Abstrict An absorbent binder desiccant composition is provided which is
capable of spontaneous crosslinking after application to a substrate,
at a temperature of about 120.degree. C. or less. The absorbent
binder desiccant composition includes a monoethylenically unsaturated
polymer, such as carboxylic acid, sulphonic acid, or phosphoric
acid, or salts thereof, or a quaternary ammonium salt, and an acrylate
or methacrylate ester that contains an alkoxysilane functionality,
or a monomer capable of co-polymerization with a compound containing
a trialkoxy silane functional group and subsequent reaction with
water to form a silanol group, and a desiccant component. The absorbent
binder desiccant composition is particularly suitable for use in
manufacturing a wide variety of humidity control articles.
Claims What is claimed is:
1. An absorbent binder desiccant composition comprising a water-soluble
ionic polymer capable of sufficient non-radiative crosslinking within
about 10 minutes at a temperature of about 120.degree. C. or less,
to reach an absorbent capacity of at least one gram of fluid per
gram of polymer using the centrifuge retention capacity test, and
at least one desiccant component.
2. The absorbent binder desiccant composition of claim 1 wherein
the water-soluble ionic polymer and the desiccant component are
present in a dry weight ratio of about 100:1 to about 1:10.
3. The absorbent binder desiccant composition of claim 1 wherein
the water-soluble ionic polymer and desiccant are present in a dry
weight ratio of about 10:1 to about 1:3.
4. The absorbent binder desiccant composition of claim 1 wherein
the ionic polymer is capable of sufficient non-radiative crosslinking
within about 10 minutes at a temperature of about 120.degree. C.
or less, to reach an absorbent capacity of at least 3 grams of fluid
per gram of polymer using the centrifuge retention capacity test.
5. The absorbent binder desiccant composition of claim 1 wherein
the water-soluble ionic polymer comprises at least about 15 mole
percent ionic polymer units.
6. The absorbent binder desiccant composition of claim 1 wherein
the ionic polymer has a negative charge.
7. The absorbent binder desiccant composition of claim 6 wherein
the ionic polymer comprises a carboxyl group-containing monomer.
8. The absorbent binder desiccant composition of claim 1 wherein
the ionic polymer has a positive charge.
9. The absorbent binder desiccant composition of claim 8 wherein
the ionic polymer comprises a quaternary ammonium group-containing
monomer.
10. The absorbent binder desiccant composition of claim 8 wherein
the ionic polymer comprises a reaction product of 1) a monomer selected
from the group consisting of acryloyloxyethyl-trialkyl-substituted
ammonium salts, acryloyloxypropyl-trialkyl-substituted ammonium
salts, acrylamidoethyl-trialkyl-substituted ammonium salts, and
acrylamidopropyl-trialkyl-substituted ammonium salts, with 2) a
monomer selected from the group consisting of methacryl esters which
contain an alkoxysilane group and acryl esters which contain an
alkoxysilane group.
11. The absorbent binder desiccant composition of claim 1 wherein
the desiccant component comprises a compound selected from the group
consisting of anhydrous salts, capillary desiccants, and combinations
thereof.
12. The absorbent binder desiccant composition of claim 1 wherein
the desiccant component comprises a desiccant selected from the
group consisting of sodium acetate, zinc chloride, zinc bromide,
calcium oxide, calcium sulfate, montmorillonite clay, synthetic
zeolites, synthetic gels, starches, and combinations thereof.
13. A combination comprising the absorbent binder desiccant composition
of claim 1 and a substrate.
14. An absorbent binder desiccant composition comprising an absorbent
binder component and a desiccant component in a dry weight ratio
of about 100:1 to about 1:10 wherein the absorbent binder component
comprises: a) about 15 to about 99.8% by mass of monoethylenically
unsaturated polymer units; b) about 0.1 to about 20% by mass polyacrylate
ester units that include an alkoxysilane functionality; and c) about
0.1 to about 75% by mass polymer units selected from the group consisting
of polyolefin glycol units, polyolefin oxide units, and combinations
thereof.
15. The absorbent binder desiccant composition of claim 14 wherein
the monoethylenically unsaturated polymer units and the polyacrylate
ester units including an alkoxysilane functionality are copolymerized.
16. The absorbent binder desiccant composition of claim 14 wherein
at least some of the polymer units selected from the group consisting
of polyolefin glycol units, polyolefin oxide units, and combinations
thereof are copolymerized with at least some of the polyacrylate
ester units.
17. The absorbent binder desiccant composition of claim 14 wherein
the absorbent binder component comprises about 25 to about 89.5%
by mass monoethylenically unsaturated polymer units, about 0.5 to
about 15% by mass ester units selected from the group consisting
of acrylate and methacrylate ester units that include an alkoxysilane
functionality, and about 10 to about 60% by mass of units selected
from the group consisting of polyolefin glycol and polyolefin oxide
units.
18. The absorbent binder desiccant composition of claim 14 wherein
the absorbent binder component comprises about 30 to about 79% by
mass monoethylenically unsaturated polymer units, about 1.0 to about
10% by mass ester units selected from the group consisting of acrylate
and methacrylate ester units that include an alkoxysilane functionality,
and about 20 to about 50% by mass of units selected from the group
consisting of polyolefin glycol and polyolefin oxide units.
19. The absorbent binder desiccant composition of claim 14 wherein
the monoethylenically unsaturated polymer units comprise a monomer
unit selected from the group consisting of a carboxyl group-containing
monomer, a carboxylic acid anhydride group-containing monomer, a
carboxylic acid salt-containing monomer, a sulfonic acid group-containing
monomer, an amide group-containing monomer, and a quaternary ammonium
salt.
20. The absorbent binder desiccant composition of claim 14 wherein
the alkoxysilane functionality comprises a trialkoxysilane group
having the following structure: 5wherein R1 R2 and R3 are alkyl
groups independently having from 1 to 6 carbon atoms.
21. The absorbent binder desiccant composition of claim 14 wherein
the absorbent binder component and desiccant component are present
in a dry weight ratio of about 10:1 to about 1:3.
22. The absorbent binder desiccant composition of claim 14 wherein
the desiccant component comprises a compound selected from the group
consisting of anhydrous salts, capillary desiccants, and combinations
thereof.
23. The absorbent binder desiccant composition of claim 14 wherein
the desiccant component comprises a compound selected from the group
consisting of sodium acetate, zinc chloride, zinc bromide, calcium
oxide, calcium sulfate, montmorillonite clay, synthetic zeolites,
synthetic gels, starches, and combinations thereof.
24. A combination comprising the absorbent binder desiccant composition
of claim 14 and a substrate.
25. A combination of an absorbent binder desiccant structure and
a substrate, wherein the absorbent binder desiccant structure is
formed from an absorbent binder component comprising a water-soluble
polymer capable of sufficient non-radiative crosslinking within
about 10 minutes at a temperature of about 120.degree. C. or less,
to reach an absorbent capacity of at least one gram of fluid per
gram of polymer using the centrifuge retention capacity test, and
a desiccant component.
26. A humidity control package comprising the combination of claim
25.
27. A bottle comprising the combination of claim 25.
28. A can comprising the combination of claim 25.
29. A bread box comprising the combination of claim 25.
30. A cup comprising the combination of claim 25.
31. The combination of claim 25 wherein the absorbent binder component
has a glass transition temperature of less than about 5.degree.
C.
32. The combination of claim 25 wherein the water-soluble polymer
is crosslinked after being combined with the substrate.
33. The combination of claim 25 wherein the water-soluble polymer
is crosslinked before being combined with the substrate.
Description [0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/427809 filed 1 May 2003 which in turn
is a continuation-in-part of U.S. patent application Ser. No. 10/324478
filed 20 Dec. 2002 which in turn is a continuation-in-part of U.S.
patent application Ser. No. 10/206883 filed 26 Jul. 2002. The
disclosures of the three prior applications are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] This invention is directed to an absorbent binder desiccant
composition and structure, a method of making the absorbent binder
desiccant composition and structure, and articles which utilize
the composition and structure.
[0003] Adhesives, or binders, are a necessary element of many products.
While adhesives beneficially hold products together, adhesives may
also have a tendency to interfere with the absorbency of fluids
in absorbent products. Adhesives are typically hydrophobic and therefore
are not conducive to absorbency or liquid transfer functions.
[0004] Hydrophilic adhesives are known, such as adhesives formulated
from water-soluble polymers such as poly(vinyl alcohol), poly(vinyl
methyl ether), poly(vinyl pyrrolidone), poly(ethylene oxide), or
cellulose derivatives such as hydroxypropyl cellulose. Dextrans,
starches and vegetable gums have been used to provide hydrophilic
adhesives. These materials provide adhesion under dry conditions.
However, upon exposure to aqueous fluids, these materials lose bonding
capability because they are substantially soluble in aqueous fluids.
[0005] Recent development efforts have provided coating materials
for a variety of uses. For example, U.S. Pat. No. 6054523 to
Braun et al., describes materials that are formed from organopolysiloxanes
containing groups that are capable of condensation, a condensation
catalyst, an organopolysiloxane resin, a compound containing a basic
nitrogen, and polyvinyl alcohol. The materials are reported to be
suitable for use as hydrophobic coatings and for paints and sealing
compositions.
[0006] Anderson et al., in U.S. Pat. No. 5196470 reported an
alcohol-based, water-soluble binder composition. Because this composition
is water-soluble and not cross-linked, it has no absorbency.
[0007] Others have reported the production of graft copolymers
having silane functional groups that permitted the initiation of
cross-linking by exposure to moisture. Prejean (U.S. Pat. No. 5389728)
describes a melt-processible, moisture-curable graft copolymer that
was the reaction product of ethylene, a 1-8 carbon alkyl acrylate
or methacrylate, a glycidyl containing monomer such as glycidyl
acrylate or methacrylate, onto which has been grafted N-tert-butylaminopropyl
trimethoxysilane. The resulting copolymers were reported to be useful
as adhesives and for wire and cable coatings.
[0008] Furrer et al., in U.S. Pat. No. 5112919 reported a moisture-crosslinkable
polymer that was produced by blending a thermoplastic base polymer,
such as polyethylene, or a copolymer of ethylene, with 1-butene,
1-hexene, 1-octene, or the like; a solid carrier polymer, such as
ethylene vinylacetate copolymer (EVA), containing a silane, such
as vinyltrimethoxysilane; and a free-radical generator, such as
an organic peroxide; and heating the mixture. The copolymers could
then be cross-linked by reaction in the presence of water and a
catalyst, such as dibutyltin dilaurate, or stannous octoate.
[0009] U.S. Pat. No. 4593071 to Keough reported moisture cross-linkable
ethylene copolymers having pendant silane acryloxy groups. The resultant
cross-linked polymers were reported to be especially resistant to
moisture and to be useful for extruded coatings around wires and
cables. The same group has reported similar moisture curable polymers
involving silanes in U.S. Pat. Nos. 5047476 4767820 4753993
4579913 4575535 4551504 4526930 4493924 4489029
4446279 4440907 4434272 4408011 4369289 4353997
4343917 4328323 and 4291136.
[0010] U.S. Pat. No. 5204404 to Werner reported crosslinkable
hydrophobic acrylate ester copolymers including 0.1 to 10% acrylic
acid. The resultant cross-linked polymers were reported to be useful
for painting and refinishing the exterior of automobiles.
[0011] Non-absorbent polymers have been mixed with desiccants for
use in humidity control packaging and the like. U.S. Pat. No. 5911937
issued to Hekal, discloses a blend of a matrix polymer, desiccating
agent and channeling agent. The matrix polymer can be polyethylene
or polypropylene. The desiccating agent can be an anhydrous salt
(or other material which absorbs water) or a compound which chemically
reacts with water. The channeling agent transports water from the
exterior of the matrix polymer to the desiccating agent within the
matrix polymer. Suitable channeling agents include ethylene vinyl
alcohol and polyvinyl alcohol. U.S. Pat. No. 6174952 issued to
Hekal, discloses a structure including a matrix polymer, desiccating
agent, and interconnecting channels, wherein the desiccating agent
is distributed within the channels.
[0012] There is a need or desire for a polymeric desiccant composition
having binder properties, which is relatively easy and inexpensive
to apply and use.
SUMMARY OF THE INVENTION
[0013] The present invention is directed to an absorbent binder
desiccant composition and a resulting absorbent binder desiccant
structure. The absorbent binder desiccant composition includes an
absorbent binder (polymer matrix) component and a desiccant component.
The absorbent binder component is a self-crosslinking hydrophilic
polymer which can be applied to a substrate in a liquid or other
flowable form. The self-crosslinking polymer is mixed with the desiccant
component. After applying the mixture to a substrate, the polymer
can be crosslinked to form an absorbent binder component which is
bound to the substrate. Alternatively, the absorbent binder component
may be applied to the substrate and dried, without crosslinking.
[0014] The resulting absorbent binder desiccant structure has particles,
fibers or other domains of the desiccant component dispersed within
the absorbent binder component. The absorbent binder component absorbs
liquid (e.g., water) or vapor from the surroundings and carries
it to the desiccant component via diffusion, thus eliminating the
need for a channeling agent or channels. The binding feature of
the absorbent binder component eliminates the need for a separate
adhesive, allowing easy application and binding of the absorbent
binder desiccant composition to a wide variety of substrates.
[0015] The absorbent binder component provides a water-soluble
ionic polymer capable of sufficient spontaneous crosslinking within
about 10 minutes, at a temperature of about 120.degree. C. or less,
to reach an absorbent capacity of at least one gram of fluid per
gram of absorbent binder component. Thereafter, the ionic polymer
continues to crosslink until full absorbent capacity is reached.
The ionic polymer may bear a positive or negative charge, or both.
[0016] The absorbent binder component includes at least 15 mass
percent monoethylenically unsaturated monomer or polymer containing
the monomer, such as carboxylic acid, sulphonic acid, phosphoric
acid, or salts thereof, or a quaternary ammonium salt; and a second
monomer. The second monomer can be a) a monomer capable of copolymerization
which by subsequent reaction can incorporate a silane functional
group capable of reaction with water to form a silanol group, and/or
b) a monomer that includes a group readily transformed into a silanol
functionality by subsequent reaction with water. Upon exposure to
water, the silanol functional group condenses to form a crosslinked
polymer. Thus, the absorbent binder component provides enhanced
adhesion in a wet condition, as well as absorbency.
[0017] In one embodiment, the absorbent binder component is a flexible
absorbent binder component (useful in a wide variety of applications
requiring flexibility and conformability) including about 15 to
about 99.8% by mass of monoethylenically unsaturated polymer units.
Suitable monoethylenically unsaturated polymers include without
limitation carboxylic acid, sulphonic acid, phosphonic acid, salts
of the foregoing, and quaternary ammonium salts. The flexible absorbent
binder component also includes about 0.1 to about 20% by mass of
acrylate or methacrylate ester units that include an alkoxysilane
functionality. Upon exposure to water, the alkoxysilane functionality
forms a silanol group which condenses to form a crosslinked polymer.
[0018] The flexible absorbent binder component also includes about
0.1 to about 75% by mass of polyolefin glycol and/or polyolefin
oxide units. The polyolefin glycol and/or oxide may include an alpha-olefin
having about 2 to about 4 carbon atoms, and may include about 30
to about 15000 olefin glycol and/or oxide units per molecule. The
polyolefin glycol and/or oxide may be graft polymerized with the
acrylate or methacrylate ester to form a graft copolymer. The polyolefin
glycol and/or oxide may be a homopolymer or copolymer. The polyolefin
glycol and/or oxide may be a block copolymer including olefin glycol
or oxide units having different numbers of carbon atoms, for instance,
block copolymers of ethylene oxide and propylene oxide. The polyolefin
glycol and/or oxide provides the absorbent binder desiccant structure
with enhanced flexibility. Thus, the flexible absorbent binder component
has enhanced adhesion in a wet condition, absorbency, and flexibility.
[0019] The absorbent binder component suitably has a glass transition
temperature below about 30 degrees Celsius, or below about 10 degrees
Celsius, or below about 5 degrees Celsius, and a bending modulus
lower than the bending modulus of a substrate to which the absorbent
binder desiccant composition is applied. Substrates include nonwoven
webs, woven webs, knitted fabrics, cellulose tissue, plastic film,
stranded composites, elastomer net composites, metal substrates,
glass, glass fiber, and other suitable substrates. Examples of suitable
plastic film substrates include those made of polypropylene, low
density polyethylene, high density polyethylene, linear low density
polyethylene, and ultra low density polyethylene.
[0020] The absorbent binder component can be made by polymerizing
monoethylenically unsaturated monomers, one of which contains an
alkoxysilane functionality. The polymerization may be induced by
a variety of initiation techniques including thermal initiation,
radiation initiation, or redox chemical reactions. Various types
of effective radiation initiation include ultraviolet, microwave,
and electron-beam radiation. The initiator generates free radicals
to cause polymerization of the monomers. The resultant copolymer
includes latent moisture-induced crosslinking capability by incorporation
of the alkoxysilane functionality. This copolymer may be applied,
in a flowable state, to a substrate or other end use application.
Moisture-induced crosslinking may be accomplished through hydrolysis
of the alkoxysilane and subsequent condensation upon removal of
the solvent from the substrate, either by evaporation of the solvent
from the substrate or using any other effective technique. Alternatively,
the hydrolysis of the alkoxysilane and subsequent condensation may
occur after solvent removal by exposure of the coating to moisture
in ambient air.
[0021] For instance, the absorbent binder component can be made
by combining a first aqueous monomer solution including a reducing
polymerization initiator with a second aqueous monomer solution
including an oxidizing polymerization initiator wherein the initiators
react to form a binder component. The polymerization of the monomer
solutions to form an absorbent binder component may be carried out
in about 100 minutes or less. The first aqueous monomer solution
includes a monoethylenically unsaturated monomer such as a carboxylic
acid salt, a sulphonic acid salt, a phosphoric acid salt or a combination
thereof and an ethylenically unsaturated monomer including an acrylate
or a methacrylate that contains an alkoxysilane functionality. The
second aqueous monomer solution includes a monoethylenically unsaturated
monomer such as a carboxylic acid salt, a sulphonic acid salt, a
phosphoric acid salt or a combination thereof. Crosslinking of the
resulting binder component may be induced by concentrating the combined
monomer solutions through the removal of water to promote condensation
of silanols generated by the hydrolysis of the alkoxysilanes.
[0022] In another embodiment, the absorbent binder component may
be made by combining a first aqueous solution including a reducing
polymerization initiator, a monoethylenically unsaturated monomer
such as a carboxylic acid, a sulphonic acid, a phosphoric acid or
a combination thereof and an ethylenically unsaturated monomer including
an acrylate or a methacrylate that contains an alkoxysilane functionality
with a second aqueous solution including an oxidizing polymerization
initiator and a monoethylenically unsaturated monomer such as a
carboxylic acid, a sulphonic acid, a phosphoric acid or a combination
thereof. An amount of a basic material effective to at least partially
neutralize the monoethylenically unsaturated monomer may be added
to the first monomer solution and/or the second monomer solution.
[0023] The flexible absorbent binder component described above
can be prepared using a template polymerization process by which
the monoethyleniclly unsaturated polymer and acrylate or methacrylate
ester are polymerized in the presence of a pre-formed template polymer,
which is the polyolefin glycol and/or polyolefin oxide. The polymerization
can be carried out by reacting two different monoethylenically unsaturated
monomers, one of which contains an alkoxysilane functionality. The
polymerization may be induced by heat, radiation, redox chemical
reactions, and other techniques. Suitable radiation initiators include
without limitation ultraviolet, microwave, and electron beam radiation.
The initiator generates free radicals to cause copolymerization
of the monomers. In one embodiment, the polymerization reaction
is carried out in an organic solvent such as ethanol. The polymerization
may also occur in an aqueous solution, or in a combined aqueous
and organic solvent.
[0024] The polyolefin glycol and/or oxide may or may not be graft
polymerized onto the acrylate or methacrylate units during the polymerization
process. The flexible absorbent binder component may contain the
polyolefin glycol and/or oxide as a separate component, or as part
of the copolymer, or a combination of both.
[0025] The flexible absorbent binder component has latent moisture-induced
crosslinking capability due to the alkoxysilane functionality. The
absorbent binder desiccant composition may thus be applied, in a
flowable state, to a substrate or other end use application. Moisture-induced
crosslinking may be accomplished through hydrolysis of the alkoxysilane
and subsequent condensation upon removal of the solvent from the
substrate, either by evaporation of the solvent from the substrate
or using any other effective technique. Alternatively, the hydrolysis
of the alkoxysilane and subsequent condensation may occur after
solvent removal by exposure of the coating to moisture in ambient
air.
[0026] The desiccant component of the absorbent binder desiccant
composition may be any suitable desiccant. Suitable desiccants include
compounds which absorb water and compounds which reversibly bond
with water. To qualify as a desiccant, the compound must have sufficient
affinity for water to render it capable of absorbing moisture from
the surrounding atmosphere. Suitable desiccants include anhydrous
salts which absorb water or moisture and form a stable hydrated
salt. Other suitable desiccants include capillary desiccants which
rely on fine capillaries between adjacent desiccant particles to
absorb moisture.
[0027] The absorbent binder component may also have desiccant properties.
For purposes of this document, the term "desiccant component"
refers to a separate component which is added to the absorbent binder
component, and does not refer to the absorbent binder component
itself.
[0028] The desiccant component is typically mixed with the absorbent
binder component before the latter is applied to a substrate or
crosslinked. The resulting absorbent binder desiccant composition
may be applied to any substrate useful in desiccant packaging, including
plastic or paper films, fibrous nonwoven fabrics, glass, metal or
the like. After application to a substrate, the absorbent binder
component can be crosslinked, resulting in the absorbent binder
desiccant structure of the invention, securely bound to the substrate.
Alternatively, the absorbent binder component need not be crosslinked,
and the absorbent binder desiccant composition may remain bound
to the substrate.
[0029] With the foregoing in mind, it is a feature and advantage
of the invention to provide an absorbent binder desiccant composition
for easy application to a substrate, a crosslinked absorbent binder
desiccant structure combined with and bound to a substrate, and
an article embodying the latter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 illustrates a bottle, such as a medicine dropper,
embodying the absorbent binder desiccant structure of the invention.
[0031] FIG. 2 illustrates a metal container embodying the absorbent
binder desiccant structure of the invention.
[0032] FIG. 3 illustrates a metal or plastic container embodying
the absorbent binder desiccant structure of the invention.
[0033] FIG. 4 illustrates a cup-like container of metal, plastic
or foam, embodying the absorbent binder desiccant composition of
the invention.
[0034] FIGS. 5 and 6 are plots illustrating the water intake properties
of absorbent binder desiccant structures of the invention, at 20.degree.
C., at 92% and 50% relative humidity, respectively.
DEFINITIONS
[0035] Within the context of this specification, each term or phrase
below will include the following meaning or meanings.
[0036] "Absorbent binder desiccant composition" refers
to a composition including an absorbent binder component and a desiccant
component prior to crosslinking of the absorbent binder component.
[0037] "Absorbent binder desiccant structure" refers
to a composition including an absorbent binder component and a desiccant
component after crosslinking of the absorbent binder component.
[0038] "Binder" includes materials which are capable
of attaching themselves to a substrate or are capable of attaching
other substances to a substrate.
[0039] "Desiccant component" is a substance (desiccant)
capable of absorbing moisture from a surrounding atmosphere. Desiccants
differ from conventional absorbent and superabsorbent materials
in that desiccants absorb water or water vapor in capillary channels
or via chemical bonding to water, such that the absorption results
in no appreciable increase in the volume of the desiccant.
[0040] "Fluid" refers to a substance in the form of a
liquid or gas at room temperature and atmospheric pressure.
[0041] "High density polyethylene (HDPE)" refers to a
polyethylene having a density of about 0.95 g/cm.sup.3 or greater.
[0042] "Knife over roll coating" refers to a process
in which a knife is positioned, with a specified gap, above a substrate
that is moving beneath the knife on a moving roll. In this manner,
the knife spreads a specified thickness of coating material onto
the substrate.
[0043] "Layer" when used in the singular can have the
dual meaning of a single element or a plurality of elements.
[0044] "Linear low density polyethylene (LLDPE)" refers
to polymers of ethylene and higher alpha-olefin comonomers such
as C.sub.3-C.sub.12 comonomers, and combinations thereof, having
a density of about 0.900 to 0.935 g/cm.sup.3.
[0045] "Low density polyethylene (LDPE)" refers to a
polyethylene having a density between about 0.91 and about 0.925
g,/cm.sup.3.
[0046] "Modifying agent" refers to a substance that may
be added to a composition to modify the physical properties of the
composition, such as the color or texture of the composition.
[0047] "Monomer(s)" as used herein includes monomers,
oligomers, polymers, mixtures of monomers, oligomers and/or polymers,
and any reactive chemical species which are capable of copolymerization
with monoethylenically unsaturated carboxylic, sulphonic or phosphonic
acid or salts thereof.
[0048] "Nonwoven" or "nonwoven web" refers
to materials and webs or material having a structure of individual
fibers or filaments which are interlaid, but not in an identifiable
manner as in a knitted fabric. The terms "fiber" and "filament"
are used interchangeably. Nonwoven fabrics or webs have been formed
from many processes such as, for example, meltblowing processes,
spunbonding processes, air laying processes, and bonded carded web
processes. The basis weight of nonwoven fabrics is usually expressed
in ounces of material per square yard (osy) or grams per square
meter (gsm) and the fiber diameters are usually expressed in microns.
(Note that to convert from osy to gsm, multiply osy by 33.91.)
[0049] "Roll printing" or "roll coating" refers
to a process in which the application of a deposited material, generally
as a paste, onto a substrate is carried out by transferring the
deposited material from a roll onto the substrate in a more or less
uniform layer using one or more rolls, which may be engraved, and
a pool cylinder. A doctor blade is used to scrape any excess deposited
material from the rolls or substrate. The doctor blade may be flat
or have a patterned edge such as slots or ridges.
[0050] "Rotary screen printing" or "rotary screen
coating" refers to a process that is a combination of roll
printing or coating and screen printing or coating.
[0051] "Screen printing" or "screen coating"
refers to a method of applying a deposited material by forcing the
material to be deposited through a screen that may have uniform
openings or patterned openings.
[0052] "Stranded composites" refer to sheets of material
to which strands of an elastomeric material are adhered to create
an elastomeric composite.
[0053] "Superabsorbent" refers to a water-swellable,
water-insoluble organic or inorganic material capable, under the
most favorable conditions, of absorbing at least about 10 times
its own weight, or at least about 15 times its own weight, or at
least about 20 times its own weight, or at least about 25 times
its own weight in an aqueous solution containing 0.9 weight percent
sodium chloride. The superabsorbent materials can be natural, synthetic,
and modified natural polymers and materials. Superabsorbent materials
differ from desiccant components (desiccants) in that absorbency
is typically driven by osmotic pressure resulting in incorporation
of water without chemical bonds, and accompanied by a substantial
increase in volume of the superabsorbent material.
[0054] "Ultra low density polyethylene (ULDPE)" refers
to polymers of ethylene and higher alpha-olefin comonomers such
as C.sub.3-C.sub.12 comonomers, and combinations thereof, having
a density of about 0.860 to less than 0.900 g/cm.sup.3.
[0055] "Unit" or "polymer unit" refers to a
monomer or polymer portion of a copolymer molecule or blend component
that includes a different molecular structure, compared to another
portion of the copolymer or blend component.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0056] The present invention is directed to an absorbent binder
desiccant composition that includes an absorbent binder (hydrophilic
polymer) component having the capability of post-application, moisture-induced
crosslinking and a desiccant component. The present invention further
includes an absorbent binder desiccant structure formed by the crosslinking
reaction. The present invention further includes a method of making
and applying such an absorbent binder desiccant composition, and
articles which utilize the absorbent binder desiccant composition
and structure. The absorbent binder desiccant composition and structure
can provide fluid retention properties in addition to adhesive properties.
The absorbent binder desiccant composition and structure are particularly
suitable for use in absorbent packaging applications where humidity
reduction is important.
[0057] The absorbent binder desiccant composition includes the
absorbent binder component and desiccant component in dry weight
ratios of about 100:0 to about 1:10 suitably about 100:1 to about
1:10 suitably about 50:1 to about 1:5 particularly about 10:1
to about 1:3. The weight ratio of absorbent binder to desiccant
may vary depending on the types of absorbent binder and desiccant
used, the specific application, the amount and duration of the humidity
reduction that is needed, and the temperature of the environment.
Because the absorbent binder component may itself exhibit desiccant
properties, the additional desiccant component may not be required
in some applications The absorbent binder component provides a water-soluble
ionic polymer capable of sufficient spontaneous crosslinking within
about 10 minutes, at a temperature of about 120.degree. C. or less,
to reach an absorbent capacity of at least one gram of fluid per
gram of absorbent binder component, suitably at least three grams
of fluid per gram of absorbent binder component, using the centrifuge
retention capacity test described herein. The term "spontaneous"
crosslinking refers to crosslinking which occurs without radiation,
catalysis, or any other inducement other than the specified temperature
of about 120.degree. C. or less, suitably about 100.degree. C. or
less. Eliminating the need for radiative crosslinking provides a
significant processing advantage. The crosslinking at temperatures
of about 120.degree. C. or less, suitably about 100.degree. C. or
less, permits the absorbent binder desiccant composition to be applied
to a substrate such as an absorbent article, and then crosslinked
without degrading or damaging the substrate. The crosslinking occurs
within about 10 minutes, suitably within about 8 minutes, particularly
Within about 6 minutes provides an efficient, commercially feasible,
cost-effective crosslinking process. The ionic polymer may bear
a positive charge, a negative charge, or a combination of both,
and should have an ionic unit content of about 15 mole percent or
greater. The ionic polymer may include a variety of monomer units
described above, and suitably contains a carboxyl group-containing
unit or a quaternary ammonium-containing unit.
[0058] The absorbent binder component includes at least 15 mass
percent monoethylenically unsaturated carboxylic, sulphonic or phosphoric
acid or salts thereof and an acrylate or methacrylate ester that
contains an alkoxysilane functionality which, upon exposure to water,
forms a silanol functional group which condenses to form a crosslinked
polymer.
[0059] Suitable monoethylenically unsaturated monomers that may
be included in the absorbent binder component include carboxyl group-containing
monomers: monoethylenically unsaturated mono or poly-carboxylic
acids, such as (meth)acrylic acid (meaning acrylic acid or methacrylic
acid; similar notations are used hereinafter), maleic acid, fumaric
acid, crotonic acid, sorbic acid, itaconic acid, and cinnamic acid;
[0060] Carboxylic acid anhydride group-containing monomers: monoethylenically
unsaturated polycarboxylic acid anhydrides (such as maleic anhydride);
[0061] Carboxylic acid salt-containing monomers: water-soluble
salts (alkali metal salts, ammonium salts, amine salts, etc.) of
monoethylenically unsaturated mono- or poly-carboxylic acids (such
as sodium (meth)acrylate, trimethylamine (meth)acrylate, triethanolamine
(meth)acrylate), sodium maleate, methylamine maleate;
[0062] Sulfonic acid group-containing monomers: aliphatic or aromatic
vinyl sulfonic acids (such as vinylsulfonic acid, allyl sulfonic
acid, vinyltoluenesulfonic acid, stryrene sulfonic acid), (meth)acrylic
sulfonic acids [such as sulfopropyl (meth)acrylate, 2-hydroxy-3-(meth)acryloxy
propyl sulfonic acid];
[0063] Sulfonic acid salt group-containing monomers: alkali metal
salts, ammonium salts, amine salts of sulfonic acid group containing
monomers as mentioned above;
[0064] Quaternary ammonium salts; and/or
[0065] Amide group-containing monomers: vinylformamide, (meth)acrylamide,
N-alkyl (meth)acrylamides (such as N-methylacrylamide, N-hexylacrylamide),
N,N-dialkyl (meth)acryl amides (such as N,N-dimethylacrylamide,
N,N-di-n-propylacrylamide), N-hydroxyalkyl (meth)acrylamides [such
as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide],
N,N-dihydroxyalkyl (meth)acrylamides [such as N,N-dihydroxyethyl
(meth)acrylamide], vinyl lactams (such as N-vinylpyrrolidone).
[0066] Suitably, the amount of monoethylenically unsaturated monomer(s)
relative to the weight of the absorbent binder component may range
from about 15 to about 99.9 weight percent. Typically, the monoethylenically
unsaturated monomer levels may be between about 25% and about 90%
of the weight of the absorbent binder component; particularly between
about 30% and about 80% of the weight of the absorbent binder component;
or between about 50% and about 70% of the weight of the absorbent
binder component for some intended uses.
[0067] Organic monomers capable of co-polymerization with monoethylenically
unsaturated monomers, which monomers contain a trialkoxy silane
functional group or a moiety that reacts with water to form a silanol
group, are useful in the practice of this invention. The trialkoxy
silane functional group has the following structure: 1
[0068] wherein R.sub.1 R.sub.2 and R.sub.3 are alkyl groups independently
having from 1 to 6 carbon atoms. The term "monomer(s)"
as used herein includes monomers, oligomers, polymers, mixtures
of monomers, oligomers and/or polymers, and any other reactive chemical
species which is capable of co-polymerization with monoethylenically
unsaturated carboxylic, sulphonic or phosphoric acid or salts thereof,
quaternary ammonium salts, or other monomers. Ethylenically unsaturated
monomers containing a trialkoxy silane functional group are appropriate
for this invention and are desired. Desired ethylenically unsaturated
monomers include acrylates and methacrylates. A particularly desirable
ethylenically unsaturated monomer containing a trialkoxy silane
functional group is methacryloxypropyl trimethoxy silane, commercially
available from Dow Corning, having offices in Midland, Mich., under
the trade designation Z-6030 Silane. Other suitable ethylenically
unsaturated monomers containing a trialkoxy silane functional group
include, but are not limited to, methacryloxyethyl trimethoxy silane,
methacryloxypropyl triethoxy silane, methacryloxypropyl tripropoxy
silane, acryloxypropylmethyl dimethoxy silane, 3-acryloxypropyl
trimethoxy silane, 3-methacryloxypropylmethyl diethoxy silane, 3-methacryloxypropylmethyl
dimethoxy silane, and 3-methacryloxypropyl tris(methoxyethoxy) silane.
However, it is contemplated that a wide range of vinyl and acrylic
monomers having trialkoxy silane functional groups or a moiety that
reacts easily with water to form a silanol group, such as a chlorosilane
or an acetoxysilane, provide the desired effects are effective monomers
for copolymerization in accordance with the present invention.
[0069] In addition to monomers capable of co-polymerization that
contain a trialkoxy silane functional group, it is also feasible
to use a monomer capable of co-polymerization that can subsequently
be reacted with a compound containing a trialkoxy silane functional
group or a moiety that reacts with water to form a silanol group.
Such a monomer may contain, but is not limited to, an amine or an
alcohol. An amine group incorporated into the co-polymer may subsequently
be reacted with, for example, but not limited to, (3-chloropropyl)trimethoxysilane.
An alcohol group incorporated into the co-polymer may subsequently
be reacted with, for example, but not limited to, tetramethoxysilane.
[0070] The amount of organic monomer having trialkoxy silane functional
groups or silanol-forming functional groups relative to the weight
of the absorbent binder component may range from about 0.1 to about
15 weight percent. Suitably, the amount of monomer should exceed
0.1 weight percent in order provide sufficient crosslinking upon
exposure to moisture. Typically, the monomer addition levels are
between about 0.1% and about 20% of the weight of the absorbent
binder component; particularly, between about 1.0% and about 10%
of the weight of the absorbent binder component; or between about
1.5% and about 5.5% of the weight of the absorbent binder component
for some intended uses.
[0071] Optionally, the absorbent binder component may include long
chain, hydrophilic monoethylenically unsaturated esters, such as
poly(ethylene glycol) methacrylate having from 1 to 13 ethylene
glycol units. The hydrophilic monoethylenically unsaturated esters
have the following structure: 2
[0072] The amount of monoethylenically unsaturated hydrophilic
esters relative to the weight of the absorbent binder component
thereof may range from about 0 to about 75 weight percent of monomer
to the weight of the absorbent binder component. Typically, the
monomer addition levels are between about 10% and about 60% of the
weight of the absorbent binder component; particularly, between
about 20% and about 50% of the weight of the absorbent binder component;
or between about 30% and about 40% of the weight of the absorbent
binder component for some intended uses.
[0073] The absorbent binder component may be prepared by adding
a solution of the above monomers to an initiator solution, at a
suitable temperature to generate free radicals, for example between
about 50 and about 90 degrees Celsius. An initiator solution may
be prepared by dissolving an initiator in a solvent. Possible solvents
include, but are not limited to, alcohols such as ethanol. A variety
of initiators may be useful in the practice of this invention. The
polymerization initiator may be activated using a variety of methods
including, but not limited to, thermal energy, ultraviolet light,
redox chemical reactions. A suitable class of initiators are organic
peroxides and azo compounds, with benzoyl peroxide and azobisisobutyronitrile
(AIBN) as examples.
[0074] Compounds containing an O--O, S--S, or N.dbd.N bond may
be used as thermal initiators. Compounds containing O--O bonds;
i.e., peroxides, are commonly used as initiators for polymerization.
Such commonly used peroxide initiators include: alkyl, dialkyl,
diaryl and arylalkyl peroxides such as cumyl peroxide, t-butyl peroxide,
di-t-butyl peroxide, dicumyl peroxide, cumyl butyl peroxide, 11-di-t-butyl
peroxy-355-trimethylcyclohexane, 25-dimethyl-25-di(t-butylperoxy)hexa-
ne, 25-dimethyl-25-bis(t-butylperoxy)hexyne-3 and bis(a-t-butyl
peroxyisopropylbenzene); acyl peroxides such as acetyl peroxides
and benzoyl peroxides; hydroperoxides such as cumyl hydroperoxide,
t-butyl hydroperoxide, p-methane hydroperoxide, pinane hydroperoxide
and cumene hydroperoxide; peresters or peroxyesters such as t-butyl
peroxypivalate, t-butyl peroctoate, t-butyl perbenzoate, 25-dimethylhexyl-25-di(perbenz-
oate) and t-butyl di(perphthalate); alkylsulfonyl peroxides; dialkyl
peroxymonocarbonates; dialkyl peroxydicarbonates; diperoxyketals;
ketone peroxides such as cyclohexanone peroxide and methyl ethyl
ketone peroxide. Additionally, azo compounds such as 22'-azobisisobutyronitrile
abbreviated as AIBN, 22'-azobis(24-dimethylpentanenitrile) and
11'-azobis(cyclohexanecarbonitrile) may be used as the initiator.
[0075] The method for making the absorbent binder component can
be carried out in a single step wherein polymerization and neutralization
of the absorbent binder component is achieved. The polymerization/neutralization
reaction is conducted in an aqueous medium thereby eliminating the
need for organic solvents.
[0076] More specifically, the absorbent binder component can be
made by combining a first aqueous monomer solution including a reducing
polymerization initiator with a second aqueous monomer solution
including an oxidizing polymerization initiator, wherein the initiators
react to form the absorbent binder component. The first aqueous
monomer solution further includes a monoethylenically unsaturated
monomer and an ethylenically unsaturated monomer that contains an
alkoxysilane functionality. The second aqueous monomer solution
includes a monoethylenically unsaturated monomer. Suitably, the
absorbent binder component is formed in about 100 minutes or less,
or 60 minutes or less, desirably in about 30 minutes or less, or
about 15 minutes or less, or in one embodiment about 10 minutes
or less. The first and second aqueous monomer solutions may include
any of the monoethylenically unsaturated monomers listed above.
[0077] In one embodiment, the first and/or second aqueous monomer
solution may include a monoethylenically unsaturated monomer such
as a carboxylic acid salt, a sulphonic acid salt, a phosphoric acid
salt, a quaternary ammonium salt, or a combination thereof.
[0078] In another embodiment, the first and/or the second aqueous
solution may include a monoethylenically unsaturated monomer such
as a carboxylic acid, a sulphonic acid, a phosphoric acid or a combination
thereof that may be at least partially neutralized or converted
to the salt form in situ. In this embodiment, an amount of a basic
material, such as sodium hydroxide, effective to at least partially
neutralize the monoethylenically unsaturated monomer may be included
in the first and/or second aqueous solution. Alternatively, the
monoethylenically unsaturated monomer may be added to a basic solution
such as, for example, a sodium hydroxide solution to form an aqueous
monomer solution. Desirably, the monoethylenically unsaturated monomer
in the first and/or second aqueous monomer solution is neutralized
to provide a solution pH of about 5 to about 8 prior to polymerization
with the ethylenically unsaturated monomer. One monoethylenically
unsaturated monomer suitable for use in this embodiment includes
acrylic acid.
[0079] Suitably, the pH of the first and/or second aqueous monomer
solution is adjusted to about 6.5 to about 7.0. The pH of the first
aqueous solution may be adjusted prior to the addition of the ethylenically
unsaturated monomer. Desirably, the pH of the first aqueous monomer
solution is adjusted prior to the addition of the reducing polymerization
initiator. The pH of the second aqueous solution may be adjusted
prior to the addition of the oxidizing polymerization initiator.
Alternatively, the pH of the combined first and second aqueous monomer
solutions may be adjusted to about 6.5 to about 7.0.
[0080] The first and second aqueous monomer solutions may include
the monoethylenically unsaturated monomer in any suitable proportion
to form an absorbent binder component including about 15 to about
99.9 composition weight percent monoethylenically unsaturated carboxylic,
sulphonic or phosphoric acid or salt thereof, quaternary ammonium
salt, or the like. Typically, the levels of monoethylenically unsaturated
carboxylic, sulphonic or phosphoric acid or salts thereof in the
absorbent binder component may be between about 25 and about 90
weight percent; particularly between about 30 and about 80 weight
percent; or between about 50 and about 70 weight percent for some
intended uses.
[0081] The first aqueous monomer solution also includes an organic
monomer capable of co-polymerization with monoethylenically unsaturated
carboxylic, sulphonic or phosphoric acid or salts thereof, or quaternary
ammonium salts. The above-described organic monomers that contain
a trialkoxy silane functional group or a moiety that reacts with
water to form a silanol group, are useful in the practice of this
invention. The above-described monomers capable of copolymerization
that can subsequently be reacted with a compound containing a trialkoxysilane
group or a moiety that reacts with water to form a silanol group,
are also useful.
[0082] The first aqueous monomer solution may include the ethylenically
unsaturated monomer containing a trialkoxy silane functional group
in any suitable proportion to provide an absorbent binder composition
including about 0.1 to about 20 composition weight percent of this
monomer. Suitably, the amount of ethylenically unsaturated monomer
containing a trialkoxy silane functional group should exceed 0.1
composition weight percent in order to provide sufficient crosslinking
upon removal of water. Typically, the monomer addition levels are
between about 0.1 and about 15 composition weight percent; particularly,
between about 1.0 and about 10 composition weight percent; or between
about 1.5 and about 5.5 composition weight percent for some intended
uses.
[0083] In one embodiment, a surfactant may be added to the first
and/or second aqueous monomer solution to disperse the ethylenically
unsaturated monomer. One surfactant suitable for use in the present
invention is a dioctyl sodium sulfosuccinate available under the
trademark AEROSOL OT from Cytec Industries, Inc. of Paterson, N.J.
[0084] The first aqueous monomer solution further includes a reducing
polymerization initiator. Suitable reducing polymerization initiators
include, but are not limited to, ascorbic acid, alkali metal sulfites,
alkali metal bisulfites, ammonium sulfite, ammonium bisulfite, alkali
metal hydrogen sulfite, ferrous metal salts such as ferrous sulfates,
sugars, aldehydes, primary and secondary alcohols, and combinations
thereof. In one embodiment, the reducing polymerization initiator
includes ascorbic acid.
[0085] The second aqueous monomer solution further includes an
oxidizing polymerization initiator. Suitable oxidizing initiators
include, but are not limited to, hydrogen peroxide, alkali metal
persulfates, ammonium persulfate, alkylhydroperoxides, peresters,
diacryl peroxides, silver salts, and combinations thereof. In one
embodiment, the oxidizing polymerization initiator includes hydrogen
peroxide.
[0086] Generally, when the first aqueous monomer solution is combined
with the second aqueous monomer solution the reducing polymerization
initiator reacts with the oxidizing polymerization initiator, e.g.
a redox reaction, thereby initiating a polymerization reaction to
form an absorbent binder component including a monoethylenically
unsaturated monomer and an ethylenically unsaturated monomer that
has post-application, moisture-induced crosslinking capability.
[0087] The desiccant component may be combined with the absorbent
binder component any time prior to crosslinking of the absorbent
binder component, to form the absorbent binder desiccant composition.
Suitable desiccant components include without limitation anhydrous
salts which absorb water or moisture to form a stable hydrated salt,
capillary desiccants which rely on fine capillaries between adjacent
desiccant particles to absorb moisture, and chemical desiccants
which chemically react with water to form stable compounds. Examples
of anhydrous salts include without limitation sodium acetate, calcium
sulfate, zinc chloride, zinc bromide, calcium oxide, and combinations
thereof. Examples of capillary desiccants include without limitation
montmorillonite clay, molecular sieves (e.g., synthetic zeolites),
silica gels, starches and the like.
[0088] The desiccant component can be combined with the absorbent
binder component using any suitable mixing apparatus. One particularly
suitable mixer is a Hobart Mixer Model N-50 manufactured by Hobart
Canada in North York, Ontario.
[0089] The absorbent binder desiccant composition may be applied
to a substrate and subsequently dried to form a cast film. Drying
conditions should be selected to provide for removal of water from
the desiccant component, as well as the absorbent binder component.
Once the absorbent binder desiccant composition is applied to the
substrate, crosslinking can be moisture-induced by hydrolysis and
condensation of alkoxysilanes. For example, crosslinking can be
induced by concentrating the absorbent binder desiccant composition
on the substrate through the removal of the water to promote condensation
of silanols generated by hydrolysis of alkoxysilanes. Typically,
crosslinking begins at a solution concentration above about 30 percent
by weight absorbent binder desiccant composition.
[0090] Alternatively, the absorbent binder desiccant composition
may be applied to a substrate during the manufacturing process of
absorbent packaging. In another embodiment, the absorbent binder
desiccant composition may be applied to a substrate as a coating
by itself, thereby serving as an absorbency additive. In either
of these embodiments, the absorbent binder desiccant composition
is suitably present in any concentration that provides a viscosity
suitable for the application process. The composition may be applied
to the substrate using any suitable application process, including
knife over roll coating, or roll coating, either in a continuous
coverage or a patterned coverage. Printing applications are other
suitable application techniques, including gravure printing, screen,
and jet printing. The absorbent binder desiccant composition may
also be applied to the substrate using a spray application.
[0091] In another embodiment, the absorbent binder desiccant composition
may be prepared using a continuous process wherein the polymerization
and/or neutralization reaction is carried out in a suitable reactor
that conveys the resulting binder composition, upon completion of
the polymerization reaction and addition of the desiccant component,
directly to an apparatus for applying the absorbent binder desiccant
composition onto the substrate. Such a continuous process may be
desirable where conditions, such as high heat, may cause premature
crosslinking of the absorbent binder component that would hinder
application of the absorbent binder desiccant composition onto the
substrate.
[0092] In addition, modifying agents such as compatible polymers,
plasticizers, colorants, and preservatives may be incorporated in
the absorbent binder desiccant composition.
[0093] For some intended uses the absorbent binder desiccant composition
provides very flexible coatings and should therefore have a glass
transition temperature below about 30 degrees Celsius, or below
about 10 degrees Celsius, or below about 5 degrees Celsius, as measured
by Differential Scanning Calorimetry (DSC), and a bending modulus
lower than the substrate to which they are applied. Suitable substrates
to which the absorbent binder desiccant composition may be applied
include, but are not limited to, nonwoven, woven, and knitted fabrics;
cellulosic tissue sheets; plastic films, including polypropylene,
low density polyethylene, high density polyethylene, linear low
density polyethylene, and ultra low density polyethylene; LYCRA
stranded composites; elastomer net composites, metals, and glass.
[0094] In one embodiment, the absorbent binder component of the
absorbent binder desiccant composition includes polyolefin glycol
and/or polyolefin oxide units for enhanced flexibility. This flexible
absorbent binder component includes about 15 to about 99.8% by mass
of monoethylenically unsaturated polymer units, suitably about 25
to about 89.5% by mass, particularly about 30 to about 79% by mass,
or about 50 to about 70% by mass. Suitable monoethylenically unsaturated
polymer units include without limitation monoethylenically unsaturated
carboxylic acid units and salts thereof, monoethylenically unsaturated
sulphonic acid units and salts thereof, and monoethylenically unsaturated
phosphonic acid units and salts thereof, and monoethylenically unsaturated
quaternary ammonium salts. Suitable monoethylenically unsaturated
monomers that can be used to form the monoethylenically unsaturated
polymer units include without limitation any of the monoethylenically
unsaturated monomers described above.
[0095] This flexible absorbent binder component also includes about
0.1 to about 20% by mass of polyacrylate ester units, such as acrylate
and/or methacrylate ester units, that include an alkoxysilane functionality.
The acrylate and/or methacrylate ester units are copolymerized with
the monoethylenically unsaturated monomer units. In particular,
the flexible absorbent binder component may include about 0.5 to
about 15% by mass of the acrylate and/or methacrylate ester units,
for instance about 1.0 to about 10% by mass, for instance about
1.5 to about 5.5% by mass.
[0096] As described above, the alkoxysilane functionality is a
functional group or moiety that reacts with water to form a silanol
group. One suitable alkoxysilane group is the above-described trialkoxy
silane group having the following structure: 3
[0097] wherein R.sub.1 R.sub.2 and R.sub.3 are alkyl groups independently
having from 1 to 6 carbon atoms. Any of the monomers described above,
which contain the trialkoxysilane functional group, are suitable.
[0098] In addition to monomers capable of co-polymerization that
contain a trialkoxy silane functional group, it is also feasible
to use a monomer capable of co-polymerization that can subsequently
be reacted with a compound containing a trialkoxy silane functional
group or a moiety that reacts with water to form a silanol group.
As described above, such a monomer may contain, but is not limited
to, an amine or an alcohol. An amine group incorporated into the
co-polymer may subsequently be reacted with, for example, but not
limited to, (3-chloropropyl)trimethoxysilane. An alcohol group incorporated
into the co-polymer may subsequently be reacted with, for example,
but not limited to, tetramethoxysilane.
[0099] This flexible absorbent binder component also includes about
0.1 to about 75% by mass polyolefin glycol and/or polyolefin oxide
units, suitably about 5 to about 75% by mass, particularly about
10 to about 60% by mass, particularly about 20 to about 50% by mass,
particularly about 30 to about 40% by mass. The polyolefin glycol
or oxide may be a glycol or oxide of an olefin polymer having about
2 to about 4 carbon atoms. Polyethylene glycol, polyethylene oxide,
polypropylene glycol and polypropylene oxide are examples of suitable
polymer units. The polyolefin glycol and/or polyolefin oxide may
include on average about 30 to about 15000 glycol and/or oxide
units per molecule. The weight average molecular weight of polyolefin
glycol units may range from about 200 to about 8000. When polyolefin
oxide units are employed, they may have a weight average molecular
weight of about 100000 to about 600000.
[0100] Polyolefin glycols and polyolefin oxides are commercially
available, and are common. To prepare this flexible absorbent binder
component, a pre-formed polyolefin glycol and/or oxide may be dissolved
or dispersed in a reaction vessel which includes an aqueous solvent
or carrier, an organic solvent or carrier such as ethanol, or a
miscible combination of aqueous and organic solvent or carrier.
The monomers used to form the monoethylenically unsaturated polymer
units and the polyacrylate ester units are added to the solution
and polymerized using a template polymerization process in which
the polyolefin glycol or oxide serves as a template polymer. Before
initiation, the polar groups of the monomers, for instance the acid
groups of acrylic acid, are attracted to the polyolefin glycol and/or
polyolefin oxide through hydrogen bonding. The steric alignment
of the monomers, with the polyolefin glycol and/or oxide serving
as backbone, aids in the polymerization and typically increases
the chain length of the polymerizing unit. During the polymerization,
radical polymerizing chains may become attached to the template
polymer, resulting in grafting of polyolefin glycol and/or oxide
to the copolymer being formed. However, this graft polymerization
need not occur. The resulting flexible absorbent binder component
includes the polyolefin glycol and/or oxide attached to, and/or
blended with, the copolymer of the monoethylenically unsaturated
polymer units and the acrylate or methacrylate ester units that
include the alkoxysilane functionality.
[0101] The polymerization may be initiated using a variety of methods,
including without limitation thermal energy, ultraviolet light,
and redox chemical reactions. A solution of the above ingredients
may be added to an initiator solution at a temperature suitable
for generating free radicals, for instance about 50 to about 90.degree.
C. An initiator may be prepared by dissolving an initiator in an
organic or aqueous solvent. A suitable class of initiators are organic
peroxides and azo compounds, with benzoyl peroxide and azobisisobutylnitrile
(ABN) as examples.
[0102] Compounds containing an O--O, S--S, or N.dbd.N bond may
be used as thermal initiators. Any of the above-described thermal
initiators can be used when preparing the flexible absorbent binder
component.
[0103] Alternatively, redox initiation can be used to prepare the
flexible absorbent binder component, as described above. The polyolefin
glycol and/or polyolefin oxide may be added to the first monomer
solution, or the second monomer solution, or both. Surfactants and
other ingredients can also be added, as described above.
[0104] In one embodiment used to prepare the flexible absorbent
binder component, the monoethylenically unsaturated polymer unit
is a cationic polymer. The cationic polymer is advantageous because
it provides a) inherent antimicrobial properties, b) enhanced attraction
and retention into cellulose fibers in a suspension, and c) enhanced
attraction to superabsorbent particles which are negatively charged.
Suitable cationic polymers include those prepared by copolymerizing
a monomer 1) selected from a) acryloyloxyethyl-trialkyl-substituted
ammonium salts, b) acryloyloxypropyl-trialkyl-substituted ammonium
salts, c) acrylamidoethyl-trialkyl-substituted ammonium salts, and
d) acrylamidopropyl-trialkyl-substituted ammonium salts, with a
monomer 2) selected from a) methacryl esters which contain an alkoxysilane
group capable of moisture-induced crosslinking and b) acryl esters
which contain an alkoxysilane group capable of moisture-induced
crosslinking. Other monomers may also be present, for instance,
an acrylic acid or acrylamide. The polymerization is conducted in
the presence of a polyolefin glycol and/or polyolefin oxide as described
above, suitably a polyethylene glycol. The cationic monoethylenically
unsaturated monomer unit and the polyolefin glycol are present in
the amounts described above.
[0105] The cationic monoethylenically unsaturated polymer may be
prepared by a redox initiation process, according to the following
reaction. The cationic copolymer is then combined with the desiccant
component, coated and dried onto a substrate to form the crosslinked
flexible absorbent binder desiccant structure. 4
[0106] Applications where the cationic flexible absorbent binder
desiccant composition is useful include without limitation the coating
of paper and plastic cartons for carrying hot food, the internal
coating of lids in medicine bottles, and the internal coating of
a wide variety of metal, glass and paper containers and packages
to keep their contents dry.
[0107] The flexible absorbent binder desiccant composition may
be applied to a substrate and subsequently dried to form an absorbent
binder desiccant structure (e.g., a film). Once the flexible absorbent
binder desiccant composition is applied to the substrate, crosslinking
can be moisture-induced by hydrolysis and condensation of alkoxysilanes.
For example, crosslinking of the flexible absorbent binder desiccant
composition can be induced by concentrating the flexible absorbent
binder desiccant composition on the substrate through the removal
of the water to promote condensation of silanols generated by hydrolysis
of alkoxysilanes. Typically, crosslinking begins at a solution concentration
of about 30 percent or greater by weight of absorbent binder desiccant
composition. Furthermore, if the substrate has hydroxyl group functionality
on its surface, then the silanols within the binder composition
may react with the hydroxyl groups to form a covalent bond between
the binder and the hydroxyl-containing surface. Non-limiting examples
of substrates with hydroxyl surface functionality include glass,
sand and cellulose. The flexible absorbent binder composition need
not be crosslinked following application to a substrate. The flexible
absorbent binder desiccant composition can be applied to a substrate
using any of the techniques described above.
[0108] In another embodiment, the absorbent binder desiccant composition
can be applied to a release liner and subsequently dried to form
an absorbent binder desiccant structure (e.g., film). The film may
be inserted into a package to provide humidity protection, or may
be joined to a substrate on one or both surfaces.
[0109] Alternatively, the absorbent binder component can be applied
to a substrate or release liner and crosslinked, without adding
the separate desiccant component. The absorbent binder component
may itself serve as a desiccant, and possesses desiccant properties.
The absorbent binder component need not be crosslinked following
application to a substrate.
[0110] FIG. 1 illustrates a bottle 10 which can be a medicine
bottle or other container in which there is a need to minimize the
moisture exposure of the contents. The bottle 10 includes a base
12 a cap 14 and a lid 16 which fits inside the cap. The lid 16
can be formed entirely of an absorbent binder desiccant structure
18 of the invention. Alternatively, the lid 16 may be formed of
paper, plastic or metal foil which is then coated with an absorbent
binder desiccant composition, subsequently crosslinked to form an
absorbent binder desiccant structure (e.g., a film). The absorbent
binder desiccant structure may be of any suitable thickness and
composition required to provide the desired level of moisture vapor
absorption. The precise ingredients and weight ratios of the absorbent
binder desiccant composition, including polymer type, desiccant
type and amounts, may be optimized with this objective in mind.
[0111] FIG. 2 illustrates a food container 20 which can be formed
of metal, plastic or thick paper (e.g., cardboard), and used to
store sugar, salt, coffee, cocoa, or another food which is suitably
maintained in a dry state. The food container 20 includes a body
22 and a lid 24. An absorbent binder desiccant structure 28 is formed
on an entire inner surface 26 of the body 22 of the container 20.
By surrounding the contents of container 20 with absorbent binder
desiccant structure 18 maximum drying of the contents is maintained.
[0112] FIG. 3 illustrates a bread box 30 including a base 32 and
a cover 34. An entire inner surface 36 of cover 34 is coated with
an absorbent binder desiccant structure 38. This bread box 30 is
designed to control humidity, to alleviate molding of bread in a
humid environment. The absorbent binder desiccant structure 38 should
therefore be designed using absorbent binder and desiccant ingredients
and amounts, which merely remove humidity from the air without causing
excessive drying of the bread.
[0113] FIG. 4 illustrates a cup-shaped container 40 which can be
used to store plant food, chemical powders or the like. Container
40 has a cup-shaped body 42 and a snap-on lid 44. An absorbent binder
desiccant structure 48 having the shape of a cup, lines the inner
surface 46 of body 42.
[0114] The above applications for the absorbent binder desiccant
structure are merely exemplary. The absorbent binder desiccant composition
and structure can be used in a wide variety of humidity control
applications. The absorbent binder desiccant composition or structure
can be applied to a substrate before or after crosslinking of the
absorbent binder component, in alternative embodiments of the invention.
EXAMPLES
[0115] An absorbent binder composition was prepared from the following
monomers using the following conditions.
[0116] Two monomer solutions were prepared separately. Solution
No. 1 was prepared as follows. To 48.4 grams of a 80% solution of
(2-acryloylethyl) trimethyl ammonium chloride (0.20 moles) was added
21.3 grams of deionized water, and 6.0 grams of PEG 200 (molecular
weight 200). Then, 0.18 grams (1.02.times.10.sup.-3 moles) of ascorbic
acid was added to the solution. This mixture was stirred with a
magnetic stir bar at about 60 rpm in a bath of water at about 23.degree.
C. until the ascorbic acid was dissolved and the mixture cooled
to 23.degree. C.
[0117] Solution No. 2 was prepared in the following manner. 48.4
grams of a 80% solution of (2-acryloylethyl) trimethyl ammonium
chloride (0.20 moles) was added 21.3 grams of deionized water, 6.0
grams of PEG 200 (molecular weight 200), 0.37 ml of 30% aqueous
hydrogen peroxide and 1.0 ml (5.42.times.10.sup.-3 moles) of 3-(trimethoxysilyl)propyl
methacrylate. This mixture was stirred with a magnetic stir bar
at about 60 rpm in a bath of water at about 23.degree. C. to provide
a clear solution cooled to 23.degree. C.
[0118] Solution No. 1 was placed into a water bath at 40.degree.
C. and Solution No. 2 was added to while stirring with a magnetic
stir bar. A thermocouple was used to monitor the temperature and
observe the reaction exotherm. The temperature of the water bath
was raised to 60.degree. C. over a time period of 15 minutes. 18
minutes after the solutions were combined, at a bath temperature
of 60.degree. C., an exotherm was evident by a rise in temperature
to 72.degree. C. over a period of 4 minutes and the solution became
highly viscous. The reaction beaker was removed from the water bath
after 60 minutes from the addition of Solution No. 2 to Solution
No. 1. 150 grams of deionized water was added to reduce the polymer
concentration to about 31%.
[0119] To 50 grams of the 31% polymer solution was added 2.5 ml
of a 0.2% solution of hydrochloric acid. This solution was poured
into two weighing dishes (100 cm.sup.2 area) and the solution was
dried for two days in the laboratory hood. The resultant film was
very soft and flexible and slightly tacky. A portion of the film
was cut off (0.5 gram) and soaked in 20 ml of 0.9% saline for 60
minutes. The film swelled and absorbed about 8000% of its dry weight
of the saline solution.
Example 1
[0120] Silica gel, available from Aldrich Chemical Co., was crushed
to a powder with a mortar and pestel. 3.5 grams of the crushed silica
gel was mixed with 35 grams of the aqueous absorbent binder composition.
Dissolution was aided by adding and mixing one gram of 0.25% by
weight aqueous hydrochloric acid. Because the aqueous absorbent
binder composition initially contained 20% by weight of absorbent
binder component, the resulting absorbent binder desiccant composition
contained the absorbent binder component and desiccant component
in a weight ratio of 2:1. The absorbent binder desiccant composition
was spread over a 5-inch by 6-inch area on a polypropylene spunbond
fabric having a basis weight of 33 grams/m.sup.2. A second piece
of the same spunbond fabric was placed on top of the absorbent binder
desiccant composition to create a sandwich structure. The sandwich
structure was dried at 80.degree. C. for one hour, crosslinking
the absorbent binder desiccant composition to form an absorbent
binder desiccant structure. The dried sandwich structure had a thickness
of 1.7 mm.
Example 2
[0121] The same silica gel, available from Aldrich Chemical Co.
and crushed to a powder, was added at 12 grams of silica gel into
30 grams of the same aqueous absorbent binder composition and 1
gram of 0.25% aqueous hydrochloric acid. Because the aqueous absorbent
binder composition initially contained 20% by weight absorbent binder,
the resulting absorbent binder desiccant composition contained the
absorbent binder component and desiccant component in a weight ratio
of 1:2. The absorbent binder desiccant composition was spread over
a 7-inch by 7-inch area on a polypropylene spunbond fabric having
a basis weight of 33 grams/m.sup.2 . A second piece of the same
spunbond fabric was placed on top of the absorbent binder desiccant
composition to create a sandwich structure. The sandwich structure
was dried at 80.degree. C. for one hour, crosslinking the absorbent
binder desiccant composition to form an absorbent binder desiccant
structure. The dried sandwich structure had a thickness of 3.0 mm.
Example 3 (Control)
[0122] Only the absorbent binder component was spread over a 4-inch
by 4-inch area on a polypropylene spunbond fabric having a basis
weight of 33 grams/m.sup.2. A second piece of the same spunbond
fabric was placed on top of the absorbent binder component to create
a sandwich structure. The sandwich structure was dried at 80.degree.
C. for one hour, crosslinking the absorbent binder component. The
dried sandwich structure had a thickness of 2 mm.
Example 4 (Control)
[0123] The same crushed silica gel, without the aqueous absorbent
binder composition, was spread over a 3.14 square inch area aluminum
weighing dish, 2 inches in diameter. The silica gel was dried at
80.degree. for one hour, dehydrating the silica gel. The silica
gel layer had a thickness of about 0.8 mm.
[0124] For each of Examples 1-4 the dry weight of the crosslinked
absorbent binder desiccant structure, crosslinked absorbent binder
component (without the desiccant component) or desiccant component
(without the absorbent binder component) was determined by subtracting
the weight of the spunbond fabric layers or weighing dish from the
weight of the dried sandwich structure or loaded weighing dish.
Samples of each sandwich structure or loaded weighing dish were
placed in a controlled environment at 20.degree. C. and 90% relative
humidity for 24 hours. The samples were weighed at periodic intervals
to determine their weight gain. The entire weight gain was attributed
to moisture absorption by the absorbent binder component, and/or
desiccant component or both, in each sample. The weight gains at
each interval, as a percentage of the dry weight of the absorbent
binder component and/or desiccant component, are plotted in FIG.
5.
[0125] Additional samples of each sandwich structure or loaded
weighing dish were placed in a controlled environment at 20.degree.
C. and 50% relative humidity for 24 hours. The samples were weighed
at periodic intervals to determine their weight gain. The weight
gains at each interval, as a percentage of the dry weight of the
absorbent binder component, desiccant component or both, are plotted
in FIG. 6.
[0126] As shown in FIGS. 5 and 6 the absorbent binder desiccant
structures (formed from the combinations of absorbent binder and
desiccant) exhibited adequate desiccant properties. The absorbent
binder desiccant structures have the added advantages of serving
both as a binder and a containment medium for the particulate desiccant
components.
TEST METHOD FOR DETERMINING ABSORBENT CAPACITY
[0127] As used herein, the Centrifugal Retention Capacity (CRC)
is a measure of the absorbent capacity of the superabsorbent material
retained after being subjected to centrifugation under controlled
conditions. The CRC can be measured by placing a sample of the material
to be tested into a water-permeable bag which will contain the sample
while allowing the test solution (0.9 percent NaCl solution) to
be freely absorbed by the sample. A heat-sealable tea bag material
(available from Dexter Nonwovens of Windsor Locks, Conn., U.S.A.,
as item #1234T) works well for most applications. The bag is formed
by folding a 5-inch by 3-inch sample of the bag material in half
and heat sealing two of the open edges to form a 2.5-inch by 3-inch
rectangular pouch. The heat seals should be about 0.25 inch inside
the edge of the material. After the sample is placed in the pouch,
the remaining open edge of the pouch is also heat-sealed. Empty
bags are also made to be tested with the sample bags as controls.
A sample size is chosen such that the teabag does not restrict the
swelling of the material, generally with dimensions smaller than
the sealed bag area (about 2-inch by 2.5-inch). Three sample bags
are tested for each material.
[0128] The sealed bags are submerged in a pan of 0.9 percent NaCl
solution. After wetting, the samples remain in the solution for
60 minutes, at which time they are removed from the solution and
temporarily laid on a non-absorbent flat surface.
[0129] The wet bags are then placed into the basket of a suitable
centrifuge capable of subjecting the samples to a g-force of 350.
(A suitable centrifuge is a Heraeus LABOFUGE 400 Heraeus Instruments,
part number 75008157 available from Heraeus Infosystems GmbH, Hanau,
Germany). The bags are centrifuged at a target of 1600 rpm, but
within the range of 1500-1900 rpm, for 3 minutes (target g-force
of 350). The bags are removed and weighed. The amount of fluid absorbed
and retained by the material, taking into account the fluid retained
by the bag material alone, is the Centrifugal Retention Capacity
of the material, expressed as grams of fluid per gram of material.
[0130] While in the foregoing specification this invention has
been described in relation to certain preferred embodiments thereof,
and many details have been set forth for purpose of illustration,
it will be apparent to those skilled in the art that the invention
is susceptible to additional embodiments and that certain of the
details described herein can be varied considerably without departing
from the basic principles of the invention. |