U.S. patent application number 10/324167 was filed with the patent office on 2003-07-31 for absorbent composite having fibrous bands.
This patent application is currently assigned to Weyerhaeuser Company. Invention is credited to Dopps, Melissa I., Edmark, Richard A., Graef, Peter A., Marsh, David G..
Application Number | 20030144642 10/324167 |
Document ID | / |
Family ID | 27616217 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030144642 |
Kind Code |
A1 |
Dopps, Melissa I. ; et
al. |
July 31, 2003 |
Absorbent composite having fibrous bands
Abstract
An absorbent composite having fibrous bands is described. The
composite includes one or more fibrous bands in a fibrous base. The
base includes a fibrous matrix and absorbent material. The fibrous
bands are substantially free of absorbent material. Absorbent
articles that include the composite and methods for forming the
composite are also disclosed.
Inventors: |
Dopps, Melissa I.; (Seattle,
WA) ; Edmark, Richard A.; (Seattle, WA) ;
Marsh, David G.; (Federal Way, WA) ; Graef, Peter
A.; (Puyallup, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Company
|
Family ID: |
27616217 |
Appl. No.: |
10/324167 |
Filed: |
December 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10324167 |
Dec 19, 2002 |
|
|
|
09666213 |
Sep 21, 2000 |
|
|
|
60155464 |
Sep 21, 1999 |
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Current U.S.
Class: |
604/368 ;
604/367; 604/378 |
Current CPC
Class: |
A61F 13/535 20130101;
Y10T 442/699 20150401; A61F 13/5376 20130101; Y10T 442/692
20150401; B32B 5/22 20130101; Y10T 442/643 20150401; A61F 13/53747
20130101; A61F 2013/530985 20130101; A61F 13/5323 20130101 |
Class at
Publication: |
604/368 ;
604/378; 604/367 |
International
Class: |
A61F 013/15; A61F
013/20 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An absorbent composite, comprising one or more fibrous bands in
a fibrous base, wherein the base comprises a fibrous matrix and
absorbent material, and wherein the bands are substantially free of
absorbent material.
2. The composite of claim 1 wherein the bands are continuous along
the composite's length in the machine direction.
3. The composite of claim 1 wherein the bands are substantially
parallel.
4. The composite of claim 1 wherein the bands are discontinuous
along the composite's length in the machine direction.
5. The composite of claim 1 wherein the fibrous matrix comprises
fibers selected from the group consisting of resilient fibers,
matrix fibers, and mixtures thereof.
6. The composite of claim 5 wherein the resilient fibers are
selected from the group consisting of chemically stiffened fibers,
anfractuous fibers, chemithermomechanical pulp fibers,
prehydrolyzed kraft pulp fibers, synthetic fibers, and mixtures
thereof.
7. The composite of claim 6 wherein the chemically stiffened fibers
comprise crosslinked cellulosic fibers.
8. The composite of claim 7 wherein the crosslinked cellulosic
fibers are crosslinked with a crosslinking agent selected from the
group consisting of urea-based and polycarboxylic acid crosslinking
agents.
9. The composite of claim 6 wherein the synthetic fibers are
selected from the group consisting of polyolefin, polyester,
polyamide, and thermobondable bicomponent fibers.
10. The composite of claim 9 wherein the polyester fibers are
polyethylene terephthalate fibers.
11. The composite of claim 5 wherein the matrix fibers comprise
cellulosic fibers.
12. The composite of claim 11 wherein the cellulosic fibers
comprise fibers selected from the group consisting of wood pulp
fibers, cotton linters, cotton fibers, hemp fibers, and mixtures
thereof.
13. The composite of claim 5 wherein the resilient fibers are
present in the base in an amount from about 10 to about 60 percent
by weight of the total composite.
14. The composite of claim 5 wherein the matrix fibers are present
in the base in an amount from about 10 to about 50 percent by
weight of the total composite.
15. The composite of claim 1 wherein the absorbent material is a
superabsorbent material.
16. The composite of claim 15 wherein the superabsorbent material
is selected from the group consisting of superabsorbent particles
and superabsorbent fibers.
17. The composite of claim 1 wherein the absorbent material is
present in an amount from about 0.1 to about 80 percent by weight
of the total composite.
18. The composite of claim 1 wherein the absorbent material is
present in about 40 percent by weight of the total composite.
19. The composite of claim 1 wherein the absorbent material absorbs
from about 5 to about 100 times its weight in 0.9 percent saline
solution.
20. The composite of claim 1 further comprising a wet strength
agent.
21. The composite of claim 20 wherein the wet strength agent is a
resin selected from the group consisting of
polyamide-epichlorohydrin and polyacrylamide resins.
22. The composite of claim 20 wherein the wet strength agent is
present in the composite in an amount from about 0.01 to about 2
percent by weight of the total composite.
23. The composite of claim 20 wherein the wet strength agent is
present in the composite in about 0.25 percent by weight of the
total composite.
24. The composite of claim 1 having a basis weight of from about 50
to about 1000 g/m.sup.2.
25. The composite of claim 1 having a density of from about 0.02 to
about 0.7 g/cm.sup.3.
26. The composite of claim 1 wherein the one or more fibrous bands
comprise fibers selected from the group consisting of resilient
fibers, matrix fibers, and mixtures thereof.
27. The composite of claim 26 wherein the resilient fibers are
selected from the group consisting of chemically stiffened fibers,
anfractuous fibers, chemithermomechanical pulp fibers,
prehydrolyzed kraft pulp fibers, synthetic fibers, and mixtures
thereof.
28. The composite of claim 27 wherein the chemically stiffened
fibers comprise crosslinked cellulosic fibers.
29. The composite of claim 28 wherein the crosslinked cellulosic
fibers are crosslinked with a crosslinking agent selected from the
group consisting of urea-based and polycarboxylic acid crosslinking
agents.
30. The composite of claim 26 wherein the matrix fibers comprise
cellulosic fibers.
31. The composite of claim 30 wherein the cellulosic fibers
comprise fibers selected from the group consisting of wood pulp
fibers, cotton linters, cotton fibers, hemp fibers, and mixtures
thereof.
32. The composite of claim 30 wherein the cellulosic fibers
comprise fluff pulp fibers.
33. The composite of claim 30 wherein the cellulosic fibers
comprise refined pulp fibers.
34. The composite of claim 26 wherein the resilient fibers are
present in the composite in an amount from about 15 to about 90
percent by weight of the total composite.
35. The composite of claim 26 wherein the matrix fibers are present
in the composite in an amount from about 10 to about 85 percent by
weight of the total composite.
36. A wetlaid absorbent composite, comprising one or more fibrous
bands in a fibrous base, wherein the base comprises a fibrous
matrix and absorbent material, and wherein the bands are
substantially free of absorbent material.
37. A foam-formed absorbent composite, comprising one or more
fibrous bands in a fibrous base, wherein the base comprises a
fibrous matrix and absorbent material, and wherein the bands are
substantially free of absorbent material.
38. An absorbent article comprising an absorbent composite
comprising one or more fibrous bands in a fibrous base, wherein the
base comprises a fibrous matrix and absorbent material, and wherein
the bands are substantially free of absorbent material.
39. An absorbent article comprising a wetlaid absorbent composite
comprising one or more fibrous bands in a fibrous base, wherein the
base comprises a fibrous matrix and absorbent material, and wherein
the bands are substantially free of absorbent material.
40. An absorbent article comprising a foam-formed absorbent
composite comprising one or more fibrous bands in a fibrous base,
wherein the base comprises a fibrous matrix and absorbent material,
and wherein the bands are substantially free of absorbent
material.
41. An absorbent article comprising: liquid pervious facing sheet;
a storage layer comprising an absorbent composite comprising one or
more fibrous bands in a fibrous base, wherein the base comprises a
fibrous matrix and absorbent material, and wherein the bands are
substantially free of absorbent material; and a liquid impervious
backing sheet.
42. An absorbent article comprising: a liquid pervious facing
sheet; an acquisition layer for rapidly acquiring and distributing
liquid; a storage layer comprising an absorbent composite
comprising one or more fibrous bands in a fibrous base, wherein the
base comprises a fibrous matrix and absorbent material, and wherein
the bands are substantially free of absorbent material; and a
liquid impervious backing sheet.
43. An absorbent article comprising: a liquid pervious facing
sheet; an acquisition layer for rapidly acquiring and distributing
liquid; a storage layer comprising an absorbent composite
comprising one or more fibrous bands in a fibrous base, wherein the
base comprises a fibrous matrix and absorbent material, and wherein
the bands are substantially free of absorbent material; an
intermediate layer interposed between the acquisition layer and the
storage layer; and a liquid impervious backing sheet.
44. The absorbent article of claim 43 wherein the intermediate
layer is selected from the group consisting of a liquid pervious
tissue and a distribution layer.
45. The absorbent article of claim 41 wherein the article is a
feminine care product.
46. The absorbent article of claim 45 wherein the top sheet is
joined to the backing sheet.
47. The absorbent article of claim 42 wherein the article is a
diaper.
48. The absorbent article of claim 47 further comprising leg
gathers.
49. An absorbent article comprising: a liquid pervious facing
sheet; an acquisition layer for acquiring and distributing liquid;
a storage layer; and a liquid impervious backing sheet; wherein the
acquisition layer comprises an absorbent composite comprising one
or more fibrous bands in a fibrous base, wherein the base comprises
a fibrous matrix and absorbent material, and wherein the bands are
substantially free of absorbent material.
50. The absorbent article of claim 49 wherein the acquisition layer
has a top surface area less than the top surface area of the
storage core.
51. The absorbent article of claim 49 wherein the acquisition layer
has a top surface area about equal to the top surface area of the
storage core.
52. The absorbent article of claim 49 wherein the storage layer
comprises absorbent material.
53. The absorbent article of claim 49 wherein the storage layer
comprises an absorbent composite comprising one or more fibrous
bands in a fibrous base, wherein the base comprises a fibrous
matrix and absorbent material, and wherein the bands are
substantially free of absorbent material.
54. The absorbent article of claim 49 wherein the article is a
diaper.
55. The absorbent article of claim 49 further comprising leg
gathers.
56. A method for forming a fibrous web, comprising the steps of:
(a) forming a first slurry comprising fibers in an aqueous
dispersion medium; (b) forming a second slurry comprising fibers in
an aqueous dispersion medium; (c) moving a first foraminous element
in a first path; (d) moving a second foraminous element in a second
path, a nip area provided at a location along the first and second
paths; (e) passing the first slurry into contact with the first
foraminous element moving in the first path; (f) passing the second
slurry into contact with the second foraminous element moving in
the second path; (g) passing a third material between the first and
second slurries, wherein the third material does not contact the
foraminous elements, and wherein the third material is introduced
at a plurality of points; and (h) withdrawing liquid from the first
and second slurries and third material through the first and second
foraminous elements, respectively, to provide a fibrous web.
57. The method of claim 56 wherein the step of passing a third
material between the first and second slurries by introducing the
third material at a plurality of points provides bands of the third
material into the web formed.
58. The method of claim 57 wherein the step of passing a third
material between the first and second slurries by introducing the
third material at a plurality of points comprises adjusting the
positions of at least some of the plurality of points to adjust the
introduction points in a first dimension toward and away from the
nip area.
59. The method of claim 57 wherein the step of passing a third
material between the first and second slurries by introducing the
third material at a plurality of points comprises adjusting the
positions of at least some of the plurality of points to adjust the
introduction points in a second dimension substantially
perpendicular to the first dimension, closer to one foraminous
element or the other.
60. The method of claim 57 wherein the step of passing a third
material between the first and second slurries by introducing the
third material at a plurality of points is practiced utilizing a
plurality of conduits.
61. The method of claim 60 wherein the plurality of conduits
comprises conduits having at least two different lengths.
62. The method of claim 60 wherein steps (e), (f), and (g) are
practiced by providing dividing walls extending part of the length
of the conduits toward the nip area.
63. The method of claim 56 wherein the step of passing a third
material between the first and second slurries step comprises
passing the third material between the first and second slurries
after the first and second slurries have contacted the first and
second foraminous elements, respectively, and withdrawing liquid
therefrom.
64. The method of claim 56 wherein the fibers are selected from the
group consisting of resilient fibers, matrix fibers, synthetic
fibers, and mixtures thereof.
65. The method of claim 56 wherein the fibers comprise crosslinked
cellulosic fibers and wood pulp fibers.
66. The method of claim 56 wherein the third material comprises a
fibrous slurry.
67. The method of claim 56 wherein the first slurry is different
from the second slurry.
68. The method of claim 56 wherein the first and second paths are
substantially vertical.
69. The method of claim 56 practiced with a twin-wire former.
70. The method of claim 69 wherein the twin-wire former is a
vertical downflow former.
71. The method of claim 56 further comprising the step of drying
the wet composite to provide an absorbent composite.
72. The method of claim 56 wherein the method is a wetlaid
method.
73. The method of claim 56 wherein the method is a foam-forming
method.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of the priority of the
filing date of copending U.S. application Ser. No. 60/155,464,
filed Sep. 21, 1999, which is expressly incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an absorbent composite and
more particularly, to an absorbent composite that includes
superabsorbent material and fibrous bands.
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 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 superabsorbent 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
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
materials. Generally, these structures include superabsorbent
materials distributed as a layer within a multilayered composite.
In these structures the superabsorbent polymer is relatively
localized and not uniformly distributed throughout the absorbent
structure and thus renders these composites susceptible to gel
blocking. Upon liquid absorption, superabsorbent materials tend to
coalesce and form a gelatinous mass that 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 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 are manifested by decreased liquid acquisition rates and
far from ideal liquid distribution on successive liquid
insults.
[0006] Accordingly, there exists a need for 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. A need also
exists for an absorbent composite that continues to acquire and
distribute liquid throughout the composite on successive liquid
insults. In addition, there exists a need for an absorbent
composition containing superabsorbent materials that exhibits the
advantages associated with wet-laid composites including wet
strength, absorbent capacity and acquisition, liquid distribution,
softness, and resilience. The present invention seeks to fulfill
these needs and provides further related advantages.
SUMMARY OF THE INVENTION
[0007] The present invention relates to a reticulated fibrous
absorbent composite containing absorbent material. The absorbent
composite is a fibrous matrix that includes absorbent material and
a three-dimensional network of channels or capillaries. The
composite's reticulated nature enhances liquid distribution,
acquisition, and wicking, while the absorbent material provides
high absorbent capacity. Wet strength agents can be incorporated
into the composite to provide wet integrity and also to assist in
securing the absorbent material in the composite.
[0008] The absorbent composite formed in accordance with the
present invention includes a stable three-dimensional network of
fibers and channels that afford rapid acquisition and wicking of
liquid. The fibers and channels distribute the acquired liquid
throughout the composite and direct liquid to absorbent material
present in the composite where the liquid is ultimately absorbed.
The composite maintains its integrity before, during, and after
liquid is introduced. In one embodiment, the composite is a
densified composite that can recover its original volume on
wetting.
[0009] In one aspect, the present invention provides an absorbent
composite having a fibrous matrix that includes absorbent material.
The fibrous matrix defines voids and passages between the voids,
which are distributed throughout the composite. Absorbent material
is located within some of the voids. The absorbent material located
in these voids is expandable into the void.
[0010] In one embodiment, the reticulated absorbent composite
includes at least one fibrous stratum. For such an embodiment, the
composite includes a reticulated core and a fibrous stratum
adjacent and coextensive with an outward facing surface of the
core. In another embodiment, the composite includes strata on
opposing outward facing surfaces of the core. The composite's
strata can be composed of any suitable fiber or combination of
fibers and can be formed from fibers that are the same as or
different from the fibers used for forming the reticulated
core.
[0011] In another embodiment, the absorbent composite includes
fibrous bands.
[0012] In another aspect of the invention, absorbent articles that
include the reticulated composite are provided. The absorbent
articles include consumer absorbent products such as diapers,
feminine care products, and adult incontinence products.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated by reference
to the following detailed description, when taken in conjunction
with the accompanying drawings, wherein:
[0014] FIG. 1 is a cross-sectional view of a portion of a
reticulated absorbent composite formed in accordance with the
present invention;
[0015] FIG. 2 is a photomicrograph of a cross section of a
representative reticulated absorbent composite formed by a wet-laid
method in accordance with the present invention at 12 times
magnification;
[0016] FIG. 3 is a photomicrograph of the wet-laid composite of
FIG. 2 at 40 times magnification;
[0017] FIG. 4 is a photomicrograph of a cross section of a
representative reticulated absorbent composite formed by a foam
method in accordance with the present invention at 12 times
magnification;
[0018] FIG. 5 is a photomicrograph of the foam-formed composite of
FIG. 4 at 40 times magnification;
[0019] FIG. 6 is a photomicrograph of a cross section of a
representative reticulated absorbent composite formed by a wet-laid
method in accordance with the present invention in a wetted state
at 8 times magnification;
[0020] FIG. 7 is a photomicrograph of the wet-laid composite of
FIG. 6 at 12 times magnification;
[0021] FIG. 8 is a photomicrograph of a cross section of a
representative reticulated absorbent composite formed by a foam
method in accordance with the present invention in a wetted state
at 8 times magnification;
[0022] FIG. 9 is a photomicrograph of the foam-formed composite of
FIG. 8 at 12 times magnification;
[0023] FIG. 10 is a cross-sectional view of a portion of an
absorbent construct incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0024] FIG. 11 is a cross-sectional view of a portion of another
absorbent construct incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0025] FIG. 12 is a cross-sectional view of a portion of an
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0026] FIG. 13 is a cross-sectional view of a portion of another
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0027] FIG. 14 is a cross-sectional view of a portion of another
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0028] FIG. 15 is a cross-sectional view of a portion of an
absorbent construct incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0029] FIG. 16 is a cross-sectional view of a portion of another
absorbent construct incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0030] FIG. 17 is a cross-sectional view of a portion of another
absorbent construct incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0031] FIG. 18 is a cross-sectional view of a portion of an
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0032] FIG. 19 is a cross-sectional view of a portion of another
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0033] FIG. 20 is a cross-sectional view of a portion of another
absorbent article incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0034] FIGS. 21A and B are cross-sectional views of portions of
reticulated absorbent composites formed in accordance with the
present invention;
[0035] FIG. 22 is a diagrammatic view illustrating a twin-wire
device and method for forming the composite of the present
invention;
[0036] FIG. 23 is a diagrammatic view illustrating a representative
headbox assembly and method for forming the composite of the
present invention;
[0037] FIG. 24 is a diagrammatic view illustrating a representative
headbox assembly and method for forming the composite of the
present invention;
[0038] FIG. 25 is a view illustrating representative conduits for
introducing absorbent material into a fibrous web in accordance
with the present invention;
[0039] FIGS. 26A-C are cross-sectional views of portions of
absorbent constructs incorporating an acquisition layer and a
reticulated absorbent composite formed in accordance with the
present invention;
[0040] FIGS. 27A-C are cross-sectional views of portions of
absorbent constructs incorporating an acquisition layer,
intermediate layer, and a reticulated absorbent composite formed in
accordance with the present invention;
[0041] FIGS. 28A-C are cross-sectional views of portions of
absorbent articles incorporating a reticulated absorbent composite
formed in accordance with the present invention;
[0042] FIGS. 29A-C are cross-sectional views of portions of
absorbent articles incorporating an acquisition layer and a
reticulated absorbent composite formed in accordance with the
present invention;
[0043] FIGS. 30A-C are cross-sectional views of portions of
absorbent articles incorporating an acquisition layer, intermediate
layer, and a reticulated absorbent composite formed in accordance
with the present invention;
[0044] FIG. 31 is a schematic illustration of a representative
composite having fibrous bands formed in accordance with the
present invention;
[0045] FIG. 32 is a graph comparing the wicking height at 15
minutes, capacity at 15 cm, and wetted zone capacity for
representative composites formed in accordance with the present
invention;
[0046] FIG. 33 is a graph correlating composite ring crush and
tensile strength for representative composites formed in accordance
with the present invention;
[0047] FIG. 34 is a graph correlating composite unrestrained
vertical wicking height and saturation capacity for representative
composites formed in accordance with the present invention;
[0048] FIG. 35 is a graph comparing composite ring crush and
tensile strength for representative composites formed in accordance
with the present invention; and
[0049] FIG. 36 is a graph comparing composite unrestrained vertical
wicking height and saturation capacity for representative
composites formed in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0050] The absorbent composite formed in accordance with the
present invention is a reticulated fibrous composite that includes
absorbent material. The absorbent material is distributed
substantially throughout the fibrous composite and serves to absorb
and retain liquid acquired by the composite. In a preferred
embodiment, the absorbent material is a superabsorbent material. In
addition to forming a matrix for the absorbent material, the
composite's fibers provide a stable three-dimensional network of
channels or capillaries that serve to acquire liquid contacting the
composite and to distribute the acquired liquid to the absorbent
material. The composite optionally includes a wet strength agent
that further increases tensile strength and structural integrity to
the composite.
[0051] The composite is a fibrous matrix that includes absorbent
material. The fibrous matrix defines voids and passages between the
voids, which are distributed throughout the composite. Absorbent
material is located within some of the voids. The absorbent
material located in these voids is expandable into the void.
[0052] The absorbent composite can be advantageously incorporated
into a variety of absorbent articles such as diapers and training
pants; feminine care products including sanitary napkins, tampons,
and pant liners; adult incontinence products; toweling; surgical
and dental sponges; bandages; food tray pads; and the like.
[0053] Because the composite is highly absorbent having a high
liquid storage capacity, the composite can be incorporated 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 distribution
layer. In a preferred embodiment, an absorbent article, such as a
diaper, includes an acquisition layer overlying a reticulated
storage core and having a liquid pervious facing sheet and a liquid
impervious backing sheet. 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 layer. Thus, in
another embodiment, the absorbent composite can be combined with a
storage layer to provide an absorbent core that is useful in
absorbent articles.
[0054] The absorbent composite formed in accordance with the
present invention is a reticulated absorbent composite. As used
herein, the term "reticulated" refers to the composite's open and
porous nature characterized as having a stable three-dimensional
network of fibers (i.e., fibrous matrix) that create channels or
capillaries that serve to rapidly acquire and distribute liquid
throughout the composite, ultimately delivering acquired liquid to
the absorbent material that is distributed throughout the
composite.
[0055] The reticulated composite is an open and stable structure.
The fibrous composite's open and stable structure includes a
network of capillaries or channels that are effective in acquiring
and distributing liquid throughout the composite. In the composite,
fibers form relatively dense bundles that direct fluid throughout
the composite and to absorbent material distributed throughout the
composite. The composite's wet strength agent serves to stabilize
the fibrous structure by providing interfiber bonding. The
interfiber bonding assists in providing a composite having a stable
structure in which the composite's capillaries or channels remain
open before, during, and after liquid insult. The composite's
stable structure provides capillaries that remain open after
initial liquid insult and that are available for acquiring and
distributing liquid on subsequent insults.
[0056] Referring to FIG. 1, a representative reticulated absorbent
composite indicated generally by reference numeral 10 formed in
accordance with the present invention is a fibrous matrix that
includes fibrous regions 12 substantially composed of fibers 16 and
defining voids 14. Some voids include absorbent material 18. Voids
14 are distributed throughout composite 10.
[0057] Representative reticulated composites formed in accordance
with the invention are shown in FIGS. 2-9. These composites include
48 percent by weight matrix fibers (i.e., southern pine
commercially available from Weyerhaeuser Co. under the designation
NB416), 12 percent by weight resilient fibers (i.e., polymaleic
acid crosslinked fibers), 40 percent by weight absorbent material
(i.e., superabsorbent material commercially available from
Stockhausen), and about 0.5 percent by weight wet strength agent
(i.e., polyamide-epichlorohydrin resin commercially available from
Hercules under the designation Kymene.RTM.). FIG. 2 is a
photomicrograph of a cross section of a representative composite
formed by a wet-laid process at 12.times.magnification. FIG. 3 is a
photomicrograph of the same cross section at
40.times.magnification. FIG. 4 is a photomicrograph of a cross
section of a representative composite formed by a foam process at
12.times.magnification. FIG. 5 is a photomicrograph of the same
cross section at 40.times.magnification. The reticulated nature of
the composites is shown in these figures. Referring to FIG. 3,
fibrous regions extend throughout the composite creating a network
of channels. Void regions, including those that include absorbent
material, appear throughout the composite and are in fluid
communication with the composite's fibrous regions. Absorbent
material appears in the composite's voids, generally surrounded by
dense fiber bundles.
[0058] Photormicrographs of the representative composites shown in
FIGS. 2-5 in a wetted state are illustrated in FIGS. 6-9,
respectively. These photomicrographs were obtained by sectioning
freeze-dried composites that had acquired synthetic urine under
free swell conditions. FIGS. 6 and 7 are photomicrographs of the
wetted wet-laid composite at 8.times.and 12.times.magnification,
respectively. FIGS. 8 and 9 are photomicrographs of the wetted
foam-formed composite at 8.times.and 12.times.magnification,
respectively. Referring to FIG. 6, absorbent material in the wetted
composite has swollen and increased in size to more fully occupy
voids that the absorbent material previously occupied in the dry
composite.
[0059] The composite's fibrous matrix is composed primarily of
fibers. 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. Fibers suitable for use in the present invention are
known to those skilled in the art and include any fiber from which
a wet composite can be formed.
[0060] 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 5 to about 60 percent by
weight, more preferably from about 10 to 40 percent by weight,
based on the total weight of the composite.
[0061] Resilient fibers include cellulosic and synthetic fibers.
Preferred resilient fibers include chemically stiffened fibers,
anfractuous fibers, chemithermomechanical pulp (CTMP), and
prehydrolyzed kraft pulp (PHKP).
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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. Mixtures of fibers can also be used.
Preferably, the composite includes matrix fibers in an amount from
about 10 to about 60 percent by weight, more preferably from about
20 to about 50 percent by weight, based on the total weight of the
composite.
[0066] 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 5 to about 20
percent by weight and matrix fibers in an amount from about 20 to
about 60 percent by weight based on the total weight of the
composite. In a more preferred embodiment, the composite includes
from about 10 to about 15 percent by weight resilient fibers,
preferably crosslinked cellulosic fibers, and from about 40 to
about 50 percent by weight matrix fibers, preferably wood pulp
fibers, based on the total weight of the composite.
[0067] Cellulosic fibers are a basic component of the absorbent
composite. Although available from other sources, cellulosic fibers
are derived primarily from wood pulp. Suitable wood pulp fibers for
use with the invention can be obtained from well-known chemical
processes such as the kraft and sulfite processes, with or without
subsequent bleaching. The pulp fibers may 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 with the present invention are available from
Weyerhaeuser Company under the designations CF416, NF405, PL416,
FR516, and NB416.
[0068] The wood pulp fibers can also be pretreated prior to use
with 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, have better wicking, and be easier to
densify than a composite that does not include crosslinked fibers.
Suitable crosslinked cellulose fibers produced from southern pine
are available from Weyerhaeuser Company under the designation
NHB416. 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.
[0069] Intrafiber crosslinked cellulosic fibers are prepared by
treating cellulose 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; 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 Steijer 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 C.sub.2-C.sub.9 polycarboxylic acids
that contain at least three carboxyl groups (e.g., citric acid and
oxydisuccinic acid) as crosslinking agents.
[0070] Suitable urea-based crosslinking agents include methylolated
ureas, methylolated cyclic ureas, methylolated lower alkyl cyclic
ureas, methylolated dihydroxy cyclic ureas, dihydroxy cyclic ureas,
and lower alkyl substituted cyclic ureas. Specific preferred
urea-based crosslinking agents include dimethyldihydroxyethylene
urea (DMeDHEU, 1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone),
dimethyloldihydroxyethylen- e urea (DMDHEU,
1,3-dihydroxymethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol
urea (DMU, bis[N-hydroxymethyl]urea), dihydroxyethylene urea (DHEU,
4,5-dihydroxy-2-imidazolidinone), and dimethylolethylene urea
(DMEU, 1,3-dihydroxymethyl-2-imidazolidinone).
[0071] 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 acid 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 can
also be used.
[0072] 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.
[0073] Although not to be construed as a limitation, examples of
pretreating fibers include the application of surfactants or other
liquids that 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.
[0074] 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.
[0075] In addition to natural fibers, synthetic fibers including
polymeric fibers, such as polyolefin, polyamide, polyester,
polyvinyl alcohol, and polyvinyl acetate fibers may also be used in
the absorbent composite. Suitable polyolefin fibers include
polyethylene and polypropylene fibers. Suitable polyester fibers
include polyethylene terephthalate fibers. Other suitable synthetic
fibers include, for example, nylon fibers. The absorbent composite
can include combinations of natural and synthetic fibers.
[0076] In one preferred embodiment, the absorbent composite
includes a combination of wood pulp fibers (e.g., Weyerhaeuser
designation NB416) and crosslinked cellulosic fibers (e.g.,
Weyerhaeuser designation NHB416). Wood pulp fibers are present in
such a combination in an amount from about 10 to about 85 weight
percent by weight based on the total weight of fibers.
[0077] When incorporated into an absorbent article, the reticulated
absorbent composite can serve as a storage layer for acquired
liquids. To effectively retain acquired liquids, the absorbent
composite includes absorbent material. As used 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 a coated absorbent material
that is resistant to absorbing water during the composite formation
process.
[0078] The amount of absorbent material present in the composite
can vary greatly depending on the composite's intended use. The
amount of absorbent material present in an absorbent article, such
as an absorbent core for an infant's diaper, is suitably present in
the composite in an amount from about 5 to about 60 weight percent,
preferably from about 30 to about 50 weight percent, based on the
total weight of the composite.
[0079] 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 materials can also
retain significant amounts of bodily fluids under moderate
pressure.
[0080] Superabsorbent materials 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.
[0081] Superabsorbent materials 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
materials are marketed under the trademarks SANWET (supplied by
Sanyo Kasei Kogyo Kabushiki Kaisha), and SXM77 (supplied by
Stockhausen of Greensboro, N.C.). Other superabsorbent materials
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 materials are described in
U.S. Pat. No. 3,699,103 and U.S. Pat. No. 3,670,731.
[0082] Suitable superabsorbent materials useful in the absorbent
composite include superabsorbent particles and superabsorbent
fibers.
[0083] In a preferred embodiment, the absorbent composite includes
a superabsorbent material 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. Generally,
the smaller the absorbent material, the more rapidly the material
absorbs liquid.
[0084] The absorbent composite can optionally include a wet
strength agent. The wet strength agent provides increased strength
to the absorbent composite and enhances the composite's wet
integrity. In addition to increasing the composite's wet strength,
the wet strength agent can assist in binding the absorbent
material, for example, superabsorbent material, in the composite's
fibrous matrix.
[0085] 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).
[0086] 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 forming the composite is a
polyamide-epichlorohydrin resin commercially available from
Hercules, Inc. under the designation Kymene.RTM.. The wet and dry
tensile strengths of an absorbent composite formed in accordance
with the present invention will generally increase with an
increasing the amount of wet strength agent. The tensile strength
of a representative composite is described in Example 7.
[0087] The absorbent composite generally has a basis weight from
about 50 to about 1000 g/m.sup.2, 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 absorbent composite generally has a density from about 0.02 to
about 0.7 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 a density of about 0.15 g/cm.sup.3.
[0088] 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
reticulated storage 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.
[0089] The composition of the reticulated absorbent composite can
be varied to suit the needs of the desired end product in which it
can be incorporated. In one preferred embodiment, the absorbent
composite includes about 60 weight percent cellulosic fibers (about
48 percent by weight wood pulp fibers and about 12 percent by
weight crosslinked cellulosic fibers), about 40 percent by weight
absorbent material (e.g., superabsorbent particles), and about 0.5
percent by weight wet strength agent (e.g.,
polyamide-epichlorohydrin resin, Kymene.RTM., about 10 pounds resin
per ton fiber) based on the total weight of the composite.
[0090] The reticulated absorbent composite can be formed by
wet-laid and foam processes known to those of ordinary skill in the
pulp processing art. 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 are 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.
[0091] In the methods, the absorbent material is incorporated into
the composite during the formation of the composite. Generally, the
methods for forming the reticulated absorbent composite include
combining the components of the composite in a dispersion medium
(e.g., an aqueous medium) to form a slurry and then depositing the
slurry onto a foraminous support (e.g., a forming wire) and
dewatering to form a wet composite. Drying the wet composite
provides the reticulated composite.
[0092] As noted above, the reticulated composite is prepared from a
combination of fibers, absorbent material, and optionally a wet
strength agent in a dispersion medium. In one embodiment of the
method, a slurry is formed by directly combining fibers, absorbent
material, and wet strength agent in a dispersion medium. In another
embodiment, the slurry is prepared by first combining fibers and
the wet strength agent in a dispersion medium to provide a fibrous
slurry to which is then added absorbent material in a second step.
In yet another embodiment, a fibrous slurry is combined with a
second slurry containing absorbent material, the combined slurry
then being deposited onto the support. Alternatively, individual
slurries, for example, a fibrous slurry and a slurry containing
absorbent material, can be deposited onto the foraminous support
through the use of a divided headbox, for example, a twin slice
headbox that deposits two slurries onto a support
simultaneously.
[0093] In one embodiment, the slurry or slurries containing the
composite's components in a dispersion medium are deposited onto a
foraminous support. Once deposited onto the support the dispersion
medium begins to drain from the deposited fibrous slurry. Removal
of the dispersion medium (e.g., dewatering) from the deposited
fibrous slurry continues through, for example, the application of
heat, pressure, vacuum, and combinations thereof, and results in
the formation of a wet composite.
[0094] The reticulated absorbent composite is ultimately produced
by drying the wet composite. Drying removes the remaining
dispersion medium and provides an absorbent composite having the
desired moisture content. Generally, the composite has a moisture
content less than about 20 percent and preferably has a moisture
content in the range from about 6 to about 10 percent by weight
based on the total weight of the composite. 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. A representative wet-laid
method for forming a reticulated absorbent composite is described
in Example 1.
[0095] For foam methods, the fibrous slurry is a foam dispersion
that further includes a surfactant. Suitable surfactants include
ionic, nonionic, and amphoteric surfactants known in the art. A
representative foam method for forming a reticulated absorbent
composite is described in Example 2.
[0096] The deposition of the components of the absorbent composite
onto the foraminous support, followed by dewatering, results in the
formation of a wet composite that includes absorbent material that
may have absorbed water and, as a result, swollen in size. The wet
composite containing the water-swollen absorbent material is
distributed onto a support from which water (i.e., the dispersion
medium) can be withdrawn and the wet composite dried. Drying causes
the water-swollen absorbent material to dehydrate and decrease in
size, thereby creating voids in the composite surrounding the
absorbent material.
[0097] In the methods, 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.
[0098] Foam methods are advantageous for forming the absorbent
composite 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 pore and void size, void size to be
maximized, 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.
[0099] For fabrication, the reticulated absorbent composite can be
formed by a foam process, preferably a process by Ahlstrom Company
(Helsinki, Finland). The process encompasses desirable
manufacturing efficiencies while producing a product with desirable
performance characteristics.
[0100] The formation of a reticulated absorbent composite by
representative wet-laid and foam processes is described in Examples
1 and 2, respectively. Absorbent properties (i.e., rewet,
acquisition time, liquid distribution, dry strength, and
resilience) for representative reticulated absorbent composites are
described in Examples 3 and 4. Wicking and liquid distribution for
a representative absorbent composite are described in Examples 5
and 6, respectively. The tensile strength of representative
composites formed in accordance with the present invention is
described in Example 7. The softness (i.e., Taber stiffness) of
representative wet-laid and foam-formed composites is described in
Example 8.
[0101] One variable that affects the absorbent composite's
performance characteristics including, for example, liquid
acquisition and distribution rate and absorbent capacity, is the
extent of swelling of the absorbent material in the composite. The
methods allow for control and variation of absorbent material
swelling. Absorbent material swelling generally depends on the
degree of crosslinking (e.g., surface and internal crosslinking)
and the amount of water absorbed by the absorbent material. The
extent of swelling depends on a number of factors, including the
type of absorbent material, the concentration of absorbent material
in an aqueous environment (e.g., the dispersion medium and the wet
composite), and the period of time that the absorbent material
remains in contact with such an environment. Generally, the lower
the concentration of the absorbent material in an aqueous medium
and the longer the contact time, the greater the swelling of an
absorbent material. Absorbent material swelling can be minimized by
dispensing the absorbent in chilled water.
[0102] In general, the greater the initial swelling of the
absorbent material, the greater the void volume and, consequently,
the lower the density of the resulting absorbent composite. The
greater the void volume of a composite, the greater its liquid
acquisition rate and, generally, the greater the composite's
absorbent capacity.
[0103] As noted above, the composite's voids are formed by the
hydration and swelling of absorbent material (i.e., during wet
composite formation) and the subsequent dehydration and decrease in
size of the absorbent material (i.e., during wet composite drying).
Ultimately, the density of the composite depends on the extent to
which the absorbent material absorbs liquid and swells during the
formation of the wet composite, and the conditions and extent to
which the wet composite incorporating the swollen absorbent
material is dried. Water absorbed by the absorbent material during
wet composite formation is removed from the absorbent material,
decreasing its size, on drying the wet composite. The dehydration
of the swollen absorbent material defines some of the voids in the
fibrous composite.
[0104] The reticulated 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.
10 and 11, can be used in combination with one or more other
layers. In FIG. 10, absorbent composite 10 is employed as a storage
layer in combination with upper acquisition layer 20. As
illustrated in FIG. 11, a third layer 30 (e.g., distribution layer)
can also be employed, if desired, with absorbent composite 10 and
acquisition layer 20.
[0105] A variety of suitable absorbent articles 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 FIG. 12, absorbent article 40 comprises absorbent
composite 10 and overlying acquisition layer 20. A liquid pervious
facing sheet 22 overlies acquisition composite 20, and a liquid
impervious backing sheet 24 underlies absorbent composite 10. The
absorbent composite will provide advantageous liquid absorption
performance for use in, for example, diapers. The reticulated
structure of the absorbent composite will aid in fluid transport
and absorption in multiple wettings. For absorbent articles that
incorporate the composite and that are suitable for use as diapers
or as incontinence products, the articles can further include leg
gathers.
[0106] The construct in FIG. 12 is shown for purposes of
exemplifying a typical absorbent article, such as a diaper or
feminine napkin. One of ordinary skill will be able to make a
variety of different constructs using the concepts taught herein.
The example, a typical construction of an adult incontinence
absorbent structure is shown in FIG. 13. The article 50 comprises a
facing sheet 22, acquisition layer 20, absorbent composite 10, and
a backing sheet 24. The facing sheet 22 is pervious to liquid while
the backing sheet 24 is impervious to liquid. In this construct, a
liquid pervious tissue 26 composed of a polar, fibrous material is
positioned between absorbent composite 10 and acquisition layer
20.
[0107] Referring to FIG. 14, another absorbent article includes a
facing sheet 22, an acquisition layer 20, an intermediate layer 28,
absorbent composite 10, and a backing sheet 24. The intermediate
layer 28 contains, for example, a densified fibrous material such
as a combination of cellulose acetate and triacetin, which are
combined prior to forming the article. The intermediate layer 28
can thus bond to both absorbent composite 10 and acquisition layer
20 to form an absorbent article having significantly more integrity
than one in which the absorbent composite and acquisition layer are
not bonded to each other. The hydrophilicity of layer 28 can be
adjusted in such a way as to create a hydrophilicity gradient among
layers 10, 28, and 20.
[0108] The reticulated 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 top surface area that is
smaller, the same size, or greater than the top surface area of the
storage layer. Representative absorbent constructs that incorporate
the reticulated absorbent composite in combination with a storage
layer are shown in FIG. 15. Referring to FIG. 15, absorbent
construct 70 includes reticulated composite 10 and storage layer
72. Storage layer 72 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. The storage
layer can be a reticulated composite.
[0109] An acquisition layer can be combined with the reticulated
composite and storage layer. FIG. 16 illustrates absorbent
construct 80 having acquisition layer 20 overlying composite 10 and
storage layer 72. Construct 80 can further include intermediate
layer 74 to provide construct 90 shown in FIG. 17. Intermediate
layer 74 can be, for example, a tissue layer, a nonwoven layer, an
air-laid or wet-laid pad, or a reticulated composite.
[0110] Constructs 70, 80, and 90 can be incorporated into absorbent
articles. Generally, absorbent articles 100, 110, and 120, shown in
FIGS. 18-20, respectively, include a liquid pervious facing sheet
22, a liquid impervious backing sheet 24, and constructs 70, 80,
and 90, respectively. In such absorbent articles, the facing sheet
is joined to the backing sheet.
[0111] In another embodiment, the reticulated absorbent composite
formed in accordance with the present invention further includes a
fibrous stratum. In this embodiment, the composite includes a
reticulated core and a fibrous stratum adjacent an outward facing
surface of the core. The fibrous stratum is integrally formed with
the reticulated core to provide a unitary absorbent composite.
Generally, the stratum is coextensive with an outward facing
surface (i.e., an upper and/or lower surface) of the composite.
Preferably, the composite includes first and second strata adjacent
each of the core's outward facing surfaces (i.e., the strata are
coextensive with opposing surfaces of the core). A representative
absorbent composite having a fibrous stratum is shown in FIG. 21A
and a representative composite having fibrous strata is shown in
FIG. 21B. Referring to FIG. 21A, absorbent composite 130 includes
reticulated core 10 and stratum 132 and, as shown in FIG. 21B,
composite 140 includes reticulated core 10 intermediate strata 132
and 134. As noted above, core 10 is a fibrous matrix that includes
fibrous regions 12 defining voids 14, some of which include
absorbent material 18.
[0112] The stratum or strata of the composite are fibrous and can
be composed of any suitable fiber or combination of fibers noted
above. The stratum's fibrous composition can be widely varied. The
stratum can be formed from fibers that are the same as or different
from the fibers used for forming the reticulated core. The stratum
can be formed from resilient fibers, matrix fibers, or combinations
of resilient and matrix fibers. The stratum can optionally include
a wet or dry strength agent. Suitable strata can be formed from a
single fiber type, for example, a stratum composed of 100 percent
wood pulp fibers (e.g., southern pine fibers). Alternatively, the
stratum can be formed from fibrous blends, such as an 80:20 blend
of wood pulp fibers and crosslinked fibers, and synthetic blends,
and blends of synthetic and cellulosic fibers.
[0113] The stratum composition can be varied to provide a composite
having desired characteristics. For example, to provide a stratum
having high liquid wicking capacity, the stratum preferably has a
relatively high wood pulp fiber content. Thus, for liquid
distribution, the stratum is preferably composed of wood pulp
fibers such as southern pine fibers. However, such a stratum has a
lower liquid acquisition rate compared to a similarly constituted
stratum containing relatively less wood pulp fiber and, for
example, greater amounts of crosslinked fibers. Conversely, to
provide a stratum having a high liquid acquisition rate, the
stratum preferably has a relatively high crosslinked or synthetic
fiber content. However, as a consequence of its high crosslinked
fiber content, such a stratum provides less liquid distribution
than a comparable stratum that includes relatively less crosslinked
fiber. For liquid acquisition, the stratum is preferably a blend of
crosslinked fibers and pulp fibers, for example, the stratum can
include from about 30 to about 50 percent by weight crosslinked
fibers and from about 50 to about 70 percent by weight pulp fibers.
Alternatively, strata having high liquid acquisition rates can also
include, in combination with cellulosic fibers, a relatively high
synthetic fiber content (e.g., PET fibers or a blend of PET and
thermobondable fibers). Optionally, one or both strata can include
synthetic fibers.
[0114] Because the composite's stratum is formed with the
reticulated core to provide an integrated unitary structure, the
overall characteristics of the composite can be optimized by
appropriate selection of the individual core and stratum
components. To further optimize the performance of the composite,
the nature of first and second strata can be selectively and
independently controlled and varied. The compositions of the first
and second strata need not be the same. The strata can be formed
from the same or different fiber furnishes. For compositions formed
by foam methods, stratum basis weight can also be independently
controlled and varied. Stratum basis weight can also be varied with
respect to the core's basis weight. In a foam method, basis weight
can be varied by adjusting the rate at which the fibrous furnish is
supplied to and deposited on the forming support. For example,
varying pump speed for a specific furnish effectively controls the
basis weight of that portion of the composite. Accordingly, in one
embodiment, the absorbent composite includes a reticulated core
intermediate first and second strata, each stratum having a
different basis weight. Stratum basis weights can also be varied
for absorbent composites formed by wet-laid methods.
[0115] The stratum can be integrally formed with the reticulated
core by wet-laid and foam methods. Generally, the composite
including the reticulated core and strata can be formed by
substantially simultaneously depositing fibrous slurries that
include the core and stratum components. The deposition of more
than a single fibrous slurry onto a forming support can be
accomplished by standard devices known in the art including, for
example, divided and/or multislice headboxes.
[0116] Representative absorbent composites can be formed using
conventional papermaking machines including, for example,
Rotoformer, Fourdrinier, and twin-wire machines. Absorbent
composites having a single stratum can be formed by Rotoformer and
Fourdrinier machines, and composites that include two strata can be
formed by twin-wire machines. A representative method for forming
the absorbent composite using a Rotoformer machine is described in
Example 9. The performance characteristics of representative
absorbent composites formed by the method are described in Examples
10-15. Absorbent composites formed using the Rotoformer machine
include a wire-side fibrous stratum. The stratum thickness and
overall composite structure can be controlled by the position of
headbox spargers, which deliver absorbent material to and
effectively mix the absorbent material with the fiber stock.
Generally, the deeper the sparger introduces the absorbent material
into the fiber stock at the Rotoformer drum, the thinner the
resulting stratum. Conversely, a relatively thicker stratum can be
formed by introducing absorbent material into the fiber stock at a
greater distance from the drum.
[0117] 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. 22. Referring to FIG. 22, 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.
[0118] 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. Referring to FIG. 22, 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. Absorbent material can be
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.
22) as described above. For example, referring to FIG. 22, nozzles
can be located at positions 2 to inject absorbent material into
partially dewatered webs on wires 202 and 204.
[0119] Depending on the position of absorbent material
introduction, the twin-wire method for forming the composite can
provide a composite having a fibrous stratum.
[0120] 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.
[0121] Basically, the position of the absorbent material 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.
[0122] Referring to FIG. 22, 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.
[0123] Preferably, the reticulated 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 absorbent material can be formed from multiple fibrous
slurries. In a preferred embodiment, the foam-forming method is
practiced on a twin-wire former.
[0124] 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.
[0125] A representative method for forming a fibrous web having an
intermediate stratum generally includes the following steps:
[0126] (a) forming a first fibrous slurry comprising fibers and a
surfactant in an aqueous dispersion medium;
[0127] (b) forming a second fibrous slurry comprising fibers and a
surfactant in an aqueous dispersion medium;
[0128] (c) moving a first foraminous element (e.g., a forming wire)
in a first path;
[0129] (d) moving a second foraminous element in a second path;
[0130] (e) passing the first slurry into contact with the first
foraminous element moving in a first path;
[0131] (f) passing the second slurry into contact with the second
foraminous element moving in the second path;
[0132] (g) passing a third material between the first and second
slurries such that the third material does not contact either of
the first or second foraminous elements; and
[0133] (h) forming a fibrous web from the first and second slurries
and third material by withdrawing liquid from the slurries through
the first and second foraminous elements.
[0134] 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.
[0135] A representative vertical downflow twin-wire former useful
in practicing the method of the invention is illustrated in FIG.
23. Referring to FIG. 23, 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 slurry into the first volume, supply
244 and means 245 for introducing a second fiber slurry into the
second volume, and supply 246 and means 247 for introducing a third
material into the interior structure. Means for withdrawing liquid
(and/or 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.
[0136] In the method, the twin-wire former includes a means for
introducing at least a third material through the interior
structure. 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.
[0137] Another representative vertical downflow twin-wire former
useful in practicing the forming method is illustrated in FIG. 24.
Referring to FIG. 24, 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.
[0138] 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 slurry into the first volume, supply 244 and means 245
for introducing a second fiber 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.
[0139] 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. 25.
[0140] Generally, the former's interior structure (i.e., structure
230 in FIGS. 23 and 24) 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
slurries may be the same, or different, from each other and from
the third material.
[0141] In a preferred embodiment, the method includes introducing
the third material at a plurality of different points. 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. 23 and 24); 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.
[0142] 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. 22 and 24.
[0143] The means for introducing first and second 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.
[0144] The means for withdrawing liquid and 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 liquid and 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. 22, 23, and
24).
[0145] In another embodiment, the composite of the invention
includes one or more fibrous bands in a fibrous base. The base
includes a fibrous matrix and absorbent material. Suitable fibrous
bases are as described above. The fibrous bands are substantially
free of absorbent material. In one embodiment, the fibrous band or
bands extend along the machine direction of the composite. The
number of bands in a particular composite is not particularly
critical, and will depend upon the nature of the absorbent article
into which the composite is incorporated. In one embodiment, the
composite includes two fibrous bands, and in other embodiments, the
composite includes more than two bands, for example, from three to
about six bands.
[0146] A representative composite of the invention having two
fibrous bands is illustrated schematically in FIG. 31. Referring to
FIG. 31, composite 300 includes base matrix 310 and fibrous bands
320. For embodiments of the composite in which the base matrix
includes absorbent material, the fibrous bands conduct fluid along
the composite's length distributing fluid throughout the composite
and to absorbent material in the base matrix where the fluid is
ultimately stored. In the FIG. 31, fluid movement is indicated by
the arrows.
[0147] Representative composites having fibrous bands and their
performance characteristics are described in Examples 18, 19, and
21. A representative composite having two fibrous bands is
described in Example 19. For this composite, wicking height at 15
minutes, capacity at 15 cm, and wetted zone capacity for
representative composites are presented graphically in FIG. 32.
Representative foam-formed composites having two fibrous bands are
described in Example 21. For these composites, ring crush and
tensile strength for are correlated graphically in FIG. 33;
unrestrained vertical wicking height and saturation capacity are
correlated graphically in FIG. 34; ring crush and tensile strength
are compared graphically in FIG. 35; and unrestrained vertical
wicking height and saturation capacity are compared graphically in
FIG. 36.
[0148] The fibrous bands can include any of the fibrous materials
described above including blends of fibers. For example, the
fibrous band can include matrix fibers, resilient fibers, and
blends of matrix and resilient fibers. In certain embodiments, the
fibrous band includes crosslinked cellulosic fibers and/or matrix
fibers. The fibrous band can include crosslinked fibers in an
amount from about 15 percent to about 90 percent by weight based on
the total weight of fibers in the band. In one embodiment, the
fibrous band includes crosslinked fibers in an amount from about 20
percent to about 80 percent by weight based on the total weight of
fibers in the band. In another embodiment, the fibrous band
includes crosslinked fibers in an amount from about 40 percent to
about 60 percent by weight based on the total weight of fibers in
the band. The fibrous band can include matrix fibers in an amount
from about 10 percent to about 85 percent by weight based on the
total weight of fibers in the band. In one embodiment, the fibrous
band includes matrix fibers in an amount from about 20 percent to
about 80 percent by weight based on the total weight of fibers in
the band. In another embodiment, the fibrous band includes matrix
fibers in an amount from about 40 percent to about 60 percent by
weight based on the total weight of fibers in the band.
[0149] As noted above, in one embodiment, the fibrous band includes
a blend of crosslinked and matrix fibers. In one embodiment, the
weight ratio of matrix fibers to crosslinked cellulosic fibers is
about 1:1, in another embodiment the ratio is about 1:4, and in
another embodiment the ratio is about 4:1.
[0150] The absorbent composite having fibrous bands offers
advantages over other composites that lack fibrous bands. Among
other advantages, the fibrous band or bands act as liquid
distribution paths or channels within the composite's fibrous
matrix that includes absorbent material. Thus, liquid acquired by
the composite is rapidly distributed along the fibrous band and is
absorbed out of these bands and into the surrounding fibrous matrix
where the liquid is ultimately absorbed and retained by absorbent
material. The composites including fibrous bands offer advantages
associated with liquid wicking, total liquid absorbed, the rate of
liquid uptake, and liquid flux, among other advantageous
properties. For example, as described below, a representative
absorbent composite having fibrous bands has an unrestrained
vertical wicking height at 30 minutes of at least about 10 cm and,
preferably, at least about 12 cm. The composite also has an
unrestrained vertical wicking total fluid absorbed value at 30
minutes of at least about 30 g and, preferably, at least about 40
g. The composite also has an unrestrained vertical wicking uptake
rate at 12 cm of at least about 1.0 g/g/min and, preferably, at
least about 2.0 g/g/min. The composite also has an unrestrained
vertical wicking flux at 12 cm of at least about 2.0
/g/cm.sup.2/min and, preferably, at least about 3.0
g/cm.sup.2/min.
[0151] The composite having fibrous bands also provides strength
and softness advantages. Fibrous bands running the length of a
composite will generally increase the softness of the composite
across its width.
[0152] Fibrous bands also offer advantages related to composite
processing. For example, the relatively porous fibrous band
increases composite drying efficiency. Also, fibrous bands can
impart breathability to the composite when utilized in an absorbent
article.
[0153] Although the composite has been described as having bands of
fibrous material, it will be appreciated that other configurations
of fiber-only regions are within the scope of the invention.
Representative configurations include circular, annular, ring,
star, cross, and rectangular shapes, among others. The width of the
band or other configuration can also be varied to suit a particular
need. Wide bands have greater capacity than thin bands. The band or
other configuration can also be tapered to facilitate, for example,
fluid movement. In addition to having a tapered or changing length
or width, the band or other configuration can also have a tapered
or changing thickness (i.e., in direction of composite
thickness).
[0154] The fibrous band can also be located in the fibrous base in
various positions (e.g., variation in composite length, width, and
thickness) to provide composites having a variety of fluid movement
properties.
[0155] The absorbent composite having fibrous bands can be formed
by wetlaid and foam-forming methods described above. The fibrous
bands can be incorporated into the fibrous matrix to provide the
composite by the methods described above. Fibrous bands can be
formed by introducing fibers as the third (or fourth) material in
the above-described method. Blends of fibers can also be introduced
as the third material. In such forming methods, absorbent material
can be introduced into the composite through other conduits, for
example, as the fourth (or third) material, as described above.
[0156] The absorbent composite formed in accordance with the
present invention can be incorporated as an absorbent core or
storage layer into an absorbent article such as a diaper. The
composite can be used alone or combined with one or more other
layers, such as acquisition and/or distribution layers, to provide
useful absorbent constructs as illustrated herein. In the figures
illustrating constructs and articles, reference numeral 10 refers
to all of the embodiments of the composites of the invention.
[0157] Representative absorbent constructs incorporating the
absorbent composite having a reticulated core and fibrous strata
are shown in FIGS. 26A-C and 27A-C. Referring to FIG. 26A,
construct 150 includes composite 130 (i.e., reticulated core 10 and
stratum 132) employed as a storage layer in combination with an
upper acquisition layer 20. FIG. 26B illustrates construct 160,
which includes composite 130 and acquisition layer 20 with stratum
132 adjacent acquisition layer 20. Construct 170, including
acquisition layer 20 and composite 140, is illustrated in FIG.
26C.
[0158] In addition to the constructs noted above that include the
combination of absorbent composite and acquisition layer, further
constructs can include a distribution layer intermediate the
acquisition layer and composite. FIG. 27A illustrates construct 180
having intermediate layer 30 (e.g., distribution layer) interposed
between acquisition layer 20 and composite 130. Similarly, FIGS.
27B and 23C illustrate constructs 190 and 200 having layer 30
intermediate acquisition layer 20 and composites 130 and 140,
respectively.
[0159] Composites 130 and 140 and constructs 150, 160, 170, 180,
190, and 200 can be incorporated into absorbent articles.
Generally, absorbent articles 210, 220, and 230 shown in FIGS.
28A-C, respectively; absorbent articles 240, 250, and 260 shown in
FIGS. 29A-C, respectively; and absorbent articles 270, 280, and 290
shown in FIGS. 30A-C, respectively, include liquid pervious facing
sheet 22, liquid impervious backing sheet 24, and composites 130,
140, and constructs 150, 160, 170, 180, 190, and 200, respectively.
In such absorbent articles, the facing sheet is joined to the
backing sheet.
[0160] The following examples are provided for the purposes of
illustration, and not limitation.
EXAMPLES
Example 1
Reticulated Absorbent Composite Formation: Representative Wet-laid
Method
[0161] This example illustrates a wet-laid method for forming a
representative absorbent composite.
[0162] A wet-laid composite formed in accordance with the present
invention is prepared utilizing standard wet-laid apparatus known
to those in the art. A slurry of a mixture of standard wood pulp
fibers and crosslinked pulp fibers (48 and 12 percent by weight,
respectively, based on total weight of dried composite) in water
having a consistency of about 0.25 to 3 percent is formed.
Consistency is defined as the weight percent of fibers present in
the slurry, based on the total weight of the slurry. A wet strength
agent such as Kymene.RTM. (0.5 percent based on total composite
weight) is then added to the fibrous mixture. Finally, absorbent
material (40 percent by weight based on total weight of dried
composite) is added to the slurry, the slurry is thoroughly mixed,
and then distributed onto a wire mesh to form a wet composite. The
wet composite is dried to a moisture content of about 9 to about 15
weight percent based on total composite weight to form a
representative reticulated absorbent composite.
[0163] Absorbent composites having a variety of basis weights can
be prepared from the composite formed as described above by pre- or
post-drying densification methods known to those in the art.
Example 2
Reticulated Absorbent Composite Formation: Representative Foam
Method
[0164] This example illustrates a foam method for forming a
representative absorbent composite.
[0165] A lab-size Waring blender is filled with 4L of water and
pulp fibers are added. The mixture is blended for a short time.
Crosslinked cellulose fibers are then added to the pulp fibers and
blended for at least one minute to open the crosslinked fibers and
effect mixing of the two fibers. The resulting mixture may contain
from 0.07 to 12 percent by weight of solids.
[0166] The mixture is placed in a container and blended for a few
seconds with an air-entrapping blade. A surfactant (Incronan 30,
Croda, Inc.) is added to the blended mixture. Approximately 1 g of
active surfactant solids per gram of fiber is added. The mixture is
blended while slowly raising the mixer blade height from the rising
foam. After about one minute, the mixing is terminated,
superabsorbent is added, and the mixing is restarted for another
one-half minute at constant mixer blade height. The resulting
foam-fiber mixture will have a volume about three times the volume
of the original mixture.
[0167] The mixture is rapidly poured into a sheet mold having an
inclined diffusion plate. After the addition of the mixture, the
plate is removed from the mold, and a strong vacuum is applied to
reduce the foam-fiber height. After most of the visible foam
disappears, the vacuum is discontinued and the resulting sheet
removed from the mold and passed, along with a forming wire, over a
slit couch to remove excess foam and water.
[0168] The sheet is then dried in a drying oven to remove the
moisture.
Example 3
Acquisition Times for a Representative Reticulated Absorbent
Composite
[0169] In this example, the acquisition time for a representative
reticulated absorbent composite formed in accordance with the
present invention (Composite A) is compared to a commercially
available diaper (Diaper A, Kimberly-Clark).
[0170] The tests were conducted on commercially available diapers
(Kimberly-Clark) from which the core and surge management layer
were removed and the surrounds used. The test diapers were prepared
by inserting the absorbent composite into the diaper.
[0171] 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.
[0172] A sample of the absorbent structure was 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 was prepared, the test was
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) was
then placed on top of the funnel acquisition plate to which was
then attached a funnel (4 inch diameter). Liquid acquisition was
then determined by pouring 100 mL synthetic urine into the funnel
and measuring the time from when liquid was first introduced into
the funnel to the time that liquid disappeared from the bottom of
the funnel into the sample. The measured time is the acquisition
time for the first liquid insult. After waiting one minute, a
second 100 mL portion was added to the funnel and the acquisition
time for the second insult was measured. After waiting an
additional one minute, the acquisition was 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 and Composite A are
summarized in Table 1.
1TABLE 1 Acquisition Time Comparison Acquisition Time (sec) Insult
Diaper A Composite A 1 45 10 2 60 11 3 75 10
[0173] 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
reticulated composite. The commercial diaper also exhibited
characteristic diminution of acquisition rate on successive liquid
insults. In contrast, the composite formed in accordance with the
invention maintained a relatively constant 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 fourfold)
than that of the commercially available diaper for initial insult.
The results reflect the greater wicking ability and capillary
network for the wet-laid composite compared to a conventional
air-laid storage core in general, and the enhanced performance of
the reticulated absorbent composite in particular.
Example 4
Acquisition Rate and Rewet for Representative Reticulated Absorbent
Composites
[0174] In this example, the acquisition time and rewet of
representative reticulated absorbent composites formed in
accordance with the present invention (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.
[0175] Certain properties of the tested composites, including the
amount of superabsorbent material (weight percent SAP) in the
composite and basis weight for each of the composites, are
summarized in Table 2.
[0176] The tests were conducted on commercially available diapers
(Kimberly-Clark) from which the cores were removed and used as
surrounds. The test diapers were prepared by inserting the tested
composites into the diapers.
[0177] The acquisition time and rewet are determined in accordance
with the multiple-dose rewet test described below.
[0178] 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.
[0179] The aqueous solution used in the tests was a synthetic urine
available from National Scientific under the trade name RICCA, and
as described above in Example 1.
[0180] A preweighed sample of the absorbent structure was 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) was placed 4 inches
above the surface of the sample at the "X". Once the sample was
prepared, the test was conducted as follows. The sample was
flattened, nonwoven side up, onto a tabletop under the liquid
application funnel. The funnel was filled with a dose (100 mL) of
synthetic urine. A dosing ring ({fraction (5/32)} inch stainless
steel, 2 inch ID.times.3 inch height) was placed onto the "X"
marked on the samples. A first dose of synthetic urine was applied
within the dosing ring. Using a stopwatch, the liquid acquisition
time was recorded in seconds from the time the funnel valve was
opened until the liquid wicked into the product from the bottom of
the dosing ring. After a twenty-minute wait period, rewet was
determined. During the twenty-minute wait period after the first
dose was applied, a stack of filter papers (19-22 g, Whatman #3,
11.0 cm or equivalent, that had been exposed to room humidity for
minimum of 2 hours before testing) was weighed. The stack of
preweighed filter papers was placed on the center of the wetted
area. A cylindrical weight (8.9 cm diameter, 9.8 lb.) was placed on
top of these filter papers. After two minutes the weight was
removed, the filter papers were weighed and the weight change
recorded. The procedure was repeated two more times. A second dose
of synthetic urine was added to the diaper, and the acquisition
time was determined, filter papers were placed on the sample for
two minutes, and the weight change determined. For the second dose,
the weight of the dry filter papers was 29-32 g, and for the third
dose, the weight of the filter papers was 39-42 g. The dry papers
from the prior dosage were supplemented with additional dry filter
papers.
[0181] 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.
[0182] 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 49.4 568 16 19 26
0.1 0.4 2.4 A2 38.3 648 17 19 22 0.1 0.7 2.5 A3 35.9 687 29 26 27
0.2 0.2 0.7 A4 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
[0183] As indicated in Table 2, the acquisition times for
representative composites formed in accordance with the invention
(Composites A1-A4) were significantly less than for the
commercially available core.
[0184] The rewet of the representative composites (Composites
A1-A4) is significantly less than for the other cores. While 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 5
Horizontal and Vertical Wicking for a Representative Reticulated
Absorbent Composite
[0185] In this example, the wicking characteristics of a
representative reticulated absorbent composite (Composite A) are
compared to a commercially available diaper storage core (Diaper B,
Procter & Gamble).
[0186] The horizontal wicking test measures the time required for
liquid to horizontally wick preselected distances. The test was
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) was cut from a pulp
sheet or other source. If the sheet has a machine direction, the
cut was made such that the 40 cm length of the strip was parallel
to the machine direction. Starting at one end of the 10 cm width of
the strip, a first line was marked at 4.5 cm from the strip edge
and then consecutive lines at 5 cm intervals were marked 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). A horizontal wicking apparatus having a
center trough with level horizontal wings extending away from
opposing sides of the trough was prepared. The nonsupported edge of
each wing was positioned to be flush with the inside edge of the
trough. On each wing's end was placed a plastic extension to
support each wing in a level and horizontal position. The trough
was then filled with synthetic urine. The sample composite strip
was then gently bent at the 4.5 cm mark to form an approximately
45.degree. angle in the strip. The strip was then placed on the
wing such that the strip lay horizontally and the bent end of the
strip extended into and contacted the liquid in the trough. Liquid
wicking was timed beginning from when the liquid reached the first
line marked on the composite 5 cm from the 4.5 cm bend. The wicking
time was then recorded at 5 cm intervals when 50 percent of the
liquid front reached the marked interval (e.g., 5 cm, 10 cm). The
liquid level in the trough was maintained 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) Diaper B Composite A 5 48 15 10 150 52 15 290 134 20 458 285
25 783 540 30 1703 1117 35 -- 1425
[0187] The results tabulated above indicate that horizontal wicking
is enhanced for the absorbent composite formed in accordance with
the invention compared to a conventional air-laid core. The wicking
time for Composite A is about 50 percent of that for the
conventional diaper core. Thus, the horizontal wicking for
Composite A is about 1.5 to about 3 times that of a commercially
available storage core.
[0188] The vertical wicking test measures the time required for
liquid to vertically wick preselected distances. The test was
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) were cut and marked
with consecutive lines 1 cm, 11 cm, 16 cm, and 21 cm from one of
the strip's edges. Preferably, samples were preconditioned for 12
hours at 50 percent relative humidity and 23.degree. C. and then
stored in sample bags until testing. The sample composite was
oriented lengthwise vertically and clamped from its top edge at the
1 cm mark, allowing its bottom edge to contact a bath containing
synthetic urine. Timing was commenced once the strip was contacted
with the liquid. The time required for 5 percent of the wicking
front to reach 5 cm, 10 cm, 15 cm, and 20 cm was then recorded. The
vertical wicking results are summarized in Table 4.
4TABLE 4 Vertical Wicking Comparison Wicking Time Distance (sec)
(cm) Diaper B Composite A 5 20 6 10 Fell Apart 54 15 -- 513 20 --
3780
[0189] As for the horizontal wicking results, Composite A had
significantly greater vertical wicking compared to the commercial
core. The results also show that the composite formed in accordance
with the invention has significantly greater wet tensile strength
compared to the conventional air-laid composite.
Example 6
Liquid Distribution for a Representative Reticulated Absorbent
Composite
[0190] In this example, the distribution of liquid in a reticulated
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).
[0191] 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 4. 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.
[0192] The liquid distribution results for a representative
reticulated absorbent composite 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 reticulated absorbent
storage core.
Example 7
Wet and Dry Tensile Strength for a Reticulated Absorbent
Composite
[0193] In this example, the measurement of wet and dry tensile
strength of a representative absorbent composite is described.
[0194] A dry pad tensile integrity test is performed on a 4 inch by
4 inch square test pad by clamping a dry test pad along two
opposing sides. About 3 inches of pad length is left visible
between the clamps. The sample is pulled vertically in an Instron
testing machine and the tensile strength measured is reported in
N/m. The tensile strength is converted to tensile index, Nm/g, by
dividing the tensile strength by the basis weight g/m.sup.2.
[0195] A wet tensile integrity test is performed by taking a sample
composite that has been immersed in synthetic urine for 10 minutes
and then allowed to drain for 5 minutes and placing the sample in a
horizontal jig. Opposite ends of the sample are clamped and then
pulled horizontally on the Instron testing machine. The wet tensile
strength, N/m, is converted to tensile index, Nm/g, by dividing the
tensile strength by the basis weight g/m.sup.2.
[0196] Typically, increasing the amount of Kymene.RTM. from 2 to
100 pounds per ton of fiber may increase the dry tensile strength
from about 0.15 Nm/g to 0.66 Nm/g and the wet tensile from about
1.5 Nm/g to about 2.4 Nm/g.
Example 8
Taber Stiffness for Representative Reticulated Absorbent
Composites
[0197] The stiffness of representative reticulated absorbent
composites formed in accordance with the present invention was
determined by the Taber Stiffness method. Representative composites
were formed by wet-laid and foam methods. These composites included
matrix fibers (48 percent by weight, southern pine commercially
available from Weyerhaeuser Co. under the designation NB416),
resilient fibers (12 percent by weight, polymaleic acid crosslinked
fibers), and absorbent material (40 percent by weight,
superabsorbent material commercially available from Stockhausen).
One of the wet-laid and one of the foam-formed composites further
included a wet strength agent (about 0.5 percent by weight,
polyamide-epichlorohydrin resin commercially available from
Hercules under the designation Kymene.RTM..
[0198] The stiffness of the foam-formed composites was
significantly lower than the similarly constituted wet-laid
composites. The results also indicate that, for the wet-laid
composites, the inclusion of a wet strength agent increases the
composite's stiffness.
Example 9
Reticulated Absorbent Composite Formation: Representative Wet-laid
Method
[0199] This example illustrates a representative wet-laid method
for forming a reticulated composite using a Rotoformer papermaking
machine.
[0200] Briefly, slurries of absorbent material and fibers in water
were introduced into the Rotoformer's headbox. The fibrous slurry
was introduced to the headbox in the conventional manner. The
absorbent slurry was introduced through the use of a dispersion
unit consisting of a set of spargers. The spargers were fed from a
header fed by the absorbent slurry supply. The dispersion unit is
mounted on the Rotoformer headbox with the spargers inserted into
the headbox fiber stock such that the flow of the absorbent slurry
is against the fiber stock flow. Such a reversed flow for the
absorbent slurry is believed to provide more effective mixing of
the absorbent material and the fibers than would occur for
absorbent material flow in the same direction as the fiber
stock.
[0201] Absorbent material is introduced into the Rotoformer headbox
as a slurry in water. One method that provides suitable results for
introducing absorbent material into the headbox is a mixing system
that includes a funnel attached directly to the inlet of a pump
into which chilled water is fed at a controlled rate. The funnel
receives water and dry absorbent material delivered from absorbent
material supply by auger metering and forms a pond that contains
absorbent material and water. The absorbent slurry is preferably
pumped from the funnel to the headbox at approximately the same
rate as water is delivered to the funnel. Such a system minimizes
the exposure of the absorbent to the water. In practice, the
absorbent slurry is delivered from the mixing system to the headbox
through a 10 to 50 foot conduit in less than about 10 seconds.
[0202] In a typical formation run, fiber stock flow to the
Rotoformer headbox was about 90 gpm (gallon/min) and absorbent
slurry (1-2.6% solids) flow was about 10 gpm. Prior to initiation
of fiber stock flow to the headbox and the introduction of
absorbent slurry to the dispersion unit, water was flowed into the
dispersion unit to the headbox to prevent fibers from plugging the
spargers. Once the target basis weight of fiber was reached, the
absorbent auger metering system was initiated and absorbent slurry
was introduced into the headbox. For the runs made in accordance
with the method described above, the target fiber basis weight was
about 370 gsm (g/m.sup.2) and the production speed was about 10 fpm
(ft/min). The relatively slow production speed was a consequence of
the relatively limited drying capability of the machine's flatbed
dryer.
[0203] The headbox contents including fibers and absorbent were
deposited on a forming wire and dewatered to provide a wet
composite. The wet composite was then dried to a moisture content
of from about 9 to about 15 weight percent based on total composite
weight to form a representative reticulated absorbent
composite.
[0204] Absorbent composites having a variety of basis weights can
be prepared from the composite formed as described above by pre- or
post-drying densification methods known to those in the art.
[0205] Examples 10-15 illustrate the formation of representative
reticulated absorbent composites using the method described
above.
Example 10
[0206] A representative composite was formed as described in
Example 9. The composite included about 60% by weight fibers and
about 40% by weight absorbent material based on the total weight of
composite. The fiber stock was a mixture of 80% by weight standard
wood pulp fibers (once-dried southern pine commercially available
from Weyerhaeuser Company under the designation FR416) and 20% by
weight crosslinked pulp fibers. The absorbent material was a
crosslinked polyacrylate commercially available from Stockhausen
under the designation SXM 77, which was screened using 300 micron
mesh to eliminate fines prior to use. The composite also included
about 25 pounds wet strength agent (a
polyacrylamide-epichlorohydrin resin commercially available from
Hercules under the designation Kymene.RTM. 557LX) per ton of
fibers.
[0207] Target density of the absorbent composite was accomplished
by calendering using a single nip with no applied load.
[0208] Performance data for the representative composite formed as
described above (Composite B) is presented in Tables 5 and 6 in
Example 16.
Example 11
[0209] A representative composite was formed as described in
Example 10 except that the composite was calendered at 25 fpm.
[0210] Performance data for the representative composite formed as
described above (Composite C) is presented in Tables 5 and 6 in
Example 16.
Example 12
[0211] A representative composite was formed as described in
Example 11 except that the amount of wet strength agent in the
composite was reduced to 12.5 pounds per ton fiber and the standard
wood pulp fibers were never-dried FR416 fibers.
[0212] Performance data for the representative composite formed as
described above (Composite D) is presented in Tables 5 and 6 in
Example 16.
Example 13
[0213] A representative composite was formed as described in
Example 12 except that the composite was not densified.
[0214] Performance data for the representative composite formed as
described above (Composite E) is presented in Tables 5 and 6 in
Example 16.
Example 14
[0215] A representative composite was formed as described in
Example 12 except that the wood pulp fibers were once-dried FR416
fibers.
[0216] Performance data for the representative composite formed as
described above (Composite F) is presented in Tables 5 and 6 in
Example 16.
Example 15
[0217] A representative composite was formed as described in
Example 12 except that the amount of fibers in the composite was
increased to about 80% by weight and the amount of absorbent
present in the composite was decreased to about 20% by weight of
the total composite.
[0218] Performance data for the representative composite formed as
described above (Composite G) is presented in Tables 5 and 6 in
Example 16.
Example 16
[0219] The performance of representative composites (Composites
B-D) prepared as described in Examples 10-15 is summarized in
Tables 5 and 6. The liquid wicking, absorbent capacity, wet and dry
tensile strength, and wet strength of the representative composites
are compared to a conventional handsheet in Table 5. The
conventional handsheet had a basis weight and density comparable to
the representative composites and included 60 percent by weight
fibers (25 percent crosslinked fibers and 75 percent standard wood
pulp fibers), 40 percent by weight superabsorbent material, and
12.5 pounds Kymene per ton fibers. The results presented in Table 5
are the average of three measurements except for the tensile
values, which average four measurements. In the table, "MD" refers
to the composites' machine direction and "CD" refers to the
cross-machine direction. The wicking values were obtained by the
methods described in Example 5 and the wet and dry tensile values
were obtained by the method described in Example 7. The wet
strength value was calculated and is defined as the ratio of wet
tensile to dry tensile values. The mass flow rate value (g/min/g)
was determined by measuring the weight gain of a portion of a
composite (22 cm.times.5 cm) divided by the lesser of the time
required for the liquid to wick 15 cm or 15 minutes, divided by the
weight of the original sample.
5TABLE 5 Performance Characteristics Wicking Final Capacity Time
Wick 5 Min. Mass 15 Minute Wet Time to to 15 (cm) (45 (Vert.) Flow
Free Wet Tensile Dry Tensile Strength 10 cm cm min Cap. Rate Swell
MD CD MD CD MD CD Composite (sec) (sec) max) (g/g) (g/min/g) Cap.
(g/g) (g/in) (g/in) (g/in) (g/in) (%) (%) B 45 234 23 7.6 1.9 20
1585 1222 >4800 4385 <32 28 C 47 221 24 8.3 2.3 19 1317 1241
>4800 4277 <27 29 D 59 >400 18 9.3 <1.4 24 673 488 2940
2455 23 20 E 160 >400 19 9.4 <1.4 22 1091 764 >4800 3771
<23 20 F 38 144 25 7.7 3.2 15 1654 1291 >5200 5100 <31
<25 G 52 245 22 8.4 2.1 20 1686 980 >5200 4800 <32 <21
handsheet 159 >300 16 10.9 2.2 31 226
[0220] The absorbent capacity of several of the representative
composites is summarized in Table 6. In this capacity test,
portions of the representative composites (i.e., 10 cm squares)
were immersed in a 1% saline solution. The samples were allowed to
absorb liquid and swell for 10 minutes. The difference in the
weight of the composite before and after the 10 minute swell is the
capacity that is reported as cc/g.
6TABLE 6 Absorbent capacity Composite Capacity (cc/g) B 16.9 C 16.9
D 20.4 B 21.5
Example 17
Method for Determining Fluid Wicking for Representative
Composites
[0221] The absorbent properties of representative composites can be
determined by measuring unrestrained vertical wicking height, which
is indicative of the composite's ability to wick and distribute
fluid.
[0222] Unrestrained vertical wicking height at 15 minutes was
measured for representative composites as described below.
[0223] Material:
[0224] Synthetic urine for wicking--"Blood Bank" 0.9% Saline
Solution
[0225] Samples:
[0226] Size: 6.5 cm(CD).times.25 cm(MD), marked with both permanent
and water permeable lines at 1, 11, 16, and 21 cm along MD.
[0227] Method:
[0228] 1) Perform % Solids on sample material and record.
[0229] 2) Cut Sample and record (as is) weight and dry caliper.
[0230] 3) Clamp sample at 1 cm from top.
[0231] 4) Dip into liquid up to the 1 cm line.
[0232] 5) Immediately start timing.
[0233] 6) At the end of 5, 10, and 15 minutes, record the Wicking
Height by measuring down from the next highest line. Report the
wicking height to the nearest 0.5 cm.
[0234] 7) At 15 minutes raise sample out of fluid and while still
clamped, cut sample at the 1 cm and 15 cm height lines. Discard the
1 cm section.
[0235] 8) Weigh wet 15 cm long sample and record.
[0236] 9) Unclamp remaining sample and add to balance in order to
record entire pad wet weight.
[0237] 10) Report Total Wick Height at 15 minutes.
[0238] 11) Report As-is and O.D. basis Entire Pad Capacity(g/g) by
calculating: 1 Entire Pad Capacity ( g / g ) = Wet Wt . - ( As Is
or O . D . Wt . ) * As - Is or O . D . Wt . *
[0239] 15) Calculate the Wicked Pad Capacity if needed: 2 Wicked
Pad Capacity = Entire Pad Capacity .times. 24 Wicking Ht at 15
min
[0240] Unrestrained vertical wicking height for representative
composites is described in the following examples.
Example 18
Performance Characteristics of Representative Composites Having
Fibrous Bands
[0241] The performance characteristics of representative composites
prepared as described above are summarized in Table 7. The
unrestrained vertical wicking height and total fluid absorbed at 30
minutes and the uptake rate and flux at 12 cm are compared for
composites formed in accordance with the present invention and for
commercially available air-laid cores. In Table 7, Composite I is a
reticulated absorbent composite formed in accordance with the
present invention having a composition that includes about 58% by
weight absorbent material, 32% by weight crosslinked fibers, and 8%
by weight matrix fibers based on the total weight of the
composition. Composites J and K are composites that include two
fibrous bands. For these composites, the fibrous matrix included
69% by weight absorbent material, 24% by weight crosslinked fibers,
and 6% by weight matrix fibers based on the total weight of the
matrix. Composite J had fibrous bands composed of crosslinked and
matrix fibers in which the ratio of crosslinked to matrix fibers
was 1:4. Composite K had a crosslinked to matrix fiber ratio of
1:1.
7TABLE 7 Representative Composite Unrestrained Vertical Wicking
Parameters Unrestrained Vertical Wicking Total Fluid Uptake Rate
Flux Composite Height (cm) Absorbed (g) (g/g/min) (g/cm.sup.2/min)
I 12.3 47.2 1.0 2.2 J 15.5 49.0 2.5 5.7 K 15.6 52.0 3.0 5.8 Airlaid
core 7.5* 27.5* -- -- *integrity loss after 6 min.
[0242] As shown in Table 7, composites formed in accordance with
the present invention vastly outperformed the commercially
available airlaid core. Composites J and K, which included fibrous
bands, had liquid wicking and distribution characteristics that
were enhanced compared to Composite I, a composite lacking the
fibrous bands.
Example 19
Performance Characteristics of a Representative Composite Having
Two Fibrous Bands
[0243] The performance characteristics for a representative
composite having two fibrous bands (Composite L) were compared to a
similarly constituted composite lacking fibrous bands (Control).
The control composite had a basis weight of 700 gsm and included 50
percent by weight superabsorbent material; 25 percent by weight
crosslinked cellulosic fibers; 25 percent by weight fluff pulp
fibers (refined southern pine) based on the total weight of the
composite. The composite having fibrous bands was constructed from
the control composite and fibrous strips. The components were
adhered together to provide the composite (see, for example, FIG.
31). The composite had a length of 25 cm, width 5 cm, and included
two fibrous strips having a width of 0.75 cm.
[0244] Wicking height at 15 minutes, capacity at 15 cm, and wetted
zone capacity for the composites are compared graphically in FIG.
32. As shown in FIG. 32, wicking height and capacity at 15 minutes
for the Composite L were increased relative to the control
composite.
[0245] The properties and characteristics of Composite L and the
control are summarized in Table 8.
8TABLE 8 Unrestrained Vertical Wicking Performance. Wet Total Zone
Basis Fluid (g/g) 15 cm Height Com- Weight Density Bulk Wicked cap
g/g at 15 posite (gsm) (g/cm.sup.3) (cm.sup.3/g) (g) OD cap OD min.
Control 700 0.144 6.93 80.90 17.16 11.80 10.4 L 810 0.165 6.05
120.37 16.63 14.58 13.8
Example 20
Method for Determining Flexibility and Softness for Representative
Composites
[0246] Composite flexibility and softness are factors for
determining the suitability of composites for incorporation into
personal care absorbent products. Composite flexibility can be
indicated by composite edgewise ring crush, which is a measure of
the force required to compress the composite as described below.
For a composite to be incorporated into a personal care absorbent
product, suitable ring crush values range from about 400 to about
1600 gram/inch. Composite softness can be indicated by a variety of
parameters including composite edgewise compression. Edgewise
compression (EC) is the force required to compress the composite
corrected by the composite's basis weight as described below. For a
composite to be suitably incorporated into a personal care
absorbent product, the composite has a ring crush value in the
range from about 400-1600 g and a basis weight in the range from
about 250 to about 650 gsm.
[0247] The flexibility and softness of representative reticulated
absorbent composites formed by wetlaid and foam-forming methods in
accordance with the present invention were determined by measuring
composite edgewise ring crush and edgewise compression.
[0248] The flexibility and softness of representative composites
was determined by an edgewise ring crush method. In the method, a
length of the composite (typically about 12 inches) is formed into
a cylinder and its ends stapled together to provide cylinder having
a height equal to the composite's width (typically about 2.5
inches). Edgewise ring crush is measured by adding mass to the top
of the composite ring sufficient to reduce the composite cylinder's
height by one-half. The more flexible the composite, the less
weight required to reduce the height in the measurement. The
edgewise ring crush is measured and reported as a mass (g).
Edgewise compression (EC) is the ring crush reported in units of
g/gsm in the tables below.
[0249] The following is a description of the ring crush method.
[0250] Samples: 6.35 cm (2.5 in).times.30.5 cm (12 in) Triplicate
analysis (A, B, C)
[0251] Method:
[0252] 1) Cut triplicate of sample size, lengthwise in the
composite machine direction (MD).
[0253] 2) Condition samples for 2 hours at 50% relative humidity or
ambient conditions.
[0254] 3) With the wire side on the outside, form the individual
samples into loops so the two narrow ends meet without any overlap.
Using four staples, attached the ends together at the top, bottom,
and twice in the middle. The top and bottom staples should be
0.3-0.5 cm from the edge and the middle staples should be less than
2 cm from each other and the respective top or bottom staple.
Finally, ensure that each staple penetrates fiber only areas.
[0255] 4) Set the bottom platen on a smooth, level surface.
[0256] 5) Place the sample, edgewise and in the center, between the
top and bottom platens.
[0257] 6) Gently place a 100-g weight on the center of the top
platen (or 500-weight) and wait 3 seconds.
[0258] 7) Then, gently stack 3 more 100-g weights at 3-second
intervals.
[0259] 8) If the ring collapses 50% or more of it's original height
within a 3-second interval, then record the total amount of weight
necessary to do so, i.e., add the weight of the top platen and the
other combined weights.
[0260] 9) If the combined weight doesn't crush the sample, then
carefully remove the four 100-g weights.
[0261] 10) Gently add a(nother) 500-g weight and weight 3
seconds.
[0262] 11) If the ring collapses 50% or more of it's original
height within a 3-second interval, then record the total amount of
weight necessary to do so, i.e., add the weight of the top platen
and weight(s).
[0263] 12) Repeat step 6 through 11, increasing the number of 500-g
weights by one for each cycle.
[0264] 13) Repeat steps 5 through 11 for the other replicates.
[0265] 14) Record the average weight for the replicates in
g.multidot.f rounded to the nearest 10 g.
[0266] Calculations:
Average ring crush weight=(Weight A+Weight B+Weight C)/3
[0267] The ring crush values determined as described above for
representative composites formed in accordance with the present
invention are summarized in Example 21.
[0268] The softness of representative reticulated absorbent
composites formed in accordance with the present invention can be
indicated by edgewise compression. Edgewise compression is
discussed in The Handbook of Physical and Mechanical Testing of
Paper and Paperboard, Richard E. Mark, Dekker 1983 (Vol. 1).
Edgewise compression was determined by correcting edgewise ring
crush, determined as described above, for composite basis weight.
The edgewise compression (EC) values for representative composites
formed in accordance with the present invention are summarized in
Example 21.
Example 21
Performance Characteristics of Representative Foam-Formed
Composites Having Fibrous Bands
[0269] The performance characteristics of representative
foam-formed composites having fibrous bands (Composites M, N, O)
were compared to similarly constituted foam-formed composites
lacking fibrous bands (Control A and B). The composites were
prepared on a twin-wire former as described above.
[0270] Fluff pulp fibers for the composites were unrefined softwood
fibers (southern pine, 745 CSF), and refined fibers were refined
softwood (southern pine, 200 CSF). The superabsorbent polymer was a
lightly crosslinked polyacrylate (SR1001). All composites included
a wet strength agent (KYMENE), 0.45 percent by weight based on the
total weight of the composite.
[0271] Control A included 58 percent by weight superabsorbent
material and 42 percent by weight fibrous material based on the
total weight of the composite. The fibrous material included 67
percent by weight crosslinked fibers and 33 percent by weight fluff
pulp fibers based on the total weight of fibers.
[0272] Control B included 50 percent by weight superabsorbent
material and 50 percent by weight fibrous material based on the
total weight of the composite. The fibrous material included 67
percent by weight crosslinked fibers and 33 percent by weight fluff
pulp fibers based on the total weight of fibers. Control B further
included the fibrous material making up the fibrous bands in
Composites M, N, and O.
[0273] Composites M-O included two fibrous bands (50 gsm) in a
fibrous base. The fibrous base included 50 percent by weight
superabsorbent material and 50 percent by weight fibrous material
based on the total weight of the composite. The fibrous material
include 67 percent by weight crosslinked fibers and 33 percent by
weight fluff pulp fibers based on the total weight of fibers.
[0274] For Composite M, the fibrous bands included 50 percent by
weight crosslinked fibers and 50 percent by weight refined fibers
based on the total weight of fibers in the bands.
[0275] For Composite N, the fibrous bands included 80 percent by
weight crosslinked fibers and 20 percent by weight refined fibers
based on the total weight of fibers in the bands.
[0276] For Composite O, the fibrous bands included 50 percent by
weight crosslinked fibers and 50 percent by weight fluff pulp
fibers based on the total weight of fibers in the bands.
[0277] The saturation capacity (Sat Cap), unrestrained vertical
wicking (URVW) height, ring crush, and tensile of Controls A and B
and Composites M, N, and O are summarized in Table 9.
9TABLE 9 Representative Composite Characteristics. Sat Cap URVW
Height Ring Crush Tensile Composite (g/g) OD at 15 min. (g)
(g/inch) Control A 19.65 9.75 350.00 258.50 Control B 19.25 10.00
500.00 310.20 M 17.36 14.50 900.00 1008.15 N 20.87 14.00 600.00
1861.20 O 19.20 14.50 675.00 878.90
[0278] As shown in Table 9, wicking for the composites having
fibrous bands is increased compared to the control composites. The
fibrous bands also enhance composite tensile significantly.
[0279] Ring crush and tensile strength for control and
representative composites are correlated graphically in FIG. 33. As
shown in FIG. 33, ring crush increases dramatically with increasing
tensile strength for the control composite. In contrast, ring crush
remains substantially constant with increasing tensile strength for
the representative composite having fibrous bands. This correlation
demonstrates that higher tensile strengths can be achieved in these
composites without significantly increasing ring crush (i.e.,
decreasing softness).
[0280] Unrestrained vertical wicking height and saturation capacity
for control and representative composites are correlated
graphically in FIG. 34. As shown in FIG. 34, wicking decreases
dramatically with increasing saturation capacity for the control
composite. In contrast, wicking remains substantially constant with
increasing saturation capacity for the representative composite
having fibrous bands. This correlation demonstrates that greater
wicking and fluid distribution can be achieved for these composites
without decreasing saturation capacity.
[0281] Ring crush and tensile strength for control and
representative composites are compared graphically in FIG. 35.
Composites M, N, and O all show increased tensile compared to the
controls.
[0282] Unrestrained vertical wicking height and saturation capacity
for control and representative composites are compared graphically
in FIG. 36. Composites M, N, and O all show increased wicking
compared to the controls.
[0283] 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 this invention.
* * * * *