EP4114889A1

EP4114889A1 - Method for manufacturing a solution of a fluorinated copolymer

Info

Publication number: EP4114889A1
Application number: EP21714646.3A
Authority: EP
Inventors: Manuel Hidalgo; Aristide LAJOUX
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2020-03-03
Filing date: 2021-03-03
Publication date: 2023-01-11
Also published as: KR20220149712A; JP2023516387A; FR3107899A1; US20230130819A1; FR3107899B1; CN115244111A; WO2021176180A1; TW202140634A

Abstract

The invention relates to a method for manufacturing a solution of a fluorinated copolymer in a solvent, the solvent having a boiling point greater than or equal to 150°C at 1013 hPa and/or a saturation vapour pressure less than or equal to 5 hPa at 20°C, the method comprising a step of mixing the fluorinated polymer with the solvent in a reactor having a stirring mechanism comprising at least one blade, at a mixing temperature ranging from 40°C to 100°C, and at a blade tip stirring speed greater than or equal to 0.1 m/s, until the polymer is dissolved in the solvent. The invention also relates to a solution of the copolymer in the solvent not comprising a co-solvent having a boiling point strictly less than 150°C at 1013 hPa and/or a saturation vapour pressure strictly greater than 5 hPa at 20°C.

Description

Title: Process for manufacturing a solution of a fluorinated copolymer Technical field

The invention relates to the field of fluoropolymers, in particular solutions of copolymers derived from vinylidene fluoride and from at least one other monomer.

Prior art

It is known from the prior art to manufacture solutions of P (VDF-TrFE) in low volatility solvents, such as g-butyrolactone (boiling point at 204.0 ° C). The dispersion of P (VDF-TrFE) in g-butyrolactone is nevertheless complex to implement in practice.

It is for example known to mix the polymer with the solvent in the form of granules at a temperature of 180 ° C. under reflux for a period of 2 hours (cf. Zirkl, M., Stadlober, B., & Leising, G. ( 2007). Synthesis of ferroelectric poly (vinylidene fluoride) copolymer films and their application in integrated full organic pyroelectric sensors. Ferroelectrics, 353 (1), 173-185). The disadvantage of this process is that it requires heating to high temperature, which is tedious to implement and requires suitable equipment, as well as appropriate safety measures. In addition, such heating is the cause of yellowing of the resulting solution, which is undesirable. In addition, by proceeding according to this process, a gel is obtained at room temperature, and not a homogeneous solution. A state of homogeneous solution is only obtained by slowly heating the gel from room temperature.

In order to work under milder temperature conditions, it has been proposed, for example in US2013 / 0153814, to mix granules of P (VDF-TrFE) in a 50:50 mixture (volume proportions) of y-butyrolactone: acetone for 24 hours with stirring of a magnetic stirrer, at room temperature. Acetone, which is a much more volatile solvent than g-butyrolactone, is also a solvent in which P (VDF-TrFE) dissolves in it more easily and more quickly.

Thanks to its high volatility, the acetone is then easily evaporated at 40 ° C. by a rotary evaporator and under reduced pressure. This process presents as advantage of not subjecting the solution to high temperatures and does not cause yellowing of the latter. However, it has the disadvantage of using a co-solvent which will ultimately have to be removed during a dedicated additional step. In addition, the presence of residual amounts of co-solvent in the solution can be detrimental for all uses leading to the manufacture of thin layers (films), and, in particular, those where the conditions of evaporation of the solvent to constitute the thin film are fast (risk of appearance of continuity defects of the final film).

There is therefore a need to provide a process for manufacturing a solution of fluoropolymer in a solvent with a high boiling point and / or low saturated vapor pressure, in particular at fairly high concentrations of fluoropolymer, making it possible to obtain a homogeneous solution, limiting impurities (no volatile co-solvent), and limiting any degradation of the fluoropolymer or of the solvent.

Goals

The object of the present invention is to provide an improved method of manufacturing a solution of fluoropolymer in a solvent having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a lower saturated vapor pressure. or equal to 5 hPa at 20 ° C, allowing complete dissolution of the polymer in a reasonable time.

According to certain embodiments, an objective is to provide a method that is simpler to implement than those of the prior art.

According to certain embodiments, an objective is to provide a method which is more economical to implement than those of the prior art.

According to certain embodiments, an objective is to provide a method which is faster to implement than those of the prior art.

According to certain embodiments, an objective is to provide a process which makes it possible to obtain a composition which exhibits substantially no yellowing.

According to certain embodiments, an objective is to provide a process which makes it possible to obtain a composition which does not have a volatile co-solvent, that is to say does not have a co-solvent having a lower boiling point. or equal to 150 ° C at 1013 hPa and / or a saturated vapor pressure greater than or equal to 5 hPa at 20 ° C.

Presentation of the invention

The invention relates to a method of manufacturing a solution of a fluoropolymer in a solvent, the fluoropolymer being a polymer comprising units derived from vinylidene fluoride as well as units derived from at least one other monomer of formula CX ₁ X ₂ = CX ₃ X ₄ , in which each X ₁ , X ₂ , X ₃ and X _{4 group} is independently selected from H, Cl, F, Br, I and alkyl groups comprising from 1 to 3 atoms of carbon, which are optionally partially or fully halogenated, the solvent having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a saturated vapor pressure less than or equal to 5 hPa at 20 ° C, the process comprising a step of mixing said fluoropolymer with said solvent in a reactor having a stirring unit comprising at least one blade, at a mixing temperature ranging from 40 ^° C. to 100 ^° C., and at a stirring speed of blade tip greater than or equal to 0.1 m / s, until said polymer has dissolved re in said solvent.

The inventors of the present invention have in fact noticed that, surprisingly, the fluoropolymer, such as P (VDF-TrFE) cited in the prior art, could be dissolved in a low volatile solvent, such as γ-butyrolactone, without having need to use a co-solvent, nor to heat the mixture excessively. The inventors have in fact selected a range of optimum temperatures as well as defined an optimum speed of stirring of a stirring mobile with blade (s) making it possible to obtain a homogeneous fluoropolymer solution, in a simple, rapid and low-speed manner. expensive.

According to certain embodiments, said at least one other monomer is chosen from: trifluoroethylene (TrFE), tetrafluoroethylene (TFE), 3,3,3-trifluoropropene, 1, 3,3,3-tetrafluoropropene, 2 , 3,3,3-tetrafluoropropene,

1, 3,3,3-tetrafluoropropene, 1, 1, 3,3,3-pentafluoropropene, 1, 2, 3,3,3-pentafluoropropene, hexafluoropropene (HFP), hexafluoroisobutylene (HFIB), perfluorobutylethylene, chlorotrifluoroethylene (CTFE), 1, 1 - chlorofluoroethylene (1, 1 -CFE), 1, 2-chlorofluoroethylene (1, 2-CFE), 2-chloro-3,3,3-trifluoropropene (1233xf) , 1 -chloro-3,3,3-trifluoropropene (1233zd), 1, 2-dichloro-1, 2-difluoroethylene, 1, 1 -dichloro-1, 1 - difluoroethylene and 1, 1, 2-trichloro-2 -fluoroethylene.

According to certain embodiments, said fluoropolymer is chosen from among P (VDF-TrFE), P (VDF-TFE), P (VDF-TrFE-TFE), P (VDF-TrFE-CTFE), P (VDF-TrFE) -CFE), P (VDF-T rFE-CTFE-CFE) and P (VDF-TrFE-TFE-CTFE-CFE). The fluoropolymer can in particular be chosen from: a P (VDF-TrFE), a P (VDF-TrFE-CFE), or a P (VDF-TrFE-CTFE).

According to certain embodiments, said fluoropolymer has a melt index (MFI), measured according to standard ASTM D1238, at 230 ° Ce under a load of 10 kg, from 0.2 g / 10 min to 20 g / 10 min, preferably from 0.5 to 10 g / 10min, even more preferably from 0.8 g / 10min to 8 g / 10min, and extremely preferably between 1 g / 10min and 6 g / 10min.

According to certain embodiments, the solvent is chosen from the group consisting of: acetate of propylene glycol monomethyl ether, N, N-dimethylformamide, cyclohexanone, N, N-dimethylacetamide, diacetone-alcohol, diisobutyl ketone, 3-methylcyclohexanone, tetramethyl urea, ethyl acetoacetate, dimethyl sulfoxide, trimethyl phosphate, monoethyl ether of diethylene glycol, N-methyl-2-pyrrolidone, gamma-butyrolactone, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, dimethyl phthalate, and a mixture thereof. Preferably, the solvent is chosen from the group consisting of the acetate of the monomethyl ether of propylene glycol, cyclohexanone, 3-methylcyclohexanone, dimethylsulfoxide, gamma-butyrolactone, triethyl phosphate, and their mixture.

According to some embodiments, the solvent is gamma-butyrolactone or triethyl phosphate. According to certain embodiments, the fluoropolymer represents from 1% by weight to 40% by weight of the total weight of the solution. Preferably, the fluoropolymer represents from 5% by weight to 30% by weight of the total weight of the solution. More preferably, the fluoropolymer represents from 10% by weight to 25% by weight of the total weight of the solution.

According to certain embodiments, the fluoropolymer represents more than 11%, or more than 12%, or more than 13%, or more than 14%, or even more than 15% by weight relative to the total weight of solution; and / or less than 24%, or less than 23%, or less than 22%, or less than 21%, or even less than 20% by weight, relative to the total weight of solution.

According to certain embodiments, the mixing temperature is less than or equal to 90 ° C, preferably less than or equal to 80 ° C, more preferably less than or equal to 70 ° C and extremely preferably less than or equal to 65 ° C.

According to certain embodiments, the stirring speed of the blade tip is greater than or equal to 0.25 m / s.

According to certain embodiments, the duration of the mixing step is between 30 minutes and 12 hours. Preferably, the duration of the mixing step is between 1 hour and 5 hours.

According to certain embodiments, the stirring mobile comprises at least three blades, preferably at least four blades.

According to certain embodiments, the characteristic internal diameter D of the reactor relative to the stirring diameter L of the stirring wheel is such that: 0.2D <L <0.9D; and, preferably such that: 0.3D <L <0.8D. According to certain embodiments, the mixing step is carried out by adding the fluoropolymer, all at once or in a fractional manner, to the solvent.

The invention also relates to the solution that can be obtained by the process according to the invention. In particular, the invention relates to a solution of a fluoropolymer in a solvent, the fluoropolymer being a polymer comprising units derived from vinylidene fluoride as well as units derived from at least one other monomer of formula CX ₁ X ₂ = CX ₃ X ₄ , in which each group X ₁ , X ₂ , X ₃ and X ₄ is independently selected from H, Cl, F, Br, I and alkyl groups comprising from 1 to 3 carbon atoms, which are optionally partially or totally halogenated, the solvent having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a slashing vapor pressure greater than or equal to 5 hPa at 20 ° C. This solution is characterized in that it does not include a co-solvent for said fluoropolymer having a boiling point strictly less than 150 ° C at 1013 hPa and / or a saturated vapor pressure strictly greater than 5 hPa at 20 ° C. .

According to certain embodiments, the solution has a viscosity as measured at room temperature (25 ° C.) using a Brookfield viscometer of the “RVDV-II + P” type, of 2000 mPa.s to 40,000 mPa. s, preferably from 8,000 mPa.s to 30,000 mPa.s, more preferably from 12,000 mPa.s to 28,000 mPa.s, and extremely preferably from 15,000 mPa.s to 25,000 mPa.s.

According to particular embodiments, the solution can have a viscosity of 18,000 mPa.s to 24,000 mPa.s.

According to certain embodiments, said fluoropolymer and / or the solvent and / or the amount of fluoropolymer in the solution is as described above.

List of Figures

[Fig. 1] represents a single-stage quadruple-bladed agitation mobile, seen in perspective.

[Fig. 2] shows the quadruple-bladed, two-stage stirring wheel used in Example 2, in side view. [Fig. 3] represents the same agitation mobile as that of FIG. 2, in top view.

Detailed description of the invention

The invention is now described in more detail and in a nonlimiting manner in the description which follows.

In the present application, the expression “a fluoropolymer” should be understood to mean “one or more fluoropolymers”. It is the same with all other species. Thus, for example, the expression "a solvent" should be understood to mean "one or more solvents".

Fluorinated polymer

The polymer is a copolymer (in the broad sense): it comprises units resulting from (that is to say which are obtained by polymerization) from the monomer of vinylidene fluoride (VDF) and from at least one other monomer X than the vinylidene fluoride. A single X monomer can be used, or several different X monomers, depending on the case.

The monomer X is of the formula: CX ₁ X ₂ = CX ₃ X ₄ , in which each group X ₁ , X ₂ , X ³ and X4 is independently selected from H, Cl, F, Br, I and alkyl groups in C1 -C3 (preferably in C1 -C2), which are optionally partially or totally halogenated. Monomer X is different from VDF, i.e. if X1 and X2 represent H, then at least one of X3 and X4 does not represent F, and vice versa if X1 and X2 represent F, at least l 'one of X3 and X4 does not represent H.

In certain embodiments, each X ₁ , X ₂ , X ₃ and X _{4 group} independently represents an H, F, Cl, I or Br atom, or a methyl group optionally comprising one or more substituents chosen from F, Cl, I and Br.

In some embodiments, each group X ₁ , X ₂ , X ₃ and X ₄ independently represents an H, F, Cl, I or Br atom.

In some embodiments, only one of X ₁ , X ₂ , X ₃ and X ₄ represents a Cl or I or Br atom, and the others of the groups X ₁ , X ₂ , X ₃ and X ₄ independently represent: an atom H or F or a C1 -C3 alkyl group optionally comprising one or more fluorine substituents; preferably, an H or F atom or a C1 -C2 alkyl group optionally comprising one or more fluorine substituents; and more preferably, an H or F atom or a methyl group optionally comprising one or more fluorine substituents.

Examples of monomers X comprising only fluorine as halogen atom are: vinyl fluoride (VF), trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropene (HFP), trifluoropropenes, and in particular 3,3,3-trifluoropropene, tetrafluoropropenes, and in particular

2.3.3.3-tetrafluoropropene or 1, 3,3,3-tetrafluoropropene (in cis or preferably trans form), hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes, and in particular 1, 1, 3,3,3-pentafluoropropene where the

1 .2.3.3.3-pentafluoropropene, perfluoroalkylvinylethers, and in particular those of general formula R _f -0-CF = CF2, in which Rf is an alkyl group, preferably C1 to C4 (preferred examples being perfluoropropylvinyl ether (PPVE) and perfluoromethylvinylether (PMVE)).

Examples of monomer X comprising at least one chlorine or bromine atom are: bromotrifluoroethylene, 1 -chloro-1 -fluoroethylene (CFE), 1 - chloro-2-fluoroethylene, chlorotrifluoroethylene (CTFE), 2- chloro-3,3,3-trifluoropropene (1233xf), 1 -chloro-3,3,3-trifluoropropene (in cis or trans form, preferably trans), 1, 2-dichloro-1, 2-difluoroethylene, 1, 1 -dichloro-1, 1 -difluoroethylene and 1, 1, 2-trichloro-2-fluoroethylene.

In certain preferred embodiments, the fluoropolymer comprises units derived from VDF and HFP or else is a polymer P (VDF-HFP) consisting of units derived from VDF and HFP. The molar proportion of repeating units derived from the HFP is preferably from 2 to 50%, in particular from 5 to 40%.

In some preferred embodiments, the fluoropolymer comprises units derived from VDF and CFE, and / or CTFE, and / or TFE, and / or TrFE. The molar proportion of repeat units derived from monomers other than VDF is preferably less than 50%. In certain preferred embodiments, the fluoropolymer comprises units derived from VDF and TrFE, or else is a polymer P (VDF-TrFE) consisting of units derived from VDF and TrFE.

In certain preferred embodiments, the fluoropolymer comprises units derived from VDF, TrFE and another monomer X as defined above, other than VDF and TrFE, or else is a polymer P (VDF-TrFE -X) consisting of units derived from VDF, TrFE and another monomer X as defined above, other than VDF and TrFE. In this case, preferably, the other monomer X is chosen from TFE, HFP, trifluoropropenes and in particular 3,3,3-trifluoropropene, tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene or 1, 3,3,3-tetrafluoropropene (in cis or preferably trans form), bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropene. Particularly preferred are CTFE or CFE.

When units derived from VDF and T rFE are present, the proportion of units derived from TrFE is preferably from 5 to 95 mol.% Relative to the sum of units derived from VDF and T rFE, and in particular: from 5 at 10 mol.%; or from 10 to 15 mol.%; or from 15 to 20 mol.%; or from 20 to 25 mol.%; or from 25 to 30 mol.%; or from 30 to 35 mol.%; or from 35 to 40 mol.%; or from 40 to 45 mol.%; or from 45 to 50 mol.%; or from 50 to 55 mol.%; or from 55 to 60 mol.%; or from 60 to 65 mol.%; or from 65 to 70 mol.%; or from 70 to 75 mol.%; or from 75 to 80 mol.%; or from 80 to 85 mol.%; or from 85 to 90 mol.%; or from 90 to 95 mol.%. A range of 15 to 55 mol. % is particularly preferred.

When units derived from another X monomer, in addition to VDF and TrFE, are present (the X monomer being in particular CTFE or CFE), the proportion of units derived from this other X monomer in the fluoropolymer (for example relative to all the units) can vary, for example, from 0.5 to 1 mol%; or from 1 to 2 mol.%; or from 2 to 3 mol.%; or from 3 to 4 mol.%; or from 4 to 5 mol.%; or from 5 to 6 mol.%; or from 6 to 7 mol.%; or from 7 to 8 mol.%; or from 8 to 9 mol.%; or from 9 to 10 mol.%; or from 10 to 12 mol.%; or from 12 to 15 mol.%; or from 15 to 20 mol.%; or from 20 to 25 mol.%; or from 25 to 30 mol.%; or from 30 to 40 mol.%; or from 40 to 50 mol.%. Ranges from 1 to 20 mol. %, and preferably from 2 to 15 mol. %, are particularly suitable. The molar composition of the units in fluoropolymers can be determined by various means such as infrared spectroscopy or RAMAN spectroscopy. Conventional methods of elemental analysis for the elements carbon, fluorine and chlorine or bromine or iodine, such as X-ray fluorescence spectroscopy, make it possible to calculate the mass composition of the polymers, from which the molar composition is deduced.

Multi-core NMR techniques can also be used, in particular proton (1 H) and fluorine (19F), by analysis of a solution of the polymer in an appropriate deuterated solvent.

It is finally possible to combine elemental analysis, for example for heteroatoms such as chlorine or bromine or iodine, and NMR analysis. Thus, the content of units obtained from CTFE, in a terpolymer P (VDF-TrFE-CTFE) for example, can be determined by measuring the chlorine content by elemental analysis.

The melt flow index (or Melt Flow Index) makes it possible to characterize an average molecular mass indirectly. MFI measurement can be performed following ASTM D1238, using equipment such as the Dynisco D4059 B Flowmeter, determining the cumulative weight that passes through the measurement die after 10 minutes when the device is operated at 230 ° C and 10 kg load on the molten polymer. In certain variants, the fluoropolymer has an MFI of between 0.2 g / 10min and 20 g / 10min under these conditions, preferably between 0.5 g / 10min and 10 g / 10min, even more preferably between 0.8 g / 10min and 8 g / 10min and extremely preferably between 1 g / 10min and 6 g / 10min.

The fluoropolymer is preferably random and linear.

The fluoropolymer can be homogeneous or heterogeneous. A homogeneous polymer has a uniform chain structure, the statistical distribution of the units resulting from the different monomers hardly varying between the chains. In a heterogeneous polymer, the chains exhibit a distribution in units resulting from the various monomers of multimodal or spread type. A heterogeneous polymer therefore comprises chains richer in a given unit and chains poorer in this unit. The fluoropolymer can be in the form of pieces, granules or in the form of powder. Preferably, the fluoropolymer is in the form of powder or in the form of granules.

Solvent

The term “solvent for the polymer” is understood to mean a liquid allowing dissolution of the polymer.

The term “dissolution” of a fluoropolymer in a solvent for the polymer is understood to mean that a homogeneous dispersion of the polymer in the solvent is obtained: the polymer particles, more or less swollen with solvent, are dispersed in a continuous phase of solvent.

The homogeneity of the dispersion can be confirmed macroscopically (that is to say by observing it with the naked eye that the dispersion is indeed of homogeneous appearance), by observing that the dispersion does not have a granular appearance or separate macro. The term “homogeneous dispersion” is thus used as opposed to a “heterogeneous dispersion”, that is to say a dispersion with a macroscopic appearance that is partially granular or exhibiting a macroscopically visible phase separation, such as a gel.

The homogeneity can alternatively be assessed quantitatively by measuring the dry extract of fractions of the dispersion. For these purposes, fractions of a few milliliters can be taken from a much larger volume of solution, for example 100 ml, or preferably 500 ml or 1 L, or even more. For each fraction of a few milliliters, the dry extract is determined by evaporation of the solvent, which involves recording the mass of the sample before the evaporation operation and after it. The solvent is evaporated as completely as possible by evaporation techniques known to those skilled in the art such as evaporation in an oven at a given temperature and for a sufficiently long time, at atmospheric pressure or under reduced pressure. . As an indication, in an oven ventilated at atmospheric pressure, a temperature of 140 ° C. and an evaporation time of at least 2 hours are sufficient for the evaporation, over a few milliliters of solution, of solvents such as those of the invention. . The dry extracts of the fractions, (at least two of them, and of preferably between 3 and 10), can thus be compared with each other in order to detect any inhomogeneity.

The solubility of the polymer in a given liquid can be determined by adding an amount of polymer of 5% w / w to said liquid at room temperature (25 ° C), stirring, if necessary with moderate heating to a temperature less than or equal to 60 ° C (for example at a temperature of 60 ° C), for 15 or 60 minutes (for example for 60 minutes), then allowing to cool to room temperature (25 ° C) and observing visually, at this temperature , after 15 or 60 minutes (for example after 60 minutes), whether or not solid polymer remains in suspension.

A method of selecting solvents suitable for fluoropolymers, applicable to the polymers of the solutions according to the invention, has been described in patent application WO19170999. This selection process makes it possible in particular to easily identify which liquids are suitable as solvents for the dissolution of fluoropolymers, by carrying out only a limited number of dissolution experiments.

The boiling point of a pure substance at a given pressure is the temperature at which the vapor pressure is equal to atmospheric pressure. The solvent has a boiling point greater than or equal to 150 ° C at 1013 hPa. According to certain embodiments, the solvent has a boiling point greater than or equal to 160 ° C, or greater than or equal to 170 ° C, or greater than or equal to 180 ° C, or greater than or equal to 190 ° C or else greater than or equal to 195 ° C, at 1013 hPa.

Alternatively, or in addition, the solvent has a saturated vapor pressure of less than or equal to 5.0 hPa at 20 ° C. The saturated vapor pressure at a given temperature is the pressure at which the gas phase of a substance is in equilibrium with its liquid or solid phase at that temperature. According to some embodiments, the solvent has a vapor pressure of less than or equal to 4.5 hPa, or less than or equal to 4.0 hPa, or less than or equal to 3.5 hPa, or less than or equal to 3.0 hPa, or less than or equal to 2.5 hPa, or less than or equal to 2.0 hPa, or less than or equal to 1, 5 hPa, or less than or equal to 1, 0 hPa, or even less than or equal to 0, 5 hPa, at 20 ° C. The solvent of the solution according to the invention can in particular be chosen from the list presented in Table 1 below, or a mixture thereof:

[Table 1]

Installation and process

The process for manufacturing a solution of the fluoropolymer is carried out, at least during the step of mixing the fluoropolymer with the solvent, in a stirred tank, hereinafter called "reactor" although no chemical reaction occurs there, having a stirring mobile comprising at least one blade.

The reactor can for example be a glass reactor, a reactor whose internal wall is made of glass or else a reactor made of stainless metallic materials, or coated with PTFE or any other fluoropolymer.

The reactor advantageously has a cylindrical shape, with a characteristic internal diameter D.

The reactor is advantageously of the vertical type.

The stirring wheel can be centered or slightly off-center within the reactor. In the case where the stirring wheel is centered, the reactor can optionally include counter blades on its outer walls.

The control of the temperature of the reactor and of its contents can be implemented by various means, well known to those skilled in the art. A simple way to ensure that the inside of the reactor is in isothermal or quasi-isothermal conditions is for example to use a jacketed reactor and to circulate in the jacketed a heat transfer fluid whose temperature is regulated.

The stirring mobile comprises at least one blade capable of rotating about an axis of rotation. Thus a blade tip speed can be defined as being the speed of the point furthest from the blade relative to the axis of rotation.

The speed at the end of the blade, Vt, of the stirring body can be calculated from the formula:

[Math 1] where N is the stirring speed in revolutions per unit of time and r the distance between the axis of the moving body and the blade tip.

There are a large number of agitation mobiles known to those skilled in the art. The agitation mobiles suitable for the dispersion and / or for relatively viscous media are particularly suitable for the process according to the invention.

A non-limiting list of basic agitation mobiles is given in Table 3-1, page 59 of the book by James Y. Oldshue: FLUID MIXING TECHNOLOGY. New York: Mc Graw Hill © 1983. In some embodiments, the stirring wheel is mainly axial flow.

In some embodiments, the stirring wheel is mainly radial flow.

In some embodiments, the stirring wheel is tangential flow. In some embodiments, the stirring wheel is axial flow and radial flow.

The agitation mobile is preferably not at a mainly tangential flow.

The stirring mobile can have various shapes and names, it can be without limitation, of the "impeller" type, a paddle stirrer, an anchor, a turbine (such as a Rushton turbine), a mobile. blades or a propeller. Preferably, the mobile is a stirrer with blades or a propeller or even an impeller with twisted blades, sometimes called a "centrifugal impeller turbine".

The stirring wheel can advantageously be based on inclined blades of type "A-2" from the aforementioned non-limiting list, as shown in FIG. 1.

Referring to Figure 1, the stirring mobile 10 comprises four blades 15. The blades 15 are straight and are arranged in the shape of a cross in the plane (xy) (angle b between two successive blades in the plane (xy) is equal to 90 °) all inclined in the same direction by an angle α (α = 0 ° means that a normal to the blade plane is perpendicular to the z axis; α = 90 ° means that a normal to the blade plane is collinear with the z axis). The width W of the blades 15 with respect to the stirring diameter L, defined as being L = 2.r, is such that L = 5W.

In certain embodiments, the agitation mobile used in the invention is a mobile obtained directly by variations of certain parameters of the mobile presented in FIG. 1, such as for example:

- the number n of blades of the stirring mobile, such as:

[Math 2]

1 ≤ n ≤ 8, and preferably such that:

[Math 3] 1 ≤ n ≤ 6; the angle b is advantageously: (360 / n) °;

- the angle a, such that:

[Math 4] and preferably such as:

[Math 5]

the shape of the blades: the blades can adopt a shape different from a straight blade, in particular be curved;

- the width W of the blades with respect to the stirring diameter L, such that:

[Math 6]

1.5 W ≤ L ≤ 8 W, and preferably such that:

[Math 7]

2 W ≤ L ≤ 7W;

- the internal characteristic diameter D of the reactor relative to the stirring diameter L of the stirring wheel can, such as:

[Math 8] and preferably such that:

[Math 9]

0.3 D ≤ L ≤ 0.8D, where D is the characteristic internal diameter of the reactor;

- the number of stages: several blades of the same or different type can be mounted on the same axis at different heights, as illustrated with the stirring wheel according to Figures 2 and 3; preferably the floors are separated by a distance H center to center (see Figure 2, side view) between 0.8 L and 1.2 L; preferably also, the stages have an angular offset Q (see Figure 3, top view), minimizing the superposition of the blades between one stage and another: for example, for a stirrer with two stages each having a movable with 2 aligned blades, the stages advantageously have a preferred angular offset of about 90 ° and for a stirrer with two movable blades with 4 blades, the stages advantageously have a preferred angular offset of about 45 °.

The stirring mobile shown in Figure 2 and in Figure 3 was used in Example 2 of the process according to the invention. The stirring unit is of the four-bladed type, with 2 stages. The blades of each stage form a cross (b = 90 °) and extend over a stirring diameter L = 5.5 cm. The blades are inclined in the same direction at an angle a equal to 45 ° so as to promote pumping from the top to the bottom of the reactor. The distance H between the two floors is 4.5 cm. The width W of the blades is 2 cm. The angular offset Q between the blades of the two stages is 45 °. The diameter of the stirrer rod is 1 cm.

A non-limiting embodiment of the method comprises the following steps, or at least some of the steps:

It comprises a step of filling the reactor with the solvent so as to obtain a reactor filled with solvent. The level of solvent in the reactor is adapted as a function of the total capacity of the reactor and of the stirring device used. The stirrer of the reactor is started as well as the temperature control system so that the solvent is stirred and maintained in a desired temperature range.

The fluoropolymer is then added to the solvent, which defines the mixing step. The mixing step is carried out in the absence of co-solvent for said fluoropolymer having a boiling point strictly less than 150 ° C at 1013 hPa and / or a saturated vapor pressure strictly greater than 5 hPa at 20 ° C.

The polymer can be added all at once to the solvent, more or less rapidly, or alternatively in several parts in a fractional manner. The first addition of polymer to the solvent constitutes the start of the mixing step.

In the embodiment in which the fluoropolymer is added fractionally to the solvent, it may be advantageous to add each new fraction after the previous fraction has been completely dispersed.

The temperature of the mixture of fluoropolymer with the solvent is maintained at a temperature ranging from 40 ° C to 100 ° C throughout the duration of the step of mixed. Below a temperature of 40 ° C, it is believed that the dispersion kinetics will be too slow to allow dispersion in a reasonable time. The temperature of the mixture can be maintained at a temperature greater than or equal to 45 ° C, and preferably greater than or equal to 50 ° C. Above 100 ° C, it is considered that the thermal degradation of the fluoropolymer and / or the solvent becomes too great. The temperature of the mixture can be maintained at a temperature less than or equal to 90 ° C, preferably less than or equal to 80 ° C, more preferably less than or equal to 70 ° C and extremely preferably less than or equal to 65 ° C.

In preferred embodiments, the temperature of the mixture is maintained at a temperature ranging from 50 ° C to 65 ° C during the mixing step. The mixing step is set up with stirring with a blade tip speed of the stirring wheel set greater than or equal to 0.1 m / s. Below a blade tip speed of 0.1 m / s, it is considered that the dispersion kinetics will be too slow to allow dispersion in a reasonable time.

In preferred embodiments, the blade tip speed is greater than or equal to 0.25 m / s. The blade tip speed can in particular be greater than or equal to 0.30 m / s, or greater than or equal to 0.35 m / s, or greater than or equal to 0.45 m / s, or greater than or equal to 0 , 5 m / s, or even greater than or equal to 1 m / s. The blade tip speed generally does not exceed 10 m / s.

In some embodiments, the temperature of the mixture is maintained at a temperature ranging from 50 ° C to 65 ° C and with stirring with a blade tip speed of the stirring wheel ranging from 0.25 m / s to 10 m / s during the mixing step.

The mixing step can end (at the earliest) once all of the fluoropolymer has been added to the solvent and has been dispersed so as to form a homogeneous dispersion, at least macroscopically. The duration of the mixing step is between 30 minutes and 12 hours. In preferred embodiments, it can be between 1 hour and 5 hours.

The stirrer mobile of the reactor can then be stopped as well as the temperature control system.

When additives must be added to form the solution according to the invention, they can be added before, during or after the dispersion of the fluoropolymer in the solvent. The additive (s) can in particular be chosen from surface tension modifiers, rheology modifiers, aging resistance modifiers, adhesion modifiers, pigments or dyes, fillers ( including nanofillers).

Solution

Dissolving the polymer in a solvent makes it possible to obtain a "solution". The term "solution" is used herein as opposed to a suspension of polymer particles in a liquid vehicle, for example a gel, and as opposed to a polymer emulsion or latex, which is a colloidal dispersion. A solution, due to mixing at the molecular level, has a homogeneous appearance and completely transparent, unlike a suspension (non-homogeneous appearance, with visible presence of grains in suspension), an emulsion (heterogeneous, cloudy, opalescent appearance or opaque) or a latex or colloidal dispersion (opalescent or bluish or cloudy or milky appearance).

The solution is advantageously homogeneous in appearance and completely transparent, at room temperature, that is to say in particular between 15 ° C and 35 ° C, and in particular at 25 ° C.

The solution does not include a co-solvent of said fluoropolymer having a boiling point strictly less than 150 ° C at 1013 hPa and / or a saturated vapor pressure strictly greater than 5 hPa at 20 ° C. This means that the solution does not include such co-solvents, even in trace amounts.

The solution in particular does not contain traces of acetone, trichloroethane or methoxycyclopentane.

In some embodiments, additives can be added (partially soluble polymers, nanofillers) which lead to non-transparent “solutions”. The term “solutions” is retained here, although it is strictly speaking slightly cloudy nano- or micro-dispersions, which nevertheless retain their macroscopic homogeneity as can be verified by the dry extract test described. above.

Thus, the solution may consist of said at least one fluoropolymer, of one or more solvents having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a saturated vapor pressure less than or equal to 5 hPa at 20 ° C, and optionally one or more additives. The process according to the invention makes it possible to obtain fairly concentrated homogeneous solutions of fluoropolymer, in a reasonable time (in particular less than or equal to 12 hours). In some embodiments, the solution can comprise from 1% by weight to 40% by weight of fluoropolymer based on the total weight of solution. Preferably, the solution can comprise from 5% by weight to 30% by weight of fluoropolymer relative to the total weight of solution. More preferably, the solution can comprise from 10% by weight to 25% by weight of fluoropolymer relative to the total weight of solution.

The solution may in particular comprise more than 11%, or more than 12%, or more than 13%, or more than 14%, or even more than 15% by weight of the fluoropolymer relative to the total weight of the solution; and / or less than 24%, or less than 23%, or less than 22%, or less than 21%, or even less than 20% by weight of fluoropolymer relative to the total weight of solution. In the embodiments where the manufactured solution comprises additives, the latter generally represent less than 15% by weight, and more preferably still less than 10% by weight of the total weight of solution.

According to certain embodiments, the solution has a viscosity as measured at room temperature (25 ° C.) using a Brookfield viscometer of the “RVDV-II + P” type, of 2000 mPa.s to 40,000 mPa. s, preferably from 8,000 mPa.s to 30,000 mPa.s, more preferably from 12,000 mPa.s to 28,000 mPa.s, and extremely preferably from 15,000 mPa.s to 25,000 mPa.s. According to particular embodiments, the solution can have a viscosity of 18,000 mPa.s to 24,000 mPa.s.

Application

A thin layer (film) of fluoropolymer can be obtained by depositing and then drying (evaporating the solvent) of a solution according to the invention (ink) of relatively high viscosity.

Screen printing consists of spreading an ink on a screen or screen printing mesh carrying the pattern to be printed, on a suitable support. The screen is placed on the support and the ink is spread using a doctor blade; then the screen is lifted and the support carrying the liquid ink layer which has passed through the screen and left to dry. After evaporation of the solvent, during drying, a thin solid ("dry") film in screen-defined pattern remains printed on the media. The polymer film can thus be deposited on a support (“carrier”), a substrate (eg, plastic, metal, glass, wood, paper, etc.), an optoelectronic device (photovoltaic cell, part or all of a transistor , electrode, sensor, actuator, etc.) in order to ultimately constitute, in its solid form, an integral part of an optoelectronic device, for example, as an active dielectric layer (such as an emitting or receptive layer of a mechanical signal ), or a passive dielectric layer (such as a high dielectric constant dielectric layer).

Examples

Example 1: Liquids that can be chosen as solvents This example takes up the example developed in application WO19170999 and shows how the solubility of a fluoropolymer in any liquid can be estimated from a set of training data known.

A training data set was formed from the following table 2:

[Table 2]

In this table, the Hansen solubility parameters are given in MPa ^1/2 . Notations (2) or (5) indicate that these Hansen solubility parameters come from either Table 2 in Chapter 7 or Table 5 in Chapter 8 of the CRC Handbook of Solubility Parameters and Other Cohesion Parameters, by Allan FM Barton, 2nd edition (1991).

The information relating to the solubility (yes / no) was obtained experimentally with a polymer P (VDF-TrFE) comprising 80% of VDF units and 20% of TrFE units (in molar proportions).

SAS JMP 13.0.0 software was used to provide a neural network as shown in Figure 1. 20 rows of the table were used for training the model and 6 for validation. The success rate obtained is 100%.

The “KFold” validation method was used. This method, as explained by the software manual, divides the data into K subgroups. Successively, each of the K subgroups is used to validate the fit or model created with the remainder of the data not included in the K subgroup, which makes it possible to obtain K different models. The model with the best statistical validation (lowest error) is chosen as the final model.

From this modeling the following prediction model was obtained. Functions of the three neurons of the middle (hidden) layer:

- H1 = tan h (0.5 x (0.288078 x δd + 0.029058 x δp + 0.092642 x δh -4.79788));

- H2 = tan h (0.5 x (0.131723 x δd - 0.16692 x δp - 0.03299 x δh -0.05098));

- H3 = tan h (0.5 x (0.399484 x δd - 0.11103x δp - 0.05299 x δh -4.13038)).

In the above, the Hansen solubility parameters are expressed in MPa ^1/2 .

Function of the output neuron: S = exp (201, 3275 x H1 + 192.4403 x H2 - 156.203 x H3 - 82.4311). The probability of non-solubility is S / (1 + S) and the probability of solubility is:

(1 - probability of non-solubility).

The model thus obtained can be applied to any new solvent not present in the previous training table. Thus, for example, Table 3 below gives the following answers for 3 new solvents unknown to the model.

[Table 3]

Experience confirms that a polymer P (VDF-T rFE) comprising 80% of VDF units and 20% of TrFE units (in molar proportions) is soluble in the acetate of the monomethyl ether of propylene glycol ( PGMEA) and 3-methylcyclohexanone, but not in 1 -octanol.

Example 2: Process according to the invention for the manufacture of a solution of P (VDF-TrFE) in triethyl phosphate - mobile agitation of the quadrupal type The assembly used comprises a vertical reactor with an internal diameter D equal to 10 centimeters, double-cased, in glass, with a maximum capacity of 2 liters, provided with a cover in the center of which passes a stirring unit, connected to a motor.

The double jacket is connected to a heating / cooling circuit using a heat transfer fluid emanating from a thermostatic bath.

The cover has obturations allowing:

- the input of material (for the introduction of the solvent and the polymer);

- connection to a vapor condensation / reflux system;

- The passage of perforated hollow tubes for the bubbling of an inert gas such as nitrogen, and / or unperforated hollow tubes for the introduction of a thermo-torque probe.

The reactor has a bottom valve for draining the polymer solution. The agitation mobile is that shown in Figures 2 and 3, as described above. Its L / D ratio is 0.55. The stirrer centered and placed near the bottom of the reactor during operation at a typical distance of 5 cm from the bottom.

Triethyl phosphate (1440 g) was introduced into the reactor at room temperature (25 ° C). The temperature-controlled bath setpoint was set at 50 °, the stirring was started at a speed of 200 rpm (blade tip speed of 0.52 m / s) and the vapor condensation / reflux system has been put into operation.

Piezotech FC-20® polymer (360 g), marketed by the company Arkema, was introduced in powder form all at once into the reactor. Piezotech FC-20® is a polymer derived from VDF and TrFE monomers, comprising a molar proportion of TrFE relative to the sum of VDF and TrFE of the order of 20%. The MFI of the polymer was measured at 3.5 g / 10 minutes at 230 ° C under a load of 10 kg, according to ASTM D1238.

The stirring speed was increased to 400 rpm (1.05 m / s blade tip speed) after all of the polymer was introduced.

Half an hour after all the polymer had been introduced, the set temperature of the thermostatic bath was increased to 60 ° G Three hours after the end of the introduction of the powder and with continuous stirring, it was observed at with the naked eye that the polymer was completely dissolved, forming a solution having a high viscosity (which creates air bubbles in the medium). The polymer solution was recovered, hot, by emptying the reactor through the bottom valve.

The ink thus obtained, after rising air bubbles, is a transparent liquid with a viscosity of between 18,000 and 30,000 mPa s, measured precisely at 21,000 mPa.s, measured at room temperature (25 ° C) at l 'using a Brookfield viscometer of the “RVDV-II + P” type with mobile no7.

The dry extract of the ink is measured by gravimetry in a ventilated oven, as indicated in the text above to give a value close to the theoretical value of 18% by weight.

Example 3: Comparative example of the production of a solution of P (VDF-TrFE) in triethyl phosphate - stirring mobile: magnetic bar The assembly used comprises a laboratory flask fitted with a magnetic bar and placed on a stirrer-heating bath. The balloon is connected to a vapor condensation / reflux system.

Triethyl phosphate (610 g) was added to the flask at room temperature (25 ° C). The temperature of the heating bath was then set at 80 °, stirring was started at a nominal speed of between 300 and 500 revolutions per minute.

The Piezotech FC-20® polymer powder (90g) was added to the flask kept under stirring and at a temperature of 80 ° C.

The time required for the complete dissolution of the polymer was 17 hours.

Claims

1. Process for manufacturing a solution of a fluoropolymer in a solvent, the fluoropolymer being a polymer comprising units derived from vinylidene fluoride as well as units derived from at least one other monomer of formula CX ₁ X ₂ = CX ₃ X ₄ , in which each group X ₁ , X ₂ , X ₃ and X ₄ is independently selected from H, Cl, F, Br, I and alkyl groups comprising from 1 to 3 carbon atoms, which are optionally partially or totally halogenated, the solvent having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a saturated vapor pressure less than or equal to 5 hPa at 20 ° C, the process comprising a step of mixing of said fluoropolymer with said solvent in a reactor having a stirring wheel comprising at least one blade, at a mixing temperature ranging from 40 ° C to 100 ° C, and at a higher blade tip stirring speed or equal to 0.1 m / s, until dissolution of said polymer in said solvent; the mixing step being carried out in the absence of co-solvent of said fluoropolymer having a boiling point strictly less than 150 ° C at 1013 hPa and / or a saturated vapor pressure strictly greater than 5 hPa at 20 ° C.

2. The manufacturing method according to claim 1, wherein said at least one other monomer is chosen from: vinyl fluoride (VF), trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropene (HFP), trifluoropropenes, and in particular 3,3,3-trifluoropropene, tetrafluoropropenes, and in particular 2,3,3,3-tetrafluoropropene or

1.3.3.3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes, and in particular

1.1.3.3.3-pentafluoropropene or 1, 2,3,3, 3-pentafluoropropene, perfluoroalkylvinyl ethers, and in particular those of general formula Rt-O- CF = CF2, in which Fit is an alkyl group, preferably of C1 at C4, bromotrifluoroethylene, 1-chloro-1-fluoroethylene (CFE), 1-chloro-2-fluoroethylene, chlorotrifluoroethylene (CTFE), 2-chloro- 3,3,3-trifluoropropene (1233xf), 1-chloro-3,3,3-trifluoropropene, 1, 2-dichloro-1, 2-difluoroethylene, 1, 1 -dichloro-1, 1 -difluoroethylene and 1, 1, 2-trichloro-2-fluoroethylene.

3. Method according to claim 2, wherein said fluoropolymer is selected from: a P (VDF-TrFE), a P (VDF-TFE), a P (VDF-TrFE-TFE), a P (VDF-TrFE- CTFE), a P (VDF-TrFE-CFE), a P (VDF-T rFE-CTFE-CFE) and a P (VDF-T rFE-TFE-CTFE-CFE); preferably, the fluoropolymer is chosen from: a P (VDF-TrFE), a P (VDF-TrFE-CFE), or a P (VDF-TrFE-CTFE).

4. Method according to any one of claims 1 to 3, wherein said fluoropolymer has a melt index (MFI), measured according to ASTM D1238, at 230 ° C and under a load of 10 kg, of 0.2 g / 10min to 20 g / 10min, preferably from 0.5 to 10 g / 10min, even more preferably from 0.8 g / 10min to 8 g / 10min, and extremely preferably between 1 g / 10min and 6 g / 10 minutes.

5. Method according to any one of claims 1 to 4, wherein the solvent is selected from the group consisting of: acetate of propylene glycol monomethyl ether, N, N-dimethylformamide, cyclohexanone, N , N-dimethylacetamide, diacetone alcohol, diisobutyl ketone, 3-methylcyclohexanone, tetramethyl urea, ethyl acetoacetate, dimethyl sulfoxide, trimethyl phosphate, monoethyl ether of diethylene glycol, N-methyl -2-pyrrolidone, gamma-butyrolactone, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, dimethyl phthalate, and a mixture thereof; and, preferably the acetate of the monomethyl ether of propylene glycol, cyclohexanone, 3-methylcyclohexanone, dimethylsulfoxide, gamma-butyrolactone, triethyl phosphate, and their mixture.

6. The method of claim 5, wherein the solvent is gamma-butyrolactone or triethyl phosphate.

7. A method according to any one of claims 1 to 6, wherein said fluoropolymer represents from 1% by weight to 40% by weight of the total weight of the solution; preferably, said fluoropolymer represents from 5% by weight to 30% by weight of the total weight of the solution; and, preferably, said fluoropolymer represents from 10% by weight to 25% by weight of the total weight of the solution.

8. Method according to any one of claims 1 to 7, wherein said fluoropolymer represents more than 11%, or more than 12%, or more than 13%, or more than 14%, or even more than 15% in weight relative to the total weight of solution; and / or less than 24%, or less than 23%, or less than 22%, or less than 21%, or even less than 20% by weight relative to the total weight of solution.

9. Method according to any one of claims 1 to 8, wherein the mixing temperature is less than or equal to 90 ° C, preferably less than or equal to 80 ° C, more preferably less than or equal to 70 ° C and so extremely preferred less than or equal to 65 ° C.

10. A method according to any one of claims 1 to 9, wherein the blade tip stirring speed is greater than or equal to 0.25 m / s.

11. A method according to any one of claims 1 to 10, wherein the duration of the mixing step is between 30 minutes and 12 hours; and, preferably, the duration of the mixing step is between 1 hour and 5 hours.

12. Method according to any one of claims 1 to 11, wherein the stirring mobile comprises at least three blades, preferably at least four blades.

13. A method according to any one of claims 1 to 12, wherein the characteristic internal diameter D of the reactor with respect to the stirring diameter L is such that: 0.2 D ≤L≤ 0.9D; and, preferably such that: 0.3 D ≤L ≤ 0.08D.

14. A method according to any one of claims 1 to 13, wherein the mixing step is carried out by adding the fluoropolymer, all at once or in a fractional manner, to the solvent.

15. Solution of a fluoropolymer in a solvent, the fluoropolymer being a polymer comprising units derived from vinylidene fluoride as well as units derived from at least one other monomer of formula CX ₁ X ₂ = CX ₃ X ₄ , in which each group X ₁ , X ₂ , X ₃ and X ₄ is independently selected from H, Cl, F, Br, I and alkyl groups comprising from 1 to 3 carbon atoms, which are optionally partially or fully halogenated , the solvent having a boiling point greater than or equal to 150 ° C at 1013 hPa and / or a saturated vapor pressure less than or equal to 5 hPa at 20 ° C, characterized in that it does not contain co- solvent for said fluoropolymer having a boiling point strictly less than 150 ° C at 1013 hPa and / or a saturated vapor pressure strictly greater than 5 hPa at 20 ° C.

16. Solution according to claim 15, having a viscosity as measured at 25 ° C using a Brookfield viscometer of the “RVDV-II + P” type, of 2000 mPa.s to 40,000 mPa.s, preferably of 8,000 mPa.s to 30,000 mPa.s, more preferably 12,000 mPa.s to 28,000 mPa.s, and extremely preferably 15,000 mPa.s to 25,000 mPa.s.

17. A solution according to any one of claims 15 and 16, wherein said fluoropolymer is according to any one of claims 2 to 4; and / or said solvent is according to any one of claims 5 and 6.

18. Solution according to any one of claims 15 to 17, wherein said fluoropolymer represents from 1% by weight to 40% by weight of the total weight of the solution; preferably, said fluoropolymer represents from 5% by weight to 30% by weight of the total weight of the solution; and, more preferably, said fluoropolymer represents from 10% by weight to 25% by weight of the total weight of the solution.

19. Solution according to any one of claims 15 to 18, obtained according to the process according to any one of claims 1 to 14.