Note: Descriptions are shown in the official language in which they were submitted.
r ,~ CA 02225467 1998-02-03
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THERMOPLASTIC FI8ROU8 NONWOVEN WE88 FOR USE AS
CORE WRAPS IN ABSORBENT ARTICLES
a
FIELD OF THE INVENTION
The present invention is directed to an absorbent article
with a tissue-wrapped absorbent core for use in personal care
absorbent products and the process for making such meltblown
tissue wrapped absorbent cores. The tissue wrap is made from
thermoplastic fibers.
BACKGROUND OF THE INVENTION
The designs of personal care absorbent products have gone
through extensive changes in recent times. Personal care
absorbent products include such items as diapers, training
pants, incontinence garments, sanitary napkins, bandages and
the like. A major thrust in the design of these products,
especially with diapers, training pants, incontinence garments
and sanitary napkins, has been a reduction in the size of
the
products while increasing their absorptive capacity. Greater
and greater usage of superabsorbents has made this possible.
Using diapers as an example, originally diapers were
very thick in design due to the high volumes of fluff or wood
pulp used to form the absorbent core of the diaper. As a
result, the diapers were very bulky and they tended to leak
because, as the absorbent fluff was wetted with urine, the
fluff tended to collapse. Typically the fluff used in such
personal care absorbent products had a liquid gram per gram
capacities of 4 to 2o grams of aqueous liquid absorbed per
gram
of fluff. In addition, this capacity was dependent upon the
amount of pressure being applied to the wet fluff. For
example, at a pressure of 0.5 pounds per square inch (psi)
the
fluff would only hold approximately 7 grams per gram. At o.l
psi the capacity would increase to approximately 12 grams
per
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gram and at zero psi the capacity would be approximately 20
grams of liquid per gram of fluff.
With the advent of superabsorbents and their
incorporation into absorbent cores, the size of the absorbent
cores have been reduced. Initial superabsorbents had gram per
gram capacities in the range of 5o grams per gram but the
particles became very mushy when wet and would often cause gel
blocking. Today, superabsorbents have higher absorbency while
under load but to do this, many of the superabsorbents have had
their capacities reduced to around 35 grams per gram. The
first commercial diapers using superabsorbents incorporated
from about 10 to 20 percent by weight superabsorbent, based
upon the total weight of the absorbent core. The
superabsorbent particles, which typically had 20 to 1,000
micron diameters, were contained within the absorbent cores
through mechanical entanglement with the wood pulp fibers. In
addition, paper tissue was sometimes wrapped around the
superabsorbent-containing batts and sometimes the tissue was
glued to itself and/or the fluff to further encapsulate and
retain the fluff and superabsorbent.
Today, personal care absorbent products such as diapers
have greatly reduced their thickness by removing large
quantities of the fluff and replacing it with higher and higher
percentages of superabsorbent particles. Some of the diapers
today have absorbent cores with over 4o percent superabsorbent.
Oftentimes the absorbent cores are compressed to further reduce
their thickness after adding the tissue wrap. As a result,
while old fluff cores tended to collapse when wetted, the new
absorbent cores with superabsorbent tend to swell as they are
wetted. This swelling coupled with the twisting and flexing
the absorbent core experiences during use, can cause the paper
tissue wrap to rip and tear, especially when wetted. When this
happens, there is a greater chance that the superabsorbent will
escape from the diaper. While this is not dangerous, it is not
desirable from an overall product performance standpoint.
In the dry state, there is also greater potential for ~
loss of the superabsorbent from the absorbent core as the
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WO 97/07761 PCT/I1S95/10916
percentages of superabsorbent are increased. With less fluff
in the core, there is less mechanical entrapment of the fibers.
Thus, if there is a rip in the paper tissue wrap or a portion
of the glued seam becomes separated, there is a higher
likelihood that some of the superabsorbent particles will
escape. An even bigger problem is that the pores in many paper
tissue wraps are too big and therefore allow the superabsorbent
to escape. Consequently, there is a need for a more effective
way of encapsulating the absorbent core.
From a processing standpoint there are also problems.
Gluing a paper tissue wrap is messy and adds cost. Shake out
of the superabsorbent particles can also cause equipment and
housekeeping problems and higher production costs due to wasted
material. As a result, there is a need for an improved
absorbent core/wrap for uses such as in personal care absorbent
products.
SUMMARY OF THE INVENTION
The present invention a.s directed to an absorbent article
with a tissue-wrapped absorbent core made from thermoplastic
fibers for use in personal care absorbent products such as
diapers, training pants, incontinence garments, sanitary
napkins, bandages and the like. The core wrap is made from a
fibrous nonwoven web comprising a plurality of thermoplastic
fibers. The core wrap has a plurality of pores with a mean
flow pore size less than about 30 microns and wherein no more
than 5 percent of the plurality of pores have a pore size
greater than 50 microns. The core wrap has a wet to dry
tensile strength ratio at peak load in the machine direction
or the cross-machine direction of 0.5 or greater. In addition,
the core wrap has a Frazier air permeability of at least 200
cubic feet per square foot per minute, a machine direction
elongation at peak load of 30 percent or less, and a cross-
machine direction elongation at peak load of 40 percent or
less. The fibrous nonwoven core wrap is used to envelope an
absorbent core including particulate superabsorbent. Due to
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the nature of the construction of the core wrap, less than 60
milligrams of shake up of particulate superabsorbent will
occur. In addition, if so desired, the absorbent core may
contain a plurality of fibers which are thermally bondable to
the fibrous nonwoven web core wrap. To insure the proper
retention of the particulate superabsorbent, it is desirable
that at least 85 percent of the plurality of fibers forming the
core wrap have fiber diameters of 8 microns or less and more
desirably where at least 95 percent of such fibers have fiber
diameters of 7 microns or less. Where particularly fine
superabsorbent particles are being used, it is desirable that
the plurality of pores in the fibrous nonwoven web core wrap
with pore sizes greater than 50 microns be restricted to one
percent or less.
The absorbent article including the fibrous nonwoven web
core wrap and an absorbent core including particulate
superabsorbent may be used by itself as a finished product or
it may be incorporated into a personal care product. Such
personal care products typically include a top sheet and a
bottom sheet with some type of absorbent material disposed
between the top and bottom sheets. In accordance with the
present invention, the absorbent material is the previously
described absorbent article.
A suitable process for forming an absorbent article
according to the present invention includes forming a fibrous
nonwoven web core wrap by extruding a molten thermoplastic
polymer into a plurality of molten streams. These molten
streams are then attenuated into a plurality of fibers which
are deposited onto a forming surface to form a fibrous nonwoven
web core wrap having a plurality of pores with a mean flow pore
size of less than about 30 microns with no more than 5 percent
of the plurality of pores having a pore size greater than 50
microns and with the fibrous nonwoven web core wrap having a
wet to dry tensile strength ratio at peak load in the machine
direction or cross-machine direction of 0.5 or greater and a
Frazier air permeability of at least 200 cubic feet per square
foot per minute. Once the fibrous nonwoven web core wrap has
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been formed, there is deposited thereon a quantity of
particulate superabsorbent after which the core wrap is sealed
to envelope the particulate superabsorbent. In addition, if
so desired, a plurality of absorbent fibers may be deposited
onto the core wrap prior to the sealing step.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of an absorbent article
according the present invention.
to
Figure 2 is a cross-sectional side view of an absorbent
article according
to the present
invention.
Figure 3 is a cross-sectional side view of another
absorbent
article according
to the present
invention.
Figure 4 is a cross-sectional side view of yet another
absorbent
article according
to the present
invention.
Figure 5 is a schematic side view of a process for
forming an absorbent article according to the present
invention.
Figure 6 is a partial cut-away top plan view of a
personal careabsorbent product including an absorbent article
according the present invention.
to
Figure 7 is a perspective view of a shake-out testing
apparatus.
Figure 8 is a partial cut-away, top plan view of a
representative
sample mount
and test
sample employed
for shake-
out testing.
Figure 9 is a side view of the sample mount and test
sample shown in Figure 8.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figures 1 through 4, the present invention
~ is directed to an absorbent article 10 including an absorbent
core 12 and a core wrap 14. The core wrap 14 is particularly
~ well-suited for containing absorbent cores which are made
partially or completely from particulate matter such as
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WO 97/07761 PC'T/US95/10916
superabsorbent particles. It should be understood, however,
that the present invention is not restricted to use with
superabsorbent particles but any particulate material such as
odor absorbing and ion exchange resin particles and controlled
release agents such as moisturizers, emollients and perfumes
which require retention.
A "superabsorbent or superabsorbent material" refers to '
a water-swellable, water-soluble organic or inorganic material
capable, under the most favorable conditions, of absorbing at
least about 20 times its weight and, more desirably, at least
about 30 times its weight in an aqueous solution containing 0.9
weight percent sodium chloride. Organic materials suitable
for use as a superabsorbent material in conjunction with the
present invention can include natural materials such as agar,
pectin, guar gum, and the like; as well as synthetic materials,
such as synthetic hydrogel polymers. Such hydrogel polymers
include, for example, alkali metal salts of polyacrylic acids,
polyacrylamides, polyvinyl alcohol, ethylene malefic anhydride
copolymers, polyvinyl ethers, methyl cellulose, carboxymethyl
cellulose, hydroxypropylcellulose, polyvinylmorpholinone; and
polymers and copolymers of vinyl sulfonic acid, polyacrylates,
polyacrylamides, polyvinylpyrridine, and the like. Other
suitable polymers include hydrolyzed acrylonitrile grafted
starch, acrylic acid grafted starch, and isobutylene malefic
anhydride polymers and mixtures thereof. The hydrogel polymers
are preferably lightly crosslinked to render the materials
substantially water insoluble. Crosslinking may, for example,
be accomplished by irradiation or by covalent, ionic, van der
Waals, or hydrogen bonding. The superabsorbent materials may
be in any form suitable for use in absorbent composites
including particles, fibers, flakes, spheres, and the like.
Such superabsorbents are usually available in particle sizes
ranging from about 20 to about 1000 microns. The absorbent
core 12 can contain from 0 to 100 percent superabsorbent by
weight based upon the total weight of the absorbent core.
Typically an absorbent core 12 for a personal care
absorbent product will include superabsorbent particles and;
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WO 97/07761 PCT/US95/10916
optionally, additional absorbent material such as absorbent
fibers including, but not limited to, wood pulp fluff fibers,
synthetic wood pulp fibers, synthetic fibers and combinations
of the foregoing. Wood pulp fluff such as CR-54 wood pulp
fluff from Kimberly-Clark Corporation of Neenah, Wisconsin is
an effective absorbent supplement. A common problem with wood
pulp fluff, however, is its lack of integrity and its tendency
to collapse when wet. As a result, it is often advantageous
to add a stiffer reinforcing fiber into the absorbent core 12
such as polyolefin meltblown fibers or shorter length staple
fibers. Such combinations of fibers are sometimes referred to
as "coform". The manufacture of meltblown fibers and
combinations of meltblown fibers with superabsorbents and/or
wood pulp fibers are well known. Meltblown webs are made from
fibers formed by extruding a molten thermoplastic material
through a plurality of fine, usually circular dye capillaries
as molten threads or filaments into a high-velocity heated
air
stream which attenuates the filaments of molten thermoplastic
material to reduce their diameters. Thereafter, the meltblown
fibers are carried by the high-velocity gas stream and are
deposited on a collecting surface to form a web of randomly
dispersed meltblown fibers. The meltblown process is well
known and is described in various patents and publications,
including NRL Report 4364, "Manufacture of Super-Fine Organic
Fibers" by V. A. Wendt, E. L. Boone and C. D. Fluharty; NRL
Report 5265, "An Improved Device For the Formation of
Super-Fine Thermoplastic Fibers" by K. D. Lawrence, R. T.
Lukas
and J. A. Young; and U.S. Patent Number 3,849,241, issued
November 19, 1974 to Buntin et al. To form "coform" materials,
additional components are mixed with the meltblown fibers
as
the fibers are deposited onto a forming surface. For example,
superabsorbent particles and/or staple fibers such as wood
pulp
fibers may be injected into the meltblown fiber stream so
as
to be entrapped and/or bonded to the meltblown fibers. See,
for example, U.S. Patent No. 4,100,324 to Anderson et al.;
U.S.
Patent No. 4,587,154 to Hotchkiss et al., U.S. Patent Nos.
4, 604, 313; 4, 655, 757 and 4,724, 114 to McFarland et al.
and U.K.
7
CA 02225467 2002-04-15
Patent GB 2,151,272 to Minto et al.
The core wrap of the present invention is a specifically
designed and engineered fibrous nonwoven web made from fine
diameter thermoplastic fibers with particular pore sizes and
air permeability. By thermoplastic fibers it is meant fibers
which are formed from polymers such that the fibers can be
bonded to themselves using heat or heat and pressure. While
not being limited to the specific method of manufacture,
meltblown .fibrous nonwoven webs have been found to work
particularly well. With respect to polymer selection,
polyolefin fibers and especially polypropylene-based polymers
have been found to work well.. The general manufacture of such
meltblown fibrous nonwoven webs is well known. See for
example, the previously mentioned meltblown patents referred
to above. The fibers may be hydrophilic or hydrophobic, though
it is desirable that the resultant web/core wrap be
hydrophilic. As a result, the fibers may be treated to be
hydrophilic as by the use of a surfactant treatment.
In order to function well as a core wrap, the meltblown
web should have certain specific properties. A common problem
with paper tissue wrap is that it has inadequate strength in
the wet state. Typically a paper tissue wrap will have a wet
to dry strength ratio in either the machine direction (MD) or
cross-machine direction (CD) as measured by the test method
outlined below of less than 0.5. In contrast, the absorbent
core wrap 14 of the present invention will have wet to dry
strength ratios above 0.5 and sometimes 1.0 or higher. In
addition, the mean flow pore size as measured by the test below
should be about 30 microns or less and less than five percent
of the total pores for any given area should be 50 microns or
greater. More desirably, less than one percent of the total
pores for a given area should be 50 microns or greater. To
accomplish this it is desirable that at least 85 percent o! the
fibers of the core wrap 14 have fiber diameters of 8 microns
or less and more desirably at least 95 percent of the fibers
should have fiber diameters of 7 microns or less. As a result,
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the absorbent core wrap 14 will have a Frazier air permeability
of 200 cubic feet per square foot par minute or greater.
Once
the absorbent core 12 has been wrapped with the core wrap
14,
the wrap 14 should not unduly expand or stretch as this might
cause the pores to enlarge and allow excessive particulate
matter to escape. Consequently, the core wrap, while in the
dry state, should have respective elongation values at peak
load in the machine and cross machine directions of 30 percent
or less and 40 percent or less.
To form the present invention, reference is made to the
process depicted schematically in Figure 5. First an absorbent
core wrap 14 must be formed using a fiber forming apparatus
which, in this case, is a meltblown apparatus. As shown in
Figure 5, the meltblown tissue wrap is formed in-line,
15 however, it is also possible to form the meltblown tissue
wrap
off-line and then feed it into the process of Figure 5 in
roll
form. Returning to Figure 5, a molten thermoplastic polymer
such as a polyolefin is heated and then extruded through
a die
tip to form a plurality of molten streams of polymer. As
the
20 streams of polymer leave the die tip of the meltblown apparatus
50, they are attenuated by high velocity air which draws
the
molten streams into a plurality of fibers 52 which are
deposited onto a forming surface 54 in a random entangled
web
to form the core wrap 14. To further assist in the web
25 formation and to impart better hold-down of the web onto
the
forming surface 54, a vacuum 56 may be used underneath the
foraminous forming surface 54.
Once the absorbent core wrap 14 has been formed on the
forming surface 54 or unrolled from a preformed roll (not
30 shown), the absorbent core 12 must be formed or deposited
onto
the surface of the absorbent core~wrap 14. As shown in Figure
5, there is a source 58 of superabsorbent or other type
particles 6o and an optional source 62 of absorbent fibers
64
' such as, for example, wood pulp fibers or meltblown fibers.
35 If both absorbent fibers 64 and superabsorbent particles
are
' to be used to form the absorbent core 12, they may be
intermixed before they are deposited onto the absorbent core
9
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wrap 14 as shown in Figure 5 or they may be layered so as to
isolate the particles .within the interior of the absorbent core
12. Again to further assist in the deposition and retention
of the absorbent core materials onto the surface of the
absorbent core wrap 14, the same vacuum source 56 or a separate
source if so desired may be used.
After the absorbent core 12 has been deposited onto the
absorbent core wrap 14, the core wrap 14 should be sealed
around the absorbent core 12 so as to envelope the absorbent
core 12 and form an absorbent article 10. As shown by Figures
1 through 4, to envelope the absorbent core, the core wrap 14
should completely wrap around the core 12 and be sealed,
preferably to itself. It is also desirable that the ends of
the absorbent article also be sealed. Due to the thermoplastic
nature of the fibers of the core wrap 14, the core wrap 14 may
be heat sealed to itself thus avoiding the need for glue though
glue can also be used if so desired. In addition, if so
desired, the absorbent core materials 6o and 64 may be cycled
on and off so that end seals can be formed in between the
deposits of core material. Further, if the absorbent fibers
64 are also thermoplastic in nature, end and side seals can be
made in the core wrap 14 which bond right through the absorbent
core 12.
As shown in Figures 2 and 3 of the drawings, if the core
wrap 14 is sufficiently wide, it may be folded over on itself
and then sealed using, for example, adhesives, heat and/or
pressure either on top or bottom (Figure 2) or' on the side
(Figure 3) of the absorbent article lo. The folding of the
core wrap 14 over onto itself can be accomplished through the
use of conventional sheet folding means 66 such as curved
plates which work the core wrap 14 over onto itself.
Alternatively, a separate sheet of core wrap 14' may be
unrolled or formed from a second source 68 so as to encapsulate
the absorbent core 12 between a first sheet of absorbent core
wrap 14 and a second sheet of absorbent core wrap 14' . See
Figure 4. As with the embodiments shown in Figures 2 and 3, ,
the loose edges of the core wrap may be sealed together using
CA 02225467 2002-04-15
a sealing means 70 such as an ultrasonic bonder or other
thermomechanical bonding means or through the use of adhesives.
The absorbent article 10, once formed, may be used by
itself or it may be incorporated into a personal care absorbent
product 18 such as is shown in Figure 6. For purposes of
illustration only, the personal care absorbent product 18 shown
in Figure 6 is in the form of a diaper. This should be
considered illustrative only as the absorbent article 10 of the
present invention may be used in all types of personal care
absorbent products including, but not limited to, diapers,
training pants, incontinence 'garments, sanitary napkins,
bandages and the like.
All such personal care absorbent products generally
include a liquid permeable top sheet 20 and a generally liquid
impermeable bottom sheet 22. Disposed between the top sheet
and the bottom sheet 22 there is an absorbent material and,
in the present application, it is the absorbent article 10.
If desired, the top sheet 20 and bottom sheet 22 may be sealed
to one another about their respective peripheries 24 so as to
20 encase the absorbent article 10.
Having thus described the present invention and the
process for making it, a series of examples were prepared to
further illustrate the present invention. These examples and
the test procedures for measuring them are set forth below.
TEST PROCEDURES
Coup er Porometer Mean Flow Pore Size and
Pore Size Distribution Test
A Coulter 15/60 porometer from Coulter Electronics, Ltd.
of Luton, England was used to determine mean flow pore size,
maximum flow pore size and pore size distribution. The
apparatus was capable of measuring pore sizes up to 300
microns. Determinations of the mean flow pore size, maximum
flow pore size and pore size distribution were made in
accordance with ASTM Standard Test Methods Designation F316-
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CA 02225467 2002-04-15
86 for Pore Size Characteristics of Membrane Filters by Bubble
Point And Mean Flow Pore Test.
The procedure used to determine Frazier air permeability
was conducted in accordance with the specifications of method
5450, Federal Test Methods Standard No. 191 A, except that
specimen sizes were 8 inches x 8 inches rather than 7 inches
x 7 inches. The larger size made it possible to ensure that
all sides of the specimen extended well beyond the retaining
ring and facilitated clamping of the specimen securely and
evenly across the orifice. Values were given in cubic feet per
square foot per minute (ft3/ft2/min) . To convert to cubic
centimeters per square centimeter per minute multiple by 30.5.
~ensi~e Strenath Swet and dryl and Elonaati~on
ASTM procedure D 5035-90 - Standard Test Method for
Breaking Force and Elongation of Textile fabrics (Strip Force)
was used to measure the wet and dry tensile strengths to peak
load. A SinTechT'~.model S2, constant-rate-of-extension type
testing machine manufactured by SinTech Corporation of Carey,
North Carolina was used for the procedure. Three inch (75 mm)
cut strip samples were used instead of the one inch (25 mm) or
two inch (50 mm) samples specified in procedure D 5035-90.
The fibers of sample nonwoven webs were sputter coated
with gold in preparation for examination with a Scanning
Electron Microscope (SEM) such as a Cambridge Stereoscan 200
microscope from Leica, Inc.of Deerfield, Illinois. One hundred
fibers were selected at random and individual fiber diameters
were measured using the electronic cursors of the SEM.
Particular care should be taken not to select fibers which have
been fused together.
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Shake Box Shaky Out Test Procedure
With reference to Figs. 8 and 9, a 4 inch by 11 inch
sample mount 80 was cut from a 350 gsm cellulose paper (or an
equivalent material which provided suitable structural
integrity with enough bending flexibility to allow an insertion
of the sample mount 80 into the test unit).
A 0.25 inch wide, two-sided pressure sensitive adhesive
tape 82, such as 3M ScotchTM brand 2 mil, high tack adhesive
transfer tape 0465) or equivalent was applied to the center
of the sample mount to form a square "window frame" having
outside dimensions of 4 inch by 4 inch.
500 mg (~ 5 mg) of superabsorbent material 84 was placed
in the center of the "window frame". The particle size
distribution of the superabsorbent material was determined by
conventional sieve analysis, and was as follows:
212-300 micrometers: 40% (by weight)
i49-212 micrometers: 35%
90-149 mi0rometers: 25%
Testing was conducted on a single sheet of the sample
core wrap 14, and a 4.5 inch by 4.5 inch piece 86 of the sample
being tested was placed over the framed area and adhered by
pressing the sample onto the adhesive tape to provide a tight
seal.
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Shake Test Unit
With reference to Fig. 7, a shaker mechanism 90, such
as a Variable Junior Orbit ShakerM(Model 3520) available from
Lab-Line;' was used to determine the ability of the core wrap
to contain superabsorbent. Alternatively, an equivalent shaker
may be employed.
A testing box 92 was operably secured to the shaker. The
box 92 had four side walls and a cooperating bottom wall which
were constructed of any suitable material such as clear
polycarbonate sheet having a thickness of about 0.025 inch.
The box measured approximately 11.5 inches along its length 94,
by about 13 inches along its width 96, by 5 inches along its
depth 98, and was sectionalized into three compartments 100,
each of which was large enough to accommodate the placement of
a sample mount therein. Accordingly, each of the shown
compartments had inside measurements of approximately 4 inches
by 11.5 inches. Each compartment was also equipped with two
conventional spring clamps 104 which were positioned on opposed
end walls of the compartment and constructed to securely hold
the sample mounts in place. One jaw of each spring clamp was
securely fastened to its corresponding compartment end wall
and the other jaw was arranged to be free to open and close
upon pressure applied to its associated activating lever 106.
For testing, the opposite ends of a sample mount were securely
held in a pair of clamps attached in the particular compartment
employed for testing. The sample mount was positioned with the
sample core wrap located closest to the bottom wall of the box.
The shaker was turned on and operated at an indicated speed of
350 rpm for a period of 5 minutes.
The amount of superabsorbent which was shaken out through
the sample core wrap was determined by a vacuum collection of
debris. For examples 5 through 8, a 37 mm diameter air
monitoring cassette (Gelman Science Product number 4338) was
14
CA 02225467 2002-04-15
prepared by placing a 37 mm cellulose support pad (Product
number 64747) in the bottom of the cassette. A 0.08 micrometer
Metricel~ membrane (Product number 64678) was placed on top of
the support pad and the top of the cassette was pressed into
the mating bottom. The prepared cassette was weighed and the
weight was recorded or tared. The cassette was hooked to a
suitable vacuum source with tubing. A plastic funnel was
fitted to the tubing'and the superabsorbent was vacuumed into
the monitoring cassette. The cassette was reweighed and the
amount of superabsorbent was, determined by the weight
differential. This test was used for examples 5 through 8 and
values given in the claims should be calculated using this
method.
Packet Shake-out Test
A second method of testing was also used to determine
particle shake-out from the absorbent core wraps. This test
was used with respect to Examples 1 through 4 and 9. To
perform the test an 8 inch by 4 inch sample of the core wrap
was cut. Next 0.5 grams of Dow 534 particulate superabsorbent
from the Dow Chemical Company was placed on top of the sample
and the sample was folded over onto itself to cover the
superabsorbent and form a 4 inch by 4 inch packet. The
superabsorbent particles ranged in size from 88 to 149 microns.
All four sides of the packet were then taped to a piece of
plastic film. The tape overlapped approximately 0.25 inch the
packet periphery. The sample and film were then inverted
(packet side down) and the combination was attached to a Model
RX-24 Shaker from the Tyler Company. Below the sample there
was placed a tared pan of sufficient size to collect any
superabsorbent shake-out. The shaker was turned on and
operated for a period of five minutes. The shaker operated at
approximately 520 cycles per minute with a 0.5 inch stroke.
After five minutes the shaker was turned off and the pan was
reweighed. The difference between the collected weight and the
tared weight represented the amount of shake-out.
CA 02225467 2002-04-15
A polypropylene meltblown fibrous nonwoven web core wrap
was made using Himont PF-015 polypropylene polymer from Himont,
USA of Wilmington, Delaware. The meltblown core wrap was made
in accordance with meltblowing teachings described above
utilizing a two bank meltblown apparatus. The polypropylene
was extruded through the two bank meltblown die assembly at a
throughput of 2.5 pounds per inch per hour (PIH) . The extruded
streams of molten polymer were attenuated with primary
attenuation air delivered at a rate of between about 1700 and
2000 cubic feet per minute at a temperature of 530°F. The
resultant meltblown core wrap had a basis weight of 8.0 grams
per square meter (gsm) and was treated with TritonT"'X-102
surfactant octylophenoxypolyethoxyethanol nonionic surfactant
from Union Carbide Chemicals and Plastics Company, Inc.,
Industrial Chemicals Division of Danbury, Connecticut.
The core wrap had dry machine direction (MD) and cross-
machine direction (CD) tensile strengths measured at peak loads
of 1010 grams and 514 grams respectively and machine direction
and cross-machine~direction elongations at peak load of 16 and
33 percent respectively. The wet machine direction and cross
machine direction tensile strengths at peak load were 998 grams
and 554 grams respectively. The wet to dry tensile strength
ratios in both the machine and cross machine directions were
respectively 0.99 and 1.08. Ratios were determined by dividing
wet and dry values for respective MD and CD directions. The
mean flow pore size for the sample was 25 microns and the
maximum flow pore size was 47 microns with 0.5 percent of the
overall pores having a pore size greater than 50 microns. The
core wrap had a Frazier air permeability of 361 cubic feet per
square foot per minute. A sample of the meltblown core Wrap
was subsequently made into a packet and filled with 0.5 grams
of Dow 534 type superabsorbent from the Dow Chemical Company
of Midland, Michigan with particle sizes ranging between 88 and
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150 microns in diameter. The packet was subjected to the
packet shake test procedure as outlined above and the fall-
out was measured to be 2.7 milligrams as compared to 395
milligrams of fall-out for the same superabsorbent when placed
within a packet made from standard paper tissue core wrap
material.
Examble 2
In Example 2 a polypropylene meltblown fibrous nonwoven
web core wrap was made using the same polymer and surfactant
treatments as listed above with respect to Example 1. The
meltblown web was made using three banks of meltblown dies
delivering polymer at a rate of 3.5 pounds per inch per hour
(PIH) with the primary attenuation airflow remaining the same
as that in Example 1. The resultant web had a basis weight of
11.0 grams per square meter. The core wrap had a dry machine
direction tensile strength at peak load of 1391 grams. The
mean flow pore size was 23 microns and the maximum flow pore
ZO size was 40 microns with zero percent of the pores being
greater than 50 microns. Frazier air permeability was measured
to be 250 cubic feet per square foot per minute. The meltblown
core wrap was subsequently made into a packet and filled with
0.5 grams of the same Dow 534 type superabsorbent as mentioned
in Example 1. The packet was then subjected to the shake test
and fall out was measured to be 5.0 milligrams.
Example 3
In Example 3 an 8.0 gram per square meter basis weight
polypropylene meltblown absorbent core wrap was made using the
same polymer as in the previous examples. The core wrap had
a dry MD tensile strength at peak load of 914 grams, a mean
- pore flow size of 24 microns and the maximum flow pore size
was 40 microns with zero percent of the pores being greater
than 50 microns. The Frazier air permeability was 327 cubic
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feet per square foot per minute and the core wrap had 1.1
milligrams of shake-out using the packet shake-out test.
Examine 4
In Example 4 the same Himont polypropylene polymer was
used to make a meltblown absorbent core wrap with a basis
weight of 8.8 grams per square meter. The core wrap had an
average fiber diameter of 2.4 microns, dry MD and CD tensile
strengths at peak load of 844 and 382 grams, respectively, and
MD and CD elongations of 15 percent and 11 percent,
respectively. Mean flow pore size was 22 microns and the
maximum flow pore size was 34 microns. The Frazier air
permeability was 484 cubic feet per square foot per minute and
the packet shake-out test yielded 0.4 milligrams of
superabsorbent.
Example 5
In Example 5 a meltblown absorbent core wrap was made
with the same Himont polypropylene polymer. Processing
conditions included a throughput of 1.5 pounds per inch per
hour with the use of attenuating air flowing at a rate of 580
cubic feet per minute at a temperature of 490°F. The forming
distance between the meltblown die tip and the forming surface
was 9.5 inches and the forming wire onto which the web was
deposited was traveling at a rate of 204 feet per minute. The
sample had a basis weight of 7.2 grams per square meter with
an average fiber diameter of 2.6 microns with 97 percent of
the fibers having fiber diameters below 7 microns. The wet and
dry MD peak load tensile strengths were 556 grams and 584 grams
respectively and the wet and dry CD peak load tensile strengths
were 251 grams and 231 grams respectively. As a result, the
wet to dry strength ratios in both the MD and CD directions
were 0.95 and 1.09 respectively. The absorbent core wrap had
dry elongation at peak load percentages in the MD and CD
directions of 6 and 10 percent respectively. Frazier air
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permeability was measured to be 492 cubic feet per square foot
per minute. Using the above described Coulter porometer pore
size test, the mean flow pore size of the meltblown core wrap
was 26 microns. Less than 5 percent of these pores were larger
than 5o microns. Using the shake box shake-out test described
above, the sample was found to have a shake out of 2.0
- milligrams of superabsorbent. A comparative diaper tissue
sample used by Kimberly-Clark Corporation will generally have
MD and CD wet and dry peak load ensile strength ratios much
less than o.5 in either direction. The Frazier air
permeability of such a paper tissue wrap was measured to be 473
cubic feet per square foot per minute and it had an average
superabsorbent shake out of 264 milligrams.
Example 6
In Example 6 a meltblown absorbent core wrap was made in
the same fashion as that of Example 5 except that the basis
weight was increased to 9.8 grams per square meter. The sample
had an average fiber diameter of 3.7 microns with 95 percent
of the fibers having fiber diameters below 7 microns. The
sample had wet MD and CD peak load tensile strengths of 884
grams and 407 grams respectively. The dry MD and CD peak load
tensile strengths were 871 grams and 407 grams respectively
and the wet to dry strength ratio in the MD and CD directions
were 1.01 and 1.0 respectively. The sample had elongations at
peak load of 7 percent in the machine direction and 13 percent
in the CD direction. The Frazier air permeability was 397
cubic feet per square foot per minute and the Coulter porometer
mean flow pore size was 27 microns. Less than 5 percent of the
pores were larger than 50 microns. Using the same shake out
test as that for Example 5, the material in Example 6 had no
measurable superabsorbent shake out.
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Example 7
In Example 7, the meltblown absorbent core wrap was also
produced with the same polymer and in the same manner as the
previous two examples except that the basis weight was further
increased to 12.2 grams per square meter. The average fiber
diameter was 4.3 microns with 89 percent of the fibers having
fiber diameters less than 7 microns. The sample material had
wet MD and CD peak load tensile strengths of 1092 grams and
542 grams respectively. The dry values were 1065 grams in the
MD direction and 519 grams in the CD direction. The wet to
dry strength ratio in the MD direction was 1.03 and 1.04 in the
CD direction. The MD and CD elongation values at peak load
were 5 percent and 12 percent respectively and the Frazier air
permeability was measured to be 317 cubic feet per square foot
per minute. The Coulter porometer mean flow pore size was 28
microns and less than 5 percent of the pores were larger than
50 microns. Shake out using the same test as with respect to
Examples 5 and 6 was less than O.1 milligrams of
superabsorbent.
Example 8'
In Example 8, the basis weight of the polypropylene
meltblown absorbent core wrap was increased to 14.2 grams per
square meter with the average fiber diameter being 4 . 0 microns .
The dry MD and CD peak load tensile strengths were 1221 grams
and 517 grams respectively and the wet MD and CD peak load
tensile strengths were 1238 grams and 530 grams respectively.
The ratio of wet to dry strength peak load tensile strengths
in the MD and CD directions were 1.01 and 1.03 respectively.
The elongation of the sample in the machine direction at peak
load was 4 percent and in the cross-machine direction was 6
percent. The Frazier air permeability of the sample was 265
cubic feet per square foot per minute and the Coulter porometer
mean flow pore size was 29 microns. Less than 5 percent of
these pores were larger than 50 microns. The sample exhibited
CA 02225467 2002-04-15
a shake out of 1.8 milligrams of superabsorbent using the same
test procedure as was used for Examples 5 through 7.
In Example 9, the same type of meltblown nonwoven web was
formed as with the previous examples using the same polymer
type. The resultant core wrap had a basis weight of 15.0 grams
per square meter and the average fiber diameter was 2.8
microns. The dry MD and CD tensile strengths at peak load were
1512 grams and 701 grams respectively and the MD and CD
elongations were 20 and 35 percent. Mean flow pore size was
microns and the maximum flow pore size was 31 microns. The
Frazier air permeability was 214 cubic feet per square foot per
15 minute and the packet shake-out superabsorbent weight was 6.8
milligrams.
The same material was also used to wrap an absorbent core
of 10 grams of the Dow 534 superabsorbent and 10 grams of
Kimberly-ClarkT CR-54 fluff to form an absorbent article. This
20 absorbent article was in turn incorporated into a diaper
construction in between a liquid pervious top sheet/body side
liner and a bottom sheet or outer cover.
Examples 1 through 9 illustrate several important
features of the present invention. The core wrap must provide
adequate superabsorbent particle containment yet the same core
wrap must provide sufficient air permeability to allow
formation of the absorbent core. The examples demonstrate that
excellent superabsorbent containment can be achieved with core
wrap materials with basis weights of 15 grams per square meter
and lower. Generally, this was found to be more achievable if
the fiber diameter of the fibers was maintained below 8 microns
and the mean flow pore size was maintained below 30 microns.
Higher basis weight materials can also be used but this adds
additional cost to the overall structure. In addition, higher
basis weights can tend to reduce the Frazier air permeability
of the material. Frazier_air permeability values below 200
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cubic feet per square foot per minute make it difficult to form
the absorbent core onto the core wrap material.
Having thus described the invention in detail, it should
be apparent that various modifications and changes can be made
to the present invention without departing from the spirit and
scope of the following claims.
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