U.S. patent application number 10/002373 was filed with the patent office on 2002-08-22 for crosslinked cellulosic product.
Invention is credited to Graef, Peter A., Grant, Terry M..
Application Number | 20020112296 10/002373 |
Document ID | / |
Family ID | 26939234 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020112296 |
Kind Code |
A1 |
Graef, Peter A. ; et
al. |
August 22, 2002 |
Crosslinked cellulosic product
Abstract
The present invention provides a bonded cellulosic fibrous
product that includes crosslinked cellulosic fibers. Methods for
forming the bonded cellulosic fibrous product and personal care
absorbent products that include the bonded product are also
provided.
Inventors: |
Graef, Peter A.; (Puyallup,
WA) ; Grant, Terry M.; (Auburn, WA) |
Correspondence
Address: |
PATENT DEPARTMENT CH2J29
WEYERHAEUSER COMPANY
P.O. BOX 9777
FEDERAL WAY
WA
98063-9777
US
|
Family ID: |
26939234 |
Appl. No.: |
10/002373 |
Filed: |
November 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60248260 |
Nov 14, 2000 |
|
|
|
60248350 |
Nov 14, 2000 |
|
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Current U.S.
Class: |
8/115.51 |
Current CPC
Class: |
D04H 1/54 20130101; A61F
2013/530489 20130101; D04H 1/587 20130101; A61F 13/15626 20130101;
D04H 1/64 20130101; A61F 13/531 20130101 |
Class at
Publication: |
8/115.51 |
International
Class: |
D06M 010/00 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for making a cellulosic fibrous product, comprising:
(a) airlaying crosslinked cellulosic fibers to provide a fibrous
web; (b) treating the web with an amount of a bonding agent
effective to provide a bonded product; and (c) heating the web to
effect bonding between the fibers to provide a bonded cellulosic
fibrous product.
2. The method of claim 1, wherein the bonding agent comprises a
latex.
3. The method of claim 1, wherein the bonding agent comprises a wet
strength agent.
4. The method of claim 1 further comprising airlaying thermoplastic
fibers with the crosslinked fibers.
5. The method of claim 1, wherein the fibrous web further comprises
other cellulosic fibers.
6. The method of claim 1, wherein the fibrous web further comprises
absorbent material.
7. A bonded cellulosic fibrous product, comprising airlaid
crosslinked cellulosic fibers treated with an amount of a bonding
agent effective to provide a bonded cellulosic fibrous product.
8. The product of claim 7, wherein the bonding agent comprises a
latex.
9. The product of claim 7, wherein the bonding agent comprises a
wet strength agent.
10. The product of claim 7, wherein the bonding agent comprises
thermoplastic fibers.
11. The product of claim 7 further comprising other cellulosic
fibers.
12. The product of claim 7 further comprising absorbent
material.
13. A method for making a cellulosic fibrous product, comprising:
(a) airlaying cellulosic fibers to provide a fibrous web, wherein
at least a portion of the cellulosic fibers are treated with an
amount of crosslinking agent effective to provide a bonded product;
and (b) heating the web to provide a bonded cellulosic fibrous
product.
14. The method of claim 13 further comprising airlaying
thermoplastic fibers with the cellulosic fibers.
15. The method of claim 13, wherein the fibrous web further
comprises other cellulosic fibers.
16. The method of claim 13, wherein the fibrous web further
comprises absorbent material.
17. A bonded cellulosic fibrous product, comprising airlaid
cellulosic fibers, wherein at least a portion of the cellulosic
fibers are treated with an amount of crosslinking agent effective
to provide a bonded product.
18. The product of claim 17 further comprising thermoplastic
fibers.
19. The product of claim 17 further comprising other cellulosic
fibers.
20. The product of claim 17 further comprising absorbent
material.
21. A method for making a cellulosic fibrous product, comprising:
(a) airlaying cellulosic fibers to provide a fibrous web, wherein
at least a portion of the cellulosic fibers are treated with an
amount of crosslinking agent effective to provide a bonded product;
(b) treating the web with an amount of a bonding agent effective to
provide a bonded product; and (c) heating the web to provide a
bonded cellulosic fibrous product.
22. The method of claim 21, wherein the bonding agent comprises a
latex.
23. The method of claim 21, wherein the bonding agent comprises a
wet strength agent.
24. The method of claim 21 further comprising airlaying
thermoplastic fibers with the cellulosic fibers.
25. The method of claim 21, wherein the fibrous web further
comprises other cellulosic fibers.
26. The method of claim 21, wherein the fibrous web further
comprises absorbent material.
27. A bonded cellulosic fibrous product, comprising airlaid
cellulosic fibers treated with an amount of a bonding agent
effective to provide a bonded cellulosic fibrous product, wherein
at least a portion of the cellulosic fibers are treated with a
crosslinking agent.
28. The product of claim 27, wherein the bonding agent comprises
thermoplastic fibers.
29. The product of claim 27, wherein the bonding agent comprises a
latex.
30. The product of claim 27, wherein the bonding agent comprises a
wet strength agent.
31. The product of claim 27 further comprising other cellulosic
fibers.
32. The product of claim 27 further comprising absorbent
material.
33. A personal care absorbent product comprising the product of any
one of claims 7, 17, or 27.
34. The product of claim 33, wherein the product is at least one of
an infant diaper, adult incontinence product, and a feminine
hygiene product.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. patent application Ser. No. 60/248,260, filed Nov. 14, 2000,
and U.S. patent application Ser. No. 60/248,350, filed Nov. 14,
2000.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a cellulosic
fibrous product and, more particularly, to a bonded cellulosic
fibrous product that includes crosslinked cellulosic fibers.
BACKGROUND OF THE INVENTION
[0003] 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.
[0004] The relatively low strength of sheets that include
crosslinked fibers is due impart 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.
[0005] 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.
[0006] 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
[0007] In one aspect, the present invention provides a bonded
cellulosic fibrous product that includes crosslinked cellulosic
fibers. In another embodiment, the product includes a bonding
agent. The product can optionally include other fibers alone,
absorbent materials alone, or other fibers and absorbent
materials.
[0008] In another aspect of the invention, methods for forming the
bonded cellulosic fibrous product is provided.
[0009] 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
[0010] 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:
[0011] FIG. 1 is a diagrammatic illustration of a representative
drum former device and method for forming the product of the
invention; and
[0012] FIG. 2 is a diagrammatic illustration of a representative
pocket former device and method for forming the product of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] In one aspect, the present invention provides a bonded
cellulosic fibrous product that includes bonded crosslinked
cellulosic fibers. The product possesses the advantageous
properties of bulk and resiliency 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.
[0014] In the present invention, bonding between fibers can be
attained by treating the fibers with a crosslinking agent and/or a
bonding agent. In one embodiment, the product is formed by treating
the crosslinked cellulosic fibers with a crosslinking agent and, if
necessary, a crosslinking catalyst. In another embodiment, the
product is formed by treating the crosslinked cellulosic fibers
with a bonding agent. In a further embodiment, the product is
formed by treating the crosslinked cellulosic fibers with a
combination of crosslinking agent and, if necessary, catalyst, and
bonding agent.
[0015] The product can be formed by (1) forming a web of
crosslinked cellulosic fibers; (2) treating the web with either (a)
a crosslinking agent and, if necessary, a crosslinking catalyst,
(b) a bonding agent, or (c) a crosslinking agent and, if necessary,
a crosslinking catalyst, and a bonding agent; and (3) heating the
web at a temperature and for a time sufficient to effect interfiber
crosslinking and bonding between fibers.
[0016] In one embodiment, the bonded cellulosic fibrous product
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 is distinguishable from webs that include
crosslinked cellulosic fibers that are first formed and then
introduced to the web during the web formation process.
[0017] For 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) that have been interfiber crosslinked (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 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.
[0018] 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; and
(2) heating the web at a temperature and for a time sufficient to
effect crosslinking. Alternatively, the product can be formed by
(1) forming a web of cellulosic fibers; (2) treating the web with a
crosslinking agent and, if necessary, a crosslinking catalyst; and
(3) heating the web at a temperature and for a time sufficient to
effect crosslinking.
[0019] 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.
[0020] 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.
[0021] Suitable urea-based crosslinking agents include substituted
ureas such as methylolated ureas, methylolated cyclic ureas,
methylolated lower alkyl cyclic ureas, methylolated dihydroxy
cyclic ureas, dihydroxy cyclic ureas, and lower alkyl substituted
cyclic ureas. Specific urea-based crosslinking agents include
dimethyldihydroxy urea (DMDHU,
1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone),
dimethyloldihydroxy-ethyle- ne 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).
[0022] Suitable crosslinking agents include dialdehydes such as
C.sub.2-C.sub.8 dialdehydes (e.g., glyoxal), C.sub.2-C.sub.8
dialdehyde acid analogs having at least one aldehyde group, and
oligomers of these aldehyde and dialdehyde acid analogs, as
described in U.S. Pat. Nos. 4,822,453; 4,888,093; 4,889,595;
4,889,596; 4,889,597; and 4,898,642. Other suitable dialdehyde
crosslinking agents include those described in U.S. Pat. Nos.
4,853,086; 4,900,324; and 5,843,061.
[0023] Other suitable crosslinking agents include aldehyde and
urea-based formaldehyde addition products. See, for example, U.S.
Pat. 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.
[0024] Suitable crosslinking agents include glyoxal adducts of
ureas, for example, U.S. Pat. No. 4,968,774, and glyoxal/cyclic
urea adducts as described in U.S. Pat. Nos. 4,285,690; 4,332,586;
4,396,391; 4,455,416; and 4,505,712.
[0025] 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. Pat. Nos. 3,526,048; 4,820,307; 4,936,865; 4,975,209; and
5,221,285. The use of C.sub.2-C.sub.9 polycarboxylic acids that
contain at least three carboxyl groups (e.g., citric acid and
oxydisuccinic acid) as crosslinking agents is described in U.S.
Pat. Nos. 5,137,537; 5,183,707; 5,190,563; 5,562,740, and
5,873,979.
[0026] Polymeric polycarboxylic acids are also suitable
crosslinking agents. Suitable polymeric polycarboxylic acid
crosslinking agents are described in U.S. Pat. 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. Pat. Nos. 6,306,251; 5,549,791; and 5,998,511.
Polymaleic acid crosslinking agents are described in U.S. Pat. No.
5,998,511.
[0027] Specific suitable polycarboxylic acid crosslinking agents
include citric acid, tartaric acid, malic acid, succinic acid,
glutaric acid, citraconic acid, itaconic acid, tartrate
monosuccinic acid, maleic acid, polyacrylic acid, polymethacrylic
acid, polymaleic acid, polymethylvinylether-co-maleate copolymer,
polymethylvinylether-co-itacon- ate copolymer, copolymers of
acrylic acid, and copolymers of maleic acid.
[0028] Other suitable crosslinking agents are described in U.S.
Pat. Nos. 5,225,047; 5,366,591; 5,556,976; and 5,536,369.
[0029] Suitable catalysts can include acidic salts, such as
ammonium chloride, ammonium sulfate, aluminum chloride, magnesium
chloride, magnesium nitrate, and alkali metal salts of
phosphorous-containing acids. In one embodiment, the crosslinking
catalyst is sodium hypophosphite.
[0030] Mixtures or blends of crosslinking agents and catalysts can
also be used.
[0031] 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.
[0032] 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.
[0033] 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, PLA16,
FR516, and NB416.
[0034] The wood pulp fibers useful in the present invention can
also be pretreated to use. This pretreatment may include physical
treatment, such as subjecting the fibers to steam, or chemical
treatment.
[0035] 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. Combinations of pretreatments also may be
employed. Similar treatments can also be applied after formation of
the fibrous product in post-treatment processes.
[0036] 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)
U.S. Pat. No. 5,543,215, entitled "Polymeric Binders for Binding
Particles to Fibers"; (2) U.S. Pat. No. 5,538,783, 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 "Method for Binding
Particles to Fibers Using Reactivatable Binders"; (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"; (12) U.S. Pat.
No. 5,308,896, entitled "Particle Binders for High-Bulk Fibers";
(13) U.S. Pat. No. 5,498,478, entitled "Polyethylene Glycol as a
Binder Material for Fibers"; (14) U.S. Pat. No. 5,609,727, entitled
"Fibrous Product for Binding Particles"; (15) U.S. Pat. No.
5,571,618, entitled "Reactivatable Binders for Binding Particles to
Fibers"; (16) U.S. Pat. No. 5,447,977, entitled "Particle Binders
for High Bulk Fibers"; (17) U.S. Pat. No. 5,614, 570, entitled
"Absorbent Articles Containing Binder Carrying High Bulk Fibers;
(18) U.S. Pat. No. 5,789,326, entitled "Binder Treated Fibers"; and
(19) U.S. Pat. No. 5,611,885, entitled "Particle Binders", each
expressly incorporated herein by reference.
[0037] 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, 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.
[0038] In one embodiment, the product farther 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 subsequently heated. 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 (i.e., curing).
[0039] 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.
[0040] 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, N.J.; latex; wet strength resins, such as
polyamide-epichlorohydrin resin (e.g., KYMENE 557LX, Hercules,
Inc., Wilmington, Del.), and polyacrylamide resin (see, e.g., U.S.
Pat. No. 3,556,932 and also the commercially available
polyacrylamide marketed by American Cyanamid Co., Stanford, Conn.,
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).
[0041] 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.
[0042] 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).
[0043] The amount of absorbent material present in the product can
vary greatly depending on the product's intended use. Absorbent
material can be present in the product in an amount greater than
about 0.5 percent by weight based on the total weight of the
product.
[0044] 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
maleic 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 fluids, superabsorbent materials can also retain
significant amounts of bodily fluids under moderate pressure.
[0045] 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-maleic anhydride
copolymers.
[0046] 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. 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, all expressly incorporated herein by reference. Products
such as diapers that incorporate superabsorbent materials are
described in U.S. Pat. No. 3,699,103 and U.S. Pat. No.
3,670,731.
[0047] Suitable superabsorbent materials useful in the product
include superabsorbent particles and superabsorbent fibers.
[0048] In another aspect of the invention, methods for forming the
bonded cellulosic fibrous product are provided. In one embodiment,
the product is formed using a drum former. In another embodiment,
the product is formed using a pocket former.
[0049] As described above, the product of the invention is formed
by subjecting a web that includes cellulosic fibers treated with
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.degree. 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
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.
[0050] In one embodiment, the product is produced using pocket
forming (mold) technology. In this method, fibers (e.g.,
crosslinked cellulosic fibers treated with crosslinking agent and,
if necessary, catalyst, and optional thermoplastic fibers; or
cellulosic fibers treated with crosslinking agent and, if
necessary, catalyst, and optional thermoplastic fibers) are
introduced into a forming device that includes a pocket or mold
that forms the fibers into a desired shape (e.g., the shape of an
acquisition zone to be used in an absorbent product such as an
infant diaper, adult incontinence product, or feminine care
product). For embodiments that do not include thermoplastic fibers
and that do include another bonding agent such as a wet strength
agent, the bonding agent can be applied to the fibers prior to
curing. For embodiments that do not include introducing cellulosic
fibers treated with crosslinking agent to the former, the
crosslinking agent can be applied to the fibers at a point prior to
their curing.
[0051] In one embodiment, the product is produced by heating the
pockets in which the treated cellulosic fiber web is formed. By
such a method, bonded webs having the desired shapes are directly
formed. By this method, a continuous web of the desired shape can
be formed and packaged into a box ready for shipping and subsequent
use by the absorbent product producer.
[0052] In one embodiment, the product is formed by airlaying
crosslinked cellulosic fibers and bicomponent fibers.
[0053] In another embodiment, the product is formed by airlaying
crosslinked cellulosic fibers and a wet strength agent.
[0054] In a further embodiment, the product is formed by airlaying
crosslinked cellulosic fibers and a crosslinking agent and, if
necessary, catalyst.
[0055] In another embodiment, the product is formed by airlaying
cellulosic fibers treated with a crosslinking agent and, if
necessary, crosslinking catalyst, and bicomponent fibers, and then
heating the airlaid fibers to cure the crosslinking agent and
effect fiber bonding.
[0056] 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.
[0057] 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.
[0058] The performance characteristics of a representative bonded
web formed in accordance with the present invention (a bonded web
including in situ crosslinked fibers) is described below. The
acquisition rate (ml/sec) for four liquid insults, rewet (g),
median uptake pressure (MUP) capacity (g/g), and median desorption
pressure (MDP, cm) for representative bonded webs compared to
controls are presented in Table
[0059] In Table 1, Control A refers to a commercial infant diaper
(Procter & Gamble) having a crosslinked cellulosic fiber
acquisition layer; and Control B refers to a commercial infant
diaper (PAMPERS) having a dual acquisition layer composed of a 44
gam synthetic layer and 300 gsm crosslinked fiber (citric acid
crosslinked fibers) layer. Webs 1A, 2A, 1B, and 2B refer to
representative products of the invention. Webs 1A and 1B refer to
products formed from 100 percent by weight flash-dried cellulosic
fibers treated with citric acid as crosslinking agent (about 6
percent by weight based on the total weight of fibers) and a
catalyst. Webs 2A and 2B refer to products formed from 90 percent
by weight flash-dried cellulosic fibers treated with citric acid as
crosslinking agent (about 6 percent by weight based on the total
weight of fibers) and a catalyst and 10 percent by weight
bicomponent binder fibers (CELBOND T105). The target basis weight
for Webs 1A and 2A was 150 g/m.sup.2, and the target basis weight
for Webs 1B and 2B was 300 g/m.sup.2.
1TABLE 1 PERFORMANCE CHARACTERISTICS OF REPRESENTATIVE PRODUCTS.
Basis MUP Weight Acquisition Rate (ml/sec) Rewet Capacity MDP Web
Density (g/cm.sup.3) (g/m.sup.2) 1 2 3 4 (g) (g/g) (cm) Control A
0.08 300 3.07 1.65 0.80 0.44 0.87 -- -- Control B 0.08 344 3.37
1.68 0.91 0.52 0.80 -- -- Web 1A 0.046 142 3.38 1.86 0.97 0.50 0.22
13.1 16.9 Web 2A 0.041 152 3.94 2.08 1.08 0.58 0.18 15.6 14.3 Web
1B 0.046 275 5.26 2.86 1.48 0.87 0.27 13.1 16.9 Web 2B 0.042 294
6.60 3.40 1.90 1.02 0.17 14.7 15.2
[0060] 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.
[0061] 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.
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