U.S. patent number 3,903,889 [Application Number 05/342,162] was granted by the patent office on 1975-09-09 for disposable liquid absorbent products.
This patent grant is currently assigned to First National Bank of Nevada, Executor of the Estate of David Torr. Invention is credited to David Torr, deceased.
United States Patent |
3,903,889 |
Torr, deceased |
September 9, 1975 |
Disposable liquid absorbent products
Abstract
An improved form of liquid absorbent product as, for example, a
diaper is sclosed. There also is disclosed an improved liquid
absorbent material composition.
Inventors: |
Torr, deceased; David (LATE OF
Las Vegas, NV) |
Assignee: |
First National Bank of Nevada,
Executor of the Estate of David Torr (Las Vegas, NV)
|
Family
ID: |
23340632 |
Appl.
No.: |
05/342,162 |
Filed: |
February 16, 1973 |
Current U.S.
Class: |
604/365; 604/368;
604/381; 428/153; 604/375 |
Current CPC
Class: |
A61L
15/20 (20130101); A61L 15/28 (20130101); A61F
13/534 (20130101); A61L 15/18 (20130101); A61L
15/28 (20130101); C08L 5/00 (20130101); A61F
2013/53908 (20130101); A61F 13/539 (20130101); Y10T
428/24455 (20150115); A61F 2013/530131 (20130101); A61F
2013/530481 (20130101); A61F 2013/530489 (20130101); A61F
2013/53445 (20130101); A61F 2013/8411 (20130101); A61F
2013/530496 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61L 15/16 (20060101); A61L
15/18 (20060101); A61L 15/20 (20060101); A61L
15/28 (20060101); A61f 013/16 () |
Field of
Search: |
;128/284,286,287,290,296,29R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Medbery; Aldrich F.
Attorney, Agent or Firm: Watson Leavenworth Kelton &
Taggart
Claims
What is claimed is:
1. In a multi-layer, disposable absorbent product such as a
disposable diaper, sanitary napkin, or the like,
a liquid-pervious body contacting layer,
an outer material layer, said outer material layer being
characterized by being liquid-impervious, and
a dry liquid-absorbent organic material disposed between said
body-contacting and outer layers in substantially fixed
relationship therewith,
there also being a core of at least one layer of a bulking material
disposed between said body-contacting and outer layers, there being
a film of a water-repellent adhesive agent overlaying said bulking
material layer at the side thereof remote from said outer layer,
said absorbent organic material being overlayingly adhered to said
film, there being a second liquid-pervious film of said adhesive
agent overlaying said absorbent organic material.
2. The disposable absorbent product of claim 1 in which said layer
of bulking material is a layer of fluffed cellulosic fibers.
3. The disposable absorbent product of claim 1 in which said layer
of bulking material is a layer of creped paper wadding.
4. In a multi-layered disposable absorbent product such as a
disposable diaper, sanitary napkin or the like comprising:
a liquid-pervious body contacting layer;
an outer material layer, said outer material layer being
characterized by being liquid-impervious; and
a dry liquid-absorbent organic material disposed between said body
contacting and outer layers;
the improvement which comprises a borate-release agent admixed with
said absorbent organic material, said borate-release agent being in
a borate compound having a solubility in water of less than about
0.1% at 25.degree.C.
5. The disposable absorbent product of claim 4, wherein said
borate-release agent is zinc borate.
6. The disposable absorbent product of claim 5, wherein said
absorbent organic material is selected from the group consisting of
water soluble proteins and polysaccharides which, upon absorption
of at least 10 parts by weight of water, are characterized by the
presence of sterically unhindered OH.sup.- radicals.
7. The disposable absorbent product of claim 6, wherein said
absorbent organic material is naturally occurring guar gum.
8. The disposable absorbent product of claim 4, in which said
absorbent material additionally contains a pH stabilizer in
sufficient amount to maintain the pH of the absorbent product
within the range of from about 7.0 to 7.4.
9. The disposable absorbent product of claim 8, wherein said pH
stabilizer is an amine, present in an amount up to about 25% by
weight of absorbent.
10. The disposable absorbent product of claim 4, wherein said
absorbent organic material is in particulate form, the particles
thereof being sized so that at least 50% thereof are between 60 and
100 mesh Tyler.
11. The disposable absorbent product of claim 10, wherein at least
70% of said particles are of a size between about 60 and 100 mesh
Tyler.
Description
BACKGROUND OF THE INVENTION
Various constructions of liquid-absorbent products such as
disposable diapers, bed pads, hospital medical and surgical pads,
sanitary napkins and like devices are known in the art. Generally,
such disposable types of products include a body contacting layer
of liquid-pervious material, an outer layer which embodies
liquid-impervious character therein, and an intermediate
liquid-absorbent component which conveniently may be provided in
the form of a particulate liquid-absorbent gel-forming material,
which when wetted absorbs many times its own weight of liquid. In
association with the absorbent or gel-forming material there may be
provided other components such as a core of fluffed fibrous pulp or
a core of creped, laminated or single ply wadding. Whether the
liquid-absorbent gel-forming material is employed in conjunction
with a fluffed pulp or a creped wadding core or not, there is a
tendency for the liquid-absorbent gel-forming material particles to
settle or shift in the product to an extent that when the product
is wetted, a major quantity of the liquid is not absorbed by such
material and in the case where a fluffed pulp or creped wadding
core is used such liquid is absorbed by the fibers of the core so
that the water-absorbent gel-forming material does not serve
completely its intended function. As a consequence, if a pressure
is applied to the product as, for example, by the weight of a
baby's body in connection with the use of a diaper, such pressure
can express or force the liquid back through the body contacting
layer to the discomfort of the wearer thus producing the
undesirable consequences sought to be avoided by using a
liquid-absorbent gel-forming material in the product.
Also, known types of liquid-absorbent gel-forming materials are not
fully satisfactory when embodied in disposable liquid-absorbent
products since generally they form, when wetted, a substantially
liquidus gel mass rather than a more desirable relatively dry
gel.
Accordingly, it is desirable that the construction of
liquid-absorbent products of the types described aforesaid be
improved to locate more advantageously therein the liquid-absorbent
gel-forming material, to optimally position same to effect maximum
liquid-absorption by such material, and further to improve
liquid-absorbent gel-forming material compositions by providing for
their conversion into relatively dry gels upon wetting.
SUMMARY OF THE PRESENT INVENTION
The present invention is concerned with improvements in the
construction of liquid-absorbent products of the type which are
disposable as, for example, by flushing in a toilet system. As used
herein "products" includes diapers, bed pads, hospital medical and
surgical pads and sheets, catamenial devices such as sanitary
napkins or vaginal tampons, continuous filament material such as
sutures, and products of similar description which are used for
absorbing body liquids.
The present invention provides an improved form of liquid-absorbent
product which can be made in various embodiments but which is
characterized by the feature that the liquid-absorbent gel-forming
material used therein is optimally positioned or disposed in the
product to insure maximum liquid-absorption thereby to overcome
prior art product shortcomings of liquid return through the body
contacting layer due to insufficient absorption by the
liquid-absorbent material. Furthermore, improved compositions
useful as the liquid-absorbent material are provided. While various
embodiments of the invention are described herein in terms of
disposable diaper construction, it will be understood that the
invention is applicable in its broadest aspects to other types of
liquid-absorbent products.
In one embodiment of the invention, the disposable diaper is
provided with a body contacting layer which can be of any suitable
material having liquid-pervious character and which is of fine and
soft texture to provide a reasonable measure of comfort to the
wearer. Such layer could be a woven or a non-woven fabric and it
could be of cotton, rayon, paper, synthetic materials etc. and
could be of plural ply structure. The diaper also includes an outer
layer of suitable material, e.g., one or more plys of tissue paper
which has been waterproofed at one or both sides by applying
thereto a suitable liquid repellent material, as for example, a
stearate, silicone, wax, paraffin, a natural or synthetic resin
etc. Intermediate the body contacting and outer layers there is
provided a core of fluffed pulp material such as a core of fibrous
cellulosic or other material. In accordance with the invention, a
liquid-absorbent gel-forming material composition as, for example,
a modified guar gum in a particulate form thereof, is distributed
throughout the fluffed pulp and is adhesively secured to the pulp
fibers by means of a suitable tacky adhesive agent which possesses
property of being permanently pliable so that it elastically
maintains the positioning of absorbent material in the diaper, such
adhesive agent being, e.g., a water soluble material such as a
sugar or even a water repellent material such as a rosin, the
adhesive serving to anchor the gel-forming material to the pulp
fibers in a uniformly distributed pattern throughout the mass
thereof, thereby to preclude migration of such material to the body
contacting layer or outer layer component sides of the fluffed pulp
core or to other such region of the diaper structure so as to limit
or inhibit proper liquid absorption during use. Thus, the
liquid-absorbent gel-forming material is elastically maintained in
an optimum position in the diaper to insure that liquid entering
the diaper structure through the body contacting layer is absorbed
principally by the gel-forming material and not by the fibers of
the pulp.
According to another embodiment of the invention, after the fluffed
pulp core has been laid down on the outer layer of the diaper
during manufacture of the same, the fluffed pulp is oversprayed
with a tacky coating of said adhesive agent, following which the
particulate, liquid-absorbent gel-forming material is sifted onto
the fluffed pulp, the adhesive overspray functioning to anchor or
position the gel-forming material in respect of the fluffed pulp
core. For further enhancement of the positioning of the absorbent
material, the underface or inner face surface of the body
contacting layer, which in manufacturing is laid down on top of the
fluffed pulp core, can be provided with a liquid-pervious coating
or film of the same tacky adhesive agent to further secure and
position the liquid-absorbent gel-forming material in the diaper
structure. If the adhesive agent is a water soluble material, the
film thereof at the inner face surface of the body contacting layer
will dissolve when the diaper is wetted and, accordingly
"liquid-pervious" in relation to such adhesive film is intended to
embrace a water soluble film. On the other hand, if the adhesive
agent is water repellent, it would be made liquid-pervious in known
manner, e.g., by perforations therein.
A further embodiment of the invention provides that in lieu of a
fluffed pulp core, a core of one or more layers of creped paper
wadding is embodied in the diaper structure, such core being
oversprayed with a tacky film of the adhesive agent, following
which the gel-forming material is sifted onto the core, such
material optionally then being further secured in the diaper
structure by an adhesive agent film coating at the inner surface of
the body contacting layer.
A still further form of the invention provides that the diaper may
embody a core of plural layers of fluffed pulp with each fluffed
pulp layer being separated from the others by an interposed tissue
sheet, each fluffed pulp layer being oversprayed with a tacky
adhesive agent prior to the sifting of the gel-forming material
onto the same. The tissue separator sheet also may be coated with
the tacky adhesive agent on the faces thereof which contact the
fluffed pulp layers.
Still a further form of the diaper of the present invention
provides that the fluffed pulp and/or creped wadding cores are not
employed, so that the diaper structure could comprise the body
contacting layer and outer layer with a film of liquid-absorbent
gel-forming material embodying said adhesive agent disposed
therebetween, the film optionally being loosely disposed between
said layers or adhered to the inner face of the body contacting
layer or the outer layer or both by means of the adhesive
agent.
As adhesives, any water-soluble adhesive agent of character
compatible with the absorbent material can be used, concentrated
sugar base materials being particularly advantageous and including
honey, corn syrup, dextrine, and the like. Other water soluble
materials such as gelatinous substances and even pressure sensitive
adhesives, if water soluble, can be used. Water repellent type
materials also can be used as the adhesive agent, for example, the
adhesive material can be rosin. If the adhesive agent is water
repellent, it will be employed in such manner and association with
the liquid-absorbent material so as to not inhibit access to the
latter by the liquid entering the diaper as, for example, by
establishing a barrier around the liquid-absorbent material.
Various forms of adhesive materials of both water soluble and water
repellent types will be described in greater detail later.
The present invention also provides an improved liquid-absorbent
gel-forming material composition which, in contrast with known
compositions of such material type, when wetted form a relatively
dry gel mass as distinguished from a relatively liquidus form of
gel mass. Particular compositions of water-absorbent gel-forming
material of improved character will be described in greater detail
later in the description.
The invention, accordingly, comprises the diaper construction
possessing the features, properties and relation of elements which
will be exemplified in the devices as well as the absorbent
material composition hereinafter described and the scope of the
present invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects of the invention will be in part obvious and will in
part appear from the following detailed description taken in
conjunction with the accompanying drawings, wherein like reference
numerals identify like parts throughout and in which:
FIG. 1 is a longitudinal sectional view through one form of diaper
made in accordance with the present invention in which a core of
fluffed pulp is disposed intermediate the body contacting and outer
layers of the diaper, the fluffed pulp having adhered thereto by
means of a suitable tacky adhesive agent, particles of a
liquid-absorbent gel-forming material.
FIG. 2 is a longitudinal sectional view of another form of diaper
in which the fluffed pulp core has been oversprayed with the tacky
adhesive agent before the liquid-absorbent gel-forming material is
sifted onto the fluffed pulp, with the inner face of the body
contacting layer also carrying a film of the tacky adhesive for
further securing or positioning the absorbent material within the
diaper structure.
FIG. 3 is a longitudinal sectional view of another form of diaper
in which plural creped wadding layers are employed therein in lieu
of fluffed pulp as a bulking material.
FIG. 4 is a longitudinal sectional view of a diaper in which the
fluffed pulp is provided in two or more layers thereof with each
layer being separated from the others by means of a tissue
sheet.
FIG. 5 is a longitudinal sectional view through a further form of
diaper made in accordance with the present invention in which no
bulking layer, such as fluffed pulp or creped wadding is used but
rather the diaper is comprised of the body contacting and outer
layers with a film of the liquid-absorbent gel-forming material in
which is embodied an adhesive agent being disposed
therebetween.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention, as indicated earlier, is applicable to the
construction of a disposable type liquid-absorbent product and
inclusive of disposable diapers, bed pads, catamenial devices,
continuous filaments such as sutures and the like, although
particular embodiments of the invention will be described at
greater length herein in terms of its applicability to disposable
diaper construction.
Referring now to FIG. 1, there is depicted a diaper 10 which
includes a body contacting layer, which body contacting layer can
be comprised of plural-ply components as, for example, an outermost
fabric sheet 12 such as a non-woven cellulosic material sheet or
other material type which possesses soft texture and accordingly,
are advantageous for contact with the skin. Succeeding plys of
tissue, e.g., paper tissue sheets 14 and 16 make up the remaining
components of the body contacting layer. Together the three sheets
12, 14 and 16 possess the structural strength, including wet
strength properties, suitable for the intended purpose and they
also have the property of being liquid-pervious to permit body
liquid to pass through the skin contacting layer for the purpose to
be described in greater detail shortly. The diaper 10 also includes
an outer layer which, is comprised of plural plys of components of
suitable material such as tissue paper sheets 18, 20 and 22, the
outer face of tissue sheet 22 being coated with a suitable
material, such as a stearate, a silicone, a wax, paraffin or like
material which will render the outer layer liquid-impervious. The
purpose of making the outer layer liquid-impervious is well-known
by those skilled in the art, e.g., it traps liquid within the
diaper, thus preventing leakage and facilitate absorption. The
liquid-impervious coating 24 also could be applied to the inner
face of sheet 18 or at the interface of sheets 18 and 20 or at the
interface of sheets 20 and 22 with equal facility.
One of the advantages of using a fluid-impervious coating of the
materials aforementioned is the convenience with which the material
coating can break up into segments when the user tears the diaper
into pieces preliminary to disposal by flushing same in a toilet
water system. Certain other types of fluid-impervious material, as
for example polyethylene, are less advantageous to use because such
material must be first removed from a diaper as a single sheet
thereof and be disposed separately and differently than the
remainder of the diaper.
The diaper 10 also includes a core or intermediate layer of fluffed
pulp of cellulosic fibers, the fibers 26 of which have been beaten
in known manner in a hammer mill to produce a three-dimensional
mass which provides a desirable quality of bulk to the diaper
structure. In accordance with the invention, a liquid-absorbent
gel-forming material 28 preferably in particulate form, is
distributed throughout the fluffed pulp mass, the particles of the
gelling material being secured to the pulp fibers by means of a
tacky adhesive agent having the property of permanent pliability to
elastically maintain the material 28 in fixed disposition in the
diaper structure. As used herein, the property of permanent
pliability of the adhesive agent is intended to mean that the
adhesive is of an essential non-drying character and remains
flexible throughout the intended life span of the disposable
product in which it is employed and does not assume any character
of brittleness which in turn would cause a stiffening of the
structure of the product and/or the absorbent material therein. The
absorbent material 28 can be provided in various forms, an example
being any of the materials enumerated in detail in U.S. Pat. No.
3,070,095, guar gum being particularly advantageous for this
purpose because upon being wetted it can absorb up to 20 times or
more of its own weight in liquid. More desirably, the
liquid-absorbent gel-forming material is provided in the novel
composition thereof to be described later herein.
For the purpose of adhering the absorbent material particles to the
fluffed pulp fibers, various adhesive agents can be used. Such
agent can be a water soluble material, e.g., corn syrup solids,
honey, dextrine, pressure sensitive adhesive material etc. Water
repellent materials also could be used as the adhesive agent, as
for example, rosin. The essential requirement is that the adhesive
agent, whether water soluble or water repellent, should possess the
property of being permanently pliable and not subject to rigidizing
into a brittle film of the adhesive after a certain period of time.
The advantage of adhesively securing the particles 28 throughout
the three-dimensional mass of particle fibers 26 is that the
particles cannot then migrate toward the tissue sheet 18, tissue
sheet 16, or such other region in the diaper where the accumulated
mass would not function to the degree intended for absorbing
liquid.
In making the diaper 10, the outer layer materials can be laid down
one on top of the other, following which the fluffed pulp core 26
is laid down on top of the outer layer sheet 18. A mixture of
absorbent material and adhesive agent can then be sifted onto the
fluffed pulp to effect adhesion of the absorbent material particles
to the fluffed pulp fibers. Following laying down of the fluffed
pulp layer and impregnation of the same with the absorbent material
tacky-adhesive mixture, the skin contacting layer components 12, 14
and 16 are laid down on top of the fluffed pulp. The diaper layers
are then secured as a unitary structure in known manner as, for
example, by employing a suitable heat-seal connection around
marginal portions of the expanse of the diaper structure.
FIG. 2 shows another form of diaper 40 which has skin contacting
and outer layers of the same construction as those of diaper 10.
However, the fluffed pulp layer 42, during the formation of the
diaper, is first given an overspray of the tacky adhesive agent 44
to form a film thereof on the fluffed pulp mass. There is then
sifted or otherwise distributed onto the adhesive film, particulate
form absorbent material 46 which becomes secured to the tacky
adhesive film 44. Following the deposition of the absorbent
material 56, there optionally but not essentially, may be employed
a further overspray of the tacky adhesive as a liquid-pervious film
48 on top of the absorbent material. The body contacting ply
components 12, 14 and 16 can then be overlaid on the tacky adhesive
film 48 and tissue sheet 16 becomes adhesively connected to the
particulate absorbent layer 46 by action of the adhesive film 48.
The advantage of this form of construction is that it provides an
optimized anchorage or positioning of the liquid-absorbent
gel-forming material in the diaper structure. If the adhesive agent
is a water soluble material, the adhesive film 48 will dissolve
upon entry of the liquid through the liquid-pervious body
contacting layer. On the other hand, if the adhesive agent is a
water repellent material, the film 48 would be rendered
liquid-pervious in known manner prior to or at the time it is laid
down, as for example, by needle piercing the film.
FIG. 3 depicts a further form of diaper construction 60 which
employs one or more creped wadding layers in place of fluffed pulp.
Thus, the diaper can have creped wadding layers 62 and 72, each of
which is separated by the tacky adhesive films 64, 68 and a layer
of liquid-absorbent gel-forming material 66. Additionally, an
overspray of tacky adhesive 74 can be applied to the upper creped
layer 72 and a second layer of liquid-absorbent gel-forming
material 76 can be laid between the tacky layer 74 and a further
tacky adhesive layer 78, the latter in turn being secured with
tissue sheet 16 in the manner shown. In such construction, if the
adhesive agent were a water repellent material, at least each of
adhesive films 78, 74 and 68 would be made or rendered
liquid-pervious.
FIG. 4 shows an embodiment 80 of diaper in which the diaper employs
fluffed pulp for bulking purposes, with the fluffed pulp being
provided in two or more layers such as at 82 and 94 with the
respective layers each being provided with an overspray film of
tacky adhesive 84 and 96, as well as particulate liquid-absorbent
gel-forming material layers 86 and 98. The two fluffed pulp layers
are further separated by an adhesive layer 88 and a layer of tissue
paper 92, with the diaper further having a tacky adhesive film 102
at the underface of the skin contacting layer. As with diaper 60,
adhesive films 102, 96 and 89, if such were of a water repellent
material would be rendered liquid-pervious.
In applying the adhesive film in each of FIGS. 2-4 diaper forms,
such films can be applied in any convenient manner such as a spray,
or as a solution deposited by a transfer roll or such other manner
as suits the intended purpose.
An exemplary adhesive particularly suited for use in connection
with the diaper construction of the present invention is a
water-soluble adhesive comprising of corn syrup. The corn syrup
adhesive should be employed in such form that its water content is
minimal, in order to reduce its hydration effect on the diaper's
absorbent composition. Accordingly, one particularly useful
adhesive is a concentrated commercially available syrup having 82%
solids (the remaining 18% of the adhesive being water which appears
to be effectively bound within the syrup).
Because such concentrated syrups are extremely viscous and
susceptible to drying into a non-tacky form, their direct incursion
within the present diaper construction is difficult; it has
therefore been discovered that they should be applied in diluted
form. In order to avoid the deleterious effect which an aqueous
diluent would have on the absorbents, the diluent should preferably
be non-aqueous and should preferably comprise an organic compound
in which the present adhesive dissolves.
With exemplary reference to the aforementioned corn syrup, it has
been discovered that alcohols -- in particular, glycerol,
polyvinylglycol and the like -- are well suited as diluent-solvent
to implement the incorporation of adhesives into diapers. These
diluent-solvents should be employed in an amount sufficient only to
reduce the viscosity of the absorbent to a convenient level. Thus,
the aforementioned concentrated corn syrup should, for example,
normally be diluted with at least about 20% by weight of alcohol,
based on the weight of syrup. More usually, dilution with from
about 30% to 50% by weight of solvent is preferred. The degree of
dilution is not, however, critical and appropriate solvents and
ranges for each of the present adhesives would be readily apparent
to those of ordinary skill in the art upon reading this
description.
When the adhesive of this invention is employed with the fluffed
pulp embodiment depicted in FIGS. 1, 2 and 4, it is preferred to
incorporate from about 10% to about 25% by weight of adhesive
solids per weight of fluffed pulp. Again, the amounts of adhesive
are not critical, however, and one of ordinary skill in the art
would readily perceive from the foregoing preferred values, the
broadest ranges of adhesive proportion which would be operable in
accordance with the present invention.
FIG. 5 shows still another form of diaper 120 in which neither
fluffed pulp nor creped wadding layers are employed. The diaper has
skin contacting and outer layers as described before, between which
is disposed a film 122 of the liquid-absorbent gel-forming material
having the tacky adhesive agent embodied therewith. The advantage
of this construction is that the diaper can be made of very much
reduced thickness to provide wearer comfort, while at the same time
retain its liquid-absorption characteristics. The film 122 can have
the adhesive agent embodied therein as by mixing same with the
absorbent material where the adhesive is a water soluble type. In
this manner the adhesive agent can be employed to secure the
absorbent material film 122 to either or both of tissue sheets 16
and 18 by applying moisture coating to the surfaces of such sheets
or to the absorbent material film during the diaper manufacturing
process. On the other hand, if a water repellent adhesive is
embodied with the absorbent material film 122, the same, for
example, can be applied at the surfaces of the film in various
manners to facilitate securement of the film to the paper tissue
sheets 16, 18 so as not to present a barrier to the passage of
liquid through the body contacting layer to the absorbent material
film 122 when the diaper is in use.
It will be apparent that the diaper structures of the foregoing
described embodiments as well as other types of disposable products
can be made with certain variation from the constructions
disclosed. For example, the diaper instead of having a fluffed pulp
or creped wadding layer may employ a tissue paper core in
association with the absorbent material. The essential requirement
is that the absorbent material be fixedly positioned in the diaper
by employing the adhesive agent to secure the absorbent material to
the tissue paper sheet used in place of the fluffed pulp and/or
creped wadding. Further, such adhesive agent should have the
character of being permanently pliable as discussed earlier.
As used herein "liquid" is intended to mean an aqueous liquid, for
example, urine.
The invention further provides a superior absorbent composition for
use in the absorbent products already described. Such desirable
objective has been achieved through the discovery of an additive
which will convert the normally liquidus or syrup-like and sticky
gels produced pursuant to hydration of the water soluble absorbents
of the prior art into a film dry gel.
Water soluble absorbents which may be improved by this discovery
include proteins such as albumin and polysaccarides such as
galactomannans, pectins, algins, starches, and natural gums. These
and additional applicable absorbents are recognized in the art as a
useful class and may further be identified in terms of their common
ability to assililate at least ten times their weight of water, aso
as to produce hydrate bearing sterically unhindered OH.sup.-
radicals.
For the sake of clarity, this discovery will be further described
in terms of an exemplary absorbent -- guar gum, which is a species
of galactomannan. Such exemplification should not, however, be
construed as limiting the scope of this discovery, as it will be
clear to those skilled in the art that all known absorbents which
produce hydrate exhibiting complexable OH.sup.- groups will also
benefit therefrom.
It has been discovered that the addition of certain compounds to
ordinary guar gum will produce a modified guar which will absorb up
to at least 20 times its weight of water to produce a relatively
dry, non-sticky, and inert gel, as opposed to the somewhat
syrup-like and sticky gel which is normally formed incident to the
hydration of pure guar gum.
The essential additive required for the formation of the modified
guar gum composition is borate anion which is utilized in an amount
sufficient to complex the gel formed from the hydration of guar gum
alone. Where present, the borate anion will successfully convert
the normally liquidus or syrup-like and sticky guar hydrate into a
firm and dry mass having substantially improved characteristics for
use in the previously described absorbent products as well as
absorbent products of other constructions which employ or use an
absorbent material as a component.
Apparently, the borate anion of this embodiment operates by
complexing with the OH units of separate molecules and agglomerates
of an absorbent such as hydrated guar gum so as to form cross-links
therebetween, thus stabilizing the hydrated guar into the desired
firm gel. Unfortunately, this cross-linkage takes place at an
almost instantaneous rate, where there exists in combination, free
borate anion, water, and guar gum. Accordingly, it has been
necessary to determine a means of regulating the formation of
cross-linkages, because once such cross-linkages have bound the
hydrated guar gum into a firm gel, the gel operates to form a water
impenetrable barrier. Such barriers may impede the flow of liquid
into the absorbent product and thereby limit the utility of
products having an absorbent layer in substantial thickness.
It has been determined that one means of retarding the
transformation of hydrated guar gum into a firm gel is to introduce
the borate anion into the absorbent product in the form of an
essentially water insoluble borate-release agent. So introduced,
free borate anion will be released to the absorbent system only
slowly, as determined by the solubility coefficient of its
insoluble form, and only after the aqueous liquid sought to be
absorbed by the product has entered the product itself.
Accordingly, one means by which the requisite slow release of
borate anion may be accomplished is through the addition, in an
amount of from about 3% to about 10% of guar (based on the weight
of borate anion), of a borate salt having a solubility in water of
less than 0.1% at 25.degree.C., preferably less than about 0.05%.
The release from such a compound -- an example of which would be
zinc borate -- would be regulated by its own solubility
coefficient, so as slowly to yield borate anion at a rate which
would allow optimal penetration of the liquid sought to be
absorbed, while still allowing the firm gellation of guar gum. This
rate dependency occurs because it is the solublization of borate
ion which is the limiting factor for the formation of a firm gel,
due to the essentially instantaneous nature of the reactions or
guar hydration and guar hydrate cross-linkage.
Accordingly, the minimum solubility coefficient of an essentially
insoluble borate such as zinc borate requires that, upon
introduction of an liquid into the absorbent pad, only a small
concentration of free borate anion will be available to cross-link
the almost instantaneously formed guar gum hydrates. Consequently,
even though some firm gel is produced by the available free borate
anion, insufficient cross-linkage to produce a liquid-impervious
barrier will occur. As the liquid is introduced and penetrates into
the pad, however, additional free borate anion is released from the
insoluble borate due to the removal of the original free borate
anion from the equilibrium system as a cross-linking complex for
guar gum hydrate. Thus, within a matter of from about 5 to about 10
minutes, sufficient borate anion is solubilized from the original
borate-release agent so as to cross-link substantially all
available guar gum hydrate.
The foregoing reaction for the production of a cross-linked guar
hydrate or for other suitable absorbents, as well as the stability
of the resultant firm gel, are both highly dependent upon the pH of
the reaction environment. Only at a pH of from about 7.0 to 7.4,
and optimally at about 7.1, does the requisite cross-linking of the
hydrated gel through the borate anion occur. Moreover, this
cross-linking reaction is reversible. Consequently, it is necessary
that, during use, the product be maintained within the
aforementioned pH range.
It has therefore been discovered that it is convenient to further
modify the aforementioned admixture of naturally occurring guar gum
and an insoluble borate-release agent through the inclusion of an
additive which will maintain the pH of the system -- during and
after the introduction of the aqueous liquid sought to be absorbed
-- within the pH range conducive to the formation of a firm gel. It
has been determined that the achievement of an appropriate pH may
best be obtained through the addition of an amount of any amine
sufficient to maintain the system comprising guar gum, an insoluble
borate-release agent, and the liquid sought to be absorbed, within
a pH of from about 7.0 to 7.4.
A particularly efficacious amine for the foregoing purpose is
2-amino, 2-methyl, 1, 3-propanediol. This amine is a solid, and
consequently presents no problem, during storage of the absorbent
product prior to use, through the introduction of any liquid
thereto. Liquid amines, for example triethanol amine, may also be
employed in the present invention. Where such liquid amines are
utilized, however, it is preferred that they be stabilized by the
further inclusion of an essentially inert carrier, for example a
magnesium or calcium silicate, so as to minimize the presence of
free liquids in the absorbent pad. Where such carriers are
employed, it is suggested that they be present in an amount of from
about 50 to about 100% by weight of the liquid amine.
As was previously indicated, the amount of amine which should be
included within the absorbent composition may vary depending upon
the intended use of the absorbent product itself. In many
instances, the liquid sought to be absorbed will already be of a pH
within the range of from about 7.0 to 7.4, and consequently no such
amine would be required. Under other circumstances, however, the pH
of the aqueous liquid sought to be absorbed would not fall within
the aforementioned range, and in such case, stabilizers such as the
present amines should be added to the absorbent composition in
amounts up to about 25% based on dry absorbent, and are readily
calculatable by those of ordinary skill in the art.
An example of an embodiment in which a pH stabilizer should be
included within the absorbent composition is one in which the
absorbent product is intended to be used as a diaper. The normal pH
of infant urine falls within the range of from about 6.5 to about
7.0. Accordingly, the inclusion of an amine such as 2-amino,
2-methyl, 1,3-propanediol in an amount of from about 5 to about 25%
by weight of dry guar gum will insure the desired formation of a
firm cross-linked guar gum hydrate.
This invention additionally includes the discovery that the
physical form in which a modified absorbent (that is a composition
comprising an absorbent such as guar gum, a borate-release agent
and, optionally, a pH stabilizer) is incorporated into an absorbent
product, may directly affect the efficiency with which the
absorbent product assimilates the liquid sought to be absorbed. As
has been previously stated, the modified guar gum of this invention
produce, upon addition of liquid, a firm gel which may block the
penetration of additional liquid into the pad. Because of this
propensity of the preferred modified absorbents to form
liquid-impervious barriers, it has been discovered that the
selection of unusually coarse grinds will facilitate the complete
absorption of the liquids for which the present products were
intended.
In the prior art, powdered guar capable of passing through a 140
mesh Tyler screen has ordinarily been employed in absorbent
products. Where such fine powder is used in conjunction with the
present borate-release agents as a modified guar gum, however, it
has been discovered that impenetrable barriers of firm gel may be
produced even before all the available liquid has entered the
absorbent product.
Accordingly, this invention offers the additional improvement that
such impenetrable barriers may be avoided through the use of coarse
particles or agglomerates of absorbent such as guar gum in the
absorbent composition. By "coarse", it is intended that the
absorbent particle sizes should be comprised in a proportion
wherein at least 50% of the particles are of a size between 60 and
100 mesh Tyler screen, more preferably, at least 70% should be of a
size between about 60 and 100 mesh.
Where the particles of guar gum in the present absorbent
composition are within the foregoing size ranges, the resultant
porosity of the absorbent composition greatly facilitates the
penetration of the liquid sought to be absorbed through such
composition. Moreover, the larger particles of such guar gum are
less quickly susceptible to hydration and subsequently
cross-linkage into a firm gel. Consequently, the slight retardation
of firm gel formation resultant from such large particles also
operates to permit more uniform penetration of the liquid sought to
be absorbed throughout the absorbent product and thus improves the
efficiency with which such liquids are absorbed.
A further feature of the present invention provides an improved
form of securement means therefor when used, especially for use in
a diaper. It is known to provide pressure sensitive tape components
at two corners of the four corners of a disposable diaper structure
with the tape components being secured in part at the outer surface
of the outer layer, the remaining lengths of such tape components
when the diaper is in folded packed condition are folded inwardly
in adhesive securement against surface portions of the body
contacting layer which have been treated with a release agent. When
the diaper is unfolded from its packaged condition for use, the
said remaining lengths of the tapes are peeled from the release
coated surfaces, the diaper wrapped about a baby's body, and the
tape segment remaining lengths secured at the other two corners of
the structure at the outer surface of the outer layer, such tapes
thus functioning in place of conventional pin fasteners. In
accordance with the present invention, two corner inner surfaces of
the diaper, that is, the inner surface of the body contacting layer
inner surface at the other two corners of the diaper structure are
provided with a release agent coating. Thus, when the diaper is
folded for packaging, the pressure sensitive adhesive surfaces
overlay the release coating surfaces to prevent any consequential
adhesion between such opposed corner surfaces. After the diaper has
been fitted on a baby, the inner surface corners carrying the
pressure sensitive adhesive are overlapped with the opposite
corners of the diaper structure but at the outer layer surface and
adhesive securement effected.
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