U.S. patent number 3,768,480 [Application Number 05/260,557] was granted by the patent office on 1973-10-30 for disposable diaper.
This patent grant is currently assigned to Johnson & Johnson. Invention is credited to Frederick K. Mesek, Virginia L. Repke.
United States Patent |
3,768,480 |
Mesek , et al. |
October 30, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
DISPOSABLE DIAPER
Abstract
A disposable multi-layer diaper of high absorptive capacity and
improved feel is provided which comprises as a first layer, to be
brought into contact with an infant'skin, a porous, fibrous,
nonwoven bonded facing web of controlled wettability made of short
cellulosic fibers and long fibers at a given overall concentration.
The outer face of the facing layer is characterized by a blend of
long and short fibers, with the concentration of long fibers being
in excess of the overall concentration, while the inner face of the
facing layer is also characterized by a blend of long and short
fibers, with the concentration of short fibers being in excess of
the overall concentration. The outer face of the facing layer has a
sufficient amount of long fibers to give the diaper improved feel
and wearing characteristics. The concentration of short cellulosic
fibers gradually, and preferably substantially uniformly, increases
from the outer face to the inner face of the facing layer to
provide a gradually increasing degree of wettability for
preferentially drawing the urine away from the outer face, through
the facing layer and into a second layer, in juxtaposition to the
facing layer. The second layer is a highly porous, loosely
compacted completely cellulosic batt having greater wettability
than that of the facing web. A third layer, integral with the
second, is a paper-like, densified, highly compacted layer of the
same cellulosic material as the second layer but of substantially
smaller average pore size and which is selectively thickened in
certain areas. The final layer is an impervious backing sheet
adhered to the densified layer over a widely distributed area of
adhesion.
Inventors: |
Mesek; Frederick K. (Downers
Grove, IL), Repke; Virginia L. (Oak Forest, IL) |
Assignee: |
Johnson & Johnson (New
Brunswick, NJ)
|
Family
ID: |
22989643 |
Appl.
No.: |
05/260,557 |
Filed: |
June 7, 1972 |
Current U.S.
Class: |
604/365; 604/366;
604/370; 604/372; 604/379; 604/371; 604/375 |
Current CPC
Class: |
A61F
13/15577 (20130101); A61F 13/536 (20130101); A61F
13/1565 (20130101); A61F 13/15674 (20130101); A61F
13/534 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61f 013/16 () |
Field of
Search: |
;128/284,286,287,290,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Claims
What is claimed is:
1. A multi-layer diaper comprising: a porous facing layer in the
form of a nonwoven web formed of staple length fibers and short
cellulosic fibers at an overall concentration of staple length
fibers from about 2 to about 55 percent by weight and an overall
concentration of short fibers from about 45 to about 98 percent by
weight, said web having an outer major face characterized by a
concentration of staple length fibers in excess of said overall
concentration and an inner major face characterized by a
concentration of short cellulosic fibers in excess of said overall
concentration; a highly porous, loosely compacted, cellulosic
fibrous batt in face-to-face juxtaposition with the inner face of
said facing layer; and a water-impervious backing sheet adhered to
the outer surface of said batt.
2. A diaper as set forth in claim 1 wherein said staple length
fibers are rayon fibers.
3. A diaper as set forth in claim 1 wherein said staple length
fibers are polyester fibers.
4. A diaper as set forth in claim 1 wherein said staple length
fibers are present at an overall concentration from about 10 to
about 40 percent by weight and are present at said outer major face
in a concentration of from about 5 to 20 percent by weight higher
than said overall concentration.
5. A multi-layer diaper comprising: a porous facing layer in the
form of a nonwoven web formed of staple length fibers and short
cellulosic fibers at an overall concentration of staple length
fibers from about 2 to about 55 percent by weight and an overall
concentration of short fibers from about 45 to about 98 percent by
weight, said web having an outer major face characterized by a
concentration of staple length fibers in excess of said overall
concentration and an inner major face characterized by a
concentration of short cellulosic fibers in excess of said overall
concentration, the intermediate portion of said web between said
faces being characterized by a transition whereby the concentration
of said staple length fibers gradually decreases from said outer
major face to said inner major face and the concentration of said
short cellulosic fibers gradually decreases from said inner major
face to said outer major face; a highly porous, loosely compacted,
cellulosic fibrous batt in face-to-face juxtaposition with the
inner face of said facing layer; and a water-impervious backing
sheet adhered to the outer surface of said batt.
6. A diaper as set forth in claim 5 wherein said staple length
fibers are present at an overall concentration from about 10 to
about 40 percent by weight and are present at said outer major face
in a concentration of from about 5 to 20 percent by weight higher
than said overall concentration.
7. A diaper as set forth in claim 6 wherein the transition of each
type of fibers between said faces is substantially uniform.
8. A diaper as set forth in claim 5 wherein said staple length
fibers are rayon fibers.
9. A diaper as set forth in claim 5 wherein said staple length
fibers are polyester fibers.
10. A multi-layer diaper comprising: a porous facing layer in the
form of a nonwoven web formed of staple length fibers and short
cellulosic fibers at an overall concentration of staple length
fibers from about 2 to about 55 percent by weight and an overall
concentration of short fibers from about 45 to about 98 percent by
weight, said web having an outer major face characterized by a
blend of staple length fibers and short cellulosic fibers with the
concentration of staple length fibers being in excess of said
overall concentration, and said web having an inner major face
characterized by a blend of short cellulosic fibers and staple
length fibers with the concentration of short cellulosic fibers
being in excess of said overall concentration, the intermediate
portion of said web between said faces being characterized by a
transition whereby the concentration of said staple length fibers
gradually decreases from said outer major face to said inner major
face and the concentration of said short cellulosic fibers
gradually decreases from said inner major face to said outer major
face; a highly porous, loosely compacted, cellulosic fibrous batt
in face-to-face juxtaposition with the inner face of said facing
layer; and a water-impervious backing sheet adhered to the outer
surface of said batt.
Description
BACKGROUND OF THE INVENTION
Disposable diapers have met with increased commercial acceptance in
recent years primarily because of their convenience, as opposed to
cloth diapers, which need to be laundered once soiled. Many
different constructions have been proposed and used, and some have
met with widespread commercial success in spite of certain
inadequacies in functional properties.
One of the most serious prior art problems has been the inability
to provide a suitable construction that would keep moisture away
from the surface of the diaper which comes into contact with the
infant's skin and thereby avoid skin irritation and infection.
Commonly assigned Mesek et al. U.S. Pat. No. 3,612,055 discloses
several diaper constructions that function extremely well in
keeping moisture away from an infant's skin, while at the same time
handling a full volume discharge of urine.
These functions are accomplished by a multi-layer diaper
comprising, in order, a fibrous facing layer in the form of a
substantially homogeneous blend of short and long fibers which is
to be brought into contact with the infant's skin, a layer of
highly porous, loosely compacted cellulosic batt, a paper-like
densified, highly compacted cellulosic fibrous layer integral with
the loosely compacted batt and an impervious backing sheet adhered
to the densified layer throughout the interface therebetween. The
facing layer is of porous construction and its fibers have less
wettability for water than the fibers of the loosely compacted
batt, resulting in a tendency for liquid to flow from the facing
web into the batt. The densified fibrous layer has a smaller
average pore size than the loosely compacted batt, resulting in a
tendency for liquid to flow preferentially from the batt into the
underlying densified layer rather than to other areas of the batt,
thus tending to restrict wetting in the batt to an area of moderate
size. Liquid flowing into the densified layer tends to spread
laterally because of its wicking action and liquid which might pass
through the densified layer during discharge (when flow is rapid)
is held back by the impervious backing sheet for sufficient time to
permit absorption to take place. Liquid in excess of the absorptive
capacity of the densified layer is forced back by the impervious
layer into the dry portion of the loosely compacted batt, thus
utilizing the additional absorptive capacity therein.
Since facing layers in diapers of the type disclosed in the
above-mentioned patent have substantially the same amount of short
cellulosic fibers adjacent the outer face thereof as adjacent the
inner face, there is essentially no wettability difference within
the facing layer itself, with the result that the diaper is
dependent, at least to some degree, upon the increased wettability
of the fibrous batt to retain urine away from the outer surface of
the facing layer.
Webs that can be used as a facing layer in diapers as disclosed in
the above-mentioned patent can be formed by an air laying
technique. Recent improvements have been made in such techniques,
such as for example, the improvements disclosed and claimed in
commonly assigned, copending Ruffo et al. application Ser. No.
108,546 filed Jan. 21, 1971, the disclosure of which is hereby
incorporated herein by this reference. Briefly, one of the air
laying techniques disclosed therein includes the steps of feeding
fibers of two different types to separate fiber opening means at a
given feed rate to provide the subseqently formed web with a given
overall concentration of the different type fibers, individualizing
fibers from said separate fiber sources, suspending the fibers from
each source in separate gaseous streams, impelling the gaseous
streams at least initially toward one another and combining said
streams to form a single combined carrier stream wherein the fibers
from each gaseous stream intermix with one another with the total
gas to total fiber volume ratio being at least 12,000:1 in the
combined gaseous carrier stream, and condensing the entrained and
individualized fibers from said combined stream to form a random
nonwoven web. At gas to fiber volume ratios above 12,000:1 the
fibers in the individual streams are spaced sufficiently from one
another that if streams are brought together at an angle without
substantial diminution in the velosity of the streams, fibers in
each stream can cross over the oncoming fibers to form a nonwoven
product wherein the product is characterized by having a
concentration of at least one fiber type on one face of the product
in excess of the overall concentration and a concentration of at
least one different fiber type on the other face of the product in
excess of the overall concentration, with a transition zone between
the faces such that the concentration of each fiber type gradually
diminishes away from the face having the maximum concentration for
that fiber type to the opposite face.
SUMMARY OF THE INVENTION
In accordance with this invention, a diaper is provided which
retains all of the advantageous functional characteristics of the
diapers disclosed in the above-mentioned patent, while at the same
time providing at no increase in cost, (1) improved feel and
resultant increased comfort to the infant, and (2) a gradually
increasing wettability gradient within the facing layer to promote
flow of urine through the facing layer and into the batt, thereby a
relative dry surface in contact with the infant's skin.
These improved functions are accomplished in a multi-layer diaper
which includes in order (1) a water-impervious backing sheet, (2)
an intermediate layer comprised entirely of short cellulosic fibers
that are loosely compacted throughout a major portion of the batt
and which are densified at one side of the batt to provide an
integral paper-like skin adjacent the backing sheet, and (3) a
facing layer that is formed of long or textile length fibers and
short cellulosic fibers, with the greatest concentration of long
fibers being adjacent the outer face of the facing layer, and with
the concentration of short cellulosic fibers gradually increasing
from the outer face to the inner face adjacent the batt. It is the
concentration of long fibers adjacent the outer surface of the
facing layer that gives the diaper improved feel and which results
in greater comfort to the infant. The concentration of long fibers
at the outer surface also effectively prevents, or at least
minimizes, any tendency of the short cellulosic fibers to dust from
the facing layer, while at the same time strengthening the outer
portion of the facing layer.
The short cellulosic fibers are at maximum concentration at the
inner face of the facing layer, and the concentration of short
cellulosic fibers most preferably substantially uniformly increases
in concentration from the outer face of the facing layer to the
inner face thereof. Because the individual short cellulosic fibers
are more wettable than the individual long fibers, there is a
gradual increase in wettability throughout the cross-sectional
thickness of the facing layer that is substantially directly
proportional to the concentration of the short cellulosic fibers.
As noted above, the wettability gradient within the facing layer
itself promotes, or enhances, passage of urine through the facing
layer and into the even more wettable, unbonded loosely compacted,
cellulosic fibrous portion of the batt layer. The facing layer may
be formed in accordance with the teachings in the above-mentioned
Ruffo et al. application. By using this process, any unground or
compacted pulp particles are confined to the interior of the
diaper.
BRIEF DESCRIPTION OF THE DRAWINGS OF
FIG. 1 is a perspective view, with certain portions broken away, of
an open unfolded diaper in accordance with this invention;
FIG. 2 is an enlarged partial cross section of the diaper of FIG.
1, taken generally along line 2--2;
FIG. 3 is a perspective view on a reduced scale of the diaper in
its configuration after being put on an infant; and
FIG. 4 is a simplified schematic view of the production line on
which the diaper is made.
DETAILED DESCRIPTION
While this invention is susceptible of embodiment in many different
forms, there is shown in the drawings and will herein be described
in detail a preferred embodiment of the invention, with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the invention to the embodiment illustrated. The
scope of the invention will be pointed out in the appended
claims.
Referring to the drawings, and particularly to FIGS. 1 and 2, the
diaper assembly 10, when fully opened and laid out flat, comprises
a lowermost water-impervious sheet 12 which is rectangular in
shape, a highly water-absorbent fibrous pad, or batt 14, which is
also rectangular in shape, but smaller than the impervious sheet
and centrally disposed thereon, and an overlying facing layer 16 of
fibrous material, which is also rectangular in shape, equal in
dimension, and coterminous with the impervious sheet and in contact
therewith in the marginal portions of the diaper extending
peripherally beyond the absorbent pad, i.e., in the portions 16b
and 12b of facing layer 16 and impervious sheet 12, respectively.
The batt 14 has a continuous paper-like densified highly compacted
lowermost fibrous layer 18 that includes spaced, parallel thickened
densified portions 19 in the form of parallel lines that extend
completely through the cross-sectional thickness of the batt.
Densified layer 18 is adhered to the impervious sheet by bead lines
of adhesive 22 substantially throughout the interface therebetween.
Marginal portions 16b and 12b are also adhered to each other by
bead lines 22.
In the preferred embodiment of the invention, moisture impervious
sheet 12 is formed of polyethylene having a thickness of
approximately 0.001 inch. The sheet may be smooth, or may be
embossed to improve its drape and feel. Other suitable flexible
moisture impervious sheets may be used in accordance with the
invention, such as, for example, polyethylene terephthalate sheets
having a thickness of about 0.0005 inch.
Batt 14 is formed of loosely compacted short cellulose fibers, such
as wood pulp fibers, or cotton linters, or mixtures thereof, which
are primarily held together by interfiber bonds requiring no added
adhesive, as is known in the art. Briefly, this batt is a low bulk
density coherent web of loosely compacted cellulose fibers
preferably comminuted wood pulp fibers in the form of so-called
"fluff".
The term "short fibers", as used herein, refers to fibers less than
about one-fourth inch in length, in contrast to "long fibers",
"staple length fibers" or "textile length fibers" which are longer
than about one-fourth inch in length, and generally are between
about 1/2 and 21/2 inches in length. The former are substantially
less costly than the latter. the classification of fibers by length
may be carried out by the Clark Classification procedure described
in the test manual of The Technical Association of Pulp and Paper
Industry (TAPPI-T233 SU64).
The paper-like densified layer 18 of batt 14 is formed by a slight
moistening of one surface of the batt followed by the application
of pressure thereto. The nature of the batt and of its densified
layer and the method of producing the same are described in U.S.
Pat. No. 3,017,304, dated Jan. 16, 1962. The thickened densified
portions 19 are formed by further compression of batt 14 while it
is still moist, as will hereinafter appear.
The composite density of batt 14, including its densified layer 18,
should be above about 0.07 gm./cc. and preferably between about
0.10 and 0.15 gm./cc. The foregoing density values are applicable
to the diaper as produced. In storage and handling, the loft or
thickness of the batt is increased to some extent, resulting in
lowered densities.
Facing layer 16, on an overall basis, is made of a given
concentration of fibers consisting predominantly of short
cellulosic fibers such as wood pulp fibers or cotton linters, in
amounts of about 50 to about 98 percent, the balance being textile
length fibers such as rayon, polyester, cellulose acetate, nylon,
etc. Short cellulosic fibers such as wood pulp fibers or cotton
linters are substantially less expensive than textile length
cellulosic fibers such as cotton and rayon, and since low cost is a
factor which is of substantial importance, it is desired to use as
large an amount of short cellulosic fibers as is consistent with
strength requirements.
Facing layer 16 is preferably formed by an air laying process, such
as for example, the process disclosed in the above-mentioned Ruffo
et al application, to produce a web having opposed outer and inner
major faces 15 and 17, respectively, with face 15 being
characterized by a concentration of staple length fibers in excess
of the overall concentration, and with face 17 being characterized
by a concentration of short cellulosic fibers in excess of the
overall concentration. The term faces, as used herein, means that
portion of the facing layer which extends inwardly from one outer
major surface to approximately one-fourth of the total
corss-sectional thickness of the facing layer. The transition zone
between the opposed faces 15 and 17 is characterized by a
decreasing concentration of the respective fiber type from the face
at which it predominates to the opposite face of the product. Face
15 preferably is comprised of a greater amount by weight of textile
length fibers and a lesser amount by weight of short cellulosic
fibers (as compared with the overall concentration of these fibers)
interspersed and blended therewith; with face 17 preferably being
comprised of a greater amount by weight of short cellulosic fibers
and a lesser amount by weight of textile length fibers (as compared
to the overall concentration of these fibers) interspersed and
blended therewith.
The overall concentration of textile length fibers within facing
layer 16 may vary from about 2 to about 50 percent, preferably from
about 10 to about 40 percent. The textile length fibers may, for
example, be 1.5 denier rayon fibers uniformly cut to 11/2 inches in
length, although the present invention is not limited to any
specific textile length fiber or concentration thereof. For
example, in facing layers with the overall concentration of textile
length fibers being from about 10 to about 40 percent by weight,it
has been found that the concentration of textile length fibers at
face 15 is about 5 to 20 percent by weight higher than the overall
concentration. In a specific embodiment of facing layer 16,which
had an overall composition of about 25 percent by weight rayon
fibers and about 75 percent by weight short cellulosic fibers, the
concentration of rayon fibers at face 15 was approximately 35-40
percent, and the textile length fibers were substantially uniformly
blended with 65-60 percent of short cellulosic fibers. In this
last-mentioned facing layer embodiment, approximately 5-10 percent
of rayon fibers were present at face 17, and were in uniform
admixture with about 95-90 percent of short cellulosic fibers.
Facing layers suitable for use in this invention have fabric
weights in the range of 1 to 5 oz/yd..sup.2, and most preferably
within the range of 1.75 to about 2.75 oz./yd..sup.2 The present
invention also contemplates that fabric having an even lower fabric
weight may be provided. After formation, the web is treated with a
bonding agent, such as a self-cross-linking acrylic emulsion, and
the facing web is treated with a wetting agent to partially
conteract the water repellency of the bonding agent and bring the
facing layer to the desired degree of wettability. One bonding
agent which has been employed with considerable success is a latex
of polyethyl-acrylate copolymer containing small amounts of
acrylonitrile and a cross-linking monomer sold under the trademark
HYCAR 2600 .times. 120. The bonding agent should preferably be of
the low viscosity type with a viscosity less than 5 centipoises. To
avoid excessive water repellency, a surfactant, preferably an
anionic surfactant, is included in the binder suspension. A typical
surfactant which has been found to be suitable is the ionic
sulfonated alkyl ester sold under the trademark TRITON GR-5. A
non-ionic surfactant may also be used, and a polyoxyethylene
sorbitan monolaurate sold under the trademark TWEEN 20 has been
found to be particularly useful. In a typical application, the
binder suspension is controlled to give the fabric a dry solds add
on in the range of from about 41/2 to 9 percent based on the fabric
weight, of which from about 0.15 to about 0.30 percent is the
amount of surfactant. In facing layers having an extremely low
percentage of textile length fibers, such as in facing layers
approaching 2 percent textile length fibers, the binder amount
would be toward the high side of the above-mentioned range. It will
be understood that the above-mentioned surfactants moderate and
reduce the water repellency which may be imparted to the short and
long fibers of thP web by the bonding agent which bonds them into
an integral layer. After treatment with a wetting agent, the facing
layer is receptive to penetration by urine but remains less
wettable than the batt.
The body of batt 14 is substantially more wettable than the facing
layer and tends to draw liquid away from the facing layer. The
individual fibers of the batt are extremely wettable, generally
having liquid-fiber contact angles below about 15 percent and
approaching zero in the optimum embodiment, as described in detail
in the above-mentioned patent. The wickability, or preferential
absorptivity of the body of the batt for water is limited, however,
by its low density which results in a large effective capillary
radius for the capillaries between adjacent fibers.
The relative wickability between facing layer 16 and the body of
batt 14 is affected by both the relative densities of the layers
and the relative wettability of the individual fibers in each
layer. The facing layer is sometimes more dense than the body of
the batt, tending to provide greater wickability in the facing
layer, but even then the individual fibers of the batt have
substantially smaller liquid-fiber contact angles than those of the
facing layer, overcoming the density difference and providing a
substantial overall increase in capillary pressure to absorb liquid
into the body of the batt.
Densified fiber layer 18 of the batt provides the maximum capillary
pressure because it combines the very low contact angle of the
fibers of the batt with the high density (small capillary radius)
of the densified fibers.
When urine is voided into an area in facing layer 16, it partially
wets the facing layer and is absorbed therein, spreading out to a
limited extent to form a roughly circular wetted zone therein. When
the urine passes through the facing layer and comes into contact
with the body of batt 14, it is preferentially absorbed into the
body of the batt because of the enhanced wettability thereof. It
spreads within the body of the batt to wet a roughly circular zone
therein that is slightly larger than the wetted zone in facing
layer 16. When the urine passes through the body of the batt it
initially contacts one or more of the thickened densified lines 19
and the urine is strongly drawn into the densified layer 18 because
of its high density and is spread laterally through a much larger
zone, or to the edges of the batt, depending on the amount of urine
passed. the urine is transported rapidly along lines 19, more
rapidly than it is transported transversely across the densified
bridging portions between lines, with the result that the roughly
circular zone in the initially wetted loosely compacted portion of
the batt is distorted into a roughly oval zone in the densified
portion of the batt.
The urine is transported relatively rapidly in all directions of
the densified layer 18 because the densified layer is continuous
over one face of the absorbent panel. However, the thickened
portions 19 provide for an increased volumetric flow rate in the
longitudinal direction to rapidly move a larger volume toward the
ends of the absorbent structure. The bridging portions provided by
the portions of the densified layer between the thickened portions
rapidly transport the liquid away from the initially wetted area of
the densified layer and into contact with previously unwetted
thickened portions, with the result that liquid is rapidly drawn
away from the initially wetted area and transported both
longitudinally and transversely into substantially all portions of
the densified layer.
On occasions when a substantial amount of urine has been voided,
the densified layer becomes saturated and excess urine, aided by
the presence of impervious sheet 12 and its adherence to the
densified layer in a discontinuous pattern substantially throughout
the interface therebetween, flows into the previously dry portions
of the body of the batt, and finally into the previously dry
portions of the facing layer. It is to be noted, however, that such
flow from a saturated densified layer is from the outermost
portions of the diaper inward so that most of the facing layer
remains dry until all other fibrous portions of the diaper are
saturated. The thickened densified portions provide for an
increased cross-sectional area in the absorbent panel, as compared
to a densified layer of uniform thickness or a plurality of spaced
densified zones, with the greater cross-sectional area providing a
capacity to absorb an increased volume of urine. Thus, with the
structure of the present invention more urine can be stored in the
densified layer, and the tendency for urine to flow back into the
batt or into the facing layer is resisted.
The densified layer of the batt, for the reasons explained above,
creates a high capillary pressure which tends to move liquid away
rapidly from the area of the original wetting. However, the speed
of liquid migration is limited in the densified layer because of
the resistance provided by its small capillaries. The composite
batt used in this invention, with its densified layer in intimate
contact with absorbent material of lesser density, provides
improved speed of liquid migration over either the densified layer
alone, or the uncompressed layer alone.
It is to be noted that the facing layer as assembled into the
diaper is coterminous with the impervious sheet and there is no
folding over of the impervious sheet to envelope any edge of
fibrous material. Thus there is no portion of the upper surface of
the diaper which is covered with any plastic material, and no
plastic material comes into direct contact with the infant's skin
when the diaper is affixed in position by pins or tabs. Prolonged
direct contact of plastic material with an infant's skin can cause
irritation and infection but, nonetheless, is employed in prior art
disposable diapers to provide an impervious seal to the infant's
skin. The superior absorptive capacity of the diaper of this
invention and its superior functioning made such plastic-to-skin
contact unnecessary.
The diaper of this invention is normally packaged and sold in a
folded condition as described in the abovementioned patent.
Briefly, the side margins 12b and 16b of the impervious sheet 12
and the facing web 16, together with a portion of batt 14, are
folded inwardly in a first fold to provide as the uppermost layer
of the fold, a portion of the moisture impervious sheet. This
sub-assembly is then folded outwardly along each edge in a second
fold to cover the first folded portion and to expose the edge
portion of the facing web as the upper layer of the double fold. In
the preferred embodiment, each double fold at the edge of the
diaper comprises approximately one-third of the resulting
transverse dimension of the folded diaper, leaving approximately
one-third of the width of the folded diaper as a central unfolded
and uncovered portion.
The diaper is held in its folded condition by two small central
spots of adhesive applied between the main body of the diaper and
the overlying sides 16b of the facing web, one spot on each folded
side of the diaper. When the diaper is to be put on the infant, the
folds are opened on one side of each of the adhesive spots, and the
open portion of the diaper is put under the infant's buttocks while
the folded portion is raised into the crotch region. The final form
of the diaper is shown in perspective on a reduced scale in FIG. 3.
In one form of the invention, as illustrated in FIG. 3, the diaper
is provided with adhesive tabs 26, each having a fixed end secured
to the impervious sheet 12 and a free end wherein the adhesive
surface is covered with a facing sheet. The facing sheets are
removed to expose the adhesive surfaces when the diaper is applied
to the infant, as in the configuration shown in FIG. 4, and the
free ends of the adhesive tabs are secured to opposite corners of
the diaper.
Suitable fibrous structures for making the pads or batts 14 used in
this invention are made from short cellulosic fibers obtained by
the grinding or comminution of compacted wood pulp fibers or cotton
linters. The batts are initially formed by air blowing the
cellulosic fibers onto a support at a total weight of about 2 to
about 10 oz./yd..sup.2, and then subjecting the air blown fibers to
heavy compression. The dense compacted paper-like layer or skin is
prepared by moistening a surface of the cellulosic batt with a fine
spray of water, and then subjecting the moistened batt to pressure.
The formation of the densified skin on the cellulosic batt is
believed to be due to the formation of strong hydrogen bonds
between contacting moistened fibers, similar to the bonds between
the fibers in paper. By the proper selection of the amount of
moisture applied to the surface of the batt and by the proper
selection of degree of compression imposed, the properties of the
densified skin may be varied as desired. The thickness, density,
strength and other characteristics of the densified skin will
depend upon the unformity by which the moisture is applied, the
depth to which it penetrates, and the degree to which the fibers
are compressed. For example, by finely spraying about 0.0015 cc. of
water per square centimeter of web surface and then exposing the
web to a pressure of about 40 lbs./in..sup.2, a suitable densified,
coherent paper-like skin 18 is obtained on the surface of the web
which has been moistened. The thickened densified portions 19 may
be obtained by subjecting the web to additional pressure, as by the
use of an embossing roll, while the web is still moist, and the
additional pressure is preferably several times higher than the
pressure that is applied to form the densified layer 18.
The short fibers used in making batt 14 of this invention are
generally entirely fibers of wood pulp or cotton linters. however,
other cellulosic fibers may be used as well as blends of cellulose
fibers with other fibers such as silk, wool, nylon and cellulose
acetate. Highly purified kraft paper pulp fibers have proven to be
most satisfactory for most applications.
The diaper of this invention may be assembled in equipment such as
that schematically shown in FIG. 4. A roll of compacted wood pulp
41 is provided to feed a source of short cellulosic fibers to
grinding mill 42 from which a stream of fibers is blown onto belt
43 as a layer 44 weighing between about 2 and about 10
oz./yd..sup.2 the air blown layer is passed under compacting roll
46 from which it emerges with enough integrity to sustain itself as
a web without the support of belt 43. The web then passes through a
pair of calender rolls 47 for further compression and then under
nozzle 48 which deposits a fine spray of moisture on the upper
surface of the web. the moistened web then passes between another
set of calender rolls 49 which exert heavy pressure on it to form a
skin 51 on its upper surface.
The amount of moisture applied to the web may vary suitably from
about 0.0005 to about 0.03 cc. of water per square centimeter of
web surface, depending on the thickness of the paper-like densified
skin desired, with lesser amounts of moisture being used for
thinner webs and very thin, paper skins and greater amounts for
thicker webs and skins of greater thickness.
the amount of pressure applied by rolls 49 may vary from about 5 to
about 100 or more lbs./in..sup.2, with the commercially preferable
range being from about 10 to about 50 lbs./in..sup.2 In a typical
embodiment, the web is sprayed with about 0.0015 cc. of water per
square centimeter of web surface and subjected to a pressure of
about 40 lbs./in..sup.2 to obtain a densified, coherent papery skin
of uniform thickness on the surface of the web which has been
moistened. The amount of moisture is selected so that the web is
still moist following formation of the skin 51. the web then passes
between an embossing roll 52 and a back up roll 53 for formation of
the thickened densified portions 19. Roll 52 has a plurality of
axially spaced, circumferentially extending rib-like projections 54
that bear upon the previously formed skin 51, and because of the
residual moisture in the web and the increased pressure applied by
projections 54, thickened densified portions 19 are produced.
The pressure applied by the projections 54 on the embossing roll
also produces recesses or air gaps 20 (FIG. 2) in alignment with
thickened portions 19. As is evident from FIG. 2, the unthickened
portions of the densified layer 18 merge with the loosely compacted
batt 14 at a generally planar interface 21, and the thickened
densified portions extend beyond interface 21 and into the loosely
compacted batt 18 to give the absorbent panel a three dimensional
strengthening effect.
After the skin and the thickened portions are formed, the absorbent
web comes into contact with a web of facing material 55 and is
supported thereby while being cut by cutter 56 into individual
batts 14. Polyethylene film 12 is fed to the assembly from roll 58,
lines of adhesive being applied from applicator 59. As described
above, the adhesive is applied as parallel lines or beads between
the impervious sheet and the densified layer of the batt (or the
facing layer in the marginal portion of the diaper). Adhesive may,
if desired, be applied as a continuous layer between the
polyethylene and the batt, but such application tends to provide
excessive stiffness. The adhesive may also be applied in other
patterns, such as spaced dots or other forms of so-called "island"
bonds, but fairly close overall adhesion between the sheet and the
batt is required and no portion of the polyethylene should be more
than about 2 inches from a point of adhesion. In the absence of
such close overall adhesion, the polyethylene film may be separated
from the densified layer to create substantial spaces in which
uncontrollably large amounts of free liquid urine can
accumulate.
After the facing material and polyethylene are brought into contact
with opposite faces of the absorbent batts, the assembly is
subjected to compression by rolls 60 and 61 to shape the diaper
assembly, and the individual diapers are cut off by cutter 62.
If desired, adhesive applicator 59 may be omitted and adhesion
between the polyethylene layer and the fibrous layers may be
achieved by heat sealing, employing a suitable sealing element in
the production line.
The facing layer, as described above, is preferably formed in
accordance with the process disclosed in the above-mentioned Ruffo
et al application. The facing layer has an overall concentration of
from about between 50 and 98 percent by weight of short fibers, not
exceeding about one-fourth inch in length. The average short fibers
are from about one-sixteenth to about three-sixteenths inch in
length. The facing layer is prepared by first feeding a supply of
short cellulosic fibers 70 and a supply of textile length fibers 71
to a fiber opening and mixing apparatus 72, which take the form of
two individual rotating lickerins as described in the
above-mentioned Ruffo et al application. The fibers 70 and 71 are
fed to the opening means 72 at a desired rate to provide a web 73
with a desired overall fiber concentration, and apparatus 73, in
addition to opening the fiber source and individualizing the
fibers, also suspends the fibers from each source in separate
gaseous streams which are impelled toward one another and combined
to form a single carrier stream wherein the fibers from each
separate stream cross over one another to form the facing layer as
described above.
The volume ratio of gas to fiber in each of the separate gaseous
streams depends on the type and length of fibers. Thus, for
example, for most commercially available shorter type fibers usable
in the facing layer of the present invention, larger volume ratios
may be employed as compared to the use of staple or longer length
fibers where higher volume ratios are desirably employed. With
shorter fibers, the volume ratio of gas to fiber in the separate
gaseous stream is at least 12,000:1 to 15,000:1 and up to
275,000:1. With the longer or textile length fibers, the volume
ratio of gas to fiber in the separate gaseous stream preferably has
a minimum of from about 15,000:1 to 18,000:1 and up to 275,000:1
(desirably between 100,000:1 to 275,000:). The minimum gas to fiber
volume ratio in the combined stream depends to some extent on the
overall concentration of short and long fibers, and preferably will
be equal to or above the minimum ratios set forth above. With gas
to fiber volume ratios of between about 12,000:1 to about 275,000:1
in the combined stream, highly uniform webs (see the definition in
the Ruffo et al application) can be produced at a high production
rate up to 550 feet per minute, or greater. As noted above, the
transition in fiber concentration from face 15 to face 17, and vice
versa, is substantially uniform. The term "substantially uniform",
as used herein, is intended to mean that at any point between the
opposed faces there is substantially no clear cut or distinct line
of demarcation between the fibers of the fabric, when the fabric is
viewed in cross section.
The web 73 emerging from apparatus 72 may be carried by a conveyor
74 to a bonding station when it is through bonded by a bonding
agent of the type described above from source 75. the web is then
dried by passing around drying drums 76, and then passes upwardly,
as shown schematically in FIG. 4, where it is bonded to the
remainder of the diaper structure.
It will be understood by those skilled in the art that variations
and modifications of the specific embodiments described above may
be employed without departing from the scope of the invention as
defined in the appended claims.
* * * * *