Densified cellulose fiber pads and method of making the same

A densified web of cellulose fibers has a high absorbent capacity and good wet strength. The web is produced by combining cellulose fibers with a bonding agent, activating the bonding agent, allowing it to contact the cellulose fibers, and thereafter deactivating the bonding agent. The web is thereafter compressed in a cooled state to form a densified web. The web exhibits an absorbent capacity superior to that of prior densified and bonded webs.

FIELD OF THE INVENTION 
The present invention relates to cellulose 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. 
BACKGROUND OF THE INVENTION 
Cellulose fibers derived from wood pulp are used in a variety of absorbent 
articles, for example, diapers and feminine hygiene products. It is 
desirable for the absorbent articles to have a high absorbent capacity for 
liquid, as well as to have good strength characteristics for durability. 
Cellulose fibers for pad formation have traditionally been shipped to end 
users, that is, manufacturers of absorbent articles, in large densified 
rolls, or less frequently in compressed bale form. The end user fluffs the 
cellulose fibers, combines them with additives, such as absorbency 
enhancing polymers or specially engineered fibers, forms them into a pad, 
and then forms them into an absorbent article for the consumer. While this 
methodology is effective, it is desirable for some applications to provide 
absorbent webs that include additives to the manufacturer of the absorbent 
article in a form that can be incorporated directly into the absorbent 
article without the intermediate steps of fluffing, additive 
incorporation, and pad construction. 
It is desirable to density webs before forming them into a roll to decrease 
the shipping costs. However, densified webs have insufficient strength for 
incorporation directly into absorbent structures. Therefore, the strength 
of the web must be increased, for example, by bonding the fibers together. 
The prior art suggests the simultaneous heating and compressing of a 
cellulose fiber web that has been combined with a thermoplastic bonding 
material to form a densified web with increased integrity. While this 
densifying technique provides higher bulk density and strength compared to 
densified webs of conventional non-bonded pulp, it has been found that the 
resulting densified web has a lower capacity for absorbing liquid than the 
non-densified, or fluffed, material normally incorporated into absorbent 
structures. 
It is therefore desirable to provide a densified web of cellulose fibers 
that has an absorbent capacity superior to prior densified webs, and that 
has a wet integrity or strength that is substantially higher than 
non-bonded, densified webs. 
SUMMARY OF THE INVENTION 
In accordance with the teaching in the following specification, the present 
invention provides a fibrous article comprising a densified web of 
cellulose 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 preferred form, 
the densified web has a minimum density of at least equal to or greater 
than 0.1 grams per cc. The resulting densified web has 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, which the comparable 
web has been densified to substantially the same degree as the densified 
web of the present invention by activating the bonding agent and 
densifying the web while the bonding agent is active. 
The densified web of the present invention can be formed into absorbent 
articles comprising one or more layers. For example, the present invention 
can take the form of a single absorbent layer composed of a densified web 
produced in accordance with the present invention. The densified web of 
the present invention can also be incorporated into multi-layer articles 
including, for example, an upper acquisition/distribution layer and a 
storage layer. In accordance with the teachings herein, the densified web 
produced with the present invention can be included 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 by 
first forming, for example, a web of cellulose fibers containing a bonding 
agent, thereafter activating the bonding agent so that the bonding agent 
contacts at least some of the cellulose fibers, deactivating the bonding 
agent to bind at least some of the cellulose fibers together, and 
thereafter densifying the bonded web of cellulose fibers to a density of 
at least about 0.1 grams per cc.

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 other 
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 chemical processes such as the Kraft and sulfite processes, 
whether bleached or unbleached. The pulp fibers may also be processed by 
thermomechanical, chemithermomechanical methods, or combinations thereof. 
The preferred pulp fiber is chemical. The preferred 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 bleached 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 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 NB316 and NB416. 
The wood pulp fibers of the present invention can also be pretreated prior 
to use with the present invention. This pretreatment may include physical 
treatment, such as subjecting the fibers to steam, or chemical treatment, 
for example, 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 
designation HB416. 
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, 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 and patent 
applications: (1) U.S. Pat. No. 5,543,215, entitled "Polymeric Binders for 
Binding Particles to Fibers;" (2) U.S. Pat. No. 5,538,785 entitled 
"Non-Polymeric Organic Binders for Binding Particles to Fibers;" (3) U.S. 
Pat. No. 5,300,192, entitled "Wet Laid Fiber Sheet Manufacturing With 
Reactivatable Binders for Binding Particles to Binders;" (4) U.S. Pat. No. 
5,352,480, entitled "Reactivatable Binders for Binding Particle to 
Fibers;" (5) U.S. Pat. No. 5,308,896, entitled "Particle Binders for 
High-Bulk Fibers;" (6) U.S. Pat. No. 5,589,256 entitled "Particle Binders 
that Enhance Fiber Densification;" (7) U.S. Pat. No. 5,672,418, entitled 
"Particle Binders;" (8) U.S. Pat. No. 5,607,759, entitled "Particle 
Binding to Fibers;" (9) U.S. Pat. No. 5,693,411, entitled "Binders for 
Binding Water Soluble Particles to, Fibers;" (10) U.S. Pat. No. 5,547,745, 
entitled "Particle Binders;" (11) U.S. Pat. No. 5,641,561, entitled 
"Particle Binding to Fibers;" and (12) U.S. Pat. No. 5,447,977, entitled 
"Particle Binders for High-Bulk Fibers," all expressly incorporated herein 
by reference. 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 spraying 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. 
Although not to be construed as a limitation, examples of pretreating 
fibers include the application of fire retardants to the fibers, such as 
by spraying the fibers with fire-retardant chemicals. Specific 
fire-retardant chemicals include, by way of example, sodium boratelboric 
acid, urea, urea/phosphates, etc. In addition, the fibers may be 
pretreated with surfactants or other liquids, such as water or solvents, 
which modify the surface of the fibers. Other pretreatments include 
exposure to antimicrobials, pigments and densification or softening 
agents. Fibers pretreated with other chemicals, such as thermoplastic and 
thermosetting resins also may be used. Combinations of pretreatments also 
may be employed with the resulting pretreated 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 otherwise 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 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 temperature, the bonding agent will upon 
solidifying from the melted state cause the cellulose fibers to be bound 
in a matrix. 
Thermoplastic materials are the preferred binders, and can be combined with 
the fibers in the form of particles, emulsions, or as fibers. Suitable 
fibers can include those made from thermoplastic polymers, cellulosic or 
other fibers coated with thermoplastic polymers, and multi-component 
fibers in which at least one of the components of the fiber comprises a 
thermoplastic polymer. Single and multicomponent fibers are manufactured 
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 
Celbon.RTM. fibers available from Hoechst Celanese Company. Suitable 
coated fibers can include cellulose fibers coated with latex or other 
thermoplastics, as disclosed in U.S. Pat. No. 5,230,959, issued Jul. 27, 
1993, to Young et al., and U.S. Pat. No. 5,064,689, issued Nov. 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 
particulate or emulsion form, the thermoplastics can be combined with the 
cellulose 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 acrylate, styrene butadiene, styrene 
acrylonitrile, butadiene acrylonitrile, acrylonitrile butadiene styrene, 
ethylene acrylic acid, urethanes, polycarbonate, polyphenylene oxide, and 
polyimides. 
Thermosetting materials also serve as excellent bonding agents for the 
present invention. Typical thermosetting materials are activated by 
heating to elevated temperatures at which cross-linking occurs. 
Alternatively, a resin can be activated by combining 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 form a matrix to bond the 
cellulose fibers. It is contemplated that other types of 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. 
Thermosetting bonding agents suitable for the present invention include 
phenolic resins, polyvinyl acetates, urea formaldehyde, melamine 
formaldehyde, and acrylics. Other thermosetting bonding agents include 
epoxy, phenolic, bismaleimide, polyimide, melamine formaldehyde, 
polyester, urethanes, 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. Alternatively, they can be sprayed onto a loose web after it has 
been formed. 
Materials that enhance 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 
polymeric material that is capable of absorbing large quantities of fluid 
by swelling and forming a hydrated gel (hydrogel). The superabsorbent 
polymers also can retain significant amounts of water under moderate 
pressures. Superabsorbent polymers generally fall into three classes, 
namely, starch graft copolymers, cross-linked carboxymethylcellulose 
derivatives and modified hydrophilic polyacrylates. Examples of such 
absorbent polymers are hydrolyzed starch-acrylonitrile graft copolymer, a 
neutralized starch-acrylic acid graft copolymer, a saponified acrylic acid 
ester-vinyl acetate copolymer, a hydrolyzed acrylonitrile copolymer or 
acrylamide copolymer, a modified cross-linked polyvinyl alcohol, a 
neutralized self-cross-linking polyacrylic acid, a cross-linked 
polyacrylate salt, carboxylated cellulose, and a neutralized cross-linked 
isobutylene-maleic anhydride 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 and polymer. Superabsorbent polymers are 
available commercially, for example, starch graft polyacrylate hydrogel 
fines from Hoechst-Celanese of Portsmouth, Va. These superabsorbent 
polymers come in a variety of sizes, morphologies and absorbent 
properties. These are available from Hoechst-Celanese under trade 
designations such as IM 1000 and IM 3500. Other superabsorbent particles 
are marketed under the trademarks SANWET (supplied by Sanyo Kasei Kogyo 
Kabushiki Kaisha), SUMIKA GEL (supplied by Sumitomo Kagaku Kabushiki 
Kaisha), which is suspension polymerized and spherical, as opposed to 
solution polymerized ground particles, FAVOR (supplied by Stockhausen of 
Greensboro, N.C.), and NORSOCRYL (supplied by Atochem). Other 
superabsorbent polymers are described in U.S. Pat. No. 4,160,059; U.S. 
Pat. No. 4,676,784; U.S. Pat. No. 4,673,402; U.S. Pat. No. 5,002,814; U.S. 
Pat. No. 5,057,166; U.S. Pat. No. 4,102,340; and U.S. Pat. No. 4,818,598, 
expressly incorporated herein by reference. Products such as diapers that 
incorporate superabsorbent polymers are shown in U.S. Pat. No. 3,669,103 
and U.S. Pat. No. 3,670,731. 
Referring now to FIG. 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 any concentration 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 
agents disclosed above can be incorporated with the cellulose 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 
preferred 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 thermoplastic 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.degree. to 145.degree. 
C. These temperatures, of course, are well under that which will cause 
damage to the bonding agent and/or the cellulose fiber. 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 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 
compress or density the deactivated, bonded web to a density significantly 
greater than in its original air-laid condition. In accordance with the 
present invention, it is preferred that the densified web 10' be 
compressed 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 
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 
substantially the same 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 cellulose fibers. It has also been found that the web 
densified in accordance 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 significantly greater 
than the absorbent capacity of a comparable web of cellulose fibers bound 
together by a bonding agent in which the web was densified to 
substantially 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 capacity for a web of cellulose 
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, 
comparison, and definition, 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 fluffing 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 FIG. 1 can be incorporated in an absorbent 
article as the absorbent layer. It can be used alone, or as illustrated in 
FIG. 2, can be used in combination with secondary layers. In FIG. 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 FIG. 3. And finally, as illustrated in FIG. 4, a third base 
layer 34 can also be employed if desired, with a storage layer 32 and an 
acquisition 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. 
EXAMPLES 
Experimental Procedures: 
All absorbent pads were formed in the laboratory on a 6" diameter circular 
laboratory pad former. The pad former was equipped with a pin mill 
fluffing device. The pad former replicates in the laboratory air-laid webs 
produced with full-scale commercial equipment. Additives, including 
bonding agent and superabsorbent polymer, were added and combined with the 
cellulose fibers in the pad former. Homogenous blending of the pad 
components was achieved by refeeding the pad through the pin mill at least 
three times. 
The 6" diameter 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 compressing it at ambient temperatures. The 
second densification procedure is referred to as "Hot Pressing." Hot 
Pressing is achieved by placing the pad in a laboratory platen press at a 
temperature elevated above ambient (platen temperature on the order of 
170.degree. C.). The third densification procedure, performed in 
accordance with the teachings of the present invention, is referred to in 
the Examples as "Thermobonding/cold pressing." Thermobonding/cold pressing 
is achieved by passing hot air (on the order of 170.degree. C.) through a 
pad at its initial as-formed density (typically on the order of 0.05 grams 
per cc), followed by cooling to room temperature at the low density and by 
subsequent Cold Pressing. In all three of the densification procedures, 
final pad density is controlled by varying the pressure applied by the 
platen press to the pad. Rectangular pads measuring 4".times.4" (10 
cm..times.10 cm.) are cut from the 6" diameter pad using die cutters, and 
are tested for capacity and strength using the following procedures. 
An Inclined Plane Capacity test is performed by initially recording the pad 
weight W.sub.1 in grams. One edge of the pad is immersed in the test 
liquid while the pad is supported on a glass plate inclined at 10.degree. 
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 at the top of the 
slope and the liquid is applied at a controlled rate (5 ml. per minute) to 
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 W.sub.2 in grams. 
The Inclined Plane Capacity is reported as (W.sub.2 -W.sub.1)/W.sub.1 in 
grams per gram. 
An Ultimate Capacity test is performed by recording the initial pad weight 
W.sub.1 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 minutes. The pad is reweighed as W.sub.2 (g). Ultimate 
capacity is reported as (W.sub.2 -W.sub.1)/W.sub.1 in grams per gram. 
(When the pad contains a coated fiber as described below, the weight 
W.sub.1 in the 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 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 is stopped 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 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./I sodium, 8.6 meq./l calcium, 7.7 meq./l magnesium, 
1.94% urea by weight (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 
designation NB316. Fibers bleached with a chlorine dioxide instead of 
chlorine are referred to by the designation NB416. A first bonding agent 
comprises a thermoplastic bicomponent fiber available from the Hoechst 
Celanese Co. under the trade name Celbond K56. Celbond K56 has a fiber 
length of 5 mm. The bicomponent fiber is comprised of a polyester core and 
a polyethylene sheath in a concentric extrusion. A cross-linked cellulose 
fiber was also employed. The cross-linked fiber comprised NB316 or NB416 
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 NB316 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 IM1000 and IM3500. 
Example 1 
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 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/m.sup.2 were formed from combinations 
of either HBA, CCF made from HBA (with 97-910 latex) or an 80/20 weight 
blend of HBA and Celbond K56 combined with SAP at levels of 15% and 45% 
total pad 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 containing 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.degree. C. for 30 
seconds. Hot Pressing was found necessary to achieve stable pad density 
because rapid springback in the Cold Pressed HBA pads resulted in 
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. 
CCF and HBA/bicomponent fiber pads were all hot pressed at 140.degree. C. 
for 30 seconds to form interfiber bond. Pads were then tested for Inclined 
Plane Capacity. The tests were each repeated three times, and the results 
averaged. The averaged results are shown in Table 1. 
TABLE 1 
______________________________________ 
Inclined Plane Capacity (g/g) 
HBA Control 
CCF from 
HBA with 
SAP Level (%) 
Density (g/cc) 
(no binder) 
HBA Celbond 
______________________________________ 
15 0.1 17.3 12.9 10.8 
15 0.3 13.3 5.1 4.5 
15 0.5 11.8 2.5 3.4 
45 0.1 22.5 19.6 11.2 
45 0.3 20.6 9.5 8.1 
45 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), maintains the capacity of an equivalent 
non-bonded 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/m.sup.2 were formed from combinations 
of NB316 CCF made from NB316 (with 40-504 latex coating), and a 95/5 
weight blend of NB316 and Celbond K56, all containing IM1000 SAP at levels 
of 15% or 30%, based on total pad weight. All pads were produced at a 
density of 0.3 g/cc. The NB316 controls were Cold Pressed. The pads 
containing a bonding agent were prepared either by Hot Pressing at 
170.degree. C. for one minute, or by Thermobonding/cold pressing, by first 
heating the pad to 170.degree. C. for one minute, followed by 2-hour 
cooling, followed by pressing to the desired density. All pads were tested 
for Ultimate Capacity and Wet Pad Integrity. Each test was repeated and 
the results averaged. The results shown in Table 2 below are the average 
of two samples. 
TABLE 2 
__________________________________________________________________________ 
Thermobonded and 
Relevant SAP Level 
Hot Pressed 
Cold Pressed 
Control NB3 16 
Ultimate 
Wet Pad 
Ultimate 
Wet Pad 
Ultimate 
Wet Pad 
Capacity 
Integrity 
Capacity 
Integrity 
Capacity 
Integrity 
Pad Type 
g/g (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 
CCF from 
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% 
--* --* 35.5 133 36.7 0 
Celbond w/30% 
SAP 
__________________________________________________________________________ 
*Not measured. 
Example 3 
This example illustrates the use of HBA fiber to provide additional 
absorbent capacity in a Thermobonded/cold pressed pad. These results are 
shown without the enhancing capability of the SAP. 
Pads having a basis weight of 550 grams per square meter were formed from 
NB 416, and formaldehyde free HBA made from NB 416 cross-linked with 
dimethyldihydroxyethyleneurea. The cellulosic fibers were combined with 5% 
by weight of a binding agent (Celbond 105). The pads were 
Thermobonded/cold pressed to a density of 0.3 g/cc. Each test was repeated 
and the results averaged. The pads were tested for ultimate capacity and 
wet pad integrity as described above. The results are set forth in Table 3 
below. 
TABLE 3 
______________________________________ 
Ultimate Capacity 
Wet Pad Integrity 
Pad Type (g/g) (g) 
______________________________________ 
NB416 13.3 1959 
HBA(NB416) 17.4 1685 
______________________________________ 
Example 4 
This example is intended to show that the present invention is useful 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 
densification/softness 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. These 
fibers were admixed with 10% by weight thermoplastic fiber, Celbond K56, 
based on the total fiber and densification/softness aids. Densified webs 
containing 0, 15%, and 45% by weight based on total weight of 
superabsorbent polymer (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 while a second set of 
webs was Thermobonded/cold pressed (by heating to approximately 
170.degree. 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 pad was tested for absorbent capacity using the inclined plane test. 
Each test was replicated three times and the results averaged. The results 
showing a significant increase in absorbent capacity using the techniques 
of the present invention are tabulated in the following Table 4 below. 
TABLE 4 
______________________________________ 
Hot Pressed 
Thermobonded/ 
Inclined Plane 
Cold Pressed 
Capacity Inclined Plane Capacity 
% SAP (g/g) (g/g) 
______________________________________ 
6 4.6 8.9 
15 6.4 13.6 
45 7.8 15.0 
______________________________________ 
The foregoing examples are intended to be representative and to assist 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 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, intended 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 invention be limited 
in its scope only by the definition contained in the appended claims and 
equivalents thereof