Note: Descriptions are shown in the official language in which they were submitted.
--. CA 02290321 1999-11-24
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NONWOVEN SURFACTANT COMPOSITIONS
FOR IMPROVED DURABTLITY AND WETTING
This application is a continuation-in-part of U.S. Patent Application Serial
No. 09/138,157 filed 21 August 1998, which in turn is a continuation-in-part
of U.S. Patent
Application 08/994,828, filed 19 December 1997, which in turn is a
continuation-in-part of
U.S. Patent Application 08/898,188, filed 22 July 1997, the disclosures of
which are
incorporated herein by reference. The earliest application claims priority
from U.S.
Provisional Application No. 60/025,621, filed 04 September 1996.
FIELD OF THE INVENTION
This invention relates to nonwoven webs treated with surfactant compositions
which provide a combination of durability and controlled wetting. More
specifically, the
invention relates to nonwoven webs treated with a durable surfactant and a
fast, slow, or
intermediate-rate wetting surfactant, either by separate treatments or a
single, combined
treatment.
BACKGROUND OF THE INVENTION
Nonwoven fabrics and their manufacture have been the subject of extensive
development resulting in a wide variety of materials for numerous
applications. For
example, nonwovens of light basis weight and open structure are used in
personal care items
such as disposable diapers as liner fabrics that provide dry skin contact but
readily transmit
fluids to more absorbent materials which may also be nonwovens of a different
composition
and/or structure. Nonwovens of heavier weights may be designed with pore
structures
making them suitable for filtration, absorbent and barner applications such as
wrappers for
items to be sterilized, wipers or protective garments for medical, veterinary
or industrial
1
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~ CA 02290321 1999-11-24
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uses. Even heavier weight nonwovens have been developed for recreational,
agricultural and
construction uses. These are but a few of the practically limitless examples
of types of
nonwovens and their uses that will be known to those skilled in the art who
will also
recognize that new nonwovens and uses are constantly being identified. There
have also
been developed different ways and equipment to make nonwovens having desired
structures
and compositions suitable for these uses. Examples of such processes include
spunbonding,
meltblowing, carding, and others which will be described in greater detail
below. The
present invention has general applicability to nonwovens as will be apparent
to one skilled
in the art, and it is not to be limited by reference or examples relating to
specific nonwovens
which are merely illustrative.
It is not always possible to efficiently produce a nonwoven having all the
desired properties as formed, and it is frequently necessary to treat the
nonwoven to improve
or alter properties such as wettability by one or more fluids, repellency to
one or more fluids,
electrostatic characteristics, conductivity, and softness, to name just a few
examples.
Conventional treatments involve steps such as dipping the nonwoven in a
treatment bath,
coating or spraying the nonwoven with the treatment composition, and printing
the
nonwoven with the treatment composition. For cost and other reasons it is
usually desired
to use the minimum amount of treatment composition that will produce the
desired effect
with an acceptable degree of uniformity.
When a nonwoven web is formed of a hydrophobic material, for example, a
polyolefin, it is often desirable to modify the surface of the nonwoven web
using a
hydrophilic surfactant to increase the wettability of the web. An external
hydrophilic
surfactant is typically applied to the surface of the nonwoven web. An
internal hydrophilic
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CA 02290321 1999-11-24
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surfactant is typically blended with the polymer used to form the nonwoven
web, and later
migrates to the surface after the nonwoven web is formed.
External and internal hydrophilic surfactants may be characterized in terms
of their durability and wettability. The durability of a surfactant refers
generally to its ability
to withstand stresses, such as repeated washing cycles of the nonwoven fabric,
without being
removed from the fabric or otherwise losing its effectiveness. The wettability
of a surfactant
refers generally to its ability to transform a hydrophobic nonwoven web into a
fabric which
readily assimilates and distributes aqueous liquids. Surfactants which cause
an otherwise
hydrophobic nonwoven web to assimilate liquids at a relatively fast pace, with
high fluid
intake volumes, are referred to as faster wetting surfactants. Surfactants
which cause the
nonwoven web to assimilate aqueous liquids at a relatively slow pace, with low
fluid intake
volume, are referred to as slower wetting surfactants. In addition to the
surfactant type, other
factors affect the ability of the nonwoven web to assimilate liquids,
including without
limitation the nonwoven web type, nonwoven polymer type, fiber size and
density, amount
of surfactant, and how it is applied.
Surfactants having high durability are desirable for a variety of reasons.
However, durable surfactants often provide insufficient wetting, and do not
lend themselves
to optimization of wetting characteristics desired for individual end use
applications. There
is a need or desire for a surfactant composition having both durability and
controlled wetting,
whether the desired wetting is fast, slow or in between. There is also a need
or desire for a
nonwoven fabric having durable wetting whose rate is predetermined and
controlled.
SUMMARY OF THE INVENTION
The present invention is directed to a surfactant combination, and a nonwoven
web treated with a surfactant combination. The surfactant combination includes
a first
3
. CA 02290321 1999-11-24
surfactant which provides durable wetting characteristics, and a second
surfactant which
controls the rate of wetting (fast, slow or intermediate). Used in
combination, the surfactant
combination provides a nonwoven fabric having wetting characteristics that are
both durable
and rate-determined.
The combination of surfactants provides a nonwoven fabric with the ability
to withstand at least two and, advantageously, at least three insults using
the cradle test
described below. The first surfactant alone need not provide this level of
durability. Instead,
what is important is that the combination of surfactants (accounting for all
synergisms
between them) provides a nonwoven fabric having this level of durability.
The combination of surfactants also provides the nonwoven fabric with a
controlled rate of wetting, as characterized by the cradle test described
below. Again, it is
not important for the second surfactant alone to provide the desired fluid
intake rate. Instead,
what is important is how the two surfactants behave in the environment in
which they coexist
with each other. In this environment, the surfactants together (accounting for
all synergisms
between them) must provide a desired wetting rate as well as durable wetting
to the
nonwoven fabric.
With the foregoing in mind, it is a feature and advantage of the invention to
provide a surfactant combination which imparts durable wettability to a
nonwoven fabric at
a fast, intermediate or slow rate of wetting by an aqueous medium.
It is alsa a feature and advantage of the invention to provide a nonwoven
fabric which is treated with the surfactant combination to effect durable
wettability at a fast,
intermediate or slow rate of wetting.
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CA 02290321 1999-11-24
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic of a cradle testing apparatus used in the test procedure
described below.
DEFINITIONS
The term "nonwoven fabric or web" means a web having a structure of
individual fibers or threads which are interlaid, but not in a regular or
identifiable manner
as in a knitted fabric. Nonwoven fabrics or webs have been formed from many
processes
such as, for example, meltblowing processes, spunbonding processes, air laying
processes,
and bonded carded web processes. The basis weight of nonwoven fabrics is
usually
expressed in ounces of material per square yard (osy) or grams per square
meter (gsm)
and the fiber diameters useful are usually expressed in microns. (Note that to
convert
from osy to gsm, multiply osy by 33.91.)
The term "microfibers" means small diameter fibers having an average
diameter not greater than about 75 microns, for example, having an average
diameter of
from about 1 micron to about 50 microns, or more particularly, microfibers may
have an
average diameter of from about 1 micron to about 30 microns. Another
frequently used
expression of fiber diameter is denier, which is defined as grams per 9000
meters of a
fiber. For a fiber having circular cross-section, denier may be calculated as
fiber diameter
in microns squared, multiplied by the density in grams/cc, multiplied by
0.00707. A
lower denier indicates a finer fiber and a higher denier indicates a thicker
or heavier fiber.
For example, the diameter of a polypropylene fiber given as 15 microns may be
converted
to denier by squaring, multiplying the result by .89 g/cc and multiplying by
.00707.
CA 02290321 1999-11-24
Thus, a 15 micron polypropylene fiber has a denier of about 1.42 (15z x 0.89 x
.00707
= 1.415). Outside the United States the unit of measurement is more commonly
the "tex,"
which is defined as the grams per kilometer of fiber. Tex may be calculated as
denier/9.
The term "spunbonded fibers" refers to small diameter fibers which are
formed by extruding molten thermoplastic material as filaments from a
plurality of fine
capillaries of a spinnerette having a circular or other configuration, with
the diameter of
the extruded filaments then being rapidly reduced as by, for example, in U.S.
Patent
4,340,563 to Appel et al., and U.S. Patent 3,692,618 to Dorschner et al., U.S.
Patent
3,802,817 to Matsuki et al., U.S. Patents 3,338,992 and 3,341,394 to Kinney,
U.S. Patent
3,502,763 to Hartman, U.S. Patent 3,502,538 to Petersen, and U.S. Patent
3,542,615 to
Dobo et al., each of which is incorporated herein in its entirety by
reference. Spunbond
fibers are quenched and generally not tacky when they are deposited onto a
collecting
surface. Spunbond fibers are generally continuous and often have average
diameters
larger than about 7 microns, more particularly, between about 10 and 30
microns.
The term "meltblown fibers" means fibers formed by extruding a molten
thermoplastic material through a plurality of fine, usually circular, die
capillaries as
molten threads or filaments into converging high velocity heated gas (e.g.,
air) streams
which attenuate the filaments of molten thermoplastic material to reduce their
diameter,
which may be to microfiber diameter. 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. Such a process is disclosed for example,
in U.S.
Patent 3,849,241 to Butin. Meltblown fibers are microfibers which may be
continuous
or discontinuous, are generally smaller than 10 microns in diameter, and are
generally self
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CA 02290321 1999-11-24
bonding when deposited onto a collecting surface. Meltblown fibers used in the
present
invention are preferably substantially continuous in length.
The term "substantially continuous filaments or fibers" refers to filaments
or fibers prepared by extrusion from a spinnerette, including without
limitation
spunbonded and meltblown fibers, which are not cut from their original length
prior to
being formed into a nonwoven web or fabric. Substantially continuous filaments
or fibers
may have average lengths ranging from greater than about 15 cm to more than
one meter,
and up to the length of the web or fabric being formed. The definition of
"substantially
continuous filaments or fibers" includes those which are not cut prior to
being formed into
a nonwoven web or fabric, but which are later cut when the nonwoven web or
fabric is
cut.
The term "staple fibers" means fibers which are natural or cut from a
manufactured filament prior to forming into a web, and which have an average
length
ranging from about 0.1-15 cm, more commonly about 0.2-7 cm.
The term "bicomponent filaments or fibers" refers to fibers which have
been formed from at least two polymers extruded from separate extruders but
spun
together to form one fiber. The polymers are arranged in substantially
constantly
positioned distinct zones across the cross-section of the bicomponent fibers
and extend
continuously along the length of the bicomponent fibers. The configuration of
such a
bicomponent fiber may be, for example, a sheath/core arrangement wherein one
polymer
is surrounded by another or may be a side-by-side arrangement or an "islands-
in-the-sea"
arrangement. Bicomponent fibers are taught in U.S. Patent 5,108,820 to Kaneko
et al.,
U.S. Patent 5,336,552 to Strack et al., and U.S. Patent 5,382,400 to Pike et
al., each of
which is incorporated herein in its entirety by reference. For two component
fibers, the
7
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CA 02290321 1999-11-24
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polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired
ratios.
Conventional additives, such as pigments and surfactants, may be incorporated
into one
or both polymer streams, or applied to the filament surfaces.
The term "monocomponent" fiber refers to a fiber formed from one or more
extruders using only one polymer. This is not meant to exclude fibers formed
from one
polymer to which small amounts of additives have been added for color, anti-
static
properties, lubrication, hydrophilicity, etc. These additives, e.g., titanium
dioxide for color,
are generally present in an amount less than 5 weight percent and more
typically about 2
weight percent.
The term "polymer" includes, but is not limited to, homopolymers,
copolymers, such as for example, block, graft, random and alternating
copolymers,
terpolymers, etc. and blends and modifications thereof. Furthermore, unless
otherwise
specifically limited, the term "polymer" shall include all possible
geometrical
configurations of the material. These configurations include, but are not
limited to
isotactic, syndiotactic and atactic symmetries.
The term "pulp fibers" refers to fibers from natural sources such as woody
and non-woody plants. Woody plants include, for example, deciduous and
coniferous
trees. Non-woody plants include, for instance, cotton, flax, esparto grass,
milkweed,
straw, jute hemp, and bagasse.
The term "average fiber length" refers to a weighted average length of
fibers determined using a Kajaani fiber analyzer Model No. FS-100 available
from
Kajaani Oy Electronics in Kajaani, Finland. Under the test procedure, a fiber
sample is
treated with a macerating liquid to ensure that no fiber bundles or shives are
present.
Each fiber sample is dispersed in hot water and diluted to about a 0.001 %
concentration.
8
CA 02290321 1999-11-24
Individual test samples are drawn in approximately 50 to 500 ml portions from
the dilute
solution and tested using the standard Kajaani fiber analysis procedure. The
average fiber
lengths may be expressed by the following equation:
k
E (X;*n;)/n
X; > 0
where k - maximum fiber length,
X; - individual fiber length,
n; - number of fibers having length X;
and n - total number of fibers measured.
The term "superabsorbent material" refers to a water-swellable, water-
insoluble organic or inorganic material capable, under the most favorable
conditions, of
absorbing at least about 15 times its weight and, more desirably, at least
about 30 times
its weight in an aqueous solution containing 0.9% by weight sodium chloride.
The term "through-air bonding" or "TAB" means a process of bonding a
nonwoven, for example, a bicomponent fiber web in which air which is
sufficiently hot to
melt one of the polymers of which the fibers of the web are made is forced
through the web.
The melting and resolidification of the polymer provides the bonding.
The term "thermal point bonding" involves passing a fabric or web of fibers
to be bonded between a heated calender roll and an anvil roll. The calender
roll is usually,
though not always, patterned in some way so that the entire fabric is not
bonded across its
entire surface. As a result, various patterns for calender rolls have been
developed for
functional as well as aesthetic reasons. One example of a pattern has points
and is the
Hansen Pennings or "H&P" pattern with about a 30% bond area with about 200
bonds/square inch as taught in U.S. Patent 3,855,046 to Hansen and Pennings.
The H&P
pattern has square point or pin bonding areas wherein each pin has a side
dimension of 0.038
9
CA 02290321 1999-11-24
inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a
depth of
bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of
about
29.5%. Another typical point bonding pattern is the expanded Hansen and
Pennings or
"EHP" bond pattern which produces a 15% bond area with a square pin having a
side
dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm)
and a depth
of 0.039 inches (0.991 mm). Another typical point bonding pattern designated
"714" has
square pin bonding areas wherein each pin has a side dimension of 0.023
inches, a spacing
of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033
inches (0.838
mm). The resulting pattern has a bonded area of about 15%. Yet another common
pattern
is the C-Star pattern which has a bond area of about 16.9%. The C-Star pattern
has a cross-
directional bar or "corduroy" design interrupted by shooting stars. Other
common patterns
include a diamond pattern with repeating and slightly offset diamonds and a
wire weave
pattern looking as the name suggests, e.g., like a window screen. Typically,
the percent
bonding area varies from around 10% to around 30% of the area of the fabric
laminate web.
As is well known in the art, the spot bonding holds the laminate layers
together as well as
imparts integrity to each individual layer by bonding filaments and/or fibers
within each
layer.
The term "personal care product" means diapers, training pants, swim wear,
absorbent underpants, baby wipes, adult incontinence products, and feminine
hygiene
products.
The term "durable wettability" or "durably wettable" means the ability to
withstand at least two and, advantageously at least 3, insults using the
runoff test
described below.
CA 02290321 1999-11-24
The term "hydrophilic" or "wettable" means that the finished polymeric
material has a surface free energy such that the polymeric material is
wettable by an
aqueous medium, i.e., a liquid medium of which water is a major component. The
finished polymeric material may have been treated with a surfactant, a
surfactant
combination, or other finishing agents.
Test Procedure
The "cradle test" referred to herein (also known as the Little MIST test)
is performed as follows. Referring to Fig. 1, two layers 12 and 14 of a sample
nonwoven
fabric are weighed, and placed in the valley of an acrylic cradle 10, against
the inner wall
of the cradle. The cradle has a length (into the page) of 33 cm with front and
back ends
blocked off, a height of 19 cm, a distance between upper arms 18 and 20 of
30.5 cm, and
an angle between the upper arms of 60 degrees. The cradle has a 6.5 cm wide
slot 16 at
its lowest point, running the length of the cradle into the page.
Each layer of the nonwoven fabric can be rectangular, with dimensions of
2.5 x 7.0 inches, or 3.0 x 7.0 inches. Then, 80 ml of blood bank saline ( 1 %
aqueous
NaCI) is injected into the center of the specimen at a rate of 20 ml/sec using
a nozzle
normal to the center of the material and 0.25 inch above the material. Fluid
not contained
by the nonwoven fabric (referred to as "mnoff ~ flows over the sample edges
and through
the center slot 16 in the cradle. The sample material is then immediately
removed from
the cradle and weighed.
Fluid held by the sample nonwoven fabric is used to calculate the
performance parameter, P, which reflects the amount of liquid withheld based
on fabric
sample volume:
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CA 02290321 1999-11-24
P - ~~rams of fluid contained x 100%
cc of dry sample
- gams of fluid contained x dry sample density,~sJcc x 100%
grams of dry sample
The nonwoven fabric sample is then desorbed by placing it on top of a
fluff/superabsorbent material composite for five minutes. The composite
contains 40%
by weight U.S. Alliance Coosa Pines CR-2054 pulp and 60% by weight of
Stockhausen
Company's FAVOR 870 superabsorbent. Other comparable materials can be used.
Then,
the desorbed sample is replaced in the cradle where it receives a second
insult of fluid.
This procedure is repeated for a total of three fluid insults, with about 30
minutes between
insults. The nonwoven fabric sample is considered to have durable hydrophilic
properties
if its performance parameter does not fall by more than 10% over three
insults.
The rate of fluid insult is also relevant to this test. Generally, the faster
the
insult, the greater the demand on the specimen to assimilate or spread out the
liquid. For the
testing of this invention, a fixed rate of 20 ml/sec was maintained.
DETAILED DESCRIPTION OF THE
PRESENTLY PREFERRED EMBODIMENTS
The starting material for the invention is a nonwoven web including a
plurality of filaments made from one or more polymers treated with a
hydrophilic surfactant
combination. The nonwoven web may be a spunbond web, a meltblown web, a bonded
carded web, or another type of nonwoven web, and may be present in a single
layer or a
multilayer composite including one or more nonwoven web layers.
The hydrophilic surfactant combination may be an internal or external
surfactant combination. An internal surfactant is one which is blended with
the polymer
used to make the nonwoven web, and which migrates to the surface of the
nonwoven web
12
f
- CA 02290321 1999-11-24
filaments during and/or after the formation of the filaments. Often, the
migration results
from a stimulus, such as heat applied to the filaments. An external surfactant
is one which
is applied externally to the surfaces of the nonwoven web filaments after they
are formed.
An external surfactant may be applied by dipping, soaking, spraying, or
otherwise coating
the nonwoven web with a medium containing the surfactant. Internal and
external surfactant
inclusion techniques are generally well known in the art.
The surfactant combination used in accordance with the invention is a
combination of two or more surfactants which impart durable hydrophilicity to
a nonwoven
web, as well as a controlled rate of wettability. Generally, the nonwoven web
is constructed
from a thermoplastic polymer which is either hydrophobic or insufficiently
hydrophilic. The
class of nonwoven webs referred to herein as "hydrophobic or insufficiently
hydrophilic"
refers to nonwoven webs which exhibit a performance parameter less than 10
using the
cradle test described above, when the nonwoven web is not treated with a
hydrophilic
surfactant.
A wide variety of thermoplastic polymers may be used to construct the
nonwoven web, including without limitation polyamides, polyesters,
polyolefins, copolymers
of ethylene and propylene, copolymers of ethylene or propylene with a C4-CZO
alpha-olefin,
terpolymers of ethylene with propylene and a C4-CZO alpha-olefin, ethylene
vinyl acetate
copolymers, propylene vinyl acetate copolymers, styrene-polyethylene-alpha-
olefin)
elastomers, polyurethanes, A-B block copolymers where A is formed of polyvinyl
arene)
moieties such as polystyrene and B is an elastomeric midblock such as a
conjugated diene
or lower alkene, polyethers, polyether esters, polyacrylates, ethylene alkyl
acrylates,
polyisobutylene, polybutadiene, isobutylene-isoprene copolymers, and
combinations of any
of the foregoing. Polyolefins are preferred. Polyethylene and polypropylene
homopolymers
13
CA 02290321 1999-11-24
and copolymers are most preferred. The webs may also be constructed of
bicomponent or
biconstituent filaments or fibers, as defined above. The nonwoven webs may
have a wide
variety of basis weights, preferably ranging from about 10 grams per square
meter (gsm) to
about 120 gsm.
It should be understood that the invention is not limited to the use of
hydrophobic and insufficiently hydrophilic polymers. The durable, controlled
wetting rate
surfactant combination may also be used to enhance the wetting performance of
nonwoven
fabric polymers which are already hydrophilic, as indicated by a performance
parameter of
at least 30% without a hydrophilic surfactant.
The hydrophilic combination of surfactants must provide durable wetting at
a controlled wetting rate. The combination may include two or more
surfactants, one of
which independently provides durable wetting, and the other of which
independently
provides controlled rate wetting. Alternatively, the surfactant combination
may include two
or more surfactants which, taken alone, do not provide one or both properties,
but which
provide durable and controlled rate wetting when acting together in synergy.
A hydrophilic surfactant combination provides "durable wetting" if the
performance parameter resulting from the third liquid insult is greater than,
equal to, or up
to 10% less than the performance parameter resulting from the first liquid
insult using the
cradle test, described above.
The hydrophilic surfactant combination must also provide wetting at a
controlled rate which may be fast, intermediate or slow. A surfactant
combination provides
a fast wetting rate if a nonwoven fabric treated with the surfactant
combination (e.g., a
nonwoven fabric made from a hydrophobic or insufficiently hydrophilic
thermoplastic
polymer) exhibits a performance parameter of at least 50% for the first fluid
insult using the
14
' , CA 02290321 1999-11-24
cradle test, described above. A hydrophilic surfactant combination provides an
intermediate
wetting rate if the performance parameter for the first fluid insult is at
least 40% and less
than 50%. A hydrophilic surfactant combination provides a slow wetting rate if
the
performance parameter for the first fluid insult is at least 30% and less than
40%.
Performance parameters below 30% are deemed insufficient.
The hydrophilic surfactant combination includes at least first and second
surfactants. The first surfactant may be a durable surfactant. The first
surfactant may
include a compound selected from an ethoxylated hydrogenated fatty acid ester,
a
monosaccharide, a monosaccharide derivative, a polysaccharide, a
polysaccharide derivative,
and combinations thereof. For instance, the first surfactant may include a
blend of
ethoxylated hydrogenated castor oil and sorbitan monooleate. One such
surfactant is
AHCOVEL~ Base N-52, available from Hodgson Chemical Co.
Another first surfactant is a castor oil derivative of ethylene oxide. One
such
surfactant is sold by ICI Surfactant, Inc. under the name ATMER~ 8174.
Another suitable first surfactant may include a selected polyolefin glycol, or
a derivative of a polyolefin glycol. Examples of derivatives include
polyolefin glycol
monooleates and dioleates, polyolefin glycol monolaurates and dilaurates, and
alkyl esters
of polyolefin glycols. MAPEG~ surfactants, available from PPG Industries, are
made from
the foregoing derivatives of polyethylene glycol.
Another suitable first surfactant is a LUROL~ surfactant, available from
Goulston Technologies, Inc. LUROL~ surfactants are believed to include a
polymer, a
hydrophilic part with multiple hydrophobic parts. The hydrophobic parts help
the surfactant
interface and adhere to a hydrophobic polymer substrate. LUROL~7463 and 7514
are two
samples of durable surfactants.
IS
' , CA 02290321 1999-11-24
The second surfactant may be a controlled rate wetting surfactant. The
second surfactant may be a fast wetting surfactant, an intermediate wetting
surfactant, or a
slow wetting surfactant.
Examples of second surfactants include organosilicon compounds. MASIL~
SF-19, available from BASF Chemical Co., is an ethoxylated trisiloxane-based
surfactant
which typically behaves as a fast wetting surfactant. Certain polyolefin
glycol derivatives
serve as slow or intermediate surfactants. ANTAROX~ surfactant, available from
Rhone-
Poluene Chemical Co., includes alkyl ether ethoxylates derived from
polyethylene glycol
and polypropylene glycol, and may cause slow or intermediate wetting depending
on the
substrate. Another second surfactant may include an alkyl polyglycoside.
GLUCOPON~
220UP is a solution of 60% octylpolyglycoside and 40% water, and may serve as
a slow or
intermediate surfactant when used in combination with a first surfactant, such
as a blend of
ethoxylated hydrogenated castor oil and sorbitan monooleate.
Other second surfactants include ionic sulfonate-based surfactants, for
example dodecylbenzene sulfonate sold under the name BIOSOFT'~ by Stephen Co.
Another
ionic surfactant is AEROSOL OT, sold by the Cytec Corporation. Ionic
surfactants alone
are often fast-wetting but not durable.
The surfactant combination may include about 5-95 parts by weight first
surfactant and about 5-95 parts by weight second surfactant, based on dry
solids, per 100
parts by weight of both surfactants combined. Commonly, the surfactant
combination may
include about 25-90 parts by weight first surfactant and about 10-75 parts by
weight second
surfactant. Desirably, the surfactant combination may include about 40-80
parts by weight
first surfactant and about 10-60 parts by weight second surfactant. Regardless
of how the
surfactants behave alone, the first surfactant generally contributes
durability to the
16
CA 02290321 1999-11-24
combination, and the second surfactant generally contributes controlled rate
wetting. Often,
the performance of both surfactants is synergized and enhanced by the
combination.
The surfactant combination may be applied using internal and/or external
application techniques well known in the art. The first and second surfactants
may be
applied in separate steps, or together. If one or both surfactants are applied
externally using
a solvent, the solvent may be removed using conventional evaporation
techniques. On a
solvent-free weight basis, the surfactant combination should constitute about
0.1-10% by
weight of the nonwoven fabric to which it is applied, preferably about 0.5-5%
by weight,
more preferably about 1-3% by weight. Higher levels of surfactant combination
are less
desirable, due to cost and other issues. Levels which are too low tend to
impart less
wettability to the nonwoven fabric.
The nonwoven fabrics thus formed have wettability which is both durable and
rate-determined. The treated nonwoven fabric can be used in a wide variety of
absorbent
product applications including, in particular, personal care absorbent
products. Personal care
absorbent products include diapers, training pants, swim wear, absorbent
underpants, baby
wipes, adult incontinence products, feminine hygiene products, and the like,
as well as other
surge and intake material products. In most absorbent products, the treated
nonwoven fabric
is used as a cover sheet or containment matrix for an absorbent media. An
absorbent
medium may include, for instance, pulp fibers alone or in combination with a
superabsorbent
material. The treated nonwoven fabric can also be used in medical absorbent
products,
including without limitation underpads, absorbent drapes, bandages, and
medical wipes.
The pulp fibers may be any high-average fiber length pulp, low-average fiber
length pulp, or mixtures of the same. Preferred pulp fibers include cellulose
fibers. The term
"high average fiber length pulp" refers to pulp that contains a relatively
small amount of
17
' CA 02290321 1999-11-24
short fibers and non-fiber particles. High fiber length pulps typically have
an average fiber
length greater than about 1.5 mm, preferably about 1.5-6 mm, as determined by
an optical
fiber analyzer, such as the Kajaani tester referenced above. Sources generally
include non-
secondary (virgin) fibers as well as secondary fiber pulp which has been
screened. Examples
of high average fiber length pulps include bleached and unbleached virgin
softwood fiber
pulps.
The term "low average fiber length pulp" refers to pulp that contains a
significant amount of short fibers and non-fiber particles. Low average fiber
length pulps
have an average fiber length less than about 1.5 mm, preferably about 0.7-1.2
mm, as
determined by an optical fiber analyzer such as the Kajaani tester referenced
above.
Examples of low fiber length pulps include virgin hardwood pulp, as well as
secondary fiber
pulp from sources such as office waste, newsprint, and paperboard scrap.
Examples of high average fiber length wood pulps include those available
from the U.S. Alliance Coosa Pines Corporation under the trade designations
Longlac 19,
Coosa River 56, and Coosa River 57. The low average fiber length pulps may
include
certain virgin hardwood pulp and secondary (i.e., recycled) fiber pulp from
sources including
newsprint, reclaimed paperboard, and once waste. Mixtures of high average
fiber length
and low average fiber length pulps may contain a predominance of low average
fiber length
pulps. For example, mixtures may contain more than about 50% by weight low-
average
fiber length pulp and less than about 50% by weight high-average fiber length
pulp.
The term "superabsorbent" or "superabsorbent material" refers to a water
swellable, water-insoluble organic or inorganic material capable, under the
most favorable
conditions, of absorbing at least about 15 times its weight and, more
desirably, at least about
30 times its weight in an aqueous solution containing 0.9% by weight sodium
chloride.
18
' CA 02290321 1999-11-24
The superabsorbent materials can be natural, synthetic and modified natural
polymers and materials. In addition, the superabsorbent materials can be
inorganic
materials, such as silica gels, or organic compounds such as cross-linked
polymers. The
term "cross-linked" refers to any means for effectively rendering normally
water-soluble
materials substantially water insoluble but swellable. Such means can include,
for example,
physical entanglement, crystalline domains, covalent bonds, ionic complexes
and
associations, hydrophilic associations, such as hydrogen bonding, and
hydrophobic
associations or Van der Waals forces.
Examples of synthetic superabsorbent material polymers include the alkali
metal and ammonium salts of poly(acrylic acid) and poly(methacrylic acid),
poly(acrylamides), polyvinyl ethers), malefic anhydride copolymers with vinyl
ethers and
alpha-olefins, polyvinyl pyrrolidone), poly(vinylmorpholinone), polyvinyl
alcohol), and
mixtures and copolymers thereof. Further superabsorbent materials include
natural and
modified natural polymers, such as hydrolyzed acrylonitrile-grafted starch,
acrylic acid
grafted starch, methyl cellulose, chitosan, carboxymethyl cellulose,
hydroxypropyl cellulose,
and the natural gums, such as alginates, xanthan gum, locust bean gum and the
like.
Mixtures of natural and wholly or partially synthetic superabsorbent polymers
can also be
useful in the present invention. Other suitable absorbent gelling materials
are disclosed by
Assarsson et al. in U.S. Patent 3,901,236 issued August 26, 1975. Processes
for preparing
synthetic absorbent gelling polymers are disclosed in U.S. Patent No.
4,076,633 issued
February 28, 1978 to Edwards et al. and U.S. Patent No. 4,286,082 issued
August 25, 1981
to Tsubakimoto et al.
Superabsorbent materials may be xerogels which form hydrogels when
wetted. The term "hydrogel," however, has commonly been used to also refer to
both the
19
CA 02290321 1999-11-24
wetted and unwetted forms of the superabsorbent polymer material. The
superabsorbent
materials can be in many forms such as flakes, powders, particulates, fibers,
continuous
fibers, networks, solution spun filaments and webs. The particles can be of
any desired
shape, for example, spiral or semi-spiral, cubic, rod-like, polyhedral, etc.
Needles, flakes,
fibers, and combinations may also be used.
Superabsorbents are generally available in particle sizes ranging from about
20 to about 1000 microns. Examples of commercially available particulate
superabsorbents
include SANWET'~ IM 3900 and SANWET~' IM-SOOOP, available from Hoescht
Celanese
located in Portsmouth, Virginia, DRYTECH~ 2035LD available from Dow Chemical
Co.
located in Midland, Michigan, and FAVOR~ 880, available from Stockhausen,
located in
Greensboro, North Carolina. An example of a fibrous superabsorbent is OASIS~
101,
available from Technical Absorbents, located in Grimsby, United Kingdom.
As indicated above, the nonwoven fabric may be a cover sheet or a matrix for
an absorbent medium. When employed as a matrix, the nonwoven filaments may be
combined with pulp fibers and (optionally) a superabsorbent material using
processes well
known in the art. For example, a coform process may be employed, in which at
least one
meltblown diehead is axranged near a chute through which other materials are
added while
the web is forming. Coform processes are described in U.S. Patent 4,818,464 to
Lau and
4,100,324 to Anderson et al., the disclosures of which are incorporated by
reference. The
substantially continuous bicomponent filaments and pulp fibers may also be
combined using
hydraulic entangling or mechanical entangling. A hydraulic entangling process
is described
in U.S. Patent 3,485,706 to Evans, the disclosure of which is incorporated by
reference.
When the thermoplastic nonwoven filaments are used as a matrix for an
absorbent nonwoven web composite, the composite should contain about 5-97% by
weight
CA 02290321 1999-11-24
pulp fibers, preferably about 35-95% by weight pulp fibers, more preferably
about 50-95%
by weight pulp fibers. When a superabsorbent material is present, it should
constitute about
5-90% by weight of the composite, preferably about 10-60% by weight, more
preferably
about 20-50% by weight. In either case, the thermoplastic nonwoven filament
matrix should
constitute about 3-95% by weight of the composite, preferably about 5-65% by
weight, more
preferably about 5-50% by weight.
After combining the ingredients together, the absorbent nonwoven composite
may be bonded together using the thermal point bonding or through-air bonding
techniques
described above, to provide a coherent high integrity structure.
Examples
For Examples 1-18, the nonwoven fabric employed was a polypropylene/
polyethylene side-by-side bicomponent. The surfactants were added internally
by
compounding into one or both polymer resins using a heated 30 mm twin screw
extruder,
prior to formation of the spunbond filaments. The resulting surfactant/
polymer concentrates
were then added to one or both melt streams in the fiber spinning process,
prior to extrusion.
The resulting treated nonwoven fabrics were then evaluated using the cradle
test described
above. For each of these tests, two rectangular fabric samples having
dimensions of 2.5 in
x 7.0 in were employed. The results of the evaluations are shown in Table 1.
21
CA 02290321 1999-11-24
Table 1: Surfactants Added Internally
Level Web Performance
Parameter,
T i Fib W W
t % Si i b
ht
rea ) er e e
- n ze, g
( ,
went Loca-Denier Ounces/Density1st 2nd 3rd
per
xam do tionFilamentdZ cc InsultInsultInsultChan Comments
le a
2.5 Intermediate,
1 SF19 in 2.1 2.48 0.02445 40 30 -33
PP Not Durable
2 Antarox3 2.2 3.32 0.02130 29 19 _37 Slow,
in
PP
Not Durable
3 Antarox3 1.7 2.67 0.02338 32 20 ~7 Slow,
in
PP
Not Durable
4 Ahcovel3 not wettable
in
PP
Antarox/
5* Mapeg 3 2.3 3.14 0.02529 28 31 +7 Insufficient,
~
PP
400 Durable
ML
1/1
SF
19/
6* 3 1.9 3.96 0.03438 36 36 -5
m
PE
00 Dm.able
ML
1/1
Antarox/
7* 3 1.9 3.35 0.03034 33 32 -6
m
PE
00 D,,~ble
ML
1/1
Antarox/
8 Atmer 3 1.9 3.60 0.03112 21 23 +92 Insufficient
in
PE
8042
1/1
SF
19/
Mapeg 2 1.2 2.68 0.02550 35 30 -40 Fit,
~
PP
400 Not Durable
ML
1/1
SF
19/
3 1.2 2.70 0.02551 45 37 -27 Fast
m
PP
00 ,
ML
1/1 Not Durable
SF
19/
11 Mapeg 3 1.2 2.77 0.02650 45 41 _ Fast,
in 1
PP g
600 Not Durable
DO
1/1
SF
19/
F~~
~covel2 1.2 2.63 0.02651 47 43 -16
in
PP
12 Not Durable
1/1
22
CA 02290321 1999-11-24
Level Web Performance
Parameter,
Treat-(%) Fiber Wei W
in Size ht b
, g e
,
ment Loca-Denier Ounces/Density1st 2nd 3rd
per
Exam atio tion Filamentd~ cc InsultInsultInsultChan Comments
to a
SF
19/
13 Mapeg 3 1.2 2.66 0.03154 50 46 -15 Fast'
in
PP
600 Not Durable
DS
1/1
14 SF19/ 2 1.2 3.01 0.02748 47 45 _6 Intermediate,
~
Atmer both Durable
SF
19/
Ahcovel,
15 PP, 2 1.2 2.60 0.03051 50 50 _2 Fast,
m
SF19/ both Durable
Atmer,
PE
SF
19/
F~~
16 Ahcovel3 1.2 2.25 0.02952 50 50 -'1
in
PP
Doable
1/1
SF
19/
Slow,
17 Ahcovel3 3.0 2.54 0.02339 43 41 +5
in
PP
Durable
1/1
SF
19/
Slow,
~, Ahcovel3 3.0 2.25 0.02531 36 37 +19
18 in
PP
Dm.able
1/2
* (Tests conducted on 3x7" samples in a different cradle setup)
For Examples 19-33, the same nonwoven fabric was used, but the surfactants
were added externally instead of internally. An aqueous surfactant
mixture/emulsion was
applied to the nonwoven fabric using dipping followed by vacuum drying, or
foam
application. The surfactant levels employed (on a solvent free basis) were
somewhat lower
than for Examples 1-18. However, when surfactants are added externally instead
of
internally, the entire amount added is present at the surface where it
achieves the greatest
wetting. The treated nonwoven fabrics were evaluated using the cradle test.
The results are
shown in Table 2.
23
CA 02290321 1999-11-24
Table 2: Surfactants Added Externally
Web
Treat- Fiber Weight,Web __Performance
Size, Parameter,
~
went Add-onDenier Ounces/Densitylst 2nd 3rd
per
xam atio % FilamentdZ cc InsultInsultInsultChan Comments
le a
Intermediate,
19 SF 0.15 1.1 2.5 0.03046 37 31 -33
19
Not Durable
Intermediate
20 SF19 0.38 1.1 2.5 0.03048 42 32 -33
Not Durable
Intermediate,
21 SF19 0.75 1.1 2.5 0.03046 43 39 -15
Not Durable
Intermediate,
22 SF19 1.5 1.1 2.5 0.03047 44 41 -13
Not Durable
Ahcovel/
23 Glucopon0.38 1.1 2.5 0.03014 18 21 +50 Insufficient
(3/1)
Ahcovel/
24 Glucopon0.75 1.1 2.5 0.03028 36 38 +36 Insufficient
(3/1)
Ahcovel/
Slow,
25 Glucopon1.5 1.1 2.5 0.03038 41 42 +11
Durable
(3/1)
Ahcovel/
Intermediate
26 Glucopon3.0 1.1 2.5 0.03043 41 42 -2
Doable
(3/1)
27 Ahcovel/0,75 1.1 2.5 0.03051 48 49 -4 Fast,
SF19 Durable
(3/1)
28 Ahcovel/1.5 1.2 2.5 0.03048 45 46 ~ ntermediate,
I
SF19 Durable
(3/1)
29 ~coveU1.0 1.1 2.6 0.03855 54 56 +2 Fit,
SF19 Durable
(3/1)
30 ~coveU1.0 3.0 2.7 0.02443 43 43 0 ntermediate,
I
SF19 Durable
(3/1)
Ahcovel/ I ntermediate,
31 1.0 2.0 3.9 0 49 44 48 -2
029
SF19 . Durable
(3/1)
32 ~coveU1,0 3.0 2.4 0.02438 38 39 +2 Slow,
SF19 Durable
(2/1)
33 ~covel/0.6 3.0 2.8 0 40 39 40 0 ntermediate,
023 I
SF19 . Durable
3/1
As shown above, for both internally and externally added surfactants, only
certain combined surfactants gave both durability and controlled wetting.
Surfactants used
24
,,
CA 02290321 1999-11-24
individually, which exhibited sufficient wetting, did not possess durability
when applied to
the nonwoven webs. Notably, only some of the surfactant combinations delivered
both
durability and controlled wetting, while others did not. Also, the performance
of a particular
surfactant combination varied with the total amount applied, and the ratio of
ingredients
used.
Examples 34-57 illustrate the performance of additional surfactants, alone and
in combination with each other. Again, a polypropylene/polyethylene side-by-
side
bicomponent nonwoven web was used (with average fiber size of 1.1 dpf, basis
weight of
2.7 osy, and density of 0.03 g/cc). The surfactants were added externally. For
some of the
samples (Examples 34-36 and 43-45), a minor quantity of hexanol (0.5%) was
added with
the surfactants to ease the treatment. Table 3 gives the results of the cradle
test. Again, a
surfactant (LLIROL), which alone is slow or insufficient, operates much faster
(with
durability) when used with a co-surfactant, and also operates more effectively
at lower levels
of the combination.
Table 3: Surfactants Added Externally
Performance
Parameter,
Treatment Add-on 1st 2nd 3rd
Exam do % InsultInsultInsultChan Comments
le a
34 Luro17463 0.5 16 20 21 +31 Insufficient
35 Luro17463 1.0 28 34 42 +50 Insufficient
Intermediate,
36 Luro17463 1.9 40 46 47 +18 Doable
37 Luro17463 0.5 27 21 28 +4 Insufficient
Intermediate,
38 Luro17463 1.0 43 49 50 +17 Durable
Intermediate,
39 Luro17463 1.9 40 49 50 +25 Durable
40 Aerosol 0.5 55 52 46 -16 Fast, Not
OT Durable
41 Aerosol 1.0 56 52 47 -16 Fast, Not
OT Durable
CA 02290321 1999-11-24
Performance
Parameter,
Treatment Add-on1st 2nd 3rd
Exam do % InsultInsultInsultChan Comments
le a
42 Aerosol 1.9 54 51 44 -19 Fast, Not
OT Durable
Lurol/Glucopon0.5 39 47 35 -10 Slow
Durable
43 (3/1) ,
Luro (3 1.0 38 49 52 +37 Slow
i~ opon Durable
,
45 Lm'ol/ Glucopon2.0 45 50 52 +16 Intermediate,
(3/1) Durable
46 Lm' ~3 ~ 0.5 61 60 52 -15 Fast
osol Not Durable
,
47 Lur ( A 1.0 58 55 56 -3 Fast
~ osol Durable
,
48 Lar ~ i~osol2.0 57 54 53 -7 Fast
Durable
,
Lurol/Aerosol Intermediate,
49 0.5 44 49 50 +14
(9/1) Dm.able
Lurol/Aerosol Intermediate,
50 I.0 47 50 56 +19
(9/1) Dm.able
Lurol/Aerosol Intermediate,
51 2.1 43 52 53 +23
(9/I) Durable
Lurol/Masil Intermediate,
52 SF19 0.5 49 50 27 -45
(3/I) Not Durable
Lurol/Masil
I~ SF19 1.0 51 53 54 +6 Fast
53 Durable
, (3/1) ,
54 L~ol/Masjl 2,0 53 50 52 -2 Fast
SF19 Durable
,
55 LurolBiosoft0.6 23 28 33 +43 Insufficient
(3/1)
56 LurolBiosoft1.1 35 45 49 +40 Slow, Durable
(3/1)
57 LurolBiosoft(3/I)2.0 45 49 53 +Ig Intermediate,
Durable
While the embodiments disclosed herein are presently preferred, various
modifications and improvements can be made without departing from the spirit
and scope
of the invention. The scope of the invention is indicated by the appended
claims, and all
26
CA 02290321 1999-11-24
changes that fall within the meaning and range of equivalents are intended to
be embraced
therein.
27
