Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to disposable
absorbent devices and more particularly to disposable diaPers.
1S Still more particularly this invention relates to disposable
diapers.havln~ a surfactant treated intermediate layer which
has improved surface runoff characteristics without a significant
degradation in surface dryness for a broad range of topsheet
materials and constructions.
2. Description of the Prior Art
Disposable, absorbent structures are intended to
be used once before being discarded ana provide substantial
cost and convenience advantages when compared with their
reusable counterparts. For example, reusable surgical
sponges and dressings have to be sterilized a~ter each use
while similar disposable structures may simply be discarded.
As a result of their cost and convenience advantages, disposable
l~Z~9~;~
absorbent structures, generally, and disposable diapers in
particular, have met with prodigious success in the market
place. In the ensuing discussion, particular reference will
be made to the art of disposable diapers slnce the present
invention has particular application to the diaper art. It
should be understood, however, that the products of the
present invention may be used broadly in the field of disposable
absorbent structures.
As is well known in the diaper art, the three
principal structural components of a disposable diaper are
the topsheet, absorbent core, and backing sheet. The backing
sheet can comprise any of the various liquid impermeable
materials well known in the art such as polyethylene film
and the absorbent core of disposable absorbent structures
lS can comprise well-knawn materials such as creped cellulose
wadding, comminuted wood pulp, or the like. The topsheet o
the disposable diaper may be manufactured from a wide variety
of materials and pursuant to a number of concepts. For
example, the topsheet may be woven, nonwoven, hydrophobic,
hydrophilic, fibrous fabric, or perforated flexible plastic
film. The above described components of a disposable diape
may be combined in any of the various manners well known in
the art. One such method of combining the diaper components
is described in detail in U.S. Patent Re 26,151 to Duncan et
al
The prior art teaches a great many variations on
the above described basic disposable diaper structure.
United States Patents 3,730,184 and 3,837,343 to Mesek, for
example, teach a diaper construction in which the center
portion of the outer surface of a hydrophobic topsheet is
treated with a surfactant to render selected portions of the
outer surface hydrophilic. In addition, each of the patents
to Mesek teach the addition of a densified layer in the
absorbent core to improve wicking of the fluid which enters
the absorbent layer. This latter structure is the subject
of U.S. Patent 3,612,055 to Mese~ et al. and is described in
detail therein. U.S. Patent 3,838,692 to Levesque describes
a variation in diaper structure in which the topsheet is of
a hydrophobic nature and is treated with a wetting agent on
the outer surface to render it hydrophilic at discrete
spaced apart points. Another variation in conventional
diaper construction is described in U.S. Patent 3,934,588 to
Mesek et al. in which the outer surface of the facing layer
is provided with areas of preferential liquid flow surrohnded
by areas of increased water repellency. The areas of preferential
liquid flow are formed by thinning selected areas of the
topsheet.
The object of the relevant prior art developments
has generally been to produce a disposable diaper which will
permit rapid penetration of the fluid through the topsheet
into the absorbent layer and which will provide a dry outer
surface in contact with the user. The rapidity with which
liquid penetrates the topsheet is indicated by measuring the
amount of surface runoff using a method to be described
hereinafter while an indication of surface dryness may be
determined by measuring the rewet characteristics of the
topsheet using a method also to be described hereinafter.
It is well known in the prior art that the surface
runoff characteristlcs of a diaper may be improved by making
the outer surface of the topsheet hydrophilic. As indicated
above, prior art struc.ures have achieved this result by
various methods such as applying surfactant to the outer
surface of the topsheet. Surface dryness is improved,
however, by making the outer surface of the topsheet hydrophobic.
The prior art developments have sought to achieve a balance
between good surface runoff characteristics and favorable
~.1 Z4951
surface dryness, but the prior art lacks the aspects of the
present invention in which improvement in the surface runoff
characteristics can be obtained without a significant sacri-
fice in the surface dryness of the topsheet for a wide range
of topsheet materials and constructions.
It is therefore an object of the present invention
to provide a disposable absorbent structure having rapid
fluid penetration through a variety of topsheets without
significant degradation in surface dryness.
An additional object of the present invention is
to provide a disposable absorbent structure having a sur-
factant treated intermediate layer.
A further object of the present invention is to
provide a disposable absorbent structure having no surfact-
ant on the outer surface of the topsheet.
These and other objects and advantages of the
present invention will be readily apparent from the following
description and claims taken in connection with the attached
drawing to which they relate.
SUMMARY OF THE INVENTION
The principal components of a conventional dis-
posable absorbent structure are the topsheet, the absorbent
core, and the impervious backing sheet. According to the
present invention, an additional component, a surfactant
treated intermediate layer, is interposed below the outer
surface of the topsheet. The surfactant treated intermediate
layer improves the surface runoff characteristics for a wide
variety of topsheets and in addition does not significantly
degrade the ability of the topsheet to provide a dry outer
surface in contact with the user.
In one embodiment of the invention, the surfactant
treated intermediate layer comprises a discrete substrate
-- 4
/ `
s.s~ .
.
treated with surfactant. In this embodiment the intermediate
layer is most effectively positioned at the interface bet-.~een
the topsheet and the absorbent core although it may also he
positioned within the absorbent core or at the interface
between the absorbent core and the impervious backing sheet.
In an alternative embodiment of the invention, the
surfactant treated intermediate layer is form~d by surEactant
treating one of the principal components of the disposable
diapar below the outer surface 0c the topsheet. Thus,
either the inner surface of the topsheet, or the absorbent
core may be treated with sur~actant.
The term "disjunctively disposed" when used
herein to describe a particular positioning of the surfactant
treated intermediate layer indicates that said inter-
mediate layer is an element separate and distinct fromthe diaper topsheet.
l~Z49Sl
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a partially cut away perspectlve view
of a disposable diaper having a surfactant treated inter-
mediate layer.
Figure 2 is a side elevation of the disposable
diaper topsheet.
Figures 3 through 5 are longitudinal section views-
of alternative embodiments of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figure 1, there is shown a pre-
ferred embodiment of the present invention as it would be
used in a disposable diaper. It should be understood that
the present invention is broadly applicable to the art of
disposable absorbent structures, such as bandages, sanitary
napkins and the like. The following description of a dis-
posable diaper is intended to merely illustrate a preferred
embodiment of the present invention.
As seen in Figure l, disposable diaper 10 basical-
ly comprises porous topsheet 12, absorbent core 14, imperv-
ious backing sheet 16, and surfactant treated intermediatelayer 22. Topsheet 12 is superposed on absorbent core 14
and is
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fastened to the impervious backing sheet 16 in a manner
well known in the disposable diaper art. Absorbent core
14 is of dimensions generally smaller than backing sheet
16 and is completely encased between porous topsheet 12
and backing sheet 16. A more detailed description of how
topsheet 12, absorbent core 14, and the impervious backing
sheet 16 may be assembled into a disposable diaper is
given in U.S. Patent Re 26,151.
Impervious backing sheet 16 is preferably a 0.001 to
- 10 0.002 inch (0.0025 to 0.0051 cm) thick polyethylene film,
although other flexible fluid impervious materials may
also be used.
Absorbent core 14 comprises absorbent layer 18 and
envelope tissue 20. Absorbent layer 18 may be manufactured
from a wide variety of the absorbent materials commonly
used in absorbent structures, such as comminuted wood pulp
generally referred to as airfelt. Other rnaterials can
also be used for absorbent layer 18 such as a multiplicity
of plys of creped cellulose wadding or any equivalent
material. In the preferred embodiment envelope tissue 20
is substantially coextensive with topsheet 12. Absorbent
layer 18 is encased between envelope tissue 20 and imper-
vious backing sheet 16 with envelope tissue 20 holding
absorbent layer 18 in place and preventing lumping of
absorbent layer 18. A preferred envelope tissue 20 has a
basis weight of about 12 pounds/3,000 square feet and an
air permeability of about 100 cubic feet per minute per
square foot over a 0.5 inch water pressure drop.
Porous topsheet 12 has an outer surface 30 and an inner
surface 31 (See Figure 3) and should be compliant, soft feel-
ing, fluid permeable, and non-irritating to the user's skin.
In addition, topsheet 12 has a capillary suction pressure
11~4~5il
lower than that of absorbent core 14. Capillary suction
pressure for a given article is the product of adhesion
tension and specific surface area. Adhesion tension is
defined as the product of the fluid's surface tension and
the cosine of the contact angle the fluid makes with the
article and may be measured using the methods detailed in
the paper printed in the Journal of Colloid and Interface
Science, Vol. 42, No. 1, January 1973 entitled Dynamic
Adhesion Tension Measurement. The specific surface area of
the article is the ratio of the solid surface area of the
article available for wetting divided by the void volume of
the article that the fluid can occupy. Capillary suction
pressure for a porous article may be determined by the
method described in the Textile Research Journal, Vol.
37(1967) pages 356-366.
Obviously, porous topsheet 12 may be manufactured from
a wide variety of materials having a broad range of struc-
tural and physical characteristics. For example, topsheet
12 may be paper, rayon, polymeric, woven, nonwoven, fibrous,
nonfibrous, hydrophobic or hydrophilic. A preferred top-
sheet 12 is shown in U.S. Patent 3,929,135 to Thompson.
As described therein, topsheet 12 is a low density poly-
ethylene film having a thickness of from about 0.001 to
about 0.002 inches (0.0025 to 0.0051 cm). The preferred
topsheet 12 is formed to a thickness of about .015 inches
(.038 cm) with an array of tapered capillary structures 24,
each having a perforated apex 26 (See Figure 2).
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,,~
1~2~5~1
In the preferred embodiment shown in Figure 1,
intermediate layer 22 comprises a discrete substrate 28
which is treated with a surfactant. Substrate 28 may be
any fluid pervious material which is flexible and compliant.
Typically, the material used for envelope tissue 20 would
also be used for substrate 28. Thus, substrate 28 preferably
has a basis weight of about 12 pounds/3,000 square feet and
an air permeability of about 100 cubic feet per minute per
square foot at a 0.5 inch water pressure drop.
In accordance with the present invention a great
many surfactants may be used. A surfactant will increase
the hydrophilicity of substrate 28 by increasing the ad-
hesion tension of fluids contacting substrate 28 and will
preferably be non-irritating to human skin. A nonionic
surfactant such as an ethylene oxide/propylene oxide block
condensation polymer having the general structure
2 2 )8 (CH2 ~ C~ ~ )46 ~ (cH2cH2o)8H
CH3
- 7a -
3~1
and marketed under the trademark Pluroni ~ L-92 by BASF
Wyandotte Inc., Wyandotte, Michigan was used in the
preferred embodiment. Many other cationic, anionic and
nonionic surfactants are equally suitable such as sodium
alkylaryl sulfonate manufactured by The Procter & Gamble
Co., Cincinnati, Ohio under the trademark Orvus~ AB
Granules or cetyl trimethyl ammonium bromide manufactured
under the trademark Acetoquat~ CTAB by Aceto Chemical
Co., Flushing, New York.
The substrate 28 may be treated with surfactant in any
suitable manner such as by spraying surfactant onto sub-
strate 28 or by dipping substrate 28 into a surfactant
bath. As used in this application, the term "treating"
also includes other methods of applying surfactant to
substrate 28 such as by printing or extruding.
Substrate 28 is treated with surfactant in concentra-
tions which depend upon the surface and the nature of the
topsheet 12 chosen. For a given substrate 28 and top-
sheet 12 the amount and type of surfactant used must be
sufficient to increase the adhesion tension of the fluid on
substrate 28 such that the capillary suction pressure ofsubstrate 28 is greater than the capillary suction pressure
of topsheet 12. The larger the difference in capillary
suction pressure between
~2~5~
substrate 28 and topsheet 12 the greater the improvement
in surface runoff characteristics of diaper 10. Substrate
28 may be more hydrophilic than absorbent core 14. In the
preferred embodiment, a concentration of 0.10 grams per
square yard was used although concentrations between 10.0
and 0.001 grams per square yard were found to be acceptable.
In Figure 1, intermediate layer 22 is shown juxtaposed
at the interface between absorbent core 14 and porous topsheet
12. Preferably, intermediate layer 22 is dimensioned to be
substantially coextensive with absorbent core 14, but may be
dimensioned so as to occupy a smaller region such as only
the crotch area of diaper 10. Intermediate layer 22 may be
held in place by being adhesively bonded to absorbent core
14 in a manner well known to one skilled in the art. A
suitable adhesive is slowly soluble, if soluble at all, in
water so as to obviate the possibility of having absorbent
core 14 and intermediate layer 22 separate in use. An
adhesive which is adequate is a latex-plasticized polyethlene
adhesive such as that sold by United Shoe Machinery Corp~ration
and identified as Thermo Grip No. 307.
Since intermediate layer 22 is below outer surface
30 of topsheet 12, intermediate layer 22 does not contact the
user. ~hus, the liklihood of irritation from the surfactant
is lower with the present invention than with diapers having
surfactant applied to outer surface 30. In addition, intermediate
layer 22 greatly improves the ability of fluids to penetrate
topsheet 12 as measured by a reduction in surface runoff.
Absorbent structures exhibiting low surface runoff are
desirable because such structures are less likely to leak
fluid and will remove fluid from contact with the user
faster. In addition intermediate layer 22 has substantially
no effect on the surface dryness of a topsheet 12 having
_ g ._
~124~1
tapered capillary structures 24. Surface dryness is indicated
by measuring the rewet of topsheet 12 and is a desirable
characteristic because the drier topsheet 12 the lower the
possibility diaper 10 will irritate the user's skin.
Surface runoff is determined at atmospheric pressure by
placing a preweighed, 9-inch length of diaper 10 on a board
inclined 10 degrees to the horizontal and dropping 25 milli-
liters of fluid on diaper 10 at a uniform rate for 3.5 sec-
onds. The fluid used simulates the physical characteristics
of urine and comprises 1% (by weight) of sodium chloride salt
and 2.5 grams of a 10% solution (by weight) of an alky phenoxy
polyethoxy ethanol such as Trito ~ X-100 as marketed by Rohm
and Haas of Philadelphia, Pennsylvania per 3,500 millimeters
of fluid. Diaper 10 is then reweighed and the percent fluid
runoff is determined by the following formula:
Surface Runoff (%) =~weight of 25 ml~ ~weight of wet diaper-~
~of fluid ~weight of dry diaper ~ 100
weight of 25 ml of fluid
The rewet of topsheet 12 is determined by wetting a 4-inch
square section of diaper 10 with a fluid simulating the physical
characteristics of urine as described above. The amount of
fluid used is 4.5 times the weight of the 4-inch square section
diaper 10. An eight pound weight is applied to the 4-inch
square section for 3 minutes thereby permitting the fluid to
approach an equilibrium condition before a preweighed absorber
is placed on topsheet 12 and the eight pound weight reapplied
for an additional 2 minutes. The absorber is then reweighed
and the weight of fluid absorbed by the absorber noted. Two 15
cm diameter sheets of Whatman No. 4 filter paper manufactured
by Whatman Inc. of Clifton, New Jersey were used successfully
in the rewet tests conducted. The larger the amount of fluid
absorbed
-- 10 --
i~ 951
by the filter paper the more likely topsheet 12 will
present a wet outer surface 30 in contact with the user.
Improvements in the surface runoff characteristics
of diaper 10 may be realized with intermediate layer 22 in
locations other than those described above. Referring
briefly to Figure 3, there is shown an alternative embodiment
of the present invention wherein intermediate layer 22 is
positioned within absorbent layer 18. It is also possible to
position intermediate layer 22 at the interface between
absorbent core 14 and backing sheet 16. The surface runoff
improvements are not as great when intermediate layer 22 is
not at the interface between absorbent core 14 and topsheet
12, but as seen in Table I the reduction in surface runoff
is still significant when compared to diapers having no
intermediate layer 22.
Table I shows the percentage reduction in surface
runoff for a diaper 10 having an intermediate layer 22
treated with 1.0 grams/s~uare yard of an ethylene oxide/
propylene oxide block condensation polymer (Pluronic L-92
as described above) and having a tapered capillary topsheet.
... .
11 -
-
4~9~ii
TABT,~. I
Surface Runoff Rewet
Position of(o6 reduction in (gms)
intermediatesurface runoff ,
layer 22of diaper having w/intermediate w/out inter-
no intennediate layer mediate layer
layer 22)
Topsheet
absorbent 76 0.06/O.OS
core
interface
~ithin
absorbent 47 0.05/0.05
core
.
Absorbent .
core 50 0.07/0.05
backing sheet
interface
,
~1~4~5~
Substrate 28 may, in some absorbent structures,
comprise other components of diaper 10 which are treated
with surfactant. Figure 4 illustrates an alternative embodime~t
of the present invention in which intermediate layer 22
comprises envelope tissue 20 which is treated with surfactant.
In addition, as shown in Figure 5, intermediate layer 22 can
comprise a portion of absorbent layer 13 which is treated
with surfactant. Further, intermediate layer 22 can comprise
the inner surface 31 of topsheet 12 which as in the example-s
given above is treated with surfactant.
Table II shows the percent reduction in surface
runoff exhibited by a diaper 10 having a tapered capillary
topsheet 12 and having various components of diaper 10 treated
with 0.001 grams/square yard of an ethylene oxide/propylene
oxide block condensation polymer (Pluronic L-92 as described
above).
~2~51
.
T~BLE II
Surface runoff Rewet
(~ reduction in (gms)
Dia~er surface runoff
component of diaper not ~with without
treated with treated with ~surfactant surfactant
surfactant surfactant)
.
Inner
surface 39 0.06/0.05
0 of topsheet
Envelope 72 0.04/0.05
tissue
Absorbent.
layer 36 0.05/0.05
. .
, ~ .
. . .
: - 14 -
.: .
11~495~
The present invention has improved surface runoff
characteristics without a degradat:ion in the rewet character-
istics for a broad range of topsheet materials and construc-
tions. These improvements are evident from Table III which
shows the percent reduction in surface runoff for a diaper
10 having topsheets of varying materials and constructions.
- 15 -
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li2~951
ii -
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.~ I
... _
~-- ~ o ~ oo
o ~
~ h
a) ~ . .
~U ~ ~ ~ ~ ~
~3~~ ~ co
~ ~ o ~
H
H
~ ~^
~
.,1 ~ ~ a~ ~ ~ ~
~^ ~ ~
~ ~ O ~ ~ ~ U~
~ ;~ .~ ~} ~
a~ ~ G~
~ ~ ~ ~ Q ~ ~ Q ~
.
~o o ~'x~ ~'x~o
~~ ~O~ U~
',~
~ u~ ~ ~
.~ ~ ~ ,u ~ ~ ~ ~ î
~ a~ ~ ~
u~ ~ ~ aJ a~
t~ ~) ~ k
h ~; u~ F~ h ~.) X
æ ~ ~1 ~ . H t~3 ~ g~
~ o o a) ~ ~ .
-- 16 --
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~ en compared to diaper 10 having surfactant ap~lied
to the outer surface 30 of the topsheet 12, the present invention
exhibits improved surface runoff characteristics for a broader
range of topsheet 12 materials and constructions and has the
additional advantage of preventing the user from contacting
the surfactant. A diaper 10 having a tapered capillar~
topsheet 12 and an envelope tissue 22 (see Figure ~) treated
with 0.001 grams/square yard of an ethylene oxide/propylene
oxide block condensation polymer (Pluronic L-92) showed
approximately a 70 percent reduction in surface runoff compared
to a diaper having the same surfactant and concentration
applied to the outer surface 30 of topsheet 12.
The preferred embodiment heretofore given has
specifically referred to the disposable diaper art. It will
be obvious to one skilled in the art of disposable absorbent
structures that the present invention may be used otherwise
than as described. In particular, other disposable absorbent
structures such as bandages and surgical dressings are
contemplated. In addition, many modifications of the above
described invention may be used and it is not intended to
- hereby limit the present invention to the particular embodiments
shown or described.
What is claimed:
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