Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
--1--
A METHOD FOR FORMING POLYMER COMPOSITE -FILMS
USING A REMOVABLE SUBSTRATE
The invention resides in a method for forming polymer
composite films using a removable substrate and partic-
ularly for forming ion exchange active composite membranes
using a removable substrate.
Ion exchange active fluoropolymer films have
been widely used in industry, particularly as ion
exchange mem~ranes in chlor-alkali cells. Such mem-
branes are made from fluorinated polymers having sites
convertible to 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 o the polyme;r,
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 than about 10
microns using such techniques. In addition, it is
34,261-F -1-
~2~i77~
--2--
difficult to make films of consistent thickness. It
would therefore be highly desirable to be able to make
thin films havin~ a consistent thickness.
Forming membrane structures and support
structures into multiple layers is the su~ject of
several pate~ts and applications including U.S. Patent
Nos. 3,925,135; 3,909,378; 3,770,567; and 4,341,605.
However, these me~hods use-complicated pr~cedures and
eguipment including such things as vacuum manifolds,
rolls and release media.
Prior art methods for fabricating films from
perfluorinated polymers have been limited by the
solubility of the polymers.and the temperature-
-dependent ~iscosity-shear rate behavior of the
polymers. To overcome these characteristics of
perfluorinated carboxylic ester polymers, workers have
tried to swell the polymers using various types of
swelling agents and to reduce the fabricat~on tem-
peratures of the polymers to practical ranges by
20; extraction. Extractions methods have been taught in,
for example, U.S. Patent No. 4,360,601. There, low mol-
ecular 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 No. 4,360,601).
Such treatments has been found to make some fluorinated
carboxylic ester ~opolymers more proces~ible and operate
more efficiently in a chlor-alkali cell when in a
hydrolyzed form. Such extractions modiy the abri-
cated polymer article, for example, by forming a grease
of the polymer as shown in Example 3 of U.S. Patent No.
. 4,360,601.
34,261-F -2-
~67~i9
--3--
In addition, such extractions seem to lower
processing _emperatures of carboxylic ester polymers
after isolation. Isolation means separation from the
polymerization latex by conventional methods of deacti-
vating the surfactant such as freezing, heating, shear-
ing, salting out or pH adjustment.
,.
British Patent No. 1,286,859 teaches that
highly`polar organic "solvents" di~ssolve 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 pro-
cessed 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 "solvents" including
butanol, ethanol, N,N-dimethylacetamide, and
N,N-dimethylaniline.
Similar approaches have been used to swell
membranes in their ionic forms. Ionic forms of mem-
branes 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
2~ solvents or mixtures of solvents on substantially
perfluorinated poiymers and less po.LaL soLvents on
fluorinatè~ 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
34,261-F -3-
~2~77~
-4-
certain shortcomings which are known to those prac-
ticing the art. Polar solvents have the potential for
water absorption or reactivity with the functional
groups during subsequent fabrication operations, thus
mak-ng poor coatings, films, etc. High boiling sol-
vents are difficult to remove and frequently exhibit
~ toxic or flammability properties. Functional form
(ionic forms) of the polymers can react with solvents.
(See Analytlcal Chem., 1982, Volume 54, pages 1639-1641).
The more polar of the solvents such as meth-
anol, butanol esters, and ketones as disclosed in U.S.
Patent No. 3,740,369; British Patent No. 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 hydro-
phobic polymers. In addition, polar solvents fre-
quently lea~e xesidues 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 monomer6. (See
British Patent No. 2,(~66,824).
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
34,261-F -4-
--5--
solubility parameters were compared to the swelling
effect of 1200 equivalent weight Nafion ion exchange
membrane (available from E. I. DuPont Company) by Yeo
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-
poIymers may be treated in such a manner, however, the
subsequent physical forming or manipulation of the
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 temper-
atures 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. Pa.int
25 Tech., Volume 41, page 495 (1969)1 predicts a norl- .
crystalline polymer will dissolve in a solven~ of
similar solubility parameter without chemical simil-
arity, association, or any intermolecular force.
However, he fails to mention anything about the
solubility of polymers demonstrating crystallinity.
34,261-F -5-
1267759
--6--
The invention is a method for forming polymer
composite films using a removable substrate comprising:
(a) ~orming a first dispersion o~ a first
perfluorinated polymer containing sites convertible to
ion exchange groups and a dispersant, said dispersant
having a boiling point less than 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;
(b) depositing the fir~t diqpersion onto a
removable substrate;
(c) heating the ~irst dispersion at a tem-
perature sufficient to form and fuse a first polymer
film;
(d) forming a second dispersion of a second
perfluorinated polymer containing sites convertible to
ion exchange groups and a second dispersant, said
second dispersant having a boiling point less than
110C a denslty o~ ~rom 1.55 to 2.97 ~ram~ per cubic
centimeter; and a solubility parameter of from greater
than 7.1 to 8.2 hildebrands;
(e) depositing the second dispersion onto the
first film;
2~ (f) heating the second dispersion for a time
and at a temperature sufficient to form and fuse a
second polymer film;
(g) bonding the first film to the second film,
thereby forming a oomposite ~ilm; and
~h) r~movlng the substrate.
Particularly preferred as a ~irst and as a
second disper~ant is a compound represented by the
general formula:
34,261-F -6-
--7--
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 perfluoroalkyl radicals
and chloroperfluor~alkyl ~ad~cals-having from 1 to 6
carbon atoms.
The most preferred first and second dis-
persant is 1,2-dibromotetrafluoroethane.
Dispersion, as used herein, means a com-
position containing a treating agent and a per-
fluorinated polymer containing sites convertible to ion
exchange groups. The polymer is at least partially
dissol~ed in the dispersant and is dispersed into the
dispersant.
The present invention can be used to make ion
exchange composite films suitable for use in electro-
lytic cells, fuel cells and gas or liquid permeationunits.
Non-ionic forms of perfluorinated polymers
.. described in the following U.S. Patents ~e sui.tab.Le
for use in the present invention: 3,282,875; 3,~0~,378;
4,025,405; 4,065,366; 4,116,8~; 4,123,336; g,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; ~,330,65~;
4,337,137; 4,337,211; 4,340,680; 4,357,218; 4,358,412;
34,261-F . -7-
1 X67759
4,358,545; 4,417,969; 4,462,877; 4,470,889; and
4,478,695; and European Patent Publication 0,027,009.
These polymers usually have equivalent weights of from
500 to 2000.
Particularly preferred for the formation of
each layer of the composite films of the present inven-
tion are copolymers of monomer I with monomer II (as
~ - defined below). Optionally, 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:
Y-(cF2)a~(cFRf)b-(cFR~f)c-o-[cF(cF2x)-cF2-o]n-cF=cF2 (II)
where:
Y is selected from -SO2Z, -CN,. -COZ and
C(R3~)(R4E)oH;
Z is selected ~rorn I, Br, C'.L~ E', OR, and
NRIR2;
R is selected from a branched or linear alkyl
radical having from 1 to 10 carbon atoms and an aryl
radical;
34,261-F -8-
lX67~5~
R3f and R~f are independently selected from
perfluoroalkyl radicals having from 1 to 10 carbon
atoms;
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 R'f are independently selected from F,
15 C1, 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 R'f are F; X is Cl or F;
and a+b+c is 2 or 3.
.
Although the polymers of each layer can have
the same or dlfferent radicals for Y, the most pre-
ferred composite polymer is one where the polymer of
one layer has Y as -SO2F and the polymer of the other
l~yer has Y as -COOCH3.
By composite films we mean ~ilms composed of
two or more different polymers. These polymers may
difer by type or concentration of sites convertible to
ion exchange group. These different polymers are
disposed in layers parallel to the film surface.
34,261-F -9_
~2677~;9
--10--
The third and optional monomer suitable is
one or more monomers selected from the compounds repre-
sented by the general ~ormula:
Y ~(CF2)al-(cFRf)b,-(cFRlf)cl-o-[cF(cF2xl )-CF2-O~n,-CF=CE'2
(III)
,
where:
- Y' is selected from F, Cl and Br; - -
a' and b' are lndependently 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 carbon atoms, and chloroperfluoroalkyl radicals
having from 1 to 10 carbon atoms; and
X' is selected from ~, 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=CF2 has a density
of about 1.65 grams per cubic centimeter and a polymer
of tetrafluoroethylene has a density of about 2.2 grams
,per cubic,centimeter. Alcopo:Lymer o this monomer Wi't}'l
tetrafluoroethylene would, thus, have a density between
the two vaLues.
It has been discovered that certain perhalo-
genated dispersants have a surprising effect of dis-
. persing the polymers, especially when the polymers are
in a finely divided state.
34,261-F -10-
~2677~;9
Dlspersants suitable for use in the present
invention should have the following characteristics:
a boiling point less than llO~C:
a density of from 1.55 to 2.97 grams per
cubic centimeter;
a solubility parameter of from greater than
7.1 to 8.2 hildebrands.
It is desira~le 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,
coatings and the like, without residual dispersant;
hence a reasonable boiling point at atmospheric pressure
allows convenient handling at room conditions yet
effective dispersant removal by atmospheric drying or
mild warming.
It is desirable that the dispersant has a
density of from 1.5~ to 2.97 grams per cubic centi-
meter. The polymers of the present invention have
2~ densities on the order of from 1.55 to 2.2 grams per
cubic centimeter. Primarily, the polymers have
densities in the rang.e of from 1.6 to 2.2 grams per
cubic centimeter. Dispersants of the present invention
will therefore swell dissolve and disperse small par-
ticles of this polymer, aided by the suspending effectsof the similarity in dens:ities.
,
The prior art did not balance density. They
were interested in forming solutions and solutions do
not separate.
34,261-F
~L2~7759
Solubility paramèters are related to the
cohesive energy density of compounds. Calculating
solubility parameters is discussed in U.S. Patent No.
4,348,310.
It is desirable that the dispersant has a
solubility paramete.r of from greater than 7.1 to 8.2
hildebrands. The similarity in cohesive energy den-
sities between the -dispersant and the polymer determine
the likelihood of dissolving, swelling and dispersing
the polvmer in the dispersant.
It is preferable that the dispersant has a
vapor pressure of up to 760 mm Hg at the specified
temperature limits at the point of dispersant removal.
The dispersant should be conveniently removed without
the necessity of higher temperatures or reduced pres-
sures involving extended heating such as would be
~ecessary in cases similar to U.S. Patent ~o. 3,692,569
or the examples in British Patent No. 2,066,82g 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 repre-
sented by the following general formula are par-
ticularly preferred provided they also meet the
charac~eristics discussed above (boi:Lirlg po;int,
density, and sol ubi1ity parclme ker):
XCF2-CYZ-X '
34,261-F -12-
~2677~;~
-13-
wherein:
X is selected from F, C1, 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)
BrCF 2 - CF 2 Br
and 1,2,3-trichlorotrifluoroethane (commonly known as
Freon 113):
ClF2C-CCl 2F
Of these two dispersants, 1,2-dibromotetrafluoroethane
is the most preferred dispersant. ~t has a boiling
point of about 47.3C, 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, ~hen 1,2-dibro-
motetrafluoroethane is associated with a polar molecule,
itæ electron dens.ity shifts and cause~ lt to behave as
a polar molecule. Yet, when 1,2-dibromotetrafluoro-
ethane is around a non-polar molecule, it behaves as a
non-polar dispersant. Thus, 1,2-dibromotetrafluoro-
ethane tends to dissolve the non-polar backbone of
34,261-F -13-
~7~
-14-
polytetrafluoroethylene and also the polar, ion-
-exchange-containing pendant groups. Its solubility
parameter is calculated to ~e from 7.13 to 7.28 hilde-
brands.
It is surprising that an off-the-shelf,
readily-available compound such as 1,2-dibromote-tra-
fluoroethane would act as a solvent for the fluoro-
- polymers described above. It is even more surpr~si~g
that 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.
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 a~d dispersion of the particles into the
dispersant. Preferably, the particle size of the
polymers is from 0.01 microns to 840 microns. Most
preferably, the particle size is less than 250 microns.
To dissolve and disperse the polymer par-
ticles 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, mil.Ling OE llltra son:ic
means. Thorough, i.ntimate con-tact betweell the polymer
and the dispersant are needed for optimum dissolution
and dispersion.
34,261-F -14-
-15~
The polymers of the present invention are
dissolved and dispersed into the dispersants at concen-
trati~s ranging from O.l to 50 weight percent of
polymer to dispersant. At c~ncentrations below 0.1
weight percent, there is insufficient polymer dissolved
and dispersed to be effective as a medium for coating
of articles or forming filrns within a reasonable number
of repetitive operations. Conversely, at concentra-
tions a~ove 50 weight percent there is sufficient
polymer present as a separate phase such that viable,
coherent films and coatings of uniform structure cannot
be ormed without particulate agglomerates, etc.
Preferably, the concentration of the polymer
in the dispersant is from 0.1 to 20 weight percent.
More preferably, t~e concentration of the polymer i~
the dispersant is from 0.3 to 10 weight percent. Most
preera~1y, the concentration is from 5 to 15 weight
percent.
The dispersion of the polymer into the dis-
persant can be conducted at room temperature con~itions.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 o~ condensing the
dispersants. Conversely, at ~temper~tures below l0C
many of the polymers of t~e presenk invention are below
their glass transition temperatures thus causing their
dispersions to be difficult to form at reasonable
conditions of mixing, stirring, or grinding.
34,261-F -15-
~267759
-16-
The dispersion of the polymers of the present
invention into the dispersant are ~est conducted at
atmospheric pressure~ However, dispers1on efects ca~
be achieved at pressures from 760 to 15, 000 mm Hg or
greater. At presslres 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 disper-
slons .
Conversely, pressures above 760 mm Hg aid in
dissolving and disp.ersing 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 di~persed in the dis-
persant is not apprecia~ly greater.
After the polymer first dispersion of ~he
present invention has been formed, it is fixed to a
substrate by sintering or compression to fix the
polymer from the dispersion to the substrate.
2~ 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-
nesa. Spraying the dispersion onto the substrate is
used to advantage for co~ering 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 fil~s. are
34,261-F -16-
-17-
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 ~e applied carl include
such things as glass, metal sheets or foil such as
al~mi~num foil, polytetrafluoroethylene tape, or sheets,
or other polymer films or sheets.
The subs,trate upon which the dispersion is to
be deposited is cleaned or treated in such ~ way as to
assure uniform contact with the dispersion. The sub-
strate 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 sufficier~t.
After being cleaned, the substrates may be
pre-conditioned by heating or vacuum drying prior to
contact with the dispersions and the coating oper~ation.
Temperatures and pressures in the following ranges are
preferably used: 20 mm Hg at a temperature of 110C or
is sufficient in all cases; however, mild heat is
usually adequate, on the order of 50~C at atmospheric
pressure.
.
~ter 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 usiny scraping
knives, rods, or other suitable means. The dispersion
can be applied in a single step or in several steps
34,261-F -17-
~2~77~i9
-18-
..
dependlng on the concentration of the polymer in the
dispersion and the desired thickness of the coating or
film.
Following the applicatlon of the dispersion,
the dispersant is removed by any of se~eral methods
includ~ng,-but not limited to, evaporatio~ or extrac- -
tion. Extraction is the use of some agent which selec-
tiv-ely dissolves or mixes with the dispersant but not -
the polymer.
These removal means should be employed until
a uniform depositi~n 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 temper-
ature selected depends upon the boiling point of the
dispersant.
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 subs.trate 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-dibromo-
tetrafluoroethane.
34,261-F -18-
:
64693-3834 JEP
~X6~7~;!3
-19-
The forming of the coating or film can be
carried out as part of the polymer deposition and
dispersant removal process or as a separate step by
adiusting the thermal and pressure conditions associ-
ated with the separation oE the polymer from the dis-
pèrsant. rf 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
polymer and substrate, as a separate step, i~ preferably
subjected to a heat source of from 150C to 380C for
times ran~ing from 10 seconds to 120 minutes, depending
upon the thermoplastic properties of the polymer.
Polymers having a melt viscosity on the order of 5 x 105
poise at a temperature of 300C at a shear rate of l
sec.~l as measured by a typical capillary rheometer
would require the longer times and higher temperatures
within the limits of the chemical group stability.
Polymers with viscosities on the order of l poise at
ambient temperatures would require no further treatment.
The mo~t preferred treatment temperatures
are from 270CC 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.
34,261-F -l9-
, ~;,
.~.~.~
~L26,77~9 64693-3834 JEP
--20--
After the polymer from the dispersion has been
fixed to its substrate, the polymer layer is contacted
with a second polymer dispersion formed in the same
manner used to form the first dispersion. Thereafter,
the second dispersion is fused to form the second film
and to bond the second film to the first film. The
second film is formed and the two films are fused
together by heating the two films at a temperature, at a
pressure and for a time su ficient to bond the two
polymers together. Such temperatures are usually from
1~0 to 380~C. Pressures up to 2000 psi (13,780 kPa) are
usually employed. The time period is generally from 10
seconds to 120 minutes.
Thereafter, the removable substrate should be
removed. A variety of means can be used to remove the
substrate including chemically etching the substrate
away, vapori2ing the s~bstrate, dissolving the sub-
strate, peeling the substrate from the film, peeling thefilm from the substrate, and other physical or chemical
means.
Composite 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 ga~
and sodium hydroxide solutions. Membranes prepared
according to the present invention have surprisingly
good current eficiencies when used in chlor-alkali
cells.
34,261-F -20-
. ~
. .
~2677~i9 64693-3834 JEP
--21--
Steps f and g in the Summary of the Invention
can be alternately accomplished in one c~ordinated
operation, rather than separately. That is, the second
film may be formed and fused at the same time it is
being fused to the first film.
EXAMPLES
Example 1
A copolymer of C~=CF and CF=CFOCFCFCOOCH was
prepared as followed:
50 9 of CF=CFOCFCFCOOCH was added to 250 g of
deoxygenated water containing 3 grams of NH4OCC7Fl5,
1.5 grams of NaHPO4"7HO and 1.0 gram of NaHPO4:HO in a
glass reactor with stirring at 800 rpm. Next, 50 ml of
deoxygenated water containing 0O05 (NH4)SO8 was injected
into the reactor and the reactor was kept under a
positive pressure of 220 psig (1516 kPaJ using a
tetrafluoroethylene gas at a temperature of 50C for 180
minutes. The reactor was vented and the contents was
acidified with 50 ml 6N HCl to coagulate the latex and
cause the polymer to separate from the emulsion. The
polymer was filtered, vigorously washed to remove
inorganics, soap and residual monomers and then vacuum
dried for 16 hours at a temperature of 85C. The dried
polymer weighed 99.2 grams and upon titration wa~ found
to be 856 equivalent weight.
A di~persion of the 856 equivalent weight
carboxylic ester polymer was made by mixing 49 grams of
the polymer with 304 grams of 1,2-dibromotetrafluoro-
ethane.
34,261-F -21-
1~6775~
-22-
A poly~.er having an equivalent weight of 850
was prepared according to the following procedure:
784 grams of CF2=CFOCF2CF2S02F was added to
4700 grams of deoxygenated water-containing 25 grams
NH402CC7F1 5, 18.9 grams of Na2HPO~ 7H20, 15.6 grams of
NaH2P04-H20 and 4 grams of (NH4 )2S208 under a positive
pressure of 192 psig (1323 kPa) of tetrafluoroethylene
~ at a temperature of 60~C for 88 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.
30 grams of the polymer was made into a
dispersion using 270 grams of 1,2-dibromotetrafluoro-
ethane. The dispersion was coated onto an aluminumfoiL and heated to a temperature of 300C for 1 minute.
The coating and heating steps were repeated until a
coating having a thickness of 4 mils (102 microns) was
achieved.
A piece of aluminum foil was coated with a
dispersion of the 856 EW carboxylic ester copolymer.
The dispersant was allowed to air dry and the coated
foil was fused for 1 minute at a temperature of 250C
between polytetrafluoroethylene coated glass cloth
25 sh~eets. The process was ~epeated to bu:i:ld a 1 mil
thick (25.4 ~I) film. 'rhe caLbo~ylic ester copolymer
film on the foil was then coated in a like manner with
an 850 equivalent weight fluorosulfonyl copolymer
dispersion to build a fluorosulfonyl copolymer film
until the total film thickness of the two combined
films was 5 mils (12.7 I~) The aoated foll was placed
34,261-F -22-
.,
lZ6~77~;~
-23-
polymer side down on top of a sized polytetrafluoro-
ethylene fa~ric (Prodesco Inc. 12 x 12 leno weave
cloth~ which was in turn placed on a vacuum table. The
vacuum was applied and the tahle was placed under a
heated platen for 4 minutes at a temperature of 250C.
The polytetrafluoroethylene fa~ric was firmly bonded to
the support layer polymer.
34,261-F -23-
