U.S. patent application number 10/526004 was filed with the patent office on 2006-02-23 for core for absorbent articles and method of making the same.
Invention is credited to Frank S. Glaug, Donald A. Sheldon.
Application Number | 20060040579 10/526004 |
Document ID | / |
Family ID | 31946961 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060040579 |
Kind Code |
A1 |
Sheldon; Donald A. ; et
al. |
February 23, 2006 |
Core for absorbent articles and method of making the same
Abstract
An absorbent core is provided for use in an absorbent article.
The core includes a plurality of substantially continuous and
coextensive filaments. At least some of the filaments have disposed
on a surface thereof a layer comprising a superabsorbent material
formed in place on the surface from a liquid superabsorbent
polymer.
Inventors: |
Sheldon; Donald A.;
(Downingtown, PA) ; Glaug; Frank S.; (Chester
Springs, PA) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
31946961 |
Appl. No.: |
10/526004 |
Filed: |
August 25, 2003 |
PCT Filed: |
August 25, 2003 |
PCT NO: |
PCT/US03/26563 |
371 Date: |
February 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60406123 |
Aug 26, 2002 |
|
|
|
Current U.S.
Class: |
442/366 ;
442/327; 442/417 |
Current CPC
Class: |
A61F 13/53 20130101;
A61F 2013/530489 20130101; Y10T 442/643 20150401; A61F 13/538
20130101; A61F 13/531 20130101; Y10T 442/60 20150401; Y10T 442/699
20150401 |
Class at
Publication: |
442/366 ;
442/327; 442/417 |
International
Class: |
D04H 13/00 20060101
D04H013/00; D04H 3/05 20060101 D04H003/05; D04H 1/00 20060101
D04H001/00 |
Claims
1. An absorbent core for use in an absorbent article, the core
comprising a plurality of substantially continuous and coextensive
filaments, at least some of the filaments having disposed on a
surface thereof a layer comprising a superabsorbent material formed
in place on the surface from a liquid superabsorbent polymer.
2. The absorbent core of claim 1, wherein the filaments are
selected from the group consisting of RAYON, cellulose acetate,
polypropylene, polyethylene, polyethylene terephthalate, and
sheath-core bi-component filaments, and combinations thereof.
3. The absorbent core of claim 1, wherein at least some of the
filaments comprise cellulose acetate.
4. The absorbent core of claim 1, wherein the surface of at least
some of the filaments is hydrophilized.
5. The absorbent core of claim 1, wherein substantially all of the
filaments have disposed on said surface thereof said layer
comprising the superabsorbent material.
6. The absorbent core of claim 1, wherein the core comprises two or
more adjacent and coextensive strata, wherein one stratum comprises
filaments having disposed on said surface thereof said layer
comprising the superabsorbent material, and another stratum is
substantially free of superabsorbent material.
7. The absorbent core of claim 6, wherein the another stratum
comprises a surfactant disposed on the surface of at least some of
the filaments.
8. The absorbent article of claim 1, wherein the liquid
superabsorbent material is selected from the group consisting of
one or more superabsorbent polymers at least partially dissolved in
a liquid carrier, a solution in a liquid carrier of one or more
superabsorbent precursors, and a combination of one or more
superabsorbent polymers and superabsorbent precursors.
9. The absorbent core of claim 1, wherein the core has two opposing
sides and the superabsorbent material is disposed in a pattern on
one or both of the opposing sides.
10. The absorbent core of claim 1 further comprising pulp fibers
Interspersed between at least some of the filaments.
11. The absorbent core of claim 1 further comprising superabsorbent
polymer particles interspersed among at least some of the
filaments.
12. A method of making an absorbent core for use in an absorbent
article, the method comprising: a) expanding a tow comprising a
plurality of substantially continuous and coextensive filaments,
each filament having a surface; and b) forming, from a liquid
superabsorbent polymer, a layer comprising a superabsorbent
material on the surface of at least some of the filaments.
13. The method of claim 12 wherein the forming step comprises:
applying to the expanded tow the liquid superabsorbent polymer to
form a treated expanded tow comprising a liquid superabsorbent
polymer coating; and curing the treated expanded tow to form the
layer comprising the superabsorbent material.
14. The method of claim 13 wherein the applying step comprises:
immersing the expanded tow in a bath comprising the liquid
superabsorbent polymer; removing the expanded tow from the bath;
and removing a portion of the liquid superabsorbent polymer
coating.
15. The method of claim 13 wherein the applying step comprises
spraying the liquid superabsorbent polymer on at least one surface
of the expanded tow.
16. The method of claim 13 wherein the curing step comprises
exposing the treated expanded tow to heat.
17. The method of claim 13 wherein the curing step comprises
exposing the treated expanded tow to radiation.
18. The method of claim 12, wherein the core has two opposing
sides, and wherein the forming step comprises patternwise spraying
the liquid superabsorbent polymer on one or both of the sides.
19. The method of claim 12, wherein the core has two opposing
sides, and wherein the forming step comprises spraying the liquid
superabsorbent polymer on one of the sides, the method further
comprising applying a surfactant to at least some of the filaments
on the other side.
20. The method of claim 12 further comprising partially separating
the filaments to form the expanded tow.
21. The method of claim 20 wherein the step of partially separating
comprises blowing the tow with jets of air.
22. The method of claim 12 further comprising at least partially
flattening the tow.
23. The method of claim 12 further comprising interspersing pulp
fibers between at least some of the filaments.
24. The method of claim 12 further comprising interspersing
superabsorbent polymer particles between at least some of the
filaments.
25. The method of claim 12 further comprising hydrophilizing at
least some of the filaments.
26. The method of claim 12 wherein the forming step comprises
forming a layer on substantially all of the filaments.
27. The method of claim 12 further comprising, after the forming
step, removing one or both of water and residual volatile reactants
from the formed layer.
28. The method of claim 12 further comprising, after the forming
step, tenderizing the filaments having thereon said layer
comprising the superabsorbent material.
29. A system for making an absorbent core for use in an absorbent
article, the system comprising: a) means for applying a liquid
superabsorbent polymer to a tow comprising a plurality of
substantially continuous and coextensive filaments, thereby forming
a treated expanded tow comprising a liquid superabsorbent polymer
coating on the surface of at least some of the filaments; and b)
means for forming, from the liquid superabsorbent polymer coating,
a layer comprising a superabsorbent material on said surface of
said at least some of the filaments.
30. The system of claim 29, wherein the means for applying
comprises a bath.
31. The system of claim 29, wherein the means for applying
comprises a spray nozzle.
32. The system of claim 29, wherein the core comprises two opposing
sides, and wherein the means for applying comprises a spray nozzle
configured to apply the liquid superabsorbent polymer on one or
both of the sides in a pattern.
33. The system of claim 29, wherein the core comprises two opposing
sides, the system further comprising means for applying a
surfactant to the expanded tow.
34. The system of claim 29, wherein the means for forming comprises
a heater.
35. The system of claim 29, wherein the means for forming comprises
a radiation source.
36. The system of claim 29 further comprising means for removing a
portion of the liquid superabsorbent polymer coating.
37. The system of claim 29 further comprising means for
interspersing pulp fibers between at least some of the
filaments.
38. The system of claim 29 further comprising means for
interspersing superabsorbent polymer particles between at least
some of the filaments.
39. The system of claim 29 further comprising means for flattening
the tow.
40. The system of claim 29 further comprising means for partially
separating filaments of the tow, thereby forming the expanded
tow
41. The system of claim 40 wherein the means for partially
separating comprises a source of air positioned to direct jets of
air toward the tow.
42. The system of claim 29 further comprising means for removing
one or both of water and residual volatile reactants from the
formed layer.
43. The system of claim 29 further comprising means for tenderizing
the filaments having thereon a layer comprising a superabsorbent
material.
Description
FIELD OF THE INVENTION
[0001] This invention relates to absorbent articles. More
particularly, it relates to absorbent cores for absorbent articles
wherein the core comprises an expanded tow having on its surface a
superabsorbent polymer.
BACKGROUND OF THE INVENTION
[0002] The use of absorbent articles, such as protective
undergarments, has increased steadily for many years. Early uses,
such as diapers for babies and sanitary products for women, have in
recent years been joined by an increasing demand for products
designed to deal with incontinence issues for adults, frequently
brought on by advanced age, obesity, or a variety of medical
conditions. At the same time, markets have grown in all of these
areas for both disposable and reusable products, depending on the
preferences of the consumer.
[0003] Currently available absorbent articles usually include
superabsorbent polymers (SAP). These materials are capable of
absorbing a large quantity of body fluid, such as urine, blood, and
menses, and thus have become the standard for absorbent articles
for hygiene purposes.
[0004] One example of the use of SAP is described in U.S. Pat. No.
5,641,561 to Hansen et al. There are described absorbent composites
made of fibrous material (e.g. cellulosic or synthetic material)
and particulate superabsorbent polymers that are bound to the fiber
via hydrogen bonding binder molecules. Superabsorbent polymer
particles are mixed as particles with bleached kraft fluff, heated
and spread out to dry. The binder adheres the SAP particles to the
fibers. The dried product is then fed through a hammermill and
shunted to an airlay line to produce a web containing 40% SAP
particles attached to individual fibers.
[0005] U.S. Pat. No. 5,593,399 to Tanzer discloses an absorbent
article, namely a diaper, having two layers attached by an adhesive
to provide attached zones and unattached zones to form pocket
regions. Tanzer describes the use of SAP particles located within
the pocket regions of the article to provide an absorbent laminate.
The pocket regions are arranged in a non-contiguous and labyrinth
configuration.
[0006] There is an ever-increasing demand for thinner absorbent
articles that nonetheless have high fluid absorption capacity.
Unfortunately, some conventional absorbent articles tend to be
bulky.
[0007] Whitmore et al., in U.S. Pat. No. 6,417,425, describe
absorbent articles including an absorbent core and an acquisition
layer designed to afford rapid uptake of fluid, good transfer
properties, good uptake upon repeated insults with fluid, and good
skin compatibility. The acquisition layer, which also has absorbent
capabilities, is prepared by a process that includes spraying onto
a fibrous web a blend containing superabsorbent polymer particles,
superabsorbent-forming monomer, initiator and water, and subjecting
the web to polymerization conditions. In the '425 patent, there is
stated the belief that the absorbent structure performs well as an
acquisition layer in a disposable diaper because the swelling of
the superabsorbent polymer particles is capable of expanding the
fibrous web, so that the interstitial pore volume of the web
increases after an insult of liquid.
[0008] Despite the foregoing developments, however, there remains a
need for improved absorbent articles.
SUMMARY OF THE INVENTION
[0009] According to one aspect of the invention, an absorbent core
is provided for use in an absorbent article. The core includes a
plurality of substantially continuous and coextensive filaments, at
least some of the filaments having disposed on a surface thereof a
layer comprising a superabsorbent material formed in place on the
surface from a liquid superabsorbent polymer.
[0010] According to another aspect of the invention, a method of
making an absorbent core for use in an absorbent article is
provided. The method includes expanding a tow comprising a
plurality of substantially continuous and coextensive filaments,
each filament having a surface. The method also includes forming,
from a liquid superabsorbent polymer, a layer comprising a
superabsorbent material on the surface of at least some of the
filaments.
[0011] According to yet another aspect of the invention, a system
is provided for making an absorbent core for use in an absorbent
article. The system includes means for applying a liquid
superabsorbent polymer to a tow comprising a plurality of
substantially continuous and coextensive filaments, thereby forming
a treated expanded tow comprising a liquid superabsorbent polymer
coating on the surface of at least some of the filaments. Means is
provided for forming, from the liquid superabsorbent polymer
coating, a layer comprising a superabsorbent material on the
surface of at least some of the filaments.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 is a side view of an embodiment of a tow material
configured to form a component of an absorbent core according to an
aspect of this invention.
[0013] FIG. 2 is a side view of the tow material shown in FIG. 1
after it has been expanded according to an aspect of this
invention.
[0014] FIG. 3 is a side view of the expanded tow material shown in
FIG. 2 with treated and untreated filaments.
[0015] FIG. 4 is a schematic representation of an embodiment of a
system for forming an absorbent core according to an aspect of this
invention.
[0016] FIG. 5 is a schematic representation of another embodiment
of a system for forming an absorbent core according to an aspect of
this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Although the invention is illustrated and described herein
with reference to specific embodiments, the invention is not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the
invention.
[0018] In one exemplary aspect, the invention provides an absorbent
core for use in an absorbent article. The core comprises a
plurality of filaments in the form of an expanded tow, and a layer
comprising a superabsorbent material on surfaces of the filaments.
In another exemplary aspect, the invention provides method of
making an absorbent core for use in an absorbent article. The
method includes providing a tow comprising a plurality of
filaments, partially separating the filaments to afford an expanded
tow, and providing a layer comprising a superabsorbent material on
surfaces of the filaments.
[0019] Absorbent cores according to one exemplary embodiment of the
invention may find particular utility in the preparation of
absorbent articles such as protective undergarments. These may
include, for example, protective underwear, training pants, adult
briefs, diapers, incontinence pads, and feminine hygiene pads. The
absorbent articles may be disposable, or the cores may be
disposable items removably incorporated in re-usable articles.
[0020] Absorbent cores according to one exemplary embodiment of the
invention are pulpless and therefore less bulky. In addition, the
use of expanded tow instead of pulp may advantageously afford a
softer, more flexible texture, providing a more cloth-like,
comfortable feel for the wearer.
[0021] The invention will next be illustrated with reference to the
figures, wherein the same numbers indicate the same elements in all
figures. Such figures are intended to be illustrative rather than
limiting and are included herewith to facilitate the explanation of
the present invention. The figures are not to scale, and are not
intended as engineering drawings.
[0022] Referring in general to FIGS. 1-5, an absorbent core 210 is
provided for use in an absorbent article. The core 10, 110, 210
includes a plurality of substantially continuous and coextensive
filaments 12, 112, 212, at least some of the filaments 218 having
disposed on a surface thereof a layer comprising a superabsorbent
material formed in place on the surface from a liquid
superabsorbent polymer.
[0023] The filaments 12, 112, 212 can be selected from RAYON,
cellulose acetate, polypropylene, polyethylene, polyethylene
terephthalate, and sheath-core bi-component filaments, for example,
and combinations thereof. At least some of the filaments 12, 112,
212 can include cellulose acetate, and the surface of at least some
of the filaments can be hydrophilized. Substantially all of the
filaments 218 optionally have disposed on the surface thereof the
layer comprising the superabsorbent material.
[0024] The absorbent core 210 optionally includes two or more
adjacent and coextensive strata, wherein one stratum includes
filaments 218 having disposed on the surface thereof the layer
comprising the superabsorbent material, and another stratum is
substantially free of superabsorbent material (e.g., filaments
212). The stratum that is substantially free of superabsorbent
material optionally includes a surfactant disposed on the surface
of at least some of the filaments.
[0025] Where the core 210 is provided with two opposing sides, the
superabsorbent material is optionally disposed in a pattern on one
or both of the opposing sides. The core 210 optionally includes
pulp fibers interspersed between at least some of the filaments 12,
112, 212, and superabsorbent polymer particles are optionally
interspersed among at least some of the filaments 12, 112, 212.
[0026] In an exemplary method of making an absorbent core 210 for
use in an absorbent article, tow 10 is expanded and a layer
comprising a superabsorbent material is formed on the surface of at
least some of the filaments 12, 112, 212.
[0027] The forming step is optionally performed by applying to the
expanded tow 110 the liquid superabsorbent polymer to form a
treated expanded tow comprising a liquid superabsorbent polymer
coating, followed by curing the treated expanded tow to form the
layer comprising the superabsorbent is material. The applying step
is optionally performed by immersing the expanded tow 110 in a bath
44 holding the liquid superabsorbent polymer, removing the expanded
tow 110 from the bath 44, and removing a portion of the liquid
superabsorbent polymer coating. The applying step alternatively
includes spraying liquid superabsorbent polymer on at least one
surface of the expanded tow 110. The curing step can be
accomplished by exposing the treated expanded tow to heat or to
radiation.
[0028] The step of forming a layer of superabsorbent material can
be completed by patternwise spraying liquid superabsorbent polymer
on one or both of the sides of the tow 110 or by spraying the
liquid superabsorbent polymer on one of the sides and applying a
surfactant to at least some of the filaments on the other side.
[0029] The filaments 12, 112, 212 can be partially separated to
form the expanded tow 110 by, for example, blowing the tow 10 with
jets of air. The tow can also be at least partially flattened.
After the layer-forming step, one or both of water and residual
volatile reactants can be removed from the formed layer. Also, the
filaments can be tenderized.
[0030] Pulp fibers and/or superabsorbent polymer particles are
optionally interspersed between at least some of the filaments 12,
112, 212, and at least some of the filaments 12, 112, 212 can be
hydrophilized. The forming step optionally includes forming a layer
on selected filaments 218 or on substantially all of the
filaments.
[0031] According to yet another aspect of the invention, a system
is provided for making an absorbent core 210 for use in an
absorbent article. The system includes means, such as a bath 44 or
a spray nozzle 50, 52, for applying a liquid superabsorbent polymer
to a tow 10 comprising a plurality of substantially continuous and
coextensive filaments 12, 112, 212, thereby forming a treated
expanded tow comprising a liquid superabsorbent polymer coating on
the surface of at least some of the filaments. Means 46, such as a
heater or radiation source, is provided for forming, from the
liquid superabsorbent polymer coating, a layer comprising a
superabsorbent material on the surface of at least some of the
filaments.
[0032] Where the core includes two opposing sides, and the means
for applying optionally includes a spray nozzle 50, 52 configured
to apply the liquid superabsorbent polymer on one or both of the
sides in a pattern. Means can also be provided for applying a
surfactant to the expanded tow 110.
[0033] Means 45 are optionally provided for removing a portion of
the liquid superabsorbent polymer coating, for interspersing pulp
fibers between at least some of the filaments, for interspersing
superabsorbent polymer particles between at least some of the
filaments, for flattening the tow (e.g., fiber spreader 42), for
partially separating filaments of the tow (e.g., jets of air formed
by air jet 43), for removing one or both of water and residual
volatile reactants from the formed layer (e.g., dryer 47), and for
tenderizing the filaments (e.g., tenderizing unit 48).
[0034] Referring now to FIG. 1, there is shown a side cross section
view of tow, generally Indicated at 10, suitable for use in
practicing one exemplary aspect of the invention. The tow 10
comprises a plurality of filaments 12 that are substantially
continuous and coextensive. Between the filaments 12 are small
interstitial spaces 14. Such tow 10 may be formed from RAYON,
cellulose acetate, polypropylene, polyethylene, polyethylene
terephthalate, or any other polymeric material known in the art,
for example sheath-core bi-component filaments.
[0035] To improve coating of a liquid superabsorbent polymer (to be
described later) onto tow 10 comprising otherwise hydrophobic
filaments such as for example polypropylene, polyethylene, and
polyethylene terephthalate, the filaments may be hydrophilized.
This may be done for example by treatment with silica, treatment
with a material which has a suitable hydrophilic moiety and is not
readily removable from the filament, or by sheathing the
nonwettable, hydrophobic filament with a hydrophilic polymer during
or after the formation of the filament. Alternatively, the surface
of the filaments may be treated with for example a corona
discharge, to afford surface hydrogen-bondable groups and thereby
increase hydrophilicity.
[0036] A combination of these filament types may also be used, and
may be intermixed or layered. In some cases, it may be advantageous
to use both hydrophilic and hydrophobic filaments, in order to
control the distribution of liquid superabsorbent polymer to
certain filaments (the hydrophilic ones), as is well as to exert
control over the flow of urine or other body fluids in the core
when used. The exemplary filaments may have a denier per filament
of between 3 and 1000 grams/9000 m, preferably between about 10 and
about 70 grams/9000 m. A combination of filament deniers may also
be used, and may be intermixed or layered. The exemplary filaments
may be shaped to increase loft, for example by flat or helical
crimping. The filaments are substantially independent of each
other; that is, they are not bonded together to any significant
degree.
[0037] FIG. 2 shows, as a side cross section view, tow 110 after it
has been expanded, by means to be discussed later. The resultant
expanded tow 110 may be substantially wider than it is thick, thus
forming a core. Between filaments 112 are large interstitial spaces
116, such that the entire expanded tow 110 has an open structure
conducive to the transport of bodily fluids, as well as a soft feel
due to the open, puffy structure.
[0038] FIG. 3 shows a side cross section of an absorbent core 210
according to one exemplary embodiment of the invention in which an
expanded tow 110 (FIG. 2) has been treated on one side with a
superabsorbent material to afford a layer of that material over at
least selected surfaces of the filaments 218. The superabsorbent
material, details of which will be discussed below, is essentially
free of particulate superabsorbent material in this exemplary
embodiment.
[0039] Treated filaments 218, indicated by broad lines, may be
concentrated on one side of the absorbent core 210, while untreated
filaments 212 are on the other side, in the embodiment shown in
FIG. 3. In order for there to be sufficient absorbency in the core,
at least about 5% of the total combined surface area of the
filaments may be treated. Preferred is at least about 50%, and
still more preferred is at least about 80%. Although the treated
filaments 218 are shown as each being completely covered with
superabsorbent polymer, some or all of them may be only partially
covered. Also, although FIG. 3 shows two relatively well-defined
strata consisting of treated filaments 218 and untreated filaments
212 respectively, there may instead be a gradual transition from
one to the other across the thickness of absorbent core 210.
Alternatively, all of the filaments may be treated with
superabsorbent polymer, which may be beneficial when maximum
absorbency is desired.
[0040] Such an embodiment of the invention may help overcome a
problem commonly encountered in traditional absorbent articles,
namely the phenomenon of "gel blocking". In this situation, the
otherwise porous structure of an article employing particulate
superabsorbent polymers becomes occluded due to swelling of the
particles when they imbibe bodily fluids. Upon exposure to another
flow of liquid, the article may not be able to handle the
additional demand quickly enough, and overflow occurs. This may
result in leakage of fluid out of the article, wetting the wearer's
clothing.
[0041] When a fluid contacts the superabsorbent material in the
embodiment shown in FIG. 3, the material swells. However, due to
the open structure created by the interstitial spaces 216, gel
blocking does not occur. Thus, when a second insult of liquid is
applied to the core in use, the flow of liquid is not occluded.
This diminishes the chances of fluid overrunning an area of the
article and wetting a user's clothing, while at the same time
ensuring that more nearly all of the superabsorbent material is
accessible to the fluid. This increases effective capacity for
fluid absorption.
[0042] According to an exemplary embodiment of the invention,
treatment of the expanded tow 110 to afford a layer of
superabsorbent material is performed by application of a liquid
superabsorbent polymer. As used herein, the term "liquid
superabsorbent polymer" means one or more superabsorbent polymers
at least partially dissolved in a liquid carrier, or a solution in
a liquid carrier of one or more superabsorbent precursors, or a
combination of one or more superabsorbent polymers and
superabsorbent precursors. Such precursors include, inter alia,
monomers that are subsequently oligomerized, polymerized, and/or
crosslinked after placement on a substrate to form superabsorbent
polymers. It may sometimes be advantageous to include particulate
superabsorbent polymers in such a formulation, for example if
increased absorbency is desired.
[0043] Alternatively, using only nonparticulate materials may be
preferred in cases where it is desired to reduce shake-out of
particulate matter, or shifting of absorbency within the article
due to shifting of some of the superabsorbent particles. Both of
these phenomena lead to inefficient superabsorbent polymer use,
requiring the addition of more superabsorbent to compensate. These
problems are largely avoided by the use of liquid superabsorbent
polymers, which attach more firmly to the substrate. The issues of
shake-out and shifting are of particular importance when tow is
used in combination with particulate superabsorbents, because the
spacing between fibers is much greater than that encountered in
traditional cores employing pulp and superabsorbent polymer
particles. In these traditional systems, the pulp fibers help keep
the superabsorbent particles in place to a greater degree than is
the case with expanded tow 110.
[0044] Numerous liquid superabsorbent polymers are known in the
art. Nonlimiting examples of these, suitable for use with this
invention, follow.
[0045] U.S. Pat. No. 4,944,963 to Dabi, incorporated herein by
reference, describes forming a terpolymer of methyl methacrylate,
acrylic acid, and glycidyl methacrylate, which is subsequently
neutralized. The resulting solution is applied to a fibrous
substrate in the aqueous form. Excess solution is removed by
vacuum, and the treated substrate is heated for 20 minutes at
120.degree. C. to create a structure comprising substrate fibers on
the surface of which is a crosslinked superabsorbent polymer.
[0046] U.S. Pat. No. 5,853,867 to Harada, incorporated herein by
reference, describes a cationic absorbent polymer applied to a
fibrous substrate as a monomer solution, with the monomer
subsequently being polymerized on the substrate by heating.
Alternatively, preformed polymer may be applied. Halogenated alkyl
quaternary salts of dialkylamino (meth)acrylates are effectively
used for the production of the polymers, and include the
halogenated alkyl quaternary salts of such monomers as
N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl
(meth)acrylate, N,N-diethylaminobutyl (meth)acrylate,
N,N-diethylaminoethyl (meth)acrylate, and
N,N-diethylaminopropyl(meth)acrylate, for example. As used here,
the term "(meth)acrylate" means that either an acrylate or a
methacrylate is suitable. Such a cationic absorbent polymer may be
applied in a suitable liquid form such as, for example, by spraying
or spreading a solution of polymer onto the substrate. Preferably,
fixation of cationic absorbent polymer to the substrate is attained
by depositing a monomer or mixture of monomers in the form of an
aqueous solution on the substrate, and polymerizing the monomers in
the applied layer of monomer solution.
[0047] Another suitable liquid superabsorbent polymer is disclosed
in U.S. Pat. No. 6,417,425 to Whitmore et al., incorporated herein
by reference. There is described a sprayable composition comprising
a monomer such as acrylic acid, methacrylic acid, and/or salts of
these; a crosslinker such as ethoxylated and propoxylated
trimethylolpropanetriacrylate derivatives (such as SR-9035 and
SR-492, available from Sartomer Co., Inc. of Exton, Pa.); and a
polymerization initiator such as
2,2'-azobis(2-(2-imidazole-2-yl))propane dihydrochloride, all in
aqueous solution. Also included in the composition are solid
superabsorbent particles. The mixture can be sprayed onto a fibrous
substrate and subsequently cured via heating or exposure to
electron-beam or ultraviolet radiation, to form a superabsorbent
polymer matrix.
[0048] For the purposes of this invention, a liquid superabsorbent
polymer may be applied to the expanded tow 110 by any means known
in the art. Examples of suitable means include spraying, dipping,
and gravure application. A preferred method, in the case where it
is desired to cover substantially all of the available filament
surface, is to submerge the tow in a bath of liquid superabsorbent
polymer (item 44 in FIG. 4), remove the tow from the bath, and
remove excess liquid superabsorbent polymer by means of blowing
with a jet of air, or several jets. Such a method affords
particularly facile and rapid coverage of the filaments.
[0049] Application may be performed such that an entire surface of
the absorbent core is treated, or may be performed in a pattern of
treated and untreated areas. Application may be from only one side
or both sides of the absorbent core, and may or may not extend
through the entire thickness of the core.
[0050] The layer of superabsorbent polymer may be substantially
continuous over the surface of the filaments, rather than in
discrete clumps, thereby maximizing the available surface area per
unit weight of superabsorbent polymer. In order to facilitate
spreading of the liquid superabsorbent polymer over the surface of
the filaments, surface modification techniques such as for example
corona discharge treatment may be applied to the filaments.
Alternatively, or in addition, the use of hydrophilic lubricants or
surfactants may facilitate even distribution of the liquid
superabsorbent polymer. Such methods are for example disclosed by
Phillips et al in U.S. Pat. No. 5,972,505, where polyethylene
terephthalate filaments are treated with one of the following
materials, all available from ICI Americas, Inc.: [0051] Hypermer
A109, a modified polyester surfactant [0052] Brij 35, a
polyoxyethylene (23) lauryl ether [0053] Brij 99, a polyoxyethylene
(20) oleyl ether [0054] G-1300, a polyoxyethylene glyceride ester
(nonionic surfactant) [0055] G-1350, a
polyoxyethylene-polyoxypropylene sorbitan linoleic phthalic
ester.
[0056] FIG. 4 shows an example of an overall process for preparing
a core for incorporation into an absorbent article, according to
the invention. Cellulose acetate or other tow is provided as a bale
41; the tow consists essentially of continuous filaments of fiber
packed together into a tight bundle. Tow 41 is fed into fiber
spreader 42, where the tow is spread apart by rollers to form a
somewhat flattened shape. The spread fibers are then fed into an
air jet fiber opener 43, where the tow may be significantly opened
up by turbulent, high-pressure air, for example. Optionally, fibers
such as pulp, cotton linters, pieces of filament, or other short
fibrous material may also be incorporated into the opened-up or
expanded tow, for example by inclusion in the stream of air from
the air jet fiber opener, or by other means. Particulate
superabsorbent polymer may also be introduced into the expanded tow
in this manner.
[0057] The opened-up tow may then be submerged in a bath 44 of
liquid superabsorbent polymer, optionally also containing
superabsorbent particles. In the embodiment where tow is used
without the addition of short fibers or particulate superabsorbent
polymer by blowing in (or other means) as described above, there is
reduced contamination of the bath with pieces of filament, since
tow filaments are essentially continuous. Submersion in this manner
may afford a high and uniform loading of liquid superabsorbent
polymer, penetrating through the entire core. This may in some
cases be advantageous, especially for thicker (higher basis weight)
cores.
[0058] Alternatively, lighter and/or somewhat one-sided application
may be favored for some applications. In such a case, application
of the liquid superabsorbent polymer may instead be done for
example by spraying, or by application using a gravure roller.
Other means are known to those skilled in the coating art.
[0059] The process of FIG. 4 is particularly suitable for cases
were the opened-up tow is of higher basis weight, for example in
the range of about 30 gsm to about 500 gsm (grams/sq. meter), in
order to achieve maximum penetration of the liquid superabsorbent
polymer into the core. It may however be used for cores of any
basis weight.
[0060] Excess liquid superabsorbent polymer may then be blown off
of the expanded tow using a compressed air source 45, for example,
with the blown-off material being recycled back into the bath 44,
reducing wastage of superabsorbent material. Air source 45 may be
one or more air jets, and may be applied from one or both sides of
the core, with various degrees of force or pressure. This may
provide means for tuning or adjusting the loading profile of
superabsorbent polymer as a function of position in the core, i.e.
to provide and/or adjust a gradient of liquid superabsorbent
polymer as a function of depth. Such adjustment may be designed to
provide one or more strong gradients, or to minimize gradients and
thereby give a more uniform profile of superabsorbent polymer with
depth.
[0061] The thus-coated filaments are then passed through a curing
unit 46, which causes polymerization and/or crosslinking reactions
to occur with the reactive ingredients of the liquid superabsorbent
polymer, thereby forming a superabsorbent polymer on surfaces of
the filaments. Curing unit 46 may for example be a heating unit, an
ultraviolet light source, or an electron beam source, as
appropriate depending upon the type of liquid superabsorbent
polymer used.
[0062] The resulting "finished" tow is then passed through a dryer
47 to remove water and/or residual volatile reactants, and then
into a tenderizing unit 48, which crimps and/or bends the coated
filaments in order to soften them, overcoming some of the stiffness
imparted by the presence of the superabsorbent layer. Finally, the
resulting "soft-finished" coated tow may be fed into a rotary die
cutter 49, where it is cut to size to fit the dimensions of a
desired absorbent article.
[0063] FIG. 5 shows an alternative process for preparing a core
according to the invention. A process generally like that described
in relation to FIG. 4 is used, with the exception that application
of the liquid superabsorbent polymer is performed with an upper
sprayer 50 and a lower sprayer 52, which may afford coverage of
both sides of the core and therefore tend to improve penetration of
the liquid superabsorbent polymer into it, as compared to spraying
on only one side. The method of FIG. 5 may be particularly
appropriate for lower basis weight cores, for example those in the
range of about 5 gsm to about 30 gsm. It may however be used for
cores of any basis weight. Air jets (not shown) may also be used
either after applying the liquid superabsorbent polymer, or
simultaneously with it, to modify or adjust the distribution of
superabsorbent polymer in the core.
[0064] In another exemplary embodiment of the invention, the method
detailed in FIG. 5 may be modified by eliminating one of sprayers
50 or 52. By using such an approach, a core may be prepared in
which superabsorbent polymer is concentrated on one side of the
core, with little or no superabsorbent on the opposing side. The
result of this is the formation, in a single structure, of regions
that perform respectively the functions of absorbency and liquid
transfer. Thus the opposing side, having little or no
superabsorbent, may be placed nearer the user's skin, and perform
the function of an acquisition-distribution layer. This may obviate
the need for a separate acquisition-distribution layer, but it may
also be used In combination with such a separate layer. Air jets
(not shown) may also be used either after applying the liquid
superabsorbent polymer, or simultaneously with it, to modify or
adjust the distribution of superabsorbent polymer in the core.
[0065] Depending upon the amount of liquid superabsorbent polymer
sprayed onto the filaments, and the pressure of the spray as it
impinges the core, it is possible to vary the total loading of the
superabsorbent polymer and the profile of its distribution through
the thickness of the core. Thus for example a relatively large
amount of superabsorbent polymer sprayed at a high pressure will
tend to result in deeper penetration into the core. It will be
readily appreciated that various combinations of spray volume and
pressure will result in various gradients of superabsorbent polymer
loading through the thickness of the core, such that the absorbency
and other properties of the product can be tailored to meet
particular needs. Standard air jet nozzles and other equipment for
such spraying operations are well known, and spraying pressures may
for example vary from about 1 to about 100 PSIG (pounds/sq. inch,
gage).
[0066] In yet another exemplary embodiment of the invention,
referring again to FIG. 5, one of the sprayers 50 and 52 may apply
a liquid superabsorbent polymer while the other applies a
surfactant solution. The surfactant-treated side of the core will
thereby have increased wettability, improving its ability to act as
an acquisition-distribution layer. Sufficient surfactant amount and
spray pressure may be applied to allow significant surfactant to
reach the opposite side, where the liquid superabsorbent polymer is
applied, or conditions may be chosen to reduce such penetration,
depending upon the needs of the particular absorbent article to be
produced. Air jets (not shown) may also be used either after
applying the liquid superabsorbent polymer, or simultaneously with
it, to modify or adjust the distribution of superabsorbent polymer
and/or surfactant In the core.
[0067] The absorbent cores of the invention are particularly
suitable for incorporation into absorbent articles for use in
protective undergarments. Such a core may be used alone or in
combination with another core of similar construction, or one of a
traditional construction comprising for example kraft fluff and
particulate superabsorbent polymer. Depending on cost, performance
requirements, particular uses, and manufacturing considerations,
various designs and materials of construction can be selected for
use in assembling such undergarments. U.S. Pat. No. 6,004,893 to
Van Tilburg, which is incorporated herein by reference, describes a
variety of such materials and associated constructions.
[0068] For example, absorbent cores may be enwrapped with 17.1-gsm
tissue from Cellu Tissue Corporation, East Hartford, Conn. The
enwrapping tends to improve wicking of fluid across more nearly the
full width and length of the core. It may be C-folded around the
core, or layered on top of and/or below the core.
[0069] Absorbent cores may also be provided with a topsheet over
the enwrapping (if used). The topsheet is liquid permeable and,
when the article is in use, is in close proximity to the skin of
the user. If used, the topsheet is preferably compliant, soft
feeling and non-irritating to the user's skin. Such topsheets can
be made from any of the materials conventional for this type of
use, for example a 15.0 gsm spunbond polypropylene nonwoven from
Avgol Nonwoven Industries, located in Holon, Israel.
[0070] One particularly suitable material for the topsheet is for
example a 17-gsm wettable nonwoven coverstock, made of thermal bond
polypropylene, available from PGI Nonwovens, Landisville, N.J.
Other non-limiting examples of suitable materials that can be used
as a topsheet are woven and non-woven polyester, polypropylene,
polyethylene, NYLON, and RAYON and formed thermoplastic films.
Suitable films are described, for example, in U.S. Pat. No.
4,324,246 to Mullane and Smith and U.S. Pat. No. 4,342,314 to Radel
and Thompson, both of which patents are incorporated herein by
reference. Formed films may be selected for the topsheet because
they are permeable to liquids and yet non-absorbent. Thus, the
surface of the formed film, which is in contact with the body,
remains substantially dry and is more comfortable to the
wearer.
[0071] If a topsheet is used, its inner surface may be secured in
contacting relation to the absorbent core. This contacting
relationship results in liquid penetrating the topsheet faster than
if it were not in contact with the absorbent core. The topsheet can
be maintained in contact with the absorbent core by applying
adhesive, optionally in spaced, limited areas, to an inner surface
of the topsheet. Examples of suitable adhesives used for this
purpose include the acrylic emulsion E-1833BT manufactured by Rohm
and Haas Company of Philadelphia, Pa. and acrylic emulsions
manufactured by H. B. Fuller Company of St. Paul, Minn. Also
contemplated are thermoplastic hot melt adhesives such as 34-563A,
available from National Starch, Inc.
[0072] Optionally, before a topsheet is applied, a fluid
acquisition layer (not shown) may be attached adjacent and
coextensive with the absorbent core, on the side of the core nearer
the wearer, to improve distribution of bodily fluid more evenly
over the full width and length of the core. A topsheet may then be
affixed on top of the fluid acquisition layer. Such a layer serves
to manage, transport, accommodate and/or direct high volumes and
high flow rates of urine into the core. The fluid-acquisition layer
can be a through-air bonded/carded web, a spun-bond bi-component
non-woven web, a web of cross-linked cellulosic fibers, apertured
3D film or the like. One particular suitable material is available
from PGI Nonwovens, Landisville, N.J., and has an overall basis
weight of 40 gsm, with high denier (10 denier) bi-component fibers
situated on the top (facing the topsheet) and low denier (6 denier)
bi-component fibers situated on the bottom (facing the core). The
bi-component fibers are made of a polypropylene inner core and
polyethylene outer sheath. The fluid-acquisition layer may be
adhesively secured in place by any suitable construction adhesive
or hydrophilic adhesive, e.g. Cycloflex adhesive available from
National Starch and Chemical, Bridgewater, N.J.
[0073] In the exemplary embodiment of the invention shown in FIG.
3, where treated filaments are concentrated to one side of the core
and untreated filaments predominate on the other side, the
untreated side may itself act to effectively distribute fluids,
making the use of a separate acquisition layer unnecessary.
[0074] Crotch portions of protective undergarments employing an
absorbent core of this invention may comprise a barrier layer made
of a material that is impermeable to liquids and thus prevents
bodily fluids and feces from soiling the clothing of the user. Any
material used in the art for such purposes can be utilized herein.
Suitable materials include, for example, embossed or non-embossed
polyethylene and polypropylene films and laminated tissue and
non-woven materials.
[0075] Optionally, the impermeable barrier layer may be affixed
substantially coextensive and parallel with the side of the
absorbent core farther from the wearer, to prevent wetting or
soiling of clothing. Suitable barrier layers may for example be a
liquid-impervious laminate comprising a soft nonwoven
(cloth-like/hydrophobic) on the outside and fluid-impervious film
(low gauge poly) on the inside. An example of this is a poly
laminate available from Clopay Plastic Products Company,
Cincinnati, Ohio, which consists of 0.6 mil polyethylene film and
17 gsm SMS (spunbond/meltblown/spunbond) nonwoven. Another version
is a poly laminate 9B-396 available from Pliant Corporation of
Newport News, Va., which consists of 0.3 mil copolymer film and 14
gsm SBPP (spunbond polypropylene) nonwoven. However, other laminate
variations may be used in various gages and basis weights. For
instance, other polymers (polypropylene, olefins, polyester,
co-extruded polymers, etc.) or coatings (adhesive, synthetic
rubber, latex, polyurethane, etc.) can be used in place of the
polyethylene film. Other material components (polypropylene,
polyethylene, bi-component fibers, polyester, cotton, rayon, nylon,
olefins, etc.) can be used in either woven or nonwoven (spunbond,
thermal bond, through-air bond, etc.) construction in place of the
SMS outer cover. The preferred fluid-impervious film for the
liquid-impervious laminate is a breathable 0.8 mil polyethylene
version, which contains calcium carbonate, available from Tredegar
Film Products, Richmond, Va. This material allows water vapor to
pass through it, but does not permit the liquid itself to pass
through it.
[0076] While preferred embodiments of the invention have been shown
and described herein, it will be understood that such embodiments
are provided by way of example only. Numerous variations, changes
and substitutions will occur to those skilled in the art without
departing from the spirit of the invention. Accordingly, it is
intended that the appended claims cover all such variations as fall
within the spirit and scope of the invention.
* * * * *