Note: Descriptions are shown in the official language in which they were submitted.
~3~J~
This invention is directed to an improved absorbent structure
designed for use in absorbent pads such as diapers, for absorbing body
fluids.
This invention relates to an absorbent structure such as may be
used in a disposable diaper, which is an imp~vement upon Applicant's
U.S. Patent No. 4,699,619 issued October 1~, 1987.
Disposable diapers generally include an inner, liquid permeable
liner that lies closest to the wearer's skin. An outer, liquid
impenneable cover is disposed at the outside of the diaper, furthest
away from the wearer. In between the liner and the cover is a fibrous
liquid absorbent material or batt.
In general, the most economical liquid absorbent material for use
in disposable diapers is cellulosic fibers such as co~minutecl wood
pulp, commonly known in the art as "fluff pulp," or simply "fluff."
Batts made from these fibers have a low density and a high capacity
for absorbing fluids, but their wicking ability is very poor. Thus,
the low central crotch portion of the diaper as worn tends to become
very wet when waste fluids are released thereupon, while the fluff
included in the higher portions of the diaper (as worn) can remain dry
with its absorbent capacity unused.
Several problems are posed by this. First, it is uneconomical to
line a diaper with fluff, the majority of which will be wasted.
Further, there can be leakage from the liquid saturated central
portion of the diaper. Still further9 this concentration of liquid
localized in one region of the diaper can cause discomfort to the
wearer of the diaper.
One prior art approach noted by Sigl in U.S. Patent No. 4,213,459
to avoid some of these problems is to decrease the pore size such that
the improved capillary action of the pores overcomes the force of
,~
gravity suf~iciently to cause the waste liquid to move upwardly in the
diaper. However, it has been noted that the total absorption capacity
is reduced by reducing the average pore size. Nevertheless, the use
of this approach to achieve a better distribution of fluid throughout
the available area in the diaper has generally been the approach of
choice despite the resulting loss in absorption capacity.
A Further step was taken towards the solution of these problems
by Sigl (in U.S. Patent No. 4,213,459, assigned to the assignee of the
present invention). Sigl discloses providing a localized area of
increased density fluff in the batt for wicking waste fluid to a
higher portion of the diaper. Although this presented an advance in
the art, it was not without drawbacks. First, the surface of the
diaper nearest the wearer's skin directly beneath the lining becomes
soaked. Further, the only places where liquid could be transferred
from the lower density material to the higher density material were at
the borders or edges where the lower density material adjoins the
higher density material. Thus, it was suggested in that pa~ent that
the areas around the densified region of the batt should remain
undensified.
Prior published British patent applications 2,132,897 and
2,063,683 of Colgate-Palmolive each disclose diapers having
multi-layered absorbent pads.~ The 2,132,~97 reference disclosed
spaced, lengthwise strips of hydrogel, coated upon and sandwiched
between the surfaces of the pads.
Likewise9 prior published British Patent Application Nos.
2,061,115, 2,089,214 and 2,111,836 of the instant assignee all
disclose sanitary napkins having multi-layered absorbent pads.
Prior published British Patent Application Nos. 2,175,024A and
2,175,212A of Procter & Gamble also disclose absorbent articles which
either have a concentration of superabsorbent material in the back
face hal~ of a single pad or a discrete superabsorbent treated core
underlying a top pad in ~he front of a diaper wherein urine is
immediately excreted.
The prior art does not recognize that fluid can be distributed to
remote areas of a diaper and retained remote from the crotch area o~ a
3l3~
wearer, as well as being retained in the immediate urination target
zone.
The present invention provides a further advancement in the art,
as will be fully explained below
SUMMARY OF THE IN~ENTION
-
According to the invention, a disposable absorbent garment is
provided of the type having an absorbent structure having opposed
longitudinal ends, a central rotch portion and wherein there is
included a body-facing sheet, a backing sheet and liquid absorbing
material therebetween. The liquid absorbing material comprises a
first layer comprising cellulosic fibers and having a density from
about 0.03 to about 0.14 g/cc, said first layer having a top surface
underlying the facing sheet and a bottom surface opposite from the top
surface thereof.
A second layer comprising cellulosic fibers is formed
substantially separately from and underlying at least a portion of
said first layer, having top and bottom surfaces, a density from about
0.14 to about 0.3 g/cc, a total void volume greater than about 80% and
an average pore size distribution generally less than the average pore
size distribution of the first layer. There is an overlap in the pore
size distributions of the first and second layers such that the
smallest pores in the first layer are smaller than the largest pores
in the second layer.
Front and rear fluid storage pouches each comprising
superabsorbent material disposed in a hydrophilic web are located
underlying the first layer and spaced from one another at the opposed
rongitudinal ends, respectively, of the absorbent structure.
In one preferred embodiment, the fluid storage pouches are
disposed beneath the bottom surface of the second layer in fluid
conductive contact therewith wherein a surface of the superabsorbent
material is in contact with the bottom surface of the second layer.
In another preferred embodiment, the front and rear retention
pouches are respectively disposed at the front one-third and rear
one-third of the absorbent structure, the central crotch portion of
~L3~J~
the absorbent structure being substantially free of superabsorbent
material.
In a further preferred embodiment, the first layer comprises
softwood fibers and the second layer comprises hardwood fibers
Objects and advantages of the invention will best be understood
with reference to the following detailed description read in
connection with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective plan view of a first preferred embodiment
of the invention without the superabsorbent material included therein.
FIG. 2 is a longitudinal cross-sectional view taken along line
2-2 of FIG. 1.
FIG. 3 is a perspective plan view of a second preferred
embodiment of the invention, without the superabsorbent included
therei n .
FIG. 4 is a longitudinal cross-sectional view taken along line
~-4 of FIG. 3.
FIG. 5 is a perspective plan view with several cutaway portions
of a third preferred embodiment of the present invention without the
superabsorbent material included therein.
FIG. 6 is a perspective~ plan view of a fourth preferred
embodiment of the present invention, including a portion of
superabsorbent matPrial incorporated therein.
FIG. 7 is a longitudinal cross-sectional view taken along line
7-7 of FIG. 6.
FIG. 8 is a perspective plan view of a fifth preferred embodiment
of the present invention including a portion of superabsorbent
material incorporated therein.
FIG. 9 is a longitudinal cross-sectional view taken along line
9-9 of FIG. 8.
FIG. 10 is a perspective plan view of a sixth preferred
embodiment of the invention wherein the superabsorbent material is
disposed in a pair of spaced fluid retention pouches.
FIG. 11 is a longitudinal cross-sectional view taken along line
11-11 of FIG. 10.
~ ~JJ~ 3l
FIG 12 is a perspective plan view of a seventh preferred
embodiment of the present invention showing an alternative arrangement
of the fluid retention pouches.
FIG. 13 is a longitudinal cross-sectional view taken along line
13 of FIG. 12.
FIG. 14 is an absorbency profile for the control diaper tested in
Example 1.
FIG. 15 is an absorbency profile for the diaper containing one
ply of compressed fluff in addition to the regular fluff component as
discussed in Example 1.
FIG. 16 is an absorbency profile for the diaper containing two
plies of compressed fluff in addition to the regular fluff component
as discussed in Example 1.
FIG. 17 is the absorbency profile for the diaper containing three
plies of compressed fluff in addition to the regular fluff component
as described in Example 1.
FIG. 18 is the absorbency profile for the diaper containing two
plies of compressed fluff plus a portion of superabsorbent mater;al as
described in Example 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to the drawings, the disposable diaper l in which the
present invention is embodied comprises generally a body facing,
liquid permeable liner 2, an outer liquid impermeable cover 3, and a
liquid absorbing material indicated generally as 4 therebetween. The
focus of this invention is directed to the liquid absorbing material
4. The liquid absorbing material 4 comprises a first, lower density
layer 5 of cellulosic fibers such as comminuted wood pulp (fluff)
which lies beneath the inner liner 2. A second, higher density layer
6 of fluff lies beneath at least a portion of the first lower density
layer 5 such that waste fluid can be transferred from the lower
density layer 5 to the higher density layer 6. Thus, a lower surface
l5 of the lower density layer 5 should be contiguous with at least a
portion of an upper surface 16 of the higher density layer 6.
However, a tissue layer can be placed between the layers 5 and 6
without departing from the scope of this invention.
~3i~
Predominantly softwood pulp ~luff can be used for each of the
layers 5 and 6. Alternatively, a layer of predominantly softwood
fluff can be used for the layer 5 and a layer o~ preponderantly
hardwood fluff can be used for the layer 6, in which case it is the
average pore size and not necessarily the density that varies between
the layers 5 and 6, as will shortly be explained. For the purposes of
this disclosure and the accompanying claims, "predominantly" is
intended to mean at least about 80% while "preponderantly" is intended
to mean at least about 50~.
In the first preferred embodiment shown in FIGS. 1 and 2, the
higher density layer 6 is formed as a strip extending from a target
area 7, where liquid waste will initially accumulate, to an upper edge
8 towards the back of the diaper. The higher density layer 6 draws
waste fluid from the lower density layer 5 in the target area 7
upwardly towards the edge 8 at the back of the diaper 1. Further,
along upper regions 18 of the higher dens~ty layer 6 towards the upper
edge 8 there is, surprisingly, substantial fluid transfer back from
the higher density layer 6 to the lower density layer 5. It ~s
important to note that although this flowback occurs from the higher
density layer 6 to the lower density layer 5, the lower density layer
5 only draws sufficient fluid to satisfy its unsaturated capillary
forces proximate to the higher density layer 6, where there is an
overlap in pore sizes such that the smallest pores in the lower
density layer 5 are smaller than the largest pores in the higher
density layer 6. The lower density layer 5 drains fluid from the
higher density layer 6 but does not become soaked, with the advantage
that the wearer's comfort is maintained while a significant proportion
of the absorption capacity of the lower density layer 5 is utilized.
Alternative embodiments according to this aspect of the invention
are shown in FIGS. 3 through 5. According to the second preferred
embodiment in FIGS. 3 and 4, the higher density layer 6 extends as a
strip along the entire length of the diaper. According to the third
preferred embodiment shown in FIG, 5, the higher density layer 6 is
coextensive with the entire lower density layer 5.
Yet another alternative to each of the embodiments described
above is that of varying the pore size without necessarily varying the
~13~
density. For example, the present inventor has discovered that the
fine fiber dimensions of hardwood fluff can be utilized to advantage
by substituting at least about 50~, and preferably about 30% to 100%,
hardwood fluff fibers of approximately the same density as the lower
density softwood fluf~ fiber layer 5 for the higher density softwood
fluff fiber layer 6. This can be done because the hardwood fluff has
a smaller pore size than the softwood fluff material. As a result, if
hardwood fluff fibers are used as a replacement for the higher density
softwood fluff fibers, two different pore size distributions will
still be obtained within the scope of the invention, even if the
density of each layer is the same. Thus, for example, a two component
fluff sandwich comprising a coarse pore structure in the upper layer 5
obtained from a predominately softwood fluff pulp and a fine pore
structure in the lower layer 6 comprised of a preponderantly hardwood
fluff pulp fluff, densified throughout to one density (preferably
approximately 0.1 g/cm3) can successfully be used with similar results
to those obtained according to the embodiments described.
The second aspect of the invention relates to including a portion
of superabsorbent material (SAM) 9 as part of the liquid absorbing
material 4. The term "superabsorbent material" as used herein refers
to one or more hydrocolloid materials capable of absorbing many times
its own weight of water or aqueous fluid. These materials are
generally prepared by polymerizing one or more monomers which, if
homopolymerized by conventional methods, would form water soluble
polymers. To render them water-insoluble and suitable for the present
invention, these polymers or mixture of polymers are typically
reacted, frequently with a crosslinking agent, to form crosslinked
polymers, thereby introducing a limited water-insolubility while
retaining susceptibility to swelling in water and water-containing
fluids. Pseudocrosslinking may also be achieved by chain entanglement
of high-molecular weight polymers, thus effecting water insolubility
(see, e.g., U.S. Patent No. 4,340,706). Typically, these
hydrocolloids are salts of polyacrylic acid and variations thereof,
such as methacrylic acid. Commercially they are available under the
trademarks WATER LOCK J-5qO from Grain Processing Co.;
ABASORB 720 from Arakawa Chemical, (U.S.A.) Inc.; and Aqualic-CA from
~3~~ 21D~
Mitsui Co. Alternative superabsorbents also may include hydrophilic
polymer grafts onto starch or cellulose backbones and crosslinked
carboxylated celluloses.
In FIGS. 6 and 7 the fourth preferred embodiment is shown wherein
the superabsorbent material 9 is sandwiched between a first higher
density component 10 and a second higher density component 11. These
first and second higher density components 10$ 11 are disposed in an
equivalent position to the higher density layer 6 in the first three
embodiments discussed above. However, it is generally preferred that
the superabsorbent material 9 is localized in an area 17 slightly
above a region midway between the target area 7 and the upper edye 8.
Thus, the superabsorbent material 9 provides an additional reservoir
for liquid waste that has been drawn up the diaper by the higher
density layer 6.
An important advantage of this aspect o~ the invention is that it
assists in fluid distribution along the length of the superabsorbent
material. Generally~ superabsorbents 9 disposed in a fiber matrix
enhance fluid distribution in the direction corresponding to the
thickness of the liquid absorbing material 4. However, due to the
swelling nature of the superabsorbent material 9, wicking in the plane
o~ the fiber matrix bearing the superabsorbent 9 is severely hindered.
According to this aspect of the present invention, wicking across the
entire length of the superabsorbent material 9 is accomplished by
sandwiching the superabsorbent material 9 between the first high
density component 10 and the second high density component 11. Thus,
the liquid waste is brought into contact across an upper surface 12
and a lower surface 13 of the superabsorbent material 9 rather than
across a bottom edge 1~ thereo~. This is an improvement over
border-to-border transfer of liquid waste, in much the same way as the
first aspect of the invention, described in connection with FIGS. 1 -
5, provides the improvement of surface to surface contact between the
lower density layer 5 and the higher density layer 6.
FIGS. 8 and 9 show an alternative embodiment wherein the
superabsorbent material 9 is disposed adjacent the outer, liquid
impermeable cover 3, and then covered with the single higher density
layer 6 which is in turn covered with the lower density layer 5.
~.3i~2~
Of course, still further alternative embodiments are provided by
using a softwood fluff pulp in the layer 5 and a hardwood fluff pulp
in the layers 6 (FIGS. 8 and 9), or lO and 11 (FIGS. 6 and 7), with
uniform densification of all layers to about 0.1g/cm3, or in the range
of about .lg/cm3 to about .lS g/cm3. Yet further variations within
the scope of this invention include using a softwood fluff pulp of a
first density in combination with a hard wood fluff pulp of a second
density, wherein the second density is preferably higher than the
first density.
The term "density" as used herein refers to the density of ~he
composite structure of the lower density layer 5 or the higher density
layer 69 and not the actual fiber density. (The actual fiber density
is about l.5 g/cm3.) The density of the lower density layer 5 should
be in the range of about 0.03 to about 0.14 g/cm3, with the preferred
rangel in light of considerations of integrity and bulk, at about 0.07
to about 0.l1 g/cm3. The higher density layer 6 should have a density
in the range of about 0.14 to about 0.3 g/cm3, and preferably in the
range of abollt 0.16 to about 0.22 g/cm3 for providing the desired
capillarity without excessive stiffness. The density for these
preferred ranges is a density measured under a load of 0.2 psi. An
important consideration in selecting suitable ranges for the higher
density fluff and lower density fluff is that although there should be
two distinct pore size distributions, one for each of the respective
layers of fluff, these pore size distributions should overlap because
this will permit flowback from the high density layer back to the low
density layer.
The densified layer 6 may be a multiple ply layer rather than
merely a single ply layer, and the ply may increase in density across
the width or length of the layer 6 within the specified range or can
be of uniform density. The basis weight of the lower density layer 5
should be in the range of abou~ 150 to about 500 9/m2 to provide the
desired aesthetic appearance and comfort of the diaper. The basis
weight of the higher density layer 6 should be in the range of about
150 to 1250 g/m .
It is preferred that the higher density layer 6 be substantially
separately rather than integrally formed with the lower density layer
~ L3~J~
5, to ~chie~e better moisture distribution therethrough. It should be
noted, however, that the layers 5 and 6 are "substantially separately"
formed even when formed in the same machine, one on top of the other,
~ith some admiYing at the interface. By the "substantial separate"
terminology, it is intended only that two substantially discrete
layers are formed, rather than a substantially single layer having a
"skinne~" surface, such as described in U.S. Patent Nos. 2,952,260,
2,955,641, 3,017,304, 3,060,936, and 3,4g4,362 to Burgeni.
Thus, densification should be achieved uniforrnly through the higher
density layer 6, and care should be taken to avoid substantial
skinning9 where such skinning is as described in the Burgeni patents
or in the Aberson U.S. Patent No. 4,1Q3,062. Skinning produces undue
stiffness in the fluff and results in low absorbent capacity in the
bonded (skinned) layer. Skinning can be prevented by avoiding excess
moisture and by maintaining both platens at approximately the same
temperature to avoid condensation through the thickness of the
material. The present invention avoids the densification of the fluff
to the point of forming a skin layer so that the densified fluff layer
6 retains at least about 80% void volume, resulting in significant
absorbent capacity.
The layer 6 is densified in a heated press, such as can be
obtained by Dake, Grand Haven, Michigan, as a "*Dake ~aboratory Press",
Model No. 44-148 which includes heated platen operated under suitable
conditions of temperature and pressure as known in the art to achieve
the desired density. Alternatively, a heated calender nip is suitable
for use in the densification process, as known in the art.
Comminuted wood pulp (fluff) is preferred for this invention, but
other cellulose fibers such as cotton linters can be used. The
preferred fluff is southern pine kraft wood pulp (i.e., made according
to the sulfate process commonly known in the art) which has been
bleached, such as can be purchased from ITT Rayoneer or International
Paper Company. A suitable hardwood fluff pulp is southern hardwood
kraft obtainable from Weyerhauser as ~'*New Bern 309".
The superabsorbent material can be obtained from the Grain
Processing Company of Muscatine, Iowa as their product Water LockTM
* Trade~marks
-10-
i.i
' ' ..,
~3~
J-sOO or A-lO0. Suitable inner liners 2 and outer covers 3 are easily
obtained and well known in the art.
Combined with these alternative absorbents is a soft,
compressible fluid transfer portion or layer comprised of synthetic
fibers such as polyester/polypropylene. This transfer layer is
integrally bonded to a top liner at spaced apart sites to provide
densified zones for fluid transfer. Such a web is described in U. S.
Patent 4,397,644. The top liner is a pattern bonded spunbonded web
also of synthetic fibers such as polypropylene, polyester and the
like. The combined basis weight of the liner/transfer layer should be
in the range of about 30-100 g/m with the liner being about 10-15
g/m2 and the transfer layer about 20-90 g/m2. It must have a wetting
finish throughout.
The transfer layer is typically a carded web of
polyester/polypropylene fiber containing from 0 to 100X polyester
fiber, preferably 25-50% polyester staple, containing sufficient
surfactant finish to be wettable. Two-inch polyester staple, Type
T808, a hollow fiber, at 5.5 denier from E. I. duPont Co. with a
wettable finish is preferred although other wettable polyester staple
fibers would work. Polypropylene Type T-123 from Hercules Inc. has a
wettable finish with the 3-denier, 1-7/8 inch staple preferred. The
web is only bonded together through the spaced apart bonds which
attached it to the top liner, which are typically achieved through
thermal or ultrasonic bonding.
The layer may also be formed by other nonwoven processes such as
spunbonding wherein the filaments are spun and collected on a wire
screen without bonding and then bonded to the prebonded liner as
described above. It must have a wetting finish as is achieved by
treating with 0.2-0.5% *Triton X-102 from Roh~ and ~aas Co.
Of course, many changes and modifications can be made to the
preferred embodiments described herein without departing from the
spirit of the invention. For example, the densified fluff layer 6
could also be used with other absorbents such as coformed (~eltblown
polymer fibers combined with wood pulp and/or staple fibers) webs,
carded webs, air-formed (staple wood pulp blends) webs and the like,
at a lower density. Further, the absorbent structures described
* Trade-mark
A
~3gi;~
herein have applications to embodiments other than diapers, such as to
sanitary napkins or other hygienic media. Therefore, it is intended
that the preferred embodiments described in this specification be
regarded as illustrative rather than limiting and it is intended that
the claims, including all equivalents, define the scope of the
invention.
The advantages resulting from this invention will be clearly
understood with respect to the following examples and test data.
EXAMPLE I
The high density fluff was prepared by running the fluff into a
hot calender nip (steel on hard rubber) at 250F at a speed of 10
ftlmin. The nip pressure was sufficient to give a measured density on
standing overnight of 0.15 g/cm3. Alternatively the fluff could have
been pressed in a blotter lined platen press heated to about 250F for
aboùt 5 seconds, with sufficient pressure to achieve the desired fluff
density.
The lower density fluff was prepared by passing it through a
calender nip at 250F at a speed of 10ft/min and sufficient pressure
to achieve a measured density on standing overnight of 0.1 g/cm3.
In both cases the fluff was prepared from southern pine bleached
kraft wood pulp, and was cut to dimensions such that the weight
conditions set forth in Table I below were met. The combined low
density fluff and high density fluff weight are given in the first
column of Table I. The total absorbent weight was maintained at about
37 grams for each diaper, except for the one containing
superabsorbent. The diaper with superabsorbent located as shown in
FIG. 8 contained an additional 7 grams of superabsorbent composite
consisting of about 3 grams of particulate superabsorbent ~Water Lock~
A-100 from Grain Processing Co., Muscatine, Iowa); about 3 grams of
polyolefin; and about l gram of porous nonwoven wrap. The composite
was made in accordance with the teaching of Mazurak and Fries, as set
forth in U.S. Patent No~ 4,381,782. The diaper construction was
completed by sandwiching the absorbent composite between a porous
spunbonded polypropylPne liner (23 g/yd ) and a polyethylene film
outer cover, sealed together with adhesive at the diaper perimeter.
-12-
2~fl~L
Five types of didpers were constructed in this fashion, corresponding
to the diaper description of Table I.
Each of the diapers was then subjected to a 15 minute vertical
wicking test with synthetic urine, followed by 15 ~inutes of
s equilibration out of contact with the urine bath. The results of this
testing are shown in Table I and FIGS. 14 - 18.
In this test the preweighed diapers were mounted on a lucite
plate (3/8" x 13" x 14") with the impervious poly backing adjacent the
plate surface. The diaper was symmetrically wrapped around the edge
I0 of the plate with the longitudinal dimension of the diaper parallel to
the long dimension of the plate. The waist line edges of the diaper
were mounted on the plate with masking tape, the elastic leg bands
being cut in 2 or 3 places to facilitate the ~ounting.
The plate was suspended vertically over a fluid bath contained in
a glass tray with the longitudinal dimension of the diaper
perpendicular to the fluid surface. The fluid was then brought into
contact with the lower edge of the diaper so that the diaper edge was
slightly immersed, and was maintained in this position for 15 minutes.
The diaper was then removed from fluid contact and allowed to hang in .
the same vertical orientation for 15 minutes equilibration. The fluid
used for the diapers in Table I was a synthetic urine composed of by
weight 1~ urea, .01% *Pluronic lOR8 surfactant to bring the surface
tension to about 56 dynes/cm, and .04% sodium azide preservative.
After equiliberation the diapers were removed from the plate and
weighed and the fluid pick up noted. The results are summarized in
Table I and represent the average of seven measurements on each diaper
design.
After weighing, the diapers were laid horizontally on a 3" x 15"
cutting die which was segmented into 9, 1.7-inch zones with cutting
edges across the die width as well as the outer perimeter. Several
quick blows with a wooden mallet divided the 3-inch wide absorbent
strip along the longitudinal axis of the diaper into 9 segments. The
absorbent component in each segment was weighed, oven dried and
reweighed and the fluid pick up determined on a gram per gram or fiber
basis (corrected for deposited solids from the fluid).
* Trade-mark
-13-
j.... . .
~l3~'%~
In the case of the diaper ~i-th the superabsorbent pouch, the
synthetic urine composition was adjusted to more closely simulate the
electrolyte composition of baby urine, namely: 0.31 g. CaH4(P04)2
H20, 0.~8 9. K H2P04, 0.48 9. MgS04 7H20, 1.33 9. K2S04, 1.24 9.
Na3P04 12H20, 4.4 9. NaCl, 3.16 g.KCl, 0.4 g. NaN3, 8.56 urea and 0.1
g. Pluronic lOR8 per liter, using distilled water as the solvent. The
components were added to 900 mls of distilled water in the order given
and each dissolved before the next component was added, and finally
diluted to 1 liter.
The dotted curve in FIG. 14 represents the equilibrium capacity
for the low density fluff at the indicated hydrostatic tensions as
measured in a capillary tension cell. It is apparent that only at
short wicking distances (4.5 cm) does the fluff reach its ultimate
capacity. At the greater wicking heights (9-18 cms) it is well below
its capacity.
Figures 15 17 demonstrate the ability of the densified fluff
layer to pull the fluid up against the hydrostatic heads indicated.
Comparison of the fluid level in the low density fluff in the back of
the diaper with that in the same material in front at the
corresponding head is a measure of the effectiveness of the high
density fluff to improve the utilization of the low density material
(e.g. 2.8 9/9 back vs. 0.1 glg front at 18 cms head, FIG. 17).
FIG. 18 shows the effectiveness of the densified layers in
carrying and transferring fluid to the superabsorbent. The levels of
fluid pickup in the superabsorbents are 12 and 22 9/9 respectively at
the 9 and 13.5 cm heads. Comparing this to Figure 16 illustrates the
effectiveness of the superabsorbent in diverting fluid from the fluff
.
components at the highest heads.
It is apparent from these results that fluid distribution is
greatly enhanced up the back of the diaper in the designs with
densified fluff layers. The contrast with the fluid distribution in
the front of the diaper, where densified fluff layer is absent, is
very evident from the figures. Of course, better fluid distribution
in the front as well as the back of the diapers would be obtained when
the second and third preferred embodiments are followed. However, the
first preferred embodiment was fo110wed for the purposes of these
-14-
~3~
tests because the diaper front tends to become fairly thoroughly
wetted when the release of waste fluid occurs when the child wearing
the diaper is lying on its stomach, for example when it is sleeping.
Moreover, the resu1ts demonstrate that the fluid distribution in
the low density fluff areas is significant. This demonstrates the
unexpected synergism obtainable in these designs.
In the instance of the superabsorbent diaper, which was made in
accordance with the fourth embodiment set forth in this specification
the superabsorbent material drained substantial fluid from the higher
regions of the diaper. However, these regions toward the upper edge 8
of the diaper provide surplus absorbing capacity if needed,
....
~ ~t~J~ L
TABLE I
Whole Diaper Vertical
Wicklng Test* _
s
Amt. of Fluid Ab-
Absorbent Weight o~F Fluid sorbed Over
Weight Comp. Fluff Absorbed Control
Diaper D~scription 9. ~. 9. %
Control Diaper 36 0 140 --
Diaper containing 1 38 7 171 22
ply of compressed
fluff
Diaper with 2 plies 37 14 191 37
of compressed fluff
Diaper with 3 plies 35 21 203 45
of compressed fluff
Diaper with 2 plies of 43** 14 215 54
compressed fluff
& SAM
~* - Absorption time: 15 minutes followed by 15 minutes equilibration
time.
** - Contains 7 g. of assembly containing 3 g. SAM.
EXAMPLE II
-
The present inventor has discovered -that similar functionality to
the higher density fluff can be achieved with finer fiber, hardwood
pulp fluff but at normal density (0.1 g/cm3). This discovery was made
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foll~ing the observation of d r-~mdrk~ble simil~rity in the pore
volume distribution of 0.1 g/cm density hardwood fluff and that of
0.2 g/cm3 softwood fluff. The following tables compare the vertical
wicking properties of softwood and hardwood fluff.
The vertical wicking test was somewhat similar to that conducted
with whole diapers described above. This test was conducted on 3" x
15" strips of the absorbent material mounted on a 3/8" x 5" x 14"
lucite plate in the same orientation and manner described for the
diapers. A nylon mesh screen was used to support the fluff strip on
the lucite (acrylic) plate. The plate and strip were then suspended
from weight-sensing means such as a load cell in an *Instron tensile
tester. The synthetic urine (in these cases the second or
salt-containing formulation) was then put in contact with the lower
edge of the absorbent strip and the amount of fluid absorbed as a
function of time is recorded at several time intervals for the 15
minute duration of the test. The amount absorbed was calculated as
the grams per unit basis weight of l gm/cm2 per unit width (l inch~.
The vertical wicking capacity is defined as the amount absorbed in the
defined units at the end of the 15 minute test. The reported rate was
that measured from the plot of amount absorbed/llnit basis weight/unit
width versus time~ over the time interval of 7-21 seconds. The test
was replicated six times and the results reported are averages of
these six measurements.
Fluid distribution in this test was measured by die cutting the
sample immediately following the completion of the test, the same
manner described for the whole diapers. In this case zones
corresponding to the same vertical heights were combined to give the
results shown in Table III.
As may be concluded from the results in Table II, the vertical
wioking capacity of 0.1 g/cm3 density hardwood fluff corresponds
closely with that of 0.2 g/cm3 density softwood fluff. The initial
wicking rate of the hardwood fluff falls between the two softwood
fluffs. The fluid distribution pattern in Table III also shows the
similarity of the hardwood fluff and the 0.2 g/cm3 density softwood
fluff. These results imply a slightly larger average pore size for
the former than the latter.
* Trade-mark
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Hence, a combination of softwood and hardwood fluff at 0.1 g/cm3
density should have similar fluid distribution properties to a
two-density sandwich of softwood fluff, as previously described in
this disclosure.
TABLE II
VERTICAL WICKING CAPACITY/RATE
(Showing similarity in capillarity of softwood kraft at
0.2 g/cm3 and hardwood kraft at 0.1 g/cm3 density)
*Vertical
Densi~yCapacity Wicking Rate
Material ~ G/UBW/UW G/UBW/UW/SEC~
Softwood Kraft Fluff 0.1 499 48
Softwood Kraft Fluff 0.2 573 36
Hardwood Kraft Fluff 0.1 580 42
* Units are grams per unit basis weight (1g/cm2) per unit width
(1 inch).
TABLE III
FLUID DISTRIBUTION IN VERTICAL WICKING
**Specific Absorbency (9/9) at Following Tensions
O cm 4.5 cm 9 cm 13.5 cm 18 cm
Softwood Kraft (O.l g/cm3) 9.0 9.0 6.4 3.0 0.7
Softwood Kraft ~0.2 g/cm3) 6.0 6.1 5.8 5.0 4.7
-~ardwood Kraft (0.1 g/cm3) 8.2 8.1 7.2 5.3 3.3
** Tensions are measured as vertical distance from fluid source.
EXAMPLE III
This example is directed to a dou~re fluff layer of softwood
fluff over hardwood fluff. The hardwood fluff was a bleached kraft,
South American Eucalyptus hardwood pulpo The two-ply fluff contained
equal weights of the softwood and hardwood pulp layers. After
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densifying the layers to 0.1 g/cm3 density, the vertical wicking
properties (same test procedure as for example II) were as follows:
TABLE IV
VERTICAL WICKING PROPERTIES OF
SOFTWOOD/HAR~WOOD LAYERE3 BATT
***Vertical ***Wicking ***Specific Absorbency
Capacity Rate t Following Tensions
O cm 4.5 cm 9 cm 13.5 cm 18 cm
544 46 7.8 7.8 6.1 4 3 3.0
~** Same units as in Tables II, ~II.
Comparing the distribution results for the double-layered fluff in
Table IV with those for softwood kraft (Table III), it is apparent
that the presence of the Eucalyptus layer greatly improves fluid
wicking against the upper two hydrostatic heads ~i.e. in the 13.5 cm
and 18 cm zones). This is particularly impressive since the
Eucalyptus only represents 50Cl of the two-ply structure.
EXAMPLE IV
A 40 g/m2 web of meltblown polypropylene containing 40 percent by
weight of superabsorbent (Wa-terlock J-500 from Grain Processing
Company) was prepared. The superabsorbent was intermixed with the
fine meltblown fibers (surface area about 1 m2/g) containing enough
surfactant (e.g., about 0.3 - 0.5 percent Triton X-102 from Rohm &
Haas Company) to assure wetting of the fiber matrix, the composite
being densified to 0.1 g/cm3 during the manufacturing process.
When this web was subjected to the vertical wicking procedure
described in Example II, the results presented in Table 5 were
obtained. From these results it is apparent that the fluid wicks
vertically 4.5 cms but then essentially stops, presumably because the
swelling particles have restricted the fluid flow in the web by
plugging the pores.
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~ hen this same web was placed beneath a softwood fluff l~yer,
having a density of 0.2 g/cm3, in a diaper construction, and the whole
diaper was subjected to the vertical wicking test (described in
Example I), the effect of the fluff layer as a fluid distributor for
the superabsorbent was apparent. In Table 6, the fluid distribution
is shown for the total absorbent composite, the fluff layer itself,
and for the meltblown/ superabsorbent web.
Comparing the vertical distribution for the
meltblown/superabsorbent web from the diaper (Table 6) with the data
in Table 5, it is apparent that the densified fluff acts to wick the
fluid higher and improves the distribution to the superabsorbent
(compare at 9 cm height, 11.6 y/g vs. 1.1 g/g; and at 13.5 cm height,
2.7 9/9 vs. 0.1 9/9). Note that both tests were similarly run for 15
minutes. Furthermore, if the tests were allowed to proceed further~
the height wicked in the diaper would continue to increase, whereas
wicking in the superabsorbent web alone would virtually stop.
Referring to Figures 10-13, it has further been found that, in
addition to placement of superabsorbent material in a hydrophilic web,
either of meltblown fibers or a composite nonwoven pouch 19, generally
in the rear of the diaper, a similar pouch 19 containing the
superabsorbent material can be disposed both in the front and the rear
of the diaper.
It will be appreciated by those skilled in the art that the term
"hydrophilic web", as used herein, is intended to encompass the
superabsorbent-treated web of meltblown fibers (Example IV) to which-
surfactant has been added, making the composite web wettable, that is,
the surfactant makes the normally hydrophobic surface of the fibers
wettable by presenting a hydrophilic contact angle on the fibers.
Hence, even though the fibers may not be hydrophilic as formed, the
resultant web is wettable by addition of surfactant, allowing liquid
distribution to the superabsorbent material contained in the web.
Likewise, the pouch previously described, which is a web comprised of
various materials randomly formed into a nonwoven matrix containing
the superabsorbent material9 may also be made hydrophilic by treatment
with surfactant for purposes of aiding liquid distribution to the
hydrogel,
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The density of superabsorbent material may be graded either in
the front or rear longitudinal direction, for example, by selecti~Je
layering (not shown) of a plurality of superabsorbent-treated
meltblown ~ebs (each constructed in accordance with Example IV). By
overlapping such a succession of webs so that the ends of the webs are
spaced longitudinally from one another a successively greater
composite web thickness, i.e., concentration of superabsorbent
material, can be achieved as fluid progresses toward the end of the
absorbent structure. Preferably, the superabsorbent material is not
located in the crotch, providing better accumulation of liquid in the
front and rear of the absorbent structure, the remaining portion of
the urine not immediately absorbed and retained by the front fluid
retention pouch 20 being absorbed through at least the first layer by
the superabsorbent material located in the rear fluid retention pouch
19. Superabsorbent material which is located in the crotch tends to
compete for liquid with superabsorbent material located remote
therefrom in the front and rear of the absorbent structure, resulting
in less urine distribution in remote areas of the absorbent structure
and greater detrimental retention of urine in the central portion of
20 the absorbent structure. Urine excreted in the "target zone" located
in the front of the absorbent structure, of course, need not be
further distributed to the rear end of the absorbent structure remote
therefrom to be absorbed by the rear retention pouch 19. Preferably,
the second layer 6 is employed to wick and distribute liquid to the
25 rear of the absorbent structure for absorption and retention in the
rear fluid retention pouch 19 as well as the upper absorbent layer 5,
which layer 5 is thereby more fully utilized for liquid and stays
-~rier to the extent fluid transported to the rear of the absorbent
structure is retained in the rear pouch 19. The liquid distributed
through the first layer may be absorbed and retained by the rear 19 as
well as front 20 fluid retention pouches without using the second
layer to wick liquid rearward, although the second layer is preferred
for this purpose. Since the front pouch 20 is closest to the urine
target zone~ it reaches saturation capacity soonest. Fluid may bypass
the front pouch 20, either before or after it is saturated, and be
distributed either via the first layer 5 or, preferably, Yia the
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second layer 6, to the rear fluid retention pouch 19 for absorption
and retention.
Remote storage of urine in the fluid retention pouches lg, 20
effectively locks the fluid away from the central crotch portion of
the absorbent structure which does not contain superabsorbent
material, which is advantageous because, among other reasons, the
urine is kept away from mixing with fecal material, an alleged cause
of diaper rash, and the urine is not allowed to pool in the crotch
causing greater skin hydration of a wearer in the highly rash prone
perineal area of a wearer. In this regard, the second layer has been
demonstrated herein as being particularly effective in wicking and
distributing liquid to the rear portion of the absorbent structure
where the liquid may then be transferred to the rear retention pouch
or back into the hitherto underutilized rear end of the first layer
due to the aforementioned overlap in pore size distributions.
An optional third 1ayer 21, as shown in Figures l2 and 13 may be
utilized to provide further wicking of fluid to the remote areas of
the absorbent structure 4 away from the target zone.
In regard to flowback of the urine from the first layer toward
the body, the composite liner described herein effectively restricts
such flowback because the open porous structure of the composite liner
effectively provides a comfortable, cushioned separation from the
liquid present in the first layer while, in the first instance,
providing a rapid drainage of excreted urine away from the body into
the finer pore structure of the first layer, thence preferably into
the still finer pore structure of the second layer by the suction
activity of a capillary pore size gradient.
~3~2~
TABL~ V
~ERTICAL WICKING TEST
MELTBLOWN/SUPERABSORBENT WEB
Basis ***5pecific Absorbency
Weigbt Densi~y at Following Tensions*
Description ~ g/cm~ 0.0 cm 4.5 cm 9.0 cm 13.5 cm 18.0 cm
Meltblown Web
with No Super-
absorbent 93 0.1 7.9 7.7 2.4 0.0 0.0
Meltblown Web
with 40% Super-
absorbent 139 0.1 23.0 20.5 1.1 0.1 0.0
*Hydrostatic Tension in cm. of water.
***Same units as in Tables II and III.
TABLE VI
VERTICAL WICKING TEST
ON DIAPER CONTAINING
MELTBLOWN/SUPERABSORBENT WEB
***Specific Absorbency
at Followiny Tensions*
Dry Absorbent Absorbent
Diaper Absorbent Weight (g.) Component0.0 cm4.5 cm 9.0 cm 13.5 cm 18.G cm
Fluff densi~ied42.7 Fluff 7.5 7.2 4.5 2.5 1.5
coextensive layer MB/SAM** 18.8 19.7 11.6 2.7 1.0
of Meltblown Web
with 40~ Combined 9.9 10.1 6.4 2.6 1.5
Superabsorbent Absorbent
(ba~is weight 139
g/m )
*Hydrostatic Tension, cms of water
**Meltblown Web/Superabsorbent
***Same units as in Tables II and III.
