Note: Descriptions are shown in the official language in which they were submitted.
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DEr ~ ~;l) CELLULOSE FIBER PADS
AND METEIOD OF MAKING T~IE SAME
Field of the Invention
SThe present invention relates to cçll~JlQse fiber pads, more particularly
to cellulose fiber pads in which the fibers have been bonded together and the pads
densified, and more particularly to such pads having an increased absorbent capacity
and good wet pad integrity relative to prior pads.
10Back~round ofthe Invention
Cellulose fibers derived from wood pulp are used in a variety of
absorbent articles, for example, diapers and ferninine hygiene products. It is desirable
for the absorbent articles to have a high absorbent capacity for liquid, as well as to
have good sller.g~h characteristics for durability. Cellulose fibers for pad formation
15 have traditionally been shipped to end users, that is, m~mlf~cturers of absorbent
articles, in large dencified rolls, or less frequently in compressed bale form. The end
user fluffs the cellulose fibers, combines them with additives, such as absorbency
enh~nci~ polymers or specially en~ineered fibers, forms them into a pad, and then
forms them into an absorbent article for the con~mer. While this methodology is
20 effective, it is desirable for some applications to provide absorbent webs that include
additives to the m~mlf~ctllrer of the absorbent article in a form that can be
incorporated directly into the absorbent article without the intermedi~te steps of
fllJffing, additive incorporation, and pad construction.
It is desirable to densify webs before forming them into a roll to
25 decrease the shipping costs. However, densified webs have insufficient strength for
incorporation directly into absorbent structures. ~herefore, the strength of the web
must be increased, for example, by bonding the fibers together. The prior art suggests
the ~imlllt~neous heating and co,."~lessh~g of a cellulose fiber web that has been
combined with a thermoplastic bonding material to form a densified web with
30 increased integrity. While this densifying technique provides higher bulk density and
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strength co~ ,d to dencified webs of conventional non-bonded pulp, it has been
found that the res~lltin~ densified web has a lower capacity for absGll,;ng liquid than
the non-densified, or fluffed, material normally incorporated into absoll,~nl structures.
It is therefore desirable to provide a densified web of cellulose fibers that has an
5 absorbent capacity superior to prior densified webs, and that has a wet integrity or
en~ that is sul.sl~,llially higher than non-bonded, densified webs.
Summary of the Invention
In accordallce with the teaching in the following specification, the
10 present invention provides a fibrous article comprising a densified web of cell~lose
fibers and a bonding agent. At least some of the fibers of the web are bound together
by activating the bonding agent prior to densification. The web is densified after the
bonding agent has been deactivated and has bound the fibers together. In a most
pr~f~ d form, the dPncified web has a miniml-rn density of at least equal to or greater
15 than 0.1 grams percc. The resulting densified web has an absorbent capacity for
synthetic urine that is signifi~ntly greater than the absorbent capacity for synthetic
urine exhibited by a co,l,parable web of cellulose fibers bound together by a bonding
agent, which the cor"l)al~ble web has been densified to subst~ntially the same degree
as the densified web of the present invention by activating the bonding agent and
20 densifying the web while the bonding agent is active.
The densified web of the present invention can be formed into
absoll,enl articles con~pli~ing one or more layers. For example, the present invention
can take the form of a single absorbent layer composed of a dencified web produced in
accol dance with the present invention. The densified web of the present invention can
25 also be incorporated into multi-layer articles including, for example, an upper
acquisition/distribution layer and a storage layer. In accordance with the teaching.c
herein, the densified web produced with the present invention can be incl~lded in one or
both of the acquisition/distribution layer and a lower storage layer.
A densified web is produced in accordance with the present invention
30 by first folllfil~g, for example, a web of cellulose fibers co~ -g a bonding agent,
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thereafter activating the bonding agent so that the bonding agent contactC at least some
of the ce.lh-lose fibers, deactivating the bonding agent to bind at least some of the
cellulose fibers together, and thereafter densifying the bonded web of celll~lose fibers to
a density of at least about 0.1 grams per cc.
s
Brief Description of the Drawin~s
A better underst~ntlinE of the present invention can be derived by
reading the ensuing specification in conjunction with the acco,..l ~..ying drawings,
wherein:
FIGURE 1 is a schematic view showing a web of cellulose fibers
cont~ining a bonding agent that is first activated and then deactivated, with the web
thereafter being densified; and
FIGURES 2, 3 and 4 are schematic cross-sectional views of various
absorl,enl structures constructed using the densified web produced in accordance with
15 the present invention.
Detailed Description of the Preferred Embodiment
Cellulosic fibers are the basic component of the densified webs
produced in accordance with the present invention. Although available from other20 sources, cellulosic fibers are currently derived primarily from wood pulp. Suitable
wood pulp fibers for use with the invention can be obtained from well-known ~
processes such as the Kraft and sulfite processes, whether blpached or unbleached.
The pulp fibers may also be processed by thermomechanical, chemith~"lG...ech~nic~l
methods, or co,.,b;ndlions thereof. The preferred pulp fiber is chemical. The p,eÇ~"ed
25 starting material is prepared from long fiber coniferous wood species, such as southern
pine, Douglas fir, spruce, and hemlock. Ground wood fibers, recycled or secondary
wood pulp fibers, and b'eached and unbleached wood pulp fibers can be used. Details
of the production of wood pulp fibers are well-known to those skilled in the art. These
fibers are commPrcially available from a number of companies, inrl-ldin~ Weyerhaeuser
30 Company, the ~sci~nPe of the present invention. For example, suitable cPll~ se fibers
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produced from southern pine that are usable with the present invention are available
from Weyerhaeuser Company under the dç~ tions NB316 and NB416.
The wood pulp fibers of the present invention can also be plel,.,aled
prior to use with the present invention. This pr~ l...e~l may include physical
5 Ir~...P..I, such as subjecting the fibers to steam, or çh~mic~l Ir~ e~ll, for ~Y~mrle~
cross-linking the cellulose fibers using any of a variety of conventional cross-linking
agents such as dimethyldihydroxyethyleneurea. Cross-linking the fibers, for example,
increases their resiliency, and thereby can improve their absorbency. The fibers may
- also be twisted or crimped, as desired. Suitable cross-linked cellulose fibers produced
from southern pine are available from Weyerhaeuser Company under the design~tionNHB416.
Cellulosic fibers treated with particle binders and/or den~ific~tion/
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
polyrners, to the cf 1lUIQS;C fibers. Cellulosic fibers treated with suitable particle binders
and/or ~encific~tion/softnPcs aids and the process for co",bi.u"g them with c~ lQse
fibers are disclosed in the following U.S. patents and patent applications: (1) Serial
No. 07/931,059, filed August 17, 1992, entitled "Polymeric Binders for Binding
Particles to Fibers;" (2) Serial No. 07/931,277, filed August 17, 1992, entitled "Non-
Polyrneric Organic Binders for Binding Particles to Fibers;" (3) Patent No. 5,300,192,
entitled "Wet Laid Fiber Sheet I~m-f~ct--ring With Reactivatable Binders for Binding
Particles to Binders;" (4) Serial No. 07/931,278, filed August 17, 1992, entitled
"Reactivatable Binders for Binding Particle to Fibers;" (5)Patent No. 5,308,896,entitled "Particle Binders for High-Bulk Fibers;" (6)Serial No. 07/931,279, filed
August 17, 1992, entitled "Particle Binders that Enhance Fiber Densification;"
(7) Serial No. 08/107,469, filed August 17, 1993, entitled "Particle Binders;" (8) Serial
No. 08/108,219, filed August 17, 1993, entitled "Particle Binding to Fibers;" (9) Serial
No. 08/107,467, filed August 17, 1993, entitled "Binders for Binding Water Soluble
Particles to Fibers;" (10) Serial No. 08/108,217, filed August 17, 1993, entitled
"Particle Binders;" (I l) Serial No. 08/108,218, filed August 17, 1993, entitled
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"Particle Binding to Fibers;" and (12) Serial No. 08/153,819, filed November 15, 1993,
entitled "Particle Binders for High-Bulk Fibers," all ~ essly incorporated herein by
c:r~;r~nce. One example of a suitable densification/softness aid is a mixture of 70%
sorbitol and 30% glycerin. The pulp is treated with sorbitol and glycerin by s~ lg
5 the pulp sheet with the mixture and passing the sheet through a roll coater, or other
means of adding a liquid to a pulp sheet familiar to those skilled in the art.
~ lshough not to be construed as a limitation, eAa.llples of p-elrealillg
fibers include the application of fire retardants to the fibers, such as by spraying the
fibers with fire-letarda"l çhPmic~lc Specific fire-retardant chemicals include, by way
10 of example, sodium borate/boric acid, urea, urea/phosphates, etc. In addition, the
fibers may be p.ellealed with surfactants or other liquids, such as water or solvents,
which modify the surface of the fibers. Other p.etle~t...ent~ include exposure to
antimicrobials, pigments and densification or softening agents. Fibers p.etrea~ed with
other chemicals, such as thermoplastic and thermosetting resins also may be used.
15 Co---binalions of p-~t-r~-.e~ls also may be employed with the resl-ltin~ pret~dled
fibers then being subjected to the application of the binder as explained below.Bonding agents useful in accordance with the present invention are
those materials that (a) are capable of being combined with and dispersed throughout a
web of cellulosic fibers, (b)when activated, are capable of coating or otherwise20 adhering to the fibers or forming a binding matrix, and (c) when deactivated, are
capable of binding at least some of the fibers together. It is important that the binding
action of the agent occur while the fibers are at a low density, and that densification
occurs only after the binding agent is deactivated.
Suitable bonding agents include thermoplastic materials that are
25 activated by melting at temperatures above room temperature. When these materials
are melted, they will coat at least portions of the cellulose fibers with which they are
combined. When the thermoplastic bonding agents are deactivated by cooling to a
temperature below their melt point, and preferably no lower than room te...pe-~ re,
the bonding agent will upon solidifying from the melted state cause the cellulose fibers
30 to be bound in a matrix.
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Thermoplastic materials are the plefe-led binders, and can be co-ul);ncid
with the fibers in the form of particles, emulsions, or as fibers. Suitable fibers can
include those made from thermoplastic polyrners, cellulosic or other fibers coated with
thc.l~opla~lic polymers, and multi-component fibers in which at least one of the5 co..,pon~uls of the fiber comprises a thermoplastic polymer. Single and
mlllticornponent fibers are m~nl~f~ct~lred from polyester, polyethylene, polypropylene
and other conventional thermoplastic fiber materials. The same thermoplastics can be
used in particulate or emulsion form. Many single component fibers are readily
available on the open market. Suitable multicomponent fibers include Celbond
10 fibers available from Hoechst Celanese Company. Suitable coated fibers can include
cellulose fibers coated with latex or other thermoplastics, as disclosed in U.S. Patent
No. 5,230,959, issued July 27, 1993, to Young et al., and U.S. Patent No. 5,064,689,
issued November 12, 1991, to Young et al. The thermoplastic fibers are preferably
combined with the cellulose fibers before or during the laying process. When used in
15 particulate or emulsion form, the thermoplastics can be combined with the cPll--lose
fibers before, during, or after the laying process.
Other suitable thermoplastic bonding agents include ethylene vinyl
alcohol, polyvinyl acetate, acrylics, polyvinyl acetate acrylate, polyvinyl dichloride,
ethylene vinyl acetate, ethylene vinyl chloride, polyvinyl chloride, styrene, styrene
20 acrylate, styrene butadiene, styrene acrylonitrile, butadiene acrylonitrile, acrylonitrile
butadiene styrene, ethylene acrylic acid, urethanes, polycarbonate, polyphenylene
oxide, and polyimides.
Thermosettin~ materials also serve as excellent bonding agents for the
present invention. Typical thermosetting materials are activated by heating to elevated
25 temperatures at which cross-linking occurs. Alternatively, a resin can be activated by
cou.bufillg it with a suitable cross-linking catalyst before or after it has been applied to
the cellulosic fiber. Thermosetting resins can be deactivated by allowing the cross-
linking process to run to completion or by cooling to room temperature, at which point
cross-linking ceases. When cross-linked, it is believed that the thermosetting materials
30 form a matrix to bond the cellulose fibers. It is contemplated that other types of
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bonding agents can also be employed, for example, those that are activated by contact
with steam, moisture, microwave energy, and other conventional means of activation.
Th~;l...os~ g bonding agents suitable for the present invention include ph~nolicresins, polyvinyl ~ret~t~c, urea formaldehyde, melamine formaldehyde, and acrylics.
5 Other t},- ....oset~ g bond,ng agents include epoxy, phenolic, bicm~lpiln;d~ polyimide,
,l~rl~m;ne formaldehyde, poiyester, ureth~nçs, and urea.
These binders are normally combined with the fibers in the form of an
aqueous emulsion. They can be combined with the fibers during the laying process.
Altematively, they can be sprayed onto a loose web after it has been formed.
10 Materials that çnh~nce absorbent capacity, such as superabsorbent polymers, can also
be combined with the densified web produced in accordance with the present
invention. A superabsorbent polymer as used herein is a polyrneric material that is
capable of abso~billg large quantities of fluid by swelling and forming a hydrated gel
(hydrogel). The superabsorbent polymers also can retain significant amounts of water
15 under moderate pressures. Superabsorbent polymers generally fall into three classes,
namely, starch graft copolyrners, cross-linked carboxymethylce~ Qse derivatives and
modified hydrophilic polyacrylates. Examples of such absorbent polymers are
hydrolyzed starch-acrylonitrile graft copolymer, a neutralized starch-acrylic acid graft
copolymer, a saponirled acrylic acid ester-vinyl acetate copolymer, a hydrolyzed20 acrylonitrile copolymer or acrylamide copolymer, a modified cross-linked polyvinyl
alcohol, a neutralized self-cross-linking polyacrylic acid, a cross-linked polyacrylate
salt, carboxylated cçlllllose7 and a neutralized cross-linked isobutylene-maleicanhydride copolymer. The superabsorbent polymers can be combined with the
cellulosic fibers in amounts up to 70% by weight based on the total weight of fibers
25 and polymer.
Superabsorbent polymers are available comm~rcially~ for c..alll},lc,
starch graft polyacrylate hydrogel fines from Hoechst-Celanese of Portsmouth,
Virginia. These superabsorbent polymers come in a variety of sizes, morphologies and
absorbent pl ope, lies. These are available from Hoechst-Celanese under trade
dçsign~tions such as IM1000 and IM3500. Other supe,abso~bent particles are
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marketed under the trademarks SANWET (supplied by Sanyo Kasei Kogyo Kabushiki
Kaisha), SUMIKA GEL (supplied by Sumitomo Kagaku Kabushiki Kaisha), which is
s-t~pçn~:on polymerized and spherical, as opposed to solution polymerized groundparticles, FAVOR (supplied by Storl~h~l.sçn of Greensboro, North Carolina), and
5 NORSOCRYL (supplied by Atochem). Other superabsorbent polymers 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, expressly incorporated herein by reference. Products
such as diapers that incorporate superabsorbent polymers are shown in U.S. Patent
No. 3,669,103 and U.S. Patent No. 3,670,731.
Referring now to FIGURE 1, one method for densifying cellulose fibers
in accordance with the present invention is illustrated. A web 10 of cellulosic fibers
can be laid on a conveyor 12 using conventional air-laying techniques. The web 10 of
cellulose fibers may be combined with a bonding agent of the type described above
before, after, or as it is being laid down. The bonding agent can be used in anyconcentration that will achieve the desired result, that is, binding at least some of the
fibers together after the bonding agent has been deactivated. The bonding agentsdi~closed above can be incorporated with the cçlll~lose fibers in an amount ranging up
to, for example, 70%, based on the weight of the fiber and bonding agent.
The web 10 can then be forwarded past an activation station 12, in the
prefelled embodiment a heat source. Heat can be supplied from the heat source 12 by
means of hot air, infrared radiation, or one of many other conventional heat sources
available to one of ordinary skill. Heat can be applied to the web as it passes under the
heat source to activate the bonding agent. In the case of the typical therrnoplastic
materials, for example, the heat source melts the bonding agent so that it will adhere to
or form a bonding network for the cellulosic fibers. For the typical thermoplastic
materials listed above, the heat source must heat the bonding agent to well above room
temperature. For example, polyethylene must be heated to temperatures on the order
of 140~ to 145~C. These temperatures, of course, are well under that which will cause
damage to the bonding agent and/or the cellulose fiber.
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The bonding agent is then deactivated to bind the cellulose fibers of the
web together. In the case of the heat activated bonding agents specifically described
above, deactivation occurs by cooling the bonding agents. Cooling can be allowed to
occur naturally over time under room temperature conditions. Optionally, the web can
5 be passed under a deactivation source 16, for example a cooling source. The cooling
source, for example, can be a stream of room temperature or refrigerated air that is
blown onto or through the web 10 to deactivate the bonding agent.
The web 10 is then passed between a pair of nip rolls 18 and 20, which
compl-ess or densify the deactivated, bonded web to a density significantly greater than
10 in its original air-laid condition. In accordance with the present invention, it is
prere"ed that the densified web 10' be colllpressed to a density of at least 0.1 grams
per cc, preferably from 0.1 to 0.7 grams per cc, and most preferably from 0.3 to 0.7
grams per cc. The densified web 10' can then be forwarded to a winding station,
where the web is slit and wound onto a core 22 to form a roll of densified material
15 suitable for handling and shipment. Upon arriving at the end user's facility, the
densified web can be unrolled, cut and used in absorbent constructs.
The densified webs prepared in accordance with the present invention
have a wet pad integrity that is greater than the wet pad integrity of a non-bonded,
densified web of cellulose fibers that has been densified to subst~nti~lly the same
20 degree. This is a direct result of employing a bonding agent to cause at least a portion
of the cellulose fibers to adhere to- each other. While prior experiments with hot
pressing resulted in lower absorbent capacity for densified webs, the absorbent
capacity of the densified web produced in accordance with the present invention is at
least about equivalent to the absorbent capacity of a non-bonded, densified web of
25 cellulose fibers. It has also been found that the web densified in acco,dance with the
present invention, that is, a web that is densified after the bonding agent has been
deactivated so that the cellulose fibers are bound together, has an absorbent capacity
that is significantly greater than prior bonded webs. Specifically, the web of the
present invention has an absorbent capacity that is signific~nsly greater than the
30 absorbent capacity of a col"pa,able web of cellulose fibers bound together by a
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W O96/15301 PCTnUSgS/12879
bonding agent in which the web was densified to subst~nti~lly the same degree as that
in accordance with the present invention, but was densified while the bonding agent
was still active.
Absorbent capacity as used herein is the capaQty for a web of ce~ ose
5 fibers to absorb aqueous solutions of metal and alkali salts of inorganic and organic
acids. Examples of such solutions include natural body fluids, such as urine, blood,
and menstrual fluids. For purposes of illustration, co~l")a~ison, and d~finition, a
standard solution of synthetic urine is chosen. The standard synthetic urine is defined
specifically in the following examples
Furthermore, the invention has been described in conjunction with first
air-laying a loose web of cellulose fibers and thereafter densifying in accordance with
the present invention. The densification method will also work with wet-laid fibers.
Normally, fibers that are formed into webs using wet-laid processes are inherently
relatively dense. Wet-laid fiber webs are also usable in the present invention by first
15 flufflng or fiberizing the wet-laid web, and thereafter forming a loose web and
densifying it in accordance with the present invention.
The densified bonded web 10' produced in accordance with the process
described above and depicted in FIGURE I can be incorporated in an absorbent article
as the absorbent layer. It can be used alone, or as illustrated in FIGURE 2, can be
20 used in combination with secondary layers. In FIGURE 2, the web 10' is employed as
an upper acquisition/distribution layer in combination with a storage layer 32. Storage
- layer 32, if desired, can also comprise a densified layer of bonded cellulose fibers 10',
as illustrated in FIGURE 3. And finally, as illustrated in FIGURE 4, a third base
layer 34 can also be employed if desired, with a storage layer 32 and an acquisition
25 layer 30. If desired, the retention layer 34 can also be composed of the densified
bonded web 10' constructed in accordance with the present invention.
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Examples
Experimental Procedures:
All absorbent pads were formed in the laboratory on a 6" ~ ..~le~
circular laboratory pad former. The pad former was equipped with a pin mill fluffing
5 device. The pad former rep!ic~tçs in the laboratory air-laid webs produced with full-
scale commercial equipment. Additives, in~luding bonding agent and supe~abso,l~,ll
polymer, were added and combined with the cellulose fibers in the pad former.
Homogenous blending of the pad components was achieved by ,ereeding the pad
through the pin mill at least three times.
The 6" di~meter pads were subjected to one of three bonding and/or
densification procedures The first densification procedure is referred to as "Cold
Pressing." Cold Pressing is accomplished by placing the pad in a laboratory platen
press and coll~pres.ing it at ambient temperatures. The second densification procedure
is referred to as "Hot Pressing." Hot Pressing is achieved by placing the pad in a
15 laboratory platen press at a temperature elevated above ambient (platen tell,pelal~re on
the order of 170~C). The third densification procedure, performed in accordance with
the teaçhing~ of the present invention, is referred to in the Examples as
"Thermobonding/cold pressing." Thermobonding/cold pressino is achieved by passing
hot air (on the order of 170~C) through a pad at its initial as-formed density (typically
20 on the order of 0.05 grams per cc), followed by cooling to room te,llpt,~ re at the
low density and by subsequent Cold Pressing. In all three of the den~ific~tion
procedures, final pad density is controlled by varying the pressure applied by the platen
press to the pad. Rect~n~ r pads measuring 4" x 4" (10 cm. x 10 cm.) are cut from
the 6" diameter pad using die cutters, and are tested for capacity and strength using the
25 following procedures.
An ~nc.lined Plane Capacity test is performed by initially recording the
pad weight Wl in grams. One edge of the pad is imrnersed in the test liquid while the
pad is supported on a glass plate inclined at 10~ to the horizontal. Liquid is allowed to
wick to the top edge of the pad. The inclined plane is reversed so that the pad then lies
30 at the top of the slope and the liquid is applied at a controlled rate (5 ml. per minute) to
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the upper edge of the pad. When liquid breaks away from the lower edge of the pad,
the test is stopped and the pad reweighed as W2 in grams. The Tnclined Plane Capacity
is reported as (W2 - Wl)/Wl in grams per gram.
An Ultimate Capacity test is performed by recording the initial pad
5 weight Wl in grams. The pad is then placed on a wire support screen and immersed in
the test liquid in a horizontal position for 30 minutes. The pad is removed from the
screen and allowed to drain in a horizontal position for five min~tes The pad isreweighed as W2(g). Ultimate capacity is reported as (W2 - W~ in grams per
gram. (When the pad contains a coated fiber as described below, the weight Wl in the
10 denominator is adjusted by subtracting from its weight the coating polymer contained
in the coated fiber.)
A Wet Pad Integrity test is performed by clamping a wet pad along two
opposing sides, leaving about 3" of pad length visible, and suspending it vertically. A
light plastic jug is suspended from the lower side of the sample. Water is run into the
15 jug at a controlled rate of 200 ml per minute to apply a constantly increasing load to
the sample. When the pad fails under the applied tension load, the water flow isstopped and the combined weight of the jug, water, lower clamp, and failed lower half
of sample is recorded as X in grams. Wet integrity is reported as X in grams. (Note:
If the pad fails under its own saturated weight after mounting vertically, the lower half
20 of the failed sample is weighed and reported as the integrity X. If the pad is too weak
to mount on the clamps, its integrity is reported as zero.)
The aqueous solution used in the tests is a synthetic urine available from
National Scientific under the trade name RICCA. It is a saline solution containing
135 meq./l sodium, 8.6 meq./l calcium, 7.7 meq./l magnesium, 1.94% urea by weight
25 (based on total weight), plus other ingredients.
The cellulose fibers used in the following examples are bleached
southern pine Kraft fluff pulp available from the Weyerhaeuser Company. Fibers
bleached with an elemental chlorine bleach are referred to by the trade de~ign~tion
NB316. ~ibers bleached with a chlorine dioxide instead of chlorine are referred to by
30 the designation NB416. A first bonding agent comprises a thermoplastic bicomponent
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fiber available from the Hoechst Celanese Co. under the trade name Celbond K56.
Celbond K56 has a fiber length of S mm. The bicomponent fiber is comprised of a
polyester core and a polyethylene sheath in a concentric extrusion. A cross-linked
ce~ lose fiber was also employed. The cross-linked fiber comprised NB3 16 or NB416
5 cross-linked with dimethylol dihydroxyethylene urea. This cross-linked fiber is also
available from the Weyerhaeuser Company, and will be referred to as the high-bulk
additive (HBA) fiber. A coated fiber, hereinafter referred to as CCF, was also used as
a bonding agent. The coated fiber was produced from NB3 16 or HBA coated with a
polyvinyl acetate latex polymer available from the Reichold Company under
designations "Latex 97-910" or "40-504". The latex polymer is coated on the fiber at a
loading of 25% by weight based on the dry-coated fiber. Superabsorbent polymers are
also incorporated into some of the pads. The superabsorbent polymer (SAP) used in
these tests are available from the Hoechst Celanese Co. under the designations IMlO00
and IM3500.
Example l
This example illustrates that bonding of pads by Hot Pressing in the
presence of bonding agents at densities at or above 0.1 grams per cc results in a
catastrophic loss of capacity relative to a non-bonded pad. The example also illustrates
20 that the loss of capacity is exacerbated at high densities, and that the capacity loss at
high density cannot be restored by the addition of SAP.
Pads having a basis weight of 550 g/m2 were formed from combinations
of either HBA, CCF made from HBA (with 97-910 latex) or an 80/20 weight blend ofHBA and CelbondK56 combined with SAP at levels of 15% and 45% total pad
25 weight. All fiber SAP combinations were made at three density levels (minimum, 0.1
gram per cc; medium, 0.3 grams per cc; and high, 0.5 grams per cc). HBA pads
cont~ining no binder or other additives served as controls. The 0.1 g/cc HBA pads
were Cold Pressed (for 30 seconds) and the 0.3 and 0.5 g/cc HBA pads were Hot
Pressed at 100~C for 30 seconds. Hot Pressing was found necessa~y to achieve stable
30 pad density because rapid springback in the Cold Pressed HBA pads resulted in
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equilibrium densities on the order of 0.15 g/cc or less. It should be noted, however,
that no interfiber bonding took place in the Hot Pressed HBA control pads.
The CCF and HBA/bicomponent fiber pads were all hot pressed at
140~C for 30 seconds to form interfiber bond. Pads were then tested for Tn~lined5 Plane Capacity. The tests were each repeated three times, and the results averaged.
The averaged results are shown in Table 1.
TABLE I
Inclined Plane Capacity (~/g)
HBA Control CCF from HBAwith
SAP Level (%) Density (g/cc) (no binder) HBA Celbond
0.1 17.3 12.9 10.8
0.3 13.3 5.1 4.5
0.5 11.8 2.5 3.4
0.1 22.5 19.6 11.2
0.3 20.6 ~9.5 8.1
0.5 15.7 3.8 7.4
Example 2
This example illustrates that bonding the fibers in the pad first at the
lowest possible density, followed by cooling and subsequent pressing
(Thermobonding/cold pressing), m~int~ins the capacity of an equivalent non-bonded
15 pad. This example also illustrates that considerable wet pad integrity can be imparted
without loss of capacity by this Thermobonding/cold pressing process.
Pads having a basis weight of 550 g/m2 were formed from combinations
of NB316, CCF made from NB316 (with 40-504 latex coating), and a 95/5 weight
blend of NB316 and CelbondK56, all containing IMI000 SAP at levels of 15% or
20 30%, based on total pad weight. All pads were produced at a density of 0.3 g/cc. The
NB 316 controls were Cold Pressed. The pads cont~ining a bonding agent were
prepared either by Hot Plesail-g at 170~C for one minute, or by Thermobonding/cold
pressing, by first heating the pad to 170~C for one minute, followed by 2-hour cooling,
followed by pressing to the desired density. All pads were tested for Ultimate Capacity
CA 022041~8 1997-04-30
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and Wet Pad Integrity. Each test was repeated and the results averaged. The results
shown in Table 2 below are the average of two s~mrles
TABLE 2
Thermobonded and Relevant SAP Level
Hot PressedCold Pressed Control NB316
Ultimate Wet PadUltimate Wet PadUltimate Wet Pad
Capacity IntegrityCapacityIntegrityCapacity Integrity
- Pad Type g/g (~) g/g (g) g/g (~)
15% SAP
CCF from 11.3 2092 32.4 135 30.4 67
NB316 w/15%
SAP
30% SAP
CCFfrom 16.9 1317 38.6 125.6 36.7 0
NB316 w/30%
SAP
15% SAP
NB316 w/5% -* -* 30.4 325 30.4 67
Celbond w/15%
SAP
30% SAP
NB316 w/5% -* -* 3S.5 133 36.7 0
Celbond w/30%
SAP
$Not measured.
Example 3
This example illustrates the use of HBA fiber to provide additional
10 absorbent capacity in a Thermobonded/cold pressed pad. These results are shown
without the enh~ncing capability of the SAP.
Pads having a basis weight of 550 grams per square meter were formed
from NB416, and formaldehyde free HBA made from NB416 cross-linked with
dimethyldihydroxyethyleneurea. The cellulosic fibers were combined with 5% by
15 weight of a binding agent (Celbond 105). The pads were Thermobonded/cold pressed
CA 02204158 1997-04-30
WO g6/1S301 PCT/US95/12879
16
to a density of 0.3 g/cc. Each test was repeated and the results averaged. The pads
were tested for llltim~te capacity and wet pad integrity as described above. The results
are set forth in Table 3 below.
TABLE 3
Ultimate Capacity Wet Pad Integrity
PadType (g/g) (g)
NB416 - 13.3 1959
~A (NB416) 17.4 1685
Example 4
This example is intended to show that the present invention is useful
10 with cellulosic fibers that have been combined with particle binders of the type
described in the specification. NB416 cellulose fibers, commercially available from
Weyerhaeuser Company, were prepared with densificationJsoftness aids by spraying a
fiber web with an aqueous solution of 70% by weight sorbitol and 30% by weight
glycerin at a level of 9% by weight based on oven dried fiber, sorbitol and glycerin.
15 These fibers were admixed with 10% by weight thermoplastic fiber, Celbond K56,
based on the total fiber and densification/softness aids. Densified webs conS~inin~ 0,
15%, and 45% by weight based on total weight of superabsorbent polyrner (SAP) were
prepared from the densification/softness aids coated cellulose fiber. The SAP used in
this example was IM3500 from Hoechst-Celanese. One set of webs was Hot Pressed
20 while a second set of webs was Thermobonded/cold pressed (by heating to
app,o~,."ately 170~C followed by 2 hours of cooling at room temperature followed by
pressing). Pads were prepared for the webs as in the previous examples. Each padwas tested for absorbent capacity using the inclined plane test. Each test was
replicated three times and the results averaged. The results showing a significant
25 increase in absorbent capacity using the techniques of the present invention are
tabulated in the following Table 4 below.
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TABLE 4
Therrnobonded/
Hot Pressed Cold Pressed
Tnclined PlaneTnclined Plane Capacity
% SAPCapacity (g/g)
(.~/g)
6 4.6 8.9
6.4 13.6
7.8 15.0
The foregoing examples are intended to be representative and to assist
5 one of ordinary skill in the art in reproducing the invention as disclosed herein. They
are not intended in any way to delimit the invention. The present invention has
therefore been described in conjunction with preferred embodiments thereof. One of
ordinary skill will understand that various changes, substitutions of equivalents, and
other alterations can be made to the invention without departing from the broad
10 concepts disclosed herein. For example, the absorbent capacity of the cellulose web
constructed in accordance with the present invention has only for comparative
purposes been defined in the context of its ability to absorb synthetic urine. It is,
however, intçnded that the claims be interpreted broadly to encompass cellulose webs
capable of absorbing a variety of aqueous fluids. It is also intended that the present
15 invention be limited in its scope only by the definition contained in the appended claims
and equivalents thereof.
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WO s6/1s301 Pcr/uS95/12879
18
The embodiments of the invention in which an exclusive property or privilege is
imed are defined as follows:
1. A fibrous article comp.isillg:
a densified web of cellulose fibers, at least some of said fibers being bonded
togeth~r by an activatable bonding agent, said dencified web having a minimum density at least
equal to or greater than 0.1 g/cc, based on the weight of the fiber and bonding material, said
densified web having a high absorbent capacity and a good wet pad integrity, said web having
been densified after the bonding agent has been deactivated and has bound the fibers together,
the d~ncified web having an absorbent capacity for synthetic urine that is significantly greater
than the absorbent capacity for synthetic urine exhibited by a comparable web of cellulose
fibers bound together by a bonding agent in which the comparable web has been densified to
subst~nti~lly the same degree as said dencified web by activating the bonding agent and
densifying the comparable web while the bonding agent is active.
2. The article of Claim 1, wherein the density of the web ranges from
0. 1 g/cc to 0.7 g/cc.
3. The article of Claim 2, wherein the density of the web ranges from 0.3
g/cc to 0.7 g/cc.
4. The article of Claim 1, wherein the densified web has a wet pad
integrity greater than the wet pad integrity of a non-bonded, densified web of cellulose fibers
that has been densified to substantially the same degree.
5. The article of Claim 1, wherein said article has an absorbent capacity
that is at least about equivalent to a non-bonded, densified web of cellulose fibers.
6. The article of Claim 1, wherein the article further comprises
superabsorbent polymer distributed in said web in an amount effective to increase the
absorbency of said web.
