Note: Descriptions are shown in the official language in which they were submitted.
2147685
PATENT
FIBER STRUCTURE FOR TRANSPORTING A LIQUID
Background of the Invention
Field of the Invention
The present invention relates to fiber structures for transporting a
liquid in a desired direction. Specifically, the present invention
relates to fiber structures having an average capillary radius gradient
that results in spontaneous interfiber transport of a liquid in the
direction of decreasing average capillary radius.
Descri~tion of the Related Art
The use of fibers to form various woven and nonwoven products is known.
For example, 1t is known to use regener~ted cellulose filaments having a
collapsed hollow structure and a multi-limbed cross section. Such fibers
possess a high capability of w~ter imbibition. These fibers can be
formed into woven fabrics like toweling and nonwoven fabrics and wadding
such as diapers, sanitary napkins, tampons and swabs.
It is also known to use cellulosic fibers having a decitex of less than5.0 and a multi-limbed cross section. The limbs have a length-to-width
aspect ratio of at least 2:1. The fibers can be formed into woven,
nonwoven, or knitted fabrics and are described ~s being especially useful
for absorbent products.
When fiber structures, such as nonwoven webs, are employed in disposable
absorbent products such as diapers, training pants, adult incontinent
products, feminine care products, wound dressings, and the like, the
simple ability to absorb a liquid is generally not sufficient to ensure
optimum perfor~ance in a product. For exan~ple, during use, ~any personal
care products are exposed to multiple insults of a liquid. In order to
ensure proper absorption of subsequent insults, it is generally desired
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that the first insult of liquid be not only absorbed but also transported
within the absorbent products to areas remote from the point of insult.
Additionally, the ability of a fiber structure to transport a liquid is
desirable for another reason. Specifically, when the fiber structure is
to be employed in an absorbent structure in an absorbent product, it is
often desirable to combine with the absorbent structure a high-absorbency
material. Such high-absorbency materials are known to those skilled in
the art and are generally capable of absorbing many times their weight in
a liquid. Thus, much of the total absorbent capacity of an absorbent
structure, employing such high-absorbency materials, results from the
presence of the high-absorbency material. In order for the
high-absorbency material to absorb a liquid, the liquid must come into
contact with the high-absorbency material. If the absorbent structure
including the high-absorbency material is not able to transport a liquid
from the point of liquid application, all of the high-absorbency material
must be placed in the general area where the liquid to be absorbed will
be applied to the absorbent structure. This is not always desirable.
Specifically, when a high concentration of a high-absorbency material is
localized in an absorbent structure, it is possible for gel blocking to
occur. That is, the high-absorbency material can swell in the localized
area to the extent that an essentially liquid-impermeable mass of
high-absorbency material is formed. Should this occur, subsequent
insults cannot be transported by the absorbent structure. Accordingly,
it is often desirable to more evenly distribute the high-absorbency
material in the absorbent structure. For this reason, it is desirable
for the absorbent structure to be able to transport a liquid from a point
of application to a high-absorbency material located remote from the
point of application.
SummarY of the Invention
It is desirable to provide a fiber structure capable of spontaneously
transporting a liquid to points remote from the point of liquid
application.
It is also desirable to provide a fiber structure capable of
spontaneously transporting a liquid in a desired or specific direction.
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These and other related goals are achieved in a fiber structure capable
of transporting a liquid in a desired direction, said fiber structure
being capable of spontaneous interfiber liquid transport. In one
embodiment, the fiber structure comprises at least two fibers, wherein
the fibers are wettable with a liquid to be contacted with the fiber
structure, and a first zone and a second zone, wherein the first zone has
an average capillary radius greater than the average capillary radius of
the second zone.
In another aspect, it is desirable to provide a thin, disposable
absorbent product, such as an infant diaper, which product employs an
absorbent structure having a relatively small volume and yet has a
relatively large liquid capacity.
In one embodiment, these goals are achieved in a disposable absorbent
product comprising a backsheet, a liquid-permeable topsheet attached to
the backsheet, and an absorbent structure located between the backsheet
and the liquid-permeable topsheet, said absorbent structure comprising a
crotch section, an end section, and a fiber structure, said fiber
structure co~prising at least two fibers, wherein the fibers are wettable
with a liquid to be contacted with the fiber structure, and a first zone
and a second zone, wherein the first zone has an average capillary radius
greater than the average capillary radius of the second zone, and wherein
the first zone is in contact with the absorbent structure crotch section
and the second zone is in contact with the absorbent structure end
section.
In another aspect, it is desirable to provide a method of spontaneously
transporting a liquid in a desired direction in a fiber structure.
In one embodiment, these goals are achieved in a method for transporting
liquid in a desired direction in a fiber structure. The method comprises
contacting a liquid with a fiber structure, wherein the fiber structure
comprises at least two fibers, wherein the fibers are wettable with the
liquid contacted with the fiber structure, and a first zone and a second
zone, wherein the first zone has an average capillary radius greater than
the average capillary radius of the second zone, wherein the liquid is
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contacted with the first zone of the fiber structure and wherein the
liquid is transported from the first zone to the second zone.
Brief Description of the Drawings
Fig. 1 represents a disposable absorbent product according to the present
invention.
Fig. 2 represents a fiber structure according to the present invention
that comprises two zones of different average capillary radii.
Fig. 3 represents a fiber structure that comprises one zone of
essentially constant capillary radii.
Fig. 4 represents a fiber structure according to the present invention
that comprises a middle zone and two end zones of different average
capillary radii.
Detailed Description of the Preferred Embodiments
As used herein, reference to interfiber liquid transport refers to the
situation wherein a liquid ~oves through a structure of fibers as a
result of capillaries formed by said fibers. The distance of interfiber
liquid transport depends on the capillary pressure of the system. The
capillary pressure of a cylindrical capillary is expressed by the
equation:
P = 2 ~ cos~
r
wherein P is the capillary pressure, ~ is the surface tension of the
liquid, 4 is the liquid-fiber contact angle, and r is the capillary
radius. With a given liquid, the capillary pressure (capillary force)
increases with the cosine of the liquid-fiber contact angle and decreases
with larger capillary radii so that smaller capillaries will generally
transport a liquid farther through the interfiber capillaries as compared
to a larger capillary.
Thus, when a liquid is contacted with a fiber structure having a
relatively constant capillary radius, the liquid will be spontaneously
transported within the fiber structure a distance that is dependent on
the capillary pressure of the fiber structure. Such spontaneous
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transport of the liquid will generally be in any direction away from the
location where the liquid contacts the fiber structure.
In contrast to interfiber liquid transport, intrafiber liquid transportrefers to the situation wherein a liquid is transported against a
pressure along the length of an individual fiber as a result of a notch
or channel defined by the surface of the individual fiber.
As used herein, reference to the contact angle formed between the liquid
to be absorbed and transported and the material from which the fibers are
formed may be determined by methods known to one skilled in the art as,
for example, set forth by Good and Stromberg in ~Surface and Colloid
Science~ Vol. 11 (Plenu~ Press, 1979).
As used herein, reference to the average capillary radius of a fiber
structure, or a zone of a fiber structure, is meant to refer to an
average of all capillary radii within the fiber structure or a zone of
the fiber structure. The average capillary radii of a fiber structure,
or a zone of a fiber structure, may be determined by methods known to one
skilled in the art. For example, image analysis may be used to determine
the equivalent pore area across a cross-sectional area of a zone of a
fiber structure from which the average capillary radius of the zone may
be determined. Other known methods for determining the average capillary
radius of a fiber structure include using a capillary tension test or the
use of a porosimeter.
As used herein, spontaneous interfiber liquid transport in a desired or
specific direction is meant to refer to the situation wherein the
interfiber liquid transport occurs essentially independently of any
external forces or conditions, such as an externally applled pressure,
gravity, or the like, but is essentially the result of the physical
structure of the fiber structure itself. Applicants have discovered that
such spontaneous interfiber liquid transport in a desired direction will
occur within a fiber structure from a first zone of the fiber structure
to a second zone of the fiber structure, wherein the first zone has an
average capillary radius greater than the average capillary radius of the
second zone. Such spontaneous interfiber liquid transport in a specific
direction occurs within the fiber structure due to the difference in
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capillary pressures between the first zone and the second zone. A fiber
structure first zone, having a relatively larger average capillary
radius, will have a smaller liquid capillary pressure than a fiber
structure second zone, having a relatively smaller average capillary
radius, so that a liquid in the first zone will spontaneously transport
to the second zone due to the driving force caused by the difference in
capillary pressures. Such spontaneous interfiber liquid transport in a
specific direction may generally occur in any desired direction, such as
horizontally, vertically, or at an angle.
As used herein, a ~zone~ of a fiber structure is meant to refer to a
section or area of the fiber structure that is distinct from another zone
or zones of the fiber structure by having a different average capillary
radius from the other zone or zones. Generally, the fiber structures of
the present invention will be unitary structures, such that the zones of
the fiber structure will be im~ediately adjacent to each other and in
liquid communication with each other, such that a liquid may be
transported from one zone to another. Depending on the physical
structure of a particular fiber structure of the present invention, the
beginning and the end of adjacent zones may not be physically distinct
and may sometimes be rather arbitrarily defined. However, it is
important that any defined zone be distinct from an adjacent zone by
having an average capillary radius that is different from the adjacent
zone. A particular zone may have a constant capillary radius or radii or
a variable capillary radius or radii along its length.
A zone of a fiber structure of the present invention will benefic~ally
have a width of from about 0.5 inch to about lO inches and suitably from
about 1 inch to about 6 inches. A zone of a fiber structure of the
present invention will beneficially have a length of fro~ about 1 inch to
about lO inches and suitably fro~ about 2 inches to about 8 inches.
The fiber structures of the present invention comprise at least two zones
having different average capillary radii and may also comprise more than
two zones having different average capillary radii. When a fiber
structure comprises more than two zones, each of the zones may have
different average capillary radii. Alternatively, several of the zones
may have essentially equal average capillary radii, although such zones
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should be separated from each other by other zones that have different
average capillary radii. In one embodiment of the present invention a
fiber struct4re comprises a middle zone and two end zones wherein the
middle zone has an average capillary radius greater than the average
capillary radius of each of the two end zones.
The capillary radii of the zones of the fiber structure should not be so
large as to prevent spontaneous liquid transport from occurring due to a
very low driving force. Suitably the zones should have an average
capillary radius that is smaller than about 200 micrometers in order for
spontaneous liquid transport to occur. The capillary radii of the zones
of the fiber structure should also not be so small as to prevent
spontaneous liquid transport from occurring due to a very large drag
force. Suitably the zones should have an average capillary radius that
is larger than about 0.1 micrometers in order for spontaneous liquid
transport to occur.
As such the average capillary radii of the zones of a fiber structure
such as each of a first and a second zones are beneficially from about
0.1 micrometer to about 200 micrometers suitably from about 1 micrometer
to about 150 micrometers and more suitably from about 5 micrometers to
about 100 micrometers. However as described herein the average
capillary radius of the first zone must be greater than the average
capillary radius of the second zone in order to achieve the desired
spontaneous interfiber liquid transport in a desired direction within the
fiber structure.
Because the average capillary radius of the first zone needs to be
greater than the average capillary radius of the second zone the ratio
of the average capillary radius of the first zone compared to the average
capillary radius of the second zone will be greater than at least 1:1,
and is beneficially greater than at least about 2:1 is suitably greater
than at least about 3:1 and is more suitably greater than at least
about 5:1.
Fig. 2 illustrates a fiber structure 20 formed from substantially
aligned individual fibers and comprising a first zone 21 and a second
zone 22 wherein the first zone 21 has an average capillary radius
214768a
greater than the average capillary radius of the second zone 22.
Accordingly when a liquid is applied to the fiber structure 20 in the
first zone 21 the fiber structure 20 is capable of spontaneous
interfiber liquid transport of the liquid in a specific direction to
second zone 22. That is the liquid is spontaneously transported in the
capillaries defined by the fibers forming the fiber structure 20 and is
transported to second zone 22. The amount of the interfiber liquid
transport occurring will depend on the amount of liquid applied and the
capillary pressure difference between the two zones of the fiber
structure system which is as discussed above dependent on capillary
radius surface tension of the liquid and contact angle between the
fibers and the liquid.
Fig. 3 illustrates a fiber structure 25 comprising essentially only one
zone wherein this zone has an average capillary radius that is
essentially constant within the zone. ~hen a liquid is applied to the
fiber structure 25 the fiber structure 25 generally transports the
liquid in the interfiber capillaries a lesser distance than that achieved
with the fiber structure 20 in Fig. 2. Also there is generally no
specific direction to the spontaneous transport of the liquid contacted
with fiber structure 25. For example a liquid contacted with the middle
portion 26 of fiber structure 25 will generally be transported towards
both fiber structure ends 27.
Fig. ~ illustrates a fiber structure 30 comprising essentially three
zones. The middle zone 32 has an average capillary radius greater than
the average capillary radii of each of two end zones 31. The end zones
31 may have essentially equal average capillary radii or may have
different average capillary radii. Accordingly when a liquid is applied
to the fiber structure 30 in the first zone 32 the fiber structure 30 is
capable of spontaneous interfiber liquid transport of the liquid in a
specific direction to each of the end zones 31. That is the liquid is
spontaneously transported in the capillaries defined by the fibers
forming the fiber structure 30 and is transported to end zones 31. The
amount of the interfiber liquid transport occurring will depend on the
amount of liquid applied and the capillary pressure difference between
the respective zones of the fiber structure system.
2147685
The fibers useful in forming the fiber structures of the present
invention can be formed from any material capable of forming a fiber
structure. As a general rule, the fibers are formed from a cellulose
derivative such as rayon or cellulose acetate or from a synthetic
polymeric material such as polyolefins, polyesters, polyamides,
polyurethanes, and the like. The materials from which the fiber can be
formed may be either wettable or nonwettable. As used herein, "wettable~
refers to fibers having a liquid-in-air contact angle of less than 90',
wherein the liquid contacting the fiber is suitably a liquid such as
water, synthetic urine, urine, menses, blood, or a 0.9 weight percent
aqueous saline solution. ~Nonwettable~ refers to fibers having a
liquid-in-air contact angle greater than 90-. The liquid-in-air contact
angle of a fiber may be determined, for example, as set forth by Good and
Stromberg in ~Surface and Colloid Science~ Vol. 11, (Plenum Press, 1979).
When the fibers are formed from nonwettable material, the fibers must
generally be treated to provide them with a wettable surface. Methods of
providing nonwettable materials with a wettable surface are known.
Exemplary of such a method is the application of a surfactant or other
wetting agent to the fibers.
Similarly, if a wettable fiber having a contact angle of less than 90- is
desired to be rendered more wettable, to thereby decrease its contact
angle with respect to a given liquid, it is possible to treat the
wettable fiber with a surfactant or other wetting agent to impart a more
wettable surface. The wetting treatment is desirably nonfugitive. That
is, the surface treatment desirably does not wash off the surface of the
fiber with the first liquid insult or contact. For the purposes of this
application " surface treatment on a generally nonwettable fiber will be
considered to be nonfugitive when a ma~ority of the fibers demonstrate a
liquid-in-air contact angle of less than 90- for three consecutive
contact angle measurements, with drying between each measurement. That
is, the same fiber is sub3ected to three separate contact angle
determinations and, if all three of the contact angle determinations
indicate a contact angle of liquid-in-air of less than 90-, the surface
treatment on the fiber will be considered to be nonfugitive. If the
surface treatment is fugitive, the surface treatment will tend to wash
off of the fiber during the first contact angle measurement, thus,
21 47~8S
exposing the nonwettable surface of the underlying fiber and will
demonstrate subsequent contact angle measurements greater than 90-.
The fibers used herein may generally be of any desired cross-sectionalshape including circular, oval, multi-lobed, or other shapes known to
those skilled in the art. Methods of forming fibers are also known to
those skilled in the art. As a general rule, fibers formed from a
synthetic polymeric material are generally prepared by extruding the
fibers through a die orifice generally corresponding to the desired
shape. Such a method is described in U.S. Patent 2,945,739 issued
July 19, 1960, to Lehmicke, or in Japanese Kokoku Patent
No. SH0 62[1987]-53605. If the fiber is to be formed from a cellulosic
derivative, such as rayon, the fibers can be formed from conventional
viscose and are conveniently spun from standard viscose compositions
using standard viscose spinning conditions. Such a method is described
in European Patent Application 0 301 874 A2 published February 1, 1989.
Alternatively, the fiber may be formed from cellulose acetate. Further,
the fiber may be formed by tw;sting two or more fibers together.
The fibers according to the present invention generally have a diameteror width of from about 0.25 micro~eter to about 500 micro~eters, suitably
of from about 0.5 micrometer to about ~0 m;crometers-.
Fiber structures according to the present invention can suitably be
formed ;n any manner capable of form;ng fiber structures known to those
skilled ;n the art. For example, the fiber structure may be formed
through a cardlng process, rando process, spunbo~d process, needlepunch
process, and the like, and may be in the form of a web, bundle, sheet or
the like. The fiber structures according to the present ;nvention
suitably have: a density of from about 0.01 gram per cubic centimeter to
about 0.5 gram per cubic centimeter, more suitably of fro~ about
0.05 gram per cubic centimeter to about 0.2 gram per cub;c cent;meter; a
thickness of from about 0.5 micrometer to about 0.05 meter, more suitably
from about 50 micrometers to about 0.015 meter; a length of from about
0.05 meter to about 0.~ meter, more suitably from about 0.075 meter to
about 0.25 meter. The fiber structures of the present invention will
compr;se at least two fibers, suitably at least about 10 fibers, and more
suitably at least about 50 fibers.
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2147685
The fiber structures according to the present invention are suited to
transfer many liquids, such as water, saline, and synthetic urine, and
body liquids, such as urine, menses, and blood, and are suited for use in
disposable absorbent products, such as diapers, adult incontinent
products, and bed pads; in catamenial devices, such as sanitary napkins
and tampons; and in other absorbent products, such as wipes, bibs, wound
dressings, and surgical capes or drapes. Accordingly, in another aspect,
the present invention relates to a disposable absorbent product
comprising a fiber structure as described herein.
Use of the described fiber structures in disposable absorbent products
allows for the fonmation of a disposable absorbent product which is able
to rapidly receive a discharged liquid and yet which product is thin.
Typically, the fiber structure will be incorporated into a disposable
absorbent product in the for~ of an absorbent structure. Such disposable
absorbent products generally comprise a liquid-permeable topsheet, a
backsheet attached to the topsheet, and an absorbent structure, such as
an absorbent structure co~prising the fiber structure of the present
invention, located between the topsheet and backsheet.
Exemplary disposable absorbent products are generally described in
US-A-~,710,187; US-A-~,762,521; US-A-~,770,656; US-A-~,798,603; and U.S.
Serial No. 08/096,65~, filed July 22, 1993, in the name of ~ansen et al.,
which references are incorporated herein by reference.
The fiber structure is present in an absorbent structure or product of
the present invention in an amount effective to spontaneously transfer in
a desired direction a desired amount of liquid so as to result in the
absorbent structure or product being able to absorb a desired amount of
liquid. The fiber structure is beneficially present in an absorbent
structure of the present invention in an amount of from about 0.1 to
about 100 weight percent, based on the total weight of the absorbent
structure.
The fiber structures of the present invention beneficially exhibit an
improvement in flux (volume delivery over time) of a liquid contacted
with the fiber structure as compared to a fiber structure having only a
single zone of essentially constant average capillary radius. A fiber
2147685
structure of the present invention exhibits a flux of a liquid contacted
with the fiber structure that is beneficially at least about 10 percent
greater, suitably at least about 20 percent greater, and more suitably at
least about 30 percent greater than a fiber structure having only a
single zone of essentially constant average capillary radius, wherein the
average capillary radius of the fiber structure having only a single zone
is similar to the average capillary radius of one of the zones of the
fiber structure of the present invention.
Because the fiber structures present in the absorbent structures of thepresent invention can transfer relatively large quantities of liquid
throughout the absorbent structure so as to utilize the entire absorbent
structure, the absorbent structures of the present invention can be
relatively thin and light weight, have a relatively small volume, and
still function in a desirable manner.
An absorbent structure of the present invention suitably comprises the
fiber structure of the present invention as well as a fibrous matrix
comprising a hydrogel-forming polymeric material wherein the fibrous
matrix constrains or entraps the hydrogel-forming polymeric material.
Hydrogel-forming polymeric materials include, for exampie,
carboxymethylcellulose, al hli metal salts of polyacrylic acids,
polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride copolymers,
polyvinyl ethers, hydroxypropylcellulose, polyvinyl morpholinone,
polymers and copolymers of vinyl sulfonic acid, polyacrylates,
polyacrylamides, polyvinyl pyridine, and the like. Other suitable
hydrogel-forming polymeric materials include hydrolyzed acrylonitrile
grafted starch, acrylic acid grafted starch, and isobutylene maleic
anhydride copolymers and mixtures thereof. The hydrogel-forming
polymeric materials are suitably lightly cross-linked to render the
material substantially water insoluble. Cross-linking may, for example,
be by irradiation or by covalent, ionic, Van der ~aals, or hydrogen
bonding. Suitable hydrogel-forming polymeric materials are available
from various commærcial vendors such as The Dow Chemical Company,
Celanese Corporation, Allied-Colloid, and Stockhausen. Typically, the
hydrogel-forming polymeric material is capable of absorbing at least
about fifteen times its weight in water and preferably is capable of
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2147585
absorbing at least about 25-30 times its weight in water. The
hydrogel-forming polymeric material can be present in the fibrous matrix
in an amount of from about 1 to about 95 weight percent, suitably of from
about 5 to about 60 weight percent based on total weight of the fibrous
matrix.
The hydrogel-forming polymeric material is suitably in liquid
communication with the fiber structure in an area of interfiber liquid
transport. As used herein, a hydrogel-forming polymeric material will be
considered to be in liquid communication with the fiber structure, in an
area of interfiber liquid transport, when a liquid present in the area of
interfiber liquid transport can flow into contact with the
hydrogel-forming polymeric material.
For example, the hydrogel-forming polymeric material may be present in
the absorbent structure in an area of interfiber liquid transport.
Alternatively, the hydrogel-forming polymeric material may be present in
a pouch or a second absorbent structure, which pouch or second absorbent
structure is, in turn, in contact with the area of interfiber liquid
transport.
Applicants have discovered that, when the hydrogel-forming polymeric
material is in liquid co~unication with the fiber structure in an area
of interfiber liquid transport, the hydrogel-forming polymeric material
may contact the liquid transported by the fiber structure. ~hen the
hydrogel-forming polymerlc material is in contact with the liquld in an
area of interfiber liquid transport, the hydrogel-forming polymeric
material is able to absorb the liquid, thus, improving utilization of the
hydrogel-forming polymeric material and allowing continued interfiber
liquid transport in a desired direction. For example, Applicants have
found that, when a hydrogel-forming polymeric ~aterial capable of, for
example, absorbing twenty times its weight in a liquid is in contact with
the liquid in the area of interfiber liquid transport, the fiber
structure will continue to transport liquid via spontaneous interfiber
liquid transport, in a desired direction, to the hydrogel-forming
polymeric material until the absorption capacity of the hydrogel-forming
polymeric material is reached or until there is no more available liquid
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214768S
for the fiber structure to transport in a desired direction. This
phenomenon is important for several reasons.
Use of the fiber structures described herein allows for improved
utilization of hydrogel-forming polymeric material present in or in
liquid communication with the fiber structure or an absorbent structure.
That is, it is possible to disperse a given amount of hydrogel-forming
polymeric material in the absorbent structure (or in liquid communication
with the fiber structure) over a greater area when a fiber structure
having an average capillary radius gradient is used than when a fiber
structure having an essentially constant average capillary radius is
used.
As used herein, the term ~fiber~ or "fibrous~ is meant to refer to a
particulate material wherein the length to diameter ratio of such
particulate material is greater than about 10. Conversely, a ~nonfiber~
or ~nonfibrous~ material is meant to refer to a particulate material
wherein the length to diameter ratio of such particulate material is
about 10 or less.
A wide variety of natural and synthetic fibers can be employed in the
preparation of the fibrous matrix of the present invention. Illustrative
fibers include, but are not limited to, wood and wood products, such as
wood pulp fibers, cellulose or cellulose acetate flocs, cotton linter
flocs and the like, inorganic fibers, synthetic fibers such as nylon
flocs, rayon flocs, polyacrylonitrile fibers, and the like.
It is also possible to use mixtures of one or more natural fibers, or one
or more synthetic fibers, or combinations of the two. Preferred fibers
are those which are wettable in nature. However, nonwettable fibers can
also be used.
Fibrous matrixes for incorporation into an absorbent structure are
generally well known. A fibrous matrix may take the form of, for
example, a batt of comminuted wood pulp fluff, a tissue layer, a
hydroentangled pulp sheet, a mechanically softened pulp sheet, or of a
web structure comprising an entangled fibrous mass formed, for example,
from an extruded thermoplastic composition. Suitably, the fibrous matrix
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2147685
is formed so as to constrain or entrap the hydrogel-forming polymeric
material within, or onto, its structure. The hydrogel-forming polymeric
material may be incorporated into or onto the fibrous matrix either
during or after the formation of the general form of the fibrous matrix.
Suitably, the fiber matrix has a basis weight ranging from about
0.025 grams per square meter of fiber matrix material to about 400 grams
per square meter of fiber matrix material.
Suitably, the fiber matrix has a density ranging from about 0.05 grams
per cubic centimeter of fiber matrix material to about 0.5 grams per
cubic centimeter of fiber matrix material.
Suitably, the fibers comprising the fiber matrix have a fiber length
ranging from about 0.1 centimeter to about 3.0 centimeters.
The fibrous matrix may be formed through an air-laying process, a
spunbond or meltblown process, a carding process, a wet-laid process, or
through essentially any other process means, known to those skilled in
the art, for forming a fibrous ~atrix.
Methods of incorporating the hydrogel-forming polymeric material into the
fibrous matrix are known to those skilled in the art. Suitable methods
include incorporating the hydrogel-forming polymeric material into the
matrix during formation of the matrix, such as by air-laying the fibers
of the fibrous matrix and the hydrogel-forming polymeric material at the
same time or wet-laying the fibers of the fibrous matrix and the -
hydrogel-forming polymeric material at the same time. It is preferable
that the hydrogel-forming polymeric material be generally uniformly
distributed within the fibrous matrix. ~owever, the hydrogel-forming
polymeric ~aterial ~ay be nonuniformly distributed as long as the desired
absorbent properties of the absorbent structure are still achieved.
Alternatively, it is possible to apply the hydrogel-forming polymeric
material to the fibrous matrix after formation of the fibrous matrix.
Other methods include sandwiching the hydrogel-forming polymeric material
between two sheets of material, at least one of which is fibrous and
liquid permeable. The hydrogel-forming polymeric material may be
2147~8~
generally uniformly located between the two sheets of material or may be
located in discrete pockets formed by the two sheets.
The fibrous matrix may be in the form of a single, integrally formed
layer or of a composite comprising multiple layers. If the fibrous
matrix comprises multiple layers, the layers are preferably in liquid
communication with one another such that a liquid present in one fibrous
layer can flow or be transported to the other fibrous layer. For
example, the fibrous layers may be separated by cellulosic tissue wrap
sheets known to those skilled in the art.
When the fibrous matrix comprises a single, integrally formed layer, the
concentration of hydrogel-forming polymeric material may increase along
the thickness of the fibrous matrix in a gradual, nonstepwise fashion or
in a more stepwise fashion. Similarly, the density may decrease through
the thickness in a nonstepwise manner or in a stepwise manner.
The absorbent structures of the present invention may generally be of any
size or dimension as long as the absorbent structure exhibits the desired
absorbent characteristics as described herein.
The absorbent structure of the present inventio~ may also be used or
combined with other absorbent structures, with the absorbent structure of
the present invention being used as a separate layer or as an individual
zone or area within a larger, co~posite absorbent structure. The
absorbent structure of the present invention may be co~bined with other
absorbent structures by methods well known to those skilled in the art,
such as by using adhesives or simply by layering the different structures
together and holding together the co~posite structures with, for example,
tissue.
In one embodiment of the present invention, a disposable absorbent
product is provided, which disposable absorbent product comprises a
liquid-permeable topsheet, a backsheet attached to the topsheet, and an
absorbent structure comprising a fiber structure of the present
invention, wherein the absorbent structure is positioned between the
topsheet and the backsheet.
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2l4768~
While one embodiment of the invention will be described in terms of the
use of a fiber structure in an infant diaper, it is to be understood that
the fiber structure is equally suited for use in other disposable
absorbent products known to those skilled in the art.
Fig. 1 illustrates a disposable diaper 1 according to one embodiment of
the present invention. Disposable diaper 1 includes a backsheet 2, a
topsheet 4, and an absorbent structure 6, located between the
backsheet 2, and the topsheet 4. Absorbent structure 6 is an absorbent
structure according to the present invention. Specifically, in the
illustrated embodiment, absorbent structure 6 comprises a fiber
structure 8 of the present invention.
Those skilled in the art will recognize materials suitable for use as the
topsheet and backsheet. Exemplary of materials suitable for use as the
topsheet are liquid-permeable materials, such as spunbonded polypropylene
or polyethylene having a basis weight of from about 15 to about 25 grams
per square meter. Exemplary of materials suitable for use as the
backsheet are liquid-impervious materials, such as polyolefin fil~s, as
2~ well as vapor-pervious materials, such as microporous polyolefin films.
Absorbent products and structures, according to all aspects of the
present invention, are generally subjected during use to multiple insults
of a body liquid. Accordingly, the absorbent products and structures are
desirably capable of absorbing multiple insults of body liquids in
quantities to which the absorbent products and structures will be exposed
during use. ~he insults are generally separated from one another by a
period of time.
The follow~ng Examples are presented to provide a more detailed understanding of the
invention. The Examples are intended to be representative and are not intended to
specifically limit the scope of the invention.
2147685
ExamDl es
Round bundles of aligned fibers, often used as cigarette filter
materials, were obtained fro~ ~oechst-Celanese Corporation. The fibers
were trilobal and Y-shaped, had a denier of 3, and were prepared from
wettable cellulose acetate. The fiber bundle was in a rod form, as shown
in Fig. 3, with a paper wrapper outer cover. The rods were about
100 millimeters long with a diameter of about 8 millimeters.
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214768S
The rods were cut to about 50 millimeter lengths, and the paper wrapper
outer cover was removed from about 40 millimeters of such cut rod
lengths. The unwrapped 40 millimeter lengths were "fanned out~, as shown
in Fig. 1, so that the far end of the fanned out zone was relatively flat
and had a width of about 50 millimeters. The unwrapped, fanned-out zone
had relatively larger capillary radii as compared to the wrapped zone
which had relatively smaller capillary radii, thus, resulting in a
capillary radius gradient between the two zones.
Example 1: Samples of the prepared fiber bundles were laid
horizontally on a bench top and 5 drops of colored water were placed on
the unwrapped, fanned-out zone of the fiber bundle. The liquid was
observed to spontaneously transport to the wrapped zone of the fiber
bundle (from low to high capillary pressure).
Example 2: A sample of the prepared fiber bundles was used. The endof the wrapped zone was moistened with water so that a hydrogel-forming
poly~eric material (a poly(acrylic acid) poly~er, obtained from The Dow
Chemical Company under the trade designation DRYTECH(TM) 533), adhered
when the wrapped end zone was dipped into a supply of the
hydrogel-forming polymeric material. The prepared structure was laid
flat on a bench top. However, the geometry of the fiber structure,
comprising a relatively flat, unwrapped zone and a round wrapped zone
with hydrogel-forming polymeric ~aterial adhered to its end, resulted in
a slight slope of about 5 millimeters upward from the unwrapped zone end
to the wrapped zone end. Five drops of colored water were placed on the
unwrapped, fanned-out zone of the fiber bundle. The liquid was observed
to spontaneously transport, against gravity, to the wrapped zone of the
fiber bundle. The hydrogel-forming poly~eric material absorbed the
colored water and drew any excess colored water from the unwrapped zone
such that the unwrapped zone became dry to the touch within about
30 seconds.
Example 3: A full-length, 100 millimeter wrapped fiber bundle had the
middle 80 millimeters of wrap paper removed, leaving about 10 millimeters
of wrapped fibers at each end. The fibers in the middle, unwrapped
80 millimeter zone were fanned out to a diameter of about 50 millimeters,
creating a fiber bundle having a zone with relatively larger capillary
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2147685
radii as compared to the wrapped end zones. The fiber bundle was place
horizontally on a bench top and colored water was added dropwise to the
middle of the fiber bundle in the unwrapped zone. The colored water was
observed to spontaneously transport to both wrapped end zones.
Example 4: Hydrogel-forming polymeric material was adhered to both
wrapped zone ends of a fiber bundle, similar to the fiber bundle used in
Example 3, by using a procedure similar to that described in Example 2.
Colored water was added dropwise to the middle of the fiber bundle in the
unwrapped zone. The colored water was observed to spontaneously
transport to both wrapped end zones. The hydrogel-forming polymeric
material absorbed the colored water and drew any excess colored water
from the unwrapped zone such that the unwrapped zone became dry to the
touch within about 30 seconds.
Example 5: Round bundles were prepared from aligned sliver fibers. Thefibers were trilobal and were prepared froa rayon with a glycerine finish
as obtained from Courtaulds Inc. The fibers were aligned by forming a
sliver and were encased in a shrink wrap outer cover. The fiber bundles
were in a rod fon~, as shown in Fig. 3. The rods were about
50 millimeters long with a diameter of about 13 millimeters. For one of
the samples, half of the outer cover was cut open and the fibers were
expanded to a larger capillary size so as to create two zones of varying
average capillary radii as shown in Fig. 2. As determined by image
analysis, the end of the wrapped zone was found to have an average
capillary radius of about 18 micrometers, and the end of the expanded
zone was found to have an average capillary radius of about
49 micrometers. Another sample was left as a rod of one zone with an
essentially unifor~ capillary radius of about 18 micrometers. The two
sample fiber structures were then compared as to liquid wicking for both
vertical and horizontal wicking along the length of the fiber structure.
For the vertical wicking test, the fiber structure with two zones wicked
colored water the 50 millimeter height, from the unwrapped zone to the
wrapped zone, in about 5 seconds, while the fiber structure with one zone
wicked colored water the 50 millimeter height in about 12 seconds. For
the horizontal wicking test, the fiber structure with two zones wicked
colored water the 50 millimeter length, from the unwrapped zone to the
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214768~
wrapped zone, in about 5 seconds, while the fiber structure with one zone
wicked colored water the 50 millimeter length in about 120 seconds.
Thus, it is seen that fiber structures having at least two zones having
different average capillary radii as described by the present invention
are capable of improved liquid transport as compared to fiber structures
having only a single zone having an essentially constant average
capillary radius. When a high-absorbency material is in liquid
communication with the area of spontaneous, interfiber liquid transport,
such as the second zone, the high-absorbency material is found to be
effective in absorbing the transported liquid within the second zone so
as to provide a means for continued spontaneous liquid transport from the
first zone to the second zone.
While the present invention has been described in particular reference to
several preferred embodiments, the present invention is susceptible of
being embodied with various alterations and modifications which may
differ, particularly from those that have been described in the preceding
specification. These variations and alterations are possible without
departing from th~ described invention.
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