U.S. patent number 3,901,238 [Application Number 05/452,095] was granted by the patent office on 1975-08-26 for disposable diaper having a resin treated absorbent pad to improve integrity, softness and dryness.
This patent grant is currently assigned to The Procter & Gamble Company. Invention is credited to Dale A. Gellert, Kendall L. Harden, John R. Noel.
United States Patent |
3,901,238 |
Gellert , et al. |
August 26, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Disposable diaper having a resin treated absorbent pad to improve
integrity, softness and dryness
Abstract
A disposable diaper combining improved softness and sufficient
strength to resist in use tearing and shredding in a single
structure, thereby producing better compliance and fit when the
structure is applied to the wearer, and hence improved comfort as
well as better containment of waste fluids deposited thereon. In a
preferred embodiment, a disposable diaper of the present invention
employs an air laid absorbent cellulosic core reinforced by the
application of a hydrophobic resin at relatively low levels of
solids addition to one side thereof with subsequent drying, curing
and calendering to the desired overall density. With sufficient
strength built into the resin treated surface of the absorbent core
structure, the unreinforced surface of the absorbent core can be
adhered directly to a soft, waterproof backsheet, thereby producing
a unique softness, texture and hand. In addition to improved
strength and softness, a resin-stabilized absorbent core of the
present invention exhibits improved surface dryness due to
favorable density and capillary gradients which provide improved
liquid penetration from the resin treated surface of the core to
the non-resin treated portions of the core. By combining the
resin-stabilized absorbent core with a fast strike-through topsheet
in a disposable diaper structure, the gasket-like waterproof side
flaps normally required to prevent liquid run-off can be
eliminated.
Inventors: |
Gellert; Dale A. (Aurora,
IN), Harden; Kendall L. (Cincinnati, OH), Noel; John
R. (Cincinnati, OH) |
Assignee: |
The Procter & Gamble
Company (Cincinnati, OH)
|
Family
ID: |
23795015 |
Appl.
No.: |
05/452,095 |
Filed: |
March 18, 1974 |
Current U.S.
Class: |
604/366; 604/370;
604/372 |
Current CPC
Class: |
A61L
15/425 (20130101); A61F 13/15585 (20130101); A61F
13/15674 (20130101); A61L 15/42 (20130101); A61F
13/534 (20130101); A61F 2013/53908 (20130101); A61F
13/537 (20130101); A61F 2013/15821 (20130101); A61F
2013/53721 (20130101); A61F 2013/51409 (20130101); A61F
2013/53445 (20130101); A61F 2013/51061 (20130101); A61F
13/539 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61L 15/16 (20060101); A61L
15/42 (20060101); A61f 013/16 () |
Field of
Search: |
;128/284,287,29R,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Medbery; Aldrich F.
Attorney, Agent or Firm: Linman; E. Kelly Braun; Fredrick H.
Gorman; John V.
Claims
Having thus defined and described the invention, what is claimed
is:
1. A method of producing a soft, reinforced body fluid absorbent
fibrous web having sufficient strength to resist tearing and
shredding when used as an body fluid absorbent core, comprising the
steps of:
a. treating one surface of an uncompacted absorbent web of
hydrophilic fibers having a basis weight between about 80 grams per
square meter and about 500 grams per square meter and a density
between about 0.03 grams per cubic centimeter and about 0.05 grams
per cubic centimeter by applying a hydrophobic, film-forming
material thereto to a depth not exceeding 50 percent of the total
thickness of said web in the uncompacted state;
b. drying the film-forming material applied to the surface of said
web while said web is in the uncompacted state so that the material
is non-tacky and will not self-adhere upon compaction of the web;
and
c. compacting said web to an overall density between about 0.09
grams per cubic centimeter and about 0.13 grams per cubic
centimeter.
2. The method of claim 1, wherein the hydrophobic, film-forming
material is comprised of a resin having a glass transition
temperature between about -15.degree.C and about +35.degree.C, said
resin being applied at a level between about 5 grams and about 16
grams of resin solids per square meter of absorbent web.
3. A method of producing a soft, reinforced absorbent fibrous web
having improved dryness characteristics on one surface thereof,
comprising the steps of:
a. treating one surface of an uncompacted absorbent web of
hydrophilic fibers having a basis weight between about 80 grams per
square meter and about 500 grams per square meter and a density
between about 0.03 grams per cubic centimeter and about 0.05 grams
per cubic centimeter by applying a hydrophobic, film-forming
material thereto;
b. drying and curing the film-forming material applied to the
surface of said web while said web is in the uncompacted state;
c. compacting said web to an overall density between about 0.07
grams per cubic centimeter and about 0.15 grams per cubic
centimeter, whereby the resulting density of the treated surface of
said web is lower than the resulting density of the untreated
portions thereof to provide a capillary size gradient favorable to
the transmission of liquid from the treated surface of said
absorbent web to the untreated portions thereof.
4. The method of claim 3, wherein the hydrophobic, film-forming
material is comprised of a resin having a glass transition
temperature between about -15.degree.C and about +35.degree.C, said
resin being applied at a level between about 5 grams and about 16
grams of resin solids per square meter of absorbent web.
5. The method of claim 4, wherein said hydrophobic film-forming
material is comprised of a styrene-butadiene resin.
6. The method of claim 4, wherein said resin is applied at a solids
content between about 10 percent and about 55 percent.
7. The method of claim 3, wherein drying and curing of the treated
surface of said absorbent web is accomplished by subjecting said
web to a forced convection of warm, dry air for a period of time
sufficient to reduce the total moisture content of said absorbent
web to below about 5 percent.
8. The method of claim 7, wherein the temperature of said warm, dry
air is at least about 270.degree.F.
9. The method of claim 3, wherein said hydrophobic, film-forming
material is applied to one surface of said uncompacted absorbent
web to a depth not exceeding 50 percent of the total thickness of
said web in the uncompacted state.
10. A disposable diaper having improved softness, texture and hand
as well as sufficient strength to resist in use tearing and
shredding, said diaper including a unitary absorbent pad of varying
density and having means for promoting rapid transmission of
liquids from the surface receiving said liquids into the interior
of said pad, said diaper comprising:
a. an absorbent pad of entangled, hydrophilic fibers, the fibers on
one surface thereof having a coating of a hydrophobic film-forming
material thereon, the surface of said absorbent pad containing said
coated hydrophilic fibers exhibiting a lower density than the
portions of said pad containing uncoated hydrophilic fibers,
thereby providing a capillary size gradient favorable to the
transmission of liquid from the surface of said absorbent pad
containing said coated fibers to the portions of said pad
containing said uncoated fibers, said absorbent pad having an
overall density between about 0.09 and about 0.13 grams per cubic
centimeter as measured under a load of 20 grams per square
centimeter and a wet tensile strength of at least about 0.5 pounds
per inch of pad width; and
b. a soft, waterproof backsheet adhered directly to the surface of
said absorbent pad containing said uncoated hydrophilic fibers,
whereby improved containment of waste fluids deposited on the
surface of said absorbent pad containing said coated hydrophilic
fibers and improved wearer comfort are provided due to better
compliance and fit when said diaper is applied to the wearer.
11. The disposable diaper of claim 10, including a liquid-pervious
topsheet secured in superposed relation to the treated surface of
said absorbent pad.
12. The disposable diaper of claim 10, wherein said waterproof
backsheet is comprised of matte finish polyethylene.
13. A disposable diaper exhibiting improved strike-through and
surface dryness characteristics, said diaper including a unitary
absorbent pad of varying density and having means for promoting
rapid transmission of liquids from the surface receiving said
liquids into the interior of said pad, said diaper comprising:
a. an absorbent pad of compressed, entangled, hydrophilic fibers,
the fibers on one surface of said absorbent pad having a coating of
a cured, hydrophobic, film-forming material thereon, the surface of
said absorbent pad containing said coated hydrophilic fibers
exhibiting a lower density than the portions of said pad containing
uncoated hydrophilic fibers, thereby providing a capillary size
gradient favorable to the transmission of liquid from the surface
of said absorbent pad containing said coated fibers to the portions
of said pad containing said uncoated fibers, said absorbent pad
having an overall density between about 0.09 grams per cubic
centimeter and about 0.13 grams per cubic centimeter as measured
under a load of 20 grams per square centimeter;
b. a soft, waterproof backsheet secured to the surface of said
absorbent pad containing said uncoated hydrophilic fibers; and
c. a liquid-pervious topsheet having a strike-through time of less
than about 5 seconds, as measured with said topsheet in adjacent
contact with the surface of said absorbent pad containing said
coated hydrophilic fibers, secured in superposed relation to the
surface of said absorbent pad containing said coated hydrophilic
fibers, whereby waste fluids deposited on said topsheet pass
rapidly through said topsheet and are absorbed by and partitioned
within the portions of said absorbent pad containing said uncoated
hydrophilic fibers.
14. The disposable diaper of claim 13, wherein said topsheet is
comprised of a low density, high loft, hydrophobic material.
15. The disposable diaper of claim 14, wherein said topsheet is
comprised of non-woven, needle-punched polyester fabric having a
density of about 0.05 grams per cubic centimeter, as measured under
a load of 20 grams per square centimeter.
16. The disposable diaper of claim 13, wherein said absorbent pad
has a minimum wet tensile strength of at least about 0.5 pounds per
inch of pad width.
17. The disposable diaper of claim 13, wherein said waterproof
backsheet is adhered directly to the surface of said absorbent pad
containing said uncoated hydrophilic fibers and said
liquid-pervious topsheet is secured at its periphery to the
overlapping portions of said waterproof backsheet to form an
envelope about said absorbent pad.
Description
FIELD OF THE INVENTION
The present invention has relation to disposable absorbent products
generally, and in particular to disposable absorbent products such
as bandages, diapers and sanitary napkins.
In a preferred embodiment, the present invention has relation to a
resin-stabilized absorbent cellulosic web suitable for use in
disposable absorbent products, said web having improved softness
and strength as well as favorable density and capillary gradients
to provide improved liquid penetration and retention
characteristics between the resin treated surface of the web and
the non-resin treated portions thereof.
In yet another preferred embodiment, the present invention has
relation to a disposable diaper exhibiting improved softness,
texture and hand as well as sufficient strength to resist tearing
or shredding of the absorbent pad in use, thereby providing greater
wearer comfort and better absorbency along with improved
containment due to better fit.
In still another preferred embodiment, the present invention has
relation to a disposable diaper exhibiting both improved surface
dryness and more rapid strike-through of fluids deposited on the
surface of said diaper, thereby eliminating the need for gasketing
means along the lateral edge portions of said structure to prevent
liquid run-off during periods of heavy flow.
BACKGROUND OF THE INVENTION
Disposable absorbent products, and particularly disposable
absorbent bandages, diapers and sanitary napkins are well known. An
object common to such products is the provision of an effective
means for absorbing aqueous liquids such as urine deposited thereon
in such a manner as to prevent run-off during maximum flow
conditions and to effectively retain such liquids absorbed within
the absorbent core member of the structure. It is likewise an
object of such structures to reduce the amount of moisture in
contact with the wearer's skin and thus reduce maceration, rash or
other unpleasantness. Such structures should preferably exhibit
both strength and softness to enhance their absorbency and
containment characteristics in addition to wearer comfort. Prior
art disposable absorbent products have not, however, successfully
combined all of the aforementioned desirable features in a single
structure.
Structures comprised of a porous hydrophobic topsheet and a
hydrophilic substrate are well known in the art. It should be
recognized that the terms "hydrophobic" and "hydrophilic" as herein
employed, while useful in their brevity actually refer,
respectively to relatively low and relatively high critical surface
tensions of the materials being characterized. The hydrophobic
nature of a prior art diaper topsheet, for example, is evidenced by
its lack of affinity for liquid human waste relative to that of the
hydrophilic or absorbent substrate. As used herein, a web is
hydrophobic when a drop of liquid waste placed thereon does not
spread to any appreciable degree on the web. Thus, when a
hydrophobic sheet is superimposed upon a layer of hydrophilic or
less hydrophobic absorbent material to form a diaper and the
hydrophobic material is placed next to wearer's skin, waste fluids
from the wearer pass through the hydrophobic sheet and are
preferentially partitioned by and absorbed within the underlying
hydrophilic layer, leaving the topsheet adjacent the wearer's skin
relatively dry.
The rate at which liquid penetration takes place varies greatly,
however, depending upon such factors as the density and capillary
gradients existing between the various layers of the absorbent
structure and the relative hydrophobicity of the various layers.
Capillary forces act to draw a liquid from a less dense structure
to a more dense hydrophilic structure, i.e., from a large pore size
to a smaller pore size, and this directional action can be
augmented further by employing a topsheet which is both lower in
density and slightly hydrophobic with respect to the hydrophilic
absorbent core to promote rapid absorption of the liquid deposited
on the topsheet by the absorbent core member, thereby minimizing
liquid run-off during periods of heavy flow. Care must be taken,
however, that the surface dryness of the structure not be adversely
affected. If an extremely thin, low density, hydrophobic topsheet
is employed in combination with a more dense hydrophilic core,
fluids absorbed by the hydrophilic core may not be effectively
prevented from re-emerging at the surface of the topsheet when the
structure is subjected to compressive forces generated by the
activities of the wearer.
In general, a more hydrophobic topsheet provides poorer
strike-through characteristics but better surface dryness, while a
less hydrophobic topsheet provides better strike-through
characteristics but poorer surface dryness. Thus to a certain
extent there has been a balancing in prior art structures between
favorable strike-through characteristics and favorable surface
dryness characteristics.
As used hereinafter, strike-through is a measure of how long it
takes for an absorbent structure to completely absorb a specified
quantity of liquid deposited on its surface. Strike-through values
are normally expressed in seconds. Low strike-through values are
indicative of high absorbency rates, and are, therefore, generally
preferred in absorbent bandages and the like. Surface wetness, on
the other hand, is a measure of the degree to which absorbed
moisture can be caused to re-emerge from an absorbing matrix, under
pressure, to appear as moisture at the surface of the structure
where it originally entered the absorbing matrix. Surface wetness
values are normally expressed in grams of re-emerging liquid
absorbed on a standard filter paper superposed on the absorbing
matrix. Low surface wetness values are indicative of a greater
ability of the absorbent structure to retain an aqueous solution
once it has been absorbed, i.e., improved surface dryness.
One prior art means of providing satisfactory surface dryness
characteristics while minimizing liquid run-off is disclosed in
U.S. Pat. Re. No. 26,151 which issued to Duncan, et al., on Jan.
31, 1967. The Duncan, et al., patent discloses a disposable diaper
structure employing an absorbent pad and a waterproof backsheet of
a width greater than that of the pad. The side portions of the
backsheet are folded inwardly over the side marginal areas of the
pad so that in use liquid run-off is minimized during periods of
heavy flow. The inwardly folded side portions assume a position
contiguous to the wearer's legs along an area of the inner, rear
and front portions of the thighs adjacent the junction thereof with
the wearer's torso, thus providing a gasketing action. In the
described embodiment, a hydrophobic topsheet encloses the absorbent
material of the pad. The gasketing action gives the absorbent pad
sufficient time to absorb liquid wastes to thus utilize, as fully
as possible, the absorptive power of the diaper while
simultaneously preventing run-off during periods of heavy flow and
consequent soiling of garments.
While side flaps have proven to be one acceptable solution to the
run-off problem in a disposable diaper exhibiting satisfactory
surface dryness characteristics, applicant's invention, in a
preferred embodiment, provides rapid strike-through and improved
surface dryness characteristics in a single structure, thus making
the use of side flaps to prevent liquid run-off unnecessary.
Applicant's structure is, therefore, simpler in terms of
construction as well as in its application to the wearer.
Another problem common to most prior art disposable absorbent
structures relates to a lack of strength in the absorbent core
materials employed. This problem is particularly apparent with
airfelt, an air laid cellulosic material which is widely used in
disposable absorbent products due to its desirable absorbency and
softness characteristics and its relatively low cost. Disposable
absorbent products, and particularly disposable diapers fabricated
with absorbent cores of unreinforced airfelt do not, however, have
sufficient strength to resist tearing and shredding in use. Tearing
and shredding of the absorbent core in a disposable diaper is
undesirable in that it adversely affects both the absorbency and
containment characteristics of the structure in addition to being
aesthetically unacceptable to the consumer. Prior art disposable
absorbent products have dealt with this problem by various means,
including, for example, wet calendering of the airfelt,
wet-strength tissue addition, embossing of the airfelt, addition of
adhesive strips to the airfelt, etc.
U.S. Pat. No. 3,612,055 which issued to Mesek, et al., on Oct. 12,
1971 discloses a disposable diaper having an absorbent core of
loosely compacted cellulosic batt having greater wettability than
that of the facing web, said batt having a highly compacted layer
on its back side which is adhered directly to a waterproof backing
sheet over a widely distributed area of adhesion. The densified
surface is produced by calendering the absorbent web while the
surface to be densified is in a moist condition. Liquid deposited
on the surface of the structure disclosed by Mesek et al. passes
through the body of the loosely compacted batt and is strongly
drawn into the densified layer due to the small capillary radius of
the of the densified fibers. Such a diaper, although effective from
a liquid absorption and liquid retention standpoint, has a rather
stiff feel due to the fact that the densified layer of the
absorbent core is in adherent contact with the waterproof
backsheet, thereby tending to impart the stiffness of the absorbent
core to the entire structure.
U.S. Pat. No. 3,444,859 which issued to Kalwaites on May 20, 1969
discloses alternative means for reinforcing a fibrous batt to
impart mechanical strength thereto by foam bonding the exterior
surfaces of the batt to form a relatively strong skin thereon. The
skin on the exterior surfaces of the batt, however, detracts from
the softness and texture of a disposable diaper structure
incorporating the batt as an absorbent core.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
resin-reinforced absorbent web of air laid cellulosic material
exhibiting sufficient strength to resist tearing and shredding when
used in absorbent products such as disposable diapers, yet
retaining much of the softness inherent in such materials prior to
the application of any reinforcing treatment.
It is a further object of the present invention to provide an
absorbent pad of compressed, entangled, hydrophilic fibers, the
fibers on one surface thereof being treated in the uncompressed
state with a hydrophobic film-forming material which acts as an
interfiber bond inhibitor and a fiber stiffener during compression,
which pad, after compression, exhibits favorable density and
capillary gradients to promote wicking of liquid from the treated
surface of the absorbent pad to the untreated portions thereof.
It is yet another object of the present invention to provide a
disposable diaper having greater wearer comfort due to improved
softness, texture and hand as well as sufficient strength to resist
tearing and shredding in use, said diaper thereby providing
improved absorbency and better containment due to better fit.
Still another object of the present invention is to provide a soft,
compliant disposable diaper exhibiting strike-through
characteristics sufficiently rapid to substantially prevent liquid
run-off during periods of heavy flow as well as improved surface
dryness characteristics.
SUMMARY OF THE INVENTION
In accordance with the present invention, an absorbent fibrous web
suitable for use as an absorbent core in disposable absorbent
products is provided, said web comprising a compressed mass of
entangled hydrophilic fibers, the fibers on one surface thereof
being treated by the addition of a film-forming, hydrophobic resin
at relatively low levels of solids addition while said web is in an
uncompressed state, with drying and curing of said resin treated
web in the uncompressed state followed by subsequent calendering of
said web to the desired overall density. The resin acts as an
interfiber bond inhibitor and fiber stiffener during compression so
that the treated portions of the absorbent web remain at a lower
density after calendering than the untreated portions, thereby
creating a favorable density and capillary gradient between the
resin treated surface and the untreated portions of the web.
Because of the hydrophobic nature of the resin, the favorable
gradients are maintained when moisture is deposited on the
structure, thus providing improved surface dryness on the resin
treated surface of the web. In addition, the resin treatment
imparts sufficient strength to the absorbent web to resist in use
tearing and shredding when the web is employed as an absorbent core
in an absorbent structure such as a disposable diaper.
In a preferred embodiment, an absorbent web of the present
invention is incorporated in a disposable diaper so that the
non-resin treated surface of the web is adhered directly to a soft,
waterproof backsheet. Due to the inherent softness of the untreated
surface of the absorbent web, a unique texture and hand which
complement softness are produced, while the resin treated surface
of the web provides the strength necessary to resist tearing and
shredding in use. Because such a diaper exhibits improved strength
and softness, better compliance and fit are achieved when the
structure is applied to the wearer. This in turn provides better
containment of discharged wastes and improved wearer comfort.
In yet another preferred embodiment, a fast strike-through topsheet
is superimposed on the resin treated surface of an absorbent pad of
the present invention and secured at its periphery to a waterproof
backsheet adhered to the untreated surface of the absorbent pad to
form a disposable diaper. By combining a fast strike-through
topsheet with an absorbent web having favorable density and
capillary gradients to rapidly transmit moisture deposited on the
surface of the diaper into the untreated portions of the absorbent
core, liquid run-off can substantially be prevented without resort
to special restraining means at the lateral edge portions of the
diaper. Such a diaper also exhibits better surface dryness than is
normally obtainable when a fast strike-through topsheet is employed
due to the tendency of the resin treated surface of the absorbent
pad to partition liquid absorbed in the non-resin treated portions
of the pad from the topsheet, at least until the full absorptive
capacity of the non-resin treated portions of the pad has been
utilized.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter which is regarded as
the present invention, it is believed that the invention will be
better understood from the following description taken in
connection with the accompanying drawings in which:
FIG. 1A is a simplified schematic illustration of a portion of a
production line used for processing an absorbent fibrous web in
accordance with the present invention and for converting the
processed web into a disposable diaper.
FIG. 1B is a continuation of the simplified schematic illustration
of FIG. 1A showing the balance of the diaper converting
operation.
FIG. 2 is an enlarged schematic illustration of an uncompressed
fibrous web shown prior to processing in accordance with the
present invention, taken along section line 2--2 in FIG. 1A.
FIG. 3 is an enlarged simplified schematic illustration of the
absorbent fibrous web illustrated in FIG. 2 shown after application
of the reinforcing resin to the lowermost side thereof, taken along
section line 3--3 in FIG. 1A.
FIG. 4 is an enlarged simplified schematic illustration, taken
along section line 4--4 in FIG. 1A, illustrating the condition of
the absorbent fibrous web shown in FIGS. 2 and 3 after compression
of the structure and prior to total encapsulation thereof between
the waterproof backsheet adhered to its uppermost surface and the
topsheet adjacent its lowermost surface.
FIG. 5 is an enlarged simplified schematic illustration of a
disposable diaper of the present invention taken along section line
5--5 in FIG. 1A, illustrating the condition of the structure after
the lateral edge portions of the topsheet have been secured to the
lateral edge portions of the waterproof backsheet and the resulting
lateral edge portions of the diaper have been folded back upon and
secured to the surface of the topsheet.
FIG. 6 is an enlarged simplified schematic illustration of a
disposable diaper of the present invention, taken along section
line 6--6 in FIG. 1B, showing a preferred configuration of the
diaper in the finished state.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1A and 1B constitute a simplified schematic illustration of a
production line suitable for preparing an absorbent fibrous web in
accordance with the present invention and for converting said web
into a disposable diaper. In a preferred embodiment of the present
invention, an absorbent fibrous web 1 of hydrophilic cellulosic
material is produced by conventional air laying techniques well
known in the art and shown schematically as 2 in FIG. 1A. The
absorbent fibrous web 1, which is commonly referred to in the
industry as airfelt, preferably has an initial basis weight between
about 80 and about 500 grams per square meter. The density of the
web 1 typically ranges between approximately 0.03 and approximately
0.05 grams per cubic centimeter, as measured under a load of 20
grams per square centimeter, prior to processing in accordance with
the present invention. As shown schematically in FIG. 2, the
fibrous structure of the web is extremely loose prior to treatment
in accordance with the present invention, and, therefore, the web
has very little cohesive strength.
The first step designed to impart integrity and strength as well as
improved surface dryness characteristics to an absorbent web of the
present invention involves the application of a film-forming
hydrophobic resin to one surface of the absorbent web. This is
preferably accomplished by applying the liquid resin 4 with one or
more spray nozzles 3 so that a substantially uniform spray extends
across the entire width of the absorbent web 1.
As shown in FIG. 3, the resin 4 does not penetrate the entire
thickness of the absorbent web 1. The resin treatment is limited to
portion 13(b) of the absorbent web. In order to realize the surface
dryness benefits of an absorbent web of the present invention, to
be described in greater detail hereinafter, the untreated
hydrophilic portion 13(a) of the absorbent web 1 should constitute
at least about 50 percent and most preferably at least about 70
percent of the total thickness of the absorbent web prior to
calendering.
The resin 4 imparts wet strength to the absorbent web by bonding
the surface fibers together at contact points while the fibers are
in an expanded lattice structure. Since the fibers are randomly
distributed in the vertical as well as the horizontal plane and
bonded only at contact points, the resulting structure remains
flexible. The resin coating on the fibers also tends to prevent the
formation of additional bonds between the treated fibers during
subsequent calendering, thereby insuring the maintenance of
flexibility in the web after calendering as well as helping to
produce improved surface dryness on the resin treated surface of
the web.
The resin employed is preferably moderately hard and is non-tacky
when dry to avoid self-adhering when the absorbent web 1 is
calendered. One such resin found to produce very good results is
styrene-butadiene, a hydrophobic resin available from the Dow
Chemical Company of Midland, Mich. under Dow specification number
7284.01. Other hydrophobic resins also found suitable include, for
example, styrene-butadiene No. 7235 also available from the Dow
Chemical Company, and an acrylic-latex resin available from the
Rohm and Haas Chemical Company of Philadelphia, Pa. under Rohm and
Haas specification number TR-407.
A distinguishing resin property used commonly by polymer
manufacturers in characterizing a resin in its behavior as a
film-forming coating is its glass transition temperature. Within a
molecular weight series of a given resin, the polymer is less tacky
and self-adhering at higher glass transition temperatures. Thus, if
after proper drying and curing of an absorbent web 1 of the present
invention, the resin treated surface 13(b) self-adheres on
calendering, the difficulty can frequently be avoided by selecting
a resin with a higher glass transition temperature. Generally it
has been found that the preferred resins fall within the glass
transition temperature range of about -15.degree.C to about
+35.degree.C.
The resin 4 is preferably applied to the absorbent web 1 at
relatively low levels of solids addition, i.e., preferably between
about 5 and about 16 grams of resin solids per square meter, at a
solids content of between about 10 percent and about 55 percent by
weight. Low levels of resin application are desirable primarily to
avoid adverse effects on the softness, texture and hand of the
structure.
Although it is feasible to apply a resin spray to both surfaces of
the absorbent web 1, in a preferred embodiment of the present
invention only one surface of the web is treated in order to
preserve a sufficient amount of hydrophilic material in the web as
well as the inherent softness of the web, essential features of a
disposable diaper of the present invention. It should be noted that
due to the inherent flexibility of the web reinforcing process
described herein, it is also feasible to apply the resin 4 only in
selected areas of the web for localized reinforcement as well as to
vary the amount of resin applied at any given point across the web
to produce varying degrees of reinforcement across the web.
Following application of the resin spray 4 to the lowermost surface
of the absorbent web 1 in the uncompacted condition, the absorbent
web is passed between a hot air blow-through dryer 5 and a suction
box 6 which serve to drive moisture from the structure and cure the
resin. Both the hot air dryer 5 and the suction box 6 extend across
the entire width of the absorbent web 1. Hot air is introduced
directly onto the resin treated surface of the web through a
plurality of orifices 7 in the hot air dryer 5. Since the web is
relatively open at this point, the bulk of the hot air passes
through the absorbent web and is collected within the suction box 6
where it is continuously reheated and recycled back to the hot air
dryer 5 by means well known in the art.
The hot air dryer 5 and suction box 6 are preferably designed so
that the absorbent web 1 will be dried and cured upon exit
therefrom. Experience has demonstrated that drying and curing can,
for example, be achieved with an absorbent fibrous web having a
density prior to treatment of approximately 0.05 grams per cubic
centimeter as measured under a load of 20 grams per square
centimeter, said web having been treated on one surface with a
styrene-butadiene resin such as Dow No. 7284.01 applied at a solids
content of about 10 percent and a level of approximately 11 grams
of resin solids per square meter, by directing a forced convection
of 270.degree.F dry air through the web at a rate of about 450
cubic feet per minute per square foot of web surface for a period
of approximately 5 seconds. Higher resin solids concentrations
and/or higher drying temperatures can be utilized to reduce the
residence time required to effect drying and curing.
In general, experience has demonstrated that a resin treated
absorbent web 1 can normally be cured by subjecting it to a forced
convection of 270.degree.F dry air for a period of time sufficient
to reduce the moisture content of the structure to below about 5
percent.
An absorbent fibrous web which has been dried and cured prior to
calendering exhibits improvements not only in pad integrity and
tensile strength, but, in addition, provides a basis for combining
improved strike-through and surface dryness characteristics in a
single absorbent structure such as a disposable diaper. An
absorbent fibrous web which has been dried but not cured prior to
calendering, on the other hand, provides a lesser degree of surface
dryness improvement.
Following the drying and curing operation, the resin-stabilized
absorbent fibrous web 1 is passed between a pair of hard-surfaced
calendering rolls 8 and 9 to increase the overall density of the
web to the desired level. When the initial density of the structure
prior to treatment in accordance with the present invention is in
the range of about 0.03 to about 0.05 grams per cubic centimeter as
measured under a load of 20 grams per square centimeter, the
structure is normally calendered to an overall density between
about 0.07 and about 0.15 grams per cubic centimeter, and most
preferably to between about 0.09 and about 0.13 grams per cubic
centimeter when the absorbent web 1 is to be utilized in a
disposable diaper. The target density of the absorbent web is
preferably controlled by adjusting the force applied to the web as
it passes between the rolls. This is accomplished by mounting roll
9 in a fixed position and controlling the vertical movement of roll
8 by means of a multiplicity of pneumatically or hydraulically
actuated cylinders 10 which are regulated to produce a constant
compressive force on the web.
As alluded to earlier herein, the aforementioned web treatment
imparts integrity, cohesiveness and tensile strength to an
otherwise weak structure. As would be expected, the wet and dry
tensile strengths of the absorbent web 1 are dependent to a large
extent upon the level of resin application as well as upon the
particular resin utilized. For a resin such as Dow No. 7284.01,
solids application levels between about 5 and 16 grams per square
meter on an absorbent web having a density between about 0.03 and
about 0.05 grams per cubic centimeter prior to treatment in
accordance with the present invention results in wet tensile
strengths between about 0.5 and about 1.5 pounds force per inch of
pad width when the treated structure is calendered to a density
between about 0.09 and about 0.13 grams per cubic centimeter. That
is, a force of between about 0.5 and about 1.5 pounds is required
to separate a 1 inch wide sample of the web which has been
uniformly wetted with a quantity of simulated urine solution equal
to four times the weight of the sample. The simulated urine
solution is comprised of a 1 percent sodium chloride solution
adjusted to a surface tension of 45 dynes per centimeter.
For use in a structure such as a disposable diaper which is
subjected to considerable in use stress both wet and dry due to the
action of the wearer, a minimum wet tensile strength of about 0.5
pounds force per inch of pad width, and preferably about 1.0 pounds
force per inch of pad width, is desirable to resist tearing and
shredding. This can normally be achieved in an absorbent pad having
a basis weight of at least 80 grams per square meter and a density
prior to treatment of approximately 0.03 to 0.05 grams per cubic
centimeter by applying a resin such as Dow styrene-butadiene No.
7284.01 at a rate of approximately 11 grams of solids per square
meter and calendering the structure after drying and curing to a
density between about 0.09 and about 0.13 grams per cubic
centimeter.
As disclosed earlier herein, an absorbent fibrous web 1 which has
been cured prior to calendering provides a basis for improved
surface dryness and strike-through characteristics in addition to
improved strength and integrity when used in an absorbent structure
such as a disposable diaper.
It is believed that the primary reason an absorbent fibrous web
prepared as herein described exhibits improved surface dryness
characteristics on its resin treated surface is due to the fact
that favorable density and capillary gradients are created between
the treated surface of the web and the untreated portions thereof.
Because the resins employed by applicants are interfiber bond
inhibitors during compression and because they impart resilience to
the fibers which have been treated therewith, the resin treated
surface of the web exhibits a lower density than the untreated
portions of the absorbent web after calendering. In the case of an
absorbent web produced as described herein, the untreated portions
of the absorbent core may range from slightly more dense than the
resin treated portions of the core to several times more dense than
the resin treated portions of the absorbent core, depending to a
large extent on the degree of calendering of the structure. In
general, the more favorable the density and capillary gradients
between the resin treated surface of the web and the untreated
portions thereof the lower will be the surface wetness values
associated therewith.
Since the absorbent web 1 is preferably comprised of hydrophilic
cellulosic fibers, the resin 4, in order to maintain the favorable
density and capillary gradients described above when the structure
is wetted, must not only be hydrophobic in nature, but further,
must be of a film-forming variety so as to encapsulate the fibers
on the treated surface of the web and prevent them from becoming
wetted.
Accordingly, when moisture is deposited on the resin treated
surface of an absorbent fibrous web 1, the favorable density and
capillary gradients existing between the resin treated surface of
the structure and the untreated portions thereof serve to rapidly
transmit the moisture from the resin treated surface to the
untreated portions. Because the resin treated fibers of the
absorbent web exhibit hydrophobic properties after the resin
treatment, they are not readily wetted by liquids deposited on the
resin treated portion 13(b) of the absorbent web 1. Hence the
favorable density and capillary gradients existing between the
treated and the untreated portions of the web are not destroyed
when the structure is subjected to moisture. Liquid deposited on
the resin treated surface 13(b) of the absorbent wet 1 is rapidly
transmitted to the absorbent hydrophilic portion of the core 13(a)
until the full absorptive capacity of the latter has been
exhausted. Surface wetness is also reduced, i.e., surface dryness
is improved, on the resin treated surface of the web due to the
tendency of liquids absorbed in the hydrophilic core to migrate
preferentially throughout the hydrophilic layer rather than in the
direction of the less dense, hydrophobic, resin treated surface of
the absorbent web when the web is subjected to pressure in use.
Rewetting or flooding of the resin treated surface 13(b) of the web
is, therefore, minimized, at least until the full absorptive
capacity of the untreated hydrophilic portion 13(a) of the web has
been exhausted.
As should be apparent from the foregoing description, an absorbent
web of the type herein described is particularly well suited to
producing a strong, absorbent disposable diaper having unique
softness, texture and hand as well as favorable surface dryness
characteristics.
FIGS. 1A and 1B illustrate schematically the processing operations
necessary to convert an absorbent fibrous web of the present
invention into a disposable diaper having the aforementioned
attributes in addition to favorable strike-through characteristics.
The resinstabilized fibrous web 1 is cut into individual pad
segments 13 by means of a rotary cutter 11 having blades 14 secured
at its periphery and a hard-surfaced anvil roll 12. The individual
pad segments 13 are separated to a predetermined spacing by means
well known in the art and fed between a layer of waterproof
backsheet material 15 and a layer of topsheet material 16.
One material which has been found particularly suitable for use as
a waterproof backsheet is a matte finish polyethylene having a
weight of approximately 29,000 square inches per pound, such as is
available from the Visqueen Division of the Ethyl Corporation of
Terre Haute, Ind. Although glossy finish polyethylenes will
function equally well as a moisture barrier to prevent wicking of
absorbed liquids from the hydrophilic portion 13(a) of the
absorbent pad 13 to the clothing of the wearer, the dull matte
finish of the preferred backsheet contributes favorably to the
unique softness, texture and hand of applicants' diaper.
In order to preserve the overall softness impression of a diaper of
the present invention, the waterproof backsheet 15 is preferably
adhered directly to the untreated surface of the absorbent pad 13
by means of a soft, pressure-sensitive, adhesive 17 applied to the
innermost surface of the waterproof backsheet by means of one or
more spray nozzles 18. One such adhesive found suitable for use in
the present invention is Covinax 62 UFP, a polyvinyl acetate base
copolymer adhesive available from the Franklin Chemical Company of
Columbus, Ohio.
The topsheet 16 used in a preferred embodiment of the present
invention exhibits fast strike-through characteristics when placed
in contact with the resin treated surface 13(b) of an absorbent pad
13 of the present invention.
In general, a topsheet material 16 which exhibits a strike-through
time of less than about 5 seconds when placed in contact with the
resin treated surface of an absorbent pad of the present invention
will produce satisfactory results. This is determined by gently
pouring 5 cubic centimeters of a 1 percent sodium chloride solution
adjusted to a surface tension of 45 dynes per centimeter through a
1 inch diameter orifice in a 4 inch .times. 4 inch .times. 3/8 inch
thick stainless steel plate placed over a 4 inch .times. 4 inch
sample of the topsheet material superposed on a 4 inch .times. 4
inch sample of the resin treated absorbent core so that the
topsheet is in contact with the resin treated surface of the
absorbent core and measuring the amount of time required for the
solution to pass through the topsheet and into the absorbent
core.
Low density, high loft, hydrophobic topsheet materials are
generally preferred in order to provide both improved
strike-through and surface dryness qualities in a disposable diaper
of the present invention. Excellent results are achievable using,
for example, non-woven, needle punched polyester fabrics having a
density of about 0.05 grams per cubic centimeter as measured under
a load of 20 grams per square centimeter. One such material which
has proven highly satisfactory in this service is a non-woven, 21/4
ounce per square yard, needle punched fabric made with 3 denier
polyester staple and having a caliper of approximately 0.09 inches,
such as is available from Troy Mills of Troy, N.H. The invention
can also be practiced with similarly good results by the use of
materials such as: a non-woven, needle punched fabric made with 6
denier polyester staple and having a caliper of approximately 0.11
inches, such as Troy Mills Code No. 3001-007500, also available
from Troy Mills; or a non-woven, needle punched fabric made with 6
denier type 209 polyester staple and having a caliper of either
0.08 or 0.09 inches, such as Stearns and Foster grade O or grade K
material, available from the Stearns and Foster Company of
Lockland, Ohio. In the alternative, a less expensive material such
as Webline No. SW-269-3, available from the Kendall Company of
Walpole, Mass., may be utilized. The latter material has a basis
weight of approximately 22 grams per square meter, a density of
approximately 0.16 grams per cubic centimeter as measured under a
load of 20 grams per square centimeter, and is comprised of 1.5
denier rayon fibers which are hydrophilic in nature. One surface of
the Webline material is imprinted by the manufacturer with Rohm and
Haas HA-8 binder in a diamond-shaped patter constituting
approximately 25 percent of the web's surface to impart a degree of
hydrophobicity to the material. The Webline material, although
comparable, from a strike-through standpoint, to the preferred
topsheet materials cited earlier herein is less desirable than the
preferred materials from a surface dryness standpoint. This is due
to the higher density, i.e., the smaller capillary size, of the
Webline material relative to the resin treated surface 13(b) of the
absorbent pad 13 and the hydrophilic nature of the untreated
portions of the Webline material which tend to absorb and retain
moisture deposited thereon.
One novel and unique feature to be emphasized in connection with a
disposable diaper of the present invention, however, is that the
surface dryness obtainable by employing any of the suggested fast
strike-through topsheet materials, whether hydrophobic or
hydrophilic in nature, in combination with a resin treated
absorbent pad of the present invention is at least equal to and is
normally superior to that of prior art disposable diaper structures
employing hydrophobic topsheets in combination with hydrophilic
absorbent cores, while the strike-through characteristics thereof
are markedly superior.
The improved surface dryness is attributed to the liquid
partitioning properties of the hydrophobic resin treated surface
13(b) which is located immediately adjacent the topsheet 16. The
aforementioned liquid partitioning properties are due not only to
the hydrophobic nature of the resin treated surface 13(b), but also
to the favorable density and capillary gradients which exist
between the resin treated portion 13(b) and the untreated portion
13(a) of the absorbent pad 13. These factors operate to transmit
fluids deposited on the resin treated portion 13(b) rapidly into
the untreated portion 13(a) of the pad and to retain the absorbed
fluids therein, at least until the absorptive capacity of the
untreated portion of the pad has been exhausted. Because an
absorbent pad 13 of the present invention combines the ability to
absorb and partition moisture within a single, unitary structure,
greater flexibility than has heretofore been possible is permitted
in the selection of topsheet materials. Hence topsheet materials
exhibiting optimum strike-through characteristics may be employed
in combination with an absorbent pad 13 of the present invention
without producing an unsatisfactory surface dryness condition, such
as would be the case if such topsheet materials were applied
directly over a non-resin treated hydrophilic core. Accordingly, an
advantage inherent in applicants' structure is that it eliminates
the need to compromise favorable strike-through characteristics in
order to provide satisfactory surface dryness characteristics, a
problem apparent in prior art disposable diaper structures.
The ability to combine fast strike-through and satisfactory surface
dryness characteristics in a single structure permits the
elimination of gasketing means used in prior art disposable diapers
to prevent liquid run-off along the lateral edge portions of the
diaper. The fast strike-through characteristic of a diaper of the
present invention permits fluids deposited on the surface of the
topsheet 16 to be transmitted into the absorbent pad 13 before
substantial run-off from the surface of the topsheet is allowed to
take place.
Another factor central to the elimination of gasketing means at the
lateral edge portions of a disposable diaper of the present
invention lies in the unique softness produced by bonding the
untreated portion 13(a) of the absorbent pad 13 directly to the
waterproof backsheet 15. The unique softness of a diaper of the
present invention in combination with an absorbent pad 13 having
sufficient strength to resist tearing and shredding in use permits
better compliance when the structure is applied to the body of the
wearer, thereby providing better fit and hence better containment
of fluids deposited on the topsheet 16.
FIG. 4 is an enlarged schematic illustration taken along section
line 4--4 in FIG. 1A. FIG. 4 depicts the condition of the absorbent
pad 13 after calendering and the position of the waterproof
backsheet 15 in relation to the topsheet 16. Beads of adhesive 19
at the lateral edge portions of the topsheet 16 are applied by
means of a pair of glue applicators 20 located at the lateral edge
portions of the topsheet. The beads of adhesive 19 are preferably
comprised of a hot melt adhesive such as No. 2933 available from
the National Starch Company of Plainfield, N.J. The beads of
adhesive 19 are used to secure the lateral edge portions of the
diaper formed by the overlapping edge portions of the backsheet 15
and the topsheet 16 to the surface of the topsheet.
The lateral edges of the assemblage shown in FIG. 4 are brought
into overlapping relation with the topsheet by passing the
assemblage between a pair of plows 21 located at the lateral edges
thereof. The assemblage is then passed between a pair of
hard-surfaced rolls 22 and 24 to secure the overlapping portions of
the topsheet 16 and the backsheet 15 together as well as to secure
the lateral edge portions of the assemblage to the face of the
topsheet 16 by means of beads of adhesive 19. In addition, the
topsheet 16 is secured to the backsheet 15 in the area between the
absorbent pads 13. This is accomplished, in a preferred embodiment,
by providing recessed areas 23 along the periphery of roll 22. The
recessed areas 23 are of the same basic shape as the absorbent pads
13 and are so positioned along the periphery of roll 22 that the
lateral edge portions of the absorbent pads are subjected to
compression between rolls 22 and 24 to secure the assemblage
together. This is best illustrated in FIG. 5. The areas between
adjacent absorbent pads 13, on the other hand, are contacted by the
non-recessed portions 25 of roll 22, which, in cooperation with the
hard-surfaced roll 24, secure the topsheet 16 directly to the
backsheet 15 and the lateral edge portions of the laminate thus
formed to the face of the topsheet by means of beads of adhesive
19.
Securing the lateral edge portions of the diaper to the topsheet 16
in the manner illustrated in FIG. 5 serves to encapsulate the
lateral edge portions of the absorbent pad 13, thereby preventing
wicking of fluids absorbed in the absorbent pad from its lateral
edge portions. This construction is preferred, since the waterproof
backsheet 15 prevents wetting of clothing which comes in contact
with the lateral edge portions of the diaper. Since overlapping the
waterproof backsheet 15 onto the surface of the diaper is designed
to prevent wicking from the absorbent core rather than run-off from
the topsheet in a diaper of the present invention, the amount of
overlap of the backsheet onto the surface of the topsheet 16 is
preferably minimized to minimize contact between the backsheet and
the wearer's skin, thereby improving wearer comfort.
In an alternate embodiment of the present invention, contact
between the waterproof backsheet 15 and the wearer's skin can be
completely eliminated by allowing the overlapping portions of the
backsheet 15 and the topsheet 16 to extend horizontally at the
edges of the diaper. In such an embodiment, however, it is
generally desirable to size or otherwise make impervious to
moisture by means well known in the art the lateral edge portions
of the topsheet 16 to prevent wicking of absorbed fluids from the
lateral edge portions of the absorbent pad 13.
Similar measures are also generally desirable with respect to the
end portions of the topsheet 16 in both embodiments of the diaper
disclosed herein to prevent wicking of absorbed fluids from the
absorbent pad 13 along the end portions of the diaper.
The balance of the diaper converting operation is illustrated
schematically in FIG. 1B. The absorbent pads 13, secured in a
spaced relation by means of the web of waterproof backsheet
material 15 and the web of topsheet material 16, the passed as a
diaper web through tape applying apparatus well known in the art
and shown schematically as 26, where a pressure-sensitive tape
structure 27 suitable for holding the diaper in place on the wearer
is applied at the lateral edge portions of the diaper web adjacent
each absorbent pad 13.
Following application of a pair of tape structures 27 for each
absorbent pad 13, the diaper web is passed through folding
apparatus well known in the art and shown schematically as 28 in
FIG. 1B, whereby the diaper web, including the absorbent pads 13,
is caused to assume the general configuration illustrated in FIG.
6.
Upon completion of the folding operation, the diaper web is passed
between a rotary knife 29 having blades 30 secured at its periphery
and a hard-surfaced anvil roll 31 where the web is cut in register
between absorbent pads 13 to form individual disposable diapers 32
of the present invention.
It is to be understood that the forms of the invention herein
illustrated and described are to be taken as preferred embodiments.
Various modifications to the structures disclosed herein and to the
method of producing said structures will be apparent to those
skilled in the art without departing from the spirit or scope of
the invention as defined in the attached claims.
* * * * *