Note: Descriptions are shown in the official language in which they were submitted.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
1
CROSSLINKED CELLULOSIC PRODUCT FORMED BY EXTRUSION PROCESS
FIELD OF THE INVENTION
The present invention relates generally to a cellulosic fibrous product and,
more
particularly, to a crosslinked cellulosic fibrous product formed by an
extrusion process.
BACKGROUND OF THE INVENTION
Crosslinked cellulosic fibers are advantageously incorporated into a variety
of
fibrous products to enhance product bulk, resilience, and dryness. Absorbent
articles,
such as diapers, are typically formed from fibrous composites that include
absorbent
fibers such as wood pulp fibers, and can additionally include crosslinked
cellulosic
fibers. When incorporated into absorbent articles, such fibrous composites can
provide
a product that offers the advantages of high liquid acquisition rate and high
liquid
wicking capacity imparted by the crosslinked fibers and absorbent fibers,
respectively.
However, fibrous composites that include relatively high percentages of
crosslinked
fibers suffer from low sheet strength.
The relatively low strength of sheets that include crosslinked fibers is due
in
part to the loss of hydrogen bonding sites that accompanies cellulose
crosslinking. As a
result of their chemical modification, crosslinked cellulosic fibers have
fewer hydroxyl
groups that are available for forming hydrogen bonds between fibers. The lower
tendency of crosslinked fibers to form interfiber bonds generally precludes
their
formation into sheets or webs having any significant structural integrity.
Historically, cellulose structures have been formed from water based sheet
forming processes. Over time, airlaid and foam-forming processes were
developed to
use new materials and impart improved properties of the resulting web. Foam-
forming
processes showed improved capability to utilize long fibers of natural or
synthetic
origin and provided a bulky web. Airlaid processes provided bulk and softness
but
limited strength without a high binder content. Crosslinked fibers have been
used in
the above mentioned processes to improve web properties such as resilience,
bulk and
acquisition. Crosslinked fibers have previously only been available as
individually
crosslinked fibers packaged in a bale. Numerous patents speak of processes to
make
and to use individually crosslinked fibers. Therefore there is a need to
develop a
process that eliminates the step of individually crosslinking the cellulose
fibers.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
2
Personal care absorbent products, for example, infant diapers, adult
incontinence products, and feminine care products, include liquid acquisition
and/or
distribution layers that serve to rapidly acquire and then distribute acquired
liquid to a
storage core for retention. To achieve rapid acquisition and distribution,
these layers
may include crosslinked cellulosic fibers, which impart bulk and resilience to
the
layers. However, as noted above, webs that include high proportions of
crosslinked
fibers suffer from a lack of structural integrity. The problem of loss of
structural
integrity is traditionally addressed by sandwiching webs that include
crosslinked fibers
between either tissues and nonwoven sheets and secured with an adhesive. Such
structures are required to seek to maintain web integrity.
Accordingly, there exists a need for a cellulosic web that possesses the
advantageous properties of webs that include crosslinked cellulosic fibers and
yet
further advantageously maintains its structural integrity. The present
invention seeks to
fulfill these needs and provides further related advantages.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a crosslinked cellulosic fibrous
product that includes in situ crosslinked cellulosic fibers. In one
embodiment, the
product further includes a bonding agent. The product can optionally include
other
fibers alone, absorbent materials alone, and other fibers and absorbent
materials.
In another aspect of the invention, methods for forming the crosslinked
cellulosic fibrous product is provided. In one embodiment, the product is
formed using
a screw extrusion device. In another embodiment, the product is formed using a
rotary
mixing extrusion device.
In a further aspect, the present invention provides absorbent articles that
include
the bonded cellulosic fibrous product. The product can be combined with one or
more
other layers to provide structures that can be incorporated into absorbent
articles such
as infant diapers, adult incontinence products, and feminine care products.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention
will become more readily appreciated as the same become better understood by
reference to the following detailed description, when taken in conjunction
with the
accompanying drawings, wherein:
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
3
FIGURE 1 is a graph illustrating liquid drainage from foam as a function of
time for foams having densities of 137g/L, 95g/L, 66g/L, and 41g/L,
respectively;
FIGURE 2 is a flow diagram illustrating a representative method for making an
extruded composite in accordance with the present invention;
FIGURE 3A is an image of a representative mixing device useful in the method
of the present invention;
FIGURE 3B is an image of the stator of the mixing device illustrated in
FIGURE 3A;
FIGURE 3C is an image of the mixing device of FIGURE 3A with the rotor
removed;
FIGURE 4 is a schematic illustration of a representative extrusion device
useful
in the present invention illustrating positions at which various materials may
be added;
FIGURE 5 is a graph comparing the density of fibrous composites made from
(a) southern pine fibers and (b) fibers crosslinked with a blend of citric and
polyacrylic
acids by four methods: foam laid, airlaid, wetlaid, and the extrusion process
of the
invention;
FIGURE 6 is a graph illustrating pore size distribution for a representative
extruded composite formed in accordance with the present invention that
includes
cellulose fibers crosslinked with a blend of polyacrylic and citric acids (13%
by weight
crosslinked based on fiber);
FIGURE 7 is a graph illustrating pore size distribution for a representative
foam
laid composite that includes cellulose fibers crosslinked with a blend of
polyacrylic and
citric acids;
FIGURE 8 is a graph illustrating pore size distribution for a representative
airlaid composite that includes cellulose fibers crosslinked with a blend of
polyacrylic
and citric acids;
FIGURE 9 is a graph illustrating pore size distribution for a representative
wetlaid composite that includes cellulose fibers crosslinked with a blend of
polyacrylic
and citric acids;
FIGURE 10 is a graph illustrating absorption and desorption curves obtained
using an autoporosimeter for an airlaid composite that includes southern pine
fibers;
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
4
FIGURE 11 is a graph that compares the mid-point desorption pressure (MDP)
of representative extruded composites formed in accordance with the present
invention
("pine fiber" refers to a composite that includes southern pine fibers, "pre-
crosslinked
Chemistry B composite" refers to a composite that includes citric acid
crosslinked
fibers, and "in situ Chemistry B composite" refers to a composite that
includes cellulose
fibers treated with citric acid and cured in the composite);
FIGURE 12 is a graph illustrating the effect on crosslinking chemistry on the
mid-point desorption pressure for representative extruded composites formed in
accordance with the present invention ("pre-crosslinked Chemistry A" refers to
a
composite that includes cellulose fibers crosslinked with a blend of
polyacrylic and
citric acids, "pre-crosslinked Chemistry B" refers to a composite that
includes citric
acid crosslinked fibers, "in situ Chemistry B" refers to a composite that
includes
cellulose fibers that had been treated with citric acid and cured in the
composite, and in
situ Chemistry C" refers to a composite that includes cellulose fibers treated
with
polyacrylic acid and cured in the composite);
FIGURE 13 is a graph illustrating the effect of latex content on the mid-point
desorption pressure as a function of crosslinking chemistry for representative
extruded
composites formed in accordance with the present invention ("pre-crosslinked
Chemistry B" refers to a composite that includes citric acid crosslinked
fibers, "pre-
crosslinked Chemistry B plus 5 percent latex" refers to a composite that
includes citric
acid crosslinked fibers and 5 percent by weight latex, "in situ Chemistry B"
refers to a
composite that includes fibers treated with citric acid and cured in the
composite, and
"in situ Chemistry B plus S percent latex" refers to a composite that includes
fibers
treated with citric acid and cured in the composite and 5 percent by weight
latex);
FIGURE 14 is a graph illustrating the effect of in situ crosslinking on the
tensile
strength of representative extruded composites formed in accordance with the
present
invention that include citric acid crosslinked fibers and polyacrylic acid
crosslinked
fibers ("2 percent in situ" refers to a composite that includes fibers treated
with
2 percent by weight crosslinking agent, "6 percent in situ" refers to a
composite that
includes fibers treated with 6 percent by weight crosslinking agent, and "6
percent pre-
crosslinked" refers to a composite that includes fibers crosslinked with 6
percent by
weight crosslinking agent);
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
FIGURE 15 is a graph illustrating the effect of latex and fiber type on the
strength of representative composites formed in accordance with the present
invention
("pine" refers to a composite that includes southern pine fibers, "blend"
refers to a
composite that includes a 50/50 blend of southern pine fibers and fibers
crosslinked
with a blend of polyacrylic and citric acids, and "Chemistry A" refers to a
composite
that includes fibers crosslinked with a blend of polyacrylic and citric
acids);
FIGURE 16 is a graph illustrating the effect of in situ crosslinking chemistry
and latex on the tensile strength of representative extruded composites formed
in
accordance with the present invention ("Chem B" refers to a composite that
includes
citric acid crosslinked fibers and "Chem C" refers to a composite that
includes
polyacrylic acid crosslinked fibers);
FIGURE 17 is a graph illustrating pore size distribution for a foam laid
composite;
FIGURE 18 is a graph illustrating the mid-point desorption pressure for the
composite of FIGURE 17;
FIGURE 19 is a graph illustrating pore size distribution for a foam laid
composite;
FIGURE 20 is a graph illustrating the mid-point desorption pressure for the
composite of FIGURE 19;
FIGURE 21 is a graph illustrating the pore size distribution for a
representative
composite formed in accordance with the present invention (a composite
including
southern pine fibers);
FIGURE 22 is a graph illustrating the mid-point desorption pressure for the
composite of FIGURE 21;
FIGURE 23 is a graph illustrating pore size distribution for a representative
extruded composite formed in accordance with the present invention ( a
composite
including southern pine fibers and 5 percent latex);
FIGURE 24 is a graph illustrating pore size distribution for a representative
extruded composite of the present invention (a composite including fibers
crosslinked
with a blend of citric and polyacrylic acids with S percent latex);
FIGURE 25 is a graph illustrating pore size distribution for a representative
extruded composite of the present invention (a composite including a 50:50
blend of
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
6
southern pine fibers and fibers crosslinked with a blend of citric and
polyacrylic acids
with S percent latex);
FIGURE 26 is a graph illustrating the fourth gush acquisition rate of
representative extruded composites formed in accordance with the present
invention
compared to control composites;
FIGURE 27 is a graph illustrating the mid-point desorption pressure for a
representative extruded composite formed in accordance with the present
invention (a
composite that includes a blend of citric and polyacrylic acid crosslinked
fibers with
15 percent latex);
FIGURES 28 is a graph illustrating the mid-point desorption pressure for a
representative extruded composite formed in accordance with the present
invention (a
composite that includes a blend of citric and polyacrylic acid crosslinked
fibers )
FIGURE 29 is a graph illustrating the mid-point desorption pressure for a foam
laid composite;
FIGURE 30 is a graph illustrating the mid-point desorption pressure for a
wetlaid composite; and
FIGURE 31 is a graph illustrating the mean desorption pressure for airlaid
composites.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In one aspect, the present invention provides a bonded cellulosic fibrous
product
that includes in situ crosslinked cellulosic fibers. As used herein, the term
"in situ
crosslinked cellulosic fibers", refers to cellulosic fibers that have been
crosslinked
during the formation of the web. Therefore, the product of the invention is
distinguished from conventional webs that include crosslinked cellulosic
fibers that are
first formed and then introduced to the web during the web formation process.
The product includes in situ crosslinked cellulosic fibers. Because the fibers
are
crosslinked during the web formation process (i.e., in situ), the product
includes
intrafiber crosslinked cellulosic fibers (i.e., fibers having crosslinks
within each fiber)
and interfiber crosslinked cellulosic fibers (i.e., fibers having crosslinks
between
fibers). The product has a bonded structure and includes intrafiber
crosslinked
cellulosic fibers that are further crosslinked to adjacent fibers through
interfiber
crosslinks. The product possesses the advantageous properties of bulk and
resiliency
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
7
associated with intrafiber crosslinked fibers and the advantage of structural
integrity
imparted to the structure by the bonding between fibers. The product is a
bonded web
in which the crosslinked fibers and the bonded structure of the web itself
contribute to
the resiliency and liquid acquisition performance of the web.
In one embodiment, the product can be produced by (1) forming a web of
cellulosic fibers, at least some of which having been treated with a
crosslinking agent
and, if necessary, crosslinking catalyst; (2) drying the web; and (3) heating
the web at a
temperature and for a time sufficient to effect crosslinking.
Suitable fibers useful in forming the product of the invention include
cellulosic
fibers that have been treated with a crosslinking agent and, if necessary,
crosslinking
catalyst and then dried without curing the crosslinking agent. These dried and
treated
fibers can be introduced into the forming device for subsequent product
formation.
Any one of a number of crosslinking agents and crosslinking catalysts, if
necessary, can be used to provide the product of the invention. The following
is a
representative list of useful crosslinking agents and catalysts. Each of the
patents noted
below is expressly incorporated herein by reference in its entirety.
Suitable urea-based crosslinking agents include substituted areas such as
methylolated areas, methylolated cyclic areas, methylolated lower alkyl cyclic
areas,
methylolated dihydroxy cyclic areas, dihydroxy cyclic areas, and lower alkyl
substituted cyclic areas. Specific urea-based crosslinking agents include
dimethyldihydroxy urea (DMDHU, 1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone),
dimethyloldihydroxyethylene urea (DMDHEU, 1,3-dihydroxymethyl-4,5-dihydroxy-2-
imidazolidinone), dimethylol urea (DMU, bis[N-hydroxymethyl]urea),
dihydroxyethylene urea (DHEU, 4,5-dihydroxy-2-imidazolidinone),
dimethylolethylene urea (DMEU, 1,3-dihydroxymethyl-2-imidazolidinone), and
dimethyldihydroxyethylene urea (DDI, 4,5-dihydroxy-1,3-dimethyl-2-
imidazolidinone).
Suitable crosslinking agents include dialdehydes such as CZ-C8 dialdehydes
(e.g., glyoxal), CZ-Cg dialdehyde acid analogs having at least one aldehyde
group, and
oligomers of these aldehyde and dialdehyde acid analogs, as described in U.S.
Patents
Nos. 4,822,453; 4,888,093; 4,889,595; 4,889,596; 4,889,597; and 4,898,642.
Other
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
8
suitable dialdehyde crosslinking agents include those described in U.S.
Patents Nos.
4,853,086; 4,900,324; and 5,843,061.
Other suitable crosslinking agents include aldehyde and urea-based
formaldehyde addition products. See, for example, U.S. Patents Nos.3,224,926;
3,241,533; 3,932,209; 4,035,147; 3,756,913; 4,689,118; 4,822,453; 3,440,135;
4,935,022; 3,819,470; and 3,658,613.
Suitable crosslinking agents include glyoxal adducts of ureas, for example,
U.S.
Patent No. 4,968,774, and glyoxal/cyclic urea adducts as described in U.S.
Patents
Nos. 4,285,690; 4,332,586; 4,396,391; 4,455,416; and 4,505,712.
Other suitable crosslinking agents include carboxylic acid crosslinking agents
such as polycarboxylic acids. Polycarboxylic acid crosslinking agents (e.g.,
citric acid,
propane tricarboxylic acid, and butane tetracarboxylic acid) and catalysts are
described
in U.S. Patents Nos. 3,526,048; 4,820,307; 4,936,865; 4,975,209; and
5,221,285. The
use of CZ-C9 polycarboxylic acids that contain at least three carboxyl groups
(e.g., citric
acid and oxydisuccinic acid) as crosslinking agents is described in U.S.
Patents
Nos. 5,137,537; 5,183,707; 5,190,563; 5,562,740, and 5,873,979.
Polymeric polycarboxylic acids are also suitable crosslinking agents. Suitable
polymeric polycarboxylic acid crosslinking agents are described in U.S.
Patents
Nos.4,391,878; 4,420,368; 4,431,481; 5,049,235; 5,160,789; 5,442,899;
5,698,074;
5,496,476; 5,496,477; 5,728,771; 5,705,475; and 5,981,739. Polyacrylic acid
and
related copolymers as crosslinking agents are described U.S. Patents Nos.
6,306,251;
5,549,791; and 5,998,511. Polymaleic acid crosslinking agents are described in
U.S.
Patent No. 5,998,511.
Specific suitable polycarboxylic acid crosslinking agents include citric acid,
tartaric acid, malic acid, succinic acid, glutaric acid, citraconic acid,
itaconic acid,
tartrate monosuccinic acid, malefic acid, polyacrylic acid, polymethacrylic
acid,
polymaleic acid, polymethylvinylether-co-maleate copolymer,
polymethylvinylether-
co-itaconate copolymer, copolymers of acrylic acid, and copolymers of malefic
acid.
Other suitable crosslinking agents are described in U.S. Patents Nos.
5,225,047;
5,366,591; 5,556,976; and 5,536,369.
Suitable catalysts can include acidic salts, such as ammonium chloride,
ammonium sulfate, aluminum chloride, magnesium chloride, magnesium nitrate,
and
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
9
alkali metal salts of phosphorous-containing acids. In one embodiment, the
crosslinking catalyst is sodium hypophosphite.
Mixtures or blends of crosslinking agents and catalysts can also be used.
The crosslinking agent is applied to the cellulosic fibers in an amount
sufficient
to effect intrafiber crosslinking and interfiber crosslinking as described
above. The
amount applied to the cellulosic fibers can be from about 1 to about 10
percent by
weight based on the total weight of fibers. In one embodiment, crosslinking
agent in an
amount from about 4 to about 6 percent by weight based on the total weight of
fibers.
Suitable cellulosic fibers for forming the product of the invention include
those
known to those skilled in the art and include any fiber or fibrous mixture
that can be
crosslinked and from which a fibrous web or sheet can be formed.
Although available from other sources, cellulosic fibers are derived primarily
from wood pulp. Suitable wood pulp fibers for use with the invention can be
obtained
from well-known chemical processes such as the kraft and sulfite processes,
with or
without subsequent bleaching. Pulp fibers can also be processed by
thermomechanical,
chemithermomechanical methods, or combinations thereof. The preferred pulp
fiber is
produced by chemical methods. Groundwood fibers, recycled or secondary wood
pulp
fibers, and bleached and unbleached wood pulp fibers can be used. Softwoods
and
hardwoods can be used. Details of the selection of wood pulp fibers are well
known to
those skilled in the art. These fibers are commercially available from a
number of
companies, including Weyerhaeuser Company, the assignee of the present
invention.
For example, suitable cellulose fibers produced from southern pine that are
usable with
the present invention are available from Weyerhaeuser Company under the
designations CF416, NF405, PL416, FRS 16, and NB416.
The wood pulp fibers useful in the present invention can also be pretreated
prior
to use. This pretreatment may include physical treatment, such as subjecting
the fibers
to steam, or chemical treatment.
Although not to be construed as a limitation, examples of pretreating fibers
include the application of surfactants or other liquids, which modify the
surface
chemistry of the fibers. Other pretreatments include incorporation of
antimicrobials,
pigments, dyes and densification or softening agents. Fibers pretreated with
other
chemicals, such as thermoplastic and thermosetting resins also may be used.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
Combinations of pretreatments also may be employed. Similar treatments can
also be
applied after formation of the fibrous product in post-treatment processes.
Cellulosic fibers treated with particle binders and/or densification/softness
aids
known in the art can also be employed in accordance with the present
invention. The
particle binders serve to attach other materials, such as superabsorbent
polymers, as
well as others, to the cellulosic fibers. Cellulosic fibers treated with
suitable particle
binders and/or densification/softness aids and the process for combining them
with
cellulose fibers are disclosed in the following U.S. patents: (1) Patent No.
5,543,215,
entitled "Polymeric Binders for Binding Particles to Fibers"; (2) Patent No.
5,538,783,
entitled "Non-Polymeric Organic Binders for Binding Particles to Fibers"; (3)
Patent
No.5,300,192, entitled "Wet Laid Fiber Sheet Manufacturing With Reactivatable
Binders for Binding Particles to Binders"; (4) Patent No. 5,352,480, entitled
"Method
for Binding Particles to Fibers Using Reactivatable Binders"; (5) Patent No.
5,308,896,
entitled "Particle Binders for High-Bulk Fibers"; (6) Patent No. 5,589,256,
entitled
"Particle Binders that Enhance Fiber Densification"; (7) Patent No. 5,672,418,
entitled
"Particle Binders"; (8) Patent No. 5,607,759, entitled "Particle Binding to
Fibers"; (9)
Patent No. 5,693,411, entitled "Binders for Binding Water Soluble Particles to
Fibers";
(10) Patent No.5,547,745, entitled "Particle Binders"; (11) Patent
No.5,641,561,
entitled "Particle Binding to Fibers"; (12) Patent No. 5,308,896, entitled
"Particle
Binders for High-Bulk Fibers"; (13) Patent No. 5,498,478, entitled
"Polyethylene
Glycol as a Binder Material for Fibers"; (14) Patent No. 5,609,727, entitled
"Fibrous
Product for Binding Particles"; (15) Patent No. 5,571,618, entitled
"Reactivatable
Binders for Binding Particles to Fibers"; (16) Patent No. 5,447,977, entitled
"Particle
Binders for High Bulk Fibers"; (17) Patent No. 5,614, 570, entitled "Absorbent
Articles
Containing Binder Carrying High Bulk Fibers; (18) Patent No. 5,789,326,
entitled
"Binder Treated Fibers"; and (19) Patent No. 5,611,885, entitled "Particle
Binders",
each expressly incorporated herein by reference.
In addition to natural fibers, synthetic fibers including polymeric fibers,
such as
polyolefin, polyamide, polyester, polyvinyl alcohol, polyvinyl acetate fibers,
can also
be incorporated into the product. Suitable synthetic fibers include, for
example,
polyethylene terephthalate, polyethylene, polypropylene, nylon, and rayon
fibers.
Other suitable synthetic fibers include those made from thermoplastic
polymers,
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
11
cellulosic and other fibers coated with thermoplastic polymers, and
multicomponent
fibers in which at least one of the components includes a thermoplastic
polymer.
Single and multicomponent fibers can be manufactured from polyester,
polyethylene,
polypropylene, and other conventional thermoplastic fibrous materials. Single
and
multicomponent fibers are commercially available. Suitable bicomponent fibers
include CELBOND fibers available from Hoechst-Celanese Company. The product
can also include combinations of natural and synthetic fibers.
In one embodiment, the product further includes a bonding agent. The bonding
agent serves to further enhance the structural integrity of the product.
Suitable bonding
agents include thermoplastic materials, such as bicomponent fibers and
latexes, and wet
strength agents. When the bonding agent is a thermoplastic fiber, the fiber
can be
combined with cellulosic fibers and then formed into the web to be treated
with the
crosslinking agent. When the bonding agent is a wet strength agent, the
bonding agent
can be applied to the web prior to subjecting the web to fiber crosslinking
conditions.
Suitable thermoplastic fibers include cellulosic and other fibers coated with
thermoplastic polymers, and multicomponent fibers in which at least one of the
components includes a thermoplastic polymer. Single and multicomponent fibers
can
be manufactured from polyester, polyethylene, polypropylene, and other
conventional
thermoplastic fibrous materials. Single and multicomponent fibers are
commercially
available. Suitable bicomponent fibers include CELBOND fibers available from
Hoechst-Celanese Company.
Suitable wet strength agents include cationic modified starch having nitrogen-
containing groups (e.g., amino groups) such as those available from National
Starch
and Chemical Corp., Bridgewater, NJ; latex; wet strength resins, such as
polyamide-
epichlorohydrin resin (e.g., KYMENE 557LX, Hercules, Inc., Wilmington, DE),
and
polyacrylamide resin (see, e.g., U.S. Patent No. 3,556,932 and also the
commercially
available polyacrylamide marketed by American Cyanamid Co., Stanford, CT,
under
the trade name PAREZ 631 NC); urea formaldehyde and melamine formaldehyde
resins; and polyethylenimine resins. A general discussion on wet strength
resins
utilized in the paper field, and generally applicable in the present
invention, can be
found in TAPPI monograph series No. 29, "Wet Strength in Paper and
Paperboard",
Technical Association of the Pulp and Paper Industry (New York, 1965).
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
12
In other embodiments, the product can include other fibers. Other fibers
include, for example, the cellulosic fibers, particularly the wood pulp fibers
described
above, as well as hemp, bagasse, cotton, groundwood, bleached and unbleached
pulp,
recycled or secondary fibers.
For embodiments of the product in which liquid retention is desired, the
product
can further include absorbent material (e.g., superabsorbent polymer
particles). As
used herein, the term "absorbent material" refers to a material that absorbs
liquid and
that generally has an absorbent capacity greater than the cellulosic fibrous
component
of the composite. Preferably, the absorbent material is a water-swellable,
generally
water-insoluble polymeric material capable of absorbing at least about 5,
desirably
about 20, and preferably about 100 times or more its weight in saline (e.g.,
0.9 percent
saline). The absorbent material can be swellable in the dispersion medium
utilized in
the method for forming the composite. In one embodiment, the absorbent
material is
untreated and swellable in the dispersion medium. In another embodiment, the
absorbent material is a coated absorbent material that is resistant to
absorbing water
during the product formation process.
The amount of absorbent material present in the product can vary greatly
depending on the product's intended use. The amount of absorbent material
present in
an absorbent article, such as an absorbent core for an infant's diaper, is
suitably present
in the composite in an amount from about 2 to about 80 weight percent,
preferably from
about 30 to about 60 weight percent, based on the total weight of the
composite.
The absorbent material may include natural materials such as agar, pectin, and
guar gum, and synthetic materials, such as synthetic hydrogel polymers.
Synthetic
hydrogel polymers include, for example, carboxymethyl cellulose, alkaline
metal salts
of polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene malefic
anhydride
copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl morpholinone,
polymers and copolymers of vinyl sulphonic acid, polyacrylates,
polyacrylamides, and
polyvinyl pyridine among others. In one embodiment, the absorbent material is
a
superabsorbent material. As used herein, a "superabsorbent material" refers to
a
polymeric material that is capable of absorbing large quantities of fluid by
swelling and
forming a hydrated gel (i.e., a hydrogel). In addition to absorbing large
quantities of
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
13
fluids, superabsorbent materials can also retain significant amounts of bodily
fluids
under moderate pressure.
Superabsorbent materials generally fall into three classes: starch graft
copolymers, crosslinked carboxymethylcellulose derivatives, and modified
hydrophilic
polyacrylates. Examples of such absorbent polymers include hydrolyzed starch-
acrylonitrile graft copolymers, neutralized starch-acrylic acid graft
copolymers,
saponified acrylic acid ester-vinyl acetate copolymers, hydrolyzed
acrylonitrile
copolymers or acrylamide copolymers, modified crosslinked polyvinyl alcohol,
neutralized self crosslinking polyacrylic acids, crosslinked polyacrylate
salts,
carboxylated cellulose, and neutralized crosslinked isobutylene-malefic
anhydride
copolymers.
Superabsorbent materials are available commercially, for example,
polyacrylates from Clariant of Portsmouth, Virginia. These superabsorbent
polymers
come in a variety of sizes, morphologies, and absorbent properties (available
from
Clariant under trade designations such as IM 3500 and IM 3900). Other
superabsorbent
materials are marketed under the trademarks SANWET (supplied by Sanyo Kasei
Kogyo Kabushiki Kaisha), and SXM77 (supplied by Stockhausen of Greensboro,
North
Carolina). Other superabsorbent materials are described in U.S. Patent No.
4,160,059;
U.S. Patent No. 4,676,784; U.S. Patent No. 4,673,402; U.S. Patent No.
5,002,814; U.S.
Patent No. 5,057,166; U.S. Patent No. 4,102,340; and U.S. Patent No.
4,818,598, all
expressly incorporated herein by reference. Products such as diapers that
incorporate
superabsorbent materials are described in U.S. Patent No. 3,699,103 and U.S.
Patent
No. 3,670,731.
Suitable superabsorbent materials useful in the product include superabsorbent
particles and superabsorbent fibers.
In one embodiment, the product includes a superabsorbent material that swells
relatively slowly for the purposes of product manufacturing and yet swells at
an
acceptable rate so as not to adversely affect the absorbent characteristics of
the product
or any construct containing the product. Generally, the smaller the absorbent
material,
the more rapidly the material absorbs liquid.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
14
In another aspect of the invention, methods for forming the bonded cellulosic
fibrous product are provided. The bonded cellulosic fibrous product can be
formed by
an extrusion process.
In general, the methods for forming the product include introducing the
components that provide the product into a forming device. Generally, fibers
are
introduced into the device as a pulp slurry (i.e., a dispersion of fibers in a
dispersion
medium). The pulp slurry can include dried pulp, never-dried pulp, treated
pulp, or
mixtures thereof. The pulp slurry can have a relatively high consistency, for
example,
in one embodiment from about 15 to about 50 percent by weight solids, and in
another
embodiment from about from about 20 to about 35 percent by weight solids. The
pulp
introduced into the mixing/extrusion device can then be combined with other
components. These components include crosslinking agent and, if necessary,
crosslinking catalyst, for embodiments that do not include the introduction of
crosslinking agent-treated pulp into the device. For embodiments of the
invention that
include a bonding agent, the bonding agent can be added to the pulp slurry in
the
device. Surfactant and air can also be added to the pulp in the device to
provide a
foam-forming medium. Other components, such as absorbent material, can be
added as
necessary to provide the desired product.
The product's components are combined and mixed in the device and then
extruded from the device. The extruded cellulosic material is then dried and
the
product ultimately formed by heat treatment. The product has an advantageous
low
density, as low as about 0.02 g/cm3. Generally, the product has a density in
the ranges
from about 0.02 to about 0.20 g/cm3.
As described above, the product of the invention is formed by subjecting a web
that includes cellulosic fibers to which crosslinking agent and, if necessary,
crosslinking catalyst, and bonding agent, if included, to a temperature and
for a time
sufficient to effect crosslinking (i.e., curing) and fiber bonding. The curing
of the
crosslinking agent to provide the product can be performed by several methods.
Crosslinking typically requires a relatively high temperature (180°C)
and long reaction
times (greater than 4 minutes). In one embodiment, the product is formed by
heating in
a curing oven in which high temperature and large volumes of air are drawn
through
the web. In another embodiment, curing takes place after the webs have been
placed in
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
boxes for shipping. In this embodiment, boxes containing the treated webs are
passed
through a dryer (e.g., a kiln dryer) to complete the crosslinking reaction.
The product of the present invention can be formed as an extended web or sheet
that has structural integrity and sheet strength sufficient to permit the
fibrous web to be
rolled, transported, and used in rolled form in subsequent processes.
The product of the present invention can be supplied in a fibrous rolled form
and readily incorporated into subsequent processes. The product can be
advantageously incorporated into a variety of absorbent articles, such as
diapers,
including disposable diapers and training pants; feminine care products,
including
sanitary napkins, tampons, and pant liners; adult incontinence products;
toweling;
surgical and dental sponges; bandages; food tray pads; and the like.
In one embodiment, the process of the invention provides a bonded composite
having intrafiber crosslinked fibers and interfiber crosslinked fibers that
impart
improved performance of the resulting composite. As noted above, the process
is a
foam-forming process that enables forming composites at high solids content
(i.e., high
consistency) without the need for the use of a forming wire and drainage. In
the
process, air content and foam density are characteristics of the foam in the
process.
Foam can be classified as either stable or unstable. However, overall, foams
are
relatively unstable thermodynamically. Foam stability depends on many factors
including surfactant type and concentration, temperature, stabilizer
concentration, and
the presence of solids. Foam collapse occurs when liquid in foam moves to the
bottom
of the foam bubble by the force of gravity causing the lamellae on top of or
between the
bubbles to thin to the point of failure. See, Porter, M. R. Handbook of
Surfactants, 2°a
Ed., Blackie Academic & Professional (Chapman & Hall), 1994 pp 65-69. In the
present process, the foam is considered to be stable.
To further understand the foam useful in the process, a discussion of foam air
content and foam density is illustrative.
Wiggins-Teape teaches foams having an air content of at least 65% by volume
(see, U.S. Patent Nos. 3,716,449 and 3,938,782). To effect dispersion, foams
having an
air content of 55-75% by volume (see U.S. Patent No. 3,871,952) or SO-70% by
volume
(see U.S. Patent No. 3,937,273). Outside this air content range (either higher
or lower),
solids in the foam, such as glassfiber, cellulose fiber, synthetic fiber,
particulates, and
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
16
the like, agglomerate. However, foam provides greater dispersion than a web or
handsheet made from an aqueous slurry at the same solids content. Ahlstrom
describes
an improved process that uses an air content of 25-75% by volume (see U.S.
Patent No.
5,904,809).
However, at high air contents (e.g., greater than about 75% by volume,
Wiggins-Teape describes that the foam viscosity rises to the point where the
liquid in
the bubble lamellae can no longer be drained (within a reasonable time) from
the
mixture (e.g., the foam is a stable foam). Thus, forming on a foraminous
support and
draining the liquid from the web, like on a paper machine, is not practical.
In the
process of the invention, the high air content foam is a stable foam acts like
a semi-
solid and drainage of the liquid is slow. Because little liquid is available
to drain out of
the foam (for example, at 95% by volume air content, 1000 ml of foam contains
only
SO ml of liquid), foam collapse by liquid movement (due to gravity or applied
suction)
takes a very long time. Total drainage time can be demonstrated as an
exponentially
decreasing rate as seen in FIGURE 1. In fact, complete liquid drainage is
never fully
achieved. Consequently, this long drain time and the stiffness or high
viscosity of the
foam make conventional drainage impractical. The process of the invention
makes use
of high air content foam, typically greater than about 75% by volume. In one
embodiment, the air content is greater than about 90% by volume, and in
another
embodiment, greater than about 98% by volume. Such high air content foams have
not
previously been practiced to produce a product that does not require a
foraminous
support through which free liquid is drained from the web. In the present
process, foam
collapse is initiated by temperature and/or by hygroscopic materials in the
system that
absorb liquid sufficient to effect foam bubble collapse.
Foam density is closely correlated with air content. In the references noted
above, foam densities in the range of 250-500 g/1 at 1 bar pressure are
described. By
eliminating the need for liquid drainage, lower foam densities can be used to
form
fibrous webs (for example, foam densities from about 20 to about 100 g/1 yield
air
contents of from about 90 to about 98% by volume). In the present invention,
foam
densities between about 20 to about 200 g/1 at 1 bar are useful. The
elimination of the
forming step in the process greatly reduces the equipment necessary. Because
liquid is
not drained from the foamed materials during web formation, there is no
typical
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
17
whitewater or reclaimed liquid or foam that needs to be reprocessed and
reused. The
reduced liquid/foam load also reduces the amount of liquid in the product
leading to
more economical drying. This is illustrated by examining the forming solids or
consistency in the process.
The Ahlstrom patents describe a foam-forming process that uses a fiber
consistency of up to 12% is possible in a foam having an air content of 25-75%
by
volume. The process of the invention makes use of fiber consistencies ranging
from
about 15 to about 50% by volume. In certain embodiments, fiber consistencies
are
between about 30 to about 50%. In other embodiments, fiber consistencies are
between
about 20 to about 35%. Dewatering of fiber at such high consistencies can be
achieved.
High solids fiber sludge can be further dewatered in an extruder with the
addition of
slip aids. Also, reclaimed fiber can be extruded at high consistencies with
the slip aids
in order to reclaim the fibers and fillers typically found in printing papers.
In the
present process, foam is used to fluidize the fiber as opposed to adding a
slip aid. The
foam is generated by the action of high speed screws in a counter or co-
rotating
extruder or the high speed rotor of a rotary mixer/foamer or pump on a
suitable
surfactant. The foam used in the process includes a surfactant. A suitable
surfactant is
one which generates a foam density of about 100 g/1 and an air content of
about 90%
with a surfactant concentration between about 0.01 to about 5 % by weight of
the
composite. In one embodiment, the surfactant is Incronam 30 produced by Croda.
High solids fiber are used in the process of the invention. High solids fiber
can
be produced from wet pulp that has been dewatered to greater than about 20%
consistency or from dry fibers obtained via a hammermill and adding water.
Thus, in
the process of the invention, high solids compositions, with appropriate
chemical
additives including binders, latex, wet strength agents, dry strength agents,
crosslinking
agents, acids, bases, dyes, powders, pigments, polymers, can be mixed and
foamed in a
mixing device.
The process of the invention uses high consistency fiber that is fluidized
with
foam. An overall diagram of a representative method of the invention is
illustrated in
FIGURE 2.
The foaming and mixing operation can be achieved by a shear inducing mixing
device. In one embodiment, the shear inducing mixing device a mixer/foamer,
for
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
18
example, Model 8M Mixer/Foamer available from E. T. Oakes Corporation,
Hauppauge, NY. This device is a rotary mixer and is illustrated in FIGURES 3A-
C.
To fluidize the fiber, the fiber at roughly 30% solids is added to the device
with a piston
that pushes the fiber toward the rotor. At the shear or mixing point where the
fiber
contacts the rotor, surfactant is injected. The foamed fiber exits into a tube
that feeds a
die. Referring to FIGURES 3A-C, air and other chemicals can also be added
along the
radial axis of the rotor. Chemical additions can be made on the front face of
the rotor
or on the rear face. The rotor and stators are shown in the FIGURES 3B and C.
In the
device, the path that the fiber must take is tortuous and without adequate
foaming the
fiber plugs the rotor. A representative plate mixer extrusion device, method,
representative products formed in accordance with the invention, and the
performance
characteristics of representative products are described in Example 2.
In another embodiment, the shear inducing mixing device is an extrusion
device. One such extruder is the ZSK 58, a mega compounder available from
Coperion
Corporation, Ramsey NJ. One possible configuration of the extruder is shown in
FIGURE 4. In the process, pulp is added into the extruder at about 20 to about
40%
solids. Then surfactant is added to initiate foaming. Additional chemicals are
added
downstream of the foaming, but could be added prior to foaming. Crosslinking
agent,
(e.g., citric acid and catalyst) can be added and mixed with the fibers in the
extruder
making fibers that are prepared for crosslinking during subsequent drying of
the
product. Binders such as KYMENE (available from Hercules, Wilmington DE) and
latex (available from DuPont, Midland MI or HB Fuller, St. Paul MN) can also
be used.
Chemicals and other binders in solid, liquid, or gaseous forms can be added.
Air can
also be added if needed to increase foaming and/or air content. A
representative twin-
screw extrusion device, method, representative products formed in accordance
with the
invention, and the performance characteristics of representative products are
described
in Example 1.
Using either device, (i.e., rotary mixer or twin-screw extruder), the foamed
fiber
and additives are extruded through a die to form a sheet or composite web. It
is also
possible to generate other shapes. The foam composite is extruded onto a solid
conveyor belt, wire, or nonwoven Garner fabric to transport the web to the
dryer. The
foamed composite is then dried (and/or optionally cured) using techniques such
as
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
19
convection drying, through air drying, impingement, microwave, radio
frequency, and
the like.
The composites formed by the processes of the invention include acquisition
and storage composites. The process of the invention enables the formation
composites
composed of any fiber, composites having low densities, and composites
including in
situ crosslinked fibers. For composites that include in situ crosslinked
fibers,
crosslinking agent can be added to the fibers before the fibers are added to
the extruder.
Alternatively, crosslinking agent can be added to the mixing device during the
extrusion process.
To achieve suitable acquisition performance, acquisition composites have a
relatively low density. The acquisition composite also has suitable absorption
and
desorption characteristics, referred to herein as the mid-point desorption
pressure
(MDP).
As shown in FIGURE 5, the density of composites produced by the process of
the invention is much less than composites formed by the other noted
processes.
FIGURE 5 illustrates the difference between the present process and the
process for
two fiber furnishes. A pine only furnish can be produced typically at about
0.14 g/cm3
with a foam process for forming cellulosic composites described in
PCT/LJS99/26560,
Reticulated Absorbent Composite, and PCT/LJS99/05997, Methods For Forming A
Fluted Composite. In a wetlaid system with traditional papermaking fibers,
density can
range from 0.1-1.4 g/cm3 depending on the grade (see Handbook of Pulp and
Paper
Technology by K. Britt, 1970, page 669). The present process can form a
composite
from the same fiber (pine) at a density of 0.037 g/cm3. This density is less
than the
density at which foam laid, or high dilution wetlaid processes can form
composites
including crosslinked fiber.
Density is related to pore size distribution. The present process, by nature
of
both the agglomeration effects and the dispersion effects of foam, creates a
web with a
wide range of pore sizes. The pore sizes are measured by the autoporosimeter
and
confirmed by measurements taken from photomicrographs of the foam. The pore
size
distribution in the range less than 750 um can easily be measured by an
autoporosimeter available from TRI/Princeton, Princeton, NJ. For a description
of the
theory, applications, and equipment, see Miller and Tyomkin in The Journal of
Colloid
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
and Interface Science (162, pages 163-170, 1994). The porosimeter tests a
sample
through an absorption and desorption cycle. Briefly, a presaturated sample is
placed in
the instrument. The pressure in the sample chamber is increased which causes
the
liquid in the sample to drain out from the largest pores first followed by the
smaller
pores. A computer interfaced with a balance monitors the amount of liquid
leaving the
sample at each pressure applied. After the last pressure point is tested, the
system can
run in reverse causing the sample to absorb liquid which is again tracked with
pressure.
From this data, pore size distributions and absorption/desorption hysteresis
can be
determined.
Mode pore size radius, ~.m, for similar webs made on several processes is
shown in Table 1. Mode is defined as the pore size with the most volume which
indicates the highest frequency of occurrence. These values indicate that the
mode pore
sizes in composites formed by the present extrusion method (pore size
contributing the
greatest volume) are larger than those produced by other processes.
Table 1. Comparison of Mode Pore Size Radius (~.m).
Method Extrusion Foam Airlaid Wetlaid
Absorption Curve330 225 210 250
Desorption Curve150 88 98 75
The data in the above table are derived from the pore size distribution charts
illustrated in FIGURES 6-9. FIGURES 6-9 illustrates the pore size distribution
charts
for representative composites formed by the present extrusion process, foam-
formed,
airlaid, and wetlaid processes, respectively. Each composite had a target
basis weight
of 300 g/m2. In these figures, mode pore sizes for absorption are indicated.
Mode
desorption pore sizes are not marked, but can be determined as for the
absorption.
Low values for capillary desorption pressure (CDP) have been indicated as
being preferred acquisition composites. Capillary desorption pressure (CDP) is
defined
as the head pressure at which 50% of the liquid in a saturated sample has been
drained
from the sample. For fluid acquisition, a value of capillary desorption
pressure of 8-40
cm HZO (8-25 cm HZO typical) is advantageous for a synthetic foam to acquire
fluid
(see, e.g., U.S. Patent No. 5,571,849; U.S. Patent No. 5,550,167; U.S. Patent
No.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
21
5,851,648). For fluid distribution, values of 12-50 cm H20 (20-40 cm HZO
typical) for
CDP are desired for good performance (see U.S. Patent No. 6,013,589).
As noted above, Miller and Tyomkin show that the capillary desorption pressure
can be determined from a plot of percent saturation vs. applied pressure
obtained from
the autoporosimeter. Absorption (uptake) and desorption (retention) curves
over a
range of pressure give an indication of a material's ability to acquire and
retain liquid.
Acquisition materials for use in absorbent products such as infant diapers
must be able
to quickly absorb liquid and also efficiently release it again to the diaper
core. The
capillary desorption pressure measured by the autoporosimeter is called the
mid-point
desorption pressure (MDP). The MDP can be used as a measure of a material's
ability
to function as an acquisition material. It is clear that any percentage of
saturation could
be chosen and, for simplicity, the mid-point of the curve has been chosen as
it is close
to the inflection point of the curve. Other than the materials formed by the
present
process, no cellulose materials have to this point in time been unable to
achieve MDP
values less than 14 cm H20. Thus, cellulose-containing materials that exhibit
lower
MDP values result in improved acquisition performance.
In one embodiment, the composites of the invention have an MDP value less
than about 14 cm H20. In another embodiment, the composites have an MDP value
less than about 12 cm HZO. In a further embodiment, the composites have an MDP
value less than about 10 cm H20.
To illustrate the current performance of cellulose-based acquisition
materials,
consider an airlaid acquisition material composed of southern pine fibers.
Using the
TRI autoporosimeter, the MDP was determined to be 44 cm H20. This data is
presented in FIGURE 10 to show the output of the autoporosimeter.
The use of crosslinked cellulosic fibers in personal care absorbent products
such
as infant diapers has improved the performance of current diapers in the
market.
Several airlaid pads were made from two crosslinked fibers were tested for
MDP. A
pad made from citric acid crosslinked fibers (Chemistry B) had an MDP of 24.2
cm
HZO. A pad made from polyacrylic acid/citric acid crosslinked fibers
(Chemistry A)
had an MDP of 14.4-15.9 cm HzO. Chemistry C refers to polyacrylic acid
crosslinked
fibers
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
22
The process of the invention provides webs having improved MDP values. For
example, an extruded pine fiber web formed by the Oakes mixer/foamer without
using
a crosslinking chemistry provides an MDP value of 18.5 cm HZO (compare to 44
cm
HZO for airlaid). The MDP value of an extruded web formed from fibers
crosslinked
with a blend of polyacrylic and citric acids (pre-crosslinked Chemistry A) was
measured to be 10.5 cm HZO (compare to 15.2 cm H20 for airlaid). The MDP value
of
an extruded web formed from citric acid crosslinked fibers (pre-crosslinked
Chemistry
B) was measured to be 12.0 cm Hz0 (compare to 24.2 cm H20 for airlaid).
The extrusion process provides MDP improvement due to the web's structure
and surface tension effects. Surface tension relates to pressure difference as
shown in
the Laplace equation:
2a
r =-cos9
OP
where OP = pressure difference, 6 = surface tension, 8 = contact angle, and r
= radius.
If the surface tension is reduced due to the presence of surfactants (as in
the
foam extrusion process of the invention), then at constant radius, the
pressure
difference (in effect the MDP) must also be reduced. But most pores collapse
when
wet unless there is resistance to collapse. Further improvements can be gained
by
increasing the bonding in the structure through interfiber crosslinking and/or
the
addition of binders. If bonding and fiber resilience increases, then the pore
radius will
not collapse yielding again lower MDP values (by minimizing the rise in
pressure due
to collapsing pore radius). The addition of latex raises the value of the
contact angle
and thus lowers the cosine. This also at constant pore radius demands a
reduction in
MDP.
The improvements described above are graphically represented in FIGURES 11
and 12. FIGURE 11 is a bar graph that demonstrates the reduction in mid-point
desorption pressure as a function of crosslinking chemistry for the present
process.
Extruded composites formed from pine fibers, citric acid crosslinked fibers,
and in situ
citric acid crosslinked fibers (i.e., fibers added to mixing device that were
treated, but
not cured, with citric acid) had MDP values of 18.5, 12.0, and 9.8 cm HZO,
respectively. FIGURE 12 is a graph that shows the effect of increasing
crosslinking
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
23
agent on MDP for extruded composites including fibers crosslinked with a blend
of
polyacrylic and citric acids (pre-crosslinked Chemistry A), citric acid
crosslinked fibers
(pre-crosslinked Chemistry B), in situ citric acid crosslinked fibers (in situ
Chemistry
B), and in situ polyacrylic acid crosslinked fibers (in situ Chemistry C). As
the amount
of crosslinking agent is increased, the MDP value for composites made from
these
fibers decreases. A reduction in MDP (from 12 to 9.8 cm HZO) is shown by the
dotted
lines compared to the solid pre-crosslinked Chemistry B line. Chemistry C
shows an
even greater reduction in MDP.
The addition of latex, such as PD8161 from HB Fuller, St. Paul MN, (e.g., 5%
by weight based on total weight of composite) also positively impacts the MDP
and
improves the acquisition performance. FIGURE 13 illustrates that latex alone
and latex
combined with in situ crosslinking reduce MDP. Again, the pre-crosslinked data
is
considered the control to show the effects of in situ crosslinking (previously
demonstrated as from 12 to 9.8 cm HZO). The effect of latex without in situ
crosslinking is a drop in MDP from 12 to 9.5 cm H20. The combined effect of in
situ
crosslinking and latex addition changes the MDP from 9.8 to 8.3 cm H20. At
higher
levels of latex, even lower MDP values are obtained. As an example, the MDP of
a
pre-crosslinked Chemistry A fiber composite with 1 S% latex was 7.7 cm HzO. A
summary of the MDP values is provided in Table 2.
Table 2. MDP Values for Representative Extruded Composites.
MDP Values,
cm H20
Chemistry
Fiber Type Level Airlaid Extruded withoutExtruded with
% Sam 1e latex latex
Southern ine 0 43.4-44.5 16.2-18.5 E & 4.8-10.7 E
O & O
Pre-crosslinked 14.4-24.9 11.5-12.1 4.7-9.1
Chemis A 13 14.4-15.9 10.5 O 7.7-9.1 O
Chemist B 6 23.8-24.9 12.0 O 4.7-9.0 E &
O
Chemistr C 6 - 11.5 O -
Crosslinked 9.1-13.5 7.6-8.8
in
situ
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
24
Chemis A - - - -
Chemistr B 2-6 - 9.8-13.5 O 7.5-8.8 O
Chemis C 2-6 - 9.1-11.0 O 7.6-8.3 O
Blend 50% 13* - 12.6 (O) 8.1-10.4 (O)
pine/50% pre-
crosslinked
Chemist A
*only applies to fiber that is cross linked
(E) = samples made on twin screw extruder
(O) = samples made on Oakes Mixer/foamer
(E&O) = includes samples made on either Oakes Mixer/foamer or twin screw
extruder
The acquisition rate of extruded composites formed in accordance with the
present invention was determined. Acquisition rate was determined as described
in
U.S. Patent No. 5,460,622 and U.S. Patent No. 4,486,167, each of which is
incorporated herein by reference. The only change to the procedure was that 75
ml
gushes were used so that the total loading was closer to the total capacity of
the diaper
making the test more stringent.
Commercial diapers were purchased (PAMPERS by Procter & Gamble) and
tested for 4th gush acquisition rate by the indicated procedures. The
commercial
diapers exhibited an acquisition rate of 0.44 ml/sec for the 4th gush of 75m1.
This
performance represents the current state of the art. In situ crosslinked
acquisition
patches were produced with both Chemistry B (citric acid crosslinked fibers)
and C
(polyacrylic acid crosslinked fibers) at levels of 4 and 6%. These patches
were then
inserted into a commercial diaper (PAMPERS of the same size and type as the
control).
The insertion was accomplished in the following manner. The cover stock was
carefully cut at one end of the diaper and peeled back to expose the
commercial
acquisition patch and Garner tissue. These materials were carefully removed
without
disturbing the diaper core. The representative extruded patch of the same
dimensions
as the commercial patch was inserted into the diaper. The cover stock was
returned to
its original position and sealed.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
At the 4% crosslinking agent level, 4'h gush acquisition rates ranged from
0.48-
1.13 ml/s depending on chemistry type. As a second control, pre-crosslinked
fibers
were also tested. At the 6% level, the rate ranged from 0.36-1.60 ml/s
depending on
basis weight and chemistry type. These data demonstrate marked improvement in
acquisition rate for extruded composites versus a commercial diaper control
and versus
acquisition materials produced from pre-crosslinked fibers. This improvement
is
especially important as the crotch area of diapers decreases thus reducing the
area
available to acquisition. The acquisition data is summarized in Table 3.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
26
Table 3. Acquisition Rates for Representative Extruded Composites.
SampleBasis In situ In situ Latex Level4'" Gush
NumberWeight Chemistry Level % Acquisition
g/m2 % Rate
ml/s
45-1 300 B 6 5 0.88
45-2 200 B 6 5 0.87
45-3 300 B 6 0 0.49
45-4 200 B 6 0 0.36
45-9 300 C 6 5 1.60
45-10200 C 6 5 1.05
45-11300 C 6 0 0.77
45-12200 C 6 0 0.58
45-17250 C 4 2.5 1.09
45-18250 C 4 2.5 1.01
45-19250 C 4 2.5 1.13
45-20250 C 4 2.5 1.07
45-21250 B 4 2. S 0.68
45-22250 B 4 2.5 0.51
45-23250 B 4 2.5 0.48
45-24250 B 4 2.5 0.62
The extruded composites of the invention also exhibit advantageous tensile
strength. Tensile was determined by a horizontal tensile method because many
of the
samples tested are very weak (e.g., air laid fluff pads). The method uses a
horizontal
jig fixed to the lower cross head of a constant rate extension tensile machine
like those
provided by Instron. A lOcm x lOcm sample is clamped into the jig. The load
cell is
re-zeroed for each sample. The sample is then pulled by the tensile machine.
The
machine measures the elongation and failure load for each sample.
In situ crosslinked samples were produced with two different chemistries and
at
three levels. Tensile data from these samples are shown in the table and chart
below. It
is clear that as in situ chemistry levels increase, the tensile increases.
This increase is
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
27
an indication of an increase in interfiber bonding. All samples (except those
indicated
as pre-crosslinked) were produced in the same manner with only the variation
in
chemistry type and level as indicated in Table 4.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
28
Table 4. Tensile Strength for Representative Extruded Composites.
Basis Tensile Tensile
Chemistry Level and Type Weight g/in std dev
g/mz
0% Chemis B 287 31 24
2% Chemis B 304 24 2.7
6% Chemist B 313 58 6.8
Pre-Crosslinked with 6% 288 5.0 0.4
Chemist B
0% Chemistr C 287 31 24
2% Chemis C 293 78 17
6% Chemistry C 294 97 33
Pre-Crosslinked with 6% 323 4.5 0.6
Chemistry C
Level based on fiber weight; all samples extruded using Oakes mixer/foamer.
Depending on the cross linking chemistry applied, the tensile rose 10-20X when
in situ crosslinking was employed. FIGURE 14 illustrates the effect on in situ
crosslinking on extruded composite tensile strength.
Latex can be used to increase the strength of extruded composite structures
and
webs. The effect of latex and fiber blend on the strength of representative
extruded
composites is illustrated in FIGURE 15. The effect of latex and crosslinking
chemistry
on the strength of representative extruded composites is illustrated in FIGURE
16.
Refering to FIGURES 15 and 16, the strength of a Chemistry B sample is 34 g/in
with
6% chemistry (BW = 205 gsm). The pre-cross linked Chemistry B composites with
5
latex is 94 g/in (BW = 157 gsm). A composite with 5% latex and 6% in situ
cross
linking has a tensile of 1065 g/in (208 gsm), which is more than ten times
greater than
either treatment alone.
In a further aspect, the present invention provides absorbent articles that
include
the crosslinked cellulosic fibrous product. The product can be combined with
one or
more other layers to provide structures that can be incorporated into
absorbent articles
such as infant diapers, adult incontinence products, and feminine care
products.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
29
EXAMPLES
Example 1
Representative Twin-Screw Extrusion Device and Method, and Representative
Products and Their Performance Characteristics
In this example, a representative twin-screw extrusion device, method for
forming the product using the device, representative products formed by the
method
using the device, and the performance characteristics of the representative
products are
described.
Laboratory tests demonstrated that extruding a fibrous web in a foam media
provides enhanced performance possibilities. In view of the laboratory
successes, pilot
trials were conducted. The following describes the use of twin screw extruders
produced by Krupp, Werner, and Pfleiderer (KW&P) in the process of the
invention to
provide representative products of the invention.
In the trial, a continuous web of material was extruded with a wide range of
basis weight 0400-2000 g/m2). A bicomponent fiber (CELBOND T105) was fed into
the system to produce samples with more integrity. The surfactant
concentration was
tested at two levels: 1% and 0.5% of the total mass. Both levels produced
adequate
foam. Foam quality was similar to that from the Oakes lab unit (plate
mixer/foamer;
94-99% air content; foam density 10-60 g/1). The opening of the fibers did not
damage
the fibers with respect to fiber length. Product quality and performance was
not
optimized and is therefore not as satifactory as the samples prepared with the
Oakes
system. The extruder units are compact and, depending on the screw diameters,
can be
installed on a concrete slab without footings or pilings. The small size and
simplicity
of the process also translates into low capital and engineering costs compared
to typical
paper industry. The ability to add SAP directly to the equipment in dry form
is an
advantage.
Equipment. A nine barrel ZSK 58mm twin screw extruder (KW&P) was used
for the trials. A diagram of the extruder set up is given in FIGURE 4. Four
Acrison
single screw feeders were used to feed the raw materials to the extruder. A
total of five
different screw designs were used to disperse the fibers and generate foam.
The
different screw designs are described in the following section.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
The device shown in FIGURE 4 shows several features worth noting. The first
is the relative size of the equipment. The extruder was contained with an area
approximately 25' x25'. The extruder was on the main floor while the feeders
were on
the second floor. Each barrel is less than 1 foot long. In a commercial design
for
absorbent products, a nine barrel system is not needed (note: counting from
the left, the
first and last barrels are not necessary). The third barrel may also be
optional.
Another important point is simplicity. This system is basically a mass in,
mass
out operation. The feed systems are simple, employing known technology: loss
weight
feeders. This point is underscored when absorbent material (e.g.,
superabsorbent
polymer, SAP) can be added in a dry form via a side feeder directly into the
wet fiber
flow without plugging. This system was easily able to process the fiber and
the SAP
which met the first two trial objectives. Addition of SAP at the very end of
the process
in a dry form kept SAP swelling to a minimum with SR1001 (a lightly
crosslinked
polyacrylate available from Stockhausen). Another polyacrylate from
Stockhausen,
SXM-77, swells and negatively affects runnability when fed dry with a
retention time
in the extruder of under 5 seconds.
Experimental Details. Extruder trials were conducted with a series of runs.
These runs are outlined in Table 7. Without fiber, foaming was no problem and
the
foam generated was in the 96-97% air content range (compare to a theoretical
optimum
67% for a foam-forming process (foam laid) described in PCT/LJS99/26560,
Reticulated Absorbent Composite, and PCT/LTS99/05997, Methods For Forming A
Fluted Composite, each expressly incorporated herein by reference in its
entirety).
Foam density was 29-30 g/1 compared to typically 350 g/1 for the foam laid
processes.
After achieving foam, the fiber feed was started. To obtain fiber dispersion,
three
different screw configurations were tried. The first configuration had quite a
few high
shear elements. While these elements generated shear, they also restricted the
flow of
material (e.g. increased retention time). This design generated some heat and
was not
efficiently dispersing the fibers. The second design was a low shear design
with no
restrictions. This design enabled a 1000 rpm screw speed without significantly
increasing the temperature. As a result, the fiber dispersion improved.
Fibrous knots
were still visible in the web. However, the dispersion was better than the
first screw
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
31
design and better than the dispersion achieved in this trial, identified below
as 1051-
XNP.
The third design reinserted a limited number of higher shear elements to
improve the fiberization. These few shear elements increased the temperature.
The fourth screw design (similar to the second design but with more kneading
blocks) allowed feed up to 225 1b. OD fiber/hr (2.5 ton/day). Processing fiber
only, this
screw design appeared to break up the fiber chunks. Feed was reduced to 0.5
ton/day
so that the fiber dispersion could be more easily seen. The slot die was then
installed
which produced a web of approximately 500 g/mz and 0.05 g/cc (26.6% "couch"
solids).
After taking samples and machine data, SR1001 was added at about the 50%
level. The side feeder worked perfectly with no SAP feed issues. This
composite (BW
1100 g/m2, density ~O. l l g/cc) was extruded through the die head and samples
were
taken (39% "couch" solids). Capacity values were 16 g/g. When SXM-77 was
tried,
all the free moisture was removed and dry chunks of SAP and fiber were
generated.
This is the same result seen in a previous trial (1050-XNP).
Since webs could be produced with the die, samples were produced with SAP at
lower basis weights to compare to foam laid materials previously made and
tested.
Bicomponent fiber CELBOND T105 was also added to increase integrity. Wet
strength agent KYMENE, an alternative to the bicomponent fiber can also be
added
into the system. Low basis weight materials were produced. Surfactant level
was
reduced to 0.5% of the total mass from 1% with no detrimental effects.
Empirically,
water availability is more the limiting factor than the gross amount of
surfactant.
Additional low basis weight materials with and without CELBOND T105 were
formed with a fifth screw design using some three lobe elements. The material
appeared to have fewer knots. Throughput studies were conducted which
determined
that this screw limited the fiber feed to 700 lb./hr (as is) or about 1170
lb./hour total
mass (assuming 40% solids and 50% SAP).
Fiber Oualit~persion Results: Screw Design and Throug-hput. Samples of
material from several screw shaft designs were tested for percent knots and
fiber length.
These two tests are typically used by the fluff lab to evaluate hammermill
efficiency.
These tools were used to evaluate the different screw designs. Table 5
indicates that
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
32
Design 5 appears to be slightly better than Design 4 based on the sonic
fractionation
data. In either design, the fibers are not being cut as evidenced by the fiber
length data.
Table 5. Comparison of Fiber Quality for Screw Design 4 and 5.
Screw Kink
Sample Design Knots FQA LWAFL Fines Curl ,~,gle
% mm % Index
Fiber Onl 4 - 2.47 5.0 0.19 1.9
, Run 19A
Run 19 with 4 22.7 2.54 6.0 0.16 1.7
SAP
Run 31 A 5 10 2.47 4.6 0.15 1.7
Other data indicated that Design 2 was least effective while the subsequent
designs improved the fiber dispersion.
Solids Content. Percent solids were measured in the 25-65% range, but do not
follow predicted values based on material balances (17-47% range). All
measured
values except one indicate higher solids than the theoretical values which
indicates that
the samples may not have been completely dry.
Capacity Results. Capacity under load values of about 11-17g/g were measured
on samples containing SAP contents of 37-46%. Capacity values were reasonable
considering the high basis weights and the increasing density due to a
constant die slot
size.
Surfactant Level. Three levels of surfactant (Incronam 30 available from
Croda) were used 5.0, 7.5 and 10.0 (as is) lb./hr. Surface tension values from
water
extracts indicate that the surfactant was present on the surface and easily
removed. The
surface tension values were 40.7, 40.4, and 35.5 dyne/cm for the three
surfactant levels
(5.0, 7.5 and 10.0 lb./hr). As foaming was successful at all levels and there
is no
"wash" step in this process, lower levels of surfactant can be utilized to
reduce the level
of residual surfactant. Lower levels of surfactant can enhance the product's
acquisition
performance. Typical extract surface tension values in foam laid webs using
Incronam
30 or Dehyton K were 40-43 dyne/cm.
Acquisition/Pore Size Distribution/Median Desorption Pressure. Acquisition
was measured by the Edana test method, the new Market Pulp Standard.
Acquisition
times for a Procter & Gamble PAMPERS control is 27 seconds, 60 seconds, and 85
seconds for the first through third doses of 100 mL, respectively. Acquisition
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
33
seconds for the first through third doses of 100 mL, respectively. Acquisition
performance of the representative samples indicated the presence of excess
surfactant.
The first dose acquisition time was between 30 and 70 second for all samples.
In
general, the second and third doses took longer than 300 seconds (5 minutes).
Pore size distribution and median desorption pressure for representative
products are presented in the Figures.
The pore size distribution (PSD) and the median desorption pressure (MDP) do
not provide additional insight beyond the surfactant level as to the
acquisition
performance. FIGURES 17-20 above show the PSD and MDP for two lower basis
weight samples produced during this trial. When compared to FIGURES 21 and 22,
the 1051-XNP samples are very similar to those produced on the Oakes during
laboratory study described in Example 2. MDP data does not show any
differences
either between the two studies. The MDP values for runs 17 and 19 were
measured to
be 17.2 cm H20 and 16.2 cm HZO, respectively, while the value for 100% pine in
the
Oakes process was 16.5 cm HZO.
Comparison to Similar Foam Laid Materials. Table 6 below shows a
comparison of materials in accordance with the invention versus foam laid made
materials. Notable differences are the density and the resulting effect on
vertical
wicking. Capacity values are similar despite differences in wood fluff pulp
(southern
pine) content. Even without optimization, the 1051-XNP material is comparable
to the
foam laid made materials.
Table 6. Comparison of 1051-XNP and Foam Laid (943 and 946) Samples.
Test\Sample 943-XNP 1051-XNP- 946-XNP
31A
Basis Wei ht, m2 420 425 411
Densit , cm3 0.13 0.09 0.14
SAP Content, % total 20 37 35
mass
SAP T a SR1001 SR1001 SR1001
Pine Content, % of 60 100 50
fiber
Ca acit under Load, 13 16 17.5
Vertical Wickin , cm - 5 10.5
15
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
34
Test\Sample 943-XNP 1051-XNP- 946-XNP
31A
min
Throughput. Throughput studies indicate that 450 OD lb./hour (5 ton/day)of
total mass can be processed through the 58 mm machine.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
Table 7. Summary of Representative Extruded Composites.
Sam 1e 1 2 3 4 5 6 7
Screw Number 1 2 2 2 2 2 2
ZSK RPM 400 400 400 600 600 600 1000
ZSK Tor ue % 40 11 14 6 7 5
Total Rate as 450 450 530 530 570 590 610
is lb./hr
Product Temperature89 47 53 40 38 - 29
C
T1 25 25 25 25 25 25 25
T2 28 27 29 28 28 28 27
T3 33 26 28 28 29 29 29
T4 69 32 36 33 32 31 30
TS 101 38 45 38 35 34 32
T6 86 31 43 42 39 36 35
T7 87 40 49 39 37 34 30
T8 67 30 40 36 33 31 29
Fiber as is lb./hr400 400 480 480 480 480 480
SAP as is lb./hr
Water (as is lb./hr40 40 40 40 80 100 120
Surfactant 10 10 10 10 10 10 10
Air
CELBOND T105
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
36
Sam 1e 8 9 10 11 12 13 14
Screw Number 3 4 4 4 4 4 4
ZSK RPM 1000 1000 1200 1200 1200 1200 1200
ZSK Tor ue % 8 5 5 6 6 5
Total Rate as 600 620 620 870 1070 620 420
is lb./hr
Product Temperature54 29 29 30 38
C)
T2 27 26 27
T3 30 25 27
T4 32 29 30
TS 42 29 31
T6 45 27 29
T7 39 26 29
T8 39 27 35
Fiber as is lb./hr470 500 500 750 750 300 300
Water as is lb./hr120 110 110 110 110 110 110
Surfactant 10 10 10 10 10 10 10
SAP (as is lb./hr) 200 200
SXM SXM
Air es es
CELBOND T105
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
37
Sam 1e 15 16 17 18 19 19A 20
Screw Number 4 4 4 4 4 4 4
ZSK RPM 1200 1200 1200 1200 1200 1200 1200
ZSK Tor ue % 4 4 4 4 3 3 3
Total Rate as 270 190 270 315 158 135 158
is lb./hr
Product Temperature26 25 27 27 31
(oC)
T2 24 25 27
T3 26 26 28
T4 26 26 29 29 29
TS 26 26 29 29 29
T6 28 26 29 29 30
T7 24 25 29 29 30
T8 27 26 29 29 29
Fiber as is lb./hr150 150 150 150 75 75 75
Water as is lb./hr)110 30 110 110 55 55 55
Surfactant 10 10 10 10 5 5 5
SAP (as is lb./hr) 45- 23 0 23
SR
Air es es es es es es es
CELBOND T105 es
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
38
Sam 1e 21 22 23 24 25 26 27 28
Screw Number 4 4 4 4 4 4 4 4
ZSK RPM 1200 1200 1200 1200 1200 1200 1200 1201
ZSK Tor ue % 3 4 4 4 4
Total Rate as 310 313 414 619 719 819 919 1171
is lb./hr
Product Temperature 29 28 29 31
(C)
T2 27 27 29
T3 28 28 30
T4 29 29 31
TS 29 29 32
T6 29 30 32
T7 29 29 31
T8 30 31 33
Fiber as is lb./hr150 150 200 300 400 S00 600 700
SAP (as is lb./hr)45 SR 45- 60-SR 90- 90-SR 90- 90- 210-~
SR SR SR SR
Water (as is lb./hr)110 110 146 219 219 219 219 250
Surfactant 5 7.5 7.5 10 10 10 10 10
Air es es es es es es es es
CELBOND T105
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
39
Sam 1e 29 30 31 31A 32 33 34
Screw Number 4 5 5 5 S 5 5
ZSK RPM 1200 1200 1200 1200 1200 1200 1200
ZSK Tor ue % 5 7 3 3 3 4
Total Rate as is lb./hr1170 1260 158 158 310 620 1220
Product Tem erature 33 42 26 30 30 30
C
T2 28 30 28 28 28 28
T3 29 30 29 29 29 29
T4 31 33 30 30 30 29
TS 32 37 32 32 32 30
T6 31 33 31 31 31 30
T7 31 37 29 29 29 30
T8 34 41 31 31 31 31
Fiber (as is lb./hr 700 1000 75 75 150 300 700
SAP (as is lb./hr) 210- 23 SR 23 45 90 210
SR SR SR
Water as is lb./hr 250 250 SS 55 110 220 300
Surfactant 10 10 5 5 5 10 10
Air es yes es es es es es
CELBOND T105
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
Example 2
Representative Plate Mixer Extrusion Device and Method, and Representative
Products
and Their Performance Characteristics
In this example, a representative plate mixer extrusion device, method for
forming the product using the device, representative products formed by the
method
using the device, and the performance characteristics of the representative
products are
described.
A plate mixer/extrusion process is one alternative to traditional forming
techniques used to make composite core materials. In this example, the Oakes
Mixer/Foamer (Oakes Continuous Mixing Head, E.T. Oakes Corporation, Hauppauge,
NY) was used to generate an extrudable foam from which webs were made by
extrusion through a simple die head. Three fiber furnishes were used: southern
pine
pulp fibers (CPine); citric acid-treated cellulosic fibers (XLA); and a 50:50
blend of
these two fibers. PD8161 latex from H. B. Fuller Company was used as the
binding
and resiliency aid in levels of 5, 10, and 15% by weight.
As used herein, the term "EXPRO" refers to the extrusion process of the
invention and the products formed by the process.
The results demonstrate the following. The device and method can form pine
and treated fibers into webs at densities lower than other current processes.
The average
pore size radii for these products are larger for extruded webs than webs
formed by
traditional processes. The products have improved acquisition over current
materials.
The products exhibit much lower median desorption pressure values than current
materials formed with traditional processes. The extrusion process has minimal
waste
of raw materials or product
General. In this example, CPine, XLA, and PD8161 latex were used to form
samples with different fiber furnishes and latex contents. The sample
descriptions are
shown in Table 8.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
41
Table 8. Extruded Composite Sample Descriptions.
Sam 1e Fiber Latex Addition
1 100% Pine 0%
2 100% Pine 5%
3 100% Pine 10%
4 100% Pine 15%
100% XLA 0%
6 100% XLA 5%
7 100% XLA 10%
8 100% XLA 15%
9 50:50 Pine: XLA 0%
50:50 Pine: XLA 5%
11 50:50 Pine: XLA 10%
12 50:50 Pine: XLA 15%
Oakes Setun. To produce these samples, a laboratory apparatus was used as
shown in FIGURES 3A-C. The specific machine and run specifications are given
below.
In general, the desired pulp fiber, along with 2% by weight Polyox (4 million
molecular weight polyethylene oxide) as a slip aid, was fed into the
mixer/foamer via a
piston feeder at 30% consistency. Other additives such as air, surfactant and
latex were
added via piston feeders to injection ports located on the Oakes device. The
current
system was a batch operation which operates on a mass in, mass out basis with
essentially no waste. The target basis weight of the samples (300 g/m2) was
controlled
by the pulp feed rate and the conveyor speed.
Pore Size Distribution. Pore size distribution is measured with the TRI
autoporosimeter. Several examples are discussed here. The three samples chosen
here
represent the differences seen among three furnishes: pine (sample2, FIGURE
23),
XLA (sample 6, FIGURE 24), and the 50:50 blend (sample 10, FIGURE 25).
In FIGURE 24, note the shift in the curves to higher average radii of each
curve.
This is indicative of the change from pine to crosslinked fiber. FIGURE 25,
the blend
sample, shows an intermediate mode value between those seen in FIGURES 23 and
24.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
42
The larger average radius is a result of the stiffer crosslinked fibers
forming a less
dense web and also due to support by the structure. The area under the curve
is
indicative of the total volume in the sample and thus the capacity of the
sample. This
arises from the fact that the PSD curves are the derivative of the cumulative
volume
chart obtained from the autoporosimeter. Thus fiber furnishes can be evaluated
based
on their impact on pore size which in turn impacts the volume or capacity of
the
structure.
However, it is best to compare processes based on only the mode pore size with
respect to acquisition. These values are listed in Table 1. These data
indicate that the
extrusion process of the invention generates the largest pore sizes of the
four processes
tested.
Acquisition. Acquisition performance is typically based on the results of a
multiple dose test. The fourth gush results, being the most stringent
conditions, are
often used as an indicator of performance. The fourth gush results for the
samples in
this study are shown in the summary data table in Table 9.
In general, the XLA results were the most promising. These results are given
in
FIGURE 26. These data show that the acquisition rate improves with XLA alone
over
the current diaper controls. When latex is present, the results continue to
improve over
the control and over the performance of 1012-XNP. The fourth gush results are
not the
only improvement. All gushes (1-4) show improved acquisition rate versus the
control.
Median Desorption Pressure. While it is important for an acquisition material
to acquire fluid quickly, the material also must to able to readily release it
to the
absorbent core. This ability to release fluid is judged by the median
desorption
pressure. This is the pressure where 50% of the acquired fluid has been
removed from
the sample during testing on the autoporosimeter.
Composites formed from citric acid crosslinked fibers have an MDP of
approximately 20-22 cm H20. Composites formed from fibers such as XLA have
only
been able to achieve MDP values of 16-19 cm H20. FIGURE 29 shows an example
where XLA was used to produced the samples in 1012-XNP. Here the MDP was 17
cm HZO.
Using the extrusion process, MDP values for composites formed from citric
acid crosslinked fibers alone were reduced to 10.5 cm H20 (see FIGURE 28).
Addition
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
43
of latex improved the MDP to 7.7 cm H20 (see FIGURE 27). Based on the range of
MDP with fiber furnish shown in Table 9, it appears possible to control an MDP
between 8 and 17 cm H20 using these fibers, latex, and the extrusion process.
These results show that different processes form different structures in terms
of
density and pore size distribution. These structural differences, along with
surface
characteristics, also impact the median desorption pressure.
FIGURES 29, 30, and 31 show the MDP of composites formed by three
different processes. FIGURE 31 shows airlaid pads made from two batches of XLA
fiber: identified as 46-O1 and 46-02. These pads have a density of 0.06 g/cm3
but do
not have any surface active agents to inhibit the MDP (14-16 cm H20). FIGURE
29 as
noted previously is a foam-formed composite. Despite the lower density, the
MDP is
slightly higher than the airlaid samples. FIGURE 30 shows the MDP for a
wetlaid
composite. This material has an MDP of 18.5 and a similar density to the foam-
formed
sample. As seen in FIGURES 27 and 28, samples formed by the extrusion process
exhibit much lower MDP values.
Tensile. Changes in tensile follow expected trends: (1) as the pine content
increases, tensile increases; (2) as the crosslinked fiber content increases,
tensile
decreases; and (3) as the latex content increases, tensile increases. These
samples were
measured with an Instron using a horizontal j ig.
The result can be summarized as follows. The density of the extruded webs is
lower than other processes of forming absorbent webs, when pine or crosslinked
fibers
are used. Average pore size radii are larger for extruded webs providing
enhanced
acquisition performance. The extrusion process is capable of producing webs
with
improved MDP using pine and crosslinked fibers which indicates this material
will
release liquid into a storage core more easily. The extrusion process is
capable of
adding latex and other additives to a web without spraying and without waste.
The effect of latex and fiber blend on extruded composite strength is shown in
FIGURE 15.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
44
Table 9. Representative Extended Composite Performance.
Average Average 4'h Gush Horizontal
SampleRun BasisRun MDP MAP MUP AcquisitionTensile
Weightb Density cm HZO cm H20 g/g ml/s g/in
g/cm3
z
m
1 287 0.0372 16.5 8.6 7.6 0.16 31
2 323 0.0374 11.2 6.1 10.9 0.26 423
3 308 0.0363 10.8 6.0 10.5 0.29 1503
4 315 0.0379 11.3 6.2 9.9 0.35 2329
249 0.0387 10.5 4.5 12.1 0.61 15
6 305 0.0273 9.1 4.1 16.7 1.13 54
7 346 0.0287 8.7 3.8 17.2 0.91 123
8 326 0.0284 7.7 3.8 16.0 1.49 269
9 280 0.0306 12.6 6.3 11.3 0.28 24
285 0.0281 10.4 5.2 12.8 0.46 447
I1 284 0.0286 8.2 4.1 14.7 0.83 806
12 316 0.0281 8.1 4.1 14.7 0.54 888
1012- 285 0.044 17.0 5.9 13.8 0.92 1200
XNP
Airlaid289 0.0646 14.4 5.5 15.0
46-1
Airlaid316 0.0663 15.9 6.1 14.2
46-2d
Wet 319 0.0430 18.5 5.0 14.4
Laid
TR867
Control 0.44
Dia
er
aSamples were tested in current Procter & Gamble PAMPERS surrounds with
an airlaid/SAP core. The same commercial diaper was used as the control.
5 bSamples closest to 300 g/m2 were chosen for testing. Average basis weight
indicates how close the process settings (fiber feed and conveyor speed) were
to
achieve the target basis weight.
°XLA fiber (WTC)
dXLA fiber (CMF)
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
Example 3
Performance Characteristics of Representative Products
In this example, the performance characteristics of representative products
formed in accordance with the invention are described.
The medium uptake pressure (MUP), medium desorption pressure (MDP), and
caliper of representative products of the invention were determined and
compared to
conventional airlaid webs. The normalized results are presented in Table 10.
In
Table 10, XLA refers to an airlaid web of cellulosic fibers crosslinked with
citric acid;
XLB refers to an airlaid web of cellulosic fibers crosslinked with a
combination of
citric and polyacrylic acid fibers; EXPRO-D refers to a composite of
celluloisc fibers
crosslinked with citric acid; EXPRO-E refers to a product of the invention
formed from
cellulosic fibers treated with citric acid; and EXPRO-F refers to a product of
the
invention formed from cellulosic fibers treated with a combination of citric
and
polyacrylic acid and latex. All samples tested at 300 gsm basis weight.
Table 10. Medium Uptake Pressure, Medium Desorption Pressure, and Caliper.
Product MUP MDP cm Cali er mm
XLA 1.00 11.3 1.00 21.6 1.00 2.7
XLB 1.15 0.79 1.50
EXPRO-D 1.20 0.83 2.10
EXPRO-E 1.50 0.55 3.06
EXPRO-F 1.52 0.356 4.44
The acquisition rate, and rewet, and tensile strength of representative
products
of the invention were determined and compared to conventional airlaid webs.
The
normalized results are presented in Table 11. In Table 11, XLA refers to an
airlaid web
of cellulosic fibers crosslinked with citric acid; XLB refers to an airlaid
web of
cellulosic fibers crosslinked with a combination of citric and polyacrylic
acid fibers;
EXPRO-D refers to a foam-formed composite of celluloisc fibers crosslinked
with
citric acid; and EXPRO-E refers to a product of the invention formed from
cellulosic
fibers treated with citric acid. All samples tested at 300 gsm basis weight.
CA 02427910 2003-05-02
WO 02/055774 PCT/USO1/45791
46
Table 11. Acquisition Rate, Rewet, and Tensile Strength.
Product Acquisition Rewet (g) Tensile
Rate ml/sec Stren h in
XLA 1.00 0.44 1.00 0.87 0
XLB 1.50 0.75 0
EXPRO-D 2.00 0.75 1000
EXPRO-E 2.64 0.5 8 13 S 0
While the preferred embodiment of the invention has been illustrated and
described, it will be appreciated that various changes can be made therein
without
departing from the spirit and scope of the invention.
