Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT CORE LAYER FOR ABSORBENT ARTICLES
S
FIELD OF THE INVENTION -
The present invention relates to absorbent webs having improved fluid
acquisition
and retention properties. The present invention further relates to absorbent
articles such
as sanitary napkins, diapers, adult incontinence pads and briefs, panty
liners, tampons,
and the like, incorporating such webs (such as for an absorbent core).
BACKGROUND OF THE INVENTION
Absorbent webs which comprise entangled masses of fibers, i.e. fibrous
absorbent
webs, are well known in the art. Such absorbent webs are used in all manner
and variety
of disposable absorbent articles such as diapers, sanitary napkins, panty
liners,
incontinence pads and briefs, tampons, and the like. Typical disposable
absorbent articles
often comprise a liquid pervious body side liner and an underlying absorbent
core. The
absorbent core may be sandwiched between a body side liner and a liquid
impervious
backsheet, which backsheet serves to protect garments and skin from contact
with
absorbed bodily discharges. Typically body side liners may comprise a topsheet
such as
an apertured formed film or a nonwoven topsheet layer. A body side liner may
also
comprise a multiple layer structure such as a topsheet in liquid communication
with a
secondary topsheet (which is also sometimes referred to as a distribution
layer, surge
management layer, wicking layer, or similar term).
The core of the typical absorbent article described above has two basic
requirements: to drain the body side liner of deposited fluids and draw these
fluids into
the absorbent core for absorption, and to resist subsequent release of
previously absorbed
fluid as a result of pressure exerted on the core or article as a whole (i.e.
avoid "squeeze
out " of the core). Other considerations, such as the overall capacity of the
absorbent
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2
core, its thickness, and its stiffness are also important with respect to the
design of
superior absorbent articles.
The body side liner of absorbent articles such as those described above,
preferably
allows deposited fluids to penetrate quickly the surface of the liner (i.e.
liner should
exhibit high strike-through). Additionally, once fluids penetrate the liner,
they should not
flow back to the surface of the liner (i.e. liner should exhibit low re-wet).
Preferred body
side liners are also as soft, comfortable, and as non-irritating to the skin
of the user as
possible.
To some extent, the desired characteristics of the body side liner and the
absorbent
core are related. For example, a core which exhibits a high capillary pressure
will also
have an increased tendency to drain fluids from the body side liner, thus
assisting the
body side liner in demonstrating low re-wet. Consequently, the design of an
overall
absorbent article may involve several tradeoffs in design considerations. It
has been
found during development of the present invention that is possible to achieve
advances in
the softness of the topsheet by designing an absorbent core which improves the
performance of the body side liner with respect to rewet as compared to other
cores. In
other words, by utilizing a core of the present invention, the body side
liner, and the
topsheet in particular may be made with a reduced caliper under pressure
without a
corresponding increase in rewet performance of the overall absorbent article.
The
absorbent core of the present invention also allows for improved positive
control of
stiffness as compared to other types of absorbent webs. Such stiffness control
provides
great flexibility in controlling the stiffness of an overall disposable
absorbent article.
The absorbent web of the present invention utilizes a combination of hardwood
pulp fibers and softwood pulp fibers in an airlaid fibrous web. The
incorporation of the
hardwood fibers in the combinations described allows for increased capillary
pressure and
improved fluid distribution compared to absorbent webs without such fiber
content.
Additionally, by making such a web an airlaid structure, it is possible to
incorporate
superabsorbent material throughout the web and to achieve improved stiffness
control
over the resulting web as compared to previous absorbent webs. Consequently,
the
absorbent web of the present invention is particularly well suited for use as
an absorbent
core of a disposable absorbent article due to its high capacity through the
use of fluid
storage by osmotic means (such as superabsorbent material), and its high
control over
stiffness and other physical properties.
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A wide variety of fibrous web structures are known in the art, and many of
these
have attempted to provide high suction and other desirable properties. For
example, U.S.
Patent 5,549,589 issued to Horney et al. describes a fluid distribution member
comprising
S chemically stiffened, twisted, and curled bulking fibers; high surface area
fibers
eucalyptus fibers, and thermoplastic binder fibers. Nevertheless, the Horney
device does
not provide the unique combination of hardwood and softwood pulp fibers in an
airlaid
structure described herein. Additionally, the Horney device does not readily
allow for the
incorporation of superabsorbent particle material throughout the web as is the
case with
the absorbent web of the present invention.
Another absorbent structure is described in U.S. Patents 5,009,650 and
4,699,619
both issued to Bernardin. The Bernardin devices incorporate a layer of
primarily
softwood pulp fiber overlaying a layer of primarily hardwood pulp fiber. The
Bernardin
device, however, does not achieve the benefits of uniform admixture of the
fibers
demonstrated by the present invention. Additionally, the Bernardin device
fails to
incorporate superabsorbent particles throughout the layer. The use of
bicomponent fibers
for bonding of the web layer is also not described.
SUMMARY OF THE INVENTION
The present invention relates to absorbent webs having improved fluid
acquisition
and retention properties. The present invention further relates to absorbent
articles
incorporating such webs as absorbent cores which can be used in absorbent
articles such
as sanitary napkins, diapers, adult incontinence pads and briefs, panty
liners, tampons,
and the like.
In one embodiment of the present invention, the absorbent web of the present
invention comprises a multiplicity of hardwood pulp fibers, a multiplicity of
softwood
pulp fibers, and a superabsorbent material. The hardwood and softwood fibers
and the
superabsorbent are present in a substantially uniform admixture throughout the
web
which is an airlaid web structure. The hardwood pulp fibers may preferably
comprise
eucalyptus fibers, the softwood pulp fibers may preferably comprise southern
softwood
kraft fibers. Preferably, the softwood and hardwood fibers are present in the
web in a
ratio of from about 4:1 to about 1:2, more preferably from about 3:1 to about
1:1.
In an additional embodiment, the absorbent web of the present invention
comprises
a multiplicity of hardwood pulp fibers, a multiplicity of softwood pulp fibers
and a binder
material. The hardwood pulp, softwood pulp and binder material are
incorporated in a
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substantially uniform admixture within an airlaid thermally bonded fibrous
web.
Preferably, the hardwood pulp fibers may comprise eucalyptus fibers, while the
softwood
pulp fibers may preferably comprise southern softwood kraft fibers.
Preferably, the
softwood fibers and the hardwood fibers are present in a ratio of from about
3:1 to about
1:1. Preferably, the web also incorporates a superabsorbent material
throughout.
The absorbent web of the present invention is preferably incorporated into a
disposable absorbent article comprising a liquid pervious topsheet, a liquid
impervious
backsheet joined to the topsheet, and an absorbent core disposed between the
topsheet and
the backsheet. The absorbent web of the present invention serves as the
absorbent core of
such disposable absorbent article. The liquid pervious topsheet of such
absorbent article
may preferably comprise a nonwoven web or an apertured formed film.
In an additional embodiment of the present invention the absorbent web of the
present invention may comprise a multiplicity of hardwood pulp fibers and
multiplicity of
softwood pulp fibers. The hardwood and softwood pulp fibers are incorporated
in a
substantially uniform admixture within an airlaid fibrous web, which web has a
Taber
stiffness of less than about 3 Taber stiffness units. Preferably, the fibrous
absorbent web
further comprises a superabsorbent material incorporated throughout the web.
The
fibrous absorbent web of may also preferably comprise a multiplicity of
bicomponent
fibers incorporated in a substantially uniform admixture within the web. In
one preferred
embodiment, the softwood pulp fibers comprise southern softwood kraft fibers.
The
hardwood pulp fibers, in one preferred embodiment may comprise eucalyptus
fibers.
The absorbent web of the present invention may also comprise a latex surface
coating (e.g. as a process aid to control dusting). The absorbent web of the
present
invention may also be incorporated into a disposable absorbent article in
which two web
layers of the present invention serve as the absorbent core. Superabsorbent
material may
be disposed between such two web layers in such an embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view, partially sectioned, of a preferred embodiment
of an
absorbent article in the form of a sanitary napkin which includes an absorbent
core
according to the present invention.
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FIG. 2 is a cross sectional view taken along line 2-2 of FIG. 1 showing the
interior
layers of sanitary napkin of FIG. 1 which includes an absorbent core according
to the
present invention.
5 FIG. 3 is a cross sectional view of a sanitary napkin in which the absorbent
core
which incorporates two absorbent webs of the present invention with a
superabsorbent
material disposed therebetween.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to absorbent webs having improved fluid
acquisition
and retention properties. The present invention further relates to absorbent
articles
incorporating such webs as absorbent cores which can be used in absorbent
articles such
as sanitary napkins, diapers, adult incontinence pads and briefs, panty
liners, tampons,
and the like.
The absorbent web of the present invention can be utilized in disposable
products
which are capable of absorbing significant quantities of body fluids, such as
urine,
perspiration, menses, and water in body wastes. Such articles may be prepared
in the form
of disposable diapers, catamenial pads, adult incontinence briefs, tampons,
and disposable
towels and wipes, and the like. The web of the present invention is
particularly suited for
use as an absorbent core of such disposable absorbent products.
The absorbent articles herein generally comprise three basic structural
components.
One such component is a substantially liquid impervious backsheet. On top of
this
backsheet is disposed an absorbent core such as any of the fibrous absorbent
webs of the
present invention described herein. On top of this absorbent core and joined
to the
backsheet is a fluid pervious topsheet. Optionally, at least one acquisition
component
(also sometimes referred to as a fluid distribution layer), may be located
between the
topsheet and the absorbent core.
A preferred embodiment of a unitary disposable absorbent article of the
present
invention is the catamenial pad, sanitary napkin 20, shown in FIGS. 1-2. As
used herein,
the term "sanitary napkin" refers to an absorbent article which is worn by
females
adjacent to the pudendal region, generally external to the urogenital region,
and which is
intended to absorb and contain menstrual fluids and other vaginal discharges
from the
wearer's body (e.g., blood, menses, and urine). Sanitary napkins which reside
partially
within and partially external of the wearer's vestibule are also within the
scope of this
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invention. As used herein, the term "pudendal" refers to the externally
visible female
genitalia. It should be understood, however, that the present invention is
also applicable to
other feminine hygiene or catamenial pads such as pantiliners, interlabial
devices, or other
absorbent articles such as incontinence pads, tampons, and the like.
FIG. 1 is a plan view of the sanitary napkin 20 of the present invention in
its flat-
out state with portions of the structure being cut-away to more clearly show
the
construction of the sanitary napkin 20. The portion of the sanitary napkin 20
which faces
or contacts the wearer is oriented towards the viewer. FIG. 2 is a cross-
sectional view of
FIG. 1 taken along line 2-2 and which more clearly shows the interior
structure of sanitary
napkin 20.
As shown in FIGS. 1-2, the sanitary napkin 20 preferably comprises a liquid
pervious topsheet 22, a liquid impervious backsheet 23 joined with the
topsheet 22, and
an absorbent core 25 of the present invention positioned between the topsheet
22 and the
backsheet 23. The sanitary napkin 20 depicted in FIGS. I-2 is a simplified
absorbent
article that could represent a sanitary napkin prior to its being placed on a
wearer's
undergarment. It should be understood, however, that the present invention is
not limited
to the particular type or configuration of sanitary napkin shown in FIGS. 1-2.
The sanitary napkin 20 has two surfaces, a body-contacting surface 20A or
"body
surface" and a garment surface 20B. The sanitary napkin 20 is shown in FIG. 1
as viewed
from its body surface. The body surface 20A is intended to be worn adjacent to
the body
of the wearer while the garment surface 20B is on the opposite side and is
intended to be
placed adjacent to the wearer's undergarments when the sanitary napkin 20 is
worn.
The sanitary napkin 20 has two centerlines, a longitudinal centerline "L" and
a
transverse centerline "T". The term "longitudinal", as used herein, refers to
a line, axis or
direction in the plane of the sanitary napkin 20 that is generally aligned
with (e.g.,
approximately parallel to) a vertical plane which bisects a standing wearer
into left and
right body halves when the sanitary napkin 20 is worn. The terms "transverse"
or "lateral"
as used herein, are interchangeable, and refer to a line, axis or direction
which lies within
the plane of the sanitary napkin 20 that is generally perpendicular to the
longitudinal
direction.
FIG. 1 also shows that the main body portion of the sanitary napkin 20 has a
periphery 30 which is defined by the outer edges of the main body portion of
the sanitary
napkin 20 in which the longitudinal edges (or "side edges") are designated 31
and the end
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edges (or "ends") are designated 32. In the embodiment depicted in FIG. l, the
sanitary
napkin 20 is symmetrical with respect to both the longitudinal and transverse
centerlines.
Sanitary napkin 20 preferably includes side flaps or "wings" 34 that are
folded around the
crotch portion of the wearer's panties. The side flaps 34 can serve a number
of purposes,
including, but not limited to, protecting the wearer's panties from soiling
and keeping the
sanitary napkin secured to the wearer's panties. While the topsheet 22, the
backsheet 23,
and the absorbent core 25 may be assembled in a variety of well known
configurations
(including so called "tube" products or. side flap products), preferred
sanitary napkin
configurations are described generally in U.S. Pat. No. 4,950,264, "Thin,
Flexible
Sanitary Napkin" issued to Osborn on Aug. 21, 1990; U.S. Pat. No. 4,425,130,
"Compound Sanitary Napkin" issued to DesMarais on Jan. 10, 1984; U.S. Pat. No.
4,321,924, "Bordered Disposable Absorbent Article" issued to Ahr on Mar. 30,
1982;
U.S. Pat. No. 4,589,876, "Shaped Sanitary Napkin With Flaps" issued to Van
Tilburg on
Aug. 18, 1987.
FIG. 1 shows a preferred embodiment of the sanitary napkin 20 in which the
topsheet 22 and the backsheet 23 have length and width dimensions generally
larger than
those of the absorbent core 25. The topsheet 22 and the backsheet 23 extend
beyond the
edges of the absorbent core 25 to thereby form not only portions of the
periphery 31 but
also side flaps 34. The backsheet 23 and the topsheet 22 are positioned
adjacent the
garment surface 20B and the body surface 20A, respectively, of sanitary napkin
20 and
are preferably joined to each other to form a perimeter 30. For example, the
backsheet 23
and the topsheet 22 can be secured to each other by a uniform continuous layer
of
adhesive, a patterned layer of adhesive, or an array of separate lines,
spirals, or spots of
adhesive. Adhesives that have been found to be satisfactory are manufactured
by H. B.
Fuller Company of St. Paul, Minn. under the designation HL-1258 or H-2031.
Alternatively, topsheet 22 and backsheet 23 can be joined to each other by
heat bonding,
pressure bonding, ultrasonic bonding, dynamic mechanical bonding, or any other
suitable
method for joining topsheets and backsheets known in the art.
FIG. 2 shows the individual components of the sanitary napkin 20 incorporating
the
absorbent web layer of the present invention. The sanitary napkin 20
preferably
comprises at least three primary components. These include a liquid pervious
topsheet
22, a liquid impervious backsheet 23, and an absorbent core 25 positioned
between the
topsheet 22 and the backsheet 23. Preferably, the sanitary napkin 20 also
comprises at
least one optional acquisition component 44. The acquisition component 44 may
either
be a separate component positioned between the topsheet 22 and the absorbent
core 25, or
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it may comprise part of a composite topsheet or part of the absorbent core 25.
A
disposable absorbent article which incorporates the web of the present
invention need not
necessarily incorporate all of the components listed above. For example, a
tampon may
only incorporate a web layer or layers of the present invention, or may
incorporate a
liquid pervious topsheet and an absorbent core comprising one or more web
layers of the
present invention.
In the sanitary napkin 20 embodiment shown in the drawings, the topsheet 22 is
a
liquid pervious component that permits liquids (e.g., menses and/or urine) to
penetrate
readily through its thickness. The topsheet 22 is preferably as compliant,
soft feeling, and
non-irritating to the wearer's skin as possible. A suitable . topsheet 22 may
be
manufactured from a wide range of materials such as woven and nonwoven
materials; -
polymeric materials such as apertured formed thermoplastic films, apertured
plastic films,
and hydroformed thermoplastic films; porous foams; reticulated foams;
reticulated
thermoplastic films; and thermoplastic scrims. Suitable woven and nonwoven
materials
can be comprised at least partially of natural fibers (e.g., wood or cotton
fibers), synthetic
fibers (e.g., polymeric fibers such as polyester, polypropylene, or
polyethylene fibers) or
from a combination of natural and synthetic fibers.
Preferred topsheets for use in the present are selected from high loft
nonwoven
topsheets and apertured formed film topsheets. Apertured formed films are
especially
preferred for the topsheet because they are pervious to body exudates and yet
non-
absorbent and have a reduced tendency to allow fluids to pass back through and
rewet the
wearer's skin. Thus, the surface of the formed film which is in contact with
the body
remains dry, thereby reducing body soiling and creating a more comfortable
feel for the
wearer. Suitable formed films are described in U.S. Patent 3,929,135, entitled
"Absorptive
Structures Having Tapered Capillaries", which issued to Thompson on December
30,
1975; U.S. Patent 4,324,246 entitled "Disposable Absorbent Article Having A
Stain
Resistant Topsheet", which issued to Mullane, et al. on April 13, 1982; U.S.
Patent
4,342,314 entitled "Resilient Plastic Web Exhibiting Fiber-Like Properties",
which issued
to Radel, et al. on August 3, 1982; U.S. Patent 4,463,045 entitled
"Macroscopically
Expanded Three-Dimensional Plastic Web Exhibiting Non-Glossy Visible Surface
and
Cloth-Like Tactile Impression", which issued to Ahr et al. on July 31, 1984;
U.S. Patent
4,780,352 entitled "Covering Structure For Absorbent Hygienic Sanitary
Products, and an
Absorbent Product Having Such A Covering", which issued to Palumbo on October
25,
1988; U.S. Patent 5,006,394 "Multilayer Polymeric Film" issued to Baird on
April 9,
1991.
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In preferred embodiments of the present invention, the body surface of the
topsheet
22 is hydrophilic so that liquids will be transferred through the topsheet
more readily.
This diminishes the likelihood that menstrual fluid will flow off the topsheet
rather than
flowing into and being absorbed by the absorbent core. The body surface of the
topsheet
22 can be made hydrophilic by treating it with a surfactant. Suitable methods
of treating a
topsheet with a surfactant are described in U.S. Patent 4,950,254 issued to
Osborn and in
U.S. Patent 5,520,875.
In a preferred embodiment, the topsheet 22 comprises an apertured formed film
made in accordance with U.S. Patents 4,342,314 issued to Radel, et al. and
4,463,045
issued to Ahr, et al., which is marketed on sanitary napkins as the DRI-WEAVE
topsheet
by The Procter & Gamble Company of Cincinnati, OH. Such an apertured film is
preferably obtained as product No. X-5652 from Tredegar Film Products of Terre
Haute,
IN. In this preferred embodiment, during manufacture the resin used to form
the
apertured film is preferably provided with a surfactant incorporated therein
as is described
in SIR No. H1670 published July 1, 1997 in the name of Aziz, et al.
In a particularly preferred embodiment, the topsheet 22 is an apertured formed
film
which comprises microscopic surface aberrations on the land areas of the
formed film.
The film also includes microscopic depositions of a low surface energy
material at least
some of which depositions are located on the land areas between the
microscopic surface
aberrations. Such a preferred apertured formed film is more fully described in
allowed
U.S. Patent Application Serial No. 08/826,508 entitled "Fluid Transport Webs
Exhibiting
Surface Energy Gradients" filed in the name of Ouellette, et al. on April 11,
1997 (PCT
Publication WO 96/00548, published January 11, 1996). The combination of the
absorbent web of the present invention as an absorbent core with the topsheet
described in
this paragraph within a sanitary napkin or similar absorbent article, provides
a unique
combination of softness and dryness characteristics (as measured by re-wet
performance).
The advantages of such combinations are more fully described in co-pending
U.S. Patent
Application Serial No. 60/128267, filed on April 8, 1999, in the name of
Walker, III.
The backsheet 23 prevents the exudates absorbed and contained in the absorbent
core 25 from wetting articles which contact the sanitary napkin 20 such as
pants, pajamas
and undergarments. The backsheet 23 is preferably resistant to the flow of
liquids, and
more preferably is impervious to liquids (e.g., menses and/or urine). The
backsheet 23 is
preferably manufactured from a flexible material. As used herein, the term
"flexible"
refers to materials which are compliant and will readily conform to the
general shape and
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contours of the human body. The backsheet 23 may comprise a woven or nonwoven
material, polymeric films such as thermoplastic films of polyethylene or
polypropylene,
or composite materials such as a film-coated nonwoven material. Preferably,
the
5 backsheet 23 is a polyethylene film having a thickness of from about 0.012
mm (0.5 mil)
to about 0.051 mm (2.0 mils). The backsheet 23 may be embossed and/or matte
finished
to provide a more clothlike appearance. Further, the backsheet 23 may permit
vapors to
escape from the absorbent core 25 (i.e., breathable) while still preventing
exudates from
passing through the backsheet 23. A suitable backsheet material is obtained as
product
10 No. 18-1401 from the Clopay Corporation of Cincinnati, Ohio. A suitable
breathable
backsheet material is a laminate of an apertured film such as that described
in U.S. Patent
3,929,135 issued to Thompson which is inverted so that the srrialler openings
of the
tapered capillaries face the absorbent core 25 which is adhesively laminated
to a
microporous film such as that described in Exxon's U.S. Patent 4,777,073.
The absorbent core 25 comprises the fibrous absorbent web layer 40 of the
present
invention. The absorbent core 2~ may be manufactured in a wide variety of
sizes and
shapes (e.g., rectangular, oval, hourglass, dog bone, asymmetric, etc.). The
configuration
and construction of the absorbent core 25 may also be varied (e.g., the
absorbent core may
have varying caliper zones (e.g., profiled so as to be thicker in the center),
or may
comprise one or more layers or structures. The total absorbent capacity of the
absorbent
core should, however, be compatible with the design loading and the intended
use of the
sanitary napkin. Further, the size and absorbent capacity of the absorbent
core may be
varied to accommodate different uses such as incontinence pads, pantiliners,
regular
sanitary napkins, or overnight sanitary napkins.
The fibrous absorbent web 40 of the present invention is an airlaid fibrous
web
comprising a substantially uniform admixture of hardwood pulp fibers and
softwood pulp
fibers. Preferably, the fibrous absorbent web also incorporates superabsorbent
material
throughout the web. Additionally, the fibrous web layer 40 may also
incorporate a binder
material such as bicomponent binder fibers in the uniform admixture of fibers
described
above.
In addition to one of more of the fibrous absorbent webs 40 of the present
invention, the absorbent core 25 may incorporate other absorbent layers. Such
other
layers may include any other suitable absorbent material known in the art for
such
products. Additionally, as shown in FIG. 3, the absorbent core 25 may
incorporate more
than one fibrous absorbent web 40 layer of the present invention. Such layers
40 may
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have any of the variations described herein and in the appended claims as
within the scope
of the present invention. In the embodiment shown in FIG. 3, the two fibrous
web layers
40 have a superabsorbent material 50 disposed therebetween. If desired, a
superabsorbent
material may also be incorporated in a uniform or non-uniform manner into one
or both of
the fibrous web layers 40 shown in FIG. 3. In the embodiment shown in FIG. 3,
each of
the fibrous absorbent web layers 40 which comprise the absorbent core 25
contains a
substantially uniform mixture of hardwood pulp fibers, softwood pulp fibers,
and a binder
material (such as bicomponent binding fibers or a powdered binder) in a
thermally
bonded airlaid structure.
Unless otherwise noted, all ratios given below are expressed.in terms of
weights of
the quantities being considered. Preferably, the fibrous absorbent web 40 of
the present
invention includes a ratio of softwood pulp fibers to hardwood pulp fibers in
the range of
from about 4:1 to about 1:2, more preferably from about 3:1 to about 1:1, most
preferably
about 2:1. A particularly preferred hardwood pulp fiber is a eucalyptus fiber.
A
particularly suitable eucalyptus fiber includes those of the eucalyptus
grandis species.
The hardwood pulp fibers, and eucalyptus in particular, have high surface
area, thereby
providing the absorbent web with a high capillary pressure. Too much hardwood
pulp
fiber, however, in the web will reduce its overall absorbent capacity.
Additionally, the
presence of excess hardwood pulp fiber may lower the fluid handling speed of
the web to
an unacceptably low level. Other suitable fibers for use as a hardwood pulp
fiber in the
fibrous web layer 40 of the present invention may include acacia, oak, maple,
or cherry
fibers.
The hardwood pulp fibers are blended in the fibrous absorbent web 40 with a
multiplicity of softwood pulp fibers. The softwood pulp fibers are preferably
blended into
the web in the ratios indicated above. A particularly preferred softwood pulp
fiber is
southern softwood kraft fibers. Other suitable softwood fibers include western
or northern
softwood kraft fibers.
The blend of hardwood pulp fibers and softwood pulp fibers provides a web with
different sized fibers incorporated throughout. This provides a good
distribution of fiber
surface area. As noted above, the use of hardwood fibers involves tradeoffs
between
capillary pressure, and capacity and/or fluid handling speed. Because the
fibrous webs 40
of the present invention are airlaid, they are readily amenable to the
inclusion of a
superabsorbent material. Such superabsorbent material will improve the overall
capacity
of the web, thereby advantageously combining high capacity and high capillary
pressure.
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The fibrous absorbent web 40 of the present invention preferably incorporates
bicomponent binding fibers and/or a superabsorbent material. In more preferred
embodiments, both the bicomponent fibers and the superabsorbent material are
present in
the web and are blended in a substantially uniform mixture throughout the web
thickness.
The addition of bicomponent fibers allows for positive stiffness control of
the
overall layer. The stiffness of the web is controlled by adjusting the amount
of
bicomponent fiber as well as the time and temperature parameters of the
thermal bonding
process. In a particularly preferred embodiment, about 5% to about 30%, more
preferably
about 15% to about 25%, of the web is bicomponent fibers. A preferred fiber
comprises
a polyethylene / polypropylene fiber in which the polypropylene core is
surrounded by a
polyethylene sheath. Such a suitable SO%/50% concentric bicomponent fiber is
available
form Danaklon of Varde, Denmark.
Other binder materials may be included within the web structure as well.
Polyethylene powder binders and/or latex binder material may be, but need not
be,
incorporated into the web structure. The use of a powder binder such as
polyethylene
allows the web to be a thermally bonded structure as is the case with the
bicomponent
binder fibers described above. If latex, or a similar binder is used, the
latex will act as the
binder and the structure may be described as "latex bonded."
Any variety of superabsorbent particulate material may be incorporated into
the
fibrous absorbent web of the present invention. One especially preferred
material is SAB
960 available from Stockhausen Louisiana, Ltd. of Garyville, LA. Other
especially
preferred superabsorbent materials include surface crosslinked polyacrylates
such as
ASAP 2300 available from Chemdal, Corp. of Palatine, IL and the mixed bed
materials
described in copending, commonly assigned US Patent application Serial No.
09/258,890,
filed in the name of Hird, et al. on March 1, 1999. A superabsorbent fiber
known as
"FIBERDRI" available from Camelot Superabsorbents, Ltd.., Calgary, Alberta, is
also
suitable. The superabsorbent material may take any suitable form including
fibers, flakes,
or small discrete particles. As used herein, the term "particles" is intended
to mean any of
these forms of superabsorbent material. In preferred embodiments, the
superabsorbent
material comprises small flakes or discrete particulate material incorporated
into the web
40. Such superabsorbent material preferably comprises from about 10% to about
50% of
the overall fibrous absorbent web. A higher amount of such superabsorbent
material
increases the overall capacity of the web layer 40. Excess superabsorbent
material,
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13
however, may reduce the permeability of the web layer 40 due to gel blocking
or similar
effects.
The fibrous absorbent web of the present invention may be made by any suitable
airlaying technique known in the art. The use of airlaying allows the
incorporation of
particulate superabsorbent material throughout the structure, as well as
greater positive
control over the web physical properties than may be possible with other web
forming
techniques.
When the web incorporates bicomponent fibers, the web is preferably formed
using
a thermally bonded airlaid technique as described above. In such a
construction, the use
of additional binder material such as powder binder or latex is not required.
Such
additional materials may, nonetheless, be included in order to form a mufti-
bonded airlaid
web. Additionally the web need not incorporate any bicomponent fiber, and may
use
latex in combination with the superabsorbent particles and hardwood and
softwood pulp
fibers as described above to form a latex bonded airlaid structure. Suitable
methods of
forming such airlaid structures are well known in the art. Another alternative
includes the
use of a powdered binder such as polyethylene together with a multiplicity of
hardwood
pulp and softwood pulp fibers to form a thermally bonded airlaid web.
U.S. Patent 5,445,777 describes a preferred method of adding a particulate
superabsorbent material and/or a powdered binder material (such as the
polyethylene
binder described above) to a fibrous airlaid web. Such techniques are suitable
for
construction of the fibrous absorbent webs 40 of the present invention.
The airlaid web may be made with any suitable basis weight and thickness for
the
article in which is to be utilized. A preferred web for use in a sanitary
napkin may have a
total basis weight of about 60 to about 400 g/m' and a preferred density of
about 0.05 to
about 0.2 g/cc. Any suitable thickness may be used. In the sanitary napkin 20
shown in
FIGS. 1-2, the thickness of the web 20 of the present invention may be about
1.5 mm.
As noted the absorbent web layer 40 of the present invention provides for high
capillary pressure, and improved control over the overall flexibility
characteristics of
absorbent articles into which it is incorporated. In particularly preferred
embodiments,
the fibrous absorbent web 40 of the present invention comprises the above
described
combination of hardwood pulp fibers and softwood pulp fibers in an airlaid
fibrous web.
The web stiffness properties are controlled as described above to yield a
layer with a
Taber stiffness of less than or equal to 3 Taber stiffness units. Taber
stiffness is measured
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14
using the Taber stiffness test described in ASTM standard D5650-97 "Standard
Test
Method for Resistance to Bending of Paper of Low Bending Stiffness (Taber-Type
Tester
in 0 to 10 Taber Stiffness Unit Configuration)," available from the American
Society for
Testing and Materials, West Conshohocken, PA.
The acquisition component (or "acquisition layer" or "distribution layer") 44,
if
used, preferably lies beneath the topsheet 22. The terms "layer" or "web", as
used herein,
include but are not limited to single unfolded sheets, folded sheets, strips
of material,
loose or bonded fibers, multiple layers or laminates of material, or other
combinations of
such materials. These two terms are thus, not limited to single unfolded
layers or sheets
of material. The acquisition component 44 may provide void volume beneath the
topsheet 22 to increase the ability of the sanitary napkin to draw liquids
through the
topsheet 22. In the preferred embodiment described herein, the acquisition
component
44 preferably provides resiliency to lateral compressive forces so that the
sanitary napkin
20 has improved resistance to bunching.
The acquisition layer 44 serves to collect quickly and temporarily hold
discharged
bodily fluids, as well as facilitating transport the fluid from the point of
initial fluid
contact to other parts of the acquisition layer 44 and the absorbent core 25.
There are
several reasons why the improved transport of exudates is important, including
providing
a more even distribution of the exudates throughout the absorbent core and
allowing the
sanitary napkin 20 to be made relatively thin. The transport referred to
herein may
encompass the transportation of liquids in one, two or all directions (i.e.,
in the x-y plane
and/or in the z-direction). The acquisition layer 44 may be comprised of
several different
materials including nonwoven or woven webs of synthetic fibers including
polyester,
polypropylene, or polyethylene, natural fibers including cotton or cellulose,
blends of
such fibers, or any equivalent materials or combinations of materials.
Examples of
sanitary napkins having an acquisition layer 44 and a topsheet 22 are more
fully described
in U.S. Pat. No. 4,950,264 issued to Osborn and U.S. patent application
Serial. No.
07/810,774, "Absorbent Article Having Fused Layers", filed Dec. 17, 1991 in
the names
of Cree, et al. Each of these references are incorporated herein by reference.
In a preferred
embodiment, the acquisition layer may be joined with the topsheet by any of
the
conventional means for joining webs together, most preferably by fusion bonds
as is more
fully described in the above-referenced Cree application.
The acquisition component 44 should be liquid permeable. The acquisition
component 44 is also preferably compliant, soft feeling, and non-irritating to
the user's
CA 02369604 2001-10-05
WO 00/59439 PCT/US00/09519
skin. The acquisition component 44 has a body-facing face (or side), and a
garment-
facing face. The acquisition component 44 may be of any suitable size and
shape. In the
embodiment shown in FIG. l, the acquisition component 44 is in the shape of a
race track
5 with slightly concave side edges, as is the portion of the topsheet 22 that
overlies the main
body portion of the sanitary napkin 20. The dimensions of the acquisition
component 44,
however, are preferably not as large as those of the topsheet 22.
The acquisition component 44 is preferably made from any materials suitable
for
the above purposes that are capable of having the topsheet 22 fused to them.
The
10 acquisition component 44 may, for example, be comprised of woven or
nonwoven
materials. The fibers or other components of these materials may be synthetic,
or
partially synthetic and partially natural. Suitable synthetic fibers include
polyester,
polypropylene, polyethylene, nylon, viscous rayon, or cellulose acetate
fibers. Suitable
natural fibers include cotton, cellulose, or other natural fibers. The
acquisition component
15 44 may also be at least partially comprised of cross-linked cellulose
fibers. The
acquisition component 44, if nonwoven, can be made by a number of different
processes.
These include, but are not limited to: air laid, wet laid, meltblown,
spunbonded, carded,
thermally bonded, air-through bonded, powder bonded, latex bonded, solvent
bonded,
spunlaced, and combinations of the foregoing.
The acquisition component 44 may be constructed in the manner described in
U.S.
Patent 5,549,589, issued on August 27, 1996 in the name of Horney et al. with
respect to
the distribution layer described therein. Another preferred construction for
the acquisition
component 44 is a laminate of two nonwoven materials. The uppermost layer of
this
laminate (or "secondary topsheet") preferably comprises an 19 g/yd2 (22.5
g/m2)
spunbonded polypropylene nonwoven material referred to as product No.
065MLPV60U
(or "P-9") obtained from Fiberweb, North America of Washougal, WA. The
underlying
layer of the laminate (or "tertiary topsheet") preferably comprises a mufti-
bonded air laid
nonwoven material that is thermally bonded using powder bonding and latex
bonding. In
a preferred embodiment, this mufti-bonded air laid nonwoven material comprises
about
77% cellulose fibers, about 20% powder binder, and about 3% latex binder (1.5%
sprayed
on each side of the web) and has a basis weight of about SO g/yd2 (about 60
g/m2).
(Unless otherwise stated, all percentages herein are by weight.) Such a mufti-
bonded air
laid nonwoven is preferably obtained as product No. 90830X312 from Merfin
Hygienic
Products, Ltd. of Delta, British Columbia. These two nonwoven layers are
preferably
laminated together by depositing the mufti-bonded air laid nonwoven material
on the
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WO 00/59439 PCT/US00/09519
16
spunbonded polypropylene nonwoven material. The spunbonded material is used as
a
process aid or Garner web in the process of forming this laminate.
In alternative embodiments, the spunbonded polypropylene nonwoven material
S may have a greater or a lower basis weight, or it may be replaced by an air
laid tissue, a
wet laid tissue, or any of the materials described above. If a wet laid tissue
is used instead
of a polypropylene nonwoven material, the orientation of the laminate is
preferably
reversed so that in the finished product, the multi-bonded air laid nonwoven
material lies
above the wet laid tissue layer. In the case of thicker sanitary napkins, any
of the
acquisition components described above can be used. Additionally, in one
preferred
thicker sanitary napkin embodiment, a low density latex bonded air laid
material can be
used as the entire acquisition component (that is, no tertiary topsheet is
required). A low
density latex bonded air laid material suitable for this purpose is a material
having a basis
weight of about 80 g/m2 known as product No. FG413MHB, which is obtained from
Walkisoft, USA of Mt. Holly, NC.
The topsheet 22 described herein is preferably fused to the acquisition
component
44 or to the absorbent core 25, or to both. A suitable manner for fusing (or
integrating)
the topsheet to underlying components at discrete sites is described in U.S.
Patent
Application Serial No. 09/074,909 filed on May 8, 1998, in the name of Daniels
et al. and
in International Patent Application Serial No. PCT/LJS96/2087, filed on
December 20,
1996, in the name of Lynard et al., which application designates the United
States. As
described in the above-referenced applications, the bonding of the topsheet to
underlying
layers is preferably done at discrete locations and the center of the article
is provided with
an "un-bonded window."
The topsheet 22, the acquisition component 44, if included, the backsheet 23,
and
the absorbent core 25 may be assembled in a variety of configurations known in
the art
(including layered or "sandwich" configurations and wrapped or "tube"
configurations).
FIGS. l and 2 show a preferred embodiment of the sanitary napkin 20 assembled
in a
sandwich construction. In FIGS. 1 and 2, the topsheet 22 and the backsheet 23
have
length and width dimensions generally larger than those of the absorbent core
25. The
topsheet 22 and the backsheet 23 extend beyond the edges of the absorbent core
25 to
form portions of the periphery 30. The garment-facing side of the topsheet 22
is
preferably joined to the body-facing side of the acquisition component 44 as
described
above. The acquisition component 44 may be joined to the absorbent core 25, if
desired.
If these components are joined, they can be joined in any of the manners
described herein
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17
for joining the topsheet 22 to the acquisition component 44. However, in the
embodiment
shown in the drawings, the acquisition component 44 is not directly joined to
the
absorbent core 25. The backsheet 23 is preferably joined to the garment-facing
side of the
absorbent core by adhesives.
The portions of the topsheet 22 and backsheet 23 that extend beyond the edges
of
the absorbent core 25 and the acquisition component 44 are preferably also
joined to each
other. These portions of the topsheet 22 and backsheet 23 can be joined in any
suitable
manner known in the art. The term "joined", as used in this specification,
encompasses
configurations in which an element is directly secured to another element by
affixing the
element directly to the other element; configurations in which the element is
indirectly
secured to the other element by affixing the element to intermediate members)
which in
turn are affixed to the other element; and configurations in which one element
is integral
with another element, i.e., one element is essentially part of the other
element. Preferably,
in the embczdiment shown, these portions of the topsheet 22 and backsheet 23
are joined
using adhesives over substantially the entire portions that extend beyond the
edges of the
absorbent core 25 and a crimp seal at the end edges 32 of the main body
portion where the
topsheet 22 and backsheet 23 are densified by the application of pressure or
heat and
pressure.
The sanitary napkin 20 shown in FIGS. 1-2, as discussed above, preferably
comprises an optional pair of flaps 34 that are joined to the main body
portion. The flaps
34 extend laterally outward beyond the longitudinal side edges of the main
body portion
from their proximal edges to their distal edges (or "free end"). The flaps 34
extend
outward from at least the central region of the main body portion.
The flaps 34 can be joined to the main body portion in any suitable manner.
Preferably, in the embodiments shown in FIGS. 1-2, the flaps 34 are integral
with the
main body portion (that is, the flaps 34 comprise integral extensions of the
topsheet 22
and backsheet 23). In other alternative embodiments, the flaps 34 can comprise
separate
components that are joined to the main body portion.
The flaps 34 can be in any suitable configuration. Suitable flaps are
described in
Reexamined Patent No. B 1 4,589,876 entitled "Sanitary Napkin", issued to Van
Tilburg,
Certificate of Reexamination issued April 27, 1993; U.S. Patent 4,687,478
entitled
"Shaped Sanitary Napkin With Flaps", which issued to Van Tilburg on August 18,
1987;
U.S. Patent 5,389,094 entitled "Absorbent Article Having Flaps and Zones of
Differential
Extensibility" issued to Lavash, et al. on February 14, 1995; U.S. Patent
5,558,663
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18
entitled "Absorbent Article Having Undergarment Covering Components With Zones
of
Extensibility" issued to Weinberger, et al. on September 24, 1996 (which
describes an
alternative to flaps that are applied by the wearer); and in International
Patent Application
Serial No. PCT US 96/15957 entitled "Absorbent Article Having Flaps With Step
Configuration and Zones of Extensibility" filed on October 3, 1996, in the
name of Lash,
et al. Other preferred features for the flaps 34 including a deformed region
that forms a
hinge and zones of extensibility or zones of differential extensibility are
described in U.S.
Patent Application Serial No. 09/074,909 filed on May 8, 1998, in the name of
Daniels et
al. and International Patent Application Serial No. PCT/LJS96/2087, filed on
December
20, 1996, in the name of Lynard et al., which application designates the
United States.
The garment surface 20B of the sanitary napkin 20 may include, and preferably
does include, fasteners for attaching the sanitary napkin to the wearer's
undergarment.
FIG. 2 shows the central pad fastener 82 which is adapted to secure the main
body portion
of the sanitary napkin to the crotch region of an undergarment. Any types of
fasteners
known in the art, such as adhesive fasteners and mechanical fasteners can be
used.
Fasteners comprising adhesives have been found to work well for this purpose,
with
pressure-sensitive adhesives being preferred. In a preferred embodiment, the
central pad
fastener 82 comprises a pair of spaced apart longitudinally-oriented strips or
zones of
adhesive that are centered about the longitudinal centerline L.
The outer surface of the flaps 34, adjacent the distal edges of the flaps, is
preferably
provided with a flap adhesive 84. The flap adhesive 84 is used to assist in
maintaining
the flaps 34 in position after they are wrapped around the edge of the crotch
portion of the
panty. Suitable adhesive fasteners are described in greater detail in U.S.
Patent
4,917,697. The flaps 34 can be maintained in position by attaching the flaps
34 to the
undergarment, or to the opposing flap.
The fasteners used with the present invention are not limited to adhesive
attachment
means. Anv type of fastener used in the art can be used for such purpose. For
example,
the sanitary napkin 20 could be secured to the wearer's undergarment by
mechanical
fasteners, such as VELCRO, or the fasteners described in U.S. Patent 4,946,527
entitled
"Pressure-Sensitive Adhesive Fastener and Method of Making the Same" issued to
Battrell on August 7, 1990, or U.S. Patent 5,392,498 entitled "Non-Abrasive
Skin
Friendly Mechanical Fastening System" issued to Goulait, et al. on February
28, 1995.
For simplicity, however, the fasteners will be described in terms of adhesive
attachment
means.
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19
The adhesive attachment means are respectively covered by removable release
liners, central pad release liner and flap release liner, both designated 86.
The pressure-
sensitive adhesives should be covered with release liners 86 to keep the
adhesives from
sticking to extraneous surfaces prior to use. Suitable release liners are
described in U.S.
Patent 4,917,697. A particularly preferred release liner which also serves as
an individual
package for wrapping the sanitary napkin is described in U.S. Patent 4,556,146
issued to
Swanson, et al.
Numerous other embodiments of the sanitary napkin 20 are possible. For
example,
the main body portion of the sanitary napkin can be provided in the form of a
compound
sanitary napkin that has its components bonded as described herein,for
improved integrity
and acquisition. General descriptions of compound sanitary napkins are found
in P&G's
U.S. Patent 4,425,130 entitled "Compound Sanitary Napkin" issued to DesMarais,
et al.
on January 10, 1984, and in Statutory Invention Registration H1614 entitled
"Body
Fitting Compound Sanitary Napkin", published in the name of Mayer, et al. on
November
5, 1996. T~ form the compound sanitary napkin, a sanitary napkin such as that
described
herein can serve as the panty protector (or "base pad") and a tube of
absorbent material
wrapped by a topsheet (or "primary menstrual pad") can be placed on top of the
sanitary
napkin and attached thereto at the ends. The fusion bonding on the base pad is
preferably
distributed in the same manner as shown on the drawings herein. The attachment
of the
tube to the sanitary napkin is preferably achieved by fusion bonding
extensions of the
topsheet material at the ends of the tube to the base pad. In some preferred
embodiments
of such a compound sanitary napkin, there may also be attachment between the
ends of
the tube of absorbent material and the base pad. The tube of the compound
sanitary
napkin can be attached to the base pad between its ends by any suitable
attachment
means, such as by adhesives.
The sanitary napkin 20 of the present invention is utilized by removing the
release
liners 86 and placing the sanitary napkin 20 in a panty. The main body portion
22 is
placed in t'.~e crotch portion of the panty with one end of the main body
portion 22
extending towards the front section of the panty and the other end towards the
back
section of ;he panty. The backsheet 23 is placed in contact with the inner
surface of the
center of tl;e crotch portion of the panty. The central pad adhesive fastener
82 maintains
main body portion in position. The distal portions of the flaps 34 are folded
around the
side edges of the panty. The flap adhesives 84 secure the flaps 34 to the
underside of the
panty or to the opposing flap.
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The absorbent web layer of the present invention may also be incorporated into
other types of disposable absorbent articles such as pantiliners, incontinence
pads,
diapers, or tampons.
5 The disclosures of all patents, patent applications (and any patents which
issue
thereon, as well as any corresponding published foreign patent applications),
and
publications mentioned throughout this patent application are hereby
incorporated by
reference herein. It is expressly not admitted, however, that any of the
documents
incorporated by reference herein teach or disclose the present invention. It
is also
10 expressly not admitted that any of the commercially available materials or
products
described herein teach or disclose the present invention.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention.
