SIMULTANEOUS POLYMERIZATION O F TWO VINYL MONOMER
BACKGROUND O F THE INVENTION
Field o f the invention
[0001] The invention relates to bi-poiar electrodes, and more particularly to a
method of simultaneously applying two dissimilar ion exchange polymers to opposite
faces of the electrode substrate.
Description o f Related Art
[0002] it is increasingly desirable to purity water using passive deionization.
Passive deionization uses bi-polar electrodes, e.g., two sheets having a first side or
face formed of material with cation-exchange functionality, and a second side or face
with anion-exchange functionality. Each of the two different layers of ion exchange
material is porous or otherwise somewhat permeable to a neutral fluid by virtue of its
chemistry, physical structure and degree of cross-linking, and each layer possesses ion
exchange functionality that operates to transport one type of ion across the material in
an electric field, while substantially or effectively blocking most ions of the opposite
polarity. With the two materials of different exchange type positioned face-to-face in
adjacent layers, ions are effectively "blocked" by one or the other layer and thus
cannot traverse the sheet.
[0003] Applying the ion exchange monomers to the separate sides of the
electrode and polymerizing them creates a bi-polar electrode that is more efficient to
operate than a series of monoplanar electrodes with ion exchange membranes pressed
against them in this regard, there is a desire to provide new processes for bi-polar
electrode fabr ication
SUMMARY O F THE INVENTION
[0004] In one aspect, the invention is directed to a method of forming a bipoiar
electrode having ion exchange polymers on opposite faces of a porous substrate
The method includes providing an electrode substrate with activated carbon layers on
opposite faces of the electrode substrate, wherein said faces have an outer perimeter
band void of the activated carbon layers. The electrode substrate is placed in a
thermoplastic envelope formed by a pair of polyethylene films. A Mylar sheet is
placed in each side of the envelope against the electrode substrate, and the envelope is
thermally sealed to the outer perimeter band of the electrode substrate void of
activated carbon to form a first pocket on one side of the electrode substrate and a
second pocket on the opposite side of the electrode substrate. The method also
includes inserting a first polymerizable monomer mixture having an anion
exchange group into the first pocket of the envelope and inserting a second
polymerizable monomer mixture having a cation exchange group into the second
pocket of the envelope. The first and second polymerizable monomers mixtures are
then polymerized in an oven.
[0005] The present invention and its advantages over the prior art will become
apparent upon readmg the following detailed description and the appended claims with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The above mentioned and other features of this invention will become
more apparent and the invention itself will be better understood by reference to the
following description of embodiments of the invention taken in conjunction with the
accompanying drawings, wherein:
[0007] FIG. 1 illustrates a schematic of a bi-poiar electrode made according to
an embodiment of the invention.
[0008] Corresponding reference characters indicate corresponding parts
throughout the views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The invention will now be described in the following detailed
description with reference to the drawings, wherein preferred embodiments are
described in detail to enable practice of the invention. Although the invention is
described with reference to these specific preferred embodiments, it will be
understood that the invention is not limited to these preferred embodiments. But to
the contrary, the invention includes numerous alternatives, modifications, and
equivalents as will become apparent from consideration of the following detailed
description.
[0010] Referring to FIG. 1, a bi-polar electrode 10 comprising a substantially
flat electrode substrate 12 with different ion exchange polymer coatings on its opposite
sides is shown. The substrate 12 is a porous support with an intermediate conductive
film. Desirably, the electrode substrate 12 is made of a thermoplastic polyethylene
film to which activated carbon layers are bonded to each face 12A, 12B of the film to
form the porous support. The opposite faces 12A, 12B of the electrode substrate are
coated with different ion exchange polymers. According to the invention the opposite
faces 12A, 12B of the electrode substrate 12 are simultaneously coated with two vinyl
monomer mixtures and undergo simultaneous polymerization. Thus, the method
described below is particularly suited for simultaneous formation of two dissimilar ion
exchange polymer coatings on opposite faces of the electrode substrate.
[0011] The electrode substrate 12 is made of a thermoplastic film to which an
activated carbon layer 14 is bonded on each face 12A, 12B of the film. The artisan
will appreciate that a host of other materials may be used to form the electrode
substrate. For example, activated carbon containing fillers such as resins and binding
agents such as TFE and PVDF can be mentioned. In one desirable embodiment, the
substrate 12 is generally rectangular-shaped with sides about 10 inches by 21.5 inches
in length. However, one skilled in the art will understand that these dimensions are
for example purposes only, and other dimensions may be used without departing from
the scope of the invention. An outer perimeter of the substrate has a band 18 that is
left void of the activated carbon layer 14.
[0012] A two-pocket envelope 20 is formed around the electrode substrate. By
covering the porous electrode substrate 12 with the envelope 20, the hindrance of
polymerization by oxygen is prevented and surface smoothness is obtained. In one
embodiment, the envelope 20 is formed with two generally rectangular polyethylene
films 22 having three sides bonded together and one side open so that the electrode
substrate 12 may be placed into the envelope. The polyethylene films 22 of the
envelope 20 are thermally sealed to the band 18 of the electrode substrate 12 void of
activated carbon 14 around the perimeter of the substrate, thereby forming a first
pocket on one side of the electrode substrate 12 and a second pocket on the opposite
side of the electrode 12 around the activated carbon 14. A plastic or Mylar sheet 30
(i.e., polyethylene terephthalate) is inserted in each pocket of the envelope 20 between
the polyethylene film 22 and the electrode substrate 12. In one embodiment, the
envelope 20 containing the electrode substrate 12 is then placed between two rigid
plates and the plates are clamped together.
[0013] A first vinyl monomer solution is added to the first pocket formed on
the first face 12A of the substrate and a second vinyl monomer solution is added to the
second pocket formed around the second face 12B of the substrate. The first and
second monomer solutions are non-identical. The liquid monomers displace the air in
the activated carbon. In one embodiment, a vacuum is drawn to remove air from the
activated carbon.
[0014] Desirably, the first pocket is filled with a first polymerizable monomers
mixture comprising a polymerizable monomer having an anion exchange group or a
group that can be converted to an anion exchange group. Means for inserting the first
polymerizable monomers mixture into the first pocket is inserted into the envelope in
one embodiment a transfer pipette may be used to insert the first polymerizable
monomers mixture into the first pocket between the Mylar and the electrode substrate.
In one embodiment, the first polymerizable monomers mixture includes a crosslinking
agent and a polymerization initiator. The first polymerizable monomers mixture is
infiltrated or imbedded into the voids of the porous substrate film, and the
polymerizable monomer mixture infiltrated is polymerized. Any known
polymerizable monomer can be used with no restriction as the first polymerizable
monomer having an anion exchange group or a group that can be converted to an
anion exchange group. Examples of polymerizable monomer having an anion
exchange group are, for example, trimethylammonium methyl methacrylate chloride,
methacryioxypropyitrimethylethyl ammonium chloride, vinylbenzyltrimethyl
ammonium chloride, dialiyldimethyl ammonium chloride and the like and other
ethylenicaliv imsaliirated quaternary ammonium and tertiary amine monomers may be
mentioned.
[0015] Desirably, the second pocket is filled with a second polymerizable
monomers mixture comprising a polymerizable monomer having a cation exchange
group or a group that can be converted to a cation exchange group Means for
inserting the second polymerizable monomers mixture into the second pocket is
inserted into the envelope. In one embodiment a transfer pipette similar to the one
used with the first pocket may be used to insert the second polymerizable monomers
mixture into the second pocket between the Mylar and the electrode substrate. In one
embodiment, the second polymerizable monomers mixture includes a crosslinking
agent and a polymerization initiator. The polymerizable monomers mixture is
infiltrated or imbedded into the voids of the porous substrate film, and the
polymerizable monomer mixture infiltrated is polymerized. Any known
polymerizable monomer can be used with no restriction as the second polymerizable
monomer having the cation exchange group or a group that can be converted to the
cation exchange group. Examples of polymerizable monomer having a cation
exchange group are, for example, sulfoethylmethacrylate, acrylamidomethylpropane,
sulfonic acid, sodium styrenesulfonate, sulfopropylmethacrylate potassium salt, and
the like may be mentioned and the like, and salts and derivatives thereof. Other
ethylenicaliv unsaturated sulfonic acids and carboxylic acids can also be mentioned.
[0016] As to the crosslinking agent added to the first or second polymerizable
monomers mixtures, there is no particular restriction. There can be mentioned, for
example, divinylbenzene, divinylsuifone butadiene chloroprene, divinylbiphenyl,
trivmylbenzene, divinylnaptheiene, diailylamine, divinylpyridine, ethylenegiycoldimethacrylate,
other di or multi acrylates or di or multimethacrylates of polyols.
Latent crosslinking systems such as hydroxymethyl acrylamide plus acrylamide or
hydroxymethylacrylamide and phenol can also be employed.
[0017] As the polymerization initiator, known compounds can be used with no
particular restriction. There can be used, for example, organic peroxides such as
octanoyl peroxide, lauroyl peroxide, tert-butyl peroxy-2-ethylhexaonate, benzoyl
peroxide, tert-butyl peroxyisobutylate, tert-butyl peroxylaurate, tert-hexyl
peroxybenzoate, di-tert-butyl peroxide, and organic azo compounds such as
azobisisobutyronitrile and the like.
[0018] In the first and second polymerizable monomers mixtures, the
proportions of the polymerizable monomer having the anion or cation exchange
groups or groups which can be converted to the anion or cation exchange groups, the
crosslinking agent and the polymerization initiator may be in wide ranges as long as
each component is present in an amount necessary for the polymerization. The
proportion of the crosslinking agent is preferably about 0.4-60 mol %, more
preferably about 1 to 50 mol %, most preferably about 1 to about 40 mol %. of the
total amount of the polymerizable monomer having an ion exchange group or a group
which can be converted to an ion exchange group and the crosslinking agent. The
polymerization initiator is used in an amount of generally.
[0019] In one embodiment, after the first and second polymerizable monomer
mixtures are inserted into the first and second chambers, the first and second
polymerizable monomer mixtures are allowed to stand for a selected duration of time.
Suitable durations are generally between about 1 and 20 minutes, more preferably
between about 5 and 15 minutes, and in one embodiment about 10 minutes. After
standing, the excessive portions of the polymerizable monomer mixtures may then be
removed before the polymerizable mixtures are polymerized.
[0020] In producing the bi-polar electrode 10, the polymerizable monomers
mixture is contacted with the porous substrate formed by the activated carbon layer on
the electrode substrate, as described previously. The polymerization is preferably
conducted after covering the porous membrane with the two-pocket envelope. In
polymerizing the polymerizable monomers mixture, a known polymerization method
is employed with no restriction. In one embodiment, the envelope containing the
electrode substrate is placed in an oven and the vinyl monomers are polymerized onto
the faces of the substrate. Thermal polymerization using a polymerization initiator is
preferred generally because the operation is easy and polymerization can be conducted
relatively uniformly. The temperature of the thermal polymerization is not
particularly restricted and a known temperature condition may be selected
appropriately. Suitable temperatures are generally between 50 and 150 °C, more
preferably between 60 and 120 °C, and in one embodiment, about 85 °C. The
duration of the thermal polymerization is also not particularly restricted and known
duration conditions may be selected appropriately. Suitable durations are generally
between about 10-120 minutes, more preferably about 45-90 minutes and in one
embodiment about 60 minutes Polymerization of the polymerizable monomers
mixture may also be by any known chemical catalytic procedure or using ultraviolet
light without departing from the scope of the invention.
[0021] In order that those skilled in the art will be better able to practice the
present disclosure, the following example is given by way of illustration and not by
way of limitation.
EXAMPLE
[0022] The electrode 10 was made by cutting the electrode substrate 12 with
activated carbon layers 14 to a size of 10 inches (25.4 cm) by 21.5 inches (54.6 cm).
The outer perimeter band 18 of the electrode substrate was maintained free of
activated carbon, leaving 1.5 inches (3.8 cm) of trim around the two long side edges
and the short bottom edge of the electrode substrate. The top edge was cut to 2
inches. The envelope 20 was made with an 11 inches (27.9 cm) by 21.5 inches (54.6
cm) polyethylene bag film with one long side open. The electrode substrate was
placed between the polyethylene bag films 22.
[0023] The polyethylene films 22 of the envelope 20 were thermally sealed to
the area 18 of the electrode substrate 12 void of carbon around the perimeter of the
substrate, thereby forming a pouch on each side of the electrode substrate aroimd the
activated carbon. The envelope 20 was sealed to the substrate ½ inch (1.3 cm) from
edge of the substrate on the two long sides and on the bottom side forming an
envelope with one open side. ½ inch (1.3 cm) of each long side of envelope was cut
off. A Mylar sheet 30 was inserted in each side of the envelope against the electrode
substrate. The envelope was placed between two glass plates and the envelope/glass
plate sandwich was clamped together. A transfer pipette was inserted into each side
of the envelope between the Mylar and the electrode substrate. Desirably, the
envelope/glass plate sandwich was held in a vertical position with the open end and
pipettes at the top. The envelope/glass plate sandwich was clamped in place using a
ring stand with two clamps on a Mylar tray.
[0024] 140 grams of the first polymerizable monomer mixture having an anion
exchange group was poured through one pipette into the first pocket of the envelope
and 140 grams of the second polymerizable monomer mixture having a cation
exchange group was poured through the other pipette into the second pocket of the
envelope. The sides of the sandwich were clipped at 2 inch (5. 1 cm) intervals,
alternately, until the level of the mixtures was above the electrode substrate. The
mixtures were allowed to stand for 10 minutes.
[0025] The envelope 20 was removed from the glass sandwich and placed in
the Mylar tray. The long edge of the electrode substrate was placed near the bottom
surface on the envelope and pushed against the envelope. The electrode substrate was
moved from the bottom of the envelope to the top of the envelope with constant
pressure, sweeping the excess monomer mixture from the envelope into the Mylar
tray. The envelope was turned over and the procedure repeated on the other side of
the envelope.
[0026] The envelope 20 was then placed between the two glass plates and four
large clips were attached at the bottom edge of the envelope/glass sandwich assembly.
Six clips were attached on each side edge of the envelope/ glass sandwich assembly
alternately putting on the clips from bottom to the top. Four clips were attached at the
top edge of the envelope/glass sandwich. The envelope/glass sandwich assembly was
then placed horizontally into a preheated 85 °C oven for one hour.
[0027] The envelope/glass sandwich assembly was removed from the oven and
was allowed to cool for ½ hour. The clips were then removed and the envelope was
separated from the glass plates. The envelope and Mylar were removed from the
electrode and the electrode was placed into IN sodium chloride until ready for use.
[0028] The artisan can also appreciate the fact that pressure can be applied to
the envelopes pressing the polymerizing AIX and CIX materials into a flat, planar
disposition within their respective envelopes.
[0029] While the disclosure has been illustrated and described in typical
embodiments, it is not intended to be limited to the details shown, since various
modifications and substitutions can be made without departing in any way from the
spirit of the present disclosure. As such, further modifications and equivalents of the
disclosure herein disclosed may occur to persons skilled in the art using no more than
routine experimentation, and all such modifications and equivalents are believed to be
within the scope of the disclosure as defined by the following claims
[0030] What is claimed is:
CLAIMS
1. A method of forming a bi-polar electrode having ion exchange
polymers on opposite faces of a porous substrate, the method comprising:
providing an electrode substrate with activated carbon layers on
opposite faces of the electrode substrate, wherein said faces have an outer
perimeter band void of the activated carbon layers,
placing the electrode substrate in a thermoplastic envelope formed by a
pair of polyethylene films;
thermally sealing the envelope to the outer perimeter band of the
electrode substrate void of activated carbon to form a first pocket on one side
of the electrode substrate and a second pocket on the opposite side of the
electrode substrate;
clamping the envelope between two rigid plates;
inserting a first polymerizable monomer mixture having an anion
exchange group into the first pocket of the envelope
inserting a second polymerizable monomer mixture having a cation
exchange group into the second pocket of the envelope; and
polymerizing the first and second polymerizable monomers mixtures.
2. The method of claim 1, wherein the first and second polymerizable
monomers mixtures are polymerized by thermal polymerization.
3. The method of claim 2, wherein the first and second polymerizable
monomers mixtures are polymerized by placing the envelope and electrode substrate
horizontally into an oven at 85° C.
4. The method of claim 1, wherein first anion polymerizable monomer
mixture is selected from the group consisting of ethylenically unsaturated tertiary
amine and quaternary amine compounds, and salts and derivatives thereof.
5. The method of claim 1 wherein second cation polymerizable monomer
mixture is selected from the group consisting of ethylenica!ly unsaturated sulfonic
acids, and carboxylic acids, and salts and derivatives thereof.
6. The method of claim 1 further comprising inserting a Mylar sheet in
each side of the envelope against the electrode substrate.
7. The method of claim 1, further comprising inserting a first transfer
pipette into the first pocket of the envelope and a second transfer pipette into the
second pocket of the envelope and inserting the first and second polymerizable
monomer mixture into the first and second pockets through the first and second
pipettes, respectively.