, Pulp and Paper, 2nd
edition, 1960, volume II, Chapter VIII--Sheet Formation.
Representative foam processes useful in forming the composite
include those known in the art and include those described in U.S.
Pat. Nos. 3,716,449; 3,839,142; 3,871,952; 3,937,273; 3,938,782;
3,947,315; 4,166,090; 4,257,754; and 5,215,627, assigned to Wiggins
Teape and related to the formation of fibrous materials from foamed
aqueous fiber suspensions, and "The Use of an Aqueous Foam as a
Fiber-Suspending Medium in Quality Papermaking," Foams, Proceedings
of a Symposium organized by the Society of Chemical Industry,
Colloid and Surface Chemistry Group, R. J. Akers, Ed., Academic
Press, 1976, which describes the Radfoam process, all expressly
incorporated herein by reference.
[0108] In the method of the present invention, absorbent material
is incorporated into the composite during the formation of the
composite. Generally, the method for forming the fluted absorbent
composite includes depositing absorbent material into a fibrous
web, and then drying the web, as necessary, to provide the
composite.
[0109] In a wet-laid method, absorbent material is preferably
applied into a fibrous slurry that has been deposited onto a
foraminous support (i.e., a forming wire). In the method, absorbent
material is injected into an at least partially dewatered fibrous
web formed by depositing a fibrous slurry onto a forming wire. The
fibrous slurry preferably includes fibers and wet strength agent in
a dispersion medium (e.g., a primarily aqueous medium such as
water). The absorbent material can be introduced into the fibrous
web as a dry particle or, preferably, as a liquid suspension in an
aqueous medium, preferably chilled (e.g., 34-40.degree. F.) water.
The absorbent material is generally injected into the partially
dewatered fibrous web immediately after the slurry's deposition
onto the forming wire. The absorbent material is preferably
deposited into the partially dewatered fibrous web (i.e., before
dewatering of the web is completed and during the formation of the
wet composite where the consistency of the web is increased
relative to the slurry and, in any event, prior to the drying
stage). After depositing the absorbent material into the partially
dewatered fibrous web, the web containing fibers and absorbent
material is subjected to further removal of at least a portion of
the dispersion medium and water, preferably by vacuum, to provide a
wet composite. The wet composite is then dried to provide the
absorbent composite.
[0110] It is desirable to inhibit liquid absorption by the
absorbent material during the web formation process. To inhibit
liquid absorption, absorbent material can be added to the at least
partially dewatered web as an aqueous suspension in chilled water
having a temperature in the range from about 0-5.degree. C.,
preferably from about 0-3.degree. C., and more preferably about
1.degree. C. Alternatively, the absorbent material can be cooled to
below O.degree. C., by placement or storage in a conventional
freezer, and then forming a suspension in water, preferably chilled
water, immediately prior to web formation. Limiting the period of
time that the absorbent material is in contact with liquid during
the forming process also has a positive effect on limiting
absorbent material liquid absorption. Preferably, the absorbent
material suspension is added to the at least partially dewatered
fibrous web within about 10 seconds, and more preferably within
about 5 seconds after preparing the suspension.
[0111] By limiting the liquid absorption by the absorbent material
during the formation process, web drying energy and/or time, and
the consequent associated expense can be greatly reduced. This
advantage can result in web formation processes that are more cost
effective and can represent significant savings for consumer
absorbent products such as diapers, feminine care products, and
adult incontinence products.
[0112] As described above, the absorbent composite includes bands
of absorbent material that are spaced laterally across the
composite's width and that extend longitudinally along the
composite's length in the machine direction of the composite. Such
a configuration of bands can be achieved by various methods
including injecting absorbent material into the fibrous web, which
has been at least partially dewatered, through openings or nozzles
spaced laterally across the width of the web. The nozzles are
connected to an absorbent material supply. The nozzles can be
positioned in various configurations and have orifices of varying
size to provide bands having various configurations including, for
example, various widths. The absorbent material is preferably
deposited as a suspension in chilled water. For aqueous
suspensions, the absorbent material is injected as a stream or jet
into the partially dewatered fibrous web. Injection of the stream
can result in significant mixing of the absorbent material and the
fibers of the web. The degree of mixing can be controlled by
several factors including stream velocity, web velocity, angle of
injection, and position of injection relative to the deposition of
fibrous slurry on the support, among others. Generally, the closer
the absorbent material injection to the point at which dewatering
of the fibrous web commences, the greater the mixing of absorbent
material and fibers. Also, the greater the mixing of absorbent
material and fibers, the lesser the resulting concentration
gradient of absorbent material in the composite.
[0113] Because the bands of absorbent material can be formed in the
composite by deposition or injection through individual nozzles,
the nature and characteristics of the flutes that are ultimately
formed in the composite can be controlled. For example, referring
to the composite illustrated in FIG. 3, the outermost flutes
contain absorbent material in relatively greater amounts compared
to the inner flutes. Such a composite can be formed by depositing
greater concentrations of absorbent material, depositing absorbent
material at a greater rate, or utilizing nozzles having larger
diameter orifices for the outermost positions. As noted above,
absorbent materials having different absorptive and retentive
capacities can be selectively deposited in the bands.
[0114] The deposition of individual bands also allows for the
formation of bands that can include materials in addition to
absorbent material. For example, additional fibers can also be
introduced into the deposited slurry through the use of these
nozzles. Consequently, flutes having additional fibers, including
fibers different from the deposited fibrous slurry, can be
incorporated into the composite. In one preferred embodiment, the
absorbent composite includes bands of absorbent material that
further include additional fibers such as, for example, hardwood
fibers and/or synthetic fibers. The use of different fibers can be
used to form flutes having, for example, higher relative basis
weights; greater bulk and softness; increased wicking; and
increased rewet performance. Thus, the composite's flutes can be
formed from completely different components compared to the base
composite (i.e., the initially deposited fibrous slurry).
[0115] The composite's absorbent material enriched regions can be
stabilized to enhance the structural integrity of the band or
flute. Flute integrity can be enhanced by depositing, in addition
to absorbent material, a wet strength agent (e.g., Kymene.RTM.)
and/or fibrous materials including, for example, microfibrillated
cellulose and fibrous superabsorbent materials. Fibrous
superabsorbent materials are described in U.S. Pat. No. 5,607,550,
expressly incorporated herein by reference.
[0116] The advantage of versatility allows for the design and
formation of various fluted absorbent composites. For example, the
base composite can be designed for strength and wicking, while the
deposited bands can be designed to maximize swelling and absorbent
capacity and to minimize rewet. More specifically, for an absorbent
composite that maximizes absorbent capacity, strength, and total
material utilization, the base composite can include a mixture of
southern pine fibers, eucalyptus fibers, crosslinked fibers and wet
strength agent, and the bands can include a mixture of absorbent
material and crosslinked cellulosic fibers or the fibers. For a
composite having increased capacity and enhanced wicking to the
absorbent material, the base composite can include a mixture of
southern pine fibers, eucalyptus fibers, and wet strength agent,
and the bands can include a mixture of absorbent material,
crosslinked cellulosic fibers, and microfibrillated cellulose.
Another preferred absorbent composite includes a base composite
composed of a refined mixture of crosslinked cellulosic fibers and
eucalyptus fibers, and includes bands composed of a mixture of
absorbent material and unrefined crosslinked fibers. To reduce
rewet, synthetic fibers (e.g., PET fibers) can be introduced into
the composite by depositing these fibers into the bands with
absorbent material or including some absorbent material in the
composite's distribution zones. The versatility of the method of
the present invention enables the creation of fluted absorbent
composites having a variety of compositions and absorbent
properties.
[0117] The method of the present invention also allows for the
deposition of foam dispersions as bands of materials into a fibrous
slurry. In one embodiment, the composite has a wet-laid fibrous
base and foam-formed bands. In another embodiment, the composite
includes a foam-formed fibrous base and wet-laid bands and, in
still another embodiment, the composite includes a foam-formed
fibrous base and bands. The ability to deposit a foam dispersion
enables the use of a wide range of fiber types, lengths, and
deniers in the composite's absorbent bands. By selection of fibers,
the bands (and ultimately the composite's flutes) can be, for
example, soft and have a degree of stretch. By forming a composite
having stretch capabilities, a shaped core can be formed from a
rectangular composite, thus eliminating the need to shape the core
by cutting, which results in material waste. Such a core also has
the greatest density of absorbent material in the crotch area, the
site of liquid insult.
[0118] As noted above, the absorbent composite can be formed from a
combination of fibers, and optionally wet strength agent, in a
dispersion medium, and absorbent material. In one embodiment, a
fibrous slurry is formed by directly combining fibers, and
optionally wet strength agent, in a dispersion medium followed by
the addition of absorbent material, preferably as a liquid
suspension of chilled water, to an at least partially dewatered
fibrous web on a foraminous support. In another embodiment,
absorbent material is added to the partially dewatered fibrous web
on a foraminous support in combination with fibers as a slurry
containing fibers and absorbent material. Such a slurry can be
prepared by first combining fibers with a dispersion medium to
which is then added absorbent material in a second step.
[0119] Once the fibrous slurry is deposited onto the foraminous
support, the dispersion medium begins to drain from the deposited
slurry to provide an at least partially dewatered fibrous web.
Removal of the dispersion medium (e.g., water) from the deposited
fibrous slurry (i.e., the partially dewatered web) continues
through, for example, the application of pressure, vacuum, and
combinations thereof, and results in the formation of a wet
composite.
[0120] The absorbent composite is ultimately produced by drying the
wet composite. Drying removes at least a portion of the remaining
dispersion medium and water and provides an absorbent composite
having the desired moisture content. Suitable composite drying
methods include, for example, the use of drying cans, air floats
and through air dryers. Other drying methods and apparatus known in
the pulp and paper industry may also be used. Drying temperatures,
pressures and times are typical for the equipment and methods used,
and are known to those of ordinary skill in the art in the pulp and
paper industry.
[0121] For foam methods, the fibrous slurry is an aqueous or foam
slurry that further includes a surfactant. Suitable surfactants
include ionic, nonionic, and amphoteric surfactants known in the
art.
[0122] The deposition of the components of the absorbent composite
onto the foraminous support ultimately results in the formation of
a wet composite that includes absorbent material that may have
absorbed water and, as a result, swollen in size. Water is
withdrawn from the wet composite containing the water-swollen
absorbent material distributed on the support and the wet composite
dried.
[0123] In the methods of the present invention, the absorbent
material preferably absorbs less than about 20 times its weight in
the dispersion medium, more preferably less than about 10 times,
and even more preferably less than about 5 times its weight in the
dispersion medium. Other preferable absorbent materials include
materials that absorb liquid only after prolonged contact with
liquid, or that absorb liquid only under certain conditions, and do
not absorb any significant amount of liquid during the forming
process.
[0124] Foam methods are advantageous for forming the absorbent for
several reasons. Generally, foam methods provide fibrous webs that
possess both relatively low density and relatively high tensile
strength. For webs composed of substantially the same components,
foam-formed webs generally have densities greater than air-laid
webs and lower than wet-laid webs. Similarly, the tensile strength
of foam-formed webs is substantially greater than for air-laid webs
and approach the strength of wet-laid webs. Also, the use of
foam-forming technology allows better control of the orientation
and uniform distribution of fibers and the incorporation of a wide
range of materials (e.g., long and synthetic fibers that cannot be
readily incorporated into wet-laid processes) into the
composite.
[0125] One machine for implementing the method of the present
invention is a conventional papermaking machine (wet-laid pulp
machine) that has been modified to include a plurality of nozzles
positioned downstream from the headbox outlet. Generally, the
nozzles are spaced laterally at intervals, for example, regular
intervals, across the width of the web. As described above, the
nozzles are connected to an absorbent material supply and, in a
preferred embodiment, a chilled aqueous suspension of absorbent
material is pumped to the nozzles to form an aqueous stream or jet
that impinges on and penetrates the surface of the deposited
fibrous slurry (i.e., partially dewatered web) as the wet composite
is formed. Because the wet composite is moving away from the
headbox as it is formed, bands of absorbent material are created in
the composite along the machine direction. Through the use of
vacuum, the machine drains water from the composite. The wet
composite is then dried to provide the final product. A
diagrammatic view of a representative machine and method for
forming the fluted absorbent composite is illustrated in FIG.
12A.
[0126] Referring to FIG. 12A, machine 100 includes foraminous
support 102 (i.e., a forming wire); vacuum heads 104 for dewatering
fibrous slurry 124 to provide wet composite 120; headbox 106 for
depositing the fibrous slurry onto support 102; nozzle manifold 108
for injecting absorbent material 122, preferably as an aqueous
suspension, into partially dewatered web 126; fibrous slurry supply
112; absorbent material supply 114; pumps 110 for delivering the
fibrous slurry and absorbent material from their respective
supplies to headbox 106 and manifold 108, respectively; and drying
means 116. Briefly, fibrous slurry 124 is deposited from headbox
106 onto support 102 and dewatered to provide partially dewatered
web 126. Absorbent material 122, preferably as an aqueous
suspension, is injected through nozzle manifold 108 into partially
dewatered web 126, preferably prior to extensive dewatering at
vacuum heads 104. As described above, manifold 108 includes a
plurality of nozzles positioned across the width of support 102
(i.e., the cross-machine direction) to deliver and inject absorbent
material in bands across the composite's width. Wet composite 120
is further dewatered along support 102 and then dried by drying
means 116 (e.g., heated cans, drying oven, through-air dryer). A
top plan view of the injection of absorbent material into the
fibrous slurry is illustrated in FIG. 12B.
[0127] The absorbent composite can be formed by devices and
processes that include a twin-wire configuration (i.e.,
twin-forming wires). A representative twin-wire machine for forming
composites is shown in FIG. 13. Referring to FIG. 13, machine 200
includes twin-forming wires 202 and 204 onto which the composite's
components are deposited. Basically, fibrous slurry 124 is
introduced into headbox 212 and deposited onto forming wires 202
and 204 at the headbox exit. Vacuum elements 206 and 208 dewater
the fibrous slurries deposited on wires 202 and 204, respectively,
to provide partially dewatered webs that exit the twin-wire portion
of the machine as partially dewatered web 126. Web 126 continues to
travel along wire 202 and continues to be dewatered by additional
vacuum elements 210 to provide wet composite 120 which is then
dried by drying means 216 to provide composite 10.
[0128] Absorbent material can be introduced into the fibrous web at
any one of several positions in the twin-wire process depending on
the desired product configuration. For example, absorbent material
can be introduced after the partially dewatered fibrous web has
exited the twin-wire portion of the machine and has traveled along
wire 202. Referring to FIG. 13, absorbent material 122 can be
injected into partially dewatered fibrous web 126 at position 1.
Alternatively, absorbent material can be introduced into the
partially dewatered fibrous web prior to the web exiting the
twin-wire portion of the machine (i.e., in the headbox). Referring
to FIG. 13, absorbent material 122 can be injected into the
partially dewatered web at positions 2, 3, or 4, or other positions
along wires 202 and 204 where the web has been at least partially
dewatered. Absorbent material can be introduced into the partially
dewatered web formed and traveling along wire 202 and/or 204. As
noted above, to form the composite having bands of absorbent
material extending in the composite's machine direction, absorbent
material is injected into the partially dewatered fibrous webs by
nozzles spaced laterally across the width of the web. The nozzles
are connected to an absorbent material supply. The nozzles can be
positioned in various positions (e.g., positions 1, 2, or 3 in FIG.
13) as described above. For example, referring to FIG. 13, nozzles
can be located at positions 2 to inject absorbent material into
partially dewatered webs on wires 202 and 204. Generally, the
extent of mixing of fibers with absorbent material decreases as the
fibrous web is dewatered (e.g., less mixing at position 1 than at
position 2, and less mixing at position 2 than at position 3).
[0129] Depending on the position of absorbent material
introduction, the twin-wire method for forming the composite can
provide a composite having a fibrous stratum. Representative
composites having fibrous strata formed by the twin-wire method of
the present invention are shown in FIGS. 14A-H. Referring to FIG.
14A, representative composites 10 include regions 12 enriched with
absorbent material, distribution zones 14 substantially free of
absorbent material, and fibrous strata 11 coextensive with the
outward surfaces of composite 10.
[0130] Referring to FIG. 14A, composite 10 can be formed by a
method that introduces absorbent material into a single partially
dewatered web (i.e., a web traveling on wire 202 or 204). FIGS. 14B
and 14C depict similarly formed composites having absorbent
material extending into the composite to relatively greater depths
(i.e., z-direction penetration). Referring to FIG. 14D, composite
10 includes absorbent material introduced into the center fibrous.
Such a composite can be formed by adjusting the depth of absorbent
material penetration by, for example, nozzle distance from the
forming wire or absorbent material injection angle.
[0131] Alternatively, the composite can be formed by a twin-wire
method that introduces absorbent material into both partially
dewatered webs (i.e., webs traveling on wires 202 and 204). Such a
method includes a two sets of nozzles, a first nozzle set for
injection into one partially dewatered web, and a second nozzle set
for injection into the other partially dewatered web. Referring to
FIG. 14E, composite 10 includes regions enriched with absorbent
material that extend substantially throughout the composite's depth
(i.e., z-direction). Such a composite configuration can be formed
from a pair of nozzle sets that are either positioned or timed to
provide absorbent material bands that align in the z-direction.
Offsetting one set of nozzles from the other, or providing
nonsynchronous absorbent material pulses from a pair of aligned
nozzle sets, provides composites having offset bands of absorbent
material. Such a composite configuration is illustrated in FIG.
14F. FIGS. 14G and 14H illustrate composites formed by methods
similar to those which provide the composites shown in FIGS. 14E
and 14F, respectively, but in contrast to those composites, the
composites of FIGS. 14G and 14H are formed by the introduction of
absorbent material to a penetration depth less than that of the
composites in FIGS. 14E and 14F.
[0132] As shown in FIG. 14, the composite can include integrated
phases having fibrous strata coextensive with the outward surfaces
of the composite. These fibrous composites can be formed from
multilayered inclined formers or twin-wire formers with sectioned
headboxes. These methods can provide stratified or phased
composites having strata or phases having specifically designed
properties and containing components to attain composites having
desired properties. The composite's regions of enriched absorbent
material (i.e., the composite's absorbent bands) can be located
throughout the z-direction by adjusting the basis weights of the
upper and lower strata.
[0133] Basically, the position of the absorbent material band in
the composite's z-direction effectively defines the fibrous stratum
covering the band. For a formation method that includes a single
fiber furnish, the band position can be adjusted by positioning the
absorbent material injection system (e.g., nozzle set) in relation
to the forming wire. For methods that include multiple furnishes,
the upper and lower strata can be composed of the same or different
components and introduced into a sectioned headbox.
[0134] Referring to FIGS. 13 and 14A, composite 10 having strata 11
can be formed by machine 200. For composites in which strata 11
comprise the same components, a single fiber furnish 124 is
introduced into headbox 212. For forming composites having strata
11 comprising different components, headbox 212 includes one or
more baffles 214 for the introduction of fiber furnishes (e.g.,
124a, 124b, and 124c) having different compositions. In such a
method, the upper and lower strata can be formed to include
different components and have different basis weights and
properties.
[0135] Preferably, the fluted composite is formed by a foam-forming
method using the components described above. In the foam-forming
method, fibrous webs having multiple strata and including bands of
absorbent material can be formed from multiple fibrous slurries. In
a preferred embodiment, the foam-forming method is practiced on a
twin-wire former.
[0136] The method can provide a variety of multiple strata
composites including, for example, composites having three strata.
A representative composite having three strata includes a first
stratum formed from fibers (e.g., synthetic fibers, cellulosic,
and/or binder fibers); an intermediate stratum formed from fibers
and/or other absorbent material such as superabsorbent material;
and a third stratum formed from fibers. The method of the invention
is versatile in that such a composite can have relatively distinct
and discrete strata or, alternatively, have gradual transition
zones from stratum-to-stratum.
[0137] A representative method for forming a fibrous web having an
intermediate stratum generally includes the following steps:
[0138] (a) forming a first foam fibrous slurry comprising fibers
and a surfactant in an aqueous dispersion medium;
[0139] (b) forming a second foam fibrous slurry comprising fibers
and a surfactant in an aqueous dispersion medium;
[0140] (c) moving a first foraminous element (e.g., a forming wire)
in a first path;
[0141] (d) moving a second foraminous element in a second path;
[0142] (e) passing the first foam slurry into contact with the
first foraminous element moving in a first path;
[0143] (f) passing the second foam slurry into contact with the
second foraminous element moving in the second path;
[0144] (g) passing a third material between the first and second
foam slurries such that the third material does not contact either
of the first or second foraminous elements; and
[0145] (h) forming a fibrous web from the first and second foam
slurries and third material by withdrawing foam and liquid from the
slurries through the first and second foraminous elements.
[0146] As noted above, the method is suitably carried out on a
twin-wire former, preferably a vertical former, and more
preferably, a vertical downflow twin-wire former. In the vertical
former, the paths for the foraminous elements are substantially
vertical.
[0147] A representative vertical downflow twin-wire former useful
in practicing the method of the invention is illustrated in FIG.
15. Referring to FIG. 15, the former includes a vertical headbox
assembly having a former with a closed first end (top), closed
first and second sides and an interior volume. A second end
(bottom) of the former is defined by moving first and second
foraminous elements, 202 and 204, and forming nip 213. The interior
volume defined by the former's closed first end, closed first and
second sides, and first and second foraminous elements includes an
interior structure 230 extending from the former first end and
toward the second end. The interior structure defines a first
volume 232 on one side thereof and a second volume 234 on the other
side thereof. The former further includes supply 242 and means 243
for introducing a first fiber/foam slurry into the first volume,
supply 244 and means 245 for introducing a second fiber/foam slurry
into the second volume, and supply 246 and means 247 for
introducing a third material into the interior structure. Means for
withdrawing foam (e.g., suction boxes 206 and 208) from the first
and second slurries through the foraminous elements to form a web
are also included in the headbox assembly.
[0148] In the method, the twin-wire former includes a means for
introducing at least a third material through the interior
structure in such a way that the third material forms bands or
stripes in the resulting web. Preferably, the introducing means
include at least a first plurality of conduits having a first
effective length. A second plurality of conduits having a second
effective length different from the first length may also be used.
More than two sets of conduits can also be used.
[0149] Another representative vertical downflow twin-wire former
useful in practicing the method of the invention is illustrated in
FIG. 16. Referring to FIG. 16, the former includes a vertical
headbox assembly having an interior volume defined by the former's
closed first end, closed first and second sides, and first and
second foraminous elements, 202 and 204, and includes an interior
structure 230 extending from the former first end and toward the
second end. In this embodiment, interior structure 230 includes
plurality of conduits 235 and 236, and optional divider walls
214.
[0150] The interior structure defines a first volume 232 on one
side thereof and a second volume 234 on the other side thereof. The
former further includes supply 242 and means 243 for introducing a
first fiber/foam slurry into the first volume, supply 244 and means
245 for introducing a second fiber/foam slurry into the second
volume, supply 246 and means 247 for introducing a third material
into plurality of conduits 236, supply 248 and means 249 for
introducing a third material into plurality of conduits 235, and
supply 250 and means 251 for introducing another material, such as
a foam slurry, within the volume defined by walls 214.
[0151] Plurality of conduits 235 can have an effective length
different from plurality of conduits 236. The third material can be
introduced through conduits 235 and 236, or, alternatively, a third
material can be introduced through conduits 235 and a fourth
material can be introduced through conduits 236. Preferably, the
ends of conduits 235 and 236 terminate at a position beyond where
the suction boxes begin withdrawing foam from the slurries in
contact with the foraminous elements (i.e., beyond the point where
web formation begins). Plurality of conduits 235 and/or 236 are
suitable for introducing stripes or bands of third material in
fibrous webs formed in accordance with the present invention.
Plurality of conduits 235 and 236 can be moved in a first dimension
toward and away from nip 213, and also in a second dimension
substantially perpendicular to the first, closer to one forming
wire or the other. Representative plurality of conduits 235 and 236
are illustrated in FIG. 17.
[0152] Generally, the former's interior structure (i.e., structure
230 in FIGS. 15 and 16) is positioned with respect to the
foraminous elements such that material introduced through the
interior structure will not directly contact the first and second
foraminous elements. Accordingly, material is introduced through
the interior structure between the first and second slurries after
the slurries have contacted the foraminous elements and withdrawal
of foam and liquid from those slurries has commenced. Such a
configuration is particularly advantageous for introducing
superabsorbent materials and for forming stratified structures in
which the third material is a foam/fiber slurry. Depending upon the
nature of the composite to be formed, the first and second
fiber/foam slurries may be the same, or different, from each other
and from the third material.
[0153] In a preferred embodiment, the method includes introducing
the third material at a plurality of different points to provide a
composite having bands or stripes of third material within the
product. The positions of at least some of the plurality of
different points for introducing the third material into the
headbox can be adjusted when it is desired to adjust the
introduction point in a first dimension toward and away from the
headbox exit (i.e., nip 213 in FIGS. 15 and 16); and to adjust at
least some of the plurality of points in a second dimension
substantially perpendicular to the first dimension, closer to one
forming wire or the other.
[0154] The method can also include utilizing a plurality of
distinct conduits, the conduits being of at least two different
lengths, for introducing the third material into the headbox. The
method can also be utilized in headboxes having dividing walls that
extend part of the length of the conduits toward the headbox exit.
Such headboxes are illustrated in FIGS. 13 and 16.
[0155] The means for introducing first and second foam slurries
into the first and second volumes can include any conventional type
of conduit, nozzle, orifice, header, or the like. Typically, these
means include a plurality of conduits are provided disposed on the
first end of the former and facing the second end.
[0156] The means for withdrawing foam from the first and second
slurries through the foraminous elements to form a web on the
foraminous elements are also included in the headbox assembly. The
means for withdrawing foam can include any conventional means for
that purpose, such as suction rollers, pressing rollers, or other
conventional structures. In a preferred embodiment, first and
second suction box assemblies are provided and mounted on the
opposite sides of the interior structure from the foraminous
elements (see boxes 206 and 208 in FIGS. 13, 15, and 16).
[0157] The fluted absorbent composite can be incorporated as an
absorbent core or storage layer in an absorbent article including,
for example, a diaper or feminine care product. The absorbent
composite can be used alone, or as illustrated in FIGS. 18 and 19,
can be used in combination with one or more other layers. FIG. 18
illustrates absorbent construct 30 where composite 10 is employed
as a storage layer in combination with an upper acquisition layer
32. As illustrated in FIG. 19 illustrating construct 40, a third
layer 42 (e.g., distribution layer) can also be employed, if
desired, with composite 10 and acquisition layer 32.
[0158] The fluted absorbent composite can also be incorporated as a
liquid management layer in an absorbent article such as a diaper.
In such an article, the composite can be used in combination with a
storage core or layer. In the combination, the liquid management
layer can have a surface area that is smaller than, the same size
as, or slightly greater than the surface area of the storage
layer's surface facing the fluted composite. Representative
absorbent constructs that incorporate the fluted composite in
combination with a storage layer are shown in FIGS. 20 and 21.
Referring to FIG. 20, absorbent construct 90 includes fluted
composite 10 and storage layer 60. Storage layer 60 is preferably a
fibrous layer that includes absorbent material. The storage layer
can be formed by any method including air-laid, wet-laid, and
foam-forming methods.
[0159] For constructs that include a storage layer and the fluted
composite as an liquid management layer, the absorbent material in
the fluted composite can be the same, similar, or different from
the absorbent material in the storage layer.
[0160] In certain embodiments, the fluted absorbent composite is
asymmetric in that the composite's facing and backing surfaces are
not identical. In these embodiments, the composite has a first
surface into which absorbent material has been injected and an
opposing surface (i.e., machine side) composed substantially of
fibers and which constitutes a surface of the composite's fibrous
base. For absorbent constructs that contain, in addition to the
fluted composite, a storage layer, the composite can be oriented in
two ways. In one embodiment, the fluted composite is oriented with
its fluted surface directed toward the wearer. A representative
construct 90 having a storage layer and fluted composite having its
fluted surface directed toward the wearer is shown in FIG. 20.
Alternatively, as shown in FIG. 21, representative construct 92
includes composite 10 having the composite's flutes directed toward
storage layer 60. The surface of the storage layer may or may not
conform to the surface of the fluted composite.
[0161] It is anticipated that the rewet of constructs that include
the fluted composite can also be reduced by incorporating synthetic
fibers (e.g., hydrophobic fibers such as polyester fibers) into the
composite's fibrous base. When used in combination with a storage
layer, the fluted composite having a fibrous base that includes
synthetic (hydrophobic) fibers is preferably incorporated into the
construct in the inverted configuration.
[0162] To further enhance rewet performance, an acquisition layer
can be combined with the fluted composite and storage layer. FIGS.
22 and 23 illustrate absorbent constructs 94 and 96, respectively,
each having acquisition layer 32 overlaying composite 10 and
storage layer 60.
[0163] Constructs 90, 92, 94, and 96 can further include
intermediate layer 70 to provide constructs 100, 102, 104, and 106,
shown in FIGS. 24A through 24D, respectively. Intermediate layer 70
can be, for example, a tissue layer, a nonwoven layer, an air-laid
or wet-laid pad, or a fluted composite.
[0164] Constructs 90, 92, 94, 96, 100, 102, 104, and 106 can be
incorporated into absorbent articles. Generally, absorbent articles
110, 112, 114, 116, 120, 122, 124, and 126, shown in FIGS. 25A
through 25H, respectively, include a liquid pervious facing sheet
52 and a liquid impervious backing sheet 54 and constructs 90, 92,
94, 96, 100, 102, 104, and 106, respectively. In such absorbent
articles, the facing sheet is joined to the backing sheet.
[0165] A variety of suitable constructs can be produced from the
absorbent composite. The most common include absorptive consumer
products, such as diapers, feminine hygiene products such as
feminine napkins, and adult incontinence products. For example,
referring to FIGS. 26A and 26B, absorbent article 50 includes
absorbent composite 10 and has a liquid pervious facing sheet 52
and a liquid impervious backing sheet 54. As shown in FIG. 26B,
facing sheet 52 is joined to backing sheet 54. Referring to FIG.
27, absorbent article 60 includes absorbent composite 10 and an
overlying acquisition layer 32. A liquid pervious facing sheet 52
overlies acquisition layer 32, and a liquid impervious backing
sheet 54 underlies absorbent composite 10. These absorbent
composites will provide advantageous liquid absorption performance
for use in, for example, diapers. FIG. 28 illustrates absorbent
construct 70, which further includes distribution layer 42
interposed between acquisition layer 32 and composite 10. As
described above, the fluted structure of the absorbent composite
aids in fluid transport and absorption in multiple wettings.
[0166] One of ordinary skill will be able to make a variety of
different constructs using the concepts taught herein. For example,
a typical construction of an adult incontinence absorbent structure
is shown in FIG. 29. The article 80 includes facing sheet 52,
acquisition layer 32, absorbent composite 10, and backing sheet 54.
Facing sheet 22 is pervious to liquid while backing sheet 24 is
impervious to liquid. In this construct, a liquid pervious tissue
44 composed of a polar, fibrous material is positioned between
absorbent composite 10 and acquisition layer 32.
[0167] The present invention provides a fibrous absorbent composite
containing absorbent material and methods for its formation. The
absorbent composite is a fibrous structure that includes absorbent
material dispersed in bands along the composite's length. Between
the bands of absorbent material, the absorbent composite has
continuously open distribution zones that preclude gel blocking in
the composite. After initial liquid insult, the composite develops
flutes that open the fibrous structure and increase the liquid
acquisition rate for subsequent liquid insults. The combination of
flutes and distribution zones allows for total utilization of the
absorbent composite as a storage core when incorporated into an
absorbent article such as a diaper. The fluted absorbent composite
can be advantageously used as a liquid management layer or a
storage core in absorbent articles such as diapers.
[0168] The following examples are provided for the purpose of
illustrating, and not limitation, the invention.
EXAMPLES
[0169] Example 1
Acquisition Times for a Representative Fluted Absorbent
Composite
[0170] In this example, the acquisition time for a representative
fluted absorbent composite (Composite A) is compared to a
commercially available diaper (Diaper A, Kimberly-Clark). Also
included in the comparison is an absorbent composite (Composite B)
having a composition similar to the composite and composed of
fibers (50:50 crosslinked fibers and southern pine pulp fibers),
wet strength agent, and absorbent material distributed relatively
uniformly throughout the composite. The formation of Composite B is
described in provisional U.S. patent application Serial No.
60/046,395, filed May 13, 1997, and international application
Serial No. PCT/US98/09682, filed May 12, 1998, assigned to
Weyerhaeuser Company, each expressly incorporated herein by
reference.
[0171] The tests were conducted on commercially available diapers
(Kimberly-Clark) from which the core and surge management layer
were removed and used as surrounds for the fluted absorbent
composite and for Composite B. The test diapers were prepared by
inserting the fluted absorbent composite or Composite B into the
diapers.
[0172] The aqueous solution used in the tests is a synthetic urine
available from National Scientific under the trade name RICCA. The
synthetic urine is a saline solution containing 135 meq./L sodium,
8.6 meq./L calcium, 7.7 meq./L magnesium, 1.94% urea by weight
(based on total weight), plus other ingredients.
[0173] A sample of the absorbent structure is prepared for the test
by determining the center of the structure's core, measuring 1 inch
to the front for liquid application location, and marking the
location with an "X." Once the sample is prepared, the test is
conducted by first placing the sample on a plastic base (43/4
inch.times.191/4 inch) and then placing a funnel acquisition plate
(4 inch.times.4 inch plastic plate) on top of the sample with the
plate's hole positioned over the "X". A donut weight (1400 g) is
then placed on top of the funnel acquisition plate to which is then
attached a funnel (4 inch diameter). Liquid acquisition is then
determined by pouring 100 mL synthetic urine into the funnel and
measuring the time from when liquid is first introduced into the
funnel to the time that liquid disappears from the bottom of the
funnel into the sample. The measured time is the acquisition time
for the first liquid insult. After waiting 1 minute, a second 100
mL portion is added to the funnel and the acquisition time for the
second insult is measured. After waiting an additional 1 minute,
the acquisition is repeated for a third time to provide an
acquisition time for the third insult. The acquisition times
reported in seconds for each of the three successive 100 mL liquid
insults for Diaper A, Composite B, and Composite A are summarized
in Table 1.
1TABLE 1 Acquisition Time COmparison Acquisition Time (sec) Insult
Diaper A Composite B Composite A 1 45 10 10 2 60 11 6 3 73 10 4
[0174] As shown in Table 1, liquid is more rapidly acquired by the
absorbent composite than for the commercially available diaper
containing an air-laid storage core. The results show that the
air-laid core does not acquire liquid nearly as rapidly as the
wet-laid composite. The commercial diaper also exhibited
characteristic diminution of acquisition rate on successive liquid
insults. In contrast, the composite shows a decrease in acquisition
time as the composite continued to absorb liquid on successive
insult. Significantly, the absorbent composite exhibits an
acquisition time for the third insult that is substantially less
(about 10-fold) than that of the commercially available diaper for
initial insult. The results reflect the greater wicking ability and
capillary network for the wet-laid composites compared to
conventional air-laid storage cores in general, and the enhanced
performance of the fluted absorbent composite in particular.
[0175] For the reasons noted above, the observed acquisition time
for wet-laid Composite B is also less than for the air-laid core.
The acquisition times for Composite B on successive insults remain
substantially constant. In contrast, Composite A exhibits a greatly
reduced acquisition times on the second and third insults. The
increased rate is attributable to the banded nature of the
absorbent material in the composite. Thus, the results show that
even among wet-laid composites containing absorbent material, the
configuration of absorbent material within the composite is a
significant factor in liquid acquisition. Whereas homogeneously
distributed absorbent material in a wet-laid composite provides
advantages over similarly composed air-laid composites, wet-laid
composites having bands of absorbent material provide further
significant advantages including enhanced and persistent liquid
acquisition.
Example 2
Acquisition Rate and Rewet for Representative Fluted Absorbent
Composites
[0176] In this example, the acquisition time and rewet of
representative fluted absorbent composites (designated Composites
A1-A4) are compared to a commercially available diaper (Diaper A,
Kimberly-Clark). Composites A1-A4 differ by the method by which the
composites were dried. Also included in the comparison are a series
of absorbent composites (Composites B1-B4) formed as described
above for Composite B in Example 1 and differing by the method by
which they were dried.
[0177] Certain properties of the tested composites including the
amount of superabsorbent polymeric material (weight percent SAP) in
the composite and basis weight for each of the composites are
summarized in Table 2.
[0178] The tests were conducted on commercially available diapers
(Kimberly-Clark) from which the cores were removed and used as
surrounds for the fluted absorbent composites and for Composites
B1-B4. The test diapers were prepared by inserting the tested
composites into the diapers.
[0179] The acquisition time and rewet are determined in accordance
with the multiple-dose rewet test described below.
[0180] Briefly, the multiple-dose rewet test measures the amount of
synthetic urine released from an absorbent structure after each of
three liquid applications, and the time required for each of the
three liquid doses to wick into the product.
[0181] The aqueous solution used in the tests is a synthetic urine
available from National Scientific under the trade name RICCA, and
as described above in Example 1.
[0182] A preweighed sample of the absorbent structure is prepared
for the test by determining the center of the structure's core,
measuring 1 inch to the front for liquid application location, and
marking the location with an "X." A liquid application funnel
(minimum 100 mL capacity, 5-7 mL/s flow rate) is placed 4 inches
above surface of sample at the "X." Once the sample is prepared,
the test is conducted as follows. Flatten the sample, nonwoven side
up, onto a table top under the liquid application funnel. Fill the
funnel with a dose (100 mL) of synthetic urine. Place a dosing ring
({fraction (5/32)} inch stainless steel, 2 inch ID.times.3 inch
height) onto the "X" marked on the samples. Apply a first dose of
synthetic urine within the dosing ring. Using a stopwatch, record
the liquid acquisition time in seconds from the time the funnel
valve is opened until the liquid wicks into the product from the
bottom of the dosing ring. Wait twenty minutes. During the twenty
minute wait period after the first dose is applied, weigh a stack
of filter papers (19-22 g, Whatman #3, 11.0 cm or equivalent, that
have been exposed to room humidity for minimum of 2 hours before
testing). The stack of preweighed filter papers are placed on the
center of the wetted area. A cylindrical weight (8.9 cm diameter,
9.8 lb.) is placed on top of these filter papers. After two minutes
the weight is removed, the filter papers are weighed and the weight
change recorded. The procedure is repeated two more times. A second
dose of synthetic urine is added to the diaper, and the acquisition
time is determined, filter papers are placed on the sample for two
minutes, and the weight change determined. For the second dose, the
weight of the dry filter papers is 29-32 g, and for the third dose,
the weight of the filter papers is 39-42 g. The dry papers from the
prior dosage are supplemented with additional dry filter
papers.
[0183] Liquid acquisition time is reported as the length of time
(seconds) necessary for the liquid to be absorbed into the product
for each of the three doses. The results are summarized in Table
2.
[0184] Rewet is reported as the amount of liquid (grams) absorbed
back into the filter papers after each liquid dose (i.e.,
difference between the weight of wet filter papers and the weight
of dry filter papers). The results are also summarized in Table
2.
2TABLE 2 Acquisition Time and Rewet Comparison Acquisition Time
Rewet SAP Basis Weight (Sec) (g) Composite % (w/w) (gsm) Insult 1
Insult 2 Insult 3 Insult 1 Insult 2 Insult 3 A1 45.0 668 20 16 18
0.1 0.2 0.5 A2 39.3 665 19 16 19 0.1 0.2 0.5 A3 37.0 715 26 16 17
0.1 0.2 0.5 A4 46.0 710 18 16 24 0.1 0.1 0.3 B1 49.4 568 16 19 26
0.1 0.4 2.4 B2 38.3 648 17 19 22 0.1 0.7 2.5 B3 35.9 687 29 26 27
0.2 0.2 0.7 B4 38.8 672 17 18 21 0.1 0.3 0.9 Commercial 40.0 625 34
35 39 0.1 4.0 12.6 air-laid core
[0185] As indicated in Table 2, the acquisition times for
representative composites (Composites A1-A4) were significantly
less than for the commercially available core.
[0186] The rewet of the representative composites (Composites
A1-A4) is significantly less than for the other cores. While most
of the composites exhibited relatively low rewet initially, after
the third insult the commercially available core showed substantial
rewet. In contrast, Composites A continued to exhibit low
rewet.
Example 3
Horizontal and Vertical Wicking for a Representative Fluted
Absorbent Composite
[0187] In this example, the wicking characteristics of a
representative fluted absorbent composite (Composite A) are
compared to a commercially available diaper storage core (Diaper B,
Procter & Gamble) and a wet-laid storage core having absorbent
material distributed uniformly throughout the composite (Composite
B).
[0188] The horizontal wicking test measures the time required for
liquid to horizontally wick preselected distances. The test is
performed by placing a sample composite on a horizontal surface
with one end in contact with a liquid bath and measuring the time
required for liquid to wick preselected distances. Briefly, a
sample composite strip (40 cm.times.10 cm) is cut from a pulp sheet
or other source. If the sheet has a machine direction, the cut is
made such that the 40 cm length of the strip is parallel to the
machine direction. For absorbent composites, the strip is centered
such that four bands of absorbent material are within the strip's
width. Starting at one end of the 10 cm width of the strip mark a
first line at 4.5 cm from the strip edge and then mark consecutive
lines at 5 cm intervals along the entire length of the strip (i.e.,
0 cm, 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, and 35 cm). Prepare
a horizontal wicking apparatus having a center trough with level
horizontal wings extending away from opposing sides of the trough.
The nonsupported edge of each wing being flush with the inside edge
of the trough. On each wings' end place a plastic extension to
support each wing in a level and horizontal position. The trough is
then filled with synthetic urine. The sample composite strip is
then gently bent at the 4.5 cm mark to form an approximately
45.degree. angle in the strip. The strip is then placed on the wing
such that the strip lays horizontally and the bent end of the strip
extend into and contacts the liquid in the trough. Begin timing
liquid wicking when the liquid reaches the first line marked on the
composite 5 cm from the 4.5 cm bend. The wicking time is then
recorded at 5 cm intervals when 50 percent of the liquid front
reaches the marked interval (e.g., 5 cm, 10 cm). The liquid level
in the trough is maintain at a relatively constant level throughout
the test by replenishing with additional synthetic urine. The
horizontal wicking results are summarized in Table 3.
3TABLE 3 Horizontal Wicking Comparison Wicking Time Distance (sec)
(cm) Diamper B Composite B Composite A 5 48 15 11 10 150 52 27 15
290 134 67 20 458 285 142 25 783 540 250 30 1703 1117 350 35 --
1425 480
[0189] The results tabulated above indicate that horizontal wicking
is enhanced for the wet-laid composites compared to a conventional
air-laid core. While the wicking time for Composite B is about 50
percent of that for the conventional diaper core, the wicking time
for Composite A is about 50 percent of that for Composite B. Thus,
the horizontal wicking for Composite A is about four times that of
a commercially available storage core. Such a result indicates the
effectiveness of the distribution zones of the composite created by
the banded nature of the absorbent material.
[0190] The vertical wicking test measures the time required for
liquid to vertically wick preselected distances. The test is
performed by vertically suspending a sample composite with one end
of the composite in contact with a liquid bath and measuring the
time required for liquid to wick preselected distances. Prior to
the test, sample composites (10 cm.times.22 cm) are cut and marked
with consecutive lines 1 cm, 11 cm, 16 cm, and 21 cm from one of
the strip's edges. Preferably, samples are preconditioned for 12
hours at 50 percent relative humidity and 23.degree. C. and then
stored in sample bags until testing. The sample composite is
oriented lengthwise vertically and clamped from its top edge at the
1 cm mark and allowing its bottom edge to contact a bath containing
synthetic urine. Timing commences once the strip is contacted with
the liquid. The time required for 50 percent of the wicking front
to reach 5 cm, 10 cm, 15 cm, and 20 cm is then recorded. The
vertical wicking results are summarized in Table 4.
4TABLE 4 Vertical Wicking Comparison Wicking Time Distance (sec)
(cm) Diamper B Composite B Composite A 5 20 6 11 10 Fell Apart 54
51 15 -- 513 257 20 -- 3780 1110
[0191] As for the horizontal wicking results, wet-laid Composites A
and B have significantly greater vertical wicking. Moreover, as
between Composites A and B, the composite can distribute liquid
remote from insult more rapidly than even for the wet-laid
composite having absorbent material distributed uniformly
throughout the composite. The results also show that the wet-laid
composites have significantly greater wet tensile strength compared
to the conventional air-laid composite.
Example 4
Liquid Distribution for a Representative Fluted Absorbent
Composite
[0192] In this example, the distribution of liquid in a fluted
absorbent composite (Composite A) is compared to that of two
commercially available diapers (Diapers A and B above). The test
measures the capacity of a diaper core to distribute acquired
liquid. Perfect distribution would have 0% deviation from average.
Ideal liquid distribution would result in equal distribution of the
applied liquid in each of the four distribution zones (i.e., about
25% liquid in each zone).
[0193] Liquid distribution is determined by weighing different
zones of a sample that has been subjected to the multiple-dose
rewet test described above in Example 2. Basically, after the last
rewet, the wings of the diaper are removed and then cut into four
equal length distribution zones. Each zone is then weighed to
determine the weight of liquid contained in each zone.
[0194] The liquid distribution results for representative fluted
absorbent composites approach ideality. The results indicate that
while the representative commercial storage cores accumulate liquid
near the site of insult, liquid is efficiently and effectively
distributed throughout the fluted absorbent storage core.
[0195] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *