SOLVENTS FOR FLUOROPOLYMERS
[0001] The present invention relates to the field of
solvents for fluoropolymers and to the use of the said
5• dissolved fluoropolymers in the preparation of films,
membranes, coatings and others.
[0002] Fluoropolymers are today very widely used for
their mechanical and chemical strength properties and
their long lifespans. In fact, the polymers are
10 increasingly used in increasingly numerous
applications.
[0003] The commonest among these applications are
those where the fluoropolymers are formed, into films,
membranes or coatings. As a general rule,
15 fluoropolymers have entirely advantageous applications
when they are in the form of films, which may or may
not be supported, the thickness of which varies from a
few tens of nanometres to several millimetres.
[0004] Thus, as nonlimiting examples, fluoropolymers
20 are used in the manufacture of films, membranes and
coatings or in the manufacture of batteries, such as
batteries of Li-ion type.
[0005] In such applications, the fluoropolymers have
first of all to be dissolved in more or less
25 concentrated solutions, the films subsequently being
produced by removing the solvent or solvents, for
example by evaporation or by extraction using a third
solvent, or any other method known to a person skilled
in the art.
30 [0006] Fluoropolymers, in particular poly(vinylidene
fluoride)s, better known under the name of PVDFs, are
today commonly dissolved in N-methyl-2-pyrrolidone
(NMP) . Although it is appropriate for the forming of
fluoropolymers, NMP however exhibits many
35 disadvantages. This is because NMP is a compound having,
a high toxi'cological risk, it being from now on
classified as reprotoxic. There is therefore an
t - 2 -
advantage in replacing NMP with solvents having a
better toxicological profile.
[0007] DMSO (or dimethyl sulphoxide) is a known
solvent which makes it possible to' dissolve certain
5 grades of PVDF, such as, for example, the Kynar® and
Kynar Flex® products sold by Arkema or also the Solef®,
Hylar®, Halar® or Hyflon® products sold by Solvay. The
use of DMSO makes it possible to obtain solutions with
viscosities comparable to those obtained with NMP.
10 However, in order to make possible this dissolution,
the DMSO has to be heated to a temperature of the order
of 50°C, indeed even greater.
[0008] In addition, the solution of PVDF in DMSO thus
prepared is not stable over time: gelling or cloudiness
15 of the solution is often observed after only from 1 to
2 days. The users, are consequently restricted to
rapidly using and applying the solution in order to
produce the required films, which constitutes a curb on
the replacement of NMP.
20 [0009] Patent Application FR 2 285 227 describes a
process for assembling PVDF parts by adhesive bonding,
the' adhesive being a dilute solution of PVDF in a
solvent, it being possible for the said solvent to be
chosen from dimethylformamide (DMF), N,N-
25 dimethylacetamide (DMAC), tetrahydrofuran (THF),
dimethyl sulphoxide (DMSO), cyclohexanone (CyHone),
hexamethylphosphoramide (HMPA), butyrolactone and their
mixtures. An example effectively shows that PVDF can be
dissolved in DMF but at a temperature of 60°C.
30 [0010] Patent EP 0 639 106 Bl teaches the preparation
of membranes using solvent/cosolvent mixtures which
make it possible to dissolve PVDFs at any temperature.
Although many possible mixtures are provided, it
clearly emerges from this teaching that . only the
35 mixtures based on NMP and. on DMF or on n-butylacetate
are effective and are the only ones to be described in
examples.
[0011] Patent Application EP 0 223 709 A2 ^Iso
describes a process for the preparation of porous
- 3 -
membranes by dissolution of a fluoropolymer in a
solvent. The solvents suitable for this process are
chosen from ketones, ethers, amides and sulphoxides,
and, their mixtures. The best solvent is shown to be the
5 acetone/DMF mixture, which is confirmed by the
examples, which only illustrate just this mixture of
solvents. In addition, these examples teach that the
dissolution has to be carried out under hot conditions
and that the polymer solution has to be used
10 immediately.
[0012] Patent US 5 387 378 also describes a process
for the preparation of membranes from fluoropolymers
which are dissolved beforehand in a mixture consisting
of a solvent with a high boiling point and of a solvent
15 with a low boiling point. Mention is made, as examples
of such mixtures of solvents, of the mixtures of
acetone and of another solvent chosen from DMF, DMAC,
DMSO and their mixtures.
[0013] The examples of Patent US 5 387 378 present
20 only dissolutions of fluoropolymers in an acetone/DMAC
mixture, where the acetone is always in a predominant
proportion with respect to the DMAC. In addition, the
mixture has to be heated at 50°C for an hour before the
formation of the film proper.
25 [0014] Patent EP 0 574 957 Bl describes composite
acrylonitrile/PVDF membranes which can be used in
separation operations. The constituent polymers of the
membranes can be dissolved in a solvent chosen from
NMP, DMF, DMSO, HMPA, DMAC, dioxane and their mixtures,
30 optionally in the presence of cosolvents chosen from
acetone, methanol, ethanol, formamide, water, methyl
ethyl ketone and others. The examples presented show
only polyacrylonitrile (PAN) membranes and • their good
resistances to attacks by solvents, such as NMP, DMF,
35 DMSO, toluene, methyl ethyl ketone, acetone and others.
[0015] Thus, among all the techniques known today of
the prior art, none of them is satisfactory as none of
them can compel recognition as a technique where the
- 4 -
solvent systems for fluoropolymers can advantageously
replace the reference solvent, which is NMP.
[0016] This is because the techniques described in the
prior art show that the dissolution of the
5 fluoropolymers in the solvent system has to be carried
out under hot conditions, that is to say at a
temperature of at least 50°C.
[0017] The techniques of the prior art also teach that
the solutions obtained have to be used rapidly after
10 preparation, a person skilled in the art thus
understanding that the solutions obtained are not
stable over time, or are not stable when they are
cooled to ambient temperature or to the temperature at
which the solution of. fluoropolymers is formed.
15 [0018] In addition, the techniques of the prior art
do not appear to be. concerned with the problem of the
viscosities of the solutions obtained, which
nevertheless is of very great importance for the
forming of the fluoropolymers and which is one of the
20 reasons why NMP is widely used today. This is because
the solutions of fluoropolymers in NMP exhibit low
viscosities, making it possible to obtain solutions
having a high content of polymers and thus to use less
solvent for the preparation of films.
25 [0019] Thus, one of the objectives of the present
invention ' is to provide a solvent system for
fluoropolymers which does not exhibit the
abovementioned disadvantages encountered in the prior
art.
30 [0020] More specifically, a first objective of the
present invention is to provide a solvent system for
f luoropolymers which is less toxic than NMP, in
particular weakly toxic, indeed even nontoxic.
[0021] Another objective is to provide- a solvent
35 system for fluoropolymers which does not require
heating the solution, or at the very least heating to a
temperature of the order of, indeed even less than,
50°C, and preferably makes possible the dissolution of
the said•fluoropolymers at ambient temperature.
- 5 -
[0022] Yet another objective is to provide a solvent
system for fluoropolymers which results in solutions
which are stable .over time, that is to say solutions
for which the stability over time is similar to that
5 obtained with solutions in NMP, and generally more
stable than with the known solvents of the prior art,
such as NMP, DMSO, ketones, DMAC and others.
[0023] Yet another objective is to provide a solvent
system for fluoropolymers resulting in polymer
10 solutions for which the viscosity is similar to the
viscosity of solutions of fluoropolymers in NMP and
generally for which the viscosity is substantially
lower than the viscosity of the solutions obtained with
the solvents used in the techniques of the prior art.
15 [0024] It has now been discovered that the
abovementioned objectives can be achieved, in all or at
least in part, by virtue of the solvent system of the
present invention. Yet other objectives which can be
achieved by virtue of the subject-matters of the
20 present invention will become apparent in the
description which follows.
[0025] According to a first aspect, the present
invention relates to a DMSO-based solvent system which
makes it possible to dissolve fluoropolymers without
25 having to heat at high temperatures, to obtain
solutions for which the viscosities are lower than
those obtained with DMSO alone, and to obtain solutions
of fluoropolymers which are much more stable over time
than with DMSO and comparable to NMP. Another advantage
30 of the solvent system according to the invention is
that it confers, on the solutions of fluoropolymers, a
lower crystallization point than that of pure DMSO,
that is to say of less than approximately 18 °C.-
[0026] More specifically, the present . invention
35 relates to a , solvent . system for fluoropolymer
comprising:
from 50 to 99.9% by weight of a composition (A)
comprising dimethyl sulphoxide (DMSO), and
- 6 -
- . from 0.1 to 50% by weight of a composition (B)
comprising at least one ketone.
[0027] This is because it has been discovered,
surprisingly, that the DMSO-based solvent systems
5 according to the, invention, although comprising an
amount of less than or equal to 50% by weight of
ketone (s), make it possible to obtain solutions of
fluoropolymers which are stable over time.and for which
• the viscosity is entirely comparable to the viscosity
10 values of the solutions of fluoropolymers in the known
solvents of the prior art, in particular, solutions in
NMP.
[0028] Thus, the fluoropolymers (or fluororesins)
which can be dissolved in the solvent system according
15 to the present invention can be of any type known to a
person skilled in the art and in particular fluorinated
and/or chlorofluorinated homopolymers and copolymers,
such as, for example, those sold by Arkema under the
Kynar® and Kynar Flex® names, for example Kynar® 7 61,
20 those sold by Solvay under the Solexis® name (homo- and
copolymers obtained by suspension polymerization) ,
under the Solef® name, such as, for example, the
homopolymers 1010, 1012, 1013, 1015, 6008, 6010, 6012,
6013, 6020 and 5130, the PVDF-HFP copolymers 11008,
25 11010, 21508 and 21216, or the PVDF-CTFE copolymers
31008, 31508 and 32008, under the Hylar® name (homoand
copolymers by emulsion polymerization, Hylar® 461),
ECTFE (ethylene/chlorotrifluoroethylene) copolymers
sold under the Halar® name, and the perfluoroionomers
30 Hyflon® E79, E87 and D83, and others, to mention only
some of them, without implied limitation.
[0029] The solvent system according to the present
invention is . particularly well suited to the
dissolution of fluororesins comprising at least one
35 poly(vinylidene fluoride) .homopolymer and/or copolymer,
denoted PVDF in the continuation.
[0030] The solvent system of the present invention
comprises an amount of greater than or equal to 50% by
weight of a DMSO-based composition (A) . According to
- 7 -
one embodiment, the composition (A) comprises DMSO
alone. DMSO alone or more simply DMSO is understood to
mean a composition (A) comprising more than 80% by
weight, preferably . more than 90% by weight and more
5 preferably more than 95% by weight of DMSO, it being
possible for the remainder to consist of the impurities
inherent in the manufacture of DMSO, after optional
purification (as described -in WO 1997/019047,
EP 0 878 454 and , EP 0 878 466), and/or of odorous
10 agents (as described . in WO 2011/012820), and/or any
other additive known to a person skilled in the art,
such as, for example and without implied limitation,
chosen from stabilizers, including UV stabilizers,
colourants, preservatives, biocides and others.
15 [0031] According to another embodiment, the
composition (A) can comprise, in addition to the DMSO,
one or more other solvents for the fluoropolymer other
than a ketone. Advantageously, the other solvent or
solvents of the composition (A) are added with the aim
20 of lowering the crystallization point of the DMSO. Such
solvents can be chosen from those known to a person
skilled in the art and in particular from esters,
diesters, and entirely preferably from propylene
carbonate, dimethyl carbonate, diethyl succinate,
25 dimethyl adipate, dimethyl glutarate, and their
mixtures, these diesters being better known under the
generic term of DBE (DiBasic Esters). Rhodia sells some
of these DBEs, in particular dimethyl glutarate under
the trade name Rhodiasolv Iris®. Dupont/Invista also
30 sells DBEs having variable compositions of dimethyl
succinate, dimethyl adipate and dimethyl glutarate
under the names DBE-2, DBE-3, DBE-4, DBE-5, DBE-6 and
DBE-9.
[0032], The amount of solvent (s) present in the
35 composition (A) with the .DMSO is generally between 0
and 50% by weight, preferably between 0 and 40% by
weight and more preferably between 0 and 30% by weight,
with respect to the total weight of the composition
(A), the remainder to 100% consisting of the DMSO,
alone or in combination with the impurities, odorous
agents and/or other additives described above.
[0033] The composition (B) for its part comprises at
least one ketone which will be of any type known to a
5 person skilled in the art, preferably at least one
aliphatic, cycloaliphatic or aromatic ketone, and the
mixtures of two or more of these ketones. Preferably,
the ketones included in the composition (B) are chosen
from linear or branched aliphatic and/or cycloaliphatic
10 ketones and, for example, without implied limitation,
the ketones are chosen from dimethyl ketone (or
acetone), diethyl ketone, methyl ethyl ketone, methyl
isobutyl ketone, optionally substituted cyclohexanone,
for example trimethylcyclohexanone (TMCHONE),
15 cyclopentanone, and others, and the mixtures of two or
more of these ketones in all proportions.
[0034] , Very surprisingly, the addition of at least one
ketone to the DMSO makes it possible to observe
nonlinear results, that is to say better than those
20 observed during the dissolution of fluoropolymers in
DMSO only or in just a ketone, the said results being
understood in terms of viscosity and of stability over
time.
[0035] In one embodiment of the invention, preference
25 is given to a ketone or a mixture of ketones having a
boiling point close to that of DMSO, more specifically
close to that of the composition (A) , or also to a
ketone or a mixture of ketones forming an azeotrope
with DMSO or with the composition (A) . In this
30 preferred embodiment, the removal of the solvent system
for the fluoropolymer in which it is dissolved will be
facilitated, it being possible for the composition (A)
and the composition (B) thus to be simultaneously
removed by heating, evaporation and others.
35 [0036] Another advantage . related to the similar or
identical boiling points of the composition (A) and the
composition (B) or else related to the formation of an
azeotrope between the composition (A) and the
_ 9 -
composition (B) is their ease of purification, and
recycling.
[0037] Acetone, cyclohexanone and trimethylcyclohexanone
are particularly suitable and effective as
5 composition (B) in the solvent system of the present
invention and confer, on ^ the solutions of
fluoropolymers, an excellent stability on storage
ranging up to 2, 3 or indeed even several weeks. In
addition, trimethylcyclohexanone has a boiling point
10 very close to that•of DMSO.
[0038] In the solvent system of the present invention,
the composition (B) represents from 0.1 to 50% by
weight of the total weight of the solvent system, the
remainder to 100% being represented by the composition
15 (A) defined above. Preferably, the composition (B)
represents from 0.1 to 25% by weight, more preferably
from 0.1 to 20% by weight and entirely preferably from
0.1 to 15% by weight of the total weight of the solvent
system according to the present invention.
20 [0039] According to a preferred embodiment of the
present invention, the solvent system for
fluoropolymers comprises:
a. from 70 to 95% by weight of DMSO, for example
approximately 75% by weight, and
25 b. from 5 to 30% by weight of at least one ketone
chosen from cyclohexanone, trimethylcyclohexanone
and their mixtures in all proportions, for example
approximately 25% by weight.
[0040] According to another preferred embodiment, the
30 solvent system for fluoropolymers according to the
invention comprises:
a. from 85 to 99% by weight of DMSO, for example
approximately 95% by. weight, and
b. from 1 to 15% by weight of acetone, for example
35 approximately 5%.by weight.
[0041] According to yet another preferred embodiment,
the solvent system for fluoropolymers of the present
invention comprises:
- 10 -
a. from 85 to 99% by weight, preferably approximately
95% by weight, of a mixture of 50% by weight of
DMSO with 50% by weight of DBE,. preferably dimethyl
glutarate, and
5 b. from 1 to 15% by , weight of acetone, preferably
approximately 5% by weight.
[0042] According to yet another preferred embodiment
of the present invention, the solvent system for
- fluoropolymers comprises:
10 a. from 70 to 95% by weight, for example approximately
75% by weight, of a mixture of 50% by weight of
DMSO with 50% by weight of DBE, preferably dimethyl
glutarate, and
b. from 5 to 30% by weight of at least one ketone
15 chosen from cyclohexanone, trimethylcyclohexanone
and their mixtures in all proportions, preferably
approximately 25% by weight.
[0043] The solvent systems of the present invention as
just defined in addition exhibit.the advantage of being
20 able to dissolve the fluoropolymers, in particular
poly(vinylidene fluoride)s, at a lower temperature than
that required when the dissolution is carried out in
DMSO alone, it even being possible for this dissolution
to be carried out in some cases, according to the
25 nature of the f luoropolymer and the nature of the
solvent system, at ambient temperature.
[0044] Yet another advantage lies in the fact that the
solvent system according to the invention confers, on
the solutions of fluoropolymers, a relatively low
30 viscosity, that is to say lower than that observed when
the only solvent is DMSO. By virtue of this advantage,
it is possible to dissolve higher contents of
fluoropolymers than with just NMP or just DMSO,' or also
to dissolve fluoropolymers having a higher molar mass.
35 . [0045] Thus, and according to another aspect, the
invention relates to the use of at least one solvent
system as defined above for • the dissolution of
fluoropolymers, in 'particular poly(vinylidene
fluoride)'.
t - 11 -
[0046] According to yet another aspect, the present
invention relates to the process for the dissolution of
fluoropolymer, in particular PVDF, comprising at least
the stage of bringing the said fluoropolymer into
5 contact with at least one solvent system as defined
above.
[0047] This contacting operation is preferably carried
out with stirring, at ambient temperature or at a
temperature between ambient temperature and 80°C,
10 preferably between ambient temperature and 60°C, more
preferably between ambient temperature and 50°C. The
fluoropolymer can be brought into contact with at least
one solvent system according to the invention in any
form but, for reasons of speed or dissolution, it is
15 preferable for the said fluoropolymer to be in a powder
form.
[0048] The solvent system according to the present
invention is entirely suitable for the dissolution of
fluoropolymers, in particular of PVDFs. In other words,
20 the solvent system of the invention makes it possible
to obtain solutions of fluoropolymers which are clear
and stable over time.
[0049] The amount of fluoropolymer(s) which can be
dissolved in the solvent system of the invention varies
25 within large proportions, according to the nature of
the polymer and the nature of the solvent system, and
is generally between 1 and 50% by weight, preferably
between 1 and 40% by weight and more preferably between
1 and 25% by weight, for example approximately 10% by
30 weight, of fluoropolymer, with respect to the total
weight of fluoropolymer + solvent system final
solution.
[0050] . According to another aspect, the present
invention relates to a solution comprising:
35 a. from 1 to 50% by weight, preferably from 1 to 40%
by weight and more preferably from 1 to 25% by
weight, for example approximately 10% by weight,, of
at least one fluoropolymer, preferably at least one
PVDF, ' and
- 12 -
b. from 50 to 99% by weight, preferably from 60 to 99%
by weight and more preferably from 75 to 99% by
weight, for example approximately 90% by weight, of
at least one solvent system as defined above.
5 [0051] As indicated above, fluororesins, in particular
PVDFs, are well known today for their excellent
chemical resistance, their noteworthy mechanical
properties and their excellent stability over time. All
these qualities make them materials of choice for the
10 uses thereof as membranes for filtration and
ultrafiltration and for the manufacture of batteries,
to mention only some of their applications.
[0052] Fluororesins, in particular PVDFs, due to their
solubility in the solvent system of the present
15 invention, can thus easily be formed by moulding in a
solvent medium according to the phase inversion
(solvent casting) process or can also be prepared in
the form of sheets, fibres, hollow fibres, pipes and
others.
20 [0053] The invention also relates to the use of the
solvent system for fluoropolymer as defined above or a
solution of fluoropolymer in the solvent system as
defined above in' the manufacture of films, membranes
and coatings.
25 [0054] The fields of application comprise the
treatment of drinking water and waste water, filtration
of blood and proteins, the preparation of water of very
high purity, medical diagnostics, and the filtrations
involved in chemical processes, in particular when an
,30 exceptional chemical resistance is required.
[0055] In addition, some PVDF resins, such as, for
example, Kynar® resins, are approved for contact with
food, which makes them a material of choice in the
field of filtration in the food processing industry and
35 of the drinks industry. High density PVDF membranes, in
particular Kynar® membranes, can be used for the
separation of solvents by pervaporation. Microporous
PVDF membranes, in particular Kynar® membranes, can be
- 13 -
used as substrate material for the preparation of
membranes made of composite polymer.
[0056] PVDF membranes, in particular Kynar® and Kynar
Flex® membranes, are also known to be used in the
5 manufacture of batteries with a high charge density.
The solvent system of the present- invention thus makes
possible in particular the dissolution of fluororesins,
in particular PVDF resins, especially Kynar® and Kynar
Flex® resins, in the manufacture of batteries or
10 Li-ion/polymer and lithium with liquid electrolyte
type, it being possible for the solvent system to be
evaporated by any system known to a person skilled in
the art, for example by heating.
[0057] For the preparation of batteries, the solvent
15 system of the invention can comprise, in addition to
the fluororesin or fluororesins, any type of additive
and filler normally employed in the synthesis of the
said batteries, in particular carbon, whether in the
form of charcoal, active charcoal, or alternatively in
20 the form of carbon nanotubes (CNTs).
[0058] The present invention is now illustrated by
means of the examples which follow and which under no
circumstances limit the scope of the protection as
requested in the appended claims.
25
Example 1
[0059] Tests of dissolution of Kynar® 761 PVDF from
Arkema were carried out with NMP, DMSO, a DMSO/TMCHONE
(70%/30% by weight) mixture, a DMSO/TMCHONE (50%/50% by
30 weight) mixture, a DMSO/TMCHONE (30%/70% by weight)
mixture and TMCHONE alone.
[0060] 10% by weight of Kynar® 761 are introduced into
the test solvent. The mixture is heated at 50°C with
gentle stirring.
35 [0061] After a few minutes, the Kynar® 761 has
completely dissolved, except in the case of the 30%/70%
by weight DMSO/TMCHONE mixture, and a transparent
solution is obtained for all these solvents. The
solutions are allowed to return to ambient temperature.
i - 14 -
[0062] The viscosities of the solutions of dissolved
Kynar® 761 are then characterized at 30°C on a
Brookfield cone-plate viscometer. The results observed
are collated in the following Table 1:
Table 1
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
10% by weight
10% by weight
10% by weight
Solvent used
NMP
DMSO
DMSO/TMCHONE
(70%/30% by weight)
DMSO/TMCHONE
(50%/50% by weight)
DMSO/TMCHONE
(30%/70% by weight)
TMCHONE
Vlscosi ty (cP)
250
323
260
230
Insoluble
Insoluble
[0063] It is noticed that the addition of ketone to
the DMSO,- in amounts of less than or equal to 50% by
weight, indeed even equal to that of the DMSO, does not
10 harm the solubility of the f luoropolymer and on the
contrary favours a decrease in the ' viscosity, with
respect to dissolution in DMSO alone. On the other
hand, a greater amount of ketone prevents the
fluoropolymer from dissolving.
15 •
Example 2
[0064] The 4 solutions of Example 1 which made it
possible to dissolve the Kynar® 761 are left at ambient
temperature in order to study their stability over
2 0 time.
[0065] After 7 days, visual analysis of the solutions
is carried out and the results are presented in the
following Table 2: ,
- 15 -
Table 2
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
10% by weight
Solvent used
NMP
DMSO
DMSO/TMCHONE
{70%/30%- by weight)
DMSO/TMCHONE
(50%/50% by weight)
Appearance
after 7 days
Transparent
viscous liquid
solution
Viscous liquid
solution but
very cloudy
Transparent
viscous liquid
solution
Completely
cloudy solid
gelled solution
[0066] With time, the unstable solutions change and
pass from the transparent liquid state to the cloudy
5 liquid state and then the solid and cloudy gel state.
Only the composition of solvents according to the
present invention exhibits similar characteristics to
NMP as regards the dissolution of fluoropolymers.
[0067] In particular, a composition comprising DMSO
10 and TMCHONE in the 70%/30% by weight proportions thus
makes it possible to obtain a 10% Kynar® 761 solution
which is stable over time, in contrast to a pure DMSO
solution or a DMSO/TMCHONE solution with a TMCHONE
content of greater than 50% by weight.
15
Example 3
[0068] Similarly, tests of dissolution of Kynar® 761
are carried out with a DMSO/TMCHONE {80%/20% by weight)
mixture.
20 [0069] 10% by weight of Kynar® 761 are introduced into
the test solvent. The mixture is heated at 50°C with
gentle stirring.
[0070] After a few minutes, the Kynar® 761 has
completely dissolved. The solution is allowed to return
25 to ambient temperature and is then left at ambient
temperature in order to study its stability over time.
- 16 -
[0071] After 21 days, visual analysis of the solution
is carried out and the solution is still liquid and
transparent.
5 Example 4
[0072] Similarly, tests of dissolution of Kynar® 761
are carried out with NMP, DMSO, a DMSO/cyclohexanone
(80%/20% by weight) mixture, a DMSO/cyclohexanone
(50%/50% by weight) mixture, a DMSO/cyclohexanone
10 (30%/70% by weight) mixture and cyclohexanone alone.
[0073] 10% by weight of Kynar® 761 are introduced into
the test solvent. The mixture is heated at 50°C with
gentle stirring. After a few minutes, the Kynar® 761
has completely dissolved, except in the case of the
15 cyclohexanone alone mixture, and a transparent solution
is obtained for all these solvents. The solutions are
allowed to return to ambient temperature.
[0074] The viscosities of the solutions of dissolved
Kynar® 761 are then characterized at 30 °C on a
20 Brookfield cone-plate viscometer. The results observed
are collated in the following Table 3:
Table 3
Content
10%
10%
10%
10%
10%
10%
of
by
by
by
by
by
by
Kynar® 761
weight
weight
weight
weight
weight
weight
Solvent used
NMP
DMSO
DMSO/cyclohexanone
(80%/20% by weight)
DMSO/cyclohexanone
(50%/50% by weight)
DMSO/cyclohexanone
(30%/70% by weight)
Cyclohexanone
Viscosity (cP)
250
323
275
240
216
Insoluble
[JD075] The solvent compositions according to the
25 invention make it possible to obtain viscosities which
are lower than those obtained with DMSO alone and
comparable with that of NMP.
10
15
- 17 -
Example 5
[0076] The solutions of Example 4 which made it
possible to dissolve Kynar® 761 are left at ambient
temperature in order to study their stability over
time.
[0077] After 3 days, visual analysis of the solutions
is carried out and the results are collated in the
following Table 4:
Table 4
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
10% by weight
• 10% by weight
Solvent used
NMP
DMSO
DMSO/cyclohexanone
(80%/20% by weight)
DMSO/cyclohexanone
(50%/50% by weight)
DMSO/cyclohexanone
(30%/70% by weight)
Appearance
after 3 days
Transparent
viscous liquid
solution
Viscous liquid
solution but
cloudy
Transparent
viscous liquid
solution
Transparent
viscous liquid
solution
Completely
cloudy solid
gelled solution
20
[0078] With time, the unstable solutions change and
pass from the transparent liquid state to the cloudy
liquid state and then the solid and cloudy gel state.
The DMSO/ketone mixtures according to the invention
make it possible to obtain a 10% solution of
fluoropolymer which is stable over time, in contrast to
a pure DMSO solution or a DMSO/ketone solution with
ketone contents of greater than 70% by weight.
[0079]- The DMSO/cyclohexanone (80%/20% by weight)
solution is- still liquid and transparent after 21 days.
Example 6
[0080] Tests of dissolution of Kynar® 761 are carried
out with NMP, DMSO, a DMSO/acetone (95%/5% by weight)
10
15
- 18 -
mixture, a DMSO/acetone (80%/20% by weight) mixture and
acetone alone.
[0081] 10% by weight of Kynar® 761 are introduced into
the test solvent. The mixture is heated at 50°C with
gentle stirring. After a few minutes, the Kynar® 761
has completely dissolved in all these solvents and a
transparent solution is obtained for all these
solvents. The solutions are allowed to return to
ambient temperature.
[0082] The viscosities of the solutions of dissolved
Kynar® 761 are then characterized at 30°C on a
Brookfield cone-plate viscometer. The results observed
are collated in the following Table 5:
Table 5
Content of Kynar® 761
'' 10% by weight
10% by weight
10% by weight
10% by weight
10% by weight
Solvent used
NMP
DMSO
DMSO/acetone
(95%/5% by weight)
DMSO/acetone
(80%/20% by weight)
Acetone
Viscosity (cP)
250
323
263
120
10
[0083] The DMSO/acetone mixtures thus make it possible
to obtain much lower viscosities than those obtained
with DMSO or NMP alone.
20 Example 7
[0084] The 5 solutions of Example 6 a-re left at
ambient temperature in order -to study their stability
over time. After 3 days, visual analysis of the
solutions is carried out. The results observed are
25 collated in the following Table 6:
• - 19 -
Table 6
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
10% by weight
10% by weight
Solvent used
NMP
DMSO
DMSO/acetone
•(95%/5% by weight)
DMSO/acetone
(80%/20% by weight)
Acetone
Appearance
after 3 days
Transparent
viscous liquid
solution
Viscous liquid
solution but
cloudy
Transparent
viscous liquid
solution
Transparent
viscous liquid
solution
Completely
cloudy solid
gelled solution
10
15
[0085] With time, the unstable solutions change from
the transparent liquid state to the cloudy liquid state
and then the solid and cloudy gel state.
[0086] After 10 days, the DMSO/acetone (95%/5%)
solution is still stable and has a • liquid and
transparent appearance. After 45 days, the DMSO/acetone
(80%/20%) solution is still stable and has a
transparent liquid appearance.
[0087] A DMSO/acetone (80%/20% by weight or 95%/5% by
weight) mixture thus makes it possible to obtain a 10%
Kynar® 761 solution which is stable over time, in
contrast to a pure DMSO solution or a pure acetone
solution.
Example 8
[0088] Tests of dissolution of Kynar® 761 are carried
out with DMSO, a DMSO/dimethyl glutarate/acetone
20 (66.5%/28.5%/5%. by weight) mixture, a .DMSO/dimethyl
glutarate (70%/30% by weight) mixture and dimethyl
glutarate alone.
[0089] 10% by weight of Kynar® 761 are introduced into
the test solvent. The mixture is heated at 50°C with
25 geijtle stirring. After a few minutes, the Kynar® 761
10
- 20 -
has completely dissolved in all these solvents, except
in the case of the dimethyl glutarate alone, and a
transparent solution is obtained for all these
solvents. The solutions are allowed to return to
ambient temperature.
[0090] The viscosities of the solutions of dissolved
Kynar® 761 are then characterized at 30 °C on. a
Brookfield cone-plate viscometer. The results observed
are collated in the following Table 7:
Table 7
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
10% by weight
Solvent used
DMSO
DMSO/diitiethyl
glutarate/acetone
(66.5%/28.5%/5%
.by weight)
DMSO/dimethyl
glutarate
(70%/30% by weight)
Dimethyl glutarate
Viscosity (cP)
323
278
335
Insoluble at 50°C
15
[0091] The DMSO/dimethyl glutarate/acetone mixt,ures
thus make it possible to obtain lower viscosities than
those obtained with DMSO alone. Dimethyl glutarate
alone does not make it possible to dissolve Kynar® 761
at 50°C. It is necessary to heat to approximately 100°C
in order to achieve this, which is not advantageous.
Example 9
20 [0092] The 3 solutions of Example 8 which made it
possible to dissolve Kynar® 761 are left at ambient
temperature in order to study their stability over
time.
[0093] After 7 days, visual analysis of the solutions
25 is carried out. The results observed are collated in
the following Table 8:
- 21 -
Table 8
Content of Kynar® 761
10% by weight
10% by weight
10% by weight
Solvent used
DMSO
DMSO/dimethyl
glutarate/acetone
(66.5%/28.5%/5%
by weight)
DMSO/dimethyl
glutarate
(70%/30% by weight)
Appearance
after 7 days
Viscous liquid
solution but
cloudy
Transparent
viscous liquid
solution
Completely
cloudy gelled
solid solution
[0094] A DMSO/dimethyl glutarate/acetone
(66.5%/28.5%/5% by weight) mixture thus makes it
possible to obtain a 10% Kynar® 761 solution which is
stable over time, in contrast to a pure DMSO solution
or a pure dimethyl glutarate solution.

CLAIMS
1. Solvent system for fluoropolymer comprising:
from 50 to 99.9% by weight of a composition (A)
5 comprising dimethyl sulphoxide (DMSO), and
from 0.1 to 50% by weight of a composition (B)
comprising at least one ketone.
2. Solvent system according to Claim 1, in which the
10 said fluoropolymer is, chosen from fluorinated and/or
chlorofluorinated homopolymers and copolymers obtained
by suspension or emulsion polymerization, ECTFE
(ethylene/chlorotrifluoroethylene) copolymers, and
perfluoroionomers, and others, preferably chosen from
15 fluororesins comprising at least one poly(vinylidene
fluoride) homopolymer and/or copolymer.
3. Solvent system according to Claim 1 or Claim 2, in
which the composition (A) comprises, in addition to the
20 DMSO, one or more other solvents for the fluoropolymer
other than a ketone.
4. Solvent system according to Claim 3, in which the
other solvent or solvents of the fluoropolymer other
25 than a ketone is (are) chosen from esters, diesters,
preferably from propylene carbonate, diethyl carbonate,
dimethyl succinate, dimethyl adipate, dimethyl
glutarate, and their mixtures.
30. 5. Solvent system according to Claim 3 or Claim 4, in
which the amount of solvent (s) present in the
composition (A) with the DMSO is between 0 and 50% by
weight, preferably between 0 and 40% by weight and more
preferably between 0 and 30% by weight, with respect to
35 the total weight of the composition (A), the remainder
to 100% consisting of the DMSO, alone or in combination
with impurities, odorous agents and/or other additives.
included in the composition (B) is chosen from linear or branched aliphatic and/or cycloaliphatic ketones, '
6. Solvent system according to any one of the
preceding claims, in which the at least one ketone^
preferably from dimethyl ketone, diethyl ketone, methyl
ethyl ketone, methyl isobutyl. ketone, optionally
substituted cyclohexanone, trimethylcyclohexanone
(TMCHONE) , cyclopentanone, and others, and the mixturesof
two or more of these ketones in all proportions.
7. Solvent system according to any one of the
preceding claims, comprising:
a. from 7 0 to 95% by weight of DMSO, for example
approximately 75% by weight, and
15 b. from 5 to 30% by weight of at least one ketone
chosen from cyclohexanone, trimethylcyclohexanone
and their mixtures in all proportions, for example
approximately 25% by weight.
20 8. Solvent system according to any one of Claims 1 to
6, comprising:
c. from 8 5 to 99% by weight of DMSO, for example
approximately 95% by weight, and
d. from 1 to 15% by weight of acetone, for example
25 approximately 5% by weight.
9. Solvent system according to any one of. Claims 1 to
6, comprising:
e. from 85 to 99% by weight, preferably approximately
30 95% by weight, of a mixture of 50% by weight of
DMSO with 50% by weight of DEE, preferably dimethyl
glutarate, and
f. from 1 to 15% by weight of acetone, preferably
approximately 5% by weight.
10. Solvent system according to any one of Claims 1 to
6, comprising:
g. from 70 to 95% by weight, for example approximately
75% by weight, of a mixture of 50% by weight of
DMSO with 50% by weight of DBE, preferably dimetl
glutarate, and
h. from 5 to 30% by weight of at least one ketone
chosen from cyclohexanone, trimethylcyclohexanone
5 and their mixtures in all proportions, preferably
approximately 25% by weight.
11. Use of at least one solvent system according to
any one of the preceding claims for the dissolution of
10 fluoropolymers, in particular poly(vinylidene
fluoride).
12. Process for the dissolution of fluoropolymer, in
particular poly(vinylidene fluoride), comprising at
15 least the stage of bringing the said fluoropolymer into
contact with at least one solvent system according to
any one of Claims 1 to 10.
13. Solution comprising:
20 i. from 1 to 50% by weight, preferably from 1 to 40%
by weight and more preferably from 1 to 25% by
weight of at least one fluoropolymer, preferably atleast
one poly(vinylidene fluoride), and
from 50 to. 99% by weight, preferably from 60 to 99%
25 by weight and more preferably from 75 to 99% by
weight of at least one solvent system according to
any one of Claims 1 to 10.
14. Use of the solvent system for fluoropolymer
30 according to any one of Claims 1 to 10, or a solution
of fluoropolymer in the solvent system according to
Claim 13, in the manufacture of films, membranes and
coatings and in the manufacture of batteries.