Treatment of materials to improve handling of viscoelastic fluids

Disclosed is an improved structure that includes a nonwoven web including a viscoelastant treatment. The treated web, when contacted by a viscoelastic fluid such as menses alters the viscoelastic properties of the fluid and enhances its wicking and distribution throughout the absorbent structure. A desirable viscoelastant is a alkyl polyglycoside, particularly those having 8 to 10 carbon atoms in the alkyl chain. When applied so as to provide an amount of about 0.1% to about 5.0% solids add-on based on the weight of the dry nonwoven web, rapid fluid wicking and distribution may be obtained. Other viscoelastants are disclosed. Advantageously the treatment may be applied as a high solids composition using conventional application means such as spray coaters and the like or as an internal additive. The absorbent structure finds particular utility as a distribution layer component of a sanitary napkin for absorbing menses as well as other blood handling products such as surgical drapes, for example.

BACKGROUND 
There are numerous applications for materials that can rapidly absorb 
and/or transfer fluids such as bodily wastes and the like. Examples 
include disposable personal care products such as disposable diapers and 
training pants, feminine hygiene products such as sanitary napkins and 
tampons, and incontinent care products such as pads and undergarments. 
Other industrial products such as wipers, oilsorb products and soakers 
have such requirements as do health care items such as bandages, for 
example. Because these fluids have different properties, it is difficult 
to provide a material adapted to fill many of these needs with an economy 
consistent with disposability that many such applications require. In 
particular, fluids such as menses, for example, have viscoelastic 
properties that challenge traditional absorption and distribution 
concepts. The viscosity and/or elastic components of such fluids tend to 
impose unique requirements for absorption and/or distribution. These 
requirements are often inconsistent with the best performance with respect 
to other components of the fluid that are less viscous or elastic with the 
result that a compromise in overall performance usually is required. For 
example, the pore and capillary sizes in an ideal material for absorbing 
and distributing less viscoelastic components are different from those 
that work best for the more viscoelastic components. Much effort has been 
expended to develop a material structure in nonwovens, foams, films and 
the like that meets all of these needs, but without complete success. 
Another approach is to modify the viscoelastic properties of the fluid 
itself. Numerous approaches have been employed to modify the bulk 
properties of viscoelastic fluids, including agents which affect 
intermolecular bonding and the physical entanglements of macromolecules. 
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. For many applications the ability to wick or 
transport viscous fluids such as menses is important for effective 
performance of these products by distributing the fluid to provide maximum 
use of absorbent properties of that or underlying materials. For other 
applications, nonwovens of heavier weights may be designed with pore 
structures making them suitable for filtration, absorbent and barrier 
applications such as wrappers for items to be sterilized, wipers or 
protective garments for medical, veterinary or industrial 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, wicking or distribution properties, 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. It is known, for example, 
that the heat of an additional drying step to remove water applied with 
the treatment composition can deleteriously affect strength properties of 
the nonwoven as well as add cost to the process. It is, therefore, desired 
to provide an improved treatment process and/or composition for nonwovens 
that can efficiently and effectively apply the desired treatment without 
adversely affecting desirable nonwoven web properties while also achieving 
the desired results. More particularly, it is desired to provide a treated 
nonwoven adapted for use with viscoelastic fluids and having the property 
of altering the characteristics such as viscosity and/or elasticity of a 
viscoelastic insult liquid so as to control fluid movement such as intake, 
distribution, and absorption, of the liquid in personal care product 
applications such as sanitary napkins. 
SUMMARY OF THE INVENTION 
The present invention is directed to structures particularly adapted to 
receive fluids having viscoelastic properties such as menses, mucous, 
blood products, feces, and others which will be apparent to those skilled 
in the art. The structures of the invention are useful as feminine hygiene 
products such as menses absorbing devices like sanitary napkins and 
tampons, infant and child care products such as disposable diapers and 
training pants, bandages, incontinent products, and products for wiping 
and absorbing oils, for example. In accordance with the invention the 
structure comprises a synthetic, often normally hydrophobic, substrate 
containing a viscoelastant agent placed so as to contact the viscoelastic 
fluid. Advantageously the substrate is a nonwoven and may be, for example, 
a spunbond, meltblown, coformed or bonded carded web. Additional 
substrates which can be used include foams and films that are fibrillated, 
apertured or otherwise treated to have fiber-like properties as well as 
laminates of these and/or nonwovens. Depending on the particular 
application, the structure may be used as a body contact liner, a 
distribution layer between a liner and an absorbent layer, an absorbent 
layer, or in more than one of these layers. On contact the structure of 
the invention alters the viscoelastic properties of the fluid so as to 
improve fluid intake, distribution and absorption properties. Desirably 
the viscoelastant agent is one that is harmless in use and environmentally 
friendly upon disposal. Useful examples include alkyl polyglycosides 
having 8-10 carbon atoms in the alkyl chain. 
These alky polyglycosides alter the viscoelastic properties of viscoelastic 
fluids as well as increase the wettability of synthetic surfaces. Other 
examples of viscoelastants include bovine lipid extract surfactant 
(Survanta, Ross Laboratories), a drug used to treat Acute Respiratory 
Distress Syndrome and Cystic Fibrosis, and enzymes such as papain or 
pepsin which cleave protein structures. Some dextrins and dextrans may 
also be used as viscoelastants. Dextrans (macrose) are polymers of glucose 
with chain-like structures and molecular weights up to, for example, 
200,000 produced from sucrose, often by bacterial action. As is known, 
dextrins (starch gum) are normally solid starch derivatives formed often 
when starch is heated either alone or with nitric acid for example, 4000 
MW dextran from Polydex Pharmaceuticals, Ltd. Of Scarborough, Canada. The 
normally hydrophobic substrate may be additionally or simultaneously 
treated for increased wettability by a surfactant if desired. The addition 
of the viscoelastant agent to the substrate may be accomplished by 
conventional means such as spraying, coating, dipping and the like 
although the use of high solids spray is advantageous in cases where 
drying and/or compression is desired to be minimized. Alternatively, in 
some cases it may be advantageous to add the viscoelastant as an internal 
additive to the polymer melt. The amount of the viscoelastant agent used 
will depend on the particular end use as well as factors such as basis 
weight and porosity of the substrate.

TEST METHODS 
The viscoelastic properties were determined by a procedure specified in the 
Operations Manual for the VILASTIC 3 Viscoelastic Analyzer (VILASTIC 
SCIENTIFIC, INC., P.O. Box 160261, Austin, Tex. 78716 USA). The instrument 
was calibrated by the manufacturer and the calibration was checked prior 
to sample measurements. The coupling fluid used was Immunosaline (VWR 
Scientific). The measurements were made in the "Stretchr" mode at a 
frequency of 0.05 Hz, with an integration time of 39 seconds, at ambient 
conditions, at the medium drive setting, and with a medium size sample 
tube (stainless steel, inside radius of 0.0916 cm, and length of 6.561 
cm). 
Wicking results were determined by a method described in U.S. Pat. No. 
5,314,582 to Nguyen and Vargas. Wicking was performed in a horizontal 
mode, at ambient conditions, with no weight used to confine samples. 
One-by-eight inch samples (eight inches in machine direction) were used, 
with a sample size of five. Results are reported as the distance wicked 
(inches) in twenty minutes. 
The following test procedure was utilized to evaluate the intake capability 
of feminine care pads. A Harvard Apparatus Syringe Pump was used to 
deliver 250 .mu.L drops of menses simulant from a 30-cc syringe at a rate 
of 3 ml/min. The fluid was delivered through 1/16 in. (I.D.) tubing 
attached to the syringe. A Plexiglas plate was used to control placement 
of the end of the tubing just slightly above the top surface of the test 
material. The pump was set to deliver a drop, then pause for thirty 
seconds before delivery of the next drop. A stopwatch was used to record 
the time taken for the drop to totally penetrate through the top layer 
into the product. A total of three drops (750 .mu.l) were delivered to a 
single test spot on a product. The product was then repositioned and a 
second test spot was insulted in the same manner. Five replicates of each 
test code were evaluated. 
The viscoelastic fluid used in the rheological and wicking studies was 
either homogenized chicken eggwhite prepared by drawing and expelling 50 
cc of eggwhite into and out of a 60 cc disposable syringe at a flow rate 
of 100 cc/minute, and repeating the process for a total of five cycles 
(Fluid A) or synthetic menses simulant as described in coassigned U.S. 
Pat. No. 5,883,231 filed as provisional patent application Ser. No. 
60/046,702 filed May 14, 1997 entitled "Artificial Bodily Fluid," the 
contents of which are incorporated herein by reference in its entirety 
(Fluid B). Fluid B contained a fluid designed to simulate the viscoelastic 
and other properties of menses. In order to prepare the fluid, blood, in 
this case defibrinated swine blood, was separated by centrifugation at 
3000 rpm for 30 minutes, though other methods or speeds and times may be 
used if effective. The plasma was separated and stored separately, the 
buffy coat removed and discarded and the packed red blood cells stored 
separately as well. Eggs, in this case jumbo chicken eggs, were separated, 
the yolk and chalazae discarded and the egg white retained. The egg white 
was separated into thick and thin portions by straining the white through 
a 1000 micron nylon mesh for about 3 minutes, and the thinner portion 
discarded. Note that alternative mesh sizes may be used and the time or 
method may be varied provided the viscosity is at least that required. The 
thick portion of egg white which was retained on the mesh was collected 
and drawn into a 60 cc syringe which was then placed on a programmable 
syringe pump and homogenized by expelling and refilling the contents five 
times. In this example, the amount of homogenization was controlled by the 
syringe pump rate of about 100 ml/min, and the tubing inside diameter of 
about 0.12 inches. After homogenizing the thick egg white had a viscosity 
of about 20 centipoise at 150 sec.sup.-1 and it was then placed in the 
centrifuge and spun to remove debris and air bubbles at about 3000 rpm for 
about 10 minutes, though any effective method to remove debris and bubbles 
may be used. 
After centrifuging, the thick, homogenized egg white, which contains 
ovomucin, was added to a 300 cc Fenwal.RTM. Transfer pack using a syringe. 
Then 60 cc of the swine plasma was added to the transfer pack. The 
transfer pack was clamped, all air bubbles removed, and placed in a 
Stomacher lab blender where it was blended at normal (or medium) speed for 
about 2 minutes. The transfer pack was then removed from the blender, 60 
cc of swine red blood cells were added, and the contents mixed by hand 
kneading for about 2 minutes or until the contents appeared homogenous. A 
hematocrit of the final mixture showed a red blood cell content of about 
30 weight percent and generally should be at least within a range of 28-32 
weight percent for artificial menses made according to this example. The 
amount of egg white was about 40 weight percent. 
The ingredients and equipment used in the preparation of this artificial 
menses are readily available. Below is a listing of sources for the items 
used in the example, though of course other sources may be used providing 
they are approximately equivalent. 
Blood (swine): Cocalico Biologicals, Inc., 449 Stevens Rd., Reamstown, Pa. 
17567, (717) 336-1990. 
Fenwal.RTM. Transfer pack container, 300 ml, with coupler, code 4R2014: 
Baxter Healthcare Corporation, Fenwal Division, Deerfield, Ill. 60015. 
Harvard Apparatus Programmable Syringe Pump model no. 55-4143: Harvard 
Apparatus, South Natick, Mass. 01760. 
Stomacher 400 laboratory blender model no. BA 7021, serial no. 31968: 
Seward Medical, London, England, UK. 
1000 micron mesh, item no. CMN-1000-B: Small Parts, Inc., PO Box 4650, 
Miami Lakes, Fla. 33014-0650. 
Hemata Stat-II device to measure hemocrits, serial no. 1194Z03127: 
Separation Technology, Inc., 1096 Rainer Drive, Altamont Springs, Fla. 
32714. 
DETAILED DESCRIPTION OF THE INVENTION 
DEFINITIONS 
As used herein the term "viscoelastic" means a composition having at least 
one significant component that is moderately viscous and/or has elastic 
properties. By "moderately viscous" it is meant that the component has a 
viscosity of at least that of normal human blood plasma. By "elastic" it 
is meant that the component has elasticity equal to or greater than normal 
human blood plasma. 
As used herein, the term "viscoelastant" means an organic agent that, when 
an effective amount is contacted by a viscoelastic composition, materially 
alters the properties of that viscoelastic composition, for example, by 
reducing its viscosity and/or elastic nature. By "materially alters" it is 
meant that the property measured as described is changed by at least a 
statistically significant amount and, advantageously, this change will be 
at least about 30% for many applications. 
As used herein 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. The term also 
includes individual filaments and strands, yarns or tows as well as foams 
and films that have been fibrillated, apertured, or otherwise treated to 
impart fabric-like properties. Nonwoven fabrics or webs have been formed 
from many processes such as for example, meltblowing processes, 
spunbonding 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). 
As used herein 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 0.5 microns to about 50 microns, or more 
particularly, microfibers may have an average diameter of from about 2 
microns to about 40 microns. Another frequently used expression of fiber 
diameter is denier, which is defined as grams per 9000 meters of a fiber 
and 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 0.89 g/cc and 
multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a denier 
of about 1.42 (15.sup.2 .times.0.89.times.0.00707=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. 
As used herein the term "spunbonded fibers" refers to small diameter fibers 
which are formed by extruding molten thermoplastic material as filaments 
from a plurality of fine, usually circular capillaries of a spinneret with 
the diameter of the extruded filaments then being rapidly reduced as, for 
example, described in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. 
Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki 
et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 
3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 to Levy, and U.S. Pat. No. 
3,542,615 to Dobo et al. Spunbond fibers are quenched and generally not 
tacky when they are deposited onto a collecting surface. Spunbond fibers 
are generally continuous and have average diameters frequently larger than 
7 microns, more particularly, between about 10 and 20 microns. 
As used herein 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, usually 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 often while still tacky to form a web of randomly dispersed 
meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. 
No. 3,849,241 to Butin. Meltblown fibers are microfibers which may be 
continuous or discontinuous and are generally smaller than 10 microns in 
average diameter. 
As used herein "bonded carded webs" or "BCW" refers to nonwoven webs formed 
by carding processes as are known to those skilled in the art and further 
described, for example, in coassigned U.S. Pat. No. 4,488,928 to Alikhan 
and Schmidt which is incorporated herein in its entirety by reference. 
Briefly, carding processes involve starting with a blend of, for example, 
staple fibers with bonding fibers or other bonding components in a bulky 
batt that is combed or otherwise treated to provide a generally uniform 
basis weight. This web is heated or otherwise treated to activate the 
adhesive component resulting in an integrated, usually lofty nonwoven 
material. 
As used herein the term "polymer" generally 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 configuration of the 
material. These configurations include, but are not limited to isotactic, 
syndiotactic and random symmetries. 
As used herein 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. 
As used herein the term "conjugate fibers" refers to fibers which have been 
formed from at least two polymers extruded from separate extruders but 
spun together to form one fiber. Conjugate fibers are also sometimes 
referred to as multicomponent or bicomponent fibers. The polymers are 
usually different from each other though conjugate fibers may be 
monocomponent fibers. The polymers are arranged in substantially 
constantly positioned distinct zones across the cross-section of the 
conjugate fibers and extend continuously along the length of the conjugate 
fibers. The configuration of such a conjugate 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. 
Conjugate fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al., 
U.S. Pat. No. 5,336,552 to Strack et al., and U.S. Pat. No. 5,382,400 to 
Pike et al. For two component fibers, the polymers may be present in 
ratios of 75/25, 50/50, 25/75 or any other desired ratios. 
As used herein the term "biconstituent fibers" refers to fibers which have 
been formed from at least two polymers extruded from the same extruder as 
a blend. The term "blend" is defined below. Biconstituent fibers do not 
have the various polymer components arranged in relatively constantly 
positioned distinct zones across the cross-sectional area of the fiber and 
the various polymers are usually not continuous along the entire length of 
the fiber, instead usually forming fibrils or protofibrils which start and 
end at random. Biconstituent fibers are sometimes also referred to as 
multiconstituent fibers. Fibers of this general type are discussed in, for 
example, U.S. Pat. No. 5,108,827 to Gessner. Bicomponent and biconstituent 
fibers are also discussed in the textbook Polymer Blends and Composites by 
John is A. Manson and Leslie H. Sperling, copyright 1976 by Plenum Press, 
a division of Plenum Publishing Corporation of New York, IBSN 
0-306-30831-2, at pages 273 through 277. 
As used herein the term "blend" as applied to polymers, means a mixture of 
two or more polymers while the term "alloy" means a sub-class of blends 
wherein the components are immiscible but have been compatibilized. 
"Miscibility" and "immiscibility" are defined as blends having negative 
and positive values, respectively, for the free energy of mixing. Further, 
"compatibilization" is defined as the process of modifying the interfacial 
properties of an immiscible polymer blend in order to make an alloy. 
As used herein, 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 air velocity is often between 
100 and 500 feet per minute and the dwell time may be as long as 6 
seconds. The melting and resolidification of the polymer provide the 
bonding. Through air bonding has restricted variability and is often 
regarded a second step bonding process. Since TAB requires the melting of 
at least one component to accomplish bonding, it is restricted to webs 
with two components such as bicomponent fiber webs or webs containing an 
adhesive fiber, powder or the like. TAB is frequently used to bond BCW 
materials. 
As used herein "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. Pat. No. 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 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 in 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. 
As used herein, the term "personal care product" means diapers, training 
pants, absorbent underpants, adult incontinence products, sanitary wipes 
and feminine hygiene products such as sanitary napkins and tampons. 
As used herein, the term "hydrophilic" means that the 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 term "hydrophobic" includes those materials that are not 
hydrophilic as defined. The phrase "naturally hydrophobic"refers to those 
materials that are hydrophobic in their chemical composition state without 
additives or treatments affecting the hydrophobicity. It will be 
recognized that hydrophobic materials may be treated internally or 
externally with surfactants and the like to render them hydrophilic. 
It is also possible to have other materials blended with the polymer used 
to produce a nonwoven according to this invention such as pigments to give 
each layer the same or distinct colors. Pigments for spunbond and 
meltblown thermoplastic polymers are known in the art and are internal 
additives. A pigment, if used, is generally present in an amount less than 
about 5 weight percent of the layer while other additives may be present 
in a cumulative amount less than about 25 weight percent. 
The fibers from which the fabric of this invention is made may be produced, 
for example, by the meltblowing or spunbonding processes, including those 
producing bicomponent, biconstituent or polymer blend fibers which are 
well known in the art. These processes generally use an extruder to supply 
melted thermoplastic polymer to a spinneret where the polymer is fiberized 
to yield fibers which may be staple length or longer. The fibers are then 
drawn, usually pneumatically, and deposited on a moving formations mat or 
belt to form the nonwoven fabric. The fibers produced in the spunbond and 
meltblown processes are microfibers as defined above. 
The manufacture of meltblown webs is discussed generally above and in the 
references. 
As mentioned, the nonwoven also may be a bonded carded web. Bonded carded 
webs are made from staple fibers, which are usually purchased in bales. 
The bales are placed in a picker, which separates the fibers. Then, the 
fibers are sent through a combing or carding unit, which further breaks 
apart and aligns the staple fibers in the machine direction to form a 
generally machine direction-oriented fibrous nonwoven web. Once the web is 
formed, it then is bonded by one or more of several known bonding methods. 
One such bonding method is powder bonding, wherein a powdered adhesive is 
distributed through the web and then activated, usually by heating the web 
and adhesive with hot air. Another suitable bonding method is pattern 
bonding, wherein heated calender rolls or ultrasonic bonding equipment are 
used to bond the fibers together, usually in a localized bond pattern, 
though the web can be bonded across its entire surface if so desired. 
Another suitable bonding method, particularly when using bicomponent 
staple fibers, is through-air bonding. 
The fabric used in this invention may be a multilayer laminate. An example 
of multilayer laminate is an embodiment wherein some of the layers are 
spunbond and some meltblown such as a spunbond/meltblown/spunbond (SMS) 
laminate as disclosed in U.S. Pat. No. 4,041,203 to Brock et al., U.S. 
Pat. No. 5,169,706 to Collier, et al, and U.S. Pat. No. 4,374,888 to 
Bornslaeger. Such a laminate may be made by sequentially depositing onto a 
moving forming belt first a spunbond fabric layer, then a meltblown fabric 
layer and last another spunbond layer and then bonding the laminate in a 
manner described below. Alternatively, the fabric layers may be made 
individually, collected in rolls, and combined in a separate bonding step. 
Such fabrics usually have a basis weight of from about 0.1 to 12 osy (6 to 
400 gsm), or more particularly from about 0.75 to about 3 osy. The 
treatment in accordance with the invention may be carried out inline with 
the nonwoven manufacturing process or offline on previously produced 
substrates or nonwovens. 
Spunbond nonwoven fabrics are generally bonded in some manner as they are 
produced in order to give them sufficient structural integrity to 
withstand the rigors of further processing into a finished product. 
Bonding can be accomplished in a number of ways such as hydroentanglement, 
needling, ultrasonic bonding, adhesive bonding, stitchbonding, through-air 
bonding and thermal bonding. 
For some applications it may be desired to apply a corona treatment to the 
web or otherwise expose it to a reactive species prior to applying the 
viscoelastant. Such treatments are described in coassigned U.S. Pat. No. 
5,814,567 to Yahiaoui, Ning, Bolian, McDowall, Potts and Van Hout filed 
Jun. 14, 1996, incorporated herein in its entirety by reference. 
The field of reactive species serves to increase the affinity of the 
hydrophilic polymeric material for the porous hydrophobic polymer 
substrate. The field of reactive species may be, by way of example, a 
corona field. As another example, the field of reactive species may be a 
plasma field. 
Without wishing to be bound by theory, it is believed that exposure of the 
porous hydrophobic polymer substrate to a field of reactive species 
results in alterations of the surfaces of the substrate, thereby 
temporarily raising the surface energy of the substrate. This, in turn, 
allows the penetration of the treating solution into the porous substrate; 
that is, the porous substrate may be saturated with the treating solution. 
Although exposure of the porous substrate to a field of reactive species is 
a desired method of temporarily raising the surface energy of the 
substrate, other procedures may be employed. For example, the porous 
substrate may be treated with ozone or passed through an oxidizing 
solution, such as an aqueous medium containing chromium trioxide and 
sulfuric acid. Care should be taken with such other procedures, however, 
to either prevent or minimize degradation of the porous substrate. 
The strength of the field of reactive species may be varied in a controlled 
manner across at least one dimension of the fibrous web. Upon coating the 
porous substrate with the hydrophilic polymeric material, the extent or 
degree of hydrophilicity of the coating is directly proportional to the 
strength of the field. Thus, the hydrophilicity of the coating of 
polymeric material will vary in a controlled manner across at least one 
dimension of the fibrous web. 
The strength of the field of reactive species is readily varied in a 
controlled manner by known means. For example, a corona apparatus having a 
segmented electrode may be employed, in which the distance of each segment 
from the sample to be treated may be varied independently. As another 
example, a corona apparatus having a gap-gradient electrode system may be 
utilized; in this case, one electrode may be rotated about an axis which 
is normal to the length of the electrode. Other methods also may be 
employed; see, for example, "Fabrication of a Continuous Wettability 
Gradient by Radio Frequency Plasma Discharge," W. G. Pitt, J. Colloid 
Interface Sci., 133, No. 1, 223 (1989); and "Wettability Gradient Surfaces 
Prepared by Corona Discharge Treatment," J. H. Lee, et al., Transactions 
of the 17.sup.th Annual Meeting of the Society for Biomaterials, May, 
1991, 1-5, page 133, Scottsdale, Ariz. 
As alluded to above, an important parameter for treated nonwovens for many 
applications involving viscoelastic fluids such as distribution layers for 
sanitary napkins is wicking or the ability to rapidly distribute menses in 
use so as to take maximum advantage of the absorbency of the product. 
Prior surfactant treatments such as ethoxylated hydrocarbons, siloxanes, 
and ionic surfactants have been shown to aid wicking, but not via the 
mechanism of the present invention. Such conventional surfactants increase 
wettability but fail to effectively reduce the viscoelasticity of menses 
in a manner to enhance wicking to the degree of the present invention. In 
accordance with the invention, it has been found that use of 
viscoelastants such as specific alkyl polyglycosides not only reduces the 
viscoelastic properties of the insult fluid but also provides surfactant 
properties to rapidly distribute the viscoelastic fluid. For best results 
the alkyl polyglycoside is one with 8-10 carbons in the alkyl chain and is 
included in an amount of about 0.2% to about 5% based on the total 
material weight and the weight of the alkyl polyglycoside composition, 
which may be aqueous, containing about 40% water, for example. Other 
viscoelastants will be apparent to those skilled in this art and include, 
for example, bovine lipid extract surfactant (Survanta.RTM., Ross 
Laboratories) and protein-cleaving enzymes such as papain and pepsin as 
well as certain dextrins and dextrans. 
Table 1 below illustrates the effects on the Theological properties of an 
eggwhite-based viscoelastic fluid (described above under TEST METHODS as 
"Fluid A") of the addition of a viscoelastant, Glucopon 220UP, obtained as 
a 60% (by weight) solution of alkyl polyglycoside in water, available from 
Henkel Corporation. Rheological measurements were made on the egg-white 
based viscoelastic fluid (Fluid A) with and without the addition of 
Glucopon 220. Glucopon was added to the viscoelastic fluid by direct 
addition and mixed intermittently for at least 24 hours to insure complete 
mixing. The final concentration of Glucopon 220 mixed into the 
viscoelastic fluid was 1.0%. The viscoelastic fluid without Glucopon 220 
was also mixed intermittently for at least 24 hours to duplicate the same 
shear history as the Glucopon containing fluid. The measurements were made 
as described in the Test Method section. The elastic stress at a strain of 
approximately 1 was reduced by 36% while the viscosity at a shear rate of 
approximately 0.1 sec.sup.-1 was reduced by 30%. Percentages were obtained 
using the difference between Control and Viscoelastant divided by Control 
and multiplying the result by 100. 
TABLE 1 
______________________________________ 
Properties 
Sample Elastic Stress (dyne/cm.sup.2) 
Viscosity (poise) 
______________________________________ 
Control 0.0848 0.423 
Viscoelastant 0.0540 0.296 
Conditions .about.1 (Strain) .about.0.1 sec.sup.- 
1 (Strain rate) 
______________________________________ 
Table 2 and FIGS. 3 and 4 show the results of a similar example (Run 1 of 
FIGS. 3 and 4) using a second viscoelastic fluid (Fluid B). For this 
example the viscoelastant and viscoelastic fluid were mixed either by 
inversion 10 times and standing for 1 hour or using a stirring rod for 1 
minute and standing for at least 30 minutes. The preparation differences 
are believed to have only slightly affected test results, if at all. In 
this case the amount of Glucopon 220 viscoelastant mixed into the 
viscoelastic fluid was at least about 1.0%. The elastic stress at a strain 
of about 1 was reduced within the range of 60 to 100% (considering the 
sensitivity limitations of the equipment) while the viscosity at a shear 
rate of about 0.1 sec.sup.-1 was reduced by about 77% indicating that the 
invention is applicable to different viscoelastic fluids. 
TABLE 2 
______________________________________ 
Properties 
Sample Elastic Stress (dyne/cm.sup.2) 
Viscosity (poise) 
______________________________________ 
Control 0.3 0.09 
Viscoelastant 0.106 0.1 
Test condition: Strain = 1 Strain rate = 0.1 Sec.sup.-1 
______________________________________ 
FIGS. 3 and 4 illustrate these results as a function of amount of 
viscoelastant added. As clearly shown, the amount of viscoelastant has a 
dramatic effect reducing both elastic stress and viscosity of the 
viscoelastic fluid (Fluid B). 
The present invention is believed applicable to reduced viscoelasticity 
treatment and improved fluid handling with a variety of viscoelastic fluid 
compositions, although the sanitary napkin application represents a very 
desirable use. 
Table 3 below shows wicking results in a bonded carded web of the type that 
might be used as a distribution layer in a sanitary napkin construction. 
The bonded carded web constructed for purposes of these tests was a 
through-air bonded carded web, or TABCW, prepared as described below. 
Washed fabrics, or the identical fabrics prepared with four different 
surface treatments, were tested. Wicking studies were conducted with an 
eggwhite-based viscoelastic fluid (described above in TEST METHODS Fluid 
A); distance wicked horizontally during a 20 minute exposure of the fabric 
to the fluid was measured. Glucopon-treated TABCW fabrics demonstrated the 
greatest wicking distances. 
TABLE 3 
______________________________________ 
WICKING (in) 
SAMPLE AVG STD DEV 
______________________________________ 
MATERIAL A 3.27 0.29 
MATERIAL B 1.63 0.19 
MATERIAL C 2.35 0.45 
MATERIAL D 0.53 0.22 
______________________________________ 
The web was composed of 100% by weight 3.0 denier polyethylene 
sheath/polypropylene core bicomponent staple fibers having a length of 38 
millimeters. The bicomponent fibers were obtained from Chisso Corporation 
and were supplied with a vendor fiber finish. The staple fibers were all 
sent through an opener and were uniformly mixed together before being 
carded into a web at a line speed of 15.24 meters per minute (50 feet per 
minute). Once the web was formed, it was sent through a through-air bonder 
(drum type) with an air temperature of 131.degree. C. The dwell time 
within the bonder was between 3 and 4.5 seconds. The resultant web had a 
basis weight of 100 gsm and a density of 0.06 gm/cm.sup.3. The web was 
then wound up on a roll. 
Material A is the above described web which was washed to remove the vendor 
fiber finish and then treated with 2.0% Glucopon 220 as described below. 
Material B is the above described web which was washed to remove the 
vendor fiber finish and then treated with 0.45% calcium alginate as 
described below. Material C is the above described web with the vendor 
fiber finish. Material D is the above described web with which was washed 
to remove the vendor fiber finish. 
FIG. 5 presents wicking distance comparisons with several other known 
nonwoven web treatments. The base web was as described as Material A 
above, and the viscoelastic fluid was menses simulant (Fluid B). Triton 
X-102 is an alkylphenol ethoxylate surfactant available from Union 
Carbide. Y12488 is an ethoxylated polydimethyl siloxane available from 
Osi. Ahcovel N-62 is a blend of ethoxylated hydrogenated castor oil and 
sorbitan monooleate available from ICI. The amount of each applied to the 
web by weight was 0.6% viscoelastant (based on active ingredients), 0.5% 
by weight, Triton 102, 1% by weight Y12488, and 1.5% by weight Ahcovel. As 
shown, the results measured after 15 minutes show that viscoelastants used 
in accordance with the invention increase wicking distance substantially. 
In order to demonstrate effectiveness of other viscoelastants such as 
dextran (4000 MW oligosaccharide available from Polydex Pharmaceuticals, 
Ltd. Of Scarborough, Toronto, Canada), a BCW sample of Chisso bicomponent 
fibers as described above was oxidized in a Branson/IPC Model PM 119 
plasma treater at 100 watts of power in an air plasma at 0.6 torr for 5 
minutes. The fabric rendered wettable by the plasma was then immediately 
immersed in an aqueous solution of the treating substance. Table 4 gives 
the concentration of the treating substances. 
TABLE 4 
______________________________________ 
Substance Being Tested 
Concentration (wt./vol.) 
______________________________________ 
Dextran (4,000 MW) 
3% 
Dextran (4,000 MW) 0.6% 
Sodium Alginate 1% 
Maltose 3% 
______________________________________ 
Excess solution was removed from the saturated fabric by vacuum extraction 
(passing the saturated fabric over a slot that a vacuum was applied to). 
After vacuum extraction the fabrics measured about 100% wet pickup of the 
treating solution by weight. The treated fabrics were dried at 80 degrees 
C. for 8 hours or until constant weight and then tested for wicking. 
The surfactants to be tested were treated as above except the oxidation 
step was omitted. The solution concentrations were as described in Table 
5. 
TABLE 5 
______________________________________ 
Substance Being Tested 
Concentration (wt./vol.) 
______________________________________ 
Glucopon 600 (alkyl polyglycoside with 
3% 
12-18 carbons in alkyl chain from 
Henkel) 
Triton X-102 2% 
Glucopon 220 (an alkyl polyglycoside 2% 
with 8-12 carbons in alkyl chain available 
from Henkel) 
______________________________________ 
FIG. 6 shows the results of wicking tests using Fluid B with regard to 
these materials as well as Material C ("HR6"). As shown surfactants alone 
such as sodium alginate and Triton X-102 have reduced wicking benefit. Use 
of viscoelastants in accordance with the invention, however, provide a 
wide range of wicking improvement allowing this property to be tailored to 
a particular use. 
Table 6 shows that selection of a particular viscoelastant can be made to 
have a predominant effect on either the viscosity or the elasticity of the 
viscoelastic fluid. Tests were run on Fluid B samples after mixing 1 gram 
of test solution (0.9% saline solution in the case of the Control) with 9 
grams of simulant by slow inversion for 15 minutes. As shown Glucopon 220 
dramatically affects both viscosity and elasticity whereas Dextran affects 
elasticity to a greater degree than it does viscosity. 
TABLE 6 
______________________________________ 
Simulant 1% Glucopon 
1% Dextran 
(Control) in Simulant in Simulant 
______________________________________ 
Viscosity (Poise) 
0.461 0.110 0.390 
Measured at a 
shear rate of 
0.1/Sec. 
Elasticity (Poise) 0.566 .about.0 0.275 
Measured at a 
shear rate of 
0.01/Sec. 
______________________________________ 
Material A was prepared by cutting the web into a sample 10 inches (about 
25 cm) by 12 inches (about 30 cm). The sample was gently rinsed in 
100.degree. F. tap water for 5 minutes followed by deionized water for one 
minute to remove essentially all of the vendor fiber finish and dried 
overnight in an air-circulating oven at 35.degree. C. The sample was then 
immersed for about 5 seconds in a solution consisting of 200 g of Glucopon 
220UP (Henkel Corporation) as supplied, which is 60% active in water, and 
30 g hexanol (Catalog No. H1,330-3, Aldrich Chemical Company, Milwaukee, 
Wiss.) in 6000 g deionized water at ambient temperature (20-25.degree. 
C.). The solution contained 2.0 percent by weight of active Glucopon 
220UP. Excess solution was removed from the wetted fabric by vacuum 
extraction (i.e. passing the wetted fabric over a slot to which vacuum was 
applied). The sample contained approximately 100 percent by weight wet 
pickup based on the dry weight of the sample of the solution after vacuum 
extraction. The sample was then dried over night in an oven at 35.degree. 
C. The hexanol was completely eliminated during drying. 
Material B was prepared by a plasma method similar to that disclosed in 
coassigned U.S. Pat. No. 5,814,567 filed Jun. 14, 1996, discussed above. 
The web was washed and dried to remove the vendor finish as described for 
Material A. The sample was oxidized in a Branson/IPC Model PM119 plasma 
treater at 80 watts of power in an air plasma at 0.6 torr for 4 minutes. 
The sample then was immersed for about 30 seconds in a solution consisting 
of 23.8 g of calcium chloride dihydrate (Catalog No. 22,350-6, Aldrich 
Chemical Company, Milwaukee, Wiss.) and 6000 g of deionized water. The 
solution contained 0.3 percent of weight of calcium chloride. Excess 
solution was removed from the wetted fabric by vacuum extraction (i.e. 
passing the wetted fabric over a slot to which a vacuum was applied). The 
sample contained approximately 150 percent by weight wet pickup (based on 
the dry weight of the sample) of the calcium chloride solution after 
vacuum extraction. The still wet sample was dipped for about 30 seconds in 
a solution composed of 18.0 g or 0.3 percent by weight of high viscosity 
sodium alginate (Catalog No. A-7128, Sigma Chemical Company, St. Louis, 
Mo.) in 6,000 g deionized water for about 30 seconds. Excess solution was 
removed from the wet sample by vacuum extraction. The sample contained a 
total of approximately 300 percent of both the calcium chloride and sodium 
alginate solutions, resulting in the formation of a calcium alginate gel 
on the fibers of the sample. The sample then was dried overnight in an 
oven at 35.degree. C. 
Material D was prepared by washing the web to remove essentially all of the 
vendor finish and drying as described for Materials A and B. 
The viscoelastant such as an alkyl polyglycoside treating composition may 
contain other additives as appropriate for the desired result so long as 
they do not have a major detrimental effect on the activity of the 
modifier such as the alkyl polyglycoside. Examples of such additives 
include additional conventional surfactants such as ethoxylated 
hydrocarbons or ionic surfactants, or co-wetting aids such as low 
molecular weight alcohols. As mentioned, the composition is desirably 
applied from high solids, advantageously 80% or less solvent or water, so 
as to minimize drying and its attendant costs and deleterious effects. The 
treating composition may be applied in varying amounts depending on the 
desired results and application. For sanitary napkin distribution layer 
applications, for example, effective results are obtained within a range 
of about 0.1% to about 5.0% solids add-on based on the dry weight of the 
fabric, with a range of about 0.2% to 3.0% being advantageous from the 
perspective of both cost and performance. Also, as will be recognized by 
those skilled in this art, many substrate materials may be treated in 
accordance with the invention including nonwovens such as spunbond, 
meltblown, carded webs and others as well as woven webs and even films and 
the like where improved fluid distribution is desired. It will also be 
recognized by those skilled in this art that some viscoelastants may be 
used as internal additives, that is, added to the polymer melt directly or 
in a concentrate form. After fiber formation, such additives will migrate 
to the fiber surface and impart the desired effect. For further discussion 
of internal addition of additives, reference may be had to coassigned U.S. 
Pat. No. 5,540,979 to Yahiaoui, Potts, Perkins, Powers and Jascomb issued 
Jul. 20, 1996, the contents of which are incorporated entirely herein by 
reference. The substrate basis weight is not critical and may vary widely 
depending on the application. For sanitary napkin distribution layer 
applications, spunbond and bonded carded webs are often used with basis 
weights generally in the range of from about 7 gsm to about 175 gsm. 
Examples of the alkyl polyglycoside viscoelastants include Glucopon 225 or 
220, both alkyl polyglycosides with 8-10 carbon atoms in the alkyl chain 
and available from Henkel Corporation as well as Crodesta SL-40 (sucrose 
cocoate) from Creda, TL 2141 (Glucopon 220 analog) from ICI. 
Referring to FIG. 1, a process will be described for application to one or 
both sides of a traveling web. It will be appreciated by those skilled in 
the art that the invention is equally applicable to inline treatment or a 
separate, offline treatment step. Web 12, for example a spunbond or 
meltblown nonwoven is directed over support rolls 15, to a treating 
station including rotary spray heads 22 for application to one side 14 of 
web 12. An optional treating station (shown in phantom) which may include 
rotary spray heads 18 can also be used to apply to opposite side 23 of web 
12 traveling over support rolls 17,19. Each treatment station receives a 
supply of treating liquid 30 from a reservoir (not shown). The treated web 
may then be dried if needed by passing over dryer cans 25 or other drying 
means and then wound as a roll or converted to the use for which it is 
intended. Alternative drying means include ovens, through air dryers, 
infra red dryers, air blowers, and the like. 
FIG. 2 illustrates a representative personal care product in the form of a 
sanitary napkin structure incorporating a distribution layer in accordance 
with the present invention. As shown, sanitary napkin 30 includes 
impervious backing 40, absorbent 38, distribution layer 36, and cover or 
body contacting layer 34. If desired, the absorbent 38 may also be 
enclosed on its bottom and sides by wrap 32 for enhanced protection 
against side leakage. In accordance with the invention, either or all of 
the cover, distribution or absorbent layers may be treated with a 
viscoelastant. 
Thus, in accordance with the invention, there has been provided an improved 
treatment process and resulting treated nonwovens and products 
incorporating them that provide the benefits described above. While the 
invention has been illustrated by specific embodiments, it is not limited 
thereto and is intended to cover all equivalents as come within the broad 
scope of the claims.