Note: Descriptions are shown in the official language in which they were submitted.
CA 02241820 1998-07-31
WET-RESILIENT WEBS AND DISPOSABLE ARTICLES MADE THEREWITH
Background of the Invention
In the manufacture of absorbent paper products such as facial tissue, bath
tissue,
paper towels, napkins and the like, many different sheet properties influence
the
performance of the particular product being made. Softness, strength,
absorbency, bulk
and the like are often the subject of improvements. However, a property of
tissue-related
products is that when wetted and crumpled in the hand, they essentially
collapse into a
dense wet mass. Stated another way, such tissue products have a low wet
compressive
modulus, low bending modulus and low wet resiliency. These properties are
undesirable
for such products when used to wipe up liquids because, once saturated, they
lose their
designed structure and thus much of their functionality.
Similar problems can be found with some disposable absorbent articles.
Generally, disposable absorbent articles include, in their construction, an
absorbent core
positioned between a liquid-permeable cover or topsheet layer and a liquid-
impermeable
baffle or backsheet layer. The cover material is generally designed to allow
body
exudates to permeate through the cover so that the absorbent core can absorb
the fluids.
The baffle or backsheet material is generally fluid impermeable and is
positioned so that it
is away from the body. The absorbent core serves to store fluid that contacts
the article.
An additional layer of material, termed a transfer layer or surge layer, may
also be
present between the absorbent core and the liquid-permeable cover. This layer
serves to
manage the transfer or distribution of the liquid to the absorbent core.
Examples of such
absorbent articles include products such as diapers, sanitary napkins,
training pants,
incontinent garments, overnight pads, panty liners, underarm shields, as well
as other
absorbent devices used for medical purposes such as surgical absorbents. Such
articles
are designed to absorb body fluids, such as urine, menses, blood, perspiration
and other
excrement discharged by the body.
One continuing problem with some disposable absorbent articles is that the
bodily
excretions are usually directed at one portion of the absorbent, whereas the
absorptive
capacity of the product is spread over a greater area. Localized insults of
body fluid may
cause a failure of the product because the fluid handling characteristics of
the liquid-
permeable cover, transfer layer and the absorbent core are inadequate to
quickly
CA 02241820 2005-09-29
distribute the fluid throughout the absorbent core material. Such failures are
often in part
due to the collapse of the low density structure of the various components
when wetted.
This is a particular problem for cellulosic materials.
Accordingly, there is a need for a wet-resilient web material that can more
effectively transfer andlor absorb fluids for use in tissues, towels and
absorbent products.
Summary of the Invention
In accordance with one aspect of the present invention, there is provided a
low-density, noncompressively-dried, three-dimensional cellulosic web
comprising at
least about 15 dry weight percent high yield pulp fibers to which a wet
strength agent
has been added, said web having a density of about 0.3 grams per cubic
centimeter
or less, an Overall Surface Depth of about 0.2 millimeter or greater, an In-
Plan
Permeability of about 5 x 10-" square meters or greater, and a Wet Compressed
Bulk
of about 6 cubic centimeters per gram or greater, the wet strength agent
having a wet
to dry geometric mean tensile strength ratio of about 0.1 or greater.
In accordance with a further aspect of the present invention, there is
provided
an uncreped through-air-dried cellulosic web comprising at least about 10 dry
weight
percent virgin high yield pulp fibers to which a wet strength agent has been
added,
said web having a density of about 0.15 gram per cubic centimeter or less, a
Wet
Compressed Buik of about 6 cubic centimeters per gram or greater and an
Overall
Surface Depth of about 0.3 millimeter or greater, the wet strength agent
having a wet
to dry geometric mean tensile strength ratio of about 0.1 or greater.
In accordance with a further aspect of the present invention, there is
provided
a noncompressively-dried cellulosic web having a density of about 0.3 gram per
cubic
centimeter or less, a wet:dry ratio of about 0.10 or greater, an Overall
Surface Depth
of about 0.2 millimeter or greater, a Wet Compressed Bulk of about 7 cubic
centimeters per gram or greater, and a wet strength agent having a wet to dry
geometric mean tensile strength ratio of about 0.1 or greater.
In accordance with a yet further aspect of the present invention, there is
provided an absorbent article comprising a backsheet layer, a liquid permeable
topsheet layer connected in a superposed relation with said backsheet layer,
and at
least one through-air-dried cellulosic sheet sandwiched between said topsheet
layer
and backsheet layer, said through-air-dried sheet comprising at least about 20
dry
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CA 02241820 2005-09-29
weight percent high yield pulp fibers to which a wet strength agent has been
added
and having a density of about 0.3 grams per cubic centimeter or less, an
overall
Surface Depth of about 0.3 millimeters or greater and a Wet Compressed Bulk of
about 7 cubic centimeters per gram or greater, the wet strength agent having a
wet to
dry geometric mean tensile strength ratio of about 0.1 or greater.
fn accordance with a yet further aspect of the present invention, there is
provided an absorbent article comprising a noncompressively-dried ceilulosic
web
having a density of about 0.3 gram per cubic centimeter or less, a wet:dry
ratio of
about 0.1 or greater, an Overall Surface Depth of about 0.2 millimeter or
greater, a
Wet Compressed Bulk of 7 cubic centimeters per gram or greater, a Wet
Springback
Ratio of about 0.75 or greater, a FIFE Test value of 125 seconds or less, an
In-Plane
Permeability of about 4 x 10-" square meters or greater and a wet strength
agent
having a wet to dry geometric mean tensile strength ratio of about 0.1 or
greater.
In accordance with a yet further aspect of the present invention, there is
provided an absorbent article comprising a backsheet layer, a liquid permeable
topsheet layer connected in a superposed relation with said backsheet layer,
and a
retention portion for storing liquid, said retention portion sandwiched
between said
topsheet layer and backsheet layer and including at least one uncreped through-
air-
dried cellulosic sheet having a density of about 0.3 grams per cubic
centimeter or
less, a FIFE Test value of about 100 seconds or less, and an Overall Surface
Depth
of about 0.3 millimeter or greater, said sheet comprising at least about 20
dry weight
percent high yield pulp fibers to which a wet strength agent has been added,
the wet
strength agent having a wet to dry geometric mean tensile strength ratio of
about 0.1
or greater.
In accordance with a yet further aspect of the present invention, there is
provided an absorbent article comprising a backsheet layer, a liquid permeable
topsheet layer connected in a superposed relation with said backsheet layer,
and an
absorbent structure sandwiched between said topsheet layer and backsheet
layer,
said absorbent structure including a retention portion for storing said
liquid, high yield
pulp fibers to which a wet strength agent has been added, the wet strength
agent
having a wet to dry geometric mean tensile strength ratio of about 0.1 or
greater and a
surge portion for managing a distribution of said liquid, said surge portion
including at
least one uncreped through-air-dried cellulosic sheet having a density of
about 0.3
grams per cubic centimeter or less, an Overall Surface Depth of about 0.3
millimeters
or greater and an In-Plane Permeability of about 5 x 10-" square meters or
greater..
-2a-
CA 02241820 2005-06-13
)t has been discovered that papermaking fibers containing high-yield fibers,
such
as chemithermomechanlca! pulp fibers, when combined with wet strength
additives, can
be made into a low-density, three-dimensional sheet or web followed by or
incorporating
largely noncornpressive drying means such that the resulting low density
cellulosic sheet
has remarkable wet resiliency properties, showing great resistance to wet
collapse.
"Noncompressive drying" refers to drying methods such as through-air drying;
air
jet impingement drying; non-contacting drying such as air flotation drying, as
taught by
E.V. Bowden, Appita Journal, 44(1): 41 (1991); through-flovv or impingement of
superheated steam; microwave drying and other radiofrequency or dielectric
drying
methods; water extraction by supercritical fluids; water extraction by
nonaqueous, low
surface tension fluids; infrared drying; drying by contact with a film of
molten metal; and
other methods for drying cellulosic webs that do not involve compressive nips
or other
steps causing significant densification or compression of a portion of the web
during the
drying process. (Standard dry creping technology is viewed as a compressive
drying
method since the web must be mechanically pressed onto part of the drying
surface,
causing significant densification of the regions pressed onto the heated
Yankee cylinder.)
The three-dimensional sheets of the present invention could be dried with any
of the
above mentioned noncompressive drying means without causing significant web
densification or a significant loss of their three-dimensional structure and
their wet
resiliency properties.
Preferably, the low-density three-dimensional structure is created in
substantial
part before the sheet reaches a solids level (dryness level) of about 80% or
higher.
Creating the low-density three-dimensional structure can be achieved in part
through a
variety of means, including but not limited to the use of specially treated
high-bulk fibers
such as curled or chemically treated fibers as an additive in the furnish,
including the
fibers taught by C. C. Van Haaften in "Sanitary Napkin with Cross-linked
Cellulosic
Layer," United States Patent No. 3,339,550, issued September 5, 1967,
- 2b -
CA 02241820 2005-06-13
mechanical debonding means such as differential velocity ("rush") transfer
between
fabrics or wires, hereafter described; mechanical straining or "wet straining"
of the moist
web, including the methods taught.by M.A. Hermans et al. in US Pat. No.
5,492,598,
"Method for Increasing the Internal Bulk of Throughdried Tissue," issued Feb.
20, 1996,
and M.A. Hermans et al. in US Pat. No. 5,411,636, "Method for Increasing the
Internal Bulk of Wet-Pressed Tissue," issued May 2, 1995; molding of the fiber
onto a three-dimensional wire or fabric, such as the fabrics disclosed by Chiu
et al. in US Pat. No. 5,429,686, "Apparatus for Making Soft Tissue Products,"
issued July 4, 1995, including differential velocity transfer .onto or from
said
three-dimensional wire or fabric; wet embossing of the sheet; wet creping; and
the optional use of chemical debonding agents.
Products of the present invention have surprisingly high wet resiliency. For
example, when the products of this invention are saturated with water and
crumpled in
one's hand into a ball about the size of a golf ball, and thereafter released,
they quickly
open up to mostly uncrumple themselves. By contrast, current commercially-
available
products such as bath tissues and paper towels remain substantially wadded up
in a wet
ball. It has been further discovered that such sheets, when properly made, can
have
unexpectedly good fluid handling properties, such as high intake rate, high in-
plane
permeability, high absorption capacity, and rapid in-plane distribution of
liquid, making
these materials ideally suited for use in tissues, paper towels and numerous
absorbent
articles. As used herein, unless otherwise stated, absorbent articles include
sanitary
napkins and other feminine care products; disposable diapers and related
personal care
products; training pants; incontinence products; breast pads; poultry pads and
meat pads
for absorbing blood and meat juices; bed pads far home and hospital use; sweat
bands
and other perspiration absorbing articles; odor and sweat absorbing pads for
use in shoes
or garments; and the like. The materials of the present invention can be
utilized in
numerous articles where fluid is absorbed or entrapped, functioning as fluid
surge webs,
transfer layers, distribution webs, absorbent cares, absorbent composites, and
so forth.
The high wet strength and significant large-scale texture of the materials
also can serve
effectively in preventing the breakup or loss of integrity of weaker, adjacent
materials such
as fluff pulp or tissue in absorbent articles, allowing the materials of the
present invention
to serve effectively as means for maintaining or improving the integrity of
the absorbent
core (superabsorbent/fluff mixture) of absorbent articles such as diapers and
the tike.
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CA 02241820 1998-07-31
Further, the combination of high wet strength, high absorption capacity, and
significant
surface texture makes these materials ideally suited for cleaning operations
such as
scrubbing, mopping, and wiping, with possible incorporation into cleaning
articles such as
mops, wipers, scrub pads, and the like. As used herein, the terms "web" and
"sheet" are
used interchangeably and mean the same.
The unique properties and characteristics of the sheets of this invention can
be
quantified by one or more of the following terms, which will hereinafter be
described and
defined: Overall Surface Depth; wet:dry ratio; Wet Wrinkle Recovery Test; Wet
Compressed Bulk; Wet Springback ratio; Loading Energy Ratio; Compression
Ratio; In-
Plane Permeability; the FIFE Test; Dry Wipe Residual Total Area and Mass
Factor; Wet
Wipe Residual Total Area and Mass Factor; Mean Volume-Weighted Pore Length;
and
the Thickness Variation Index. All of these terms relate to the superior
performance of the
sheets of this invention when used in various product applications.
Hence, in one aspect, the invention resides in a non-compressively dried
cellulosic
web, such as a through-air-dried web, more specifically an uncreped through-
air-dried
web, having a density of about 0.3 gram per cubic centimeter or less and a
three-
dimensional surface having an Overall Surface Depth of about 0.10 millimeter
or greater,
said web comprising a wet strength agent and at least about 10 dry weight
percent high
yield pulp fibers, preferably virgin high yield pulp fibers, and more
preferably virgin
softwood fibers, said three-dimensional surface preferably being created in
substantial
part by mechanical means prior to reaching a dryness level of about 80
percent, more
preferably with the use of through-drying fabrics, and preferably with a rush
transfer level
exceeding 10 percent.
The basis weight of the webs of this invention can be about 10 grams per
square
meter (gsm) or greater, more specifically from about 10 to about 80 gsm, still
more
specifically from about 20 to about 60 gsm, and still more specifically from
about 30 to
about 50 gsm.
The fiber composition of the webs of this invention can have from about 10 to
about 100 percent wood pulp fibers, particularly containing about 70 percent
or greater,
more specifically about 80 percent or greater, more specifically about 90
percent or
greater, and still more specifically about 95 percent wood pulp fibers or
greater.
Additionally, it is preferred that the fiber composition of the webs of this
invention
comprise about 70 percent or greater softwood fibers, more specifically about
80 percent
or greater, and still more specifically about 90 percent or greater softwood
fibers.
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CA 02241820 2005-06-13
In another aspect, the present invention resides in an absorbent article
comprising
a backsheet layer, a liquid permeable topsheet layer connected in a superposed
relation
with the backsheet layer, and at least one cefiulosic web as described above
sandwiched
between the topsheet layer and the backsheet layer. The cellulosic web can
also serve
as an absorbent core material to retain and store liquid, particularly when
incorporated
into the absorbent article in multiple plies (such as from about 2 to about 20
or more, more
specifically from about 2 to about 5 or 10) or it can serve to receive and
distribute liquid to
the absorbent core by being positioned in liquid communication with the
absorbent. As
such the webs of this invention can be used as "transfer" layers, "surge"
layers,
"distribution" layers and the like.
Representative patents illustrating absorbent products in which the web or
sheets
of this invention can be used include: U.S. 5,386,595 issued February 7, 1995
to Kuen et
al. entitled "Garment Attachment System"; U.S. 4,500,316 issued February 19,
1985 to
Damico entitled "Disposable Garment°; U.S. 5,364,382 issued November
15, 1994 to
Latimer et al. entitled NAbsorbent Structure Having Improved Fluid Surge
Management
and Product Incorporating Same"; U.S. 4,940,464 issued July 10, 1990 to Van
Gompel et
al. entitled "Disposable Incontinence Garment or Training Pant"; and U.S.
Patent 5,549,592 issued August 27, 1996 to D. Fries et al., entitled
"Absorbent
Article With Laminated Tape".
Although the reasons for the unexpectedly good material properties and product
performance results obtained with the present invention are not fully
understood, it
appears that three factors interact synergistically to yield unusually high
wet resiliency
perfom~ance: (1 ) a high bulk (low density) three-dimensional structure
obtained without
significant compression during drying and preferably obtained without creping,
(2) high
yield pulp fibers, preferably comprising at feast about 20 percent of the
fiber furnish used
to make the sheet; and (3) the use of one or more wet strength resins or
agents such that
the wet to dry geometric mean tensile strength ratio is about 0.1 or greater.
It has been
found that if any of these three factors is missing, a wetted sheet will lack
the high wet
resiliency and/or other properties which are important for many of the uses
for the webs of
the present invention.
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CA 02241820 1998-07-31
Definition of Terms and Test Procedures
In describing the webs of this invention and their fluid-handling
characteristics, a
number of terms and tests are used which are described below.
As used herein, "high yield i~ul~ fibers" are those natural papermaking fibers
produced by pulping processes providing a yield of about 65 percent or
greater, more
specifically about 75 percent or greater, and still more specifically from
about 75 to about
95 percent. Yield is the resulting amount of processed fiber expressed as a
percentage of
the initial raw material mass. Such pulping processes include bleached
chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP)
pressure/pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP),
thermomechanical chemical pulp (TMCP), high yield sulfite pulps, and high
yield kraft
pulps, all of which leave the resulting fibers with high levels of lignin.
High yield fibers are
well known for their stiffness (in both dry and wet states) relative to
typical chemically
pulped fibers. The cell wall of kraft and other non-high yield fibers tends to
be more
flexible because lignin, the "mortar" or "glue" on and in part of the cell
wall, has been
largely removed. The preferred high yield pulp fibers can also be
characterized by being
comprised of comparatively whole, relatively undamaged fibers, high freeness
(250
Canadian Standard Freeness (CFS) or greater, more specifically 350 CFS or
greater,
and still more specifically 400 CFS or greater), and low fines content (less
than 25
percent, more specifically less than 20 percent, still more specifically less
that 15 percent,
and still more specifically less than 10 percent by the Britt jar test). Webs
made with
recycled fibers are less likely to achieve the wet resiliency properties of
the present
invention because of damage to the fibers during mechanical processing. In
addition to
common papermaking fibers listed above, high yield pulp fibers also include
other natural
fibers such as milkweed seed floss fibers, abaca, hemp, cotton and the like.
Fibers from
wood are preferred.
The amount of high yield pulp fibers in the sheet can be at least about 10 dry
weight percent or greater, more specifically about 15 dry weight percent or
greater, more
specifically about 30 dry weight percent or greater, still more specifically
about 50 dry
weight percent or greater, and still more specifically from about 20 to 100
percent. For
layered sheets, these same amounts can be applied to one or more of the
individual
layers such that the overall unitary web has at least about 10 or 15 percent
high yield
fibers. Because high yield pulp fibers are generally less soft than other
papermaking
fibers, in some applications it is advantageous to incorporate them into the
middle of the
- 6 -
CA 02241820 1998-07-31
final product, such as placing them in the center layer of a three-layered
sheet or, in the
case of a two-ply product, placing them in the inwardly-facing layers of each
of the two
plies.
"Water retention value" (WRV) is a measure that can be used to characterize
some fibers useful for purposes of this invention. WRV is measured by
dispersing 0.5
grams of fibers in deionized water, soaking overnight, then centrifuging the
fibers in a 1.9
inch diameter tube with a 100 mesh screen at the bottom at 1000 G for 20
minutes. The
samples are weighed, then dried at 105° C. for two hours and then
weighed again. WRV
is (wet weight - dry weight)/dry weight. Fibers useful for purposes of this
invention can
have a WRV of about 0.7 or greater, more specifically about 0.9 or greater,
still more
specifically from about 0.9 to about 2. High yield pulp fibers often have a
WRV of about 1
or greater.
"D n i H can be determined by measuring the caliper of a single sheet using a
TMI tester with a load of 0.289 psi. Density is calculated by dividing the
caliper by the
basis weight of the sheet. The webs of this invention commonly have low,
substantially
uniform densities (high bulks). Substantial density uniformity can be
achieved, for
example, by noncompressive drying means such as throughdrying to final dryness
without
differentially compressing the web. While the webs of this invention have a
three-
dimensional contour imparted by the topography of a throughdrying fabric, the
side-to-side
thickness of the web is relatively uniform. In general, the density of the
products of this
invention can be about 0.3 gram per cubic centimeter or less, more
specifically about 0.15
gram or less, still more specifically about 0.1 gram per cubic centimeter or
less. It is
believed to be important that the absorbent structure, once formed, be dried
without
substantially reducing the number of wet- resilient interfiber bonds.
Throughdrying, which
is a common method for drying tissues and towels, is a preferred method of
preserving
the structure. Absorbent structures made by wet laying followed by
throughdrying
typically have a density of about 0.1 gram per cubic centimeter, whereas
airlaid structures
normally used for diaper fluff typically have densities of about 0.05 gram per
cubic
centimeter. All of such structures are within the scope of this invention.
"Wet strength agents". An integral part of the invention is the material used
to
immobilize the bonds between the fibers in the wet state. Typically the means
by which
fibers are held together in paper and tissue products involve hydrogen and
sometimes
combinations of hydrogen bonds and covalent and/or ionic bonds. In the present
invention, it is important to provide a material that will allow bonding of
fibers in such a
CA 02241820 1998-07-31
way as to immobilize the fiber to fiber bond points and make them resistant to
disruption
in the wet state. In this instance the wet state usually will mean when the
product is
exposed to water or other aqueous solutions, but could also mean exposure to
body fluids
such as urine, blood, mucus, menses, lymph and other body exudates.
There are a number of materials commonly used in the paper industry to impart
wet strength to paper and board that are applicable to this invention. These
materials are
known in the art as "wet strength agents" and are commercially available from
a wide
variety of sources. Any material that when added to a paper web or sheet
results in
providing the sheet with a wet geometric tensile strength:dry geometric
tensile strength
ratio in excess of 0.1 will, for purposes of this invention, be termed a wet
strength agent.
Typically these materials are termed either as permanent wet strength agents
or as
"temporary" wet strength agents. For the purposes of differentiating permanent
from
temporary wet strength, permanent will be defined as those resins which, when
incorporated into paper or tissue products, will provide a product that
retains more than
50% of its original wet strength after exposure to water for a period of at
least five
minutes. Temporary wet strength agents are those which show less than 50% of
their
original wet strength after exposure to water for five minutes. Both classes
of material find
application in the present invention. The amount of wet strength agent added
to the pulp
fibers can be at least about 0.1 dry weight percent, more specifically about
0.2 dry weight
percent or greater, and still more specifically from about 0.1 to about 3 dry
weight percent
based on the dry weight of the fibers.
Permanent wet strength agents will provide a more or less long-term wet
resilience
to the structure. This type of structure would find application in products
that would
require long-term wet resilience such as in paper towels and in many absorbent
consumer
products. In contrast, the temporary wet strength agents would provide
structures that
had low density and high resilience, but would not provide a structure that
had long-term
resistance to exposure to water or body fluids. While the structure would have
good
integrity initially, after a period of time the structure would begin to lose
its wet resilience.
This property can be used to some advantage in providing materials that are
highly
absorbent when initially wet, but which after a period of time lose their
integrity. This
property could be used in providing "flushable" products. The mechanism by
which the
wet strength is generated has little influence on the products of this
invention as long as
the essential property of generating water-resistant bonding at the
fiber/fiber bond points
is obtained.
CA 02241820 2005-06-13
The permanent wet strength agents that are of utility in the present invention
are
typically water soluble, cationic oligomeric or polymeric resins that are
capable of either
crosslinking with themselves {homocrosslinking) or with the cellulose or other
constituent
of the wood fiber. The most widely-used materials for this purpose are the
class of
polymer known as polyamide-polyamine-epichlorohydrin (PAE) type resins. These
materials have been described in patents issued to Keim (U.S. 3,700,623 and
3,772,076)
TM
and ace sold by Hercules, Inc., Wilmington, Delaware, as K,ymene 557H. Related
materials are marketed by Henkel Chemical Co., Charlotte, North Carolina and
Georgia-
Pacific Resins, lnc., Atlanta, Georgia.
Polyamide-epichlorohydrin resins are also useful as bonding resins in this
TM
invention. Materials developed by Monsanto and marketed under the Santo Res
label are
base-activated polyamide-epichlorohydrin resins that can be used in the
present
invention. These materials are described in patents issued to Petrovich (U.S.
3,885,158;
U.S. 3,899,388; U.S. 4,129,528 and U.S. 4,147,586) and van Eenam (U.S.
4,222,921).
Although they are not as commonly used in consumer products, polyethylenimine
resins
are also suitable for immobilizing the bond points in the products of this
invention.
Another class of permanent-type wet strength agents are exemplified by the
aminoplast
resins obtained by reaction of formaldehyde with melamine or urea.
The temporary wet strength resins that can be used in connection with this
invention
include, but are not limited to, those resins that have been developed by
American
TM
Cyanamid and ace marketed under the name Parez 631 NC (now available from
Cytec
Industries, West Paterson, New Jersey). This and similar resins are described
in U.S.
3,556,932 to Coscia et al. and 3,556,933 to Williams et al. Gather temporary
wet strength
agents that should find application in this invention include modified
starches such as
TM
those available from National Starch and marketed as Co-Bond 1000. It is
believed that
these and related starches are covered by U.S. 4,675,394 to Sofarek et al.
Derivatized
dialdehyde starches, such as described in Japanese Kokai Tokkyo Koho JP
03,185,197,
should also find application as useful materials for providing temporary wet
strength. It is
also expected that other temporary wet strength materials such as those
described in U.S.
4,981,557; U.S. 5,008,344 and U.S. 5,085,736 to Bjorkquist would be of use in
this
invention. With respect to the classes and the types of wet strength resins
listed, it should
be understood that this listing is simply to provide examples and that this is
neither meant
to exclude other types of wet strength resins, nor is it meant to limit the
scope of this
invention.
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CA 02241820 1998-07-31
Although wet strength agents as described above find particular advantage for
use
in connection with in this invention, other types of bonding agents can also
be used to
provide the necessary wet resiliency. They can be applied at the wet end or
applied by
spraying or printing, etc. after the web is formed or after it is dried.
As used herein, the Nwet:dry ratio" is the ratio of the geometric mean wet
tensile
strength divided by the geometric mean dry tensile strength. Geometric mean
tensile
strength (GMT) is the square root of the product of the machine direction
tensile strength
and the cross-machine direction tensile strength of the web. Unless otherwise
indicated,
the term "tensile strength" means "geometric mean tensile strength." The webs
of this
invention have a wet:dry ratio of about 0.1 or greater, more specifically
about 0.15 or
greater, more specifically about 0.2 or greater, still more specifically about
0.3 or greater,
still more specifically about 0.4 or greater, and still more specifically from
about 0.2 to
about 0.6. Tensile strengths can be measured using an Instron tensile tester
using a 3
inches jaw width, a jaw span of 4 inches, and a crosshead speed of 10 inches
per minute
after maintaining the sample under TAPPI conditions for 4 hours before
testing. The
webs of this invention also preferably have a minimum absolute ratio of dry
tensile
strength to basis weight of 10 grams/gsm, preferably 15 grams/gsm, more
preferably 20
grams/gsm, more preferably 30 grams/gsm, and still more preferably 40
grams/gsm and
preferably from about 20 to about 100 grams/gsm. The webs of this invention
also
preferably have a minimum absolute ratio of wet tensile strength to basis
weight of about
1 gram/gsm, preferably about 2 grams/gsm, more preferably about 5 grams/gsm,
more
preferably about 10 grams/gsm and still more preferably about 20 grams/gsm and
preferably from about 15 to about 50 grams/gsm.
"Overall Surface De~t_h°. A three-dimensional basesheet or web is a
sheet with
significant variation in surface elevation due to the intrinsic structure of
the sheet itself. As
used herein, this elevation difference is expressed as the "Overall Surface
Depth." The
webs of this invention possess three-dimensionality and have an Overall
Surface Depth of
about 0.1 mm. or greater, more specifically about 0.3 mm. or greater, still
more
specifically about 0.4 mm. or greater, still more specifically about 0.5 mm.
or greater, and
still more specifically from about 0.4 to about 0.8 mm.
The three-dimensional structure of a largely planar sheet can be described in
terms of its surface topography. Rather than presenting a nearly flat surface,
as is typical
of conventional paper, the molded sheets of the present invention have
significant
topographical structures that derive in part from the use of sculptured
through-drying
- io -
CA 02241820 2005-06-13
fabrics such as those taught by Chiu et al. in United States Patent No. US
5,429,686,
°Apparatus for Making Soft Tissue Products," issued July 4, 1995. The
resulting paper surface topograph typically comprises a regular repeating
unit cell that is typically a parallelogram with sides between 2 and 20 mm in
length. It is
important that these three-dimensional structures be created by molding the
moist sheet
or be created prior to drying, rather than by creping or embossing or other
operations after
the sheet has been dried. In this manner, the three-dimensional structure is
more likely to
be well-retained upon wetting, helping to provide high wet resiliency and to
promote good
in-plane permeability.
In addition to the regular geometrical structure imparted by the sculptured
fabrics
and other fabrics used in creating a sheet, additional fine structure, with an
in-plane length
scale less than about 1 mm, can be present in the sheet. Such a fine structure
can stem
from microfolds created during differential velocity transfer of the web from
one fabric or
wire to another pr7or to drying. Some of the materials of the present
invention, for
example, appear to have fine structure with a fine surface depth of 0.1 mm or
greater, and
sometimes 0.2 mrn or greater, when height profiles are measured using a
commercial
moire interferometer system. These fine peaks have a typical half width less
than 1 mm.
The fine structure from differential velocity transfer and other treatments
may be useful in
providing additional softness, flexibility, and bulk. Measurement of the
surface structures
is described below.
An especially suitable method for measurement of Overall Surface Depth is
moire
interferometry, which permits accurate measurement without deformation of the
surface.
For reference to the materials of the present invention, surface topography
should be
measured using a computer-controlled white-light field-shifted moire
interferometer with
about a 38 mm field of view. The principles of a useful implementation of such
a system
are described in Bieman et al. (L. Bieman, K. Harding, and A. Boehnlein,
"Absolute
Measurement Using Field-Shifted Moire," SPIE Optical Conference Proceedings,
Vol.
1614, pp. 259-264, 1991). A suitable commercial instrument for moir~
interferometry is the
CADEYES~ interferometer produced by Medar, Inc. (Farmington Hills, Michigan),
constructed for a 38-mm field-of view (a field of view within the range of 37
to 39.5 mm is
adequate). The CADEYES~ system uses white light which is projected through a
diffraction grid to project fine black lines onto the sample surface. The
surface is viewed
through a similar diffraction grid, creating moire fringes that are viewed by
a CCD camera.
Suitable lenses and a stepper motor adjust the optical configuration for field
shifting (a
CA 02241820 2005-06-13
technique described below). A video processor sends captured fringe images to
a PC
computer for processing, allowing details of surface height to be back-
calculated from the
fringe patterns viewed by the video.camera.
In the CADEYES moir~ interferometry system, each pixel in the CCD video image
is said to belong to a moire fringe that is associated with a particular
height range. The
method of field-shifting, as described by Bieman et al. (L. 5lieman, K.
Harding, and A.
Boehnlein, "Absolute Measurement Using Field-Shifted Moire," SPIE C3ptical
Conference
Proceedings, Vol. 1614, pp. 259 - 264, 1991 ) and as originally patented by
Boehnlein
(United States Patent 5,069,548), is used to identify the fringe number for
each point in the video image (indicating which fringe a point belongs to).
The fringe
number is needed to determine the absolute height at the measurement point
relative to a
reference plane. A field-shifting technique (sometimes termed phase-shifting
in the art) is
also used fvr sub-fringe analysis (accurate determination of the height of the
measurement point within the height range occupied by its fringe). These field-
shifting
methods coupled with a camera-based interferometry approach allows accurate
and rapid
absolute height measurement, permitting measurement to be made in spite of
possible
height discontinuities in the surface. The technique allows absolute height of
each of the
roughly 250,000 discrete points (pixels) on the sample surface to be obtained,
if suitable
optics, video hardware, data acquisition equipment, and software are used that
incorporates the principles of moire interferometry with field-shifting. Each
point measured
has a resolution of approximately 1.5 microns in its height measurement.
The computerized interferometer system is used to acquire topographical data
and
then to generate a grayscale image of the topographical data, said image to be
hereinafter called "the height map." The height map is displayed on a computer
monitor,
typically in 256 shades of gray and is quantitatively based on the
topographical data
obtained for the sample being measured. The resulting height map for the 38-mm
square
measurement area should contain approximately 250,000 data points
corresponding to
approximately 500 pixels in both the horizontal and vertical directions of the
displayed
height map. The pixel dimensions of the height map are based on a 512 x 512
CCD
camera which provides images of moire patterns on the sample which can be
analyzed by
computer software. Each pixel in the height map represents a height
measurement at the
corresponding x- and y-location on the sample. In the recomrnended system,
each pixel
has a width of approximately 70 microns, i.e. represents a region on the
sample surface
about 70 microns long in both orthogonal in-plane directions). This level of
resolution
- 12 -
CA 02241820 1998-07-31
prevents single fibers projecting above the surface from having a significant
effect on the
surface height measurement. The z-direction height measurement must have a
nominal
accuracy of less than 2 microns and a z-direction range of at least 1.5 mm.
(For further
background on the measurement method, see the CADEYES Product Guide, Medar,
Inc.,
Farmington Hills, MI, 1994, or other CADEYES manuals and publications of
Medar, Inc.)
The CADEYES system can measure up to 8 moire fringes, with each fringe being
divided into 256 depth counts (sub-fringe height increments, the smallest
resolvable
height difference). There will be 2048 height counts over the measurement
range. This
determines the total z-direction range, which is approximately 3 mm in the 38-
mm field-of-
view instrument. If the height variation in the field of view covers more than
eight fringes, a
wrap-around effect occurs, in which the ninth fringe is labeled as if it were
the first fringe
and the tenth fringe is labeled as the second, etc. In other words, the
measured height will
be shifted by 2048 depth counts. Accurate measurement is limited to the main
field of 8
fringes.
The moire interferometer system, once installed and factory calibrated to
provide
the accuracy and z-direction range stated above, can provide accurate
topographical data
for materials such as paper towels. (Those skilled in the art may confirm the
accuracy of
factory calibration by pertorming measurements on surfaces with known
dimensions.)
Tests are performed in a room under Tappi conditions (73°F, 50%
relative humidity). The
sample must be placed flat on a surface lying aligned or nearly aligned with
the
measurement plane of the instrument and should be at such a height that both
the lowest
and highest regions of interest are within the measurement region of the
instrument.
Once properly placed, data acquisition is initiated using Medar's PC software
and
a height map of 250,000 data points is acquired and displayed, typically
within 30 seconds
from the time data acquisition was initiated. (Using the CADEYES~ system, the
"contrast
threshold levels for noise rejection is set to 1, providing some noise
rejection without
excessive rejection of data points.) Data reduction and display are achieved
using
CADEYES~ software for PCs, which incorporates a customizable interface based
on
Microsoft Visual Basic Professional for Windows (version 3.0). The Visual
Basic interface
allows users to add custom analysis tools.
The height map of the topographical data can then be used by those skilled in
the
art to identify characteristic unit cell structures (in the case of structures
created by fabric
patterns; these are typically parallelograms arranged like tiles to cover a
larger two-
dimensional area) and to measure the typical peak to valley depth of such
structures. A
- 13 -
CA 02241820 1998-07-31
simple method of doing this is to extract two-dimensional height profiles from
lines drawn
on the topographical height map which pass through the highest and lowest
areas of the
unit cells. These height profiles can then be analyzed for the peak to valley
distance, if
the profiles are taken from a sheet or portion of the sheet that was lying
relatively flat
when measured. To eliminate the effect of occasional optical noise and
possible outliers,
the highest 10% and the lowest 10% of the profile should be excluded, and the
height
range of the remaining points is taken as the surface depth. Technically, the
procedure
requires calculating the variable which we term "P10," defined at the height
difference
between the 10% and 90% material lines, with the concept of material lines
being well
known in the art, as explained by L. Mummery, in Surface Texture Analysis: The
Handbook, Hommelwerke GmbH, Muhlhausen, Germany, 1990. In this approach, the
surface is viewed as a transition from air to material. For a given profile,
taken from a flat-
lying sheet, the greatest height at which the surface begins - the height of
the highest
peak - is the elevation of the "0% reference line" or the "0% material line,"
meaning that
0% of the length of the horizontal line at that height is occupied by
material. Along the
horizontal line passing through the lowest point of the profile, 100% of the
line is occupied
by material, making that line the "100% material line." In between the 0% and
100%
material lines (between the maximum and minimum points of the profile), the
fraction of
horizontal line length occupied by material will increase monotonically as the
line elevation
is decreased. The material ratio curve gives the relationship between material
fraction
along a horizontal line passing through the profile and the height of the
line; this
relationship is sketched in FIG 2. The material ratio curve is also the
cumulative height
distribution of a profile. (A more accurate term might be "material fraction
curve.")
Once the material ratio curve is established, one can use it to define a
characteristic peak height of the profile. The P10 "typical peak-to-valley
height" parameter
is defined as the difference between the heights of the 10% and 90% material
lines. This
parameter is relatively robust in that outliers or unusual excursions from the
typical profile
structure have little influence on the P10 height. The units of P10 are mm.
The Overall
Surface Depth of a material is reported as the P10 surface depth value for
profile lines
encompassing the height extremes of the typical unit cell of that surface.
"Fine surface
depth" is the P10 value for a profile taken along a plateau region of the
surface which is
relatively uniform in height relative to profiles encompassing a maxima and
minima of the
unit cells. Measurements are reported for the most textured side of the
materials of the
present invention, which is typically the side that was in contact with the
through-drying
- 14 -
CA 02241820 2005-06-13
fabric when air flow is toward the through-dryer. Figures 3A, 3B and 3C show
typical
TM
profiles from a sample of SURPASS, which is a commercial uncreped, through-
dried
material made with secondary fibers. The Overall Surface Depth is seen to be
about 0.3
mm. Typical fine elements have a fine surface depth less than 0.15 mm. Figures
4A, 4B
and 4C present profiles from Sample U2 of the present invention, described
hereafter in
the Examples. The Overall Surface Depth is over 0. 4 mm, and the fine
structure has a
surtace depth of about 0.3 mm. Figure 5 represents a profile of Sample U8 of
the present
invention, having an Overall Surface Depth of about 0.5 mm.
Overall Surface Depth is intended to examine the topography produced in the
basesheet, especially those features created in the sheet prior to and during
drying
processes, but is intended to exclude "artificially" created large-scale
topography from dry
converting operations such as embossing, perforating, pleating, etc.
Therefore, the
profiles examined should be taken from unembossed regions if the sheet has
been
embossed, or should be measured on an unembossed sheet. Overall Surface Depth
measurements should exclude large-scale structures such as pleats or folds
which do not
reflect the three-dimensional nature of the original basesheet itself. It is
recognized that
sheet topography may be reduced by caiendering and other operations which
affect the
entire basesheet. Overall Surface Depth measurement can be appropriately
performed
on a calendered sheet.
The "Wet Wrinkle Rec~ral Test" is used to quantify wet bending resiliency. It
is a
slight modification of AATCC Test Method 66-1990 taken from the Technical
Manual of
the American Association of Textile Chemists and Colorists (1992), page 99.
The
modification is to first wet the samples before carrying out the method. This
is done by
TM
soaking the samples in water containing 0.01 percent TRITON X-100 wetting
agent
(Rohm 8~ Haas) for five minutes before testing. Sample preparation is carried
out at 73°F.
and 50 percent relative humidity. The sample is gently removed from the water
with a
tweezers, drained by pressing between two pieces of blotter paper with 325
grams of
weight, and placed in the sample holder to be tested as with the dry wrinkle
recovery test
method. The test measures the highest recovery angle of the sample being
tested (in any
direction, including the machine direction and the cross-machine direction),
with 180°
representing total recovery. The Wet Wrinkle Recovery, expressed as a percent
recovery, is the measured recovery angle divided by 180°, multiplied by
100. Absorbent
structures of this invention can exhibit a Wet Wrinkle Recovery of about 60
percent or
- 15 -
CA 02241820 1998-07-31
greater, more specifically about 70 percent or greater, and still more
specifically about 80
percent or greater.
"Wet comr~ressive resiliency " of the new materials is defined by several
parameters and can be demonstrated using a materials property procedure that
encompasses both wet and dry characteristics. A programmable strength
measurement
device is used in compression mode to impart a specified series of compression
cycles to
an initially dry, conditioned sample, after which the sample is carefully
moistened in a
specified manner and subjected to the same sequence of compression cycles.
While the
comparison of wet and dry properties is of general interest, the most
important information
from this test concerns the wet properties. The initial testing of the dry
sample can be
viewed as a conditioning step. The test sequence begins with compression of
the dry
sample to 0.025 psi to obtain an initial thickness (cycle A), then two
repetitions of loading
up to 2 psi followed by unloading (cycles B and C). Finally, the sample is
again
compressed to 0.025 psi to obtain a final thickness (cycle D). (Details of the
procedure,
including compression speeds, are given below). Following the treatment of the
dry
sample, moisture is applied uniformly to the sample using a fine mist of
deionized water to
bring the moisture ratio (g water/g dry fiber) to approximately 1.1. This is
done by
applying 95-110% added moisture, based on the conditioned sample mass. This
puts
typical cellulosic materials in a moisture range where physical properties are
relatively
insensitive to moisture content (e.g., the sensitivity is much less than it is
for moisture
ratios less than 70%). The moistened sample is then placed in the test device
and the
compression cycles are repeated.
Three measures of wet resiliency are considered which are relatively
insensitive to
the number of sample layers used in the stack. The first measure is the bulk
of the wet
sample at 2 psi. This is referred to as the "Wet Compressed Bulk" (WCB). The
second
measure is termed "Wet S ringback Ratio~WS)", which is the ratio of the moist
sample
thickness at 0.025 psi at the end of the compression test (cycle D) to the
thickness of the
moist sample at 0.025 psi measured at the beginning of the test (cycle A). The
third
measure is the "Loading Energy Ratio" (LER), which is the ratio of loading
energy in the
second compression to 2 psi (cycle C) to that of the first compression to 2
psi (cycle B)
during the sequence described above, for a wetted sample. The final wet bulk
measured
at the end of the test (at 0.025 psi) is termed the "final bulk" or "FB"
value. When load is
plotted as a function of thickness, loading energy is the area under the curve
as the
sample goes from an unloaded state to the peak load of that cycle. For a
purely elastic
- 16 -
CA 02241820 1998-07-31
material, the springback and loading energy ratio would be unity. We have
found that the
three measures described here are relatively independent of the number of
layers in the
stack and serve as useful measures of wet resiliency. Also referred to herein
is the
"Compression Ratio", which is defined as the ratio of moistened sample
thickness at peak
load in the first compression cycle to 2 psi to the initial moistened
thickness at 0.025 psi.
In carrying out the foregoing measurements of the wet compressive resiliency,
samples should be conditioned for at least 24 hours under TAPPI conditions
(50% RH,
73°F.). Specimens are die cut to 2.5" x 2.5" squares. Conditioned
sample weight should
be near 0.4 g, if possible, and within the range of 0.25 to 0.6 g for
meaningful
comparisons. The target mass of 0.4 to 0.5 gram is achieved by using a stack
of 2 or
more sheets if the sheet basis weight is less than 65 gsm. For example, for
nominal 30
gsm sheets, a stack of 3 sheets will generally be near 0.4 g total mass. Three
sheets are
preferred for 40 gsm sheets, while 2 sheets should be used for 60 gsm sheets.
Compression measurements are performed using an Instron 4502 Universal
Testing Machine interfaced with a 286 PC computer running Instron Series XII
software
(1989 issue) and Version 2 firmware. The standard "286 computer" referred to
has an
80286 processor with a 12 MHz clock speed. The particular computer used was a
Compaq DeskPro 286e with an 80287 math coprocessor and a VGA video adapter. A
1
kN load cell is used with 2.25" diameter circular platens for sample
compression. The
lower platen has a ball bearing assembly to allow exact alignment of the
platens. The
lower platen is locked in place while under load (30-100 Ibf) by the upper
platen to ensure
parallel surfaces. The upper platen must also be locked in place with the
standard ring
nut to eliminate play in the upper platen as load is applied.
Following at least one hour of warm-up after start-up, the instrument control
panel
is used to set the extensionometer to zero distance while the platens are in
contact (at a
load of 10-30 Ib). With the upper platen freely suspended, the calibrated load
cell is
balanced to give a zero reading. The extensionometer and load cell should be
periodically checked to prevent baseline drift (shirting of the zero points).
Measurements
must be performed in a controlled humidity and temperature environment,
according to
TAPPI specifications (50% + 2% rh and 73° F). The upper platen is then
raised to a
height of 0.2 in. and control of the Instron is transferred to the computer.
Using the Instron Series XII Cyclic Test software with a 286 computer, an
instrument sequence is established with 7 markers (discrete events) composed
of 3 cyclic
blocks (instructions sets) in the following order:
- i7 -
CA 02241820 1998-07-31
Marker 1: Block 1
Marker 2: Block 2
Marker 3: Block 3
Marker 4: Block 2
Marker 5: Block 3
Marker 6: Block 1
Marker 7: Block 3.
Block 1 instructs the crosshead to descend at 1.5 in./min. until a load of 0.1
Ib. is
applied (the Instron setting is -0.1 Ib., since compression is defined as
negative force).
Control is by displacement. When the targeted load is reached, the applied
load is
reduced to zero.
Block 2 directs that the crosshead range from an applied load of 0.05 Ib. to a
peak
of 8 Ib. then back to 0.05 Ib. at a speed of 0.4 in./min. Using the Instron
software, the
control mode is displacement, the limit type is load, the first level is -0.05
Ib., the second
level is -8 Ib., the dwell time is 0 sec., and the number of transitions is 2
(compression,
then relaxation); "no action" is specified for the end of the block.
Block 3 uses displacement control and limit type to simply raise the crosshead
to
0.2 in. at a speed of 4 in./min., with 0 dwell time. Other Instron software
settings are 0 in
first level, 0.2 in second level, 1 transition, and "no action" at the end of
the block.
When executed in the order given above (Markers 1-7), the Instron sequence
compresses the sample to 0.025 psi (0.1 Ibf), relaxes, then compresses to 2
psi (8 Ibs.),
followed by decompression and a crosshead rise to 0.2 in., then compress the
sample
again to 2 psi, relaxes, lifts the crosshead to 0.2 in., compresses again to
0.025 psi (0.1
Ibf), and then raises the crosshead. Data logging should be performed at
intervals no
greater than every 0.02" or 0.4 Ib. (whichever comes first) for Block 2 and
for intervals no
greater than 0.01 Ib. for Block 1. Preferably, data logging is performed every
0.004 Ib. in
Block 1 and every 0.05 Ib. or 0.005 in. (whichever comes first) in Block 2.
The results output of the Series XII software is set to provide extension
(thickness)
at peak loads for Markers 1, 2, 4 and 6 (at each 0.025 and 2.0 psi peak load),
the loading
energy for Markers 2 and 4 (the two compressions to 2.0 psi previously termed
cycles B
and C, respectively), the ratio of the two loading energies (second
cycle/first cycle), and
the ratio of final thickness to initial thickness (ratio of thickness at last
to first 0.025 psi
compression). Load versus thickness results are plotted on the screen during
execution
of Blocks 1 and 2.
- ie -
CA 02241820 1998-07-31
In performing a measurement, the dry, conditioned sample is centered on the
lower platen and the test is initiated. Following completion of the sequence,
the sample is
immediately removed and moisture (deionized water at 72-73° F) is
applied. Moisture is
applied uniformly with a fine mist to reach a moist sample mass of
approximately 2.0
times the initial sample mass (95-110% added moisture is applied, preferably
100%
added moisture, based on conditioned sample mass; this level of moisture
should yield an
absolute moisture ratio of about 1.1 g. water/g. oven dry fiber - with oven
dry referring to
drying for at least 30 minutes in an oven at 105° C). (For the uncreped
throughdried
materials of this invention, the moisture ratio could be within the range of
1.05 to 1.7
without significantly affecting the results). The mist should be applied
uniformly to
separated sheets (for stacks of more than 1 sheet), with spray applied to both
front and
back of each sheet to ensure uniform moisture application. This can be
achieved using a
conventional plastic spray bottle, with a container or other barrier blocking
most of the
spray, allowing only about the upper 10-20% of the spray envelope - a fine
mist - to
approach the sample. The spray source should be at least 10" away from the
sample
during spray application. In general, care must be applied to ensure that the
sample is
uniformly moistened by a fine spray. The sample must be weighed several times
during
the process of applying moisture to reach the targeted moisture content. No
more than
three minutes should elapse between the completion of the compression test on
the dry
sample and the completion of moisture application. Allow 45-60 seconds from
the final
application of spray to the beginning of the subsequent compression test to
provide time
for internal wicking and absorption of the spray. Between three and four
minutes will
elapse between the completion of the dry compression sequence and initiation
of the wet
compression sequence.
Once the desired mass range has been reached, as indicated by a digital
balance,
the sample is centered on the lower Instron platen and the test sequence is
initiated.
Following the measurement, the sample is placed in a 105° C oven for
drying, and the
oven dry weight will be recorded later (sample should be allowed to dry for 30-
60 minutes,
after which the dry weight is measured).
Note that creep recovery can occur between the two compression cycles to 2
psi,
so the time between the cycles may be important. For the instrument settings
used in
these Instron tests, there is roughly a 30 second period (typically ~ 4 sec.)
between the
beginning of compression during the two cycles to 2 psi. The beginning of
compression is
defined as the point at which the load cell reading exceeds 0.03 Ib. Likewise,
there is a 5-
- 19 -
CA 02241820 1998-07-31
8 second interval between the beginning of compression in the first thickness
measurement (ramp to 0.025 psi) and the beginning of the subsequent
compression cycle
to 2 psi. The interval between the beginning of the second compression cycle
to 2 psi and
the beginning of compression for the final thickness measurement is
approximately
20 seconds.
The utility of a web or absorbent structure having a high Wet Compressed Bulk
(WCB) value is obvious, for a wet material which can maintain high bulk under
compression can maintain higher fluid capacity and is less likely to allow
fluid to be
squeezed out when it is compressed.
High Wet Springback Ratio values are especially desirable because a wet
material
that springs back after compression can maintain high pore volume for
effective intake
and distribution of subsequent insults of fluid, and such a material can
regain fluid during
its expansion which may have been expelled during compression. In diapers, for
example, a wet region may be momentarily compressed by body motion or changes
in
body position. If the material is unable to regain its bulk when the
compressive force is
released, its effectiveness for handling fluid is reduced.
High Loading Energy Ratio values in a material are also useful, for such a
material
continues to resist compression (LER is based on a measure of the energy
required to
compress a sample) at loads less than the peak load of 2 psi, even after it
has been
heavily compressed once. Maintaining such wet elastic properties is believed
to
contribute to the feel of the material when used in absorbent articles, and
may help
maintain the fit of the absorbent article against the wearer's body, in
addition to the
general advantages accrued when a structure can maintain its pore volume when
wet.
The webs of this invention can exhibit one or more of the foregoing
properties.
More specifically, the webs of this invention can have a Wet Compressed Bulk
of about 6
cubic centimeters per gram or greater, more specifically about 7 cubic
centimeters per
gram or greater, more specifically about 8 cubic centimeters per gram or
greater, and still
more specifically from about 8 to about 13 cubic centimeters per gram. The
Compression
Ratio can be about 0.7 or less, more specifically about 0.6 or less, still
more specifically
about 0.5 or less, and still more specifically from 0.4 to about 0.7. Also,
they can have a
Wet Springback Ratio of about 0.75 or greater, more specifically about 0.85 or
greater,
more specifically about 0.90 or greater, and still more specifically from
about 0.8 to about
0.93. The Loading Energy Ratio can be about 0.7 or greater, more specifically
about 0.8
or greater, and still more specifically from about 0.7 to about 0.9.
- 20 -
CA 02241820 1998-07-31
"In-Plane Permeability". An important property of porous media, particularly
for
absorbent products, is the permeability to liquid flow. The complex,
interconnected
pathways between the solid particles and boundaries of a porous media provide
routes for
fluid flow which may offer significant flow resistance due to the narrowness
of the
channels and the tortuosity of the pathways.
For paper, permeability is commonly expressed in terms of gas flow rates
through
a sheet. This practice is useful for comparing similar sheets, but does not
truly
characterize the interaction of flowing fluid with the porous structure and
provides no
direct information about flow in a wet sheet. The standard engineering
definition of
permeability provides a more useful parameter, though one less easily
measured. The
standard definition is based on Darcy's law (see F.A.L. Dullien, Porous Media:
Fluid
Transport and Pore Structure, Academic Press, New York, 1979), which, for one-
dimensional flow, states that the velocity of fluid flow through a saturated
porous medium
is directly proportional to the pressure gradient:
y_ KOP
(1)
where V is the superficial velocity (flow rate divided by area), K is the
permeability, ~ is the
fluid viscosity, and OP is the pressure drop in the flow direction across a
distance L. The
units of K are m2. In Equation (1 ), the permeability is an empirical
proportionality
parameter linking fluid velocity to pressure drop and viscosity. For a
homogeneous
medium, K is not a function of OP, sample length, or viscosity, but is an
intrinsic parameter
describing the flow resistance of the medium. In a compressible medium,
permeability will
be a function of the degree of compression. Darcian permeability is a
fundamental
parameter for processes involving fluid flow in fibrous webs.
Darcian permeability has units of area (m2) and for simple uniform cylindrical
pores
is proportional to the cross sectional area of a single pore. However, the
permeability of
most real materials cannot be predicted from an optical assessment of pore
size.
Permeability is determined not only by pore size, but also pore orientation,
tortuosity, and
interconnectedness. Large pores in the body of an object may be inaccessible
to fluid
flow or accessible only through minute pores offering high flow resistance.
Even with a
full three-dimensional description of the pore space of a material from x-ray
tomography
or other imaging techniques, it is difficult to predict or calculate the
permeability.
Permeability and pore size determinations are related but distinct pieces of
information
- 21 -
CA 02241820 1998-07-31
about a material. For example, a sheet of metal with discreet, nonoverlapping
holes
punched in it may have very large pores (the holes), while still having
negligible In-Plane
Permeability. Swiss cheese has many large pores, but typically has negligible
permeability in any direction unless sliced so thin that individual holes can
extend from
one face to the other of the cheese sample.
Most studies of permeability in paper have focused on flow in the z-direction
(normal to the plane of the sheet), which is of practical importance in wet
pressing and
other unit operations. However, paper is an anisotropic material (for example,
see E. L.
Back, "The Pore Anisotropy of Paper Products and Fibre Building Boards,"
Svensk
Papperstidning, 69: 219 (1966)), meaning that fluid flow properties are a
function of
direction. In this case, different flow directions will appear to have
different apparent
permeabilities. The many possibilities of flow direction and pressure
gradients in such a
medium can be encompassed with a multidimensional form of Darcy's law,
- -K~vP
v = , (2)
where v is the superficial velocity vector (volumetric flow rate divided by
cross-sectional
area of the flow), N is the viscosity of the fluid, K is a second-order tensor
and OP is the
pressure gradient. If a Cartesian coordinate system is chosen to correspond
with the
principal flow directions of the porous medium, then the permeability tensor
becomes a
diagonal matrix (see Jacob Bear, "Dynamics of Fluids in Porous Media.,"
American
Elsevier, New York, NY, 1972, pp. 136-151 ):
~KX o o l
K =~ 0 Ky 0 ~ , (3)
~ 0 0 KZ J
where Kx, Ky, and Kz are the principal permeability components in the x-, y-,
and z-
directions, respectively. In paper, these directions will generally correspond
to the cross-
direction (taken here as y) and the machine-direction (taken as x, the
direction of
maximum In-Plane Permeability) in the plane, and the transverse or thickness
direction
(z). Thus, the anisotropic permeability of typical machine-made paper can be
characterized with three permeability parameters, one for the machine-
direction, one for
the cross-direction, and one for the z-direction. (In some cases, as when
there are
unbalanced flows in the headbox of the paper machine, the direction of maximum
permeability may be slightly off from the machine direction; the direction of
maximum In-
- 22 -
CA 02241820 1998-07-31
Plane Permeability and the direction orthogonal to that should be used for the
x- and y-
directions, respectively, in that case.) In handsheets, there may be no
preferential
direction of orientation for fibers lying in the plane, so the x- and y-
direction permeability
values should be equal (in other words, such a sheet is isotropic in the
plane).
In spite of the past focus on z-direction permeability in paper, In-Plane
Permeability (both KX and Ky are in-plane factors) is important in a variety
of applications,
especially in absorbent articles. Body fluids or other liquids flowing into
the absorbent
article usually enter the article in a narrow, localized region. Efficient use
of the absorbent
medium requires that the incoming fluid be distributed laterally through in-
plane flow in the
absorbent article, otherwise the local capacity of the article to handle the
incoming liquid
may be overwhelmed resulting in leakage and poor utilization of the absorbent
core. The
ability of fluid to flow in the plane of the article is a function of the
driving force for fluid
flow, which can be a combination of capillary wicking and hydraulic pressure
from fluid
source, and of the ability of the porous medium to conduct flow, which is
described in
large part by the Darcian permeability of the material. Two-phase flow and non-
Newtonian
liquids or suspensions complicate the physics, but the in-plane permeability
of the porous
medium is a critical factor for rapid in-plane distribution of liquid insults.
Especially in the
case of urine management, where liquid flow rates may occur far in excess of
the ability of
capillary forces, high In-Plane Permeability is needed in the intake layer to
allow the fluid
to be distributed laterally rather than to leak.
While many past studies of liquid permeability in paper focused exclusively on
measuring KZ for z-direction flow, more recently, methods have been taught for
measuring
permeability in the plane of a paper sheet. J.D. Lindsay and P.H. Brady teach
methods for
in-plane and z-direction permeability measurements of saturated paper in
"Studies of
Anisotropic Permeability with Applications to Water Removal in Fibrous Webs:
Part I,"
Tappi J., 76(9): 119-127 (1993) and "Studies of Anisotropic Permeability with
Applications
to Water Removal in Fibrous Webs: Part II," Tappi J., 76(11 ): 167-174 (1993).
Related
methods have been published by K. L. Adams, B. Miller, and L. Rebenfeld in
"Forced In-
Plane Flow of an Epoxy Resin in Fibrous Networks," Polymer Engineering and
Science,
26(20): 1434-1441 (1986); J.D. Lindsay in "Relative Flow Porosity in Fibrous
Media:
Measurements and Analysis, Including Dispersion Effects," Tappi J., 77(6): 225-
239 (June
1994); J.D. Lindsay and J.R. Wallin, "Characterization of In-Plane Flow in
Paper," AIChE
1989 and 1990 Forest Products Symposium, Tappi Press, Atlanta, GA (1992), p.
121; and
- 23 -
CA 02241820 1998-07-31
D.H. Horstmann, J.D. Lindsay, and R.A. Stratton, "Using Edge-Flow Tests to
Examine the
In-Plane Anisotropic Permeability of Paper," Tappi J., 74(4): 241 (1991 ).
The basic method used in most of these publications is injection of fluid into
the
center of a paper disk that is constrained between two flat surfaces to force
the fluid flow
to be in the radial direction, proceeding from the injection point at the
center of the disk to
the outer edge of the disk. This is illustrated in Figure 6, which depicts a
sheet in which a
central hole has been punched and into which fluid is injected by means of an
injection
port of the same size as the punched hole. For a liquid-saturated sheet of
constant
thickness subject to steady radial fluid flow in the manner described in the
work of Lindsay
and others, the equation relating average In-Plane Permeability to fluid flow
is:
K - KX +Ky - Qp In(IR~/R~) (4)
2 2~ LP 0P '
where Ro is the radius of the paper disk, Ri is the radius of the central hole
in the sample
into which fluid is injected through an injection port; Lp is the thickness of
the paper; OP is
the constant pressure above atmospheric pressure at which fluid is injected
into the disk
(the gauge pressure at the injection pore); Q is the volumetric flow rate of
liquid, and Kr is
the In-Plane Permeability, technically the average radial permeability,
defined as the
average of the two in-plane permeability components.
Details of the disk geometry used in the experimental work are shown in Figure
7.
The disk diameter is typically 5 inches, although in some cases, the maximum
available
sample size was 4.5 inches. The central inlet hole was consistently 0.375
inches (3/8
inch) and was created using a paper punch tool. The test apparatus for In-
Plane
Permeability measurements is depicted in Figures 8 and 9, which is identical
in principle
to the apparatus taught by Lindsay and Brady (op. cit.). Tubing connects water
from a
water reservoir to an injection port drilled into a 1-inch thick Plexiglas
support plate. (The
support plate is transparent to permit viewing of the wetted sample,
especially in cases
when an aqueous dye solution is injected into the sample. A mirror at a 45
degree angle
below the support plate facilitates viewing and photography.) The water
reservoir
provides a nearly constant hydraulic head for fluid injection during the test.
The
volumetric flow rate is obtained by noting the change in water reservoir mass
as a function
of time, and converting the water mass flow rate to a volumetric flow rate.
Vacuum-
deaerated deionized water at room temperature is used.
- 24 -
CA 02241820 1998-07-31
In the apparatus of Figure 8, a paper disk, cut to the dimensions shown in
Figure 7
(5-inch diameter and 0.375-inch central hole), is placed over the injection
port (0.375
inches diameter also) and is then saturated with water. The fluid injection
line and the
injection port should be filled with water and efforts should be taken to
avoid air bubbles
being trapped in the sheet or in the injection area. To help eliminate air
pockets, the
sample should be bent gently in the center as it is placed on the wet support
plate to
initiate liquid contact in the center of the sample; the edges can then be
lowered gradually
to create a wedge-like motion of the liquid meniscus to sweep air bubbles out
from under
the sheet. Multi-ply stacks of sheets can be handled in the same way, although
preliminary sample wetting may be needed to remove interply air bubbles. The
goal in
removing air bubbles is to reduce the flow blockage that trapped air bubbles
can cause.
Once the wetted sample is in place, a cylindrical metal platen, 5-inches in
diameter, is gently lowered on top of the sample to provide a constant
compressive load
and to provide a reference surface on its top for thickness measurement with
displacement gauges. Three displacement gauges are used, spaced approximately
evenly around the edge of the top of the metal cylinder, in order to measure
the average
thickness of the sheet. The sample thickness is taken as the average of the
three
displacement values relative to a zero point when no sample is present. A
suitable
thickness gauge is the Mitutoyo Digimatic Indicator, Model 543-525-1, with a 2-
inch stroke
(traveling distance of the contacting spindle) and a precision of 1
micrometer. The
thickness gauges are rigidly mounted relative to the support plate. The
contacting
spindles of the thickness gauges can be raised and lowered (without changing
the
position of the body of the gauge) by use of a cable to provide clearance for
moving the
metal platen onto the sample. The small force applied by the thickness gauges
should be
added to the weight of the metal platen to obtain the total force applied to
the sample; this
force, when divided by the cross sectional area of the sample and platen,
should be 0.8
psi.
A hydraulic head of 13 inches is used to drive the liquid flow. This head is
achieved by placement of a water bottle, filled to a specified level, on a
mass balance at a
fixed height relative to the support plate on which the sample rests. As the
sample is
being placed on the support plate, the water reservoir is at such a height
that the water
level in the reservoir is nearly the same as (or slightly greater than) the
support plate on
which the sample rests. When the sample has been moistened and placed under
the
compressive load of the metal platen, the water reservoir is then raised and
placed on a
- 25 -
CA 02241820 1998-07-31
mass balance such that the water level is 13 inches above the support platen.
A timer is
activated and the water reservoir mass is recorded at 20 seconds or 30 seconds
intervals
for a least 90 seconds. The thickness readings of the three gauges is also
recorded
regularly during the test. To reduce creep, the saturated sample should be
allowed to
equilibrate under the compressive load for at least 30 seconds before the
water bottle is
raised and forced flow through the sample begins.
The change in water reservoir mass as a function of time gives the mass flow
rate,
which can easily be converted to a volumetric flow rate for use in Equation 4.
Normal
engineering principles should be used to ensure that the proper units
(preferably SI units)
are used in applying Equation 4.
In performing In-Plane Permeability measurements, it is important that the
sample
be uniformly compressed against the restraining surfaces to prevent large
channels or
openings that would provide paths of least resistance for substantial liquid
flow that could
bypass much of the sample itself. Ideally, the liquid will flow uniformly
through the sample,
and this can be ascertained by injecting dyed fluid into the sample and
observing the
shape of the dyed region through the transparent support plate. Injected dye
should
spread out uniformly from the injection point. In isotropic samples, the shape
of the
moving dye region should be nearly circular. In materials with in-plane
anisotropy due to
fiber orientation or small-scale structural orientation, the shape of the dye
region should
be oval or elliptical, and nearly symmetric about the injection point. A
suitable dye for
such tests is Versatint Purple II made by Milliken Chemical Corp. (Inman, SC).
This is a
fugitive dye that does not absorb onto cellulose, allowing for easy
visualization of liquid
flow through the fibrous medium.
In addition to specifying the average In-Plane Permeability, the ratio of the
two in-
plane components, or the in-plane anisotropy factor, a, is also of interest.
This factor is
the ratio of the x-direction to y-direction permeability components, or
a-K/~ . (5)
y
Radial flow tests performed with dyed fluid can be used to determine the in-
plane
anisotropy factor, using an approximate solution to the fluid flow equations
obtained by
J.D. Lindsay in "The Anisotropic Permeability of Paper: Theory, Measurements,
and
Analytical Tools," IPC Technical Paper Series No. 289, Institute of Paper
Science and
Technology, Atlanta, GA, July 1988, and applied in J. D. Lindsay, "The
Anisotropic
Permeability of Paper," Tappi J., 73(5): 223 (May 1990). To relate in-plane
anisotropy to
- 26 -
CA 02241820 1998-07-31
the shape of a moving dye boundary resulting from injection of dye into a disk
saturated
with clear water, Lindsay obtained an approximate analytical solution in polar
coordinates
by neglecting flow in the tangential or q-direction. In the selected polar
coordinate frame,
q = 0 corresponds to the x-direction and q = p/2 to the y-direction. Let Rx
and Ry be the
radial locations of the dye boundary in the x- and y-directions, respectively.
Then the
approximate solution allows a to be determined from the geometry of the
colored zone
from the equation:
R2 _ R2
a - ~R2 _R2) (6)
y i
where Ri is the radius of the injection port at the center of the paper disk.
This
approximate solution was found to be highly accurate (when compared to
numerical
solutions of the flow problem) for the case of dye injected into a saturated
disk and was
also reasonably accurate for the case of dye injected into an initially dry
disk.
For the In-Plane Permeability results to be a proper measure of the material
in
question, the permeability should reflect the resistance of the material
itself and not the
resistance of a large scale channel or void which has been created in some
manner such
as cutting, slitting, folding, pleating, etc. We therefore require that the
material provide a
radial flow uniformity that can be assessed by visualization of dye flow
injected into the
sample. Radial flow uniformity exists when dye injected into a dry sample with
the
previously described in-plane permeability apparatus results in a symmetric,
roughly
elliptical dye pattern. Such a dye pattern should yield a value of a (from
Equation 6) less
than 4 when Rx is taken to be the radial position of the portion of the dye
boundary
furthest from the inlet, and Ry is the radial position of the portion of the
boundary closest
to the inlet, at a time when Rx is between 1 and 2 inches. If a sample with
longitudinal
channels is tested in this manner, there will be rapid flow in the
longitudinal direction as
fluid gushes through the channels, but in other flow directions (along paths
proceeding
radially outward from the periphery of the inlet port) that do not align well
with the open
channels, the flow will be much slower, resulting in a moving dye boundary
that is greatly
extended in the direction of the channels but which travels much less in other
directions.
Such a moving dye boundary will be irregular, possibly asymmetric, and will
have long
path lengths in some directions but much shorter path lengths in others,
yielding a values
over 4. Values of a as great as 2 may be achieved in machine made papers due
to fiber
orientation, so a limiting value of 4 has been selected to distinguish the
effects of
- z7 -
CA 02241820 1998-07-31
macroscopic nonuniformities from the effects of inherent small scale sheet
structures on
the measured In-Plane Permeability.
Three-dimensional materials for absorbent articles in which a structure is
obtained
by folding, pleating, cutting, etc., to generate a macroscopic structure lack
the uniform
nature of the material of the present invention. While the material of the
present invention
can be so arranged in various three-dimensional methods, it is important to
differentiate
the high In-Plane Permeability intrinsic to the materials of the present
invention from the
possibility of high In-Plane Permeability results obtained from macroscopic
structures
(those which do not have a representative unit area less than about 15 mm. by
15 mm.
using the concept of representative elementary area in the sense known to
those skilled in
the art of flow through porous media and as explained by Jacob Bear in Chapter
1 of
Dynamics of Fluids in Porous Media, Elsevier Publications Company, 1972, or
those
which do not have a nearly uniform basis weight distribution). For example, a
pleated and
folded structure may have long, macroscopic channels in the direction of
folding which
can provide large, open pathways for fluid flow. Such a material could be
positioned in
such a manner that it would offer little flow resistance in measurements of In-
Plane
Permeability, for the fluid would be flowing in the open channels, not through
the sheet.
High In-Plane Permeability results must be obtained in a structure with an a
value less
than 4 when measured with dilute aqueous, fugitive dye injection into the dry
material, as
described previously. An important advantage to having the sheet be uniform
with respect
to large length scales is that the uniform material provides continuous
wicking paths and
prevents fluid leakage through large channels. The surface pores and other
three-
dimensional structures are small enough to still provide capillary transport
and good fluid
retention, whereas pleated, folded, cut, or other large-scale three-
dimensional sheets
have channels which are ineffective at capillary transport because of their
large diameter
and which also can promote leaking.
The radial uniformity of flow in typical materials of the present invention is
demonstrated in Figures 26 and 27, which are photographs of dye injection
experiments,
with optical access to the moving dye boundary made possible by a mirror at a
45° angle
below the Plexiglas support plate of the permeability apparatus. The camera is
directed
towards the mirror which provides a view of the underside of the clear support
plate,
where the growth of the dye boundary is visible. In these tests, an aqueous
dye solution
was prepared from 40 ml of 7% Versatint Purple II dye (Milliken Chemical,
Inman, S.C.)
added to 1000 ml of deionized water. Figure 26 shows successive images of the
moving
- 28 -
CA 02241820 2005-06-13
dye boundary advancing in a stack of two disks of dry material from the
present invention,
an uncreped through-air-dried 40 gsm basesheet of spruce BCTMP produced with
30 Ibs.
of Kymene per ton of fiber. The motion of the fluid is slightly faster in the
machine
direction, resulting in an elliptical shape aligned with the machine direction
of the paper.
Application of Equation 6 for FIGS. 26A and 26B results in a; values of 1.70
and 1.76,
respectively (edge effects in FIG. 26C have hindered flow in the machine
direction,
resulting in a lower a value of about 1.6). F1G. 27 shows a rnoving dye
boundary in a
slightly moistened 60 gsm basesheet of spruce BCTMP with 20 Ibs. of Kymene
added per
ton of fiber, made with a T-116-1 throughdrying fabric (Lindsay Wire Division,
Appleton
Mills, Appleton, Wisconsin). An a value of about 1.4 is obtained in this case.
These dye
injection tests also show that the motion of the dye is through the porous
medium and not
through large channels in the sheet or through random gaps between the sample
and the
constraining surfaces.
As will be illustrated in the Examples, the webs of this invention possess
very high
In-Plane Permeability. More specifically, the In-Plane Permeability can be
about 5x10'"
square meters or greater, more specifically about 8x10'" square meters or
greater, more
specifically about 10x10'" square meters or greater, still more specifically
from about
5x10'" to about 80x10'" square meters, and still more specifically from about
8x10'" to
about 30x10'" square meters.
The "FIFE Test" is substantially as described in U.S. Patent No. 5,147,343
issued
September 15, 1992 to Kellenberger entitled "Absorbent Products Containing
Hydragels
With Ability to Swell Against Pressure". For purposes herein, the FIFE Test is
carried out as described except for the following differences: the raised
platform on the lower plate has been removed so the lower surface is entirely
flat; the
sample area is 8 inches square and the blotter paper sheets are also cut to
this
size; multiple sheets were used to obtain a stack with a basis weight of
about 240 gsm (roughly 10 grams total mass); samples were tested with a thin
layer of
poly film beneath them to enable them to be picked up more easily for flowback
measurement; and each liquid insult was 40 milliliters. Since actual sample
masses will
vary slightly from the target of 10 grams, insult times are normalized to a
mass of
10.0 grams by multiplying each observed intake time by a factor of
(conditioned dry
sample mass/10 grams). The combined time of the first, second and third
insults is the
FIFE Test value of the sample. ,
- 29 -
CA 02241820 2005-06-13
The webs of this invention can have FIFE Test values of about 125 seconds or
less, more specifically about 75 seconds or less, still more specifically
about 25 seconds
or less, and still more specifically from about 25 to about 100 seconds.
The "~nr Wine Residue" test provides a means of quantifying the ability of a
web
to wipe a surface dry. This property is of particular interest far products
such as wipes,
paper towels, cleaning articles and absorbent articles. To carry out this
test, a piece of
material approximating kitchen towel dimensions is attached to an 8 inches x 8
inches x
112 inch aluminum plate with adhesive tape. The material is wrapped over the
top of the
plate and taped there. There is a 1I2 inch diameter hole in the center of the
plate. The
plate with the material wrapped over it is illustrated in Figure 17. It is
placed on a 10
inches x 12 inches x 1/8 inch clear glass plate. A 3 cubic centimeter insult
of 0.5% MBNS
dye solution (Keystone Aniline, Chicago, Illinois, available at 10.5% solids)
is imparted into
the hole and 10 seconds is allowed for absorption. The plate is then picked up
vertically
and the pattern on the glass allowed to dry (about 20 minutes). The glass
plate is then
TM
placed dye-side down on a sheet of pink paper (Neenah Bond 02651, Neenah Paper
Company, Neenah, Wisconsin) to provide optical contrast for imaging the blue
dye against
the paper when viewed through the opposite side of the glass plate. The
residues are
imaged with a Quantimet 900 Image Analysis system (Leica, Inc., Deerfield,
Illinois) using
the optical set-up and conditions shown by the following routine, "WIN1".
Cambridge Instruments QUANTIMET 900 QUIPS/MX : V03.02 USER : NEENAH
ANALYTICAL
ROUTINE . WINI DATE : 27-FEB-96 RUN : 0 SPECIMEN
COND = 35mm Nikkon Lens, f/4, 90 cm Pole-posn (autosts);"
4 Incandescent Floods; Pink Paper w/ Residues down; .5~5 MBNS
soln
Enter specimen identity
Scanner ( No. 2 Newvicon LV= 0.00 SENS= 1.65 PAUSE )
Load Shading Corrector ( pattern - SCLIN1)
Calibrate User Specified (Calibration Value = 0.2170 millimetres per
pixel )
CALL STANDARD
TOTPERCAR . 0.
TOTFIELDS . 0.
TOTSIZE . 0.
TOTSPACIN . 0.
TOTSHAPE . 0.
TOTAREA . 0,
TOTAVEBRT . 0.
- 30 -
CA 02241820 1998-07-31
TOTDARK . 0.
TOTMASS . 0.
For FIELD
Detect 2D ( Darker than 57 PAUSE ) [Comment: adjust as needed]
Amend ( OPEN by 0 )
Pause Message
EDIT OUT ANY ARTIFACTS . . . .
Edit (pause)
Measure field - Parameters into array FIELD
Measure field - Integrated Brightness masked by Binary into array FIELD
AREA . FIELD AREA
AVEBRIGHT . ( FIELD TOTBRIGHT / ( AREA / ( CAL.CONST * CAL.CONST ) ) )
SIZE . FIELD AREA / ( ( FIELD V.PROJECT + FIELD H.PROJECT ) / 2.
)
ANISOT . 1. / FIELD ANISOTRPY
TEMP . ( FIELD V.PROJECT + FILED H.PROJECT ) / 2.
DARKNESS . 64. - AVEBRIGHT
MASSFACT .= AREA * DARKNESS / 1000.
Detect 2D ( Darker than 9 )
Pause Message
DRAW PATTERN CIRCLE AROUND DOTS . . .
Edit (pause)
Measure field - Parameters into array FIELD
PATTERN . FIELD AREA
PERCAREA . 100.
* AREA
/ PATTERN
SPACING . ( PATTERN- AREA ) /
TEMP
TOTAREA . TOTAREA AREA
+
TOTPERCAR .= TOTPERCAR+ PERCAREA
TOTSIZE . TOTSIZE SIZE
+
TOTSPACIN . TOTSPACIN+ SPACING
TOTSHAPE .= TOTSHAPE
+ ANISOT
TOTAVEBRT . TOTAVEBRT+ AVEBRIGHT
TOTDARK . TOTDARK DARKNESS
+
TOTMASS .= TOTMASSMASSFACT
+
TOTFIELDS . TOTFIELDS+ 1.
Pause Message
PLEASE CHOOSE ANOTHER FIELD, OR 'FINISH' . .
Pause
Next FIELD
Print " "
Print " AVE TOTAL AREA ( sq mm) - " , TOTAREA / TOTFIELDS
Print " "
Print "PERCENT COVERAGE = " , TOTPERCAR / TOTFIELDS
Print " "
- 31 -
CA 02241820 1998-07-31
Print "AVERAGE SIZE (mm) - " , TOTSIZE / TOTFIELDS
Print " "
Print "AVERAGE SPACING (mm) - " , TOTSPACIN / TOTFIELDS
Print " "
Print "AVERAGE SHP:PE = " , TOTSHAPE / TOTFIELDS
Print " "
Print "AVE DARKNESS (masked) - " , TOTDARK / TOTFIELDS
Print " "
Print " AVE MASS FACTOR = " , TOTMASS / TOTFIELDS
Print " "
Print "TOTAL NUMBER OF FIELDS = " , TOTFIELDS
For LOOPCOUNT = 1 to 5
Print " "
Next
End of Program
The results of the Dry Wipe Residue testing provide a Total Area coverage for
the
residue, a percent area coverage of the residue and a Mass Factor (area
darkness/1000) which represents the mass of material in the residue. The
"Total Area" of
the residues pattern is simply the sum of all "black" pixels in the image of
the residues
pattern, regardless of how deeply black they might be. In practice, the
detection level is
set to accept all pixels from 0 to about 55 (adjust as needed) on a 6-bit gray
scale running
from 0 to 64. The "Mass Factor" is a parameter that weights the area of the
image of the
residues by the mean gray level underlying all pixels and dividing by 1000 to
generate
more manageable numbers. This has been shown to give a value approximately
proportionate to the mass (milligrams) remaining on the glass plate, provided
that optical
saturation does not occur (i.e., there are not very dark residues regions
present). The
"percent coverage" is simply 100 times the ratio of the area of the "black"
pixels within the
boundary of the image "Total Area" to the entire area enclosed in a cover
region drawn
around the residues pattern using the mouse editor.
Webs of this invention can have Dry Wipe Residue Total Area coverage values of
about 2000 square mm. or less, more specifically about 1500 square mm. or
less, and still
more specifically from about 500 to about 1000 square mm. The Dry Wipe Residue
Mass
Factor can be about 30 or less, more specifically about 20 or less, and still
more
specifically from about 5 to about 20 or 30.
A test similar to the Dry Wipe Residue test just described is the "Wet Wig
Residue" test, which is conducted with an initially saturated wet sheet rather
than starting
with a dry sheet. Specifically, a 3 inches x 3 inches piece of the test
material is truncated
at 1/3 edge distances to form an octagon as illustrated in Figure 18. The
octagonal test
- 32 -
CA 02241820 2005-06-13
material is placed in a 100 millimeter crystallization dish and saturated to
350 weight
percent with a 0.5% MBNS solution as described above. The area of the octagon
is about
7 square inches. The dwell time for saturation is 3 minutes. The saturated
material is
picked up with a tweezers and placed on a 10 inches x 12 inches x 1l8 inch
clear glass
plate. An 8 inches x 8 inches x 1 inch piece of aluminum is placed on top of
the material
and allowed to dweN for 30 seconds. The piste is then picked up vertically and
the test
material removed from the glass plate with tweezers. The residues are allowed
to dry
(about 5 minutes). (See Figure 19.) The plate is placed dye-side down on a
sheet of pink
paper as described above and the residues are imaged with a Quantimet 900
Image
Analysis system using the same optical set-up and imaging conditions shown by
the
"WiN1" routine identified above.
As with the Dry Wipe Residues test , the same "WIN1" routine yields values for
Total Area and percent area coverage by the residues and a Mass Factor for the
residues. Webs of this invention can have a Wet Wipe Residue Total Area
coverage of
about 1500 square mm. or less, more specifically about 1000 square mm. or
less, and still
more specifically from about 400 to about 800 square mm. The Mass Factor for
the Wet
Wipe Residue test can be about 5 or less, more specifically from about 2 to
about 5.
Some of the webs of this invention may also be characterized in part by the
"Mean
Volume-Weighted Pore Length", expressed in microns. This structural parameter
is
related to the wicking ability of the material when wetted. The Mean Volume-
Weighted
Pore Length is determined by placing a 6 inches x 6 inches piece of the
material to be
TM
tested on a plastic sheet (e.g. "Glad Wrap" or similar material) on a
horizontal flat surface.
The sample is then flooded with distilled water. The material is allowed to
dry over night
at less than 40% relative humidity. Subsections of the dried material are cut
off and
cross-sectioned under liquid nitrogen for back-scattered electron
photomicroscopy as
described in U.S. Patent No. 5,492,598 issued February 20, 1996 to Hermans et
al.
entitled "Method for Increasing the Internal Bulk of Throughdried Tissue".
However, for purposes of measuring Mean Volume-Weighted Pore Length, only
7 photos are taken at a constant 50X magnification for all samples. The photos
are not assembled into a photomontage, but placed individually under plate
glass on a Kreonite Macroviewer (J. Kelly, Inc., Darien, Illinois) and viewed
with a 50 mm.
EL-Nikkor lens (Nikon, Inc., OEM Sales Group, Melville, New York). The image
is
oriented horizontally across the photo as illustrated in Figure 23 and
analyzed by the
routine "TSAI3" which follows below. The cross-section boundaries are selected
by
- 33 -
CA 02241820 1998-07-31
ACCEPT and REJECT operations using "mouse" EDIT on the Quantimet 970 Image
Analysis System (Leica, Inc., Deefield, Illinois). The parameters are
described by
equations in NTSAI3".
Cambridge Instruments QUANTIMET 970 QUIPS/MX: V08.00 USER : NEENAH
ANALYTICAL
ROUTINE : TSAI3 DATE : 28-FEB-96 RUN: 1 SPECIMEN :#4CHF 40GSM 20PPT K
COND = 50mm EL-Nikkor Lens: 2 1/4" field of view; 4 photofloods on
Kreonite Macroviewer; Horizontal section orientation
Scanner ( No. 1 Chalnicon LV 0.00 SENS= 1.94 PAUSE )
SUBRTN STANDARD
Load Shading Corrector ( pattern - LINERO)
Calibrate User Specified (Cal Value = 1.393 microns per pixel)
FLAG3 . 3.
Pause Message
Please Position Sample
Pause
TOTFIELDS . 0.
Enter specimen identity
For FIELD
Scanner ( No. 1 Chalnicon LV= 0.00 SENS= 1.94 PAUSE )
Live Frame is Standard Image Frame
Image Frame is Rectangle ( X: 12, Y: 15, W: 860, H: 668, )
Detect 2D ( Darker than 32, Delin PAUSE )
Amend ( OPEN by 1 )
Edit (pause) EDIT [Comment: for "ACCEPT" of cross-section only,
and "REJECT" of background region.]
TOTFIELDS .= TOTFIELDS + 1.
Measure feature AREA PERIMETER LENGTH
using 32 ferets
into array FEATURE1 ( of 500 features and 7 parameters )
FEATURE1 CALC.A .=((PERIMETER/2.)-(2.*AREA/PERIMETER)) [Comment: pore length]
FEATURE1 CALC.B .= 0.84880 * AREA * AREA / LENGTH [Comment: pore volume]
Distribution of COUNT v CALC.A (Units MICRONS )
from FEATURE1 in HIST02 from 1.000 to 2000.
in 10 bins (LOG)
Distribution of CALC.B (Units CUMICRONS ) v CALC.A ( Units MICRONS )
from FEATURE1 in HIST03 from 1.000 to 2000.
in 10 bins (LOG)
Pause
Next FIELD
Print " "
Print " "
Print Distribution ( HIST02, + cumulative, bar chart, scale = 0.00 )
Print "COUNT VS TRUE LENGTH, um"
Print " "
Print " "
Print Distribution ( HIST03, + cumulative, bar chart, scale = 0.00 )
[Comment: The volume-weighted mean Print "CUM
ELLIP VOLE VS TRUE LENGTH, um" pore length
(um) is read from this histogram.]
- 34 -
CA 02241820 2005-06-13
Print " "
Print ~~TOTAL NUMBER OF FIELDS ( PHOTOS) _ " , TOTFIELDS
For LOOPCOUNT = 1 to 13
Print
Next '
End of PROGRAM
Some of the webs of this invention can have a Mean Volume-Weighted Pore
Length of about 550 microns or greater, more specifically about 700 microns or
greater,
and still more specifically from about 600 to about 1000 microns.
Additionally, the webs of this invention have a substantially uniform
thickness, as
evidenced by a relatively low thickness percent coefficient of variation
(%COV), referred
to herein as the ickn ~s V ~ ~.t~'.o_0 Index. The Thickness Variation Index
can be about
25 percent or less, more specifically from about 5 to about 15 percent. To
determine the
thickness percent coefficient of variation, photomicrograph montages of tissue
cross-
sections are prepared by the scanning electron-microscopy method described in
United States Patent No. 5,492,598 (on tissues that were not previous wetted).
For this method, however, montages need not be assembled (since autostage
control is unnecessary) and the ideal magnification of 50X can be held
constant
across ail photos. Individual photos were viewed in horizontal orientation
(Figure 28A)
with a 50 mm. EL-Nikkor lens that provides a 2 1l4 inches field of view with
the Chalnicon
scanner attached to a Quantimet 970 Image Analysis System. Illumination is
provided by
a Kreonite Macroviewer using 4 photo-flood lamps. Using the routine "TSAl2n
set forth
below, the image of the tissue cross-section is filled as a solid detection
region (Figure
28B) by various binary operations and then "LINE" slices are taken at local
maxima and
minima to represent thickness samples (Figure 28C). These are assembled into a
histogram from which MEAN and standard deviation values are extracted for
°l°COV=
100(a/p.).
Cambridge Instruments QUANTIMET 970 QUIPS/MX: V08.00 USER : NEENAH ANALYTICAL
ROUTINE : TSAI2 DATE : 28-FEB-96 RUN : 3 SPECIMEN : #4 CHF 40GSM 20PPT K
AUTH = S. E. KRESSNER
DATE = 24 APR 1995
COND = ANY INPUT, PHOTO OR LIVE FOAM IMAGE.
Scanner ( No. 1 Chalnicon LV= 0.00 SENS= 1.94 PAUSE )
SUBRTN STANDARD
Load Shading Corrector ( pattern - LINERO)
Calibrate User Specified (Cal Value = 0.6964 microns per pixel)
IComment: change as appropriate for
photo magnification)
FLAG3 . 3.
Pause Message
- 35 -
CA 02241820 1998-07-31
Please Position Sample
Pause
TOTCLOSAP . 0.
TOTFIELDS .= 0.
Enter specimen identity
For FIELD
Scanner ( No. 1 Chalnicon LV=0.00 SENS= 1.94 PAUSE
)
Live Frame is Standard Image Frame
Image Frame is Rectangle ( X: 12, Y: 15, W: 860, H:668,
)
Detect 2D ( Lighter than 32, Delin PAUSE )
Amend ( OPEN by 1 )
Edit (pause) DRAW (Comment: for the "planting of a dilation
seed at edges of photo to insure true
section thickness]
Amend ( CLOSE by 25 )
Image Transfer from Binary B <FILL HOLES> to Binary
Output
Amend ( OPEN by 25 )
Edit (pause) EDIT (Comment:to take vertical "LINE" slices
at
local maxima and minima down the section
length. ]
Measure feature AREA PERIMETER LENGTH
using 32 ferets
into array FEATURE1 ( of 500 features and 7 parameters
)
Accept FEATURE1 LENGTH from 0. to 487. (Comment: changeas needed]
Distribution of COUNT v LENGTH (Units MICRONS )
from FEATURE1 in HISTO1 from 100.0 to 500.0 (Comment:as needed]
change
in bins (LIN)
Distribution of COUNT v LENGTH (Units MICRONS )
from FEATURE1 in HIST03 from 50.00 to 950.0
in 20 bins (LIN)
Pause
Next FIELD
Print " "
Print Distribution ( HISTO1, differential, bar chart,
scale = 0.00 )
(Comment: The mean and standard deviation
from this histogram are used to
calculate ~ COV, =100* (a-/~) ]
Print " "
Print
Print Distribution ( HIST03, differential, bar chart,
scale = 0.00 )
Print
Print
END OF PROGRAM
Brief Descrir~tion of the Drawing
Figure 1 is a schematic diagram of an uncreped throughdried papermaking
process useful for making wet resilient absorbent structures of this
invention.
- 36 -
CA 02241820 1998-07-31
Figure 2 is a surface profile illustrating the relationship between a surface
profile
and its material ratio curve. Also shown are the 10% and 90% material lines
used to
define the "P10" peak height parameter.
Figure 3A illustrates the Overall Surface Depth profile of a Surpass hand
towel.
Figure 3B is the fine structure surface depth profile of the same sample.
Figure 3C is the
overall Surface Depth profile in the cross-machine direction.
Figure 4A illustrates the Overall Surface Depth profile to Sample U2. Figure
4B
illustrates the fine structure surface depth (P10) for a 35 mm. long profile
taken along an
elevated region of Sample U2. Figure 4C illustrates the surface depth of
Sample U2
taken along a line dominated by low knuckle areas.
Figure 5 illustrates the Overall Surface Depth profile of Sample U8 (P10 =
0.509
mm).
Figure 6 illustrates the flow pattern in a paper disk during In-Plane
Permeability
measurement (angle view).
Figure 7 is a plan view of the paper disk used for In-Plane Permeability
testing,
illustrating the dimensions of the disk.
Figure 8 is a schematic side view of the apparatus used for In-Plane
Permeability
testing.
Figure 9 is a perspective view of the brass platen and thickness gauges used
for
In-Plane Permeability testing.
Figure 10 is a table identifying Samples U1-U10.
Figure 11 is a table summarizing the results of the wet resiliency testing.
Figure 12 is a bar chart summarizing the wet resiliency testing.
Figure 13 is a table summarizing wet resiliency testing for air-laid
materials.
Figure 14 is a table summarizing the In-Plane Permeability test results for
various
materials.
Figure 15 is a table summarizing the FIFE test results for various samples,
expressed in seconds. The times have been normalized to 10 grams of sample
weight
(original FIFE time x dry weight/10 grams).
Figure 16 is a bar chart illustrating the FIFE test results of Figure 14.
Figure 17 is a perspective sketch of the sample prepared for testing in the
Dry
Wipe Residue test.
Figure 18 is a plan view of the octagonal sample cut for the Wet Wipe Residue
test.
- 37 -
CA 02241820 1998-07-31
Figure 19 is a schematic plan view of the glass plate showing the dryness
residues
to be measured for the Wet Wipe Residue test.
Figure 20 is a table summarizing the results of the Dry Wipe Residue tests.
Figure 21 is a table summarizing the results of the Wet Wipe Residue tests.
Figure 22 is a table summarizing the results of the Mean Volume-Weighted Pore
Length tests.
Figure 23 is a representation of a typical cross-sectional photo used to
analyze the
Mean Volume-Weighted Pore Length.
Figure 24 is a top plan view of disposable absorbent article according to the
present invention, taken from the inner bodyside of the absorbent article in a
stretched
and laid flat condition and with portions broken away for purposes of
illustration.
Figure 25 is an enlarged transverse section view taken generally from the
plane of
the line 25-25 in Figure 24.
Figures 26 a, b, and c are sequential photographs of dye injection into a dry,
uncreped through-air-dried web of this invention, illustrating the
permeability flow pattern.
Figure 27 is another photograph of dye injection into an uncreped, through-air-
dried web of this invention.
Figures 28A, 28B and 28C are illustrations of photographs used to determine
the
Thickness Variation Index.
Detailed Des rir~tion of the Drawing
Referring to Figure 1, shown is a method for making throughdried paper sheets
in
accordance with this invention. (For simplicity, the various tensioning rolls
schematically
used to define the several fabric runs are shown but not numbered. It will be
appreciated
that variations from the apparatus and method illustrated in Figure 1 can be
made without
departing from the scope of the invention). Shown is a twin wire former having
a layered
papermaking headbox 10 which injects or deposits a stream 11 of an aqueous
suspension
of papermaking fibers onto the forming fabric 13 which serves to support and
carry the
newly-formed wet web downstream in the process as the web is partially
dewatered to a
consistency of about 10 dry weight percent. Additional dewatering of the wet
web can be
carried out, such as by vacuum suction, while the wet web is supported by the
forming
fabric.
The wet web is then transferred from the forming fabric to a transfer fabric
17
traveling at a slower speed than the forming fabric in order to impart
increased stretch into
- 38 -
CA 02241820 2005-06-13
the web. This is commonly referred to as a °rush" transfer. Preferably
the transfer fabric
can have a void volume that is equal to or less than that of the forming
fabric. The relative
speed difference between the two fabrics can be from 0-60 percent, more
specifically from
about 10-40 percent. Transfer is preferably carried out with the assistance of
a vacuum
shoe 18 such that the forming fabric and the transfer fabric simultaneously
converge and
diverge at the leading edge of the vacuum slot.
The web is then transferred from the transfer fabric to the throughdrying
fabric 19
with the aid of a vacuum transfer roll 20 or a vacuum transfer shoe,
optionally again using
a fixed gap transfer as previously described. The thraughdrying fabric can be
traveling at
about the same speed or a different speed relative to the transfer fabric. If
desired, the
throughdrying fabric can be run at a slower speed to further enhance stretch.
Transfer is
preferably carried out with vacuum assistance to ensure deformation of the
sheet to
conform to the throughdrying fabric, thus yielding desired bulk and
appearance. Suitable
throughdrying fabrics are described in U.S. Patent No. 5,429,686 issued to Kai
F. Chiu et
al.
The level of vacuum used for the web transfers can be from about 3 to about 15
inches of mercury {75 to about 380 millimeters of mercury), preferably about 5
inches
(125 millimeters) of mercury. The vacuum shoe (negative pressure) can be
supplemented or replaced by the use of positive pressure from the opposite
side of the
web to blow the web onto the next fabric in addition to or as a replacement
for sucking it
onto the next fabric with vacuum. Also, a vacuum roll or rolls can be used to
replace the
vacuum shoe(s).
While supported by the throughdrying fabric, the web is final dried to a
consistency
of about 94 percent or greater by the throughdryer 21 and thereafter
transferred to a
carrier fabric 22. The dried basesheet 23 is transported to the reel 24 using
carrier fabric
22 and an optional carrier fabric 25. An optional pressurized turning roll 26
can be used
to facilitate transfer of the web from carrier fabric 22 to fabric 25.
Suitable carrier fabrics
for this purpose are Albany International 84M or 94M and Asten 959 or 937, all
of which
are relatively smooth fabrics having a fine pattern. Although not shown, reel
calendering
or subsequent off line calendering can be used to improve the smoothness and
softness
of the basesheet.
Figures 2-7 have already been discussed above.
Figures 8 - 23 will be described in connection with the Examples to follow.
- 39 -
CA 02241820 1998-07-31
Figures 24 and 25 show an absorbent article utilizing a web according to the
present invention as illustrated by an incontinence pad 100 . The pad 100
includes a
moisture barrier 102, a bodyside liner 104, and a retention portion in the
form of an
absorbent assembly 106 disposed between the moisture barrier and bodyside
liner.
Desirably although not necessarily, the pad 100 may also include side elastic
members
108 and a liquid acquisition/distribution layer 110. The pad 100 desirably
further
comprises a means for holding the pad 100 in position during use (not shown).
For
example, the pad 100 may comprise a garment attachment adhesive, a body
attachment
adhesive, belts, straps, wings, mechanical fasteners, and/or other suitable
fastening
devices to secure the pad in position to absorb body exudates.
The absorbent assembly 106 of the pad 100 comprises a thin, layered structure
capable of providing a relatively large liquid retention capacity. The
absorbent assembly
106 includes upper and lower sheets 120 and 122 according to the present
invention with
high-absorbency materials 124 disposed between the sheets. The liquid wicking
properties of the sheets 120 and 122 enable particularly effective and
efficient utilization
of the high-absorbency materials 124. The absorbent assembly 106 desirably but
not
necessarily also includes a support layer 126 disposed between the sheets 120
and 122
and the moisture barrier 102. Other materials know in the art, such as odor
adsorbing
particles (not shown), may also be incorporated into the pad 100, and in
particular into the
absorbent assembly 106.
With particular reference to Fig. 24, the illustrated pad 100 defines a
longitudinal
axis or center line represented by arrow 130, which generally corresponds to
the greatest
planar dimension of the product. The pad 100 has opposite, longitudinal end
edges 132
and opposite, longitudinal side edges 134 that extend between the longitudinal
end edges.
The longitudinal side edges 134 are shown as generally straight, but
optionally, may be
curvilinear and contoured, for example so that the pad 100 is generally
hourglass shaped.
The moisture barrier 102 and bodyside liner 104 are desirably longer and wider
than the absorbent assembly 106 so that the peripheries of the moisture
barrier and
bodyside liner may be bonded together using ultrasonic bonds, thermal bonds,
adhesives,
or other suitable means. Additionally, the absorbent assembly 106 may be
bonded
directly to the moisture barrier 102 and/or the bodyside liner 104 using
ultrasonic bonds,
thermal bonds, adhesives, or other suitable means. As used herein, the term
bonded
refers to the joining, adhering, connecting, attaching, or the like, of two
elements. Two
elements will be considered to be bonded together when they are bonded
directly to one
- 40 -
CA 02241820 2005-06-13
another or indirectly to one another, such as when each is directly bonded to
intermediate
elements.
The moisture barrier or backsheet 102 desirably comprises a material that is
formed or treated to be liquid impermeable. Alternatively, the moisture
barrier 102 may
comprise a liquid permeable material and other suitable means may be provided
to
impede liquid movement away from the absorbent assembly 106, such as a liquid
impermeable layer (not shown associated with the absorbent assembly. The
moisture
barrier 102 may also be gas permeable over either all or part of its surface
area.
The moisture barrier 102 may comprise a single layer of material or a laminate
of two or more separate layers of material. Suitable moisture barrier
materials include
films, wovens, nonwovens, laminates of films, wovens, andlor nonwovens, or the
like. For
example, the moisture barrier 102 may comprise a thin, substantially liquid
impermeable
web or sheet of plastic film such as polyethylene, polypropylene, polyvinyl
chloride or
similar material. The moisture barrier material may be transparent or opaque
and have an
embossed or matte surface. One particular material for the moisture barrier
102 is a
polyethylene film that has a nominal thickness of about 0.028 millimeter and a
systematic
matte embossed pattern, and that has been corona treated an both sides.
The absorbent assembly 106 comprises materials adapted to absorb, distribute,
and retain liquid waste. The individual sheets 120 and 122 may be formed from
a single
web that is C-folded to enclose the high-absorbency materials 124 within an
envelope.
The sheets 120 and 122 and the high-absorbency materials 124 are desirably
bonded
together at least in a dry state by adhesives, chemical bonds, or other
suitable means.
The C-folded composite may then be cut or trimmed as needed, for example to
provide
the hourglass shaped structure as illustrated in Figs. 24 and 25.
Alternatively, the sheets
120 and 122 may comprise separate layers that are united during assembly of
the pad
100.
The absorbent assembly 106 may include 0 - 95 weight percent of organic
or inorganic high- absorbency materials to increase the absorbency of the
assembly. As used herein, the term high-absorbency materials refers to
materials
that are capable of absorbing at least about 15 and desirably more than 25
times their
weight in water. Suitable high-absorbency materials are described in United
States
Patents 4,699,823 issued October 13, 1987 to Kellenberger et al. and 5,147,343
issued September 15, 1992 to Kellenberger. High-absorbency materials are
available from various commercial vendors, such as The Dow Chemical Company;
- 41 -
CA 02241820 2005-06-13
Hoechst Celanese Corporation; Chemische Fabrik Stockhausen, GMBH; and Allied
Colloids, Inc.
The support layer 126 desirably comprises materials that are adapted to
absorb,
distribute and retain liquid waste, and the support layer functions in part to
enhance the
ability of the pad 100 to resist twisting and roping during use. The support
layer 126 may
comprise various absorbent materials, such as an air-formed batt of cellulosic
fibers (i.e.,
wood pulp fluff), a coform material composed of a mixture of cellulosic fibers
and synthetic
polymer fibers, and/or high-absorbency materials. By way of illustration, the
support layer
126 may comprise a single, compressed layer of wood pulp fluff having a
density of about
0.2 g/cc.
The acquisitionldistribution layer 110 is desirably provided to help
decelerate
and diffuse surges of liquid that may be introduced into the absorbent
assembly 106. The
acquisitionldistribution layer 110 may be positioned subjacent the bodyside
liner 104 as
illustrated, or aftematively disposed on the inwardly facing, bodyside surface
of bodyside
liner. Suitable configurations of the acquisition/distribution layer 110 are
described in
U.S. Patent 5,192,606 issued Match 9, 1993, to D. Proxmire et al.; U.S. Patent
5,486,166
issued January 23, 1996 to Eliis et al.; U.S. Patent 5,490,846 issued February
13, 1996 to
Ellis et al.; and U.S. Patent Application Ser. No. 096,654 of VV. Hanson et
al., titled "Thin
Absorbent Article Having Rapid Uptake of Liquid" and filed July 22, 1993. By
way of
illustration, the acquisitionldistribution layer 110 may comprise a through-
air bonded
carded web composed of a blend of 40% of 6 denier polyester fibers,
commercially
available from Hoechst Celanese Corporation, and 60% of 3 denier
polypropylene/polyethylene side-by-side bicomponents fibers, commercially
available from BASF Corporation, and have an overall basis weight of from
about 50 to about 120 gsm .
The bodyside liner or topsheet 104 is formed of a liquid permeable material so
that liquid waste, and possibly semi-solid waste as well, can pass through the
liner and be
absorbed by the absorbent assembly 106. Suitable bodyside liners 104 may
comprise a
nonwoven web or sheet of wet strength tissue paper, an apertured film, a
spunbonded,
meltblown or bonded-carded web composed of synthetic polymer filaments or
fibers, such
as polypropylene, polyethylene, polyesters or the like, or a web of natural
polymer
filaments or fibers such as rayon or cotton. In addition, the bodyside liner
104 may be
treated with a surfactant to aid in liquid transfer. In one particular
embodiment, the liner
104 comprises a nonwoven, spunbond polypropylene fabric having a basis weight
of
- 42 -
CA 02241820 2005-06-13
about 17 gsm. The fabric is pin apertured and surtace treated with a
surfactant
commercially available from Union Carbide Chemicals and Plastics Company, Inc.
under
TM
the trade designation TRITON X-102. As used herein, the term fabric is used to
refer to
ail of the woven, knitted and nonwoven fibrous webs. The term nonwoven web
means a
web of material that is formed without the aid of a textile weaving or
knitting process.
In the illustrated embodiment, the elongated side elastic members 108 are
longitudinally orientated contiguous with each side edge 134 and extend toward
the end
edges 132. The side elastic members 108 may be bonded in a stretched condition
intermediate the moisture barrier 102 and the bodyside liner 104 using
ultrasonic bonds,
adhesives, thermal bonds, or other suitable means, in either a straight or a
curved shape.
Alternatively, the side elastic members 108 may be bonded fn a relaxed state
to a
gathered portion of the moisture barrier 102, the bodyside liner 104, or both.
As used
herein, the terms elastic, elasticized and elasticity mean that property of a
material by
virtue of which it tends to recover its original size and shape after removal
of a force
causing a deformation.
The side elastic members 108 may be formed of a dry-spun coalesced
TM
multifilament elastomeric thread sold under the tradename LYCRA and available
from E.I.
Du Pont de Nemours and Company. Alternately, the elastic members may be formed
of
other typical elastics utilized in making incontinence products, such as a
thin ribbon of
natural rubber, a stretch bonded laminate material comprising a prestretched
elastic
meltblown inner layer sandwiched between and bonded to a pair of spunbond
polypropylene nonwoven webs, or the like. Elasticity could also be imparted to
the
absorbent article by extruding a hat melt~elastomeric adhesive between the
moisture
barrier 102 and the liner 104. Other suitable elastic gathering means are
disclosed in
U.S. Patents 4,938,754 to Mesek and 4,388,075 to Mesek et al.
Figures 26 and 27 have already been discussed above in connection with the In-
Plane Permeability procedure.
~am~l~~
In order to illustrate a method of making absorbent structures of this
invention,
paper sheets were produced using non-wet resilient northern softwood kraft
fibers
(NSWK), with and without a wet strength agent (20 Ibs/ton Kyrnene}, and wet
resilient
- 43 -
CA 02241820 2005-06-13
fibers (spruce BCTMP), with and without a wet strength agent (20 Ibslton
Kymene), using
an uncreped throughdried process as described in Figure 1.
The fiber was pulped at 4%.consistency in the hydropulper for 30 minutes. The
fiber was pumped into a stock chest and diluted to 1.0% consistency. 20
Ibs/ton of Kymene
557 LX was added to the stock chest and allowed to mix for 30 minutes. A
single-layer,
blended sheet of 30 gsm dry weight was formed on an Albany 94M forming fabric
and
dewatered with 5 inches (127 millimeters) of mercury vacuum. The forming
fabric was
traveling at 69 fpm (.35 meters per second). The sheet was transferred at a
15% rush
transfer to a Lindsay 952-S05 transfer fabric traveling at 60 fpm (.30 meters
per second).
The vacuum in the transfer between the forming fabric and transfer fabric was
10 inches
(254 millimeters) of mercury.
The sheet was vacuum transferred at 12 inches (305 millimeters) of mercury to
a
throughdryer fabric (Lindsay T116-1 ) traveling at the same speed as the
transfer fabric, 60
fpm (.30 meters per second). The sheet and throughdryer fabric traveled over a
fourth
vacuum at 12 inches (305 millimeters) of mercury just prior to entering a
Honeycomb
throughdryer operating at 200°F (93°C) and dried to a final
dayness of 94-98%
consistency.
The sheets were aged for over 5 days at less than 50% humidity at 70°F
(21 °C).
The sheets were tested for physical characteristics in a controlled
environment of 50% ~
2% humidity and 23°C ~ 1 °. The wet and dry strength were
lnstron tested with a 3-inch
(7.62 cm) sample width, 4-inch (10.16 cm) jaw span at 10 inlrnin (25.4 cmlmin)
crosshead
speed. Caliper was measured with the TMl tester at 0.289 psi.
- 44 -
CA 02241820 2005-06-13
g,~ ~mrle 2 Example Exan~gle
Furnish NSWK NWSK 3 4
Spruce Spruce
BCTMP BCTMP
Kymene 0 . 20#/ton 0 20#/ton
MD grams dry 1592 2761 1678 2257
MD % stretch dry 7.6 10,0 1.8 1.8
CD grams dry 1671 2459 1540 1872
CD % stretch dry 5.0 5.7 3.5 3.2
GMT grams dry 1631 2606 1608 2056
MD grams wet 106 892 49 826
MD % stretch wet 13.4 8.8 6.8 3.2
CD grams wet 71 715 47 759
CD % stretch wet 9.0 5.3 5.5 3.2
GMT grams wet 87 798 48 792
MD % wet/dry 6,6 32.3 2.9 36.6
CD % wet/dry 4.2 29.1 3.1 40.5
GMT % wet/dry 5.3 30.6 3.0 38.5
Hasis Weight gam 31.7 32.2 32.4 32.7
1-Sheet TMI mm .602 .605 .630 .602
10-Sheet TMI mm 3.34 3.68 3.91 3.95
Density, g/cc .053 .053 .051 .054
Bulk cc/g 19.0 18.8 19.4 18.4
Absorbency a 0.075
psi
Horizontal g/g 7.6 8.7 10.2 10.1
45 g/g 7.1 7.6 9.7 9.3
Percent Wet Wrinkle 34.4 52.7 35.0 81.6
Recovery
As shown, Example 4 (this invention) exhibited substantially greater wet
resiliency,
as measured by the Wet Wrinkle Recovery Test, than the other three samples. In
addition, Example 4 also showed a high wet:dry ratio,
Examg~es 5-8
Further examples were carried out similar to those described in Examples 1-4,
but
for the purpose of exploring the basis weight effect on a bulky, absorbent,
wet resilient
structure. Four basis weight levels of 30, 24, 18 and 13 gsm of 100% Spruce
BCTMP
with 20 Ibslton Kymene were produced .
The fiber was pulped at 4% consistency in the hydropulper for 30 minutes. The
fiber was pumped into a stock chest and diluted to 1.0% consistency. 20
Ibs/ton of Kymene
557 LX was added to the stock chest and allowed to mix for 30 minutes. A
single-layer,
blended sheet was formed on an Albany 94M forming fabric and dewatered with 4
inches
(102 millimeters) of mercury vacuum. The forming fabric was traveling at 69
fpm (.35
meters per second). The sheet was transferred at a 15% rush transfer to a
Lindsay 952-
S05 transfer fabric traveling at 60 fpm (.30 meters per second). The vacuum in
the
transfer between the forming fabric and transfer fabric was 7 inches (178
millimeters) of
- 45 -
CA 02241820 1998-07-31
mercury. The 13 gsm sample was produced without a rush transfer, the forming
fabric
was traveling at 60 fpm (.30 meters per second), the same as the transfer
fabric and
throughdryer fabric.
The sheet was vacuum transferred at 10 inches (254 millimeters) of mercury to
a
throughdryer fabric (Lindsay T116-1 ) traveling at the same speed as the
transfer fabric, 60
fpm (.30 meters per second). The sheet and throughdryer fabric traveled over a
fourth
vacuum at 11 inches (279 millimeters) of mercury just prior to entering a
Honeycomb
throughdryer operating at 260°F (127°C) and dried to a final
dryness of 94-98%
consistency.
The sheets were aged for over 5 days at less than 50% humidity at 70°F
(21 °C).
The sheets were tested for physical characteristics in a controlled
environment of 50% _+
2% humidity and 23°C + 1 °. The wet and dry strength were
Instron tested with a 3-inch
(7.62 cm) sample width, 4 inch (10.16 cm) jaw span at 10 in/min (25.4 cm/min)
crosshead
speed. The caliper was measured with the TMI tester at 0.289 psi. (The only
difference
in this example from the previous example is the vacuum level and dryer
temperature).
Exams Example Example Example
6 7 8
Hasis Weight 13 gsm 18 gsm 24 gsm 30 gsm
MD grams dry 1167 649 1091 1605
MD % stretch dry 1.4 3.7 4.0 5,1
CD grams dry 630 727 1130 1624
CD % stretch dry 2.6 3.5 4.0 4.0
GMT grams dry 857 687 1110 1614
MD grams wet 393 294 465 671
MD % stretch wet 1.5 5.0 5.5 5.5
CD grams wet 223 251 429 586
CD % stretch wet 2.4 3.3 3.5 3.5
GMT grams wet 296 272 447 627
MD % wet/dry 33.7 45.3 42.6 41.8
CD % wet/dry 35.4 34.5 38.0 36.1
GMT % wet/dry 34.5 40.0 40.3 38.8
Basis Weight gsm 13.6 17.6 23.9 30.1
1-Sheet TMI, mm .335 .533 .610 .655
10-Sheet TMI, mm 1.94 2.91 4.00 4.55
Bulk cc/g 24.6 30.3 25.5 21.8
Absorbency ~ 0.075
psi
Horizontal g/g 12.2 13.3 13.0 11.8
45 g/g 11.4 11.8 11.3 10.2
Density, g/cc .041 .033 .039 .046
Percent Wet Wrinkle 73.8 76.7 85.0 86.7
Recovery
As shown, all examples exhibited high wet resiliency as determined by the Wet
Wrinkle Recovery Test.
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CA 02241820 2005-06-13
Ex;~~phs 9-12
In order to further illustrate this invention, uncreped throughdried tissues
were
produced using the method substantially as illustrated in Figure 1. More
specifically,
single-layer, single-ply tissues were made in which all layers comprised
unrefined
northern softwood bleached chemithermomechanical pulp (BCTMP) fibers. Prior to
formation, the BCTMP fibers were pulped for 20 minutes at 4.6 percent
consistency and
diluted to 2.8 percent consistency after pulping. Kymene 557LX was added at 10-
18
kilograms per metric ton of pulp.
A four-layer headbox was used to form the wet web with the unrefined northern
softwood BCTMP stock in all four layers. Turbulence-generating inserts
recessed about 3
inches (75 millimeters) from the slice and layer dividers extending about 6
inches (150
millimeters) beyond the slice were employed. Flexible lip extensions about 6
inches (150
millimeters) beyond the slice were also used, as taught in U.S. Patent No.
5,129,988
issued July 14, 1992 to Farrington, Jr. and entitled "Extended Flexible
Headbox Slice With
Parallel Flexible Lip Extensions And Extended Internal Dividers". The net
slice
opening was about 0.75 inch (19 millimeters), and water flows in all four
headbox
layers were comparable. The consistency of the stock fed to the headbox was
ranged
from about 0.3 to about 0.5 weight percent.
The resulting single-layered sheet was formed on a twin-wire, suction form roN
former in which both forming fabrics {12 and 13 in Figure 1 ) were Asten 866
fabrics. The
speed of the forming fabrics ranged from 5.3 to 6.6 meters per second. The
newly-
formed web was then dewatered to a consistency of about 20-27 percent using
vacuum
suction from below the forming fabric before being transferred to the transfer
fabric, which
was traveling from 3.6 to 5.1 meters per second. The resulting rush transfer
ranged
between 30 percent and 50 percent. The transfer fabric was a Lindsay 2164
fabric. A
vacuum shoe pulling about 6-15 inches (150-380 millimeters) of mercury vacuum
was
used to transfer the web to the transfer fabric.
The web was then transferred to a throughdrying fabric (Lindsay Wire T116-3).
The throughdrying fabric was traveling at a speed substantially the same as
the transfer
fabric. The web was carried over a Honeycomb throughdryer operating at a
temperature
of about 400°F. (204°C.) and dried to final dryness of about 94-
98 percent consistency.
The resulting uncreped throughdried tissue sheets had the following
properties:
- 47 -
CA 02241820 1998-07-31
Ex$mgle 99 Example 10 Example 11 Example 12
Kymene, kg/MT 10 18 10
10
Rush Transfer, % 30 30 30
50
Forming Fabric Speed,'6 6
M/S 6 6
. . 5.9 5.3
Transfer Fabric Speed,5.1 5 4
M/S 1 6
. . 3.6
Forming Consistency, 0 0
% 3 4
. . 0.4 0.5
MD grams dry 4040 6340 7360 6190
MD % stretch dry 22.0 24.4 24.6 40.3
CD grams dry 2940 6560 4690 5140
CD % stretch dry 5.3 4.0 4.7 4.1
GMT grams dry 3446 6449 5875 5640
MD grams wet 2702 4383 3786 3562
MD % stretch wet 20.5 21.5 20.5 36.0
CD grams wet 1252 2840 1917 2101
CD % stretch wet 6.8 4.7 5.7 5.6
GMT grams wet 1839 3528 2694 2736
MD % wet/dry 66.9 69.1 51.4 57.5
CD % wet/dry 42.6 43.3 40.9 40.9
GMT % wet/dry 53.4 54.7 45.9 48.5
Basis Weight gsm 65.2 82.8 88.8 109
1-Sheet TMI mm 0.899 0.884 0.950 1.01
10-Sheet TMI mm 7.01 7.21 7.89 8.92
Bulk cc/g 13.8 10.7 10.7 9.27
Absorbency o .075
psi
Horizontal g/g 10.8 8.3 8.3 7.6
45 g/g 8.8 7.4 6.9 6.8
Density g/cc 0.073 0.094 0.093 0.108
Percent Wet Wrinkle 75.0 83.9 78.9 -
Recovery
As shown, all three examples for which the Wet Wrinkle Recovery Test was
measured exhibited high wet resiliency as measured by that test.
In order to further illustrate the properties of the absorbent structures of
this
invention, the wet compressive resiliency properties of some of the foregoing
samples
were measured and are set forth below.
Wet Compressive Resiliency
1 2 3 4 b 7 8 9 10 12
~
Basis Weight, 31.732.232.432.717.623.930.165.2 82.8109
gsm
A) Initial
Bulk o1
0.025 psi 18.418.519.921.328.722.921.215.2 12.511.0
B) Compressed 5.2 6.0 7.1 7.9 8.2 8.1 8.0 8.7 8.0 7.7
Bulk
C) Final Bulk
a
0.025 psi 8.4 13.613.018.022.719.317.714.1 11.410.2
Compression 0.280.320.360.370.2860.3450.3780.5710.6390.704
Ratio (B/A)
Springback 0.460.730.660.850.7910.8410.8380.9290.9170.926
Ratio (C/A)
Loading Energy0.490.650.650.830.8020.7830.8080.8350.8190.822
Ratio
As shown, the examples of this invention (Examples 4-12) all exhibit high
Springback Ratios and high Loading Energy Ratios compared to the controls
(Examples 1-3). In addition, some of the examples of this invention also
exhibited a high
- 48 -
CA 02241820 2005-06-13
Wet Compressed Bulk of about 7.5 cclg or greater (Examples 9, 10 and 12).
Also, the
examples of this invention presented above ail exhibit Compression Ratios of
about 0.7 or
less in combination with Springback Ratios of about 0.8 or greater and Loading
Energy
Ratios of about 0.7 or greater, resulting in a web having a low wet modules
and high wet
resiliency.
To further illustrate the properties of the webs of this invention (Samples U1-
U11)
relative to other types of webs, comparative testing was carried out on
uncreped through-
air-dried webs made with different fibers, as well as comparing the properties
of different
types of webs. Some of the materials and the process conditions for Samples U1-
U11
are summarized in the table of Figure 10. The various fiber types and
different types of
webs tested are identified below:
"HBAFF° is a softwood kraft fiber which has been chemically crossiinked
with a
urea-glyoxal resin. ft is produced by Weyerhaeuser Gomp. and is commercially
available.
HBAFF has a Water Retention Value of approximately 0.5 g/g.
"Curly-Q" fibers are taken from the transfer layer of 1993 Pampers diapers
made
by the Procter and Gamble Company. Citric acid is used as a crosslinking
agent. In
addition to being chemically stiffened through crosslinking, the fibers are
highly twisted
and curled, giving additional bulk and resiliency to fluff pads made from the
material.
Curly-Q fibers have a Water Retention Value of approximately 0.4 g/g. The
method of
manufacture of these fibers is believed to be disclosed in part. in the
following US patents:
C.M. Herron, D.J. Cooper, T.R. Hanser, and B.S. Hersko, "Process for Preparing
Individualized, Polycarboxylic Acid Crosslinked Fibers," US Patent No.
5,190,563 (1993);
G.A. Young, D.R. Moore, J.T. Cook, "Absorbent Structures Containing
Superabsorbent
Material and Web of Wetlaid Stiffened Fibers," US Patent No. 5,217,445 (1993);
J.T.
Cook, G.R. Lash, D.R. Moore, ad G.A. Young, "Absorbent Structures Containing
Stiffened
Fibers and Superabsorbent Material," US Patent No. 5,360,420 (1994). "Curly-Qn
fiber
samples are labeled with prefrxes of "CQ.~
CR-1654 is a softwood pulp produced largely from southern pine at the Coosa
River mill in Alabama. CR-1654 fibers have a WRV of about 1.1 glg.
"HPZ" is a commercial mercerized pulp made by Buckeye with a WRV value of
about 0.87.
- 49 -
CA 02241820 2005-06-13
"LL-19" is a northern pine kraft fiber made at the Terrace Bay mill in Canada.
It has
a WRV value of about 1.0 g/g.
"Air-laid softwood" is an airfaid fluff pad made of blended southern softwood
kraft
fibers from the Kimberly-Clark Coosa River mill. Air laying was done in a
pulsed-air
device in which the fibers were dispersed by air flow alone and redeposited
gradually into
a 4-inch wide mat lying on top of a thin tissue sheet.
Several commercial products used for testing were purchased from stores in
Wisconsin, including "Viva Ultra" (1996), "Quilted Bounty" (1996)(printed and
unprinted
varieties), and "Brawny" towels (1994). Viva Ultra is a paper towel produced
by the Scott
Paper Company and is made with latex binder for high wet strength. Brawny is a
paper
towel product from the James River Company. Printed Quilted Bounty and
unprinted
Quilted Bounty are paper towel products from the Procter and Gamble Company,
made
with a mixture of fiber types including a percentage of CTMP pulp and added
wet strength
resins. Quilted Bounty purchased in mid-1994 was also used in additional
testing.
Another commercial product used in testing is the "SURPASS~" handtowel from
Kimberly-Clark Corporation, which is made with an uncreped, through-air dried
process
and with added wet-strength agents according to the patent of R.F. Cook and
D.S.
Westbrook, "Non-creped Hand or Wiper Towel," US Pat. No. 5,048,589, issued
Sept. 17,
1991. The Surpass towel is a typical example of uncreped, through-air dried
technology
without the improvements of the present invention; namely, a highly three-
dimensional
drying fabric with the additional synergistic combination of wet resilient
fibers and wet
strength agents. Samples from both 1995 and 1994 were used.
Three other materials were manufactured with the uncreped through-air dried
process of the present invention, but without the synergistic combination of
high wet
strength and wet resilient fibers (high yield fibers). One such material is a
40 gsm tissue
sheet made of northern softwood kraft fibers (LL-19) on a Lindsay wire T116-3
through-
drying fabric, with 20 pounds of added Kymene per ton of dry t~iber. The sheet
was
manufactured on a pilot tissue machine. This material is hereafter labeled as
Sample 02.
Another material was made in the same way but with spruce BCTMP fibers and no
added
Kymene, at a basis weight of 60 gsm. This material is labeled as Sample 03. A
third
material is similar to sample 02, but made at a basis weight of 60 gsm with 10
Iblton of
Kymene, hereafter labeled sample 04.
The wet resiliency of the materials of the present invention is compared to
several
other materials in the table of Figure 11. SpecificaNy, the table of Figure 11
shows that
- 50 -
CA 02241820 1998-07-31
the materials of the present invention can have exceptional Wet Compressed
Bulk (WCB)
values relative to other wet laid materials. Values of 7 cc/g and higher are
achieved, while
other wet laid products investigated have Wet Compressed Bulk values less than
7.
Sample U10 has a WCB of about 11 cc/g. This sample also has a wet:dry strength
ratio
of about 0.5 and was produced at 50 percent rush transfer. Further, the
materials of the
present invention have high Wet Springback Ratio (WS) values, typically 0.8 or
greater,
with the value of Sample U2 exceeding 0.9. Creped materials seem incapable of
achieving such high wet resiliency. The LER values are also unusually high for
the
materials of the present invention, typically in excess of 0.7 and sometimes
above 0.8.
Some other materials may exhibit high values for one or two of the three wet
resiliency
parameters considered here, but the materials of the present invention are
especially
novel in displaying high values for all three parameters simultaneously.
Figure 12 is a bar
chart that compares all three wet resiliency parameters for several other
materials
(including some air-laid materials to be discussed below) and for several
materials of the
present invention, showing again the unusual combination of high wet
resiliency in all
three parameters.
In addition to the materials listed in Figure 11, several replicate runs with
Quilted
Bounty from 1994 were run, yielding a mean LER of 0.65, a mean Wet Springback
ratio of
0.66, and a mean WCB of 6.14. A run with a stack of three 1994 Surpass
handtowels
yielded an LER of 0.66, a Wet Springback ratio of 0.75, and a WCB of 5.9.
These values
are similar to those for the related materials reported in Table 2.
To illustrate the wet resiliency of additional materials, details of wet
resiliency
measurements are discussed for several air laid materials incorporating
chemically
stiffened fibers. Important values from specific runs are shown in the table
of Figure 13.
In gathering the data for this table, three types of fibers were used in these
examples.
Samples labeled with °CQ° were taken from 1993 Pampers~ diapers
made by the Procter
and Gamble company. These chemically stiffened fibers are crosslinked with
citric acid to
yield a stiff fiber. In addition to being chemically stiffened through
crosslinking, the fibers
are highly twisted and curled, giving additional bulk and resiliency to fluff
pads made from
the material. HBAFF has a Water Retention Value of approximately 0.4 g/g.
In moistening airlaid pads, the surfaces of the pad were lightly blotted with
facial
tissue after spraying to remove any unabsorbed or excess moisture from the
outer
surfaces. Measurements have also been made in which the sample was allowed to
sit for
- 51 -
CA 02241820 1998-07-31
several hours to allow equilibration of moisture content, though longer
equilibration times
seemed to have no clear effect on the wet resiliency measurements.
After preliminary work revealed the low Wet Springback Ratio values obtained
by
typical airlaid cellulose, it was hypothesized that precompression could
create a denser
web that might have better Wet Springback Ratio values. Thus, some air-laid
samples
were precompressed and then tested. Minor gains in Wet Springback Ratios were
possible with this strategy, at the expense of Wet Compressed Bulk. In the
case of
chemically stiffened fibers, moistening the precompressed sample results in an
increase
in bulk (especially when the fibers are curled and twisted, for they
straighten out to a
degree upon wetting and can then increase the bulk of a calendered or
precompressed
web, as taught by Cook et al. in US Pat. No. 5,360,420, previously cited).
Some of the runs in Table 14 involved special procedures. Prior to testing,
Sample CQ-A had been precompressed to a load of about 18 kg (40 pounds) by the
Instron compression platens (giving 10 psi over the 2.25-inch diameter
circular target
area). After Sample CQ-A was dried and had reached room temperature, the
entire dry
sample was uniformly loaded under a 35 kg weight (giving a pressure of about
12 psi) for
about 30 seconds. It was then tested again for wet resiliency, giving run CQ-
A2. After
drying and cooling, this sample was again tested for wet resiliency, resulting
in run CQ-
A3. Samples CQ-B and CQ-C were tested in the normal manner, without
precompression, with the exception that Sample CQ-C experienced a delay of
about 5
minutes from the beginning of moistening to the beginning of the wet
compression test.
Sample CQ-D was precompressed under a 15 kg weight (33 Ib, for a pressure of
about
5.3 psi) for about 30 seconds and was allowed to equilibrate in the moistened
state while
in a plastic bag for about 15 minutes before the wet compression test began.
Sample
CQ-E was precompressed by the Instron compressive platens to a pressure of 10-
12 psi
for about 90 seconds, followed by a pressure of 25 psi for about 10 seconds.
The sample
then sat uncompressed for 1 minute prior to testing. (Again, the compressive
testing
involves a first series of compressions in the dry state, followed by
moistening and then a
second identical series of compressions in the moist state.) Sample CQ-F was
tested in
the normal manner.
The results in the table of Figure 13 again show that some other materials may
achieve high values for WCB, but are unable to simultaneously provide WS and
LER
values comparable to the materials of the present invention. The combination
of high z-
direction fiber orientation from air forming plus the stiff and somewhat water-
insensitive
- 52 -
CA 02241820 1998-07-31
nature of these fibers yields relatively good wet bulk under compression (WCB
values of 6
to 8.2). However, their intrinsic stiffness and brittleness not only makes
them difficult to
process but hinders their dynamic elastic properties when wet, resulting in
poor LER and
WS values (LER<0.75 and WS < 0.7).
The table of Figure 14 summarizes In-Plane Permeability results for materials
made in accord with the present invention (having sample labels beginning with
"lJ") as
well as materials outside the scope of the present invention (sample labels
beginning with
"P"). For materials of the present invention are reported for the case of two
plies, the
table of Figure 14 shows details of the process used, including the Kymene add
on, the
through-drying fabric type (fabrics from Lindsay wire), the percent of
differential velocity
(rush) transfer. For all materials in Figure 14, the In-Plane Permeability and
the bulk of
the wet sheet at 0.8 psi are shown.
Materials outside the scope of the present invention include Surpass towel,
which
is an uncreped, through-air dried towel produced by Kimberly-Clark for
industrial and
commercial use. Quilted Bounty is a commercial, high-bulk, creped through-air-
dried
towel product from the Proctor and Gamble Company, which contains some BCTMP
fiber
and wet strength agents, but lacks the pore structure, wet resiliency, and
three-
dimensional structure of the present invention.
Several air-laid fluff pads were examined. Air-laying is often said to be
especially
advantageous for maintaining high bulk and an open, permeable structure
because it
results in many z-direction fibers which can resist compression and hold the
sheet open,
especially when stiffened fibers are used. Two sources of chemically stiffened
fibers were
used to produce air-laid sheets for testing. The first source is HBAFF fluff,
a commercial
cross-linked wood fiber pulp produced by Weyerhaeuser Company. The other is
"Curly-Q"
fibers taken from the transfer layer of 1993 Pampers diapers, produced by the
Proctor
and Gamble Company. Both of these fiber types are much stiffer and have higher
wet
bulk than is possible with untreated or conventional fluff pulps or air-laid
sheets, but
neither can provide the high In-Plane Permeability of the present invention.
Samples P6
and P7 are two forms of conventional fluff pulp. Sample P6 is from a
continuous operation
for producing fluff pulp on a tissue backing sheet, while sample P7 is from an
air-laying
batch operation. Sample P5 is an uncreped, through-dried sheet of hardwood
produced
without wet strength resins.
The materials of the present invention show higher permeability than is
possible
with other wet laid processes and also show higher permeability than is
achieved by air-
- 53 -
CA 02241820 1998-07-31
laying of conventional or chemically stiffened fibers. The increased
permeability is due in
part to the excellent wet resiliency of the three-dimensional structures,
which maintains
high bulk under compression. But the high bulk (and thus high pore space) does
not
account for all of the enhanced permeability. This can be seen by comparing
Samples U8
and U9, with wet bulks under 8 cc/g, to Samples P3 and P4, which have similar
or higher
wet bulks yet have significantly lower in-plane permeabilities. The higher in-
plane
permeability of the materials of the present invention is believed to be
partially due to the
nature of the pore size distribution, which provides a combination of
microscopic pores
and larger surface pores which provide less tortuous flow paths and lower
resistance to
in-plane flow. It is believed that this advantageous sheet and pore structure
for in-plane
flow is achieved by avoiding significant densification of the sheet during
water removal
and drying operations, by using rush transfer to create additional pore space
distributed
heterogeneously, and by using a three-dimensional through-drying fabric to
create
texture.
The table of Figure 15 summarizes the FIFE test data for some of the samples
previously identified. These same results are presented in the bar chart of
Figure 16. As
these results illustrate, for all three insults, the materials of the present
invention allow
rapid distribution of the fluid. The Surpass and Bounty materials require
substantially
more time.
The table of Figure 20 summarizes the Dry Wipe Residue data comparing the
webs of this invention (Samples 3-8) with the prior art Bounty and Surpass
towels. As the
results illustrate, the webs of this invention leave a residue that covers a
lower percentage
of the area tested than do the prior art samples. Also, the residue Mass
Factor for the
webs of this invention are also significantly lower. The low residue values
suggest that
these materials might be well suited for keeping fluid away from the user's
skin in
absorbent articles, and also point to the possible utility of such materials
in articles for
cleaning and wiping.
The table of Figure 21 summarizes the Wet Wipe Residue data for the same
samples of Figure 20. As shown, the webs of this invention again leave behind
a smaller
residue area coverage and a lower Mass Factor than the prior art samples.
The table of Figure 22 summarizes some structural properties of the webs of
this
invention compared to the prior art. Specifically, the Mean Volume-Weighted
Pore Length
values for the webs of this invention are substantially larger than those of
the prior art
samples. Also, the Thickness Variation Index of the webs of this invention is
substantially
- 54 -
CA 02241820 1998-07-31
less than that of the Bounty sample, which is indicative of the differences
between the
uncreped throughdried method of making the webs of this invention and the more
conventional creped, throughdried method used for making the Bounty product.
All of the foregoing examples serve to illustrate the unique wet-resiliency
and
absorbency properties of the novel cellulosic webs of this invention that make
them
especially well suited for use in absorbent articles and other products.
However, it will be
appreciated that the foregoing examples, given for purposes of illustration,
are not to be
considered as limiting the scope of this invention which is defined by the
following claims
and all equivalents thereto.
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