U.S. patent application number 11/870828 was filed with the patent office on 2009-04-16 for hydrophilic porous substrates.
Invention is credited to Clinton P. WALLER, JR., Douglas E. Weiss.
Application Number | 20090098359 11/870828 |
Document ID | / |
Family ID | 40070685 |
Filed Date | 2009-04-16 |
United States Patent
Application |
20090098359 |
Kind Code |
A1 |
WALLER, JR.; Clinton P. ; et
al. |
April 16, 2009 |
HYDROPHILIC POROUS SUBSTRATES
Abstract
Hydrophilic porous substrates, methods of making hydrophilic
porous substrates from hydrophobic polymers are disclosed.
Inventors: |
WALLER, JR.; Clinton P.;
(White Bear Lake, MN) ; Weiss; Douglas E.; (Golden
Valley, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
40070685 |
Appl. No.: |
11/870828 |
Filed: |
October 11, 2007 |
Current U.S.
Class: |
428/308.4 ;
427/496; 427/501 |
Current CPC
Class: |
Y10T 428/249958
20150401; B32B 2307/306 20130101; B32B 5/24 20130101; B01D 71/38
20130101; B32B 5/022 20130101; B32B 2307/728 20130101; B32B 27/12
20130101; Y10T 442/60 20150401; B32B 2260/046 20130101; B32B
2260/021 20130101; C08J 7/18 20130101; C08J 2323/10 20130101 |
Class at
Publication: |
428/308.4 ;
427/496; 427/501 |
International
Class: |
B32B 5/14 20060101
B32B005/14; C08F 2/50 20060101 C08F002/50 |
Claims
1. A method of making a functionalized substrate, the method
comprises the steps of: 1) providing a porous base substrate having
interstitial and outer surfaces; 2) imbibing the porous base
substrate with a first solution to form an imbibed porous base
substrate, the first solution comprising (a) at least one grafting
monomer having an acrylate group and a photoinitiator group and (b)
one or more monomers having at least one acrylate group and at
least one additional ethylenically unsaturated, free-radically
polymerizable group; and optionally (c) one or more additional
monomers having at least one ethylenically unsaturated,
free-radically polymerizable group and a hydrophilic group; wherein
at least one of (b) or (c) monomers are hydrophilic. 3) exposing
the imbibed porous base substrate to a controlled amount of
electron beam radiation so as to form a first functionalized
substrate comprising grafted photoinitiator group attached to the
surfaces of the porous base substrate, and 4) exposing the porous
base substrate comprising grafted photoinitiator groups to a
controlled amount of UV radiation to crosslink the remaining
ethylenically unsaturated, free-radically polymerizable groups.
2. The method of claim 1, wherein the porous base substrate is
microporous.
3. The method of claim 1, wherein the porous base substrate is
selected from a porous membrane, porous non-woven web, or porous
fiber.
4. The method of claim 1, wherein the monomer (b) comprises a
poly(alkylene oxide) di(meth)acrylate.
5. The method of claim 1 wherein said monomers (b) having two or
more free-radically polymerizable groups comprises a first acrylate
group for grafting to said porous base substrate and a second
methacrylate group for subsequent UV crosslinking.
6. The method of claim 1, wherein said first solution comprises (c)
one or more additional monomers monomer having a free-radically
polymerizable group and a hydrophilic group.
7. The method of claim 2, wherein the microporous base substrate is
formed by a thermally-induced phase separation (TIPS) method.
8. The method of claim 7, wherein the microporous base substrate
comprises propylene polymer membrane formed by a thermally-induced
phase separation (TIPS) method.
9. The method of claim 1, wherein the controlled amount of electron
beam radiation exposure comprises a dosage of less than 10 kGy.
10. A method of making a functionalized substrate, the method
comprises the steps of: 1) providing a porous base substrate having
interstitial and outer surfaces; 2) imbibing the porous base
substrate with a first solution to form an imbibed porous base
substrate, the first solution comprising (a) at least one grafting
monomer having an acrylate group and a photoinitiator group and (b)
one or more monomers having at least one acrylate group and at
least one additional ethylenically unsaturated, free-radically
polymerizable group; and optionally (c) one or more additional
monomers monomer having at least one ethylenically unsaturated,
free-radically polymerizable group and a hydrophilic group; wherein
at least one of (b) or (c) monomers are hydrophilic, 3) positioning
the imbibed porous base substrate between a removable carrier layer
and a removable cover layer to form a multilayer structure; 4)
exposing the multilayer structure to a controlled amount of
electron beam radiation so as to form a functionalized substrate
positioned between the removable carrier layer and the removable
cover layer, the functionalized substrate comprising grafted
photoinitiator groups attached to the surfaces of the porous base
substrate; 5) exposing the multilayer structure to UV radiation to
initiate polymerization of the ungrafted ethylenically unsaturated
groups; and 6) removing the carrier layer and cover layers from the
multilayer structure.
11. An article comprising a porous base substrate having
interstitial and outer surfaces and grafted photoinitiator groups
extending from the surfaces of the porous base substrate.
12. The article of claim 11 further comprising grafted
ethylenically unsaturated groups extending from the surfaces of the
porous base substrate.
13. The article of claim 11 further comprising grafted hydrophilic
groups extending from the surfaces of the porous base
substrate.
14. The article of claim 11 further comprising the polymerization
reaction product of: (b) one or more monomers having at least one
acrylate group and at least one additional ethylenically
unsaturated, free-radically polymerizable group; and optionally (c)
one or more additional monomers monomer having at least one
ethylenically unsaturated, free-radically polymerizable group and a
hydrophilic group; wherein at least one of (b) or (c) monomers are
hydrophilic.
15. The article of claim 12 wherein the grafted ethylenically
unsaturated groups are derived from one or more monomers having at
least one acrylate group and at least one additional ethylenically
unsaturated, free-radically polymerizable group.
16. The article of claim 14 derived from a poly(alkylene oxide)
di(meth)acrylate.
17. The article of claim 11, wherein the porous base substrate is
microporous.
18. The article of claim 11, wherein the porous base substrate
comprises a porous membrane, a porous nonwoven web, or a porous
fiber.
19. The article of claim 11, wherein the porous base substrate
comprises a microporous, thermally-induced phase separation
membrane.
20. The article of claim 19, wherein the thermally-induced phase
separation membrane comprises a propylene polymer.
21. The article of claim 11, wherein the grafted photoinitiator
comprises the reaction product of a monomer having an acrylate
group and a photoinitiator group upon exposure to electron beam
irradiation.
22. The article of claim 11, wherein the grafted ethylenically
unsaturated groups comprises the reaction product of
di(meth)acrylate poly(alkylene oxide) with the surfaces of the
porous base substrate upon exposure to an electron beam.
23. The article of claim 11, wherein the article comprises (a) a
first grafted species comprising the reaction product of a monomer
having a free-radically polymerizable group and a photoinitiator
group; and (b) a second grafted species comprising the reaction
product of a partially acrylated polyol upon exposure to an
electron beam irradiation.
24. The article of claim 11 comprising the crosslinked reaction
product of the unreacted ethylenically unsaturated groups on
exposure to UV radiation.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to hydrophilic, porous
substrates, and methods for preparing the same.
BACKGROUND
[0002] There is a need in the art for porous polymeric substrates
having enhanced hydrophilicity. Further, there is a need in the art
for methods of making polymeric substrates having enhanced
hydrophilicity from hydrophobic polymers.
SUMMARY OF THE INVENTION
[0003] The present invention is directed to hydrophilic substrates
and methods of making hydrophilic substrates. More specifically,
the hydrophilic substrates include a hydrophobic porous base
substrate that has been modified to provide the requisite
hydrophilicity.
[0004] Methods of making a hydrophobic substrate are provided. In
some embodiments, the method comprises:
[0005] 1) providing a porous base substrate having interstitial and
outer surfaces;
[0006] 2) imbibing the porous base substrate with a first solution
to form an imbibed porous base substrate, the first solution
comprising (a) at least one grafting monomer having an acrylate
group and a photoinitiator group and (b) one or more monomers
having at least one acrylate group and at least one additional
ethylenically unsaturated, free-radically polymerizable group; and
optionally (c) one or more additional monomers having at least one
free-radically polymerizable group and a hydrophilic group; wherein
at least one of (b) or (c) monomers are hydrophilic.
[0007] 3) exposing the imbibed porous base substrate to a
controlled amount of electron beam radiation so as to form a first
functionalized substrate comprising grafted photoinitiator group
attached to the surfaces of the porous base substrate, and
[0008] 4) exposing the porous base substrate comprising grafted
photoinitiator groups to a controlled amount of UV radiation to
polymerize or crosslink the remaining ethylenically unsaturated,
free-radically polymerizable groups.
[0009] An article is provided that comprises (a) a first grafted
species comprising the reaction product of a monomer having an
acrylate group and a photoinitiator group; and (b) a second species
comprising the reaction product of a monomers having at least one
acrylate group and at least one additional ethylenically
unsaturated, free-radically polymerizable group and optionally (c)
a third species comprising the reaction product of monomers having
at least one ethylenically unsaturated, free-radically
polymerizable group and a hydrophilic group, with the surfaces of
the porous base substrate upon exposure to an electron beam and UV
irradiation. At least one of (b) or (c) monomers is hydrophilic.
Any free ethylenically unsaturated groups that remain ungrafted to
the porous base substrate may crosslink upon subsequent exposure to
UV radiation.
[0010] With respect to the method and article, all or a portion of
the acrylate groups of the photoinitiator monomer (a) will be
grafted to the surface of the porous base substrate upon e-beam
irradiation. The unreacted photoinitiator monomers may be
subsequently incorporated into the growing polymer chain on
exposure to UV radiation. The remaining (b) and (c) monomers may be
directly grafted to the surfaces (for example by grafting of an
acrylate group), or indirectly grafted by incorporation into the
growing polymer chain on exposure to UV radiation.
[0011] These and other features and advantages of the present
invention will become apparent after a review of the following
detailed description of the disclosed embodiments and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 depicts exemplary method steps for making hydrophilic
substrates of the present invention; and
DETAILED DESCRIPTION OF THE INVENTION
[0013] In the article and methods of this invention, hydrophilic
porous articles are provided by a two-step process of e-beam
grafting of monomers and subsequent UV crosslinking of free,
ungrafted ethylenically unsaturated polymerizable groups.
[0014] Compared to the porous base substrate before surface
modification, the functionalized substrate typically has
hydrophilicity. The hydrophilic porous substrate comprises a number
of components including, but not limited to, (1) a porous base
substrate having interstitial and outer surfaces and (2) the UV
initiated reaction product of (a) a grafted photoinitiator group
extending from the surfaces of the porous base substrate, (b) one
or more monomers having at least one acrylate group and at least
one additional free-radically polymerizable group; and optionally
(c) one or more additional monomers having at least one
free-radically polymerizable group and a hydrophilic group; wherein
at least one of (b) or (c) monomers are hydrophilic.
[0015] Suitable porous base substrates include, but are not limited
to, porous membranes, porous nonwoven webs, and porous fibers. The
porous base substrate may be formed from any suitable thermoplastic
polymeric material. Suitable polymeric materials include, but are
not limited to, polyolefins, poly(isoprenes), poly(butadienes),
fluorinated polymers, chlorinated polymers, polyamides, polyimides,
polyethers, poly(ether sulfones), poly(sulfones), poly(vinyl
acetates), copolymers of vinyl acetate, poly(phosphazenes),
poly(vinyl esters), poly(vinyl ethers), poly(vinyl alcohols), and
poly(carbonates).
[0016] Suitable polyolefins include, but are not limited to,
poly(ethylene), poly(propylene), poly(1-butene), copolymers of
ethylene and propylene, alpha olefin copolymers (such as copolymers
of ethylene or propylene with 1-butene, 1-hexene, 1-octene, and
1-decene), poly(ethylene-co-1-butene) and
poly(ethylene-co-1-butene-co-1-hexene).
[0017] Suitable fluorinated polymers include, but are not limited
to, poly(vinyl fluoride), poly(vinylidene fluoride), copolymers of
vinylidene fluoride (such as poly(vinylidene
fluoride-co-hexafluoropropylene), and copolymers of
chlorotrifluoroethylene (such as
poly(ethylene-co-chlorotrifluoroethylene).
[0018] Suitable polyamides include, but are not limited to,
poly(imino(1-oxohexamethylene)),
poly(iminoadipoyliminohexamethylene),
poly(iminoadipoyliminodecamethylene), and polycaprolactam. Suitable
polyimides include, but are not limited to,
poly(pyromellitimide).
[0019] Suitable poly(ether sulfones) include, but are not limited
to, poly(diphenylether sulfone) and
poly(diphenylsulfone-co-diphenylene oxide sulfone).
[0020] Suitable copolymers of vinyl acetate include, but are not
limited to, poly(ethylene-co-vinyl acetate) and such copolymers in
which at least some of the acetate groups have been hydrolyzed to
afford various poly(vinyl alcohols).
[0021] Preferably, the porous base substrate is formed from a
propylene homo- or copolymers, most preferably propylene
homopolymers. Polypropylene polymers are often a material of choice
for porous articles, such as nonwovens and microporous films, due
to properties such as non-toxicity, inertness, low cost, and the
ease with which it can be extruded, molded, and formed into
articles. However, polypropylene is hydrophobic. While it is
desirable to render hydrophobic polymers such as polypropylene
hydrophilic, polypropylene treated with ionizing radiation is
subject to degradation, e.g., embrittlement, discoloration, and
thermal sensitivity, during or subsequent to irradiation, which
therefore limits the ability to render such thermoplastic polymers
hydrophilic by e-beam grafting.
[0022] The present invention overcomes such polymer degradation by
using a low dose of electron beam radiation to graft photoinitiator
groups and optionally grafting other hydrophilic monomers on a
portion of the surface, then polymerizing or crosslinking any
ungrafted, unreacted ethylenically unsaturated groups by UV
radiation.
[0023] In one exemplary embodiment, the porous base substrate
comprises a microporous base substrate having an average pore size
that is typically less than about 1.0 microns. Suitable microporous
base substrates include, but are not limited to, microporous
membranes, microporous nonwoven webs, and microporous fibers. The
microporous base substrate is often initially hydrophobic and is
rendered hydrophilic by the methods described herein.
[0024] In some embodiments, the porous base substrate is a
microporous membrane such as a thermally-induced phase separation
(TIPS) membrane. TIPS membranes are often prepared by forming a
homogenous solution of a thermoplastic material and a second
material above the melting point of the thermoplastic material.
Upon cooling, the thermoplastic material crystallizes and phase
separates from the second material. The crystallized thermoplastic
material is often stretched. The second material is optionally
removed either before or after stretching. Microporous membrane are
further disclosed in U.S. Pat. Nos. 4,539,256 (Shipman), 4,726,989
(Mrozinski), 4,867,881 (Kinzer), 5,120,594 (Mrozinski), 5,260,360
(Mrozinski et al.), and 5,962,544 (Waller), all of which are
assigned to 3M Company (St. Paul, Minn.), the subject matter of all
of which is hereby incorporated by reference in its entirety.
Further, the microporous film can be prepared from ethylene-vinyl
alcohol copolymers as described in U.S. Pat. No. 5,962,544
(Waller), incorporated herein by reference.
[0025] Some exemplary TIPS membrane comprise poly(vinylidene
fluoride) (i.e., PVDF), polyolefins such as polyethylene homo- or
copolymers or polypropylene homo- or copolymers, vinyl-containing
polymers or copolymers such as ethylene-vinyl alcohol copolymers
and butadiene-containing polymers or copolymers, and
acrylate-containing polymers or copolymers. For some applications,
a TIPS membrane comprising PVDF is particularly desirable. TIPS
membranes comprising PVDF are further described in U.S. Patent
Application Publication No. 2005/0058821, which is assigned to 3M
Company (St. Paul, Minn.), the subject matter of which is hereby
incorporated by reference in its entirety.
[0026] In other embodiments, the porous base substrate is a
nonwoven web which may include nonwoven webs manufactured by any of
the commonly known processes for producing nonwoven webs. As used
herein, the term "nonwoven web" refers to a fabric that has a
structure of individual fibers or filaments which are randomly
and/or unidirectionally interlaid in a mat-like fashion.
[0027] For example, the fibrous nonwoven web can be made by carded,
air laid, spunlaced, spunbonding or melt-blowing techniques or
combinations thereof. Spunbonded fibers are typically small
diameter fibers that are formed by extruding molten thermoplastic
polymer as filaments from a plurality of fine, usually circular
capillaries of a spinneret with the diameter of the extruded fibers
being rapidly reduced. Meltblown fibers are typically formed by
extruding the molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into a high velocity, usually heated gas (e.g. air)
stream which attenuates the filaments of molten thermoplastic
material to reduce their diameter. Thereafter, the meltblown fibers
are carried by the high velocity gas stream and are deposited on a
collecting surface to from a web of randomly disbursed meltblown
fibers. Any of the non-woven webs may be made from a single type of
fiber or two or more fibers that differ in the type of
thermoplastic polymer and/or thickness.
[0028] Further details on the manufacturing method of non-woven
webs of this invention may be found in Wente, Superfine
Thermoplastic Fibers, 48 INDUS. ENG. CHEM. 1342 (1956), or in Wente
et al., Manufacture Of Superfine Organic Fibers, (NavaL Research
Laboratories Report No. 4364, 1954).
[0029] The functionalized substrate has grafted species attached to
the surfaces of the porous base substrate which includes (a) at
least one photoinitiator group (or the reaction product thereof),
(b) at least one ethylenically unsaturated group (or the reaction
product thereof) and (c) optionally other hydrophilic groups,
wherein at least one of (b) or (c) is a hydrophilic group. The
grafting of monomers to the surface of the porous base substrate
results in a hydrophilic surface imparted to an otherwise
hydrophobic base substrate. The hydrophilic monomer, whether "(b)"
or "(c)", are used in amounts sufficient to render the porous
substrate wettable as described herein.
[0030] The monomers that are grafted to the surface of the porous
base substrates usually have both (a) an acrylate group for
grafting by e-beam and (b) at least one additional function group
thereon, which includes (a) a photoinitiator group to initiate the
crosslinking on exposure to UV radiation, (b) an acrylate or a
non-acrylate, free-radically polymerizable ethylenically
unsaturated group for subsequent crosslinking and optionally (c) a
hydrophilic group.
[0031] Acrylate groups are preferred for direct grafting of the
monomer to the porous substrate surface due to the greater
reactivity of such acrylates on exposure to e-beam irradiation.
However, not all such acrylate groups may be directly grafted (i.e.
forming a covalent bond with the porous surface); some may remain
free, and are subsequently "indirectly grafted" by incorporation
into the polymer chain on exposure to UV radiation. Other
ethylenically unsaturated groups, such as (meth)acrylamides,
methacrylates, vinyl and vinyloxy groups, allyl and allyloxy
groups, and acetylenic groups are less reactive during e-beam, and
are less likely to be directly grafted to the porous base
substrate. Therefore a portion of such non-acrylate groups may be
directly grafted, but largely remain unreacted, and are indirectly
grafted to the substrate by incorporation into the polymer chain
during UV initiated polymerization.
[0032] The photoinitiator monomers may be directly grafted onto
interstitial and outer surfaces of the porous base substrate to
provide the requisite grafted photoinitiator group via the acrylate
group. The "(b)" monomers, in addition to the acrylate group, the
free-radically polymerizable groups of monomer (b) are typically
other ethylenically unsaturated groups such as a (meth)acrylamides,
methacrylates, vinyl groups and acetylenic groups having reduced
reactivity during grafting, and are therefore free and unreacted
for the subsequent UV initiated polymerization and crosslinking.
The acrylate group of the "(b)" monomers typically can directly
graft (i.e. forming a covalent bond) to the surface of the porous
base substrate when exposed to an electron beam. That is, reaction
of acrylate groups of the (b) monomers with the surface of the
porous base substrate in the presence of the electron beam results
in the formation of ethylenically unsaturated groups directly
grafted to the porous base substrate via the acrylate group.
[0033] A third grafting monomer "(c)" may also be grafted via an
acrylate group, and may provide hydrophilic groups to the surfaces
of the porous base substrate. In other embodiments the third
monomer may have an ethylenically unsaturated group of reduced
reactivity during the grafting step, but is subsequently
incorporated by free-radical polymerization during the UV curing
step (indirectly grafted). At least one of the monomers (b) and (c)
is a hydrophilic monomer.
[0034] The grafting photoinitiator monomers include an acrylate
group and a photoinitiator group and may be represented by the
generalized formula:
##STR00001##
where; R.sup.4 is a divalent linking group connecting the acrylate
group with the PI group, and PI is a photoinitiator represented by
the structure:
##STR00002##
wherein R.sup.2 is
##STR00003##
wherein R.sup.1 is H or a C.sub.1 to C.sub.4 alkyl group, each
R.sup.3 is independently a hydroxyl group, a phenyl group, a
C.sub.1 to C.sub.6 alkyl group, or a C.sub.1 to C.sub.6 alkoxy
group. Such photoinitiator monomers are described, for example, in
U.S. Pat. Nos. 5,902,836 (Babu et al.) and 5,506,279 (Babu et al.),
the disclosures of which are herein incorporated by reference.
Further details regarding the linking R.sup.4 group may be found
with reference to the method of preparing the photoinitiator
grafting monomer herein, and in the cited references.
[0035] The weight percentage of the photoinitiator monomers in the
imbibing solution can be at least about 0.01%, and preferably at
least about 0.15%, and no more than about 2.5%, preferably no more
than about 1%, relative to the total weight of other monomers (i.e.
"(b)" and "(c)" monomers). It will be understood that all or a
portion of the photoinitiator monomers may be directly grafted to
the surfaces of the base substrate upon exposure to e-beam
irradiation. Those unreacted, ungrafted photoinitiator monomers
will be incorporated into the growing polymer chain on exposure to
UV radiation, thereby indirectly grafting the monomers to the
porous base substrate.
[0036] A variety of photoinitiator grafting monomers can be made by
reacting 1) an acrylate monomer comprising a first reactive
functional group with 2) a compound that comprises a
radiation-sensitive group (photoinitiator group) and second
reactive functional group, the two functional groups being
co-reactive with each other. Preferred co-reactive compounds are
ethylenically unsaturated aliphatic, cycloaliphatic, and aromatic
compounds having up to 36 carbon atoms, optionally one or more
oxygen and/or nitrogen atoms, and at least one reactive functional
group. When the first and second functional groups react, they form
a covalent bond and link the co-reactive compounds.
[0037] Examples of useful reactive functional groups include
hydroxyl, amino, oxazolinyl, oxazolonyl, acetyl, acetonyl,
carboxyl, isocyanato, epoxy, aziridinyl, acyl halide, and cyclic
anhydride groups. Where the pendent reactive functional group is an
isocyanato functional group, the co-reactive functional group
preferably comprises a amino, carboxyl, or hydroxyl group. Where
pendent reactive functional group comprises a hydroxyl group, the
co-reactive functional group preferably comprises a carboxyl,
isocyanato, epoxy, anhydride, acyl halide, or oxazolinyl group.
Where the pendent reactive functional group comprises a carboxyl
group, the co-reactive functional group preferably comprises a
hydroxyl, amino, epoxy, vinyloxy, or oxazolinyl group.
[0038] Representative examples of acrylate compounds having a
reactive functional group include hydroxyalkyl acrylates such as
2-hydroxyethyl acrylate and 2-(2-hydroxyethoxy)ethyl acrylate;
aminoalkyl acrylates such as 3-aminopropyl acrylate; oxazolinyl
compounds such as 2-ethenyl-1,3-oxazolin-5-one and
2-propenyl-4,4-dimethyl-1,3-oxazolin-5-one; carboxy-substituted
compounds such as acrylic acid and 4-carboxybenzyl acrylate;
isocyanato-substituted compounds such as isocyanatoethyl acrylate
and 4-isocyanatocyclohexyl acrylate; epoxy-substituted compounds
such as glycidyl acrylate; aziridinyl-substituted compounds such as
N-acryloylaziridine; and acryloyl halides.
[0039] Representative examples of co-reactive compounds include
functional group-substituted compounds such as
1-(4-hydroxyphenyl)-2,2-dimethoxyethanone,
1-[4-(2-hydroxyethyl)phenyl]-2,2-dimethoxyethanone,
(4-isocyanatophenyl)-2,2-dimethoxy-2-phenylethanone,
1-{4-[2-(2,3-epoxypropoxy)phenyl]}-2,2-dimethyl-2-hydroxyethanone,
1-[4-(2-aminoethoxy)phenyl]-2,2-dimethoxyethanone, and
1-[4-(carbomethoxy)phenyl]-2,2-dimethoxyethanone.
[0040] It will be understood that all or a portion of the acrylate
groups of the photoinitiator monomer may be directly grafted to the
surface of the porous substrate on exposure of e-beam irradiation.
Those ungrafted, free acrylate groups may be subsequently
indirectly grafted to the substrate by incorporation into the
polymer chain on UV initiated polymerization.
[0041] The second grafting monomers comprises (a) one or more
acrylate groups for grafting and (b) one or more second,
ethylenically unsaturated, free-radically polymerizable groups for
subsequent crosslinking. The second ethylenically unsaturated group
may be an acrylate or a non-acrylate; i.e. other ethylenically
unsaturated groups having reduced reactivity relative to the
acrylate group during the e-beam grafting step. Preferably the
second ethylenically unsaturated group is a non-acrylate group and
is left largely free and unreacted during the grafting step for
subsequent UV crosslinking. Useful second, non-acrylate
ethylenically unsaturated groups include methacrylates,
(meth)acrylamides, vinyl groups, vinyloxy, acetylenic groups, allyl
and allyloxy groups.
[0042] Useful second grafting monomers may have the generalized
structure:
[CH.sub.2.dbd.CH--C(O)--O].sub.a--R.sup.5-Q-Z.sub.b, III
where Z is an acrylate or non-acrylate, ethylenically unsaturated
polymerizable group, Q is a divalent linking group selected from a
covalent bond "--", --O--, --NR.sup.1--, --CO.sub.2-- and
--CONR.sup.1--, where R.sup.1 is H or C.sub.1-C.sub.4 alkyl; and
R.sup.5 is an alkylene group of valence a+b, and optionally
containing one or more catenary oxygen atoms and/or one or more
hydroxyl groups; and a and b are each at least one. Preferably the
Z group is a non-acrylate of reduced reactivity that is indirectly
grafted into the polymer chain during UV initiated
polymerization.
[0043] In certain embodiments, R.sup.5 is a poly(alkylene oxide
group) to provide the desired hydrophilicity, and is of the
formula:
Z-Q-(CH(R.sup.1)--CH.sub.2--O).sub.n--C(O)--CH.dbd.CH.sub.2, IV
wherein Z is an acrylate or non-acrylate, polymerizable
ethylenically unsaturated group, R.sup.1 is a H or a C.sub.1 to
C.sub.4 alkyl group, and n is from 2 to 100, preferably 5 to 20,
and Q is a divalent linking group selected from a covalent bond
"--", --O--, --NR.sup.1--, --CO.sub.2-- and --CONR.sup.1--, where
R.sup.1 is H or C.sub.1-C.sub.4 alkyl. Preferably the Z group is a
non-acrylate of reduced reactivity that is indirectly grafted into
the polymer chain during UV initiated polymerization.
[0044] In one embodiment, the poly(alkylene oxide) group (depicted
as --(CH(R.sup.1)--CH.sub.2-Q).sub.n--) is a poly(ethylene oxide)
(co)polymer. In another embodiment, the pendent poly(alkylene
oxide) group is a poly(ethylene oxide-co-propylene oxide)
copolymer. Such copolymers may be block copolymers, random
copolymers, or gradient copolymers.
[0045] Suitable monomers having a first acrylate group for grafting
and a second ethylenically unsaturated group for subsequent UV
crosslinking include, but are not limited to, polyalkylene glycol
acrylate methacrylate including those derived from polyethylene
glycol and polypropylene glycol acrylated monomers.
[0046] In another embodiment, the second monomer is a partially
acrylated polyol, having at least one acrylate groups and at least
one other ethylenically unsaturated polymerizable group, which is
preferably not a acrylate group and may be selected from
methacrylates, (meth)acrylamides, vinyl groups, vinyloxy,
acetylenic groups, allyl and allyloxy groups. Such partially
acrylated polyols may have one of more free hydroxyl groups.
[0047] Polyols useful in the present invention include aliphatic,
cycloaliphatic, or alkanol-substituted arene polyols, or mixtures
thereof having from about 2 to about 18 carbon atoms and two to
five, preferably two to four hydroxyl groups.
[0048] Examples of useful polyols include 1,2-ethanediol,
1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol,
2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol,
2-ethyl-1,6-hexanediol, 1,5-pentanediol, 1,6-hexanediol,
1,8-octanediol, neopentyl glycol, glycerol, trimethylolpropane,
1,2,6-hexanetriol, trimethylolethane, pentaerythritol, quinitol,
mannitol, sorbitol, diethylene glycol, triethylene glycol,
tetraethylene glycol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol,
2-ethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol,
1,4-benzenedimethanol, and polyalkoxylated bisphenol A derivatives.
Most preferably "(b)" monomers are those monoacrylates of glycerol
having a free hydroxyl group and a methacrylate group such as
3-(acryloxy)-2-hydroxypropylmethacrylate).
[0049] In some preferred embodiments, the ethylenically unsaturated
groups of the "(b)" and "(c)" monomers are chosen to be efficiently
copolymerizable with each other. That is, it is preferred that each
of the "(b)" and "(c)" monomers have the same ethylenically
unsaturated groups.
[0050] In one exemplary embodiment, the grafted species result from
the reaction of a polyethylene glycol acrylate monomer of Formulas
III or IV with the porous base substrate upon exposure to an
electron beam. These grafting monomers can be used to change a
hydrophobic porous base substrate into a hydrophilic functionalized
substrate due to the presence of the poly(alkylene oxide) group.
The resulting hydrophilic can have a number of desired properties
such as instant wettability following exposure to 1N NaOH for 20
hours as described in more detail below.
[0051] The optional third monomer ("(c)", hydrophilic monomer)
comprises at least one acrylate or other non-acrylate,
ethylenically unsaturated group of reduced reactivity, and a
hydrophilic group, such as an ionic group, for providing
hydrophilicity to the substrate. If the optional third monomer
contains an acrylate group, it may be directly grafted to the
surfaces of the porous bases substrate. If it contains a
non-acrylate, ethylenically unsaturated group it will remain
largely unreacted during the grafting step, and will be
incorporated during the UV polymerization step. It will be
understood that all or a portion of the acrylate groups may be
directly grafted to the porous substrate, and a portion may be
unreacted, but will be indirectly grafted into the polymer upon UV
initiated irradiation. Conversely, a portion of other ethylenically
unsaturated groups of reduced reactivity may be directly grafted,
but such groups generally remain largely unreacted during the
grafting step and are indirectly grafted into the polymer upon UV
initiated irradiation.
[0052] The ionic groups may be neutral, have a positive charge, a
negative charge, or a combination thereof. With some suitable ionic
monomers, the ionic group can be neutral or charged depending on
the pH conditions. This class of monomers is typically used to
impart a desired hydrophilicity to the porous base substrate in
addition to the second monomer.
[0053] In some preferred embodiments, the third monomer may have an
acrylate group, or other ethylenically unsaturated groups of
reduced reactivity, and a poly(alkylene oxide) group; e.g.
monoacrylated poly(alkylene oxide compounds, where the terminus is
a hydroxy group, or an alkyl ether group.
[0054] In some embodiments the ionic monomers having a negative
charge include (meth)acrylamidosulfonic acids of Formula II or
salts thereof.
##STR00004##
wherein, Y is a straight or branched alkylene (e.g., an alkylenes
having 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon
atoms) and L is oxy or --NR.sup.1--, where R.sup.1 is H or
C.sub.1-C.sub.4 alkyl-. Exemplary ionic monomers according to
Formula I include, but are not limited to,
N-acrylamidomethanesulfonic acid, 2-acrylamidoethanesulfonic acid,
2-acrylamido-2-methyl-1-propanesulfonic acid, and
2-methacrylamido-2-methyl-1-propanesulfonic acid. Salts of these
acidic monomers can also be used. Counter ions for the salts can
be, for example, ammonium ions, potassium ions, lithium ions, or
sodium ions. It will be understood with respect to Formula V that
the grafting acrylate group may be replaced by another
ethylenically unsaturated group of reduced reactivity for
subsequent incorporation (indirect grafting) during UV initiated
polymerization.
[0055] Other suitable ionic grafting monomers having a negative
charge include sulfonic acids such as vinylsulfonic acid and
4-styrenesulfonic acid; (meth)acrylamidophosphonic acids such as
(meth)acrylamidoalkylphosphonic acids (e.g.,
2-(meth)acrylamidoethylphosphonic acid and
3-(meth)acrylamidopropylphosphonic acid; acrylic acid and
methacrylic acid; and carboxyalkyl(meth)acrylates such as
2-carboxyethyl(meth)acrylate, and 3-carboxypropyl(meth)acrylate.
Still other suitable acidic monomers include (meth)acryloylamino
acids, such as those described in U.S. Pat. No. 4,157,418
(Heilmann), incorporated herein by reference. Exemplary
(meth)acryloylamino acids include, but are not limited to,
N-acryloylglycine, N-acryloylaspartic acid,
N-acryloyl-.beta.-alanine, and 2-acrylamidoglycolic acid. Salts of
any of these acidic monomers can also be used.
[0056] Some exemplary ionic grafting monomers that are capable of
providing a positive charge are amino (meth)acrylates or amino
(meth)acrylamides of Formula II or quaternary ammonium salts
thereof. The counter ions of the quaternary ammonium salts are
often halides, sulfates, phosphates, nitrates, and the like.
##STR00005##
where L is oxy or --NR.sup.1--, where R.sup.1 is H or
C.sub.1-C.sub.4 alkyl-; and Y is an alkylene (e.g., an alkylene
having 1 to 10 carbon atoms, 1 to 6, or 1 to 4 carbon atoms). Each
R.sup.5 is independently hydrogen, alkyl, hydroxyalkyl (i.e., an
alkyl substituted with a hydroxy), or aminoalkyl (i.e., an alkyl
substituted with an amino). Alternatively, the two R.sup.5 groups
taken together with the nitrogen atom to which they are attached
can form a heterocyclic group that is aromatic, partially
unsaturated (i.e., unsaturated but not aromatic), or saturated,
wherein the heterocyclic group can optionally be fused to a second
ring that is aromatic (e.g., benzene), partially unsaturated (e.g.,
cyclohexene), or saturated (e.g., cyclohexane).
[0057] It will be understood with respect to Formula VI that the
grafting acrylate group may be replaced by another ethylenically
unsaturated group of reduced reactivity, such as methacrylate,
(meth)acrylamide, vinyl, vinyloxy, ally, alloxy, and acetylenyl for
subsequent incorporation (indirect grafting) during UV initiated
polymerization.
[0058] In some embodiments of Formula VI, both R.sup.5 groups are
hydrogen. In other embodiments, one R.sup.5 group is hydrogen and
the other is an alkyl having 1 to 10, 1 to 6, or 1 to 4 carbon
atoms. In still other embodiments, at least one of R.sup.5 groups
is a hydroxy alkyl or an amino alkyl that have 1 to 10, 1 to 6, or
1 to 4 carbon atoms with the hydroxy or amino group being
positioned on any of the carbon atoms of the alkyl group. In yet
other embodiments, the R.sup.5 groups combine with the nitrogen
atom to which they are attached to form a heterocyclic group. The
heterocyclic group includes at least one nitrogen atom and can
contain other heteroatoms such as oxygen or sulfur. Exemplary
heterocyclic groups include, but are not limited to imidazolyl. The
heterocyclic group can be fused to an additional ring such as a
benzene, cyclohexene, or cyclohexane. Exemplary heterocyclic groups
fused to an additional ring include, but are not limited to,
benzoimidazolyl.
[0059] Exemplary amino acrylates (i.e., L in Formula VI is oxy)
include N,N-dialkylaminoalkyl acrylates such as, for example,
N,N-dimethylaminoethylacrylate, N,N-dimethylaminoethylacrylate,
N,N-diethylaminoethyl acylate, N,N-diethylaminoethylacrylate,
N,N-dimethylaminopropylacrylate, N,N-dimethylaminopropylacrylate,
N-tert-butylaminopropylmethacrylate,
N-tert-butylaminopropylacrylate and the like.
[0060] Exemplary amino (meth)acrylamides, that would be
incorporated during the UV polymerization, (i.e., L in Formula VI
is --NR.sup.1--) include, for example,
N-(3-aminopropyl)methacrylamide, N-(3-aminopropyl)acrylamide,
N-[3-(dimethylamino)propyl]methacrylamide,
N-(3-imidazolylpropyl)methacrylamide,
N-(3-imidazolylpropyl)acrylamide,
N-(2-imidazolylethyl)methacrylamide,
N-(1,1-dimethyl-3-imidazoylpropyl)methacrylamide,
N-(1,1-dimethyl-3-imidazoylpropyl)acrylamide,
N-(3-benzoimidazolylpropyl)acrylamide, and
N-(3-benzoimidazolylpropyl)methacrylamide.
[0061] Exemplary quaternary salts of the ionic monomers of Formula
VI include, but are not limited to,
(meth)acrylamidoalkyltrimethylammonium salts (e.g.,
3-methacrylamidopropyltrimethylammonium chloride and
3-acrylamidopropyltrimethylammonium chloride) and
(meth)acryloxyalkyltrimethylammonium salts (e.g.,
2-acryloxyethyltrimethylammonium chloride,
2-methacryloxyethyltrimethylammonium chloride,
3-methacryloxy-2-hydroxypropyltrimethylammonium chloride,
3-acryloxy-2-hydroxypropyltrimethylammonium chloride, and
2-acryloxyethyltrimethylammonium methyl sulfate).
[0062] Other monomers that can provide positively charged groups to
an ion exchange resin include the dialkylaminoalkylamine adducts of
alkenylazlactones (e.g., 2-(diethylamino)ethylamine,
(2-aminoethyl)trimethylammonium chloride, and
3-(dimethylamino)propylamine adducts of vinyldimethylazlactone) and
diallylamine monomers (e.g., diallylammonium chloride and
diallyldimethylammonium chloride).
[0063] A third monomer, that may be incorporated by grafting or by
subsequent UV polymerization are poly(alkylene oxide) monomers
having at least one acrylate or non-acrylate ethylenically
unsaturated group and a non-polymerizable terminus. Such monomers
are of the general formula:
R.sup.1--O--(CH(R.sup.1)--CH.sub.2--O).sub.n--C(O)--C(R.sup.1).dbd.CH.su-
b.2, VII,
wherein each R.sup.1 is independently H or C.sub.1-C.sub.4
alkyl.
[0064] As described in further detail below, functionalized
substrates of the present invention may be prepared using
above-described monomers to provide hydrophilicity to the surface
of a porous base substrate. When two or more of the above-described
monomers are used to alter the surface properties of a porous base
substrate, the monomers may be grafted onto the porous base
substrate in a single reaction step (i.e., the two or more grafting
monomers are all present upon exposure to an electron beam) or in
sequential reaction steps (i.e., a first grafting photoinitiator
monomer "(a)", and present upon a first exposure to an electron
beam and a second grafting monomer "(b) and/or (c)" is present upon
a second exposure to the electron beam). Similarly, all of such
monomers (a), (b) and (c) may be present during a first grafting
step and directly grafted, or indirectly grafted by incorporation
during the subsequent UV initiated polymerization. Alternatively,
all or a potion of such monomers may be imbibed in a first step, or
in subsequent imbibing steps.
[0065] In some embodiments, the grafted species imparts a
hydrophilic character to the functionalized substrate that contains
a porous base substrate that has a hydrophobic character prior to
surface modification. The hydrophilic character of the
functionalized substrate results from the reaction of the porous
base substrate with the "(b) and/or (c)" monomers that contain a
hydrophilic group upon exposure to an electron beam and UV
initiated polymerization.
[0066] The above-described hydrophilic substrates may be prepared
using a combination of process steps. The method comprises:
[0067] 1) providing a porous base substrate having interstitial and
outer surfaces;
[0068] 2) imbibing the porous base substrate with a first solution
to form an imbibed porous base substrate, the first solution
comprising (a) at least one grafting monomer having an acrylate
group and a photoinitiator group and (b) one or more monomers
having at least one acrylate group and at least one additional
ethylenically unsaturated, free-radically polymerizable group; and
optionally (c) one or more additional monomers having at least one
ethylenically unsaturated, free-radically polymerizable group and a
hydrophilic group; wherein at least one of (b) or (c) monomers are
hydrophilic. The imbibing step may comprise a single solution or
multiple solutions.
[0069] 3) exposing the imbibed porous base substrate to a
controlled amount of electron beam radiation so as to form a first
functionalized substrate comprising grafted photoinitiator group
attached to the surfaces of the porous base substrate, and
[0070] 4) exposing the porous base substrate comprising grafted
photoinitiator groups to a controlled amount of UV radiation to
crosslink the remaining free-radically polymerizable groups.
[0071] Some of the porous base substrates used in this embodiment
can be porous, microporous, nonwoven, or a combination thereof.
[0072] One exemplary method for making functionalized substrates is
depicted in FIG. 1. As shown in FIG. 1, exemplary method 10
comprises the following steps: an imbibing step 100, a sandwiching
step 200, an irradiation step 300, a UV initiated polymerization
step 400, a peeling step 500, a wash/rinse step 600, a drying step
700, and a take-up step 800. Each of these exemplary steps is
described in further detail below.
[0073] Methods of making functionalized substrates of the present
invention may comprise one or more of the following steps.
Imbibing Step
[0074] As shown in FIG. 1, a roll 11 comprising a porous base
substrate 12 may be unwound so that porous base substrate 12 enters
into imbibing step 100. In imbibing step 100, porous base substrate
12 is brought into contact or into proximity with applicator 14
that is connected to a reservoir of solution 13 containing one or
more grafting monomers. Rollers 15 and 16 guide porous base
substrate 12 past applicator 14 so that porous base substrate 12 is
exposed to solution 13 for a desired amount of time. Typically, the
exposure time of the porous base substrate 12 to solution 13 is up
to about 1.0 minutes, more typically, less than about 15 seconds.
Porous base substrate 12 usually proceeds through imbibing step 100
and to irradiation step 300 in less than 1 minute. In some imbibing
steps, the porous base substrate 12 is saturated with the solution
13.
[0075] As discussed above, solution 13 may comprise one or more
grafting suitable for grafting onto interstitial and outer surfaces
of porous base substrate 12. Any of the exemplary grafting monomers
described above can be included in solution 13. In addition to
grafting monomers, solution 13 can contain other materials such as,
for example, one or more other non-grafting monomers for UV curing,
and solvents. The concentration of each grafting monomer in
solution 13 may vary depending on a number of factors including,
but not limited to, the grafting monomer or monomers in solution
13, the extent of grafting desired, the reactivity of the grafting
monomer(s), and the solvent used. Typically, the concentration of
each monomer in solution 13 ranges from about 1 wt % to about 100
wt %, desirably, from about 5 wt % to about 30 wt %, and more
desirably from about 10 wt % to about 20 wt % based on a total
weight of solution 13.
[0076] Once porous base substrate 12 has been imbibed in solution
13 for a desired period of time, the porous base substrate 12 is
directed toward sandwiching step 200 via guide roller 17. Guide
roller 17 may be used to meter excess solution 13 from the imbibed
porous base substrate 12 if so desired. Alternately, rollers (not
shown) could be used to squeeze air bubbles and excess solution 13
from the imbibed porous base substrate 12. Typically, porous base
substrate 12 enters sandwiching step 200 in a substantially
saturated condition (i.e., porous base substrate 12 contains a
maximum amount of solution 13 or close to a maximum amount) wherein
substantially all of the interstitial and outer surfaces of porous
base substrate 12 are coated with solution 13.
[0077] It should be noted that imbibing step 100 is only one
possible method of introducing solution 13 into porous base
substrate 12. Other suitable methods include, but are not limited
to, a spray coating method, flood coating method, knife coating,
etc.
Sandwiching Step
[0078] In sandwiching step 200, imbibed porous base substrate 12 is
sandwiched (i.e., positioned) between a removable carrier layer 22
and a removable cover layer 19 to form multilayer sandwich
structure 24. As shown in exemplary method 10, removable cover
layer 19 may be unwound from roll 18 and brought into contact with
an outer surface of imbibed porous base substrate 12 via roller 20,
while removable carrier layer 22 may be unwound from roll 21 and
brought into contact with an opposite outer surface of imbibed
porous base substrate 12 via roller 23. Rollers 20 and 23 form a
gap that may be used to regulate the amount of imbibing solution 13
imparted to the porous substrate.
[0079] Removable cover layer 19 and removable carrier layer 22 may
comprise any inert sheet material that is capable of providing
temporary protection to functionalized substrate 30 (i.e., grafted
porous base substrate 12) from direct exposure to oxygen upon
exiting chamber 25. Suitable inert sheet materials for forming
removable cover layer 19 and removable carrier layer 22 include,
but are not limited to, polyethylene terephthalate film material,
other aromatic polymer film materials, and any other non-reactive
polymer film material. In some embodiments, removable carrier layer
22 may be selected from materials that are transparent to UV
radiation. Once assembled, multilayer sandwich structure 24
proceeds to irradiation step 300.
[0080] In irradiation step 300, multilayer sandwich structure 24 is
exposed to a sufficient quantity of radiation so as to graft one or
more monomers within solution 13 onto interstitial and outer
surfaces of porous base substrate 12 so as to form multilayer
sandwich structure 27 comprising functionalized substrate 30
sandwiched between removable carrier layer 22 and removable cover
layer 19. As shown in exemplary method 10, multilayer sandwich
structure 24 proceeds through chamber 25, which contains at least
one device 26 capable of providing a sufficient dose of radiation.
A single device 26 is capable of providing a sufficient dose of
radiation, although two or more devices 26 may be used especially
for relatively thick porous base substrates 12. Typically, chamber
25 comprises an inert atmosphere such as nitrogen, carbon dioxide,
helium, argon, etc. with a minimal amount of oxygen, which is known
to inhibit free-radical polymerization. In embodiments wherein
porous base substrate 12 is irradiated without removable cover
layer 19, the amount of oxygen within chamber 25 can be more of a
concern. When removable carrier layer 22 and removable cover layer
19 cover the porous base substrate 12, exposure to oxygen within
chamber 25 is minimal.
[0081] The irradiation step 300 provides the further advantage of
converting any dissolved oxygen to peroxy compounds, which would
interfere with the subsequent UV initiated polymerization.
Therefore the e-beam irradiation step 300 facilitates the
subsequent UV initiation 400 by the removal of oxygen.
[0082] Although other sources of irradiation may be used, desirably
device 26 comprises an electron beam source. Electron beams
(e-beams) are generally produced by applying high voltage to
tungsten wire filaments retained between a repeller plate and an
extractor grid within a vacuum chamber maintained at about
10.sup.-6 Torr. The filaments are heated at high current to produce
electrons. The electrons are guided and accelerated by the repeller
plate and extractor grid towards a thin window of metal foil. The
accelerated electrons, traveling at speeds in excess of 10.sup.7
meters/second (m/sec) and possessing about 100 to 300 kilo-electron
volts (keV), pass out of the vacuum chamber through the foil window
and penetrate whatever material is positioned immediately beyond
the foil window.
[0083] The quantity of electrons generated is directly related to
the extractor grid voltage. As extractor grid voltage is increased,
the quantities of electrons drawn from the tungsten wire filaments
increase. E-beam processing can be extremely precise when under
computer control, such that an exact dose and dose rate of
electrons can be directed against multilayer sandwich structure
24.
[0084] Electron beam generators are commercially available from a
variety of sources, including the ESI "ELECTROCURE" EB SYSTEM from
Energy Sciences, Inc. (Wilmington, Mass.), and the BROADBEAM EB
PROCESSOR from PCT Engineered Systems, LLC (Davenport, Iowa). For
any given piece of equipment and irradiation sample location, the
dosage delivered can be measured in accordance with ASTM E-1275
entitled "Practice for Use of a Radiochromic Film Dosimetry
System." By altering extractor grid voltage, beam diameter and/or
distance to the source, various dose rates can be obtained.
[0085] The temperature within chamber 25 is desirably maintained at
an ambient temperature by conventional means. Without intending to
be limited to any particular mechanism, it is believed that the
exposure of the imbibed porous base substrate to an electron beam
results in free radical initiation on the substrate which can then
react with monomers having a double bond such as monomers having an
ethylenically unsaturated group.
[0086] The total dose received by multilayer sandwich structure 24
primarily affects the extent to which the grafting monomer is
grafted onto the porous base substrate. In general, it is desirable
and typical to convert at least 10 wt %, desirably 20 wt %, even
more desirably greater than 50 wt % of the grafting monomers added
during the imbibing step to grafted species. Further, it is
desirable and typical to graft as much as about 5 wt %, desirably
as much as about 10 wt %, more desirably as much as about 20 wt %
(or as much as about 100 wt %) of one or more grafting monomers
added during the imbibing step onto porous base substrate 12, based
on a total weight of porous base substrate 12. Dose is dependent
upon a number of processing parameters, including voltage, speed
and beam current. Dose can be conveniently regulated by controlling
line speed (i.e., the speed with which multilayer sandwich
structure 24 passes under device 26), and the current supplied to
the extractor grid. A target dose (e.g., <10 kGy) can be
conveniently calculated by multiplying an experimentally measured
coefficient (a machine constant) by the beam current and dividing
by the web speed to determine the exposure. The machine constant
varies as a function of beam voltage.
[0087] While the controlled amount of electron beam radiation
exposure is dependent upon the residence time, as a general matter,
the monomers imbibed on the porous base substrate 12 that is part
of multilayer sandwich structure 24 will generally be significantly
grafted upon receiving a controlled amount of dosage ranging from a
minimum dosage of about 1 kilograys (kGy) to a maximum dosage of
less than about 50 kGy, depending on the particular polymer. For
propylene polymers the amount typically ranges from a minimum
dosage of about 1 kilograys (kGy) to a maximum dosage of less than
about 10 kGy. Typically, the total controlled amount of dosage
ranges from less than about 9 kGy to about 7 kGy for propylene
polymers to avoid degradation. While low dose rates and longer
residence times are preferred for radiation grafting, practical
operation may necessitate speeds that force higher dose rates and
shorter residence. Exclusion of oxygen in a multilayer sandwich
allows free radical chemistry to continue after E-beam exposure for
duration sufficient to improve the grafting yield.
UV Curing Step
[0088] In UV irradiation step 400, multilayer sandwich structure 24
is exposed to a sufficient quantity of ultraviolet radiation so as
to initiate free radical polymerization from the grafted
photoinitiator monomer and any free, unreacted acrylate groups
and/or ethylenically unsaturated groups. The polymerization of the
unreacted ethylenically unsaturated groups onto the grafted
interstitial and outer surfaces of porous base substrate 12 forms
multilayer sandwich structure 27 comprising functionalized
substrate 30 sandwiched between removable carrier layer 22 and
removable cover layer 19. As shown in exemplary method 10,
multilayer sandwich structure 24 proceeds through chamber 40, which
contains at least one device 41 capable of providing a sufficient
dose of UV radiation. A single device 41 is capable of providing a
sufficient dose of radiation, although two or more devices 41 may
be used especially for relatively thick porous base substrates 12
or to double the lamp output. Upon UV irradiation, essentially all
remaining acrylate and non-acrylate groups are incorporated into a
polymer coating on the surfaces of the base substrate 12, rendering
it hydrophilic
[0089] Typically, chamber 40 comprises an inert atmosphere such as
nitrogen, carbon dioxide, helium, argon, etc. with a minimal amount
of oxygen, which is known to inhibit free-radical polymerization.
In embodiments wherein porous base substrate 12 is irradiated
without removable cover layer 19, the amount of oxygen within
chamber 25 can be more of a concern. When removable carrier layer
22 and removable cover layer 19 cover the porous base substrate 12,
exposure to oxygen within chamber 25 is minimal.
[0090] UV light sources can be of two types: 1) relatively low
light intensity sources such as blacklights which provide generally
10 mW/cm.sup.2 or less (as measured in accordance with procedures
approved by the United States National Institute of Standards and
Technology as, for example, with a UVIMAP.TM. UM 365 L-S radiometer
manufactured by Electronic Instrumentation & Technology, Inc.,
in Sterling, Va.) over a wavelength range of 280 to 400 nanometers
and 2) relatively high light intensity sources such as medium
pressure mercury lamps which provide intensities generally greater
than 10 mW/cm.sup.2, preferably between 15 and 450 mW/cm.sup.2.
Where actinic radiation is used to fully or partially crosslink the
oligomer composition, high intensities and short exposure times are
preferred. For example, an intensity of 600 mW/cm.sup.2 and an
exposure time of about 1 second may be used successfully.
Intensities can range from about 0.1 to about 150 mW/cm.sup.2,
preferably from about 0.5 to about 100 mW/cm.sup.2, and more
preferably from about 0.5 to about 50 mW/cm.sup.2.
Peeling Step
[0091] Upon exiting chamber 25, multilayer sandwich structure 27
proceeds toward peeling step 500. In peeling step 500, multilayer
sandwich structure 27 is disassembled by separating removable
carrier layer 22 and removable cover layer 19 from functionalized
substrate 30. As shown in exemplary method 10, removable cover
layer 19 is separated from an outer surface of functionalized
substrate 30 and taken-up as roll 28, while removable carrier layer
22 is separated from an opposite outer surface of functionalized
substrate 30 and taken-up as roll 29.
[0092] In one desired embodiment, after exposure to an electron
beam, UV curing, and exiting chamber 40, removable carrier layer 22
and removable cover layer 19 are allowed to remain on
functionalized substrate 30 for a period of time prior to peeling
step 400 so as to provide prolonged protection of functionalized
substrate 30 from exposure to oxygen. Desirably, removable carrier
layer 22 and removable cover layer 19 remain on functionalized
substrate 30 for at least 15 seconds, more desirably, for about 30
to about 60 seconds after exiting chamber 25. However, there is no
upper time limit that will reduce grafting quality and multilayer
sandwich structure 27 can remain intact for an extended time period
as would be the case if batch processing rolls of multilayer
sandwich structure 27 are prepared. Once multilayer sandwich
structure 27 is disassembled, functionalized substrate 30 can
proceed to an optional washing/rinsing step 600.
[0093] In optional washing/rinsing step 600, functionalized
substrate 30 is washed or rinsed one or more times in rinse chamber
31 to remove any unreacted monomers, solvent or other reaction
by-products from functionalized substrate 30. Typically,
functionalized substrate 30 is washed or rinsed up to three times
using a water rinse, an alcohol rinse, a combination of water and
alcohol rinses, and/or a solvent rinse (e.g., acetone, MEK, etc).
When an alcohol rinse is used, the rinse may include one or more
alcohols including, but not limited to, isopropanol, methanol,
ethanol, or any other alcohol that is practical to use and an
effective solvent for any residual monomer. In each rinse step,
functionalized substrate 30 may pass through a rinse bath or a
rinse spray.
[0094] In optional drying step 700, functionalized substrate 30 is
dried to remove any rinse solution from functionalized substrate
30. Typically, functionalized substrate 30 is dried in oven 32
having a relatively low oven temperature for a desired period of
time (referred to herein as "oven dwell time"). Oven temperatures
typically range from about 60.degree. C. to about 120.degree. C.,
while oven dwell times typically range from about 120 to about 600
seconds. Any conventional oven may be used in optional drying step
700 of the present invention. Suitable ovens include, but are not
limited to, a convection oven.
[0095] It should also be noted that in other embodiments drying
step 700 can proceed before washing/rinsing step 600 eliminating
volatile components before extraction of non-grafted residue.
[0096] Following optional drying step 700, dried hydrophilic
substrate 30 can be taken up in roll form as roll 33 in step 800.
Hydrophilic substrate 30 may be stored for future use in roll form,
used immediately as is, or further processed to further alter the
surface properties of hydrophilic substrate 30.
[0097] In one exemplary embodiment, hydrophilic substrate 30 is
further processed to alter the surface properties of hydrophilic
substrate 30. In this embodiment, functionalized substrate 30 is
processed through a grafting process such as exemplary method 10
for a second time (or even more times) in order to (i) graft
additional grafting monomers onto interstitial and outer surfaces
of functionalized substrate 30, (ii) graft additional monomers onto
grafted species extending from interstitial and outer surfaces of
functionalized substrate 30, or (iii) both (i) and (ii).
[0098] For example, in one exemplary embodiment, functionalized
substrate 30 is prepared by imbibing a porous base substrate with a
first solution comprising one or more grafting monomers in a
solvent, wherein the one or more grafting monomers comprise at
least one grafting monomer having an acrylate group and a
photoinitiator group thereon; and then exposing the porous base
substrate imbibed with the first solution to a controlled amount of
electron beam radiation so as to graft the photoinitiator monomers
to interstitial and outer surfaces of the porous base
substrate.
[0099] The resulting first functionalized substrate is rinsed to
remove any unreacted grafting monomer, and may then subsequently
imbibed with a second solution comprising one or more grafting
monomers in a solvent, wherein the one or more grafting monomers
comprise at least one grafting monomer having and acrylate group
for grafting and at least one additional ethylenically unsaturated
group for subsequent UV crosslinking; and then exposing the first
functionalized substrate imbibed with the second solution to a
controlled amount of electron beam radiation to form a second
functionalized substrate having both photoinitiator groups and
ethylenically unsaturated polymerizable groups.
[0100] The further modified functionalized substrate 30 can then
proceed through an optional washing/rinsing step, such as exemplary
washing/rinsing step 500 in exemplary method 10, and an optional
drying step, such as exemplary drying step 600 in exemplary method
10. Subsequent to the two-step grafting process, the imbibed
substrate can be further processed by the UV irradiation step.
[0101] In optional heating step (not shown), hydrophilic substrate
30 is heated. Typically, during the optional heating step,
hydrophilic substrate 30 is subjected to an oven having an oven
temperature of up to about 120.degree. C. depending on a number of
factors including, but not limited to, the reactants, the porous
base substrate, the functional groups present on the grafted
species, and the dwell time within oven 36. Typically, the oven
temperature used in optional heating step is 30.degree. C. of
greater (desirably, 40.degree. C. or greater, 50.degree. C. or
greater, or 60.degree. C. or greater). The oven temperature
typically ranges from about 60.degree. C. to about 120.degree. C.
Typically, oven dwell time in optional heating step ranges from
about 60 seconds to about 1 hour.
[0102] Any conventional oven may be used in the optional heating
step of the present invention, such as optional heating step.
Suitable ovens include, but are not limited to, the above-described
ovens used in optional drying step 600 of exemplary method 10.
Desirably, the oven used in optional heating step 800 of exemplary
method 50 comprises a circulating air oven.
[0103] The hydrophilic substrate 33 may be stored for future use in
roll form, used immediately as is, or further processed in one or
more additional process steps (not shown). Suitable additional
process steps may include, but are not limited to, a reaction step
or a coating step wherein a coating composition is applied to
further hydrophilic substrate 35, a lamination step wherein one or
more additional layers are temporarily or permanently joined to
further hydrophilic substrate 33, an assembling step wherein
further hydrophilic substrate 33 is combined with one or more
additional components to form a finished product (e.g., a filter
assembly), a packaging step wherein further hydrophilic substrate
33 or a finished product comprising further hydrophilic substrate
33 is packaged within a desired packaging material (e.g., a
polyethylene film or bag), or any combination thereof.
[0104] The methods of making functionalized substrates of the
present invention may also be described by one or more process
parameters including, but not limited to, the process parameters
provided below.
1. Batch Versus Continuous Process
[0105] It should be noted that the methods of making functionalized
substrates of the present invention may be performed using a
continuous process, such as exemplary method 10 shown in FIG. 1, or
alternatively, using a batch process wherein one or more of the
above-described process steps are performed separate from one
another. Desirably, the methods of making functionalized substrates
are performed using a continuous process, such as exemplary method
10 shown in FIG. 1.
2. Line Tension
[0106] When using a continuous process, such as exemplary method
10, one or more drive rolls (not shown) may be used to move porous
base substrate 12 or functionalized substrate 30 through the
continuous process. The one or more drive rolls provide sufficient
tension on porous base substrate 12 and functionalized substrate 30
to move porous base substrate 12 and functionalized substrate 30
through a given apparatus. Care should be taken when determining
the amount of tension to apply in order to prevent shrinkage and/or
tearing of porous base substrate 12 or functionalized substrate 30
during processing. If a stronger carrier web (e.g., removable
carrier layer 22) is used to convey porous base substrate 12 or
functionalized substrate 30, then the tension load is easier to
adjust without transmitting the tension load through the substrate
itself.
[0107] In the exemplary continuous grafting process of the present
invention, the one or more drive rolls typically operate in a range
of 5 to 40 lbs (22 to 178 Newtons) of tension on a (12 inch) 30 cm
wide web of porous base substrate 12 or functionalized substrate 30
in order to move porous base substrate 12 or functionalized
substrate 30 through a given apparatus, resulting in a tension of
0.7 to 5.9 Newtons per lineal centimeter of porous base substrate
12 or functionalized substrate 30. In one desired embodiment, the
one or more drive rolls operate in a range of 1.4 to 3.0 Newtons
per lineal centimeter of porous base substrate 12 or functionalized
substrate 30.
3. Line Speed
[0108] In the exemplary continuous grafting process of the present
invention, the one or more drive rolls also provide a desired line
speed through a given apparatus. Desirably, porous base substrate
12 and functionalized substrate 30 move through a given apparatus
at a line speed of at least about 1.52 meters/minute (mpm) (5 fpm).
In one desired embodiment, porous base substrate 12 and
functionalized substrate 30 move through a given apparatus at a
line speed ranging from about 3.05 mpm (10 fpm) to about 30.5 mpm
(100 fpm).
[0109] The disclosed methods of making functionalized substrate may
be used to prepare a variety of hydrophilic substrates. The
hydrophilic substrates have a polymerized coating derived from
grafting followed by UV initiated polymerization from the grafted
photoinitiator (a), the monomer having an ethylenically unsaturated
group (b), and (c) optional other hydrophilic monomers that may be
grafted or non-grafted.
[0110] In any of the above-described methods of making a
functionalized substrate, any of the above-mentioned porous base
substrates, grafting monomers, and reactants may be used to form a
given functionalized substrate. The porous base substrate is often
in the form of a porous membrane such as a microporous membrane, a
nonwoven web, or porous fibers. In some embodiment, the porous base
substrate comprises a hydrophobic microporous membrane formed by a
thermally-induced phase separation (TIPS) method.
[0111] In one embodiment, the methods provide a porous article
having a hydrophilic polymer coating on the surface thereof, the
polymer coating comprising the UV polymerization reaction product
of a grafted photoinitiator group and one or more ethylenically
unsaturated polymerizable monomers, which may be ungrafted acrylate
groups or other non-acrylate ethylenically unsaturated
polymerizable groups. In another embodiment, the methods provide a
porous article having a hydrophilic polymer coating on the surface
thereof, the polymer coating comprising the UV polymerization
reaction product of a grafted photoinitiator group, a grafted
monomer having and one or more non-acrylate ethylenically
unsaturated polymerizable groups, and one or more ethylenically
unsaturated polymerizable monomers.
[0112] The method of making a hydrophilic substrate alters the
original hydrophobic nature of the porous base substrate, as the
grafted and UV polymerized species include a hydrophilic group. In
one embodiment, the grafting monomer having a first grafting
acrylate group and a second non-grafting ethylenically unsaturated
group may comprise a hydrophilic groups, as illustrated in Formula
IV (supra).
[0113] For example, poly(alkylene oxide) compounds of Formula IV
can be used to impart a hydrophilic character to a hydrophobic
porous base substrate. These grafting monomers have an acrylate
group, a non-acrylate ethylenically unsaturated group and a
hydrophilic polyalkylene glycol (i.e., polyalkylene oxide) group.
Alternatively grafting monomers of Formula II may be used which do
not contain the hydrophilic polyalkylene glycol (i.e. poly(alkylene
oxide)) group. In these instances, hydrophilicity is imparted using
a third monomer, which may contain a grafting acrylate group or a
non-acrylate ethylenically unsaturated group, and a hydrophilic
group, such as a quaternary ammonium group.
[0114] The present invention enables the formation of
functionalized substrates having many of the advantages of a
hydrophobic porous bases substrate (e.g., a hydrophobic microporous
membrane), but with permanent hydrophilicity on the surfaces of the
functionalized substrate. The present invention reduces or
eliminates many of the known problems associated with porous bases
substrates formed from hydrophilic polymers including, but not
limited to, hygroexpansive issues; brittleness without
humidification problems; mechanical strength weakness; and poor
solvent, caustic and/or acidic resistance. The present invention
also enables the formation of functionalized substrates having
various degrees of hydrophilicity depending on the materials and
steps used to form a given functionalized substrate.
[0115] The hydrophilic porous membranes are particularly suited as
filter media, such as the filter media found in water filtration
devices. As the polymer is grafted, either directly or indirectly,
to render it hydrophilic, the filter media is durable. In many
water filtration media, such as filter cartridges, the filter media
is cleaned or sanitized by contact or flushing with aqueous NaOH.
The hydrophilic porous substrate described herein, can be contacted
or flushed with NaOH and retain the hydrophilic properties as
evidenced by the surface energy and wettability.
[0116] The present invention is described above and further
illustrated below by way of examples, which are not to be construed
in any way as imposing limitations upon the scope of the invention.
On the contrary, it is to be clearly understood that resort may be
had to various other embodiments, modifications, and equivalents
thereof which, after reading the description herein, may suggest
themselves to those skilled in the art without departing from the
spirit of the present invention and/or the scope of the appended
claims.
EXAMPLES
Materials
[0117] "VAZPIA" refers to 2-propenoylaminoethanoic acid,
2-(4-(2-hydroxy-2 methylpropanoyl)phenoxy)ethyl ester prepared
according to Example 1 of U.S. Pat. No. 5,506,279 (Babu et
al.).
[0118] "PEG 400" Polyethyleneglycol, molecular weight 400, Aldrich
Chemical Co.
[0119] "LUCIRIN TPO" is s 2,4,6-trimethylbenzoy diphenyl phosphine
oxide, available from BASF, Charlotte, N.C.
[0120] Electron beam irradiation was carried out using a Model
CB-300 electron beam system, obtained from Energy Sciences, Inc.,
Wilmington, Mass. The film samples were placed between two sheets
of poly(ethylene terephthalate) film for the irradiation.
[0121] The following procedure was adhered to unless otherwise
specified. Samples of film were placed between two larger area size
pieces of 4-mil thick PET and taped together at one end. This
sandwich was then opened and the sample film was wetted with
monomer solution and the sandwich reclosed. Trapped air bubbles
were removed and excess liquid was squeezed out by gently applying
a rubber roller over the surface of the sandwich. The sandwich was
taped to a moving web of PET and conveyed through the electron beam
processor at a speed of 20 fpm and at a voltage of 300 keV with
sufficient beam current applied to the cathode to deliver the
targeted dose. The beam was calibrated using thin film dosimeters,
calibrated and traceable to a national standards laboratory (RISO,
Denmark). In some cases, to lower the overall dose rate and
increase residence time while under the beam, the dose was
fractionated by multiple passes through the beam to simulate a
longer exposure time more characteristic of electron beams with
cathodes extended in the web direction (i.e. BroadBeam, etc).
Water Flux Test
[0122] Water flux was determined by placing a disk of the test film
having a diameter of approximately 47 millimeters (1.85 inches) in
a Model 4238 Pall Gelman magnetic filter holder (available from
Pall Corp., East Hills, N.Y.). The filter holder was then placed on
a filter flask that was attached to a vacuum pump. A vacuum gauge
was used to monitor the vacuum. Approximately 150 milliliters of
water was placed in the filter holder and then vacuum was applied.
After approximately 50 milliliters of water passed through the film
(the vacuum gauge at this time indicated approximately 0.83
millimeters of mercury (approximately 21 inches of mercury), timing
was commenced using a stopwatch. When all of the remaining water
had passed through the film, timing was stopped. The water flux was
the time, measured in seconds, that elapsed for 100 milliliters of
water to pass through the membrane under a vacuum of 0.83
millimeters of mercury.
Average Pore Diameter
[0123] The principle for determining average pore diameter is by
allowing a wetting liquid to spontaneously fill the pores in the
sample membrane and then using a non-reacting gas to displace the
liquid from the pores of the membrane, where the gas pressure and
flow rates are accurately measured. An Automated Capillary Flow
Porometer, model number APP-1200-AEX with supplied software, Capwin
version 6.71.54 from Porous Materials Inc. (PMI) of Ithaca N.Y. was
used to obtain these values. Fluorinert FC-43 (available from 3M)
was used as the wetting fluid and compressed nitrogen gas was used
for displacement with a maximum pressure setting of 100 psi (689
kPa).
Penetrating Drop Method:
[0124] The surface energy of the samples was measured using. Dyne
Test Solutions.TM. available from Jemmco LLC., Mequon Wis. 53092
(general test method disclosed in Journal of Membrane Science, 33
(1987) 315-328 Wetting Criteria For The Applicability of Membrane
Distillation). A series of the test solutions of increasing surface
tension are applied to the samples to until the solution beads up
on the sample surface. The surface tension is then recorded.
[0125] The hydrophilic substrates of the present invention can
exhibit various degrees of wettability upon exposure to various
solutions or solvents. Wettability can often be correlated to the
hydrophilic character of the hydrophilic substrate. As used herein,
the term "instant wet" or "instant wettability" refers to the
penetration of droplets of water into a given substrate as soon as
the water contacts the substrate surface, typically within less
than 1 second. For example, a surface wetting energy of about 72
dynes or larger usually results in instant wetting. As used herein,
the term "no instant wet" refers to penetration of droplets of
water into a given substrate but not as soon as the water contacts
the substrate surface. As used herein, the term "no wetting" refers
to the lack of penetration of droplets of water into a given
substrate. For example, a surface wetting energy of about 60 dynes
or less usually results in no wetting.
[0126] The hydrophilic substrates also exhibit resistance to
multiple exposures to heat.
Example 1
[0127] A sample of a thermally induced phase separation (TIPS)
microporous polypropylene film was prepared using the method
described in U.S. Pat. No. 4,726,989 (Mrozinski). The TIPS film had
the following properties: about 4.5 mils thick, Gurley (air flow)
about 6 sec/50 cc air with an pore size range of about 0.44 0.8
microns, has a surface wetting energy of about 35 dynes (using
JEMMCO LLC solutions for the penetrating drop method) and has a
water flux of 25 sec (47 mm holder, 23 in Hg vacuum, IPA prewet).
The sample was imbibed with a solution of 10% PEG 400 diacrylate
with 0.5% VAZPIA (added to solids) in methanol. The samples were
conveyed through the beam on a web carrier and were sandwiched
`wet` between layers of 4 mil PET in order to delay the diffusion
of oxygen back into the membranes when they exited the beam
chamber.
[0128] The sandwiched sample was irradiated by E-beam on an ESI
CB-300 electron beam with a dose of 10 kGy set at a voltage of 300
keV. The samples (still sandwiched) were then UV irradiated with a
Spectroline model SP-100P 365 nm light for 20 minutes.
[0129] Following UV irradiation, the grafted, crosslinked TIPS
sample was soaked in a tray of water and exchanged three times with
clean water to wash the sample. The sample was dried with an air
gun with low heat and then heated to 60.degree. C. for 1/2 hour in
an oven. The resulting porous film sample was instantly wettable
with water. As used herein, the term "instant wet" or "instant
wettability" refers to the penetration of droplets of water into a
given substrate as soon as the water contacts the substrate
surface, typically within less than 1 second.
Comparative Example 2
[0130] This comparative example was prepared as in Example 1 except
no VAZPIA was imbibed and the sample was not subsequently UV
irradiated. The sample after drying and heating was not
spontaneously wettable, indicating the TIPS sample was
insufficiently grafted to render the film hydrophilic. Using the
penetrating drop method for determining surface wetting energy, the
surface wetting energy was now found to be about 56 dynes. The
increase in surface wetting energy (relative to the starting TIPS
sample) indicates some grafting to the membrane was initiated.
Example 3
[0131] This example was prepared as in Example 1 except the E-beam
was 5 kGy. The sample, after drying and heating, was spontaneously
wettable, indicating sufficient polymerization of the PEG 400
diacrylate (from UV cure and E-beam grafting) to render the film
hydrophilic. Using water for the penetrating drop method for
determining surface wetting energy (desired hydrophilicity) the
surface wetting energy was found to be at or above 72 dynes.
Comparative Example 4
[0132] This comparative example was prepared as in Example 3 except
no VAZPIA was imbibed and the sample was not subsequently UV
irradiated. The sample after drying and heating was not
spontaneously wettable or with vacuum (pressure) assistance,
indicating insufficient grafting to render the film hydrophilic.
Using the penetrating drop method for determining surface wetting
energy, the surface wetting energy was found to be about 42 dynes.
The increase in surface wetting energy (relative to the starting
TIPS sample) indicates some grafting to the membrane was
initiated.
Comparative Example 5
[0133] This comparative example was prepared as in Example 3 except
no VAZPIA was imbibed, the sample was not subsequently UV
irradiated and the sample was irradiated at 20 kGy instead of 11
kGy. The sample after drying and heating was spontaneously
wettable, indicating sufficient grafting with the extra E-beam
radiation to render the film hydrophilic. However, physical
properties of the PP membrane are compromised--the strength was
poor and would crumble after exposure to heat, indicating polymer
chain degradation at the indicated e-beam dose.
Example 6
[0134] This example was prepared as in Example 1 except only 5%
PEG400 diacrylate was used in the imbibing solution. The sample,
after drying and heating, was not spontaneously wettable with
water, but was wettable with vacuum (pressure) assistance,
indicating insufficient grafting occurred to render the film
instantly wettable.
Comparative Example 7
[0135] This comparative example was prepared as in Example 6 except
no VAZPIA was imbibed and the sample was not subsequently UV
irradiated. The sample after drying and heating was not
spontaneously wettable or with vacuum (pressure) assistance,
indicating insufficient grafting occurred to render the film
hydrophilic.
Example 8
[0136] This example was prepared as in Example 1 except the sample
was E-beam processed at about 0.75 Mrads and the imbibing solution
contained 10% PEG 400 dimethacrylate, 2%
3-(Acryloxy)-2-hydroxypropylmethacrylate, and VAZPIA (at 0.42% to
monomer weight). The sample after washing was dried by heating in a
frame at 60.degree. C. for 1/2 hour in an oven and was found to be
spontaneously wettable. This indicates sufficient E-beam grafting
and subsequent polymerization (from UV cure) to render the film
hydrophilic.
[0137] Using water for the penetrating drop method for determining
surface wetting energy (desired hydrophilicity), the surface
wetting energy was found to be at or above 72 dynes. The bubble
point pore size was slightly reduced to about 0.38 microns and had
a water flux of about 30 seconds when coated and irradiated with
the tight pore size up (bubble point of 0.36 microns and water flux
of 43 seconds tight pore side down, (no IPA pre-wetting needed)).
Two separate pieces of this sample were soaked in both 1N HCl and
1N NaOH at room temperature for 75 hours without a change in the
film properties.
Comparative Example 9
[0138] This example was prepared as in Example 8 except no VAZPIA
or 3-(Acryloxy)-2-hydroxypropylmethacrylate was added to the
imbibing solution and the sample was not subsequently UV
irradiated. The sample was dried at 55.degree. C. for an hour on an
Emerson Speed Dryer (Thwing Albert) Model 130. After drying, the
porous film was not spontaneously wettable. The surface wetting
energy was found to be 39 dynes. Despite the amount of
hydrophilicizing monomer (PEG 400 dimethacrylate) used, grafting
was insufficient to render the film hydrophilic because of the
reduced reactivity of the methacrylate groups in the e-beam
grafting step.
Comparative Example 10
[0139] This example was prepared as in Example 8 except the sample
was irradiated at 20 kGy instead of 7.5 kGy, no VAZPIA or
3-(Acryloxy)-2-hydroxypropylmethacrylate was added to the coating
solution, the sample was not subsequently UV irradiated and was
dried on the Speed Dryer as in Example 9. After drying, the sample
was not spontaneously wettable, indicating insufficient grafting to
render the film hydrophilic, despite with the extra E-beam
radiation, as the methacrylate groups are less reactive than the
acrylate groups in the grating step (compare with Example 5).
However, with the extra radiation, the surface wetting energy was
found to be slightly better than Example 9, measured at 45
dynes.
Example 11
[0140] This example was prepared as in Example 8 (E-beam dose of
7.5 kGy) except the VAZPIA was added 1.0% to monomer weight. After
washing, the sample was dried by heating in a frame at 60.degree.
C. for 1/2 hour in an oven and was found to be spontaneously
wettable, indicating that after E-beam grafting there was
sufficient polymerization (from UV cure) to render the film
hydrophilic.
[0141] Using water for the penetrating drop method for determining
surface wetting energy (desired hydrophilicity), the surface
wetting energy was found to be at or above 72 dynes. The bubble
point pore size was not reduced and remained at about 0.44 microns
and had a water flux of about 25 seconds (coated and irradiated
with the tight pore size down).
[0142] It is surmised that, during the UV cure, the larger amount
of grafted VAZPIA generated more free radical initiation sites on
the membrane substrate. This effectively limited the grafted chain
length as the supply of monomer in solution was depleted, thereby
reducing or eliminating pore plugging from the coating while still
remaining very hydrophilic.
Example 12
[0143] This example was prepared as in Example 11 except the VAZPIA
was added at 0.25% to monomer weight. The sample, after washing,
was dried by heating it in a frame at 60.degree. C. for 1/2 hour in
an oven. The sample was not found to be spontaneously wettable,
indicating that after E-beam grafting there was not a sufficiently
high enough concentration of initiation sites for continued
polymerization (from UV cure) to render the film hydrophilic. Using
JEMMCO LLC solutions for the penetrating drop method, the surface
wetting energy was found to be about 64 dynes.
Example 13
[0144] This example was prepared as in Example 1 except the sample
was not E-beam radiated. The imbibing solution contained 10% PEG400
dimethacrylate and 2% 3-(Acryloxy)-2-hydroxypropylmethacrylate,
with 1.0% VAZPIA (to monomer weight) in methanol. After 20 minutes
of UV cure, the sample, after washing and drying, was not
spontaneously wettable, indicating polymerization from the UV cure
alone was insufficient to render the film hydrophilic.
Example 14
[0145] This example was prepared as in Example 1 except the sample
was not E-beam radiated. The imbibing solution contained 11.5%
PEG400 dimethacrylate and 4%
3-(Acryloxy)-2-hydroxypropylmethacrylate, with 2.0% VAZPIA (to
monomer weight) in methanol. After 4 minutes of UV cure with
Quantum Technologies (Quant 48) UVA lamps, the sample, after
washing and drying, was not spontaneously wettable, indicating
polymerization from the higher intensity UV cure was insufficient
to render the film hydrophilic.
Comparative Example 15
[0146] This example was prepared as in Example 1 except the sample
was not E-beam radiated. The imbibing solution contained 11.5%
PEG400 dimethacrylate and 4%
3-(Acryloxy)-2-hydroxypropylmethacrylate, with 1.0% Lucerin TPO to
monomer weight (a non-grafting photoinitiator)) in methanol. After
4 minutes of UV cure with Quantum Technologies (Quant 48) UVA
lamps, the sample, after washing and drying, was not spontaneously
wettable. This indicates polymerization from the higher intensity
UV cure in this system and more efficient photo initiator was not
enough to make the film hydrophilic.
Example 16
[0147] This example was prepared as in Example 1 except the
imbibing solution contained 10% PEG400 dimethacrylate, no
3-(Acryloxy)-2-hydroxypropylmethacrylate, with 1.0% VAZPIA (to
monomer weight) in methanol. After E-beam and UV processing,
washing and drying, the sample was not spontaneously wettable,
indicating insufficient E-beam grafting or polymerization (from the
UV cure) occurred to render the film hydrophilic.
Example 17
[0148] This example was prepared as in Example 1 except the
imbibing solution contained 11.5% PEG400 dimethacrylate, 4% PEG400
diacrylate with 2.0% VAZPIA (to monomer weight) in methanol. After
E-beam and UV processing, washing and drying, the sample was
spontaneously wettable, indicating the E-beam grafting sufficiently
modified the surface for polymerization from the UV cure to render
the film hydrophilic. The significance of having a faster grafting
acrylate or diacrylate in the coating formula is demonstrated.
Comparative Example 18
[0149] This example was prepared as in Example 1 except the
imbibing solution contained 11.5% PEG400 dimethacrylate, and 1.4%
Lucerin TPO (to monomer weight) in methanol. After E-beam and UV
processing, washing and drying the sample was not spontaneously
wettable, indicating the low dose E-beam grafting did not modify
the surface enough for subsequent polymerization from the UV cure
to make the film hydrophilic, in the absence of a grafting
photoinitiator.
Example 19
[0150] This example was prepared as in Example 1 except the
imbibing solution contained 12% acrylic acid, 4%
3-(acryloxy)-2-hydroxypropylmethacrylate with 2% VAZPIA (to monomer
weight) in methanol. After E-beam and UV processing, washing and
drying, the sample was spontaneously wettable, indicating the
E-beam grafting modified the surface enough for polymerization from
the UV cure to render the film hydrophilic.
Example 20
[0151] This example was prepared as in Example 1, except the
imbibing solution contained 12% acrylic acid and 4%
3-(acryloxy)-2-hydroxypropylmethacrylate, with 2.0% VAZPIA (to
monomer weight) in methanol. After E-beam and 4 minutes of UV cure
with Quantum Technologies (Quant 48) UVA lamps, washing and drying,
the sample was spontaneously wettable.
Example 21
[0152] This example was prepared as in Example 1 except the
imbibing solution contained 12% N-vinyl pyrrolidone, 4%
3-(acryloxy)-2-hydroxypropylmethacrylate with 2% VAZPIA (added to
solids) in methanol. After E-beam and UV processing, washing and
drying, the sample was wettable, but not as complete as other
samples.
Comparative Example 22
[0153] This example was prepared as in Example 1 except the sample
was not E-beam radiated, and the imbibing solution contained 12%
N-vinyl pyrrolidone and 4%
3-(Acryloxy)-2-hydroxypropylmethacrylate, with 2.0% VAZPIA (to
monomer weight) in methanol. After 4 minutes of UV cure with
Quantum Technologies (Quant 48) UVA lamps, washing and drying, the
sample was not spontaneously wettable.
Example 23
[0154] A sample of TIPS porous polypropylene (PP) film was made
using methods disclosed in U.S. Pat. No. 4,726,989 (Mrozinski),
where the oil diluent was extracted before stretching. The porous
membrane has a surface wetting energy of about 35 dynes measured
using JEMMCO LLC solutions for the Penetrating Drop Method and has
a water flux time of 46 sec (100 ml, 47 mm Gelman Magnetic Filter
Funnel (4238), 21 inches Hg vacuum, IPA prewet).
[0155] The porous polypropylene TIPS sample was imbibed with a
solution of 9% PEG 400 dimethacrylate, 2%
3-(acryloxy)-2-hydroxypropylmethacrylate with 1.0% VAZPIA
photoinitiator (to monomer weight) in methanol. The PP membrane
sample was sandwiched `wet` between layers of 4 mil PET film with
any excess solution squeezed out with a hand held rubber roller.
The assembly was conveyed through the beam on a carrier web. (The
PET covers delay the diffusion of oxygen back into the membranes
when they exit the beam chamber.) The sandwiched assembly was
irradiated by E-beam on an ESI CB-300 electron beam with a dose of
7.5 kGy set at a voltage of 300 keV. The samples (still sandwiched)
were then UV irradiated with a Spectroline model SP-100P 365 nm
light for 10 minutes on each side.
[0156] Following UV irradiation, the grafted, crosslinked PP sample
was removed from the PET covers, soaked in a tray of water and that
was exchanged three times with clean water to wash the sample. The
sample was mounted on a frame and dried by heating to 60.degree. C.
for 1/2 hour in an oven. The resulting hydrophilic porous film
sample was instantly wettable with a drop of water. The starting
films average pore size was measured at 0.51 microns compared with
the finished product's average pore size at 0.56 microns indicating
no pore plugging occurred from the grafting process. (The very
slight pore size expansion is well within experimental error and
sampling film variations.)
[0157] The framed PP sample was steam autoclaved for three half
hour cycles at 121.degree. C. and found to be still instantly water
wettable after exposure. A 47 mm disk was cutout and the flux time
was essentially unchanged measuring 48 seconds. The grafted
hydrophilic PP disk was then placed into a 40 ml vial and filled
with 0.625 N NaOH and heated to 60.degree. C. for 300 minutes. The
sample was removed from the vial and thoroughly washed with water
and dried. The sample was still instantly wettable with a drop of
water.
* * * * *