U.S. patent number RE39,919 [Application Number 09/314,492] was granted by the patent office on 2007-11-13 for heterogeneous surge material for absorbent articles.
This patent grant is currently assigned to Kimberly Clark Worldwide, Inc.. Invention is credited to Richard Norris Dodge, II, Clifford Jackson Ellis, Connie Lynn Hetzler, Eric Scott Kepner, Candace Dyan Krautkramer, Sylvia Bandy Little, Lawrence Howell Sawyer.
United States Patent |
RE39,919 |
Dodge, II , et al. |
November 13, 2007 |
Heterogeneous surge material for absorbent articles
Abstract
There is provided a surge material for personal care products
comprising a layered structure of at least one relatively high
permeability layer on a top side toward a wearer and at least one
relatively low permeability layer where the structure has a
capillary tension range between about 1 and 5 cm with a
differential capillary tension of at least about 1 cm from top to
bottom. The surge material should have a high permeability layer
with a permeability of at least 1000 Darcys and a low permeability
layer with a permeability of less than 1000 Darcys. The surge
material should also have a said high permeability layer which has
a permeability of at least 250 Darcys greater than the low
permeability layer. Such a layered structure should have a first
insult run-off value of at most 30 ml from a 100 ml insult
delivered at 20 ml/second. Such a surge material is useful in
personal care products like diapers, training pants, absorbent
underpants, adult incontinence products, feminine hygiene products
and the like.
Inventors: |
Dodge, II; Richard Norris
(Appleton, WI), Ellis; Clifford Jackson (Woodstock, GA),
Hetzler; Connie Lynn (Sparta, NJ), Kepner; Eric Scott
(Woodstock, GA), Little; Sylvia Bandy (Marietta, GA),
Sawyer; Lawrence Howell (Neenah, WI), Krautkramer; Candace
Dyan (Neenah, WI) |
Assignee: |
Kimberly Clark Worldwide, Inc.
(Roswell, GA)
|
Family
ID: |
25034709 |
Appl.
No.: |
09/314,492 |
Filed: |
May 18, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
08754417 |
Nov 22, 1996 |
05820973 |
Oct 13, 1998 |
|
|
Current U.S.
Class: |
428/218; 604/358;
442/381; 604/378; 604/385.01; 428/212 |
Current CPC
Class: |
A61F
13/15203 (20130101); A61F 13/53 (20130101); Y10S
428/903 (20130101); Y10T 442/621 (20150401); Y10T
428/24992 (20150115); Y10T 442/614 (20150401); Y10T
442/641 (20150401); Y10T 442/659 (20150401); Y10T
428/24942 (20150115); Y10T 442/651 (20150401) |
Current International
Class: |
B32B
7/02 (20060101); B32B 5/26 (20060101) |
Field of
Search: |
;428/212
;442/340,346,364,373 ;604/358,378 |
References Cited
[Referenced By]
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Other References
Research Disclosure 37421, "Thermally Bonded Absorbent Structures
Having Discrete, Stepped Density Zones in the Z-Dimension," Jun.
1995, Inventor--Anonymous. cited by other .
Polymer Blends and Composites, John A. Manson and Leslie H.
Sperling, copyright 1976, Plenum Press, ISBN-0-306-30831-2, pp.
273-277. cited by other .
Article by R.W. Hoyland and R. Field in Paper Technology and
Industry, Dec. 1976, pp. 291-299 and Porous Media Fluid Transport
and Pore Structure, F.A.L. Dullien, 1979, Academic Press, Inc. ISBN
0-12-223650-5. cited by other.
|
Primary Examiner: Ruddock; Ula C.
Attorney, Agent or Firm: Brinks, Hofer, Gilson &
Lione
Claims
What is claimed is:
.[.1. A surge material for personal care products comprising a
layered structure of at least one relatively high permeability
layer on a top side toward a wearer and at least one relatively low
permeability layer, wherein said structure has a capillary tension
range between about 1 and 5 cm with a differential of at least
about 1 cm from top to bottom..].
.[.2. The surge material of claim 1 wherein said high permeability
layer has a permeability of at least 1000 Darcys and said low
permeability layer has a permeability of less than 1000
Darcys..].
.[.3. The surge material of claim 2 wherein said high permeability
layer has a permeability of at least 250 Darcys greater than said
low permeability layer..].
.[.4. The surge material of claim 2 wherein said high permeability
layer has a permeability of at least 500 Darcys greater than said
low permeability layer..].
.[.5. A personal care product selected from the group consisting of
diapers, training pants, absorbent underpants, adult incontinence
products and feminine hygiene products comprising the material of
claim 1..].
.[.6. The surge material of claim 1 wherein said high permeability
layer is oriented..].
.[.7. The surge material of claim 1 wherein said low permeability
layer is oriented..].
.[.8. The surge material of claim 1 wherein said high and low
permeability layers are oriented..].
.[.9. The product of claim 3 wherein said personal care product is
a feminine hygiene product..].
.[.10. The product of claim 3 wherein said personal care product is
an adult incontinence product..].
.[.11. The product of claim 3 wherein said personal care product is
a diaper..].
.[.12. The diaper of claim 11 having a crotch width of at most 7.6
cm..].
.[.13. The surge material of claim 2 having a thickness of less
than 3 cm..].
.[.14. The surge material of claim 1 wherein a first insult run-off
value is at most 30 ml from a 100 ml insult delivered at 20
ml/second..].
.[.15. The surge material of claim 14 wherein two additional insult
runoffs are at most 30 ml each..].
.[.16. The surge material of claim 15 wherein all three insults
have run-off values of at most 25 ml..].
.[.17. A surge material for personal care products comprising a
layered structure of at least one relatively high permeability
layer on a side toward a wearer and at least one relatively low
permeability layer, wherein said relatively high permeability layer
has a capillary tension range between about 1 and 2.5 cm and said
relatively low permeability layer has a capillary tension range
between about 2.5 and 5 cm..].
.[.18. The surge material of claim 17 wherein said high
permeability layer is oriented..].
.[.19. The surge material of claim 17 wherein said low permeability
layer is oriented..].
.[.20. The surge material of claim 17 wherein said high and low
permeability layers are oriented..].
.[.21. A surge material for personal care products comprising a
layered structure of at least one relatively high permeability
layer on a side toward a wearer and at least one relatively low
permeability layer, wherein said relatively high permeability layer
is comprised of conjugate sheath/core microfibers and has a
permeability at least 500 Darcys greater than said low permeability
layer and a capillary tension range between about 1 and 2 cm, and
said relatively low permeability layer comprises homopolymer
microfibers and has a capillary tension range between about 2.5 and
5 cm, wherein at least one of said layers has an orientation of at
least 3:1 in MD:CD..].
.[.22. The surge material of claim 21 wherein said high
permeability layer is oriented..].
.[.23. The surge material of claim 21 wherein said low permeability
layer is oriented..].
.[.24. The surge material of claim 21 wherein said high and low
permeability layers are oriented..].
.Iadd.25. An absorbent article for absorption of liquids, said
article comprising: an absorbent core structure containing liquid
retention materials, an outer porous non-woven bodyside liner over
said absorbent core structure, a nonwoven surge material between
said bodyside liner and said absorbent core structure to provide
for intake of liquids from said bodyside liner, said surge material
comprising a layered structure having at least one first surge
layer and at least one second surge layer, said at least one first
surge layer being adjacent said nonwoven bodyside liner and having
a first density, and comprising fibers of a first average denier,
and said at least one second surge layer being adjacent said at
least one first surge layer, said second surge layer having a
second density greater than said first density and comprising
fibers of a second average denier which is smaller than said first
average denier..Iaddend.
.Iadd.26. The absorbent article of claim 25 wherein said fibers in
said at least one first surge layer and said at least one second
surge layer differ on average by at least about one
denier..Iaddend.
.Iadd.27. The absorbent article of claim 26 wherein the fibers in
said at least one first surge layer have an average denier up to
about 8 denier and the fibers in the said at least one second surge
layer have an average denier of about 2 denier or
less..Iaddend.
.Iadd.28. The absorbent article of claim 25 wherein said at least
one first surge layer and said at least one second surge layer
comprise thermally bondable bicomponent fibers..Iaddend.
.Iadd.29. The absorbent article of claim 25 wherein the denier of
the fibers in said at least one first surge layer and said at least
one second surge layer on average differ by more than about 2.5
denier..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to absorbent articles particularly absorbent
structures which are useful in personal care products such as
disposable diapers, incontinence guards, child care training pants,
or sanitary napkins. More particularly, the invention relates to
absorbent articles which have a portion designed for rapid intake,
temporary liquid control, and subsequent release of repeated liquid
surges to the remainder of the article.
BACKGROUND OF THE INVENTION
Personal care products are absorbent articles including diapers,
training pants, feminine hygiene products such as sanitary napkins,
incontinence devices and the like. These products are designed to
absorb and contain body exudates and are generally single-use or
disposable items which are discarded after a relatively short
period of use--usually a period of hours--and are not intended to
be washed and reused. Such products usually are placed against or
in proximity to the wearer's body to absorb and contain various
exudates discharged from the body. All of these products typically
include a liquid permeable bodyside liner or cover, a liquid
impermeable outer cover or backsheet, and an absorbent structure
disposed between the bodyside liner and outer cover. The absorbent
structure may include a surge layer subjacent to and in liquid
communicating contact with the bodyside liner, and an absorbent
core often formed of a blend or mixture cellulosic pulp fluff
fibers and absorbent gelling particles subjacent to and in liquid
communicating contact with the surge layer.
Desirably, personal care absorbent articles exhibit low leakage
from the product and a dry feel for the wearer. It has been found
that urination can occur at rates as high as 15 to 20 milliliters
per second and at velocities as high as 280 centimeters per second
and that an absorbent garment, such as a diaper, may fail by
leaking from the leg or front or back waist areas. The inability of
the absorbent product to rapidly uptake liquid can also result in
excessive pooling of liquid on the body-facing surface of the
bodyside liner before the liquid is taken up by the absorbent
structure. Such pooled liquid can wet the wearer's skin and can
leak from leg or waist openings of the absorbent article, causing
discomfort, potential skin health problems, as well as soiling of
the outer clothing or bedding of the wearer.
Leakage and pooling can result from a variety of performance
deficiencies in the design of the product, or individual materials
within the product. One cause of such problems is an insufficient
rate of liquid intake into the absorbent core, which functions to
absorb and retain body exudates. The liquid intake of a given
absorbent product, therefore, and particularly the bodyside liner
and surge materials used in absorbent product, must attempt to meet
or exceed the expected liquid delivery rates into the absorbent
product. An insufficient intake rate becomes even more detrimental
to product performance on second, third, or fourth liquid surges.
In addition, leakage may occur due to poor wet product fit that
results when multiple insults are stored in the target location and
cause sagging and drooping from the wet, heavy retention material
structure.
Various approaches have been taken to reduce or eliminate leakage
from personal care absorbent articles. For example, physical
barriers, such as elasticized leg openings and elasticized
containment flaps, have been incorporated into such absorbent
products. The amount and configuration of absorbent material in the
zone of the absorbent structure in which liquid surges typically
occur (sometimes referred to as a target zone) also have been
modified.
Other approaches to improving overall liquid intake of absorbent
articles have focused on the bodyside liner and its capacity to
rapidly pass liquid to the absorbent structure of the absorbent
article. Nonwoven materials, including bonded carded webs and
spunbond webs, have been widely used as bodyside liners. Such
nonwoven materials generally are intended to be sufficiently open
and/or porous to allow liquid to pass through rapidly, while also
functioning to keep the wearer's skin separate from the wetted
absorbent underlying the liner. Attempts to improve the liquid
intake of liner materials have included, for example, aperturing
the liner material, treating the fibers forming the liner material
with surfactants to enhance the wettability of the liner, and
altering the durability of such surfactants.
Yet another approach has been to introduce one or more additional
layers of material, typically between the bodyside liner and
absorbent core, to enhance the liquid intake performance of the
absorbent product and to provide separation between the absorbent
core and the bodyside liner adjacent the wearer's skin. One such
additional layer, commonly referred to as a surge layer, can
suitably be formed of thick, lofty nonwoven materials. Surge
layers, particularly high loft, high bulk, compression resistant
fibrous structures, provide a temporary retention or absorption
function for liquid not yet absorbed into the absorbent core, which
tends to reduce fluid flowback or wetback from the absorbent core
to the liner.
Despite these improvements, the need exists for further improvement
in the liquid intake performance of liner materials employed in
absorbent articles. In particular, there is a need for liner
materials that can rapidly intake and then control the spreading of
a liquid insult to the underlying layers. This improved handling is
critical for narrow crotch absorbent product designs that utilize
less retention storage material in the target region and
incorporate distribution features that remove fluid for storage in
remote locations in order to alleviate fit problems as a means to
reduce leakage. The present invention provides a heterogeneous
surge material that provides for such improved liquid intake and
controlled spreading when used in absorbent articles.
SUMMARY OF THE INVENTION
The objects of this invention are achieved by a surge material for
personal care products which is a layered structure of at least one
relatively high permeability layer and at least one relatively low
permeability layer where the structure has a capillary tension
range between about 1 and 5 cm with a differential of at least
about 1 cm from top (wearer side) to bottom. Such a layered
structure should provide a first insult run-off value of at most 30
ml from a 100 ml insult delivered at 20 ml/second. Such a surge
material is useful in personal care products like diapers, training
pants, absorbent underpants, adult incontinence products, feminine
hygiene products and the like and should have a thickness of less
than 3 cm. The surge material of this invention is particularly
well suited for use in narrow crotch (7.6 cm width maximum)
diapers.
BRIEF DESCRIPTION OF THE DRAWINGS
The FIGURE is a drawing of a side view of a cradle used for the
MIST Evaluation test.
DEFINITIONS
"Disposable" includes being disposed of after usually a single use
and not intended to be washed and reused.
"Front" and "back" are used throughout this description to
designate relationships relative to the garment itself, rather than
to suggest any position the garment assumes when it is positioned
on a wearer.
"Hydrophilic" describes fibers or the surfaces of fibers which are
wetted by the aqueous liquids in contact with the fibers. The
degree of wetting of the materials can, in turn, be described in
terms of the contact angles and the surface tensions of the liquids
and materials involved. Equipment and techniques suitable for
measuring the wettability of particular fiber materials can be
provided by a Caln SFA-222 Surface Force Analyzer System, or a
substantially equivalent system. When measured with this system,
fibers having contact angles less than 90.degree. are designated
"wettable" or hydrophilic, while fibers having contact angles equal
to or greater than 90.degree. are designated "nonwettable" or
hydrophobic.
"Inward" and "outward" refer to positions relative to the center of
an absorbent garment, and particularly transversely and/or
longitudinally closer to or away from the longitudinal and
transverse center of the absorbent garment.
"Layer" when used in the singular can have the dual meaning of a
single element or a plurality of elements.
"Liquid" means a nongaseous substance and/or material that flows
and can assume the interior shape of a container into which it is
poured or placed.
"Liquid communication" means that liquid such as urine is able to
travel from one location to another location.
"Longitudinal" and "transverse" have their customary meanings. The
longitudinal axis lies in the plane of the article when laid flat
and fully extended and is generally parallel to a vertical plane
that bisects a standing wearer into left and right body halves when
the article is worn. The transverse axis lies in the plane of the
article generally perpendicular to the longitudinal axis.
"Particles" refers to any geometric form such as, but not limited
to, spherical grains, cylindrical fibers or strands, or the
like.
"Spray" and variations thereof include forcefully ejecting liquid,
either as a stream such as swirl filaments, or atomized particles
through an orifice, nozzle, or the like, by means of an applied
pressure of air or other gas, by force of gravity, or by
centrifugal force. The spray can be continuous or
non-continuous.
"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 by, for example, 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 Hartman, and U.S. Pat. No.
3,542,615 to Dobo et al. Spunbond fibers are generally not tacky
when they are deposited onto a collecting surface. Spunbond fibers
are generally continuous and have average diameters (from a sample
of at least 10) larger than 7 microns, more particularly, between
about 10 and 20 microns. The fibers may also have shapes such as
those described in U.S. Pat. No. 5,277,976 to Hogle et al., U.S.
Pat. No. 5,466,410 to Hills and U.S. Pat. Nos. 5,069,970 and
5,057,368 to Largman et al., which describe fibers with
unconventional shapes.
"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 hot, 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
disbursed meltblown fibers. Such a process is disclosed, for
example, in U.S. Pat. No. 3,849,241. Meltblown fibers are
microfibers which may be continuous or discontinuous, are generally
smaller than 10 microns in average diameter, and are generally
tacky when deposited onto a collecting surface.
As used herein, the term "coform" means a process in which at least
one meltblown diehead is arranged near a chute through which other
materials are added to the web while it is forming. Such other
materials may be pulp, superabsorbent particles, cellulose or
staple fibers, for example. Coform processes are shown in commonly
assigned U.S. Pat. Nos. 4,818,464 to Lau and 4,100,324 to Anderson
et al. Webs produced by the coform process are generally referred
to as coform materials. "Conjugate fibers" refers to fibers which
have been formed from at least two polymer sources 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, a pie 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. The fibers may
also have shapes such as those described in U.S. Pat. Nos.
5,277,976 to Hogle et al., and 5,069,970 and 5,057,368 to Largman
et al., hereby incorporated by reference in their entirety, which
describe fibers with unconventional shapes.
"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 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.
"Bonded carded web" refers to webs that are made from staple fibers
which are sent through a combining or carding unit, which separates
or breaks apart and aligns the staple fibers in the machine
direction to form a generally machine direction-oriented fibrous
nonwoven web. Such fibers are usually purchased in bales which are
placed in an opener/blender or picker which separates the fibers
prior to the carding unit. 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 and well-known
bonding method, particularly when using conjugate staple fibers, is
through-air bonding.
"Airlaying" is a well known process by which a fibrous nonwoven
layer can be formed. In the airlaying process, bundles of small
fibers having typical lengths ranging from about 3 to about 19
millimeters (mm) are separated and entrained in an air supply and
then deposited onto a forming screen, usually with the assistance
of a vacuum supply. The randomly deposited fibers then are bonded
to one another using, for example, hot air or a spray adhesive.
"Personal care product" means diapers, training pants, absorbent
underpants, adult incontinence products, and feminine hygiene
products.
TEST METHODS
Multiple Insult Test (MIST Evaluation): In this test a fabric,
material or structure composed of two or more materials is placed
in an acrylic cradle to simulate body curvature of a user such as
an infant. Such a cradle is illustrated in FIG. 2. The cradle has a
width into the page of the drawing as shown of 33 cm and the ends
are blocked off, a height of 19 cm, an inner distance between the
upper arms of 30.5 cm and an angle between the upper arms of 60
degrees. The cradle has a 6.5 mm wide slot at the lowest point
running the length of the cradle into the page.
The material to be tested is placed on a piece of polyethylene film
the same size as the sample and placed in the cradle. The material
to be tested is insulted with 100 ml of a saline solution of 8.5
grams of sodium chloride per liter, at a rate of 20 cc/sec with a
nozzle normal to the center of the material and 1/4 inch (6.4 mm)
above the material. The amount of runoff is recorded. The material
is immediately removed from the cradle, weighed, and placed on a
dry 40/60 pulp/superabsorbent pad having a density of 0.2 g/cc in a
horizontal position under 0.01 psi pressure and weighed after 5, 15
and 30 minutes to determine fluid desorption from the material into
the superabsorbent pad as well as fluid retention in the material.
The pulp fluff and superabsorbent used in this test is
Kimberly-Clark's (Dallas Tex.) CR-2054 pulp and Stockhausen
Company's (of Greensboro, N.C. 27406) FAVOR 870 superabsorbent
through other comparable pulp and superabsorbents could be used
provided they yield a desorption pad of 500 gsm and 0.2 g/cc which
after immersion into saline solution under free-swell conditions
for 5 minutes, retains at least 20 grams of saline solution per
gram of desorption pad after being subjected to an air pressure
differential, by vacuum suction for example, of about 0.5 psi
(about 3.45 kPa) applied across the thickness of the pad for 5
minutes. If the tested piece is made of other components (e.g. is a
laminate) the components or layers are separated and weighed to
determine liquid partitioning between them and then reassembled
after each weighing and placed back onto the fluff/superabsorbent.
This test is repeated using fresh desorption pads on each insult so
that a total of three insults are introduced and fluid partitioning
measured over 1.5 hours with 30 minutes between insults. Five tests
of each sample material are recommended.
Permeability: Permeability (k) may be calculated from the
Kozeny-Carman equation. This is a widely used method. References
include an article by R. W. Hoyland and R. Field in the journal
Paper Technology and Industry, December 1976, p. 291-299 and Porous
Media Fluid Transport and Pore Structure by F. A. L. Dullien, 1979,
Academic Press, Inc. ISBN 0-12-223650-5.
TABLE-US-00001 Calculated Variable Equation Dimensions Permeability
= k .epsilon..function..epsilon..times..times. ##EQU00001## Darcys
Kozeny = Constant K
.times..epsilon..epsilon..function..times..epsilon. ##EQU00002##
dimension- less Surface area per = mass of the material S.sub.v
.SIGMA..times..tau..times..rho. ##EQU00003## cm.sup.2/g Mass
weighted = average com- ponent density .rho..sub.avg
.SIGMA..times..rho. ##EQU00004## g/cm.sup.3 Surface area per =
solid volume of the material S.sub.0 = S.sub.v.rho..sub.avg
cm.sup.-1 Porosity = .epsilon. .SIGMA..times..times..rho..rho.
##EQU00005## dimension- less Effective fiber = radius
.tau..sub.i,eff ##EQU00006## cm Density of web = .rho..sub.web
##EQU00007## g/cm.sup.3 for long cylinders .tau..sub.i,eff
.pi..times..pi..times..times. ##EQU00008## for spheres r.sub.i,eff
.times..pi..pi..times. ##EQU00009## where d.sub.i = diameter of
component i (microns) .rho..sub.i = density of component i
(g/cm.sup.3) x.sub.i = mass fraction of component i in web BW =
weight of sample/area (g/cm.sup.2) t = thickness of sample (mm)
under 0.05 psi (23.9 dyne/cm.sup.2) or 2.39 Pascal (N/m.sup.2)
load
Permeability Example Calculation
For a structure which contains 57% southern softwood pulp, 40%
superabsorbent and 3% binder fiber, and has a basis weight of
617.58 g/m.sup.2 and a bulk thickness of 5.97 mm at 0.05 psi the
example permeability calculation follows. The component properties
are as follows (note shape is approximated):
TABLE-US-00002 Diameter d.sub.i Density .rho..sub.i Mass Component
Shade (microns) (g/cm.sup.3) Fraction x.sub.i Southern softwood
Cylinder 13.3 1.55 0.57 Superabsorbent Sphere 1125 1.50 0.40 Binder
Cylinder 17.5 0.925 0.03 .rho..function. ##EQU00010##
.rho..function..times. ##EQU00011## .rho..sub.web(g/cm.sup.3) =
0.1034 .epsilon..SIGMA..times..times..rho..rho. ##EQU00012##
.epsilon..times..times..times. ##EQU00013## .epsilon. = 0.9309
.function..SIGMA..times..tau..times..rho. ##EQU00014##
.function..times..times..times..times..times..times. ##EQU00015##
S.sub.v (cm.sup.2/g) = 1194 .rho..function..SIGMA..times..rho.
##EQU00016## .rho..function. ##EQU00017## .rho..sub.avg(g/cm.sup.3)
= 1.496 S.sub.0(cm.sup.-1) = S.sub.v.rho..sub.avg
S.sub.0(cm.sup.-1) = 1194 .times. 1.496 S.sub.0(cm.sup.-1) = 1786
.times..epsilon..epsilon..function..times..epsilon. ##EQU00018##
.times..function..times. ##EQU00019## K = 10.94
.epsilon..function..epsilon..times..times. ##EQU00020##
.times..times..times..times. ##EQU00021## k = 491 darcys
Material Caliper (Thickness)
The caliper of a material is a measure of thickness and is measured
at 0.05 psi with a Starret-type bulk tester, in units of
millimeters.
Density
The density of the materials is calculated by dividing the weight
per unit area of a sample in grams per square meter (gsm) by the
bulk of the sample in millimeters (mm) at 68.9 Pascals and
multiplying the result by 0.001 to convert the value to grams per
cubic centimeter (g/cc). A total of three samples would be
evaluated and averaged for the density values.
Wicking Time and Vertical Liquid Flux of an Absorbent Structure
A sample strip of material approximately 2 inches (5 cm) by 15
inches (38 cm) is placed vertically such that when the sample strip
is positioned above a liquid reservoir at the beginning of the
test, the bottom of the sample strip will just touch the liquid
surface. The liquid used was a 8.5 g/l saline solution. The
relative humidity should be maintained at about 90 to about 98
percent during the evaluation. The sample strip is placed above the
known weight and volume of liquid and a stopwatch started as soon
as the bottom edge of the sample strip touches the surface of the
solution.
The vertical distance of the liquid front traveling up the sample
strip and the liquid weight absorbed by the sample strip at various
times is recorded. The time versus liquid front height is plotted
to determine the Wicking Time at about 5 centimeters and at about
15 centimeters. The weight of the liquid absorbed by the sample
strip from the beginning of the evaluation to about 5 centimeters
and to about 15 centimeters height is also determined from the
data. The Vertical Liquid Flux value of the sample strip at a
particular height was calculated by dividing the grams of liquid
absorbed by the sample strip by each of: the basis weight (gsm), of
the sample strip; the time, in minutes, needed by the liquid to
reach the particular height; and the width, in inches, of the
sample strip. Capillary tension in materials not containing
superabsorbents (e.g. surge materials) is measured simply by the
equilibrium vertical wicking height of a 8.5 g/l saline solution
after 30 minutes.
DETAILED DESCRIPTION
Traditional absorbent systems for personal care products may be
generalized as having the functions of surge control and
containment (retention) or SC.
Surge control materials, the "S" in SC, are provided to quickly
accept the incoming insult and either absorb, hold, channel or
otherwise manage the liquid so that it does not leak outside the
article. The surge layer may also be referred to as an intake
layer, transfer layer, transport layer and the like. A surge
material must typically be capable of handling an incoming insult
of between about 60 and 100 cc at an insult volumetric flow rate of
from about 5 to 20 cc/sec, for infants, for example.
Containment or retention materials, the "C" in SC, must absorb the
insult quickly and efficiently. They should be capable of pulling
the liquid from the distribution layer and absorbing the liquid
without significant "gel blocking" or blocking of penetration of
liquid further into the absorbent by the expansion of the outer
layers of absorbent. Retention materials are often high rate
superabsorbent materials such as blends of polyacrylate
superabsorbent and fluff. These materials rapidly absorb and hold
liquid.
As mentioned above, traditional absorbent systems having the
functions of surge control and containment usually hold the vast
majority of any insult in the target area, usually the crotch. This
results in personal care products having crotches which are quite
wide. Examples of the holding ability and location of containment
of various commercial diapers is presented in Table 3 of U.S.
patent application Ser. No. 08/755,136, filed The same day and
assigned to the same assignee as this application and entitled
ABSORBENT ARTICLES WITH CONTROLLABLE FILL PATTERNS.
In contrast with traditional absorbent systems, the patent
application ABSORBENT ARTICLES WITH CONTROLLABLE FILL PATTERNS
presents an absorbent system which includes components that have
been designed, arranged, and assembled so that within a certain
time after each insult, liquid will be located in a pre-specified
area of the absorbent system, i.e. remote from the target area.
Using an absorbent system arbitrarily divided into five zones,
these absorbent systems have a "fill ratio" of grams of fluid
located in the center target zone, usually in the crotch, to each
of the two end zones which is less than 5:1 after three insults of
100 ml separated by 30 minutes. It is preferred that this fill
ratio be less than 3:1, and most preferred to be less than 2.5:1.
Many currently available commercial diapers have fill ratios of
20:1, 50:1 or even greater, i.e. they hold most insult liquid in
the crotch.
In addition to the surge control and containment materials in
traditional absorbent systems, recent work has introduced another
layer interposed between the S and C layers. This new layer is a
distribution layer, producing a system with surge control,
distribution and containment or "SDC".
Distribution materials, the "D" in SDC, must be capable of moving
fluid from the point of initial deposition to where storage is
desired. Distribution must take place at an acceptable rate such
that the target insult area, generally the crotch area, is ready
for the next insult. By "ready for the next insult" it is meant
that sufficient liquid has been moved out of the target zone so
that the next insult results in liquid absorption and runoff within
acceptable volumes. The time between insults can range from just a
few minutes to hours, generally depending on the age of the
wearer.
Absorbent products such as, for example, diapers, generally also
have a liner which goes against the wearer, a backsheet which is
the most exterior layer. An absorbent product may also contain
other layers such as the multifunctional materials described in
patent application Ser. No. 08/754,414, filed The same day and
assigned to the same assignee as this application and entitled
MULTIFUNCTIONAL ABSORBENT MATERIALS AND PRODUCTS MADE THEREFROM.
The retention materials in an absorbent product may also be zoned
to provide specific fill patterns and to move liquids from the
target zone to remote storage areas as described in patent
application Ser. No. 08/755,136, filed The same day and assigned to
the same assignee as this application and entitled ABSORBENT
ARTICLES WITH CONTROLLABLE FILL PATTERNS. While it may appear
obvious, it should be noted that in order to function effectively,
the materials used in personal care product absorbent systems must
have sufficient contact to transfer liquid between them.
The liner is sometimes referred to as a bodyside liner or topsheet
and is adjacent the surge material. In the thickness direction of
the article, the liner material is the layer against the wearer's
skin and so the first layer in contact with liquid or other exudate
from the wearer. The liner further serves to isolate the wearer's
skin from the liquids held in an absorbent structure and should be
compliant, soft feeling and non-irritating.
Various materials can be used in forming the bodyside liner of the
present invention, including apertured plastic films, woven
fabrics, nonwoven webs, porous foams, reticulated foams and the
like. Nonwoven materials have been found particularly suitable for
use in forming the bodyside liner, including spunbond or meltblown
webs of polyolefin, polyester, polyamide (or other like fiber
forming polymer) filaments, or bonded carded webs of natural
polymers (for example, rayon or cotton fibers) and/or synthetic
polymers (for example, polypropylene or polyester) fibers. For
example, the bodyside liner can be a nonwoven spunbond web of
synthetic polypropylene filaments having an average fiber size
(from a sample of at least 10) ranging from about 12 to about 48
microns, and more particularly from about 18 to about 43 microns.
The nonwoven web can have a basis weight (for example, ranging from
about 10.0 grams per square meter (gsm) to about 68.0 gsm, and more
particularly from about 14.0 gsm to about 42.0 gsm, a bulk or
thickness ranging from about 0.13 millimeter (mm) to about 1.0 mm,
and more particularly from about 0.18 mm to about 0.55 mm, and a
density between about 0.025 grams per cubic centimeter (g/cc) and
about 0.12 g/cc, and more particularly between about 0.068 g/cc and
about 0.083 g/cc. Additionally, the permeability of such nonwoven
web can be from about 150 Darcy to about 5000 Darcy. The nonwoven
web can be surface treated with a selected amount of surfactant,
such as about 0.28% Triton X-102 surfactant, or otherwise processed
to impart the desired level of wettability and hydrophilicity. If a
surfactant is used, it can be an internal additive or applied to
the web by any conventional means, such as spraying, printing,
dipping, brush coating and the like.
The surge layer is most typically interposed between and in
intimate, liquid communicating contact with the bodyside liner and
another layer such as a distribution or retention layer. The surge
layer is generally subjacent the inner (unexposed) surface of
bodyside liner. To further enhance liquid transfer, it can be
desirable to attach the upper and/or lower surfaces of the surge
layer to the liner and the distribution layer, respectively.
Suitable conventional attachment techniques may be utilized,
including without limitation, adhesive bonding (using water-based,
solvent-based and thermally activated adhesives), thermal bonding,
ultrasonic bonding, needling and pin aperturing, as well as
combination of the foregoing or other appropriate attachment
methods. If, for example, the surge layer is adhesively bonded to
the bodyside liner, the amount of adhesive add-on should be
sufficient to provide the desired level(s) of bonding, without
excessively restricting the flow of liquid from the liner into the
surge layer. The surge material of this invention will be discussed
in greater detail below.
As described in the previously cited, co-owned patent application
MULTIFUNCTIONAL ABSORBENT MATERIALS AND PRODUCTS MADE THEREFROM,
the multifunctional material has been designed to assist the surge
material 1) by accepting a portion of the insult volume during
forced flow, i.e. during an actual insult, 2) by desorbing the
surge material of liquid during and after insults, 3) by allowing a
portion of the insult volume to pass through itself (the
multifunctional material) to the distribution material and 4) by
permanently absorbing a portion of the liquid insult. If such a
multifunctional material is used, the multifunctional material and
surge should be designed to function together as described in
previously cited, co-owned patent application MULTIFUNCTIONAL
ABSORBENT MATERIALS AND PRODUCTS MADE THEREFROM. The basic
structure of the multifunctional material is a unique blend of
superabsorbent material, high bulk wet resilient pulp, and a
structure stabilizing component such as a polyolefin binder fiber.
The multifunctional material has a permeability of between about
100 and 10000 Darcys, a capillary tension between about 2 and 15
cm, and a runoff rate of less than 25 ml per 100 ml insult, over
its life. The "life" of the multifunctional material is considered
to be three insults of 100 ml each where each insult is separated
by 30 minutes. In order to achieve the required capillary tension
and permeability, its preferred that the multifunctional material
have between 30 and 75 weight percent of slow rate superabsorbent,
between 25 and 70 weight percent of pulp and from a positive amount
up to about 10 percent of a binder component. The material should
have a density between about 0.05 and 0.5 g/cc. The basis weight of
the material will vary depending on the product application but
should generally be between about 200 and 700 gsm. The
multifunctional material is preferably located between the surge
and distribution layers.
The distribution layer must be capable of moving fluid from the
point of initial deposition to where storage is desired.
Distribution must take place at an acceptable rate such that the
target insult area, generally the crotch area, is ready for the
next insult. The time between insults can range from just a few
minutes to hours, generally depending on the age of the wearer. In
order to achieve this transportation function, a distribution layer
must have a high capillary tension value. Capillary tension in
distribution materials is measured simply by the equilibrium
wicking of a 8.5 g/ml saline solution according to the Vertical
Liquid Flux rate test, not by the test method given for materials
containing superabsorbents. A successful distribution layer must
have a capillary tension greater than the adjacent layer (on the
side toward the wearer) and preferably a capillary tension of at
least about 15 cm. Because of the generally inverse relationship
between capillary tension and permeability, such a high capillary
tension indicates that the distribution layer will usually have a
low permeability.
Another liquid transport property desired of a suitable
distribution material is that it exhibit a Vertical Liquid Flux
rate, at a height of about 15 centimeters, suitably of at least
about 0.002 grams of liquid per minute per square meter (gsm) of
distribution material per inch of cross-sectional width of the
distribution material g/(min*gsm*inch), up to about 0.1
g/(min*gsm*inch). As used herein, the Vertical Liquid Flux rate
value of a distribution material is meant to represent the amount
of liquid transported across a boundary a specified vertical
distance away from a centralized liquid insult location per minute
per normalized quantity of the distribution material. The Vertical
Liquid Flux rate, at a height of about 15 centimeters, of a
distribution may be measured according to the test method described
herein.
Another liquid transport property desired of a distribution
material is that it exhibit a Vertical Liquid Flux rate, at a
height of about 5 centimeters, suitably of at least about 0.01
g/(min*gsm*inch) up to about 0.5 g/(min*gsm*inch). The Vertical
Liquid Flux rate, at a height of about 5 centimeters, of an
absorbent structure may be measured according to the test method
described herein.
Materials from which the distribution layer may be made include
woven fabrics and nonwoven webs. For example, the distribution
layer may be a nonwoven fabric layer composed of a meltblown or
spunbond web of polyolefin, polyester, polyamide (or other web
forming polymer) filaments. Such nonwoven fabric layers may include
conjugate, biconstituent and homopolymer fibers of staple or other
lengths and mixtures of such fibers with other types of fibers. The
distribution layer also can be a bonded carded web, an airlaid web
or a wetlaid pulp structure composed of natural and/or synthetic
fibers, or a combination thereof. The distribution layer may have a
basis weight of from 35 to 300 gsm, or more preferably from 80 to
200 gsm, a density of between about 0.1 and 0.5 g/cc and a
permeability between about 50 and 1000 Darcys.
Retention materials are typically cellulosic materials or
superabsorbents or mixtures thereof. Such materials are usually
designed to quickly absorb liquids and hold them without, usually
without release. Superabsorbents are commercially available from a
number of manufactures including Dow Chemical Company of Midland,
Mich. and Stockhausen Corporation of Greensboro, N.C. As described
in the previously cited, co-owned patent application entitled
ABSORBENT ARTICLES WITH CONTROLLABLE FILL PATTERNS, retention
materials may be zoned and their composition chosen to move liquids
away from the target zone to more remote storage locations. Such a
design more efficiently uses the entire absorbent article, and in
the case of a diaper, for example, helps allows for the production
of a more narrow crotch item where "narrow crotch" means diapers
having a width of at most 7.6 cm. The fill patterns and materials
taught in ABSORBENT ARTICLES WITH CONTROLLABLE FILL PATTERNS result
in liquid by weight in the target zone of less than 5 times that in
the remote storage locations, a significant improvement over prior
designs.
The backsheet is sometimes referred to as the outer cover and is
the farthest layer from the wearer. The outer cover is typically
formed of a thin thermoplastic film, such as polyethylene film,
which is substantially impermeable to liquid. The outer cover
functions to prevent body exudates contained in an absorbent
structure from wetting or soiling the wearer's clothing, bedding,
or other materials contacting the diaper. The outer cover may be,
for example, a polyethylene film having an initial thickness of
from about 0.5 mil (0.012 millimeter) to about 5.0 mil (0.12
millimeter). The polymer film outer cover may be embossed and/or
matte finished to provide a more aesthetically pleasing appearance.
Other alternative constructions for outer cover include woven or
nonwoven fibrous webs that have been constructed or treated to
impart the desired level of liquid impermeability, or laminates
formed of a woven or nonwoven fabric and thermoplastic film. The
outer cover may optionally be composed of a vapor or gas permeable,
microporous "breathable" material, that is permeable to vapors or
gas yet substantially impermeable to liquid. Breathability can be
imparted in polymer films by, for example, using fillers in the
film polymer formulation, extruding the filler/polymer formulation
into a film and then stretching the film sufficiently to create
voids around the filler particles, thereby making the film
breathable. Generally, the more filler used and the higher the
degree of stretching, the greater the degree of breathability.
Backings may also serve the function of a mating member for
mechanical fasteners, in the case, for example, where a nonwoven
fabric is the outer surface.
In regard to surge materials, various woven fabrics and nonwoven
webs can be used to construct a surge layer. For example, the surge
layer may be a nonwoven fabric layer composed of a meltblown or
spunbond web of polyolefin filaments. Such nonwoven fabric layers
may include conjugate, biconstituent and homopolymer fibers of
staple or other lengths and mixtures of such fibers with other
types of fibers. The surge layer also can be a bonded carded web or
an airlaid web composed of natural and/or synthetic fibers. The
bonded carded web may, for example, be a powder bonded carded web,
an infrared bonded carded web, or a through-air bonded carded web.
The bonded carded webs can optionally include a mixture or blend of
different fibers, and the fiber lengths within a selected web may
range from about 3 mm to about 60 mm. Previous surge layers have
had have a basis weight of at least about 0.50 ounce per square
yard (about 17 grams per square meter), a density of at least about
0.010 gram per cubic centimeter at a pressure of 68.9 Pascals, a
bulk of at least about 1.0 mm at a pressure of 68.9 Pascals, a bulk
recovery of at least about 75 percent, a permeability of about 500
to about 5000 Darcy, and a surface area per void volume of at least
about 20 square centimeters per cubic centimeter. Examples of surge
materials may be found in U.S. Pat. No. 5,490,846 to Ellis et al.
And in U.S. Pat. No. 5,364,382 to Latimer. A homogeneous surge
material is disclosed in patent application Ser. No. 08/755,514,
filed The same day and assigned to the same assignee as this
application and entitled HIGHLY EFFICIENT SURGE MATERIAL FOR
ABSORBENT ARTICLES. Surge layers may be composed of a substantially
hydrophobic material, and the hydrophobic material may optionally
be treated with a surfactant or otherwise processed to impart a
desired level of wettability and hydrophilicity. Surge layers can
have a generally uniform thickness and cross-sectional area.
Surge control materials must take insult liquids in at the rate and
volume of delivery to avoid top surface pooling or runoff and keep
the liquid within the material structure once it is taken in to
prevent runoff. Traditional surge control materials are low
density, high permeability structures with low capillary tension
that facilitate intake and spreading, especially during an insult.
However, these high permeability, low capillary structures exert a
low level of control on the liquid and the spreading liquid can
rapidly approach the perimeter of the surge control material and
run out. This is a source of leakage in the crotch area of personal
care products where the product width is generally less than the
product length and is of special concern in narrow crotch, (less
than 7.6 cm) personal care products.
If the void volume of the surge control material is maintained, the
thickness of a narrow crotch surge control material must be greater
than wider crotch examples or more surge control material must be
made available in the length dimension of the product. Additional
thickness and/or length will not be beneficial unless this extra
void volume is filled with liquid prior to runout. Lower
permeabilities are required to cause thicker surge control
materials to fill to higher height during an insult and higher
capillary tensions are required to control the liquid, keeping it
in the structure as well as wicking liquid so that more void volume
along the length of the product can be used. The lower permeability
acts to increase liquid height and slow the planar spread from
reaching the material edges while the higher capillary tension acts
to hold the liquid in the material so that it will not come out at
the edges during and after filling.
The benefits of lower permeability high capillary tension surge
control materials is demonstrated in the patent application
entitled HIGHLY EFFICIENT SURGE MATERIAL FOR ABSORBENT ARTICLES.
However, as permeability is reduced, the potential for surface
pooling or runoff of liquid from the top surface of the material
increases, especially at high insult rates or when an insult
impinges the surface of the surge control material at an acute
angle, limiting liquid penetration of the surge control structure.
These effects can be very dependent on user habits and use
conditions. It has been found that a surge control material with a
decreasing permeability gradient in the z-direction, where a
capillary tension gradient can also be imparted, provides improved
intake and control performance especially for high rate and volume
insult conditions with narrow crotch products over many use
conditions.
The surge material of this invention is designed to address a
number of the important aspects of liquid intake and controlled
spreading.
Liquid intake is important since it has been found that urination
can occur at volumetric rates as high as 15 to 20 milliliters per
second and at velocities as high as 280 centimeters per second.
Failure to rapidly intake this liquid may result in leakage from
the leg or front or back waist areas. The inability of an absorbent
product to rapidly uptake liquid can also result in excessive
pooling of liquid on the body-facing surface of the bodyside liner
before the liquid is taken up by the absorbent structure. Such
pooled liquid can wet the wearer's skin and can leak from leg or
waist openings of the absorbent article, causing discomfort,
potential skin health problems, as well as soiling of the outer
clothing or bedding of the wearer.
Controlled spreading of the liquid from an insult is important,
particularly in narrow crotch absorbent articles, since it
increases the contact area of the layer subjacent the surge layer
with the incoming liquid insult. This larger contact area more
efficiently uses all of the mass of the subjacent layers.
The intake and controlled spreading objectives of this invention
are achieved by using a surge material having a permeability
gradient in the z direction combined with an increasing level of
capillary control in the z-direction. More particularly, the
inventive surge has a relatively high permeability on the side of
the material towards the wearer and a relatively lower permeability
on the side away from the wearer and towards the subjacent layers.
Sill more particularly, the inventive surge has a permeability on
the side toward the wearer of greater than 1000 Darcys and on the
side away from the wearer of less than 1000 Darcys. Even more
particularly, the inventive surge should have a permeability
differential between the layers of at least about 250 Darcys and
more particularly at least 500 Darcys.
In addition to the permeability requirements of the inventive surge
material, such a surge material must also have a capillary tension
gradient in the z-direction where the surge has a relatively low
capillary tension on the side of the material towards the wearer
and a relatively higher capillary tension on the side away from the
wearer and towards the subjacent layers. More particularly, the
inventive surge has a capillary tension range between about 1 and 5
cm with a differential of at least about 1 cm from top to
bottom.
The exact permeabilities of a finished surge material will be
dependent on the width of the absorbent article as well as the
thickness of the surge material's layers. As the thickness of the
surge material's high permeability upper layer is reduced, for
example, the permeability of the lower layer must be reduced. As
the overall width of the surge material is reduced the permeability
of the lower surge layer must be reduced also. For example, if the
width of the surge material is 7.6 cm and the upper layer has a
permeability of 1000 Darcys and a thickness of 1.1 cm, the
thickness and permeability of the lower layer should be 1.1 cm and
980 Darcys. If the width of the surge material is reduced to 5.1 cm
with the same upper layer permeability and thickness, the thickness
and permeability of the bottom layer should be 4 cm and 74 Darcys.
If the width of the surge material is 7.6 cm and the upper layer
permeability is 2000 Darcys and the thickness 0.77 cm, the
thickness and permeability of the lower layer should be 1.4 cm and
590 Darcys.
The layers of the surge material may also be oriented, as
determined by tensile testing, in the machine direction (MD) or
cross-machine direction (CD). They may be oriented at least 3:1,
MD:CD or more. Such a surge is given in Example 6.
The permeability and thickness of the upper and lower surge layers
can be controlled by selecting the proper combination of fiber size
and web density. Further, the materials from which the surge layers
are constructed may be selected to ensure that the targeted
permeability levels are maintained through numerous liquid insults.
In addition, though for purposes of discussion the surge has been
referred to as having two layers, the surge may have any number of
layers provided the permeability and capillary tension of the
overall layered structure are within the claimed invention.
A number of surge layers were tested according to the Mist
Evaluation Test to determine run-off. The width of the surge
material was 5.1 cm and the length 17.4 cm in Examples 1-6 to
result in an available void volume of about 100 cc. The insult was
delivered at a rate of 20 ml/sec in a total amount of 100 ml of 8.5
g/l saline solution at room temperature. The data is shown in the
Table where the density (Den.) is in grams/cc, the number of layers
in the sample is given in the "No. of Layer" column, the
permeability (Perm.) is given in Darcys, the capillary tension
(C.T.) is given in centimeters according to equilibrium vertical
wicking, the overall sample thickness (Thick.) is in centimeters
(cm), the runoff after each insult (1.sup.st R, etc.) is given in
milliliters (ml) and the fluid retained after each insult (1.sup.st
F, etc.) in the three right-hand columns in grams. Note that
Examples 4 and 5 are multilayer surge materials as indicated in the
permeability and cap. Tension columns which give the data for each
component layer.
In the examples that follow the component properties used in the
calculations herein were as follows:
TABLE-US-00003 Approximate Density Diameter shape Denier (g/cc)
(microns) 1.5 denier rayon Cylinder 1.5 1.550 11.70 1.8 denier BASF
PE/PET Cylinder 1.8 1.165 14.78 3 denier BASF PE/PET Cylinder 3
1.165 19.09 10 denier BASF PE/PET Cylinder 10 1.165 34.85 Polymer
Density (g/cc) PET 1.38 PE 0.95 Rayon 1.55
Note that the relationship between denier and diameter is as
follows: diameter (microns)=(denier/pi.times.fiber
density.times.9.times.10.sup.5).sup.1/2.times.10.sup.4.
For the surge material of this invention, the first insult run-off
value should be equal to or less than 30 ml from a 100 ml insult
delivered at 20 ml/second, with the remaining two insult runoffs
being equal to or less than 30 ml each. In the most preferred
embodiments, all three insults have run-off values less than or
equal to 25 ml.
The materials described in Examples 1-4 are through air bonded
carded web structures produced on a dual 40 inch (102 cm) card
pilot line. The bonded carded web structures were produced at a
basis weight of approximately 100 gsm. The test samples for
Examples 1-4 had length and width dimensions of 6 inches (15 cm) by
2 inches (5.1 cm) respectively. Layers of 100 gsm material were
plied as indicated in the Table to give the required thickness also
indicated in the Table. The resulting test samples contained
approximately 150 cc of total volume calculated by multiplying
length times width times thickness. The test configuration,
however, resulted in less than 10.2 cm of the 15.2 length
accessible and usable to the insults resulting in approximately 100
cc of accessible void volume. It has been empirically found that
samples in the MIST test cradle use about 2 inches of length on
either side of the point of insult, or 4 inches (10.2 cm), not the
entire sample length, which results in the calculated 100 cc of
void volume.
EXAMPLE 1
Example 1 is a through-air bonded carded web that contains 90
weight percent of a 1.8 denier, 1.5 inch (3.8 cm) conjugate
sheath/core polyethylene/polyethylene terephthalate (PE/PET) fibers
and 10 weight percent of a 1.5 denier, 1.5 inch rayon fiber. The
PE/PET fibers are available from BASF Fibers, 6805 Morrison
Boulevard, Charlotte, N.C. 28211-3577 and were conjugate
sheath/core polyethylene/polyethylene terephthalate (PE/PET) fibers
with a polyethylene glycol based C S-2 finish. The rayon fibers
were 1.5 denier Merge 18453 fibers from Courtaulds Fibers
Incorporated of Axis, Ala.
EXAMPLE 2
Examples 2 is a through-air bonded carded web that contains 90
weight percent of a 3.0 denier, 1.5 inch conjugate sheath/core
PE/PET fibers and 10 weight percent of 1.5 denier, 1.5 inch rayon
fiber. The PE/PET fibers are available from BASF Fibers, 6805
Morrison Boulevard, Charlotte, N.C. 28211-3577 and were conjugate
sheath/core polyethylene/polyethylene terephthalate (PE/PET) fibers
with a polyethylene glycol based C S-2 finish.
EXAMPLE 3
Examples 3 is a through-air bonded carded web that contains 90
weight percent of a 10.0 denier, 1.5 inch conjugate sheath/core
PE/PET fibers and 10 weight percent of 1.5 denier, 1.5 inch rayon
fiber. The PE/PET fibers are available from BASF Fibers, 6805
Morrison Boulevard, Charlotte, N.C. 28211-3577 and were conjugate
sheath/core polyethylene/polyethylene terephthalate (PE/PET) fibers
with a polyethylene glycol based C S-2 finish.
EXAMPLE 4
Examples 4 is a two component gradient structure meeting the
criteria of the invention. The top component is as given in Example
3 and the bottom as given in Example 1.
EXAMPLE 5
Examples 5 is a two component gradient structure meeting the
criteria of the invention. The top component is as given in Example
2 and the bottom as given in Example 1.
EXAMPLE 6
Example 6 is a two component gradient structure meeting the
criteria of the invention. The top component is a homogeneous blend
of 60 weight percent 3.0 denier, 1.5 inch conjugate PE/PET fiber
and 40 weight percent 6 denier, 1.5 inch PET fiber. Nine layers of
each component were plied together to produce material for
testing.
The top component fibers were from the Hoechst Celanese
Corporation, Charlotte, N.C. under the codes T256 and T295
respectively. The top component had a basis weight of about 1.5 osy
(50 gsm) and a density of about 0.014 g/cc. The top component blend
was carded using a Master Card with a Web-Master.RTM. take off roll
from John D. Hollingworth of Wheels, Inc., Greenville, N.C. The top
component had about a 3 to 5:1 MD:CD fiber orientation ratio as
determined by tensile strength ratios in the MD and CD.
The bottom component was 100 weight percent 2.2 denier, 1.5 inch
polypropylene fiber available from the Hercules Chemical Co.,
Wilmington, Del. under the code T186 and had a basis weight of
about 1.0 osy (35 gsm). After through air bonding this layer had a
density of about 0.067 g/cc. This layer was carded using a Master
Card with a Dof-Master.RTM. take off roll from John D.
Hollingsworth on Wheels, Inc. The bottom component had about a 12
to 15:1 MC:CD fiber orientation ratio as determined by tensile
strength ratios.
The top component had a capillary tension of about 0.6 and the
bottom about 2.7 cm.
EXAMPLE 7
Example 7 is a two component gradient structure similar to Example
6 meeting the criteria of the invention. The top component is a
homogeneous blend of 30 weight percent 3.0 denier, 1.5 inch
conjugate PE/PET fiber and 70 weight percent 6 denier, 1.5 inch PET
fiber. The bottom component was 100 weight percent 2.2 denier, 1.5
inch polypropylene fiber. The suppliers and basis weights of each
layer were the same as in Example 6. Neither layer was carded to
increase orientation.
TABLE-US-00004 TABLE Ex. No. of layers Den. Perm. C.T. Thick.
1.sup.st R 2.sup.nd R 3.sup.rd R 1.sup.st F 2.sup.nd F 3.sup.rd F 1
10 0.056 500 3.0 1.93 18 38 28 29.6 23.0 23.2 2 7 0.036 1650 1.7
2.08 37 25 23 7.0 9.5 11.0 3 9 0.047 2500 1.2 2.03 36 34 31 3.1 3.9
4.4 4 4 of 3/5 of 1 0.052 2500/500 1.2/3.0 1.85 25 23 19 4.9 6.0
6.7 5 3 of 2/5 of 1 0.047 1650/500 1.7/3.0 1.85 29 20 20 6.3 7.7
8.5 6 18 0.024 7645/770 0.6/2.6 2.09 29 29 28 N/A N/A N/A 7 2 N/A
3400/770 N/A N/A N/A N/A N/A N/A N/A N/A
!
It is quite striking from examining the data in the Table that a
multilayer surge material of about the same thickness as a single
layer surge material can have better (lower) runoff results. This
may be seen by comparing Example 3 to Examples 4 and 5, which,
while slightly thinner overall, have lower runoff values than
homogeneous, high permeability Example 3. Such a result is
counterintuitive.
Although only a few exemplary embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. In the claims, means
plus function claims are intended to cover the structures described
herein as performing the recited function and not only structural
equivalents but also equivalent structures. Thus although a nail
and a screw may not be structural equivalents in that a nail
employs a cylindrical surface to secure wooden parts together,
whereas a screw employs a helical surface, in the environment of
fastening wooden parts, a nail and a screw may be equivalent
structures.
* * * * *