Note: Descriptions are shown in the official language in which they were submitted.
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SELECTIVE PLACEMENT OF ABSORBENT PRODUCT
MATERIALS IN SANITARY NAPKINS AND THE LIKE
Background of the Invention
Field of the Invention
This invention relates to products useful in the
absorption of body fluids, such as sanitary protection
products, adult incontinence products, diapers, wound
dressings and the like. More particularly, this invention
relates to absorbent products which contain a means for
resisting the transmission of body fluids form the central
absorbent element of the product to the body or garments of
the wearer of such a product.
Prior Art
One of the major problems inherent in absorbent
products has been that bodily fluids absorbed by such
absorbent products tend to follow pathways and run off such
products and/or fail to remain contained within an absorbent
product. In the case of sanitary protection products, this
results in menstrual fluid overflowing the absorbent product
and staining a wearer's undergarment and/or outergarments.
Various approaches have been taken in the past to remedy
this situation. For example, flaps have been utilized to
protect and wrap around a wearer's undergarment in order to
prevent staining from the sides of a sanitary protection
product. However, such flaps do not protect the end
portions of such sanitary protection products from leaking.
In a related U.S Patent No. 4,936,839, issued June 26, 1990,
repellant fibers have been placed at the transverse ends of
a flapped or winged sanitary protection product. However,
__ 20 1 ~ 9 43
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this design relates only specifically to winged sanitary
protection products. V~linged products are inconvenient as
they require additional work by the wearer to attach them to
undergarments. They are also more expensive to make due to
the additional adhesive and release paper which must be
placed on the wing portions of the product and due to the
high level of waste typically associated with such
processes.
In U.S. Patent No. 4,015,604 (Cilag), issued April
5, 1977, an absorbent product is provided with side leakage
control means comprising a narrow longitudinally extending
zone along each side edge of the product but spaced away
from each of the side edges. This zone is impregnated with
a liquid hydrophobic material from the garment facing
surface to the body facing surface of the product. The
extreme longitudinal edges of the absorbent element are free
of the impregnation. Cilag merely applies hydrophobic
impregnate to a hydrophilic pad as the pad passes through
the manufacturing equipment. This can result in uneven
placement of hydrophobic material and does not protect the
pad wearer from staining at the extreme edges of the pad
which are not hydrophobic. In addition, the process
according to Cilag does not guarantee that a uniform coating
of repellant is applied. This is also a wet process which
tends to have more problems related to machine efficiency
and microbial contamination issues.
",
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Canadian Patent No. 884,608 issued November 2, 1971,
(Levesque) relates to treating the edges of a sanitary napkin
product with hydrophobic material in order to prevent side
leakage. In accordance with Levesque, the absorbent layer in
the zone of the edges of the absorbent is rendered hydrophobic
while being maintained in a gas and moisture vapor permeable
condition. The hydrophobic zone may be coated with a liquid
repellent composition or chemically modified to render the
fibers hydrophobic. However, such chemical transformation of
hydrophilic fibers into hydrophobic fibers may be imprecise and
may not be particularly accurate. This can result in uneven
and/or inconsistent presence of hydrophobic fibers. This leads
to a lack of uniformity of the distribution of fibers in the
fibrous structure which is desired to be rendered hydrophobic.
Such lack of uniformity may lead to failure of the fibers to
repel body fluids. Thus, there is a need for a sanitary napkin
which has a consistent and precise availability of different
kinds of fibers and/or materials which can act in a napkin to
provide greater protection for the individual wearing such
napkin or absorbent product. This leads to a lack of
uniformity of the distribution of fibers in the fibrous
structure which is desired to be rendered hydrophobic. Such
lack of uniformity may lead to failure of the fibers to repel
body fluids.
Summary of the Invention
This invention relates to sanitary protection and absorbent
products, such as diapers, incontinent devices and wound
dressings and the like, which have fibers and/or other
materials specifically placed in particular areas of said
products in order to fulfill a particular function as desired
or needed. The invention also relates to absorbent products in
which dry fibers or other absorbent or repellent or
repellent-treated materials have been selectively and
accurately placed in strategic positions in a manner so as to
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maintain the stability of a product containing two or more
distinct fibers or material zones, as well as performing other
functions, such as repellency, superabsorption and the like. A
density gradient for absorption may also be created. In
addition, this invention relates to a method for treating
fibrous materials to enhance their fluid-repellency and, in
particular, to enhance their repellency to menstrual fluids,
and to the repellent materials so made. By providing discreet
zones of material, a uniform distribution of selected materials
is made so as to increase its effectiveness. It also relates
to a type of fiber material with defined properties which
enables effective repellency of body fluids.
It is, therefore. an object of this invention to provide
the selective placement of repellent fibers in a sanitary
protection product in order to improve protection by reducing
side and end leakage.
It is another object of this invention to increase the
absorbent capacity of a sanitary napkin by substantially
reducing staining and side and end failure.
It is a further object of this invention to reduce the
occurrence of side and end failures of sanitary protection
products when such products have been improperly placed or
shift during use.
A further object of this invention is to create a softer,
drier, more resilient napkin edge that is resistant to collapse
under wetting conditions.
Another object of this invention is to provide a sanitary
protection product which can be made using a dry, cureless
process without using liquids and curing devices such as ovens.
microwave products and the like.
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Yet another object of this invention is to provide
an absorbent product in which superabsorbents or other
materials may be placed so as to enhance the absorbent
capacity of the absorbent product without deformation,
instability and/or wet collapse. This is accomplished by
means of enhanced fluid containment or fluid management
designs for improved absorbent pulp efficiency.
A further object of this invention is to define the
properties of fluid-repellant fiber which will provide
adequate resistance to menstrual fluid.
A further object of this invention is to provide a
method for enhancing the fluid-repellency of fibrous
materials and, in particular, to provide fibrous materials
for use in catamenial products which are suited for
repelling menstrual fluids.
Additional objects of this invention will become
apparent through its description.
Brief Description of the Drawinas
Figure 1 is a perspective view of a sanitary napkin
according to this invention having hydrophobic or repellent
portions selectively placed therein.
Figure lA is a partial cross-sectional view of
sanitary napkins according to this invention having
hydrophobic or repellent portions selectively placed
therein.
Figure 2 is a top view of STAYFREE* MAXIPAD a
and a selective placement menstrual pad according to this
invention b illustrates shows the fluid wicking behavior of
both pads.
* Registered trade-mark
':'*
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Figure 3A is top view of a sanitary napkin of this
invention incorporating superabsorbent materials, and Figure 3B
is a longitudinal cross-section of the same napkin.
Figure 4A is a top view of a central absorbent portion of a
sanitary napkin, formed from a pulp and heat-activated fiber
blend, and Figure 4B is a top view of a sanitary napkin
according to this invention incorporating the central absorbent
portion illustrated in Figure 4A and a repellant pulp barrier.
Figure 5 is a perspective view of a sanitary napkin
according to this invention in which the central absorbent
section comprises both an uncompressed section at the body
facing side and a compressed high density layer on the
undergarment facing side.
Figure 6 is a perspective view of a sanitary napkin
according to this invention which has been shaped in a three-
dimensional manner in order to improve contact between the
wearer's body and the product.
Figures 7A and 7B are top views of sanitary napkins
according to this invention exhibiting different patterns of
absorbent and repellent zones.
Figure 8 is a cross-sectional view across the width of a
sanitary napkin according to this invention illustrating an
embodiment directed to reducing wet collapse of the napkin
structure.
Figures 9 and 10 are top views of sanitary napkins
according to this invention in "winglet" form.
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Detailed Descriptions of the Preferred Embodiments
In one preferred embodiment of the product of this
invention, a sanitary napkin product is provided which contains
both hydrophobic and hydrophilic fibers, the hydrophobic fibers
being placed in a particular configuration which enhances the
stability, or integrity, and efficiency of the entire product.
The repellent fibers may be placed in a configuration
around the periphery of a napkin as depicted in Figure 1. Such
a napkin has undergarment facing surface 10 and body facing
surface 20 as well as longitudinal edges 30 and transverse ends
40. Hydrophobic pulp fibers 50 may be placed around the
periphery of the product to a depth from body facing surface 20
to garment facing surface 10 of less than 100% of the height of
the product. Hydrophobic pulp 50 forms a hydrophobic barrier
portion. This hydrophobic barrier portion forms a body-fluid
repellent border or area which aids in containing fluid within
the absorbent, hydrophilic areas. Preferably, the hydrophobic
barrier portion extends between about 50 and 95%, and more
preferably between about 70 and 80%, of the height of the
product from body facing surface to the undergarment-facing
surface of the product.
The hydrophobic barrier portion thus cuts into the center
absorbent area so that the absorbent area, when viewed in
cross-section, is in the approximate form of a "T", the base of
which forms the body-facing side of the absorbent product.
Although the extension of the border to 100% of depth is
achievable, it may significantly decrease the stability of the
product, as the materials will tend to separate more easily
within the process and in use. Use of heat activated elements
may help to achieve up to 100% depth without loss in
stability. Constructing the hydrophobic repellent border such
that its height is approximately 70 to 80% of the height of the
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product allows for better fiber entanglement between the
hydrophobic and hydrophilic fibers and stability required to
maintain a unitized structure throughout production and use.
This structure also makes more hydrophilic fibers available
for absorption. The repellent barrier portion may also extend
higher than the height of the hydrophilic absorbent core, so
as to provide a gasket-like edge surrounding the absorbent
core. This can result in a structure which physically
discourages the movement of fluid outside the edges of the
napkin. Both the hydrophilic and hydrophobic areas may
contain thermoplastic fibers such that, upon exposure to heat
or other energy sources, the fibers will adhere to each other
and the pad will become a unitized stable whole.
The hydrophobic barrier portion of the pad should be
at least 1/16" wide at the face of the product. It may taper
off below the surface, as shown in Figure lA, so as to provide
greater absorbent capacity in the core where absorbent
capacity is needed.
Preferably, a polymeric barrier film is applied to
the garment-facing side of the absorbent core in order to
protect the garment from leakage from the absorbent core. The
barrier film may also be wrapped around the side portion of
the napkin in order to provide an extra barrier adjacent to
the hydrophobic/hydrophilic barrier. Wrapping the barrier
film completely around the napkin with the exception of the
body-facing side of the napkin product will also aid in
maintaining structural stability.
In lieu of a polymeric barrier film, a repellent or
hydrophobic fiber blanket may be applied to the garment-facing
side of the absorbent core to protect the wearer's garment
from leakage from the absorbent core. For example, as
illustrated in Figure lA, a hydrophobic or repellent blanket
60 may be applied to the absorbent core 70 so as to extend as
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a single unit around three sides of core 70. The hydrophobic
or repellent fiber blanket 60 creates a boat-like or U-shaped
cross directional structure. The hydrophobic or repellent
fiber blanket 60 serves the dual purpose of preventing leakage
from both the sides and the back of the absorbent product.
When used in lieu of a polymeric barrier film, this
hydrophobic or repellent fiber blanket provides a "breathable"
absorbent product construction. The hydrophobic or repellent
fiber blanket might also, however, be used in combination with
a polymeric barrier film, hydrophobically-treated nonwovens or
a superabsorbent material to provide an enhanced barrier
protection system and better occlusive breathability.
Under normal conditions, fluid wicks in every
direction, toward the bottom, sides and ends of the pad,
radially. Normal forces of use and compression accelerate
this wicking. When fluid reaches a repellent edge in the
products of this invention, the edge resists further lateral
flow of fluid towards the sides of the napkin. Normal
capillary action then allows fluids to wick preferentially
toward the ends of the napkin, resulting in the better use of
the central absorbent core and capacity available therein. In
conventional rectangular sanitary protection pads, napkin
leakage occurs mostly when fluids reach the napkin sides or
one end of the pad and stain the undergarment before the
absorbent is efficiently used over the full pad length.
Of course, placement of the hydrophobic portion of
the fibers need not be limited to a so-called "racetrack"
design which follows around the periphery of the napkin.
Additional configurations include a series of "stripes", or
channels located along the longitudinal axis of the napkin.
Such hydrophobic fibers may be placed also along the
longitudinal sides or edges of the napkin. Alternatively, the
';s.~::.~
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repellent zones may be intermittently spaced in the body of
the pad in patterns desired by one of ordinary skill in the
art.
The hydrophobic and hydrophilic pulp are preferably
colored differently. For example, the hydrophilic pulp may be
white and the hydrophobic pulp may be blue.
Figure 2 illustrates the difference in fluid wicking
behavior in which a STAYFREE* MAXIPAD has been exposed to the
deposition of 50 cc of synthetic menstrual fluid and subjected
to the placement of a 6 kg load over the pad surface for 30
seconds. The same treatment has been accorded the selective
placement pad. Figure 2 illustrates that the synthetic
menstrual fluid tends to stay in the middle and radiate in a
circular area of the STAYFREE* pad, thus increasing the
possibility of side leakage. In the selective placement pad
of this invention, the synthetic menstrual fluid flowed along
the longitudinal axis of the pad and was stopped from
overflowing the sides of the pad.
Thus, it can be seen that the repellent fiber edge
resists wetting, although fluid may be temporarily forced into
the interstitial spaces in the edge when subjected to
compression. When such forces are released, the absorbent
section of the product will reabsorb the fluid and it will be
prevented from leaking over the sides or through the repellent
fiber section of the pad and therefore prevent staining.
Another preferred embodiment of the product of this
invention is illustrated in Figures 3A and 3B. Using the
concepts discussed above with respect to placing repellent
fibers in a specific configuration, an absorbent product also
may be enhanced by strategically placing superabsorbent
materials within the structure. Superabsorbent materials 310
can be effectively used to reduce leakage from areas of
;3$ * Registered trade-mark
w2013943
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saturated absorbent pulp which can cause staining if subjected
to sudden changes in pressure or forces exerted on the pad.
For example, superabsorbent materials 310 may be placed with a
powder spray between the repellent fiber zones 320 and
absorbent fiber zones 330. This design permits the repellent
fibers to resist lateral fluid wicking and allows the
superabsorbent material time to absorb and retain large volumes
of fluids. In other circumstances such as those in the prior
art, superabsorbent materials can be less than totally
effective because they are subjected to large amounts of fluid
which cause gel blocking. With the advent of the novel
products of this invention, superabsorbent material may be used
in a much more effective way to be placed and to provide time
for absorption.
Figures 4A and 4B illustrate sanitary protection product
400 having a zone containing heat-activated stabilizing
elements 410. The entire napkin or the central absorbent
portion 420 alone or the repellent portion 430 alone of napkin
400 contains heat activated fiber, for example, PULPFXt" fiber
available from Hercules Corporation, which is incorporated with
other pulp fibers and may be exposed to thermal energy and
stabilized. Repellant pulp 430 may be placed around this
absorbent pulp, as illustrated in Fig. 4B, creating a discrete
interface between the repellent and absorbent pulp. When the
napkin 400 is heat activated, the repellent pulp will bond to
the absorbent pulp at the interface to form a unitized
structure. This structure may then be heat calendared or a heat
active table cover material can be heat calendared or heat
embossed into the core in order to form a stable structure able
to resist deformation. This would also allow the depth of the
repellent pulp to be increased to 100% of the pad depth without
sacrificing product stability.
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Figure 5 illustrates another preferred embodiment of
the product of this invention in which central absorbent section
510 has a low density, uncompressed section 520 at the body
facing side and a compressed high density layer 530 below the
top section on the undergarment facing side. Compressed layer
530 may provide a higher degree of stability in use, however,
compression of pulp in this layer may sacrifice some of its
absorbent capacity. Thus, a highly absorbent material in soft
board form may be provided in lieu of or in addition to
compressed pulp layer 530 in order to provide both stability and
higher capacity. For example, compressed peat moss board, such
as that described in U.S. Patent No. 4,992,324, issued February
12, 1991 may be placed as the lowest layer of this construction.
This provides a high capacity fluid drawing "pulp" which draws
fluid into the interior of the product, leaves less fluid on the
surface adjacent to the body facing side.
Figure 6 illustrates sanitary protection product 600
which has been shaped in a three-dimensional manner in order to
improve contact between the wearer's body and the product. This
provides a means 610 to capture menstrual fluid in the product
quickly as it is exuded from the body and to reduce the
probability of staining undergarments. The incorporation of
three-dimensional shaping in the selective placement products of
this invention (for example the raised-center design illustrated
in Figure 6) enhances their design by delivering the fluid into
the napkin structure where it is maintained within absorbent
section 610. Since absorbent sliver 620 is surrounded by the
repellent fiber material 630, the fluid does not leak from
either the sides or the ends. Thermoplastic materials such
as PULPEXTM in the absorbent and/or repellent pulp sections of
the napkins of this invention provide ease in achieving these
designs. The application of heat and pressure to compress
the peripheral area and leaving the uncompressed section to
project out of the napkin for improved body contact
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can be_achieved in this manner. Upper portion 610 may be
formed as an integral part of section 620; or, it can be formed
as a separate shaped sliver and placed on top of the bottom
sliver. Alternatively, it can be formed as a combination of
the above and calendared.
Likewise, the repellent zone of the product depicted in
Figure 1 may be shaped in an hourglass or other aesthetic and
functional shape in order to provide additional protection in
certain areas where it is required. This provides a means for
the consumer to discern the availability of the repellent
edge. Thus, Figure 7A provides an illustration of a preferred
embodiment where central absorbent portion 710 is shaped in an
hourglass configuration whereby repellent zone 720 is wider at
the center edges at the central portion of the napkin so as to
provide additional protection where it is most needed and a
resistance to the lateral flow of fluids within the napkin.
Figure 7B illustrates another embodiment in which repellent
zone 750 is shaped in an hourglass pattern within the central
absorbent zone having absorbent pulp fibers 725. Shaping of the
absorbent pads can be achieved with the use of contoured dies
or molds in the vacuum forming device. The advantages of such
a shaped zone include reducing the area of surface wetness
which can contact the body and limiting the effects of wicking
and failure at the napkin sides.
Figure 8 illustrates another preferred embodiment of the
sanitary protection products of applicant's invention. This
embodiment is directed to promoting the stability of wet pulp
structures after compression and providing resilience to such
structures. In sanitary protection products or the like where
ground communitive grade wood pulp or cellulose is used as the
primary absorbent medium, wet collapse of the absorbent begins
at the point of initial fluid deposition and continues over the
available surface area with increasing deposits of fluid and
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subsec~.uent wicking within the absorbent structure. Faster
wicking and subsequent wet collapse are accelerated with the
various forces normally applied to a pad in dynamic use. This
wicking typically occurs along paths of least resistance to the
fluid. As illustrated by Figure 8, a repellent treated pulp
fiber blanket in the form of a "W" 820 aids in resisting wet
collapse in the center 810 and peripheral edges 830 of the
product by maintaining a critical thickness at the center of
the pad for enhanced body contact after initial wetting of the
pad and, at the eztreme edges of the pad, for reduced leakage
by containing the fluid within the pad. This design also
enhances absorbence by channeling fluids along the napkins
length within the valleys of the "W" section. Fluid is
absorbed in the center of the pad where the depth of absorbent
pulp is sufficient for absorption and wicking. Wet collapse is
reduced at the center and ends of the pad by virtue of the
presence of the nonwettable pulp. Materials which wick fluids
very well may also be placed in the central portion of the "W"
conducive to wicking the material along the longitudinal axis
of the napkin. A breathable barrier 840 may be placed below
the "W" section in order to provide a breathable product
construction. The nonwettable pulp will provide an initial
barrier, which is also breathable, and the second barrier,
which may be composed of a breathable film or repellant treated
tissue layer, provides another protective layer to prevent
staining and leakage. The higher the density of this
nonwetting pulp, the lower its porosity and the higher its
resistance to strikethrough of fluids under pressure in a
breathable construction.
The concepts of this invention may also be used in order to
provide a "winglet" type sanitary protection product such as
that illustrated in Figure 9 and Figure 10. In general, the
wing portions of "winglet" type napkins are designed to spread
over or around the crotch of the wearer's undergarment and
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enhang_,e stain- protection of that garment. Winged-type
sanitary protection products with flimsy wings may become
saturated with fluid and wick fluid onto the thighs of the
wearer. Moreover, the wings tend to collapse under exposure to
fluid and fail to contain the fluid within the central
absorbent element of the product. Placing repellent resilient
fiber in the winglet portions 910 of such a pad and/or
completely around the periphery 101 of such a pad provides the
advantage of placing a protective barrier around the winglet
area which reduces leakage from the wing onto undergarments,
the body, or outer clothing. Moreover, it provides a more
resilient product construction. The contoured placement of the
repellent pulp in the wings allows a wider absorbent pulp
coverage at the center of the pad where it is most needed.
Thus. fluid entering the wings can be absorbed in larger
amounts due to the presence of absorbent pulp within the
repellent pulp border.
Of course, the concepts of the product of this invention
may be applied in other ways to provide layered products, in
which layers of different kinds of material may be selectively
placed within an absorbent core so as to maintain a stable
construction. For example, aesthetically pleasing high quality
white absorbent pulp may be placed in a top layer facing the
body and covering unbleached or semi-bleached pulp fiber or
other less aesthetic fiber for the purpose of lowering costs
without sacrificing the performance or visual attributes of the
napkin. Alternatively, hydrophobic fibers may be placed over
an absorbent core to reduce surface staining, in order to
increase softness and comfort and enhance surface and napkin
resilience. In another embodiment, a low density layer of pulp
may be formed over a higher density pulp layer in order to aid
in wicking fluid from the facing to the high density layer,
thus leaving a drier surface. A low wicking fiber may also be
placed toward the body facing surface over a high wicking
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fiber. A soft, resilient layer of fibers may be layered over
an absorbent core, or a blend of long and short fibers may be
covered over an absorbent core to improve stability.
Absorbent and heat activated fibers may be blended in a layer
to enhance overall pad stability. Thermoplastic fibers and
other fibers covering an absorbent core may be blended to
form a cover. This construction is less costly than using
web or film cover and improves the cover-to-core contact
without the use of adhesives. In addition, a hydrophobic,
fibrous layer, acting as a "breathable" fluid barrier may be
layered under an absorbent batt. This barrier may be used in
conjunction with "breathable" barrier film, superabsorbents
or hydrophobically treated nonwoven inserts.
The specific embodiments of this invention described
above utilize selectively placed hydrophobic or fluid-
repellent areas in absorbent products also incorporating
hydrophilic or fluid-absorbing materials. Suitable
hydrophobic or fluid-repellent materials which can be used
for this purpose include polyester, polyethylene,
polypropylene and bicomponent-type fibers. Bicomponent
fibers consist of a core composed of a synthetic fiber (e. g.,
polyester) and an outer sheath having a lower melting
temperature (e.g., polyester or polyethylene), which can
be heat-activated to enhance the stability of a fibrous
structure. Examples of bicomponent fibers useful in the
products of this invention are EnkaTM available from American
Enka Company or ChissoTM fibers available from Chisso Company
of Japan. Alternatively, and preferably, due to cost and
process considerations, conventional absorbent materials
such as pulp can be treated via a repellent sizing process
to yield repellent materials useful in these embodiments.
For example, a pulp material can be sized with a cationic
repellent (e. g., fatty acid ketene dimer, such as Aquapel*
360XC, available from Hercules, Inc., Wilmington, DE)
or subjected to treatment with silicone resins
---r~' ' ;" * Registered trade-mark
.y ~n
-17- 2 0 1 3 9 4 3
or fluorocarbons, to yield a repellent material suitable for
use in the selective placement absorbent products of this
invention. This pre-sizing of an absorbent pulp fiber, which,
in the untreated state has no resistance to absorption and
wicking of body fluids, gives it repellent properties to resist
or substantially prevent absorption or wicking of said fluids
within the products of this invention. In addition to treated
wood pulp, hydrophobic materials such as the aforementioned
polyester, polyethylenes. polypropylenes, heat fusible fiber
and the like can also be used in the illustrated product
designs, as they possess similar properties which would allow
them to resist absorption and wicking. These fibers can also
be chemically sized with repellents to further increase their
resistance to fluids.
In addition, hydrophobic materials such as the
aforementioned polyester, polyethylenes, etc. can be sized or
treated as mentioned above to further lower their critical
surface energy. The ability to pretreat materials to enhance
their repellency, and the use of vacuum forming capabilities
allow one to place repellent fibers virtually anywhere within
the X, Y and Z planes of an absorbent product during its
manufacture, allowing products to be made with specifically
designed fluid flow properties.
The type and variables of the treatment utilized to imbue a
material with greater fluid repellency will be adjusted to
provide a repellent material with the optimal properties for
its intended use. Research has shown that, while the surface
tension of water is generally in the range of 69-72 dynes/cm.,
that of menstrual fluid is in the range of less than 45-57
dynes/cm. Therefore, a repellent or hydrophobic material used
according to this invention in an absorbent catamenial product
should preferably have a critical surface energy less than
about 44 dynes/cm. Otherwise, menstrual fluid will wet the
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surface and, in the case of conventional materials like pulp,
also absorb and wick into the pulp. By the same token, it
would be within the skill of one skilled in the art to
determine the ideal critical surface energy for other absorbent
5, products, e.g., diapers, incontinent products, and the like.
For example, repellent treated pulp, Enka bicomponent
fibers washed with methanol to remove surfactants,
polypropylene and polyester fibers were measured for critical
surface energy. The fibers had critical surface energy
measurements as follows:
Critical Surface Energies For Certain Fibers
Fiber Tvpe Critical Surface Energy
Sdvnes/cm)
Repellent treated
pulp 28-33
Enka bicomponent 28-33
Polypropylene 28-33
Polyester 43
Repellent fibers suitable for use in selective placement
catamenial products according to this invention can be made by
sizing a pulp material with adequate (cationic) repellent at
concentrations of at least about 0.19% on total weight of pulp.
Table 1 provides data showing the repellency of untreated pulp
and repellent-treated pulp to synthetic and actual menstrual
fluid. High and low viscosity synthetic fluids were prepared
by dissolving a water soluble polyacrylamide polymer in
isotonic phosphate buffer (pH 7.4). Low and high viscosity
fluids contain 0.15% and 0.4% polymer, respectively, and have
viscosities of 30 cps and 280 cps, respectively. A germicide
is used to prevent bacterial growth.
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- TABLE 1
Repellence of Pulp vs. Synthetic Menstrual Fluid
Type I1 Type III2
Synthetic Synthetic
Concentration Menstrual Fluid Menstrual Fluid Menstrual Fluid3
(% total wt.)
0 wetting wetting wetting
0.11 wetting no wetting no wetting
0.19 no wetting no wetting no wetting
0.26 no wetting no wetting no wetting
0.34 no wetting no wetting no wetting
Repellent is Aquapel 360XC from Hercules, Inc.
1
Type I synthetic menstrual fluid is formulated with
physical properties (surface tension, viscosity, specific
gravity) consistent with that of whole blood. This would
represent the worst case type of discharge during normal
menstrual flow in which fluid viscosities are lowest and other
fluid properties are consistent with that of whole blood.
2
Type III synthetic menstrual fluid is formulated with a
viscosity that is much greater than that of whole blood and
represents the very viscous, gelatinous material common to
menstrual discharges.
3 Menstrual fluid was collected in-vivo and pooled to
represent a typical fluid discharge.
It has been shown that the visco-elastic properties of
menstrual fluids will vary greatly within a cycle and,
generally, within any given population. The data presented in
Table 1 indicate that 0.19% sizing by weight is the minimum
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level at which the hydrophobic material can
be ezpected to repel the full range of menstrual fluids,
independent of viscosity. Preferably, the pulp should be
treated with adequate repellent to provide a product having
between about 0.19% and 0.34% repellent per total weight of the
product.
To reduce the static potential of the pretreated repellent
pulp or the high cost contributed by use of either a pretreated
repellent pulp or hydrophobic fiber, it may be desirable to
blend the pretreated repellent pulp or other hydrophobic fiber
with absorbent pulp. The data presented in Table 2 indicate
that effective repellency versus menstrual fluid (surface
energy of less than 45 dynes/cm) can be maintained if the
pretreated pulp or hydrophobic fiber is mixed with percentages
of absorbent pulp or fiber up to 50%. The data in Table 2 were
obtained by applying fluids of known surface tensions to the
surface of the repellent treated material. Starting with a
fluid with a relatively high surface tension, fluid drops were
applied to the test substrate until the material began to wet
out. The critical surface energy of the substrate was
estimated to be equal to the surface tension of the fluid where
initial wetting was noted.
TABLE 2
Surface Energy of Hydrophobic/Hydrophilic Pulp Fiber Blends
Blend (%) Critical Surface Energy
H~rdrophobic /Hydrophilic Pulps dynes/cm
25/75 58
50/50 43
75/25 37
100/0 32
Hydrophobic portion treated with 0.34% repellent by weight.
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Osie must consider not only the critical surface energy of
the repellent or hydrophobic material utilized in an absorbent
product, but also the density of the material. Greater
hydrostatic pressures are required to penetrate repellent
versus absorbent pulp. This is shown by Table 3 in which the
resistance of pulp to fluid flow is measured as a function of
repellent treatment. Samples were evaluated at two densities,
0.5 g/cc and 0.15 g/cc. The higher density pulp was tested in
a Flow Through Tester from TRI. In this test, water is forced
through the pulp under pressure and the resistance to flow is
measured via a pressure transducer. Since the lower density
pulp fluff is much more sensitive due to its more open or
porous fibrous structure, a more sensitive technique was
employed to measure resistance, namely, a Buoyancy Tester from
TRI. The Buoyancy Tester allows the automatic monitoring of
liquid penetration and breakthrough under constant or variable
hydrostatic heads. In this test, if one side of the fabric is
placed in contact with liquid in a reservoir, the buoyancy
force will decrease systematically as liquid displaces air
'20 within the fabric pores.
TABLE 3
Resistance of Pule to Fluia Flow
Critical
Surface Energy
% of Sizing (dYnes/cm~
Resistance, psi Resistance, psi
0.5 gv/cc 0.15 a/cc
0 70 0 0
0.11 58 3.2 0.045
0.19 34 5.75 0.24
0.26 33 6.08 0.24
0.34 32 6.16 0.24
Aquapel 360XC. Hercules, Inc.
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The data in Table 3 indicate that, as the repellent
amount increases, critical surface energy (wettability)
decreases and the resistance to fluid flow increases. It also
indicates that barrier protection for this particular
repellent treatment is maximized at a relatively low add-on
(between about 0.19 and 0.26 $ repellent).
As shown above, the ability of a fibrous material zone or
layer to resist fluid flow within the products of this
invention is a function of each individual fiber's ability to
repel fluids as well as the porosity or density of said zone
within the product. Individual fibers must first possess
sufficient properties to resist menstrual fluids, by virtue of
their inherent hydrophobic properties and/or repellent
treatments such as those already discussed, and as measured as
a function of critical surface energy. Given any fiber with a
critical surface energy of less than 45 dynes/cm and
preferably less than 40 dynes/cm, resistance to menstrual flow
can then be enhanced by increasing the density of the material
one or layer containing said fibers.
Tables 4A and 4B below examine the impact of increasing
densities on flow resistance for two different fibers with
similar hydrophobic properties. Table 4A sets forth the raw
data obtained by increasing the density of the fibrous mass
made by the conjugation of the fibers. Table 4B represents
the linear comparison between the two materials - a repellent
treated pulp and a washed Enka Hicomponent (polyester core,
polyethylene sheath) fiber. Each fiber recorded critical
surface energies of less than 33 dynes/cm and greater than 28
dynes/cm.
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~'~OD~II' A
The basic concept of this invention is the selective
placement of a mixture of absorbent pulp and a super-
absorbent with a rapid absorption rate at the edge or
periphery of a napkin to trap fluid as it moves toward
the outer edge of the napkin. The superabsorbent would
be at a sufficient concentration to form a swollen gel
as it absorbed and act to block further movement of
fluid. These actions would tend to reduce leakage of
fluid out of the napkin.
The central section of the napkin would consist of
absorbent pulp and could contain a slower absorbing,
high capacity superabsorbent mixed with pulp or con-
centrated in a continuous or discontinuous layer to
enhance absorbency and fluid retention.
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- TABLE 4A
Resistance of Pul~ to Fluid Flow
Resistance Resistance
~Psi) ~Psi)
Density(q/cc) Repellent Pulp Washed Enka
0.39 0.22
0.37 0.176
0.36 0.264
0.23 0.22
0.23 0.176
0.29 0.176
0.17 0.132
0.19 0.176
0.16 0.132
0.06 0.033
0.07 0.022
0.05 0.044
0.39 0.363
0.33 0.186
0.32 0.226
0.3 0.242
0.23 0.147
0.19 0.142
0.05 0.039
0.05 0.035
0.05 0.035
35
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- TABLE 4H
Flow Resistance of A Fibrous Structure
Resistance Resistance
(Psi) (Psi)
Density(a/cc) Repellent Puln Washed Enka
0.05 0.082 0.089
0.1 0.15 0.147
0.15 0.217 0.204
0.2 0.285 0.261
0.25 0.353 0.319
0.3 0.421 0.376
Tables 4A and 4B expand on the data presented in Table
3. The same increase in fluid flow resistance is found with
increasing densities for both fibers having similar
hydrophobic properties. Typical densities of the hydrophobic
material zones within the products of this invention are
between about 0.05 and about 0.1 gm/cc. Within this range of
densities no individual value of flow resistance for either
fiber falls below 0.02 psi. Based upon the linear
relationship established between resistance to fluid flow and
density for the data obtained, set forth in Table 4B, normal
resistance to flow would be anticipated to average between
about 0.08 and about 0.15 psi and to have no individual values
less than about 0.02 psi independent of fiber type used, given
that the material has a critical surface energy less than the
lowest surface tension of normal menstrual fluid (45 dynes/cm)
and a material density between the densities of about 0.05 and
about 0.10 gm/cc to be used in the majority of the product
design executions of this invention. To achieve higher
densities for some of the synthetic hydrophobic fibers for use
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in the-products of this invention, it may be necessary to
apply heat to the sample under compression.
Fibers pretreated to enhance their repellency are also
useful in enhancing the structural stability of the absorbent
products in which they are incorporated. As opposed to
hydrophilic or absorbent fibrous layers which tend to readily
absorb fluids and collapse in the wet state, hydrophobic or
pretreated repellent pulp fibrous structures, used according
to this invention to provide enhanced fluid management within
an absorbent structure, will resist wetting by menstrual and
other bodily fluids and thus will not readily collapse in the
presence of these fluids. Measureable resistance to wetting
and fluid flow through the hydrophobic fibrous structures, and
subsequently greater resistance to wet collapse, allows an
efficient utilization of absorbent fibers in a repellent
fiber/absorbent fiber matrix. Enhanced resistance to wetting
and wet collapse is not only dependent on wettability but also
on pore size or density of the fibrous structure. Fluids need
to be forced under pressure into a repellent-treated or
hydrophobic fibrous structure as opposed to an absorbent fiber
mat where no force is necessary. The smaller the pore size,
the greater the density and the greater the resistance to wet
collapse in a dynamic state under pressure.
The sanitary protection products and absorbent products
of this invention may be made by hand, by selectively placing
materials in the appropriate configurations, or they may be
made in vacuum forming equipment, using molds and dies and/or
baffles which are capable of directing the different types of
materials to be selectively placed in the desired areas.
Conventional pulp web generating equipment can also be
modified to provide different material zones for similar
executions. They may also be made by any other known
processes available to those of skill in the art which are
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capably of achieving the configurations set forth in the
foregoing specification.
10
20
30
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