Note: Descriptions are shown in the official language in which they were submitted.
~29892'7
--1--
NOVEL FLUOROPOLYMER DISPERSIONS
Ion exchange active fluoropolymer films or
sheets have been widely used in industry, particularly
as ion exchange membranes in chlor-alkali cells. Such
membranes are made from fluorinated polymers having ion
exchange active groups attached to pendant groups on
the polymeric backbone.
Such polymers are usually thermoplastic and
may be fabricated into films or sheets while in their
molten form using mechanical extrusion equipment.
However, such equipment is operated in the temperature
region near the crystalline melting point of the polymer,
which is commonly near the decomposition temperature of
some of the polymers. Thus, decomposition may be a
problem when some polymers are formed into films by
conventional methods. Likewise, it is difficult to
make such polymers into films thinner tha~ about 10
microns using such techniques. In addition, it is
difficult to make films of consistent thickness. It
would therefore be highly desirable to be able to make
thin films having a consistent thickness.
34,247-F -1-
1298927
--2--
,
Forming membrane structures and support
st uctures into multiple layers is the subject of
several patents and applications including U.S. Patents
3,925,135; 3,909,378; 3,770,567; and 4,341,605. However,
these methods use complicated procedures and equipment
including such things as vacuum manifolds, rolls and
release media.
Prior art methods for fabricating films from
perfluorinated polymers have been ~imited by the solubil-
ity of the polymers and the temperature-dependent
viscosity-shear rate behavior of the polymers. To
overcome these characteristics of perfluorinated carboxy-
lic ester polymers, workers have tried to swell the
polymers using various types of swelling agents and to
reduce the fabrication temperatures of the polymers to
practical ranges by extraction. Extractions methods
have been taught in, for example, U.S. Patent 4,360,601.
There, low molecular weight oligomers were removed from
carboxylic ester polymers. Polymer "fluff" was extracted
in a Soxhlet device at atmospheric pressure for 24
hours (see Examples 1 and 3 of U.S. Patent 4,360,601).
Such treatments has been found to make some fluorinated
carboxylic ester copolymers more processible and operate
more efficiently in a chlor-alkali cell when in a
hydrolyzed form. Such extractions modify the fabricated
polymer article, for example, by forming grease of the.
polymer as shown in-Example 3 of U.S. Patent 4,360,601.
In addition, such extractions seem to lower
processing temperatures of carboxylic ester polymers
after isolation. Isolation means separation from the
polymerizatian latex by conventional methods of deacti-
vating the surfactant such as freezing, heating, shearing,
salting out or pH adjustment.
34,247-F -2-
1298927
--3--
British Patent No. 1,286,859 teaches that
highly polar organic "solvents" dissolve small amounts
of fluorinated vinyl ether~tetrafluoroethylene copolymer
in its thermoplastic form. Thermoplastic form means
the polymer is in a form which can be molded or proces-
sed above some transition temperature (such as the
glass transition temperature or the melting point)
without altering its chemical structure or composition.
The patent teaches the use of the "solvents" including
butanol, ethanol, N,N-dimethylacetamide, and N,N-dimethyl-
aniline.
Similar approaches have been used to swell
membranes in their ionic forms. Ionic forms of membranes
are membranes which have been converted from their
thermoplastic form (-SO2F or -COOCH3) to their ionic
forms (-SO3M or -COOM where M is H , K , Na , or NH4
or other metal ion.
Prior art workers have used highly polar
solvents or mixtures of solvents on substantially
perfluorinated polymers and less polar solvents on
fluorinated polymers containing hydrocarbon components
as co-monomers, ter-monomers or crosslinking agents.
However, each of the prior art methods for
swelling, dispersing or extracting the polymers has
25 certain shortcomings which are known to those practic-
ing the art. Polar solvents have the potential for
water absorption or reactivity with the functional
groups during subsequent fabrication Qperations, thus
making poor coatings, films, etc. High boiling solvents
are difficult to remove and frequently exhibit toxic or
flammability properties. Functional form (ionic forms)
of the polymers can react with solvents. (C~e Analyt-
ical Chem., 1982, Volume 54, pages 1639-1641).
34,247-F -3-
12989Z7
--4--
The more polar of the solvents such as methanol,
butanol esters, and ketones as disclosed in U.S. Patent
3,740,369; British Patent 1,286,859; and Chemical
Abstracts 7906856 have high vapor pressures at ambient
conditions, which is desirable for solvent removal;
however, they tend to absorb water. Their water content
is undesirable because it causes problems in producing
continuous coatings and films of hydrophobic polymers.
In addition, polar solvents frequently leave residues
which are incompatible with the polymers. Also, they
frequently leave residues which are reactive during
subsequent chemical or thermal operations if they are
not subsequently removed.
Another approach taken by the prior art
workers to form films from fluoropolymers include the
use of high molecular weight "solvents" which have been
produced by halogenating vinyl ether monomers. (See
British Patent No. 2,066,824).
The swelling of the functional (ionic) forms
of the fluoropolymers by polar or hydrophilic agents
has been known for some time. In addition, the solvent
solubility parameters were compared to the swelling
effect of 1200 equivalent weight Nafion ion exchange
membrane (available from E. I. DuPont Company) by Yeo
2S at Brookhaven Laboratory (see Polymer, 1980, Volume 21,
page 432).
The swelling was found to be proportional to
two different ranges of the solubility parameter and a
calculation was developed for optimizing ratios of
solvent mixtures. Ionic forms of functional fluoro-
polymers may be treated in such a manner, however, the
subsequent physical forming or manipu'ation of the
34,247-F -4-
~298927
64693-3832
polymers into usable configurations by any thermal
operation is limited when the polymers are in the
functional forms. In addition, non-ionic forms of
polymers treated in this manner are also limited in the
thermoplastic processing range by the stability of the
functional group bonds.
Other solvation methods have used temperatures
near the crystalline melting points of the polymers
being solvated, thus requiring either high boiling point
"solvents" or high pressure vessels to maintain the
system in a solid/liquid state. See Analytical Chem.,
1982, Volume 54, pages 1639-1641.
Burrell states the theory of Bagley [J. Paint
Tech., Volume 41, page 495 (1969)] predicts a
noncrystalline polymer will dissolve in a solvent of
similar solubility parameter without chemical
similarity, association, or any intermolecular force.
However, he fails to mention anything dbut ~he
solubility of polymers demonstrating crystallinity.
More particularly, the invention resides in a
dispersion composition for dispersing perfluorinated
polymer particles in a dispersant wherein said
perfluorinated polymer contains sites convertible to ion
exchange groups and wherein said dispersant has
a boiling point less than 110C;0
a solubility parameter of from greater than 7.1
to 8.2 hildebrands, and wherein the densities of the
dispersant and the fluorinated polymer are selected such
that they are balanced with each other.
34,247-F -5-
i~
,~
~2989%~
-5a-
64693-3832
The invention also resides in a method for
dispersing perfluorinated polymer particles containing
sites convertible to ion exchange groups comprising the
steps of:
contacting the polymer with a dispersant for a
time and at a temperature sufficient to disperse at
least a portion of the polymer in the solvent, wherein
the dispersant has:
0
a boiling point less than 110C; and
a solubility parameter of from greater than 7.1
to 8.2 hildebrands, and selecting the densities of the
dispersant and the fluorinated polymer such that they
are balanced with each other.
34,247-F -5a-
--6--
XCF2-CYZX'
wherein:
X is selected from F, Cl, Br, and I;
X' is selected from Cl, Br, and I;
Y and Z are independently selected from H, F,
Cl, Br, I and R';
R' is selected from perfluorcalkyl radicals
and chloroperfluoroalkyl radicals having from 1 to 6
carbon atoms.
The most preferred dispersant is 1,2-dibromo-
tetrafluoroethane.
Dispersion, as used herein, means a composi-
tion containing a dispersant and a perfluorinated
polymer containing sites convertible to ion exchange
groups, wherein the polymer is dispersed in the disper-
sant, but is only partially dissolved in the dispersant.
The present invention can be used to make ion
exchange media, films and articles for use in electro-
lytic cells, fuel cells and gas or liquid permeation
units.
Non-ionic forms of perfluorinated polymers
described in the following U.S. Patents are suitable
for use in the present invention: 3,282,875; 3,909,378;
4,025,405; 4,065,366; 4,116,888; 4,123,336; 4,126,588;
4,151,052; 4,176,215; 4,178,218; 4,192,725; 4,209,635;
4,212,713; 4,251,333; 4,270,996; 4,329,435; 4,330,654;
4,337,137; 4,337,211; 4,340,680; 4,357,218; 4,358,412;
34,247-F -6-
~29892~
4,358,545; 4,417,969; 4,462,877i 4,470,889; and 4,478,695
European Patent Publication No. 0,027,009. Such polymers
usually have equivalent weights of from 500 to 2000.
Particularly preferred are copolymers of
monomer I with monomer II (as defined below). Option-
ally, a third type of monomer may be copolymerized with
I and II.
The first type of monomer is represented by
the general formula:
CF2=CZZ' (I)
where:
Z and Z' are independently selected from -H,
-Cl, -F, and CF3.
The second monomer consists of one or more
monomers selected from compounds represented by the
general formula:
2 a ( Rf)b (CFRf,)c-O-[CF[CF2X)-CF -O] CF=CF (II)
where:
Y is selected from -SO2Z, -CN, -COZ, and
C(R3f)(R4f)0H;
- Z is selected from I, Br, Cl, F, OR and
NR1R2;
R is selected from a branched or linear alkyl
radical having from 1 to 10 carbon atoms or an aryl
radical;
R3f and R4f are independently selected f-rom
perfluoroalkyl radicals having from l to 10 carbon
atoms;
34,247-F -7-
--8--
Rl and R2 are independently selected from H,
a branched or linear alkyl radical having from 1 to 10
carbon atoms and an aryl radical;
a is 0-6;
b is 0-6;
c is 0 or 1;
provided a+b+c is not equal to 0;
. X is selected from Cl, Br, F and mixtures
thereof when n>1;
n is 0 to 6; and
Rf and Rf, are independently selected from F,
Cl, perfluoroalkyl radicals having from 1 to 10 carbon
atoms and fluorochloroalkyl radicals having from 1 to
10 carbon atoms.
Particularly preferred is when Y is -SO2F or
-COOCH3; n is 0 or 1; Rf and Rf, are F; X is Cl or F;
and a+b+c is 2 or 3.
The third.and optional monomer suitable is
; one or more monomers selected from the compounds repre-
sented by the general formula:
Y ~(C~F2)a~-(cFRf)b~-(cFR~f)c~-o-[cF(cF2x~ )-CF2-Oln,-CF=CF2
. . where: . .
~ Y' is selected from F, Cl and Br;
a' and b' are independently 0-3;
c' is 0 or 1;
provided a'+b'+c' is not equal to 0
n' is 0-6;
Rf and R'f are independently selected from
Br, Cl, F, perfluoroalkyl radicals having from 1 to 10
34,247-F -8-
1298927
carbon atoms, and chloroperfluoroalkyl radicals having
from 1 to 10 carbon atomsi and
X' is selected from F, Cl, Br, and mixtures
thereof when n'>1.
Conversion of Y to ion exchange groups is
well known in the art and consists of reaction with an
. alkaLine solution.
The monomer FSO2CF2CF2OCF=CF, has a density
of about 1.65 grams per cubic centimeter and polytetra-
fluoroethylene has a density of about 2.2 grams percubic centimeter. A copolymer of this monomer with
tetrafluoroethylene would, thus, have a density between
the two values.
It has been discovered that certain perhalo-
genated dispersant have a surprising effect of dispers-
ing the polymers, especially when the polymers are in a
finely divided state.
Dispersants suitable for use in the present
invention should have the following characteristics:
a boiling point less than about 110C;
a density of from 1.55 to 2.97 grams per
cubic centimeter; and
a solubility parameter of from greater than
7.1 to 8.2 hildebrands.
It is important that the dispersant has a
boiling point of from 30C to 110C. The ease of
removal of the dispersant and the degree of dispersant
removal is important in the producing of various films,
34,247-F -9-
1298927
--10--
coatings and the like, without residual dispersanti
hence a reasonable boiling point at atmospheric pressure
allows convenient handling at ambient temperature
conditions yet effective dispersant removal by atmos-
pheric drying or mild warming.
It is important that the dispersant has adensity of from 1.55 to 2.97 grams. per cub~c centimeter.
The polymers of the present invention have densities on
the order of from 1.55 to 2.2 grams per cub~c centimeter.
Primarily, the polymers have densities in the range of
from 1.6 to 2.2 grams per cubic centimeter. Dispersants
of the present invention will therefore swell, dissolve
and disperse small particles of this polymer, aided by
the suspending effects of the similarity in densities.
In the prior art, there was no recognition
and thus no attempt was made to balance density. The
prior art was only interested in forming solutions, and
solutions do not separate.
Solubility parameters are related to the
cohesive energy density of compounds. Calculating
solubility parameters is discussed in U.S. Patent
4,348,310.
It is important that the dispersant has-a
~ solubility parameter of from greater than 7.1 to 8.2
hildebrands. The similarity in cohesive energy densities
between the dispersant and the pol~mer determine the
likelihood of dissolving and swelling the polymer in
the dispersant.
.
34,247-F -10-
1298927
It is preferable that the dispersant has a
vapor pressure of up to about 760 millimeters of mercury
at the specified temperature limits at the point of
dispersant removal. The dispersant should be conveni-
ently removed without the necessity of higher tempera-
tures or reduced pressures involving extended heating
such as would be necessary in cases similar to U.S.
Patent 3,692,569 or the examples in British Patent
2,066,824 in which low pressures (300 mm) had to be
employed as well as non-solvents to compensate for
the higher boiling points and low vapor pressures
of the complex solvents.
It has been found that dispersants represented
by the following general formula are particularly
preferred provided they also meet the characteristics
discussed above (boiling point, density, and solubility
parameter):
XCF2-CYZ-X'
whereln:
X is selected from F, Cl, Br, and I;
X' is selected from Cl, Br, and I;
Y and Z are independently selected from H, F,
Cl, Br, I and R';
R' is selected from perfluoroalkyl radicals
and chloroperfluoroalkyl radicals having from 1 to 6
carbon atoms.
The most preferred dispersants are 1,2-dibromo-
~ tetrafluoroethane (commonly known as Freon 114 B 2)
5..~.
BrCF2 -CF2Br
~ 7-M~
34,247-F -11-
1~9892~
-12-
.
and 1,2,3-trichlorotrifluoroethane (commonly known as
Freon 113):
ClF2C-CCl~F
- Of these two dispersants, 1,2-dibromotetrafluoroethane
is the most preferred dispersant. It has a boiling
- point of about 47.3~, a density of about 2.156 grams
per cubic centimeter, and a solubility parameter of
about 7.2 hildebrands.
1,2-dibromotetrafluoroethane is thought to
work particularly well because, though not directly
. polar, it is highly polarizable. Thus, when 1,2-dibromo-
tetrafluoroethane is associated with a polar molecule,
its electron density shifts and causes it to behave as
a polar molecule. Yet, when 1,2-dibromotetrafluoro-
ethane is in contact with a non-polar molecule, it
behaves as a non-polar dispersant. Thus, 1,2-dibromo-
tetrafluoroethane tends to dissolve the non-polar
backbone of polytetrafluoroethylene and also the polar
pendant groups. The solubility parameter of 1,2-di-
bromotetrafluoroethane is calculated to be from 7.13 to7.28 hildebrands.
It is surprising that an off-the-shelf,
readïly-available compound such as 1,2-dibromotetra-
fluoroethane would act as a solvent for the fluoro-
polymers described above. It is even more surprisingthat 1,2-dibromotetrafluoroethane happens to have a
boiling point, a density and a solubility parameter
such that it is particularly suitable for use as a
solvent/dispersant in the present invention.
34,247-F -12-
lX-91~-927
In practicing the present invention, the
polymer may be in any physical form. However, it is
preferably in the form of fine particles to speed
dissolution and dispersion of the particles into the
dispersant. Preferably, the particle size of the
polymers is from 0.01 microns to 840 microns. More
preferably, the particle size is less than about 250
microns..
To dissolve and disperse the polymer particles
into the dispersant, the polymer particles are placed
in contact with the dispersant of choice and intimately
mixed. The polymer and the dispersant may be mixed by
any of several means including, but not limited to,
shaking, stirring, milling or ultra sonic means.
Thorough, intimate contact between the polymer and the
dispersant are needed for optimum dissolution and
dispersion.
The polymers of the present invention are
dissolved and dispersed into the dispersants at concen-
trations ranging from 0.1 to 50 weight percent ofpolymer to dispersant. At concentrations below 0.1
weight percent, there is insufficient polymer dissolved
and dispersed to be effective as a medium for coating
of articles or forming films within a reasonable number
of repetitive operations. Conversely, at concentrations
above 50 weight percent there-is sufficient polymer
present as a separate phase such that viable, coherent
films and coatings of uniform structure cannot be
formed without particulate agglomerates, etc.
Preferably, the concentration of the polymer
in the dispersant is from 1 to 20 weight percent. Most
preferably, the concentration of the polymer in the
dispersant is from 5 to 15 weight percent.
34,247-F -13-
~2989Z7
-14-
The dispersion of the polymer into the disper-
sant can be conducted at room temperature conditions.
However, the optimum dispersion effects are best achieved -
at temperatures from 10C to 50C. At temperatures
above 50C the measures for dissolving and dispersing
the polymer have to include pressure confinement for
the preferred dispersants or method of condensing the
dispersants. Conversely, at temperatures below 10C
many of the polymers of the present invention are below
their glass transition temperatures thus causing their
dispersions to be difficult to form at reasonable
conditions of mixing, stirring, or grinding.
The dispersion of the polymers of the present
invention into the dispersant are best conducted at
atmospheric pressure. However, dispersion effects can
be achieved at pressures from 760 to 15,000 mm Hg or
greater. At pressures below 760 mm Hg, the operation
of the apparatus presents no advantage in dissolving
and dispersing polymers, rather hindering permeation
into the polymers and thus preventing forming of the
dispersions.
Conversely, pressures above 760 mm Hg aid in
dissolving and dispersing polymers very little compared
to the difficulty and complexity of the operation.
Experiments have shown that at about 20 atmospheres the
amount of polymer dissolved and dispersed in the.disper-
sant is not appreciably greater.
After the polymer dispersions of the present
invention have been formed, they may be fixed to other
polymer films or substrates by sintering or compression
to fix the polymer from the dispersion to the substrate.
34,247-F -14-
1298927
-15-
,
The following methods are suitable for fixing
the dispersion of the present invention to a substrate.
Dipping the substrate into the dispersion, followed by
air drying and sintering at the desired temperature
with sufficient repetition to build the desired thick-
ness. Spraving the dispersion onto the substrate is
used to advantage for covering large or irregular
shapes. Pouring the dispersion onto ~the substrate is
sometimes used. Painting the dispersion with brush or
roller has been successfully employed. In addition,
coatings may be easily applied with metering bars,
knives, or rods. Usually, the coatings or films are
built up to the thickness desired by repetitive drying
and sintering.
The type of substrate upon which the disper-
sion of the present invention may be applied can include
such things as glass, polytetrafluoroethylene tapes, or
sheets, expanded mesh metal electrodes, scrim materials
made of, for example, fibers selected from carbon or
graphite, PTFE and metal, metal foil or sheets, prefer-
ably aluminum foil or other polymer films or objects.
The substrate upon which the dispersion is to
be deposited is cleaned or treated in such a way as to
assure uniform contact with the dispersion. The sub-
str,ate can be cleansed by washing with a degreaser-or
similar solvent followed by drying to remove any dust
or oils from objects to be used as substrates. Metals
should usually be acid etched, then washed with a
solvent to promote adhesion, if desired, unless the
metal is new in which case degreasing is sufficient.
34,247-F -15-
1298927
-16-
After being cleaned, the substrates may be
pre-_onditioned by heating or vacuum drying prior to
contact with the dispersions and the coating operation.
Temperatures and pressures,in the following ranges are
preferably used: 20 mm Hg at 110C is sufficient in
all cases; however, mild heat is usually adequate
when applied at a temperature of 50C at atmospheric
pressure.
After preparation, the substrates are coated
with the dispersion by any of several means including,
but not limited to, dipping, spraying, brushing, pouring.
Then the dispersion may be evened out using scraping
knives, rods, or other suitable means. The dispersion
can be applied in a single step or in several steps
depending on the concentration of the polymer in the
dispersion and the desired thickness of the coating or
film.
Following the application of the dispersion,
the dispersant is removed by any of several methods
including, but not limited to, evaporation or extraction.
Extraction is the use of some agent which selectively
dissolves or mixes with the dispersant but not the
polymer.
These removal means should be emp~oyed until
a uniform deposition of polymer is obtained and a
continuous film is formed.
The dispersant removal is typically carried
out by maintaining the coated substrate at temperatures
ranging from 10C to 110C, with the preferred heating
range being from 20C to 100C. The heating temperature
selected depends upon the boiling point of the dispeLsant.
34,247-F -16-
1298927
-17-.
Heating temperatures are customarily in the
range of from 20C to 50C for 1,2-dibromotetrafluoro-
ethane.
The pressures employed for the removal of the
dispersant from the coated substrate can range from 20
mm Hg to 760 mm Hg depending on the nature of the
. dispersant, although pressures are typically in the
range of from 300 mm Hg to 760 mm Hg for 1,2-dibromotetra-
fluoroethane.
10The forming of the coatir,g or film can be
carried out as part of the polymer deposition and
dispersant removal process or as a separate step by
adjusting the thermal and pressure conditions associated
with the separation of the polymer from the dispersant.
If the dispersion is laid down in successive steps, a
continuous film or coating free from pinholes can be
formed without any subsequent heating above ambient
temperature by control of the rate of evaporation.
This can be done by vapor/liquid equilibrium in a
container or an enclosure; therefore, the dispersant
removal step can be merely a drying step or a controlled
process for forming a coating or film. If the dispersant
is removed as by flash evaporation, a film will not
form without a separate heating step.
After the dispersant has been removed, the
residual polymer, as a separate step, is preferably
subjected to a heat source of from 250C to 380C for
times ranging from 10 seconds to 120 minutes, depending
upon the thermoplastic properties of the polymers. The
polymers having melt viscosities on the order of 5 x
105 poise at a temperature of 300C at a shear rate of
1 sec. 1, as measured by a typical capillary rheometer,
34,247-F -17-
1298927
-18-
would require the longer times and higher temperatures
within the limits of the chemical group stability.
Polymers with viscosities on the order of 1 poise at
ambient temperatures would require no further treatment.
The most preferred treatment temperatures are
from 270C to 350C and a time of from 0.2 to 45 minutes .
for the most preferred polymers for use in the present
invention. Such polymers form thin continuous films
under the conditions described above.
Films of varying thicknesses can be easily
produced by the methods and means described above.
Such films are suitable as membranes when in their
ionic forms, for use in electrochemical cells. They
are particularly useful for the electrolysis of sodium
chloride brine solutions to produce chlorine gas and
sodium hydroxide solutions. Membranes prepared according
to the present invention have surprisingly good current
efficiencies when used in chlor-alkali cells.
EXAMPLES
ExamPle 1
A copolymer of CF2=CF2 and CF2=CFOCF2CF2SO2F
having equivalent weight of about 1144 was prepared.
The polymer was prepared according to the following
^ procedure. 784 grams of CF2=CFOCF2CF2SO2F was
added to 4700 grams of deoxygenated water contain-
ing 25 grams NH4O2CC7Fl 5, 18.9 grams of Na2HPO4 7H2O,
15.6 grams of NaH2PO4 H2O and 4 grams of (NH4)2S2O8
- under a positive pressure of 250 psig (1722 kPa~ of
tetrafluoroethylene at 60C for 58 minutes. The
34,247-F -18-
~298927
-19-
reactor was vented under heat and vacuum to remove
residual monomers. The reactor contents was frozen,
thawed, and vigorously washed to remove residual
salts and soap. After vacuum drying, a dispersion was
prepared by placing 56 grams of polymer prepared above
. in a laboratory-size single tier 290 revolutions per
minute roller Norton Jar Mill with 168 grams of i,2-di-
bromotetrafluoroethane. Th.e mixture was mixed in the
ball mill overnight at ambient temperature and at
atmospheric pressure.
To the resulting soft paste about 300 addi-
tional grams of 1,2-dibromotetrafluoroethane was added
and the mill was rolled an additional 3 hours. The
resulting dispersion was found to contain 12.5 weight
percent polymer. The mixture was coated onto a sheet
of aluminum foil having a thickness of 38 microns by
dipping the foil into the dispersion. The coated
aluminum foil was allowed to air dry. Thus, the dispers-
ant evaporated from the dispersion at ambient tempera-
ture.
The coated aluminum foil was then heated to a
temperature of 300C in a muffle furnace for 1 minute
to sinter the polymer into a more uniform film form.
The resulting film was found to be a continuous
film and had a thickness of 0.5 mils (12.7 microns).
The dipping and heating process was repeated5 times until a 2.5 mil (63.5 microns) thick polymer
film was built up.
34,247-F -19-
~2989Z7
-20-
Two pieces of aluminum foil which had been
coated in the above described manner were pressed
together, coated side to coated side, under a pressure
of 800 psi (5512 kPa) at a temperature of 595F (313C)
for 4 minutes. The resulting film, with aluminum foil
on both sides, was hydrolyzed for 16 hours in a 25
weight percent sodium hydroxide aqueous solution at a
temperature of 90C. This treatment dissolved the
aluminum foil and left only the two layer film. The
two layer film was tested in a chlor-alkali membrane
cell. The cell was operated at a temperature of 89C
at a current density of 2 amps/in2 (Q.31 amps/cm2) of
electrode surface areas with a 3 mm (3000 micron) gap
between the anode and cathode. A cathode having an
electrocatalyst on its surface was used. The cell
voltage was 3.11 volts at 12.9 weight percent sodium
hydroxide concentration being produced in the cathode
chamber. The caustic current efficiency was found to
be 92.2 percent. The caustic produced in the catholyte
chamber was analyzed and found to contain 1030 parts
per million sodium chloride. The total energy consumed
for the production of one metric ton of sodium hydroxide
was calculated to be 2259 kilowatt hours.
Examp~e 2
A copolymer of CF2=CF2 and CF2=CFOCF2CF2CO3CH3
was prepared having an equivalent weight of abou~ 847.
- 50 Grams of CF2=CFOCF2CF2CO3CH3 was added to 300 grams
of deoxygenated water containing 3.0 grams of NH4O2CC7Fl 5,
1.5 grams of Na2HPO4 7H2O, 1.0 gram NaH2PO4 H2O, and
0.20 gram (NH4)2S2O8 under a positive pressure of
tetrafluoroethylene of 250 psig (1722 kPa) pressure at
50C for 180 minutes in a glass reactor. The reactor
was vented and the reactor contents was acidified with
- 34,247-F -20-
1298927
-21-
6 normal HCl to coagulate the polymer. The coagulam
was filtered out, vigorously washed and vacuum dried.
35 Grams of the polymer was ground and mixed
overnight in 315 grams of 1,2-dibromotetrafluoroethane
5. in the laboratory jar mill described in Example 1.
. The dispersant was analyzed and found to
contain about 10 weight percent solids. The dispersion
was used to coat a sheet of aluminum foil having a
thickness of 38 microns by dipping the foil, allowing
the coating to air dry and sintering the coating at a
temperature of 250C (482F) for 1 minute in the muffle
furnace described in Example 1.
This coating procedure was repeated until a
series of coated foils had been made in which the
coating thickness varied. From 2 to 5 dips on the
various films resulted in film thicknesses of the
sintered coating of from 0.7 to 1.8 mils (17.8 to 48.6
microns).
The coated foils were then pressed onto an
850 equivalent weight fluorosulfonyl copolymer films
which was 4 mils (101.6 microns) thick. The 850 equi-
valent weight polymer was prepared as the previous
fluorosulfonyl copolymer example except for using a
pressure of 192 psi~ (1323 kPa) and a run time of 88
2~ minutes. The dried polymer was extruded at a tempera-
ture of 500F (260C) to 550F (288C) using a Haake
Rheomiex 254 1.9 cm vented 25:1 length/diameter 316
stainless steel screw extruder and a 15 cm die. With a
20 mil (508 microns) die gap, the film was drawn down
to 4-5 mils (101 to 127 microns) thickness and quenched
34,247-F -21-
12989;~
-22-
.
on an unheated 316 stainless steel roll. The cast film
samples were cleaned by degreasing with acetone and air
dried. The coated side of the foil was placed against
the cast film and the two were placed between two
sheets of polytetrafluoroethylene coated glass cloth.
These were then placed between two photographic plates.
The entire sandwich was compressed at a temperature of
. 250C in a hydraulic hot press using about 20 tons
force for five minutes.
.
The combinations were hydrolyzed in a 25
weight percent sodium hydroxide aqueous solution at a
temperature of 90C for 16 hours. This treatment
dissolved the aluminum foil from each combination. The
resulting two layer films were tested in a chlor-alkali
test cell. The cell has an exposed electrode surface
of 56 cm2 with a titanium anode compartment and a
plexiglass cathode compartment. The anode was a ruthenium
oxide coated expanded metal electrode. A cathode
having an electrocatalyst as its surface was used.
Brine containing 20 weight ~ercent sodium chloride was
introduced into the anode compartment and water was
added to the cathode compartment as the direct current
was passed through the electrodes at 2 amps/in2 (0.3
amps/cm2) of electrode surface area. The membrane was
disposed between the electrodes and bolted between the
two cell halves with gas exits and overflows from each
half.
The data on these films is set forth in Table
I following:
34,247-F -22-
12989Z7
TABLE I
Sample No. 1 2
# of Dippings 2 5
Thickness of Coatings
mils (microns) 0.8 (20) 1.8 .(4~)
Thickness of Pressed
- Loading mils-(microns) 0.2 (5.1) - 0.4-0.6
(10.2-15.2)
Caustic Current
Efficiency (%) 95.6 96.7
Voltage 3.22 3.33
% NaOH 34.7 35-4
Energy (kwh/metric
ton NaOH) 2256 2307
The caustic current efficiency is determined
as the moles of caustic per Faradays of current times
100. That is, the number of moles of caustic which
were produced in a test period, divided by the time in
seconds times the current over the test period, all
divided by 96,520 coulombs per equivalent (Faraday).
The resultant decimal fraction represents the proportion
of electrons that produced NaOH. This fraction times
100 gives the caustic current efficiency.
The above data was taken after 13 days of
operation and was essentially unchanged after 90 days
operation.
ExamPle 3
A copolymer of CF2=CF2 and CF2=CFOCF2CF2CO3CH3
was prepared having an equivalent weight of 755. 50 Grams
34,247-F -23-
12989Z7
-24-
of CF2=CFOCF2CF2CO3CH3 was added to 300 grams of deoxygen-
ated water containing 3.0 grams of NH4O2CC7F1 5, 1 5
grams of Na2HPO4-7H2O, 1.0 gram NaH2PO4 H2O, and 0.10
gram (NH~)2S2O8 under a positive pressure of tetrafluoro-
ethylene of 235 psig (1619 kPa) pressure at a temperature
of 50C fQr 5 hours in a glass reactor. The reactor
was vented and the reactor contents was acidified with
6 normal HCl to coagulate the latex. ~he coagulam was
filtered and washed vigorously to remove inorganics and
soap. The polymer was vacuum dried for 16 hours at a
temperature of 85C.
15 Grams of the polymer prepared above was
ground in a lab mortar and pestle with 135 grams of
1,2-dibromotetrafluoroethane to produce a viscous
dispersion. The dispersion was used to coat a sheet of
aluminum foil which was 38.1 microns thick. The coated
foil was pressed in a heated hydraulic press at a
pressure of 2000 psi (13,780 kPa) and at a temperature
of 540F (282C) for 4 minutes and 20 seconds between
glass reinforced polytetrafluoroethylene backing sheets.
The backing sheets were removed from the
first polymer film and the coated side of the foil
placed against a 5 mil (127 micron) thick film of the
second ion exchange polymer film. The pressing opera-
tion was repeated using 670 psig (4616 kPa) to attach
the first film to the second film. The resulting-
two-layer film was hydrolyzed in a 25 weight percent
sodium hydroxide aqueous solution for 16 hours at a
temperature of 90C. The aluminum foil dissolved in
this process. The two-layer film was mounted in a test
cell with the 755 equivalent weight polymer facing the
cathode compartment.
34,247-F -24-
~ ;~98927
-25-
After 190 days of operation in a chlor-alkali
test cell as described in Example 2 to produce chlorine
gas and NaOH from the electrolysis of a NaCl brine,
produced a 33 weight % NaOH in an aqueous solution at a
95.6% caustic current efficiency and 3.38 volts.
Example 4
.. A copolymer of CF~=CF2 and CF2=CFOCF2CF2SO2F
having an equivalent weight of 1160 was prepared accord-
ing to the following procedure. 50 Grams of
CF2=CFOCF2CF2SO2F was added-to 300 milliliters of
deoxygenated water containing 3 grams NH4CO2C7F1s, 1.5
grams of Na2HPO4-7H2O, 1 gram of NaH2PO4 H2O and 0.1
grams of (NH4)2S2Og under a positive pressure of 245
psig (1688 kPa) of tetrafluoroethylene at a temperature
of 60C for 75 minutes in a glass reactor. The reactor
was vented under heat and acidified to coagulate the
latex. The coagulated polymer was washed repeatedly to
remove inorganics and soap. The polymer was vacuum
dried for 16 hours at a temperature of 110C.
30 Grams of the fluorosulfonyl copolymer was
ground with 270 grams of 1,2-dibromotetrafluoroethane
in a lab mortar and pestle until a viscous dispersion
was produced.
.This dispersion was used to coat a sheet of
aluminum foil having a thickness of 38.1 microns. The
coating was allowed to air dry. The coated foil was
then pressed between glass reinforced polytetrafluoro-
ethylene backing sheets which were held between photo-
graphic plates in a heated press. The pressure was
2000 psig (13,780 kPa) and the temperature was 595F
(313C). The time was 4 minutes and 20 seconds.
34,247-F -25-
1298927
-26-
Thereafter, the backing sheet was removed from the
press and a thin polymeric film emained on the foil.
A second copolymer was prepared. It was a
copolymer of CF2=CF2 and CF2=CFOCF2CF2SO2F having an
equivalent weight of 974. The polymer was prepared
according to the following procedure. 784 Grams of
CF2=CFOCF2CF~SO2F was added to 4700 grams of deoxygen-
ated water containing 25 grams NH4COzC7Fl5~ 18.9 grams
of Na2HPO4-7H2O, 15.6 grams of NaH2PO4 H2O and 4 grams
of (NH4 )2S208 under a positive pressure of 220 psig
(1516 kPa) of tetrafluoroethylene at a temperature of
60C for 30 minutes. The reactor was vented under
heat and vacuum to remove residual monomers. The
reactor contents was frozen, thawed, and vigorously
washed to remove residual salts and soap. The film
was vacuum dried for 16 hours at a temperature of 85C.
The second film was extruded on a commercially
available Killion laboratory extruder with a regular
Xaloy barrel and screw. The screw was a standard type
commonly used to extrude polyethylene. Blown film was
made with a 3.2 cm die with a 20 mil (508 micron) gap
heated to a temperature of 550C using no cooling ring.
The extruder was operated at a temperature of from 450
to 550F (232 to 288C) and 20 to 40 revolutions per
minute. The hauloff (a mechanical device to roll up
the film) operated a~ a rate of 30 to 60 cm/min.
Various thicknesses of blown film were produced as
desired by varying speeds and the blowing of the bubble.
A 5 mil (127 microns) extruded polymeric film
30 of 84K3023 fluorosulfonyl copolymer was placed against
the coated side of the foil and pressed as above except
34,247-F -26-
,
1~98927
-27-
only 670 psig (4613 kPa) pressure was used. This two
layer film was hydrolyzed in 25 weight percent sodium
hydroxide aqueous solution for 16 hours at a tempera-
ture of 90C. The foil was etched away in this process.
The resulting two layer film was placed in a test cell
(the same cell described in Example 3) with the 83P019
polymer facing the cathode compartment. After 2 days
of operating the following results were obtained.
Cell voltage was found to be 3.02 volts and
the caustic current efficiency was 91.5 percent at a
caustic concentration of 12.56 weight percent. The
sodium chloride concentration in the caustic was analyzed
and found to be 940 parts per million. The cell energy
was calculated to be about 2211 kilowatt hours per
metric ton of caustic.
34,247-F -27-
