WO2018228872A1

WO2018228872A1 - Piezoelectric fluoropolymer

Info

Publication number: WO2018228872A1
Application number: PCT/EP2018/064794
Authority: WO
Inventors: Alessio Marrani; Francesco PEDROLI; Valeriy KAPELYUSHKO; Vito Tortelli
Original assignee: Solvay Specialty Polymers Italy S.P.A.
Priority date: 2017-06-14
Filing date: 2018-06-05
Publication date: 2018-12-20

Abstract

The present invention pertains to a piezoelectric fluoropolymer, to a process for manufacturing said fluoropolymer and to uses of said fluoropolymer in electric and/or electronic applications.

Description

Piezoelectric fluoropolymer Cross-Reference to Related Application

[0001] This application claims priority to European application No. 17175936.8 filed June 14, 2017, the whole content of this application being

incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention pertains to a piezoelectric fluoropolymer, to a

process for manufacturing said fluoropolymer and to uses of said fluoropolymer in electric and/or electronic applications.

Background Art

[0003] Vinylidene fluoride (VDF) copolymers comprising recurring units derived from trifluoroethylene (TrFE) have been used extensively in the manufacture of both electrical and electronic devices due to their ease of processing, chemical inertness and attractive ferroelectric, piezoelectric, pyroelectric, ferrorelaxor and dielectric properties.

[0004] In particular, due to their high dielectric constants and attractive

ferrorelaxor properties, vinylidene fluoride (VDF) terpolymers comprising recurring units derived from trifluoroethylene (TrFE) and

chlorotrifluoroethylene (CTFE) have been used in the manufacture of thin film transistor (TFT) devices.

[0005] As is well known, the term piezoelectric means the ability of a material to exchange electrical for mechanical energy and vice versa and the electromechanical response is believed to be essentially associated with dimensional changes during deformation or pressure oscillation. The piezoelectric effect is reversible in that materials exhibiting the direct piezoelectric effect (the production of electricity when stress is applied) also exhibit the converse piezoelectric effect (the production of stress and/or strain when an electric field is applied). [0006] Ferroelectricity is the property of a material whereby this latter exhibits a spontaneous electric polarization, the direction of which can be switched between equivalent states by the application of an external electric field.

[0007] Pyroelectricity is the ability of certain materials to generate an electrical potential upon heating or cooling. Actually, as a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e. the material becomes polarized) and hence an electrical potential is established.

[0008] Ferrorelaxor is the property of an electroactive material whereby this latter exhibits a large displacement when an electrical field is applied but with no force transfer while actuating.

[0009] Materials having good dielectric properties are known in the art.

[0010] In particular, high dielectric materials have become even more desirable for manufacturing high performance electrical and electronic devices.

[001 1] In view of the above, there is still the need in the art for piezoelectric

fluoropolymers which can be easily processed thereby providing films endowed with high values of the dielectric constant to be suitably used in electrical and/or electronic devices.

[0012] CA678492 (PENNSALT CHEMICALS CORP) discloses solutions in

certain organic solvents of various VDF polymers; Ex. 6 specifically describes an example of an emulsion-polymerized copolymer of VDF (about 95 % moles) and of 1 ,2-difluoro-1 ,2-dichloroethylene. No mention is made of VDF-TrFE copolymers.

[0013] GB942956 (PENNSALT CHEMICALS CORP) discloses solutions in

certain organic solvents of various VDF polymers; Ex. 8 specifically describes an example of an aqueous dispersion containing 30 parts by weight of a copolymer of vinylidene fluoride and symmetrical difluoro- dichloroethylene containing about 5 mol percent of the latter and having a particle size in the range 0.05 to 20 microns.

[0014] WO201 1/073254 (to Solvay Specialty Polymers Italy SpA) discloses

process for manufacturing dispersions of vinylidene fluoride (VDF) thermoplastic polymers in the presence of a combination of (i) a

hydrogenated or fluorinated surfactant and of (ii) a said functional PFPE. VDF may be copolymerized with fluorinate monomers being selected in the group consisting of vinylfluoride (VF-1 ), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE),

perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom.

[0015] EP27091 13 (BPP CABLES LTD) discloses a cable comprising a first

conductor, a first insulator layer and a first plurality of wires, wherein the first insulator layer comprises a first fluoropolymer which is a copolymer comprising:

- a first monomer selected from a group consisting of 1 ,1 ,2,2- tetrafluoroethylene, 1 -fluoroethylene, 1 ,1 -difluoroethylene, 1 ,2- difluoroethylene, 1 ,1 ,2-trifluoroethylene, hexafluoropropene,

perfluoropropyl vinyl ether, perfluoroethyl vinyl ether, perfluoromethyl vinyl ether, perfluorobutyl ether, 1 -chloro-1 ,2,2-trifluoroethylene, 1 ,1 dichloro- 2,2-difluoroethylene, 1 ,2-dichloro-1 ,2-difluoroethylene, 1 ,1 ,2-trichloro-2- fluoroethylene, and hexafluoropropylene, and

- a second monomer selected from a group consisting of ethylene, propylene, 1 ,1 ,2,2-tetrafluoroethylene, 1 -fluoroethylene, 1 ,1- difluoroethylene, 1 ,2-difluoroethylene, 1 , 1 ,2-trifluoroethylene,

hexafluoropropylene, perfluoropropyl vinyl ether, perfluoroethyl vinyl ether, perfluoromethyl vinyl ether, perfluorobutyl ether, 1 -chloro-1 ,2,2- trifluoroethylene, 1 ,1 dichloro 2,2, difluoroethylene, 1 1 ,2-dichloro-1 ,2- difluoroethylene, 1 ,1 ,2-trichloro-2-fluoroethylene and hexafluoropropylene.

Summary of invention

[0016] It has been now found that the fluoropolymer of the present invention is advantageously endowed with high values of the dielectric constant and low values of the coercive field to be suitably used in electric and/or electronic devices, while advantageously maintaining high values of both residual polarization and maximum polarization properties.

[0017] Thus, in a first instance, the present invention pertains to a fluoropolymer [polymer (F)] comprising:

- recurring units derived from vinylidene fluoride, and - from 0.30% to 1 1 % by moles, preferably from 1 % to 10% by moles of recurring units derived from 1 ,2-dichloro-1 ,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

[0018] The polymer (F) of the invention typically comprises recurring units derived from cis-1 ,2-dichloro-1 ,2-difluoroethylene or trans-1 ,2-dichloro-1 ,2- difluoroethylene, preferably trans-1 , 2-dichloro-1 ,2-difluoroethylene (trans- 1 ,2-dichloro-1 ,2-difluoroethylene is hereinafter referred to as "1 1 12").

[0019] The polymer (F) of the invention typically comprises at least 50% by

moles, preferably at least 56% by moles, more preferably at least 62% by moles of recurring units derived from vinylidene fluoride, with respect to the total moles of recurring units in said polymer (F).

[0020] The polymer (F) of the invention may further comprise recurring units

derived from at least one other fluorinated monomer.

[0021] For the purpose of the present invention, the term "fluorinated monomer" is intended to denote an ethylenically unsaturated monomer comprising at least one fluorine atom.

[0022] The fluorinated monomer may further comprise one or more other halogen atoms (CI, Br, I).

[0023] Should the polymer (F) of the invention further comprise recurring units derived from at least one other fluorinated monomer, said polymer (F) typically further comprises recurring units derived from at least one fluorinated monomer different from vinylidene fluoride and 1 ,2-dichloro- 1 ,2-difluoroethylene.

[0024] Should the polymer (F) of the invention further comprise recurring units derived from at least one other fluorinated monomer, said polymer (F) typically comprises from 0.1 % to 30% by moles, preferably from 15% to 30% by moles of recurring units derived from at least one other fluorinated monomer, with respect to the total moles of recurring units in said polymer (F).

[0025] The polymer (F) of the invention preferably comprises, more preferably consists of:

- recurring units derived from vinylidene fluoride,

- from 0.30% to 1 1 % by moles, preferably from 1 % to 10% by moles of recurring units derived from 1 ,2-dichloro-1 ,2-difluoroethylene, and

- optionally, from 0.1 % to 30% by moles, preferably from 15% to 30% by moles of recurring units derived from at least one other fluorinated monomer,

with respect to the total moles of recurring units in said polymer (F).

[0026] According to an embodiment of the present invention, the polymer (F) of the invention may further comprise recurring units derived from at least one fluorinated monomer selected from trifluoroethylene,

chlorotrifluoroethylene and 1 ,1 -chlorofluoroethylene.

[0027] The polymer (F) of the invention may further comprise from 15% to 30% by moles, preferably comprises from 19% to 28% by moles of recurring units derived from trifluoroethylene, with respect to the total moles of recurring units in said polymer (F).

[0028] In a second instance, the present invention pertains to a process for manufacturing the polymer (F) of the invention, said process comprising polymerizing vinylidene fluoride, 1 ,2-dichloro-1 ,2-difluoroethylene and, optionally, at least one other fluorinated monomer in the presence of at least one radical initiator.

[0029] The process of the invention is typically carried out in the presence of an aqueous medium.

[0030] The process of the invention may be carried out by aqueous emulsion polymerization or by aqueous suspension polymerization.

[0031] The process of the invention is typically carried out at a temperature of less than 125°C, preferably of less than 80°C.

[0032] The aqueous emulsion polymerization is typically carried out in an

aqueous medium comprising:

- at least one surfactant [surfactant (S)],

- at least one radical initiator,

- optionally, at least one non-functional perfluoropolyether (PFPE) oil, and

- optionally, at least one chain transfer agent.

[0033] For the purpose of the present invention, by "surfactant [surfactant (S)]" it is intended to denote an amphiphilic organic compound containing both hydrophobic groups and hydrophilic groups. [0034] The surfactant (S) is typically selected from the group consisting of:

- hydrogenated surfactants [surfactants (H)],

- fluorinated surfactants [surfactants (F)], and

- mixtures thereof.

[0035] The surfactant (H) may be an ionic hydrogenated surfactant [surfactant (IS)] or a non-ionic hydrogenated surfactant [surfactant (NS)].

[0036] Non-limiting examples of suitable surfactants (IS) include, notably, 3- allyloxy-2-hydroxy-1 -propane sulfonic acid salts, polyvinylphosphonic acid salts, polyacrylic acid salts, polyvinyl sulfonic acid salts and alkyl phosphonates.

[0037] The surfactant (H) is preferably a surfactant (NS).

[0038] Non-limiting examples of suitable surfactants (NS) include, notably,

octylphenol ethoxylates and fatty alcohol polyethers comprising recurring units derived from ethylene oxide and/or propylene oxide.

[0039] The surfactant (NS) has generally a cloud point of advantageously 50°C or more, preferably of 55°C or more, as measured according to EN 1890 standard (method A: 1 % by weight water solution).

[0040] The surfactant (NS) is preferably selected from the group consisting of non-ionic hydrogenated surfactants commercially available under the trademark names TRIXON^® X and PLURONIC^®.

[0041] According to a first embodiment of the invention, the surfactant (F) may be a cyclic fluorocompound of formula (II):

wherein Χι, X2 and X3, equal to or different from each other, are

independently selected from the group consisting of H, F and C1 -C6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non- catenary oxygen atoms, L is a bond or a divalent group, RF is a divalent fluorinated C1 -C3 bridging group, and Y is an anionic functionality.

[0042] In formula (II), the anionic functionality Y is preferably selected from the group consisting of those of formulae:

wherein X_a is H, a monovalent metal (preferably an alkaline metal) or an ammonium group of formula -N(R'_n)₄, wherein R'_n, equal or different at each occurrence, is a hydrogen atom or a C1-C6 hydrocarbon group (preferably an alkyl group).

[0043] Most preferably, the anionic functionality Y is a carboxylate of formula (3") as defined above.

[0044] According to a first variant of this first embodiment of the invention, the surfactant (F) is a cyclic fluorocompound of formula (III):

wherein Xi, X2, X3, RF and Y have the same meaning as defined above.

[0045] More preferably, the cyclic fluorocompound of this first variant of this first embodiment of the invention is of formula (IV):

wherein Xi, X2, X3, RF and X_a have the same meaning as defined above.

[0046] According to a second variant of this first embodiment of the invention, the surfactant (F) is a cyclic fluorocompound of formula (V):

wherein R^F and X_a have the same meanings as defined above, X*i, X*2, equal to or different from each other, are independently a fluorine atom, -R 'f or -OR'f, wherein R'f is a C1-C3 perfluoroalkyl group, R^Fi is F or CF3, and k is an integer from 1 to 3. More preferably, the surfactant (F) of this first embodiment of the invention is a cyclic fluorocompound of formula (VI):

wherein X_a has the same meaning as defined above and, in particular, with X_a being NH₄.

[0048] According to a second embodiment of the invention, the surfactant (F) may be a fluorinated surfactant of formula (VII):

R_f§(X-)_k(M⁺)_k (VII)

wherein:

- Rf§ is selected from a C₄-Ci6 (per)fluoroalkyl chain, optionally comprising one or more catenary or non-catenary oxygen atoms, and a

(per)fluoropolyoxyalkyl chain,

- X- is selected from -COO- , -PO₃- and -SO₃-,

- M⁺ is selected from NH₄ ⁺ and an alkaline metal ion, and

- k is 1 or 2.

[0049] Non-limiting examples of surfactants (F) according to this second

embodiment of invention suitable for use in emulsion polymerization in an aqueous polymerization medium include, notably, the followings:

(a') CF3(CF₂)noCOOM', wherein no is an integer ranging from 4 to 10, preferably from 5 to 7, preferably no being equal to 6, and M' represents NH₄, Na, Li or K, preferably NH₄;

(b') T-(C3F₆O)ni(CFYO)miCF₂COOM", wherein T represents a CI atom or a perfluoroalkoxyde group of formula C_xF2x+i-x'Cl_xO, wherein x is an integer ranging from 1 to 3 and x' is 0 or 1 , ni is an integer ranging from 1 to 6, mi is 0 or an integer ranging from 1 to 6, M" represents NH₄, Na, Li or K and Y represents F or -CF3;

(c') F-(CF2CF2)n2-CH2-CH2-X^*O₃M"', wherein X^* is a phosphorus or a sulphur atom, preferably X^* being a sulphur atom, M'" represents NH₄, Na, Li or K and n2 is an integer ranging from 2 to 5, preferably n2 being equal to 3; (cT) A-Rbf-B bifunctional fluorinated surfactants, wherein A and B, equal to or different from each other, have formula -(O)_pCFY"-COOM*, wherein M* represents NH₄, Na, Li or K, preferably M* representing NH₄, Y" is F or - CF3 and p is 0 or 1 , and Rbf is a divalent (per)fluoroalkyl chain or

(per)fluoropolyether chain such that the number average molecular weight of A-Rbf-B is in the range of from 300 to 1800; and

(e') mixtures thereof.

[0050] An aqueous latex is typically obtainable by a process carried out by

aqueous emulsion polymerization. The aqueous latex of the invention preferably comprises at least one polymer (F) in the form of primary particles having an average primary particle size comprised between 50 nm and 450 nm, preferably between 250 nm and 300 nm, as measured according to ISO 13321 .

[0051] For the purpose of the present invention, by "average primary particle size" it is intended to denote the average size of primary particles of polymer (F) obtainable by emulsion polymerization.

[0052] For the purpose of the present invention, "primary particles" of polymer (F) are to be intended distinguishable from agglomerates of primary particles. Aqueous latexes comprising primary particles of polymer (F) are

advantageously obtainable by emulsion polymerization in an aqueous polymerization medium. Agglomerates of primary particles of polymer (F) are typically obtainable by recovery and conditioning steps of polymer (F) manufacture such as concentration and/or coagulation of aqueous polymer (F) latexes and subsequent drying and homogenization thereby providing polymer (F) powders.

[0053] The aqueous latex of the invention is thus to be intended distinguishable from an aqueous slurry prepared by dispersing polymer (F) powders in an aqueous medium. The average particle size of polymer (F) powders dispersed in an aqueous slurry is typically higher than 1 μηη, as measured according to ISO 13321 .

[0054] The aqueous latex of the invention advantageously has homogeneously dispersed therein primary particles of at least one polymer (F) having an average primary particle size comprised between 50 nm and 450 nm, preferably between 250 nm and 300 nm, as measured according to ISO 13321.

[0055] The aqueous emulsion polymerization is typically carried out at a pressure comprised between 10 bar and 80 bar, preferably between 15 bar and 35 bar.

[0056] The skilled in the art will choose the polymerization temperature having regards, inter alia, of the radical initiator used. The aqueous emulsion polymerization is typically carried out at a temperature comprised between 50°C and 90°C, preferably between 60°C and 80°C.

[0057] While the choice of the radical initiator is not particularly limited, it is

understood that water-soluble radical initiators suitable for aqueous emulsion polymerization are selected from compounds capable of initiating and/or accelerating the polymerization process.

[0058] Inorganic radical initiators may be used and include, but are not limited to, persulfates such as sodium, potassium and ammonium persulfates, permanganates such as potassium permanganate.

[0059] Also, organic radical initiators may be used and include, but are not limited to, the followings: acetylcyclohexanesulfonyl peroxide;

diacetylperoxydicarbonate; dialkylperoxydicarbonat.es such as

diethylperoxydicarbonate, dicyclohexylperoxydicarbonate, di-2- ethylhexylperoxydicarbonate; tert-butylperneodecanoate; 2,2'-azobis(4- methoxy-2,4-dimethylvaleronitrile; tert-butylperpivalate;

dioctanoylperoxide; dilauroyl-peroxide; 2,2'-azobis

(2,4-dimethylvaleronitrile); tert-butylazo-2-cyanobutane;

dibenzoylperoxide; tert-butyl-per-2ethylhexanoate; tert-butylpermaleate; 2,2'-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane; tert-butyl- peroxyisopropylcarbonate; tert-butylperacetate; 2,2'-bis (tert- butylperoxy)butane; dicumyl peroxide; di-tert-amyl peroxide; di-tert-butyl peroxide (DTBP); p-methane hydroperoxide; pinane hydroperoxide;

cumene hydroperoxide; and tert-butyl hydroperoxide.

[0060] Other suitable radical initiators notably include halogenated free radical initiators such as chlorocarbon based and fluorocarbon based acyl peroxides such as trichloroacetyl peroxide, bis(perfluoro-2-propoxy propionyl) peroxide, [CF3CF2CF2OCF(CF3)COO]2, perfluoropropionyl peroxides, (CF₃CF₂CF₂COO)2, (CF₃CF₂COO)₂,

{(CF₃CF₂CF₂)-[CF(CF3)CF₂O]m-CF(CF₃)-COO}₂ where m= 0-8,

[CICF₂(CF₂)nCOO]₂, and [HCF₂(CF₂)_nCOO]₂ where n= 0-8; perfluoroalkyl azo compounds such as perfluoroazoisopropane, [(CF3)₂CFN=]₂, RⁿN=NR n, where Rⁿ is a linear or branched perfluorocarbon group having 1 -8 carbons; stable or hindered perfluoroalkane radicals such as

hexafluoropropylene trimer radical, [(CF3)₂CF]₂(CF₂CF₂)C* radical and perfluoroalkanes.

[0061] Redox systems, comprising at least two components forming a redox

couple, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide and diphenylamine-benzoyl peroxide may also be used as radical initiators to initiate the polymerization process.

[0062] Among inorganic radical initiators, ammonium persulfate is particularly preferred.

[0063] Among organic radical initiators, the peroxides having a self-accelerating decomposition temperature (SADT) higher than 50°C are particularly preferred, such as for instance: di-tert-butyl peroxide (DTBP),

diterbutylperoxyisopropylcarbonate, terbutyl(2-ethyl- hexyl)peroxycarbonate, terbutylperoxy-3,5,5-trimethylhexanoate.

[0064] One or more radical initiators as defined above may be added to the

aqueous polymerization medium of the emulsion polymerization process in an amount ranging advantageously from 0.001 % to 20% by weight based on the weight of the aqueous polymerization medium.

[0065] By "non-functional perfluoropolyether (PFPE) oil" it is hereby intended to denote a perfluoropolyether (PFPE) oil comprising a

(per)fluoropolyoxyalkylene chain [chain (Rf)] and non-functional end- groups.

[0066] The non-functional end groups of the non-functional PFPE oil are

generally selected from fluoro(halo)alkyl groups having 1 to 3 carbon atoms, optionally comprising one or more halogen atoms different from fluorine or hydrogen atoms, e.g. CF3-, C₂Fs-, C3F6-, CICF₂CF(CF3)-, CF₃CFCICF₂-, CICF₂CF₂-, CICF2-. [0067] The non-functional PFPE oil typically has a number average molecular weight comprised between 400 and 3000, preferably between 600 and 1500.

[0068] The non-functional PFPE oil is preferably selected from the group

consisting of:

(V) non-functional PFPE oils commercially available from Solvay Solexis S.p.A. under the trademark names GALDEN^® and FOMBLIN^®, said PFPE oils generally comprising at least one PFPE oil complying with either of formulae here below:

CF₃-[(OCF₂CF₂)_m-(OCF₂)_n]-OCF₃

m+n = 40 -180; m/n = 0.5 - 2

CF₃-[(OCF(CF₃)CF₂)_p-(OCF₂)_q]-OCF₃

p+q = 8 - 45; p/q = 20 - 1000

(2') non-functional PFPE oils commercially available from Daikin under the trademark name DEMNUM^®, said PFPEs generally comprising at least one PFPE complying with formula here below:

F-(CF₂CF₂CF₂0)_n-(CF₂CF₂CH₂0)_j-CF₂CF₃

j = 0 or integer > 0; n+j = 10 - 150

(3') non-functional PFPE oils commercially available from Du Pont de Nemours under the trademark name KRYTOX^®, said PFPEs generally comprising at least one low-molecular weight, fluorine end-capped, homopolymer of hexafluoropropylene epoxide complying with formula here below:

F-(CF(CF₃)CF₂0)_n-CF₂CF₃

n = 10 - 60

[0069] The non-functional PFPE oil is more preferably selected from those having formula (V) as defined above. [0070] The chain transfer agent, if any, is generally selected from those known in the polymerization of fluorinated monomers such as ethane, ketones, esters, ethers or aliphatic alcohols having from 3 to 10 carbon atoms like, e.g., acetone, ethyl acetate, diethylether, methyl-ter-butyl ether, isopropyl alcohol; chloro(fluoro)carbons, optionally containing hydrogen, having from 1 to 6 carbon atoms, like, e.g., chloroform, trichlorofluoromethane;

bis(alkyl)carbonates wherein the alkyl has from 1 to 5 carbon atoms like, e.g., bis(ethyl)carbonate, bis(isobutyl)carbonate.

[0071] The chain transfer agent, if any, may be fed to the aqueous polymerization medium at the beginning, continuously or in discrete amounts (step-wise) during the polymerization, continuous or stepwise feeding being preferred.

[0072] Aqueous emulsion polymerization processes as detailed above have been described in the art (see e.g. US 4990283 (AUSIMONT S.P.A.)

05/02/1991 , US 5498680 (AUSIMONT S.P.A.) 12/03/1996 and US

6103843 (AUSIMONT S.P.A.) 15/08/2000 ).

[0073] The aqueous latex of the invention preferably comprises from 20% to 30% by weight of at least one polymer (F).

[0074] The aqueous latex may be up-concentrated according to any techniques known in the art.

[0075] In a third instance, the present invention pertains to a composition

[composition (C)] comprising at least one polymer (F) as defined above.

[0076] The composition (C) of the invention may further comprise a liquid medium [medium (L)].

[0077] For the purpose of the present invention, the term "liquid medium [medium

(L)]" is intended to denote a medium comprising one or more compounds in liquid state at 20°C under atmospheric pressure.

[0078] The nature of the medium (L) is not particularly limited provided that it is suitable for dissolving the polymer (F).

[0079] The medium (L) typically comprises one or more organic solvents.

[0080] In a fourth instance, the present invention pertains to a fluoropolymer film

[film (F)] comprising the composition (C) as defined above. [0081] In a fifth instance, the present invention pertains to a process for manufacturing the film (F) of the invention, said process comprising processing the composition (C) as defined above into a film.

[0082] The film (F) of the invention is typically dried and, then, optionally

annealed.

[0083] Should the composition (C) further comprise a medium (L), the film (F) of the invention is typically obtainable by a process comprising:

(i) providing a substrate,

(ii) providing a composition [composition (C)] as defined above, said composition further comprising a liquid medium [medium (L)],

(iii) applying the composition (C) provided in step (ii) onto at least one surface of the substrate provided in step (i) thereby providing a wet film,

(iv) drying the wet film provided in step (iii) thereby providing a dried film, and

optionally, (v) annealing the dried film provided in step (iv).

[0084] It has been found that the film (F) obtainable by the process of the

invention is advantageously a homogeneous fluoropolymer film having good mechanical properties to be suitably used in various applications.

[0085] For the purpose of the present invention, the term "film" is intended to

denote a flat piece of material having a thickness smaller than either of its length or its width.

[0086] Under step (i) of the process for manufacturing the film (F) of the invention, the substrate is typically a non-porous substrate.

[0087] By the term "non-porous substrate" it is hereby intended to denote a dense substrate layer free from pores of finite dimensions.

[0088] Under step (iii) of the process for manufacturing the film (F) of the

invention, the composition (C) is applied onto at least one surface of the substrate provided in step (i) typically by using a processing technique selected from the group consisting of casting, spray coating, roll coating, doctor blading, slot die coating, gravure coating, ink jet printing, spin coating, screen printing, brush, squeegee, foam applicator, curtain coating and vacuum coating. [0089] The drying temperature will be selected so as to effect removal by evaporation of one or more organic solvents from the film (F) of the invention.

[0090] Drying is typically carried out at a temperature of at least 50°C. Drying is preferably carried out at a temperature comprised between 50°C and 100° C. Drying can be performed either under atmospheric pressure or under vacuum. Alternatively, drying can be performed under modified

atmosphere, e.g. under an inert gas, typically exempt notably from moisture (water vapour content of less than 0.001 % v/v).

[0091] Annealing is typically carried out at a temperature comprised between 60° C and 1 15°C. Annealing can be performed during a time comprised between 15 and 120 minutes, typically depending upon the thickness of the film (F).

[0092] The film (F) is typically free from any organic solvent.

[0093] The film (F) advantageously has a thickness comprised between 100 nm and 100 μηη.

[0094] The thickness of the film (F) can be measured according to any suitable techniques such as reflectometry, profilometry, scanning electron microscopy and atomic force microscopy.

[0095] The composition (C) may further comprise one or more additives.

[0096] The choice of the additives is not particularly limited provided that they do not interfere with solubility of the polymer(s) (F) in the medium (L), if any.

[0097] Non-limitative examples of suitable additives include, notably, pigments, UV absorbers, crosslinking agents, crosslinking initiators, organic and inorganic fillers such as ceramics, glass, silica, conductive metal particles, semiconductive oxides, carbon nanotubes, graphenes, core-shell particles, encapsulated particles, conductive salts, silicon-based particles.

[0098] Should the composition (C) further comprise one or more additives, the film (F) thereby provided typically comprises a composition (C) further comprising at least one additive.

[0099] Should the composition (C) further comprise one or more additives

selected from the group consisting of crosslinking agents and crosslinking initiators, the film (F) thereby provided is advantageously a crosslinkable fluoropolymer film [film (FC)] which typically comprises a composition (C) further comprising at least one additive selected from the group consisting of crosslinking agents and crosslinking initiators.

[0100] In a sixth instance, the present invention pertains to use of the polymer (F) or the film (F) of the invention in electric and/or electronic devices.

[0101] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0102] The invention will be now described in more detail with reference to the following examples whose purpose is merely illustrative and not limitative of the scope of the invention.

[0103] Raw materials

[0104] Polymer (F-a): VDF (98.2% by moles)-1 1 12 (1.8% by moles).

[0105] Polymer (F-b): VDF (96.5% by moles)-1 1 12 (3.5% by moles).

[0106] Polymer (F-c): VDF (90.1 % by moles)-1 1 12 (9.9% by moles).

[0107] Polymer (a): VDF (99.75% by moles)- 1 1 12 (0.25% by moles).

[0108] Polymer (b): VDF (75% by moles)-TrFE (25% by moles).

[0109] Bi-stretched film made of polymer (c): SOLEF^® 1010 VDF homopolymer.

[01 10] Film made of polymer (d): VDF (91 % by moles)-CTFE (9% by moles).

[01 1 1] Manufacture of the polymer (F-a)

In an AISI 316 steel horizontal autoclave, equipped with baffles and a stirrer, 46.2 ml of demineralized water were introduced. At room

temperature, 6 g of a 34% w/w aqueous solution of cyclic surfactant of formula (VI) as defined above, with X_a = NH₄, 20.8 bar of vinylidene fluoride and 1.5 ml of trans-1 ,2-dichloro-1 ,2-difluoroethylene were introduced.

By a metering pump, 270 ml of a 0.1 % by weight aqueous solution of sodium persulfate (NaPS) was fed to start polymerization. The

polymerization temperature was brought to the set-point temperature of 80 °C. The polymerization pressure was maintained constant to 33.2 bar, then it was by let fall down up to 10 bar. The reactor was cooled to room temperature, the latex was discharged, frozen for 48 hours and, once unfrozen, the coagulated polymer was washed with demineralized water and dried at 80°C for 48 hours thereby recovering 31.5 g of polymer (F-a).

[01 12] Manufacture of the polymer (F-b)

The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but feeding 21.1 bar of vinylidene fluoride and 3 ml of trans-1 ,2-dichloro-1 ,2-difluoroethylene to a polymerization pressure of 34.7 bar.

The polymer (F-b) was recovered in an amount of 27.6 g.

[01 13] Manufacture of the polymer (F-c)

The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but feeding 22.4 bar of vinylidene fluoride and 8 ml of trans-1 ,2-dichloro-1 ,2-difluoroethylene to a polymerization pressure of 37.7 bar.

The polymer (F-c) was recovered in an amount of 32.4 g.

[01 14] Manufacture of the polymer (a)

The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but feeding 21.6 bar of vinylidene fluoride and 0.2 ml of trans-1 ,2-dichloro-1 ,2-difluoroethylene to a polymerization pressure of 31.5 bar.

The polymer (a) was recovered in an amount of 28.5 g.

[01 15] Manufacture of the polymer (b)

In an AISI 316 steel vertical autoclave, equipped with baffles and a stirrer working at 570 rpm, 3.5 liter of demineralized water were introduced. The temperature was then brought to reaction temperature of 85°C; when this temperature was reached, 50 g of a 34% w/w aqueous solution of cyclic surfactant of formula (VI) as defined above, with X_a = NH₄, and VDF were introduced so as to reach a pressure of 6.9 bar. A gaseous mixture of VDF-TrFE in a molar nominal ratio of 75/25 was added via a compressor, until reaching a pressure of 30 bar. The composition of the gaseous mixture present in the autoclave head was analysed by G.C. At

polymerization inception, the gaseous phase was found to be composed of: 78.8% moles VDF, 21.2% moles TrFE. Then, 50 ml of solution of a 3% by volume aqueous solution of sodium persulphate (NaPS) was fed to start polymerization. The polymerization pressure was maintained constant by feeding the above-mentioned VDF-TrFE mixture; when 500 g of the mixture were fed, the feeding mixture was interrupted and, while keeping constant the reaction temperature, the pressure was left to fall down up to 15 bar. The reactor was then cooled to room temperature, the latex was discharged, frozen for 48 hours and, once unfrozen, the coagulated polymer was washed with demineralized water and dried at 105°C for 48 hours.

[01 16] General procedure for the manufacture of a fluoropolymer film

A solution of the polymer in methylethylketone having a concentration of 20% w/w was prepared and a film was casted therefrom by doctor blade technique, using an Elcometer automatic film applicator, model 4380, onto a glass substrate.

The polymer layer so casted was dried at 100°C for 2 hours under vacuum. On the so obtained dried film, 12 patterns of 1 cm x 1 cm were printed by inkjet printing technique as electrodes on both sides of the films using as conductive material a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOTPSS) purchased by Agfa-Gevaert under the trademark name ORGACON®.

The thickness of the sample was measured using a Mitutoyo micrometer.

[01 17] Annealing of the fluoropolymer film

The fluoropolymer film was placed in a vented over set at an inner temperature of 135°C for one hour. The oven was then switched off and cooled for five hours until reaching room temperature.

[01 18] Poling of the fluoropolymer film

A LC Precision poling equipment equipped with a High Voltage Interface with 10 KV maximum field generated by RADIANT was used for poling of the fluoropolymer film. The annealed film was placed in the polarization cell where a field from 150 V/μηη was applied trough the annealed film specimen.

[01 19] Determination of the melting point of the fluoropolymer

The melting point of the fluoropolymers was measured by differential scanning calorimetry according to ASTM D3418 standard method. [0120] Determination of the dielectric constant of the fluoropolymer film

The value of dielectric permittivity [k] was derived from the direct measurement of dielectric capacitance by a piezo meter system provided by Piezotest. The capacitance values were all measured at 1 10 Hz.

Capacitance [F] x Thickness [m]

Dielectric permittivity [k] =

8₀ [F/m] x Area [m²]

[0121] Determination of the ferroelectric hysteresis measurements

The hysteresis determination was performed by submitting the annealed film to poling in a field from 80 V/microns to 250 V/microns, obtaining an hysteresis curve were the maximum polarization (Pmax), the residual polarization (P_r) and the coercive field (V_c) were measured. The Pmax is the value of maximum polarization achievable with the maximum field applied. The P_r is the value of residual polarization in the samples after the removal of the applied field. The V_c is the value of coercive field as minimum voltage needed to start orienting crystal dipoles.

[0122] The results are shown in Table 1 here below:

Table 1

Film Tmelting Dielectric permittivity Hysteresis loop

[°C]

Pr [M Pmax Vc

C/cm²] [pC/cm²] M

(F-a) 1 56.7 1 3.0 2.1 5.1 41

(F-b) 142.1 1 3.0 2.4 5.8 40

(F-c) 144.0 12.8 1 .9 4.8 38

(a) 1 69.1 1 1 .6 0.8 3.9 36

(b) 146.0 1 1 .0 7.6 9.6 74

(c) 1 72.0 7.5 0.3 2.1 28

(d) 1 67.0 7.2 0.2 2.4 34 [0123] As shown in Table 1 , a film made of the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b) and (F- c) according to the invention advantageously exhibits higher values of the dielectric constant as compared to films made of any of the polymers (a), (b), (c) and (d).

[0124] Each of the polymers (a), (b) and (c) films exhibits piezoelectric properties.

The polymer (d) represents an example of melt-processible fluoropolymer.

[0125] Also, as shown in Table 1 , a film made of the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b) and (F- c) according to the invention advantageously exhibits lower values of the coercive field as compared to a film made of the polymer (b), that means that polymer (F) of the present invention can be polarized at a lower voltage than the polymer (b).

[0126] In particular, as shown in Table 1 , a film made of the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b) and (F-c) according to the invention advantageously exhibits significantly higher values of both the residual polarization and the maximum

polarization as compared to films made of any of the polymers (a), (c) and (d).

[0127] In view of the above, it has been found that the polymer (F) of the present invention or any films thereof is particularly suitable for use in electric and/or electronic devices.

Claims

Claim 1. A fluoropolymer [polymer (F)] comprising:

- recurring units derived from vinylidene fluoride, and

- from 0.30% to 1 1 % by moles, preferably from 1 % to 10% by moles of recurring units derived from 1 ,2-dichloro-1 ,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

Claim 2. The polymer (F) according to claim 1 , said polymer (F) comprising recurring units derived from cis-1 ,2-dichloro-1 ,2-difluoroethylene or trans-1 ,2- dichloro-1 ,2-difluoroethylene, preferably from trans-1 ,2-dichloro-1 ,2- difluoroethylene.

Claim 3. The polymer (F) according to claim 1 or 2, said polymer (F) further comprising recurring units derived from at least one other fluorinated

monomer.

Claim 4. The polymer (F) according to claim 3, said polymer (F) further

comprising recurring units derived from at least one fluorinated monomer selected from trifluoroethylene, chlorotrifluoroethylene and 1 , 1- chlorofluoroethylene.

Claim 5. A process for manufacturing the polymer (F) according to any one of claims 1 to 4, said process comprising polymerizing vinylidene fluoride, 1 ,2- dichloro-1 ,2-difluoroethylene and, optionally, at least one other fluorinated monomer in the presence of at least one radical initiator.

Claim 6. The process according to claim 5, said process being carried out in the presence of an aqueous medium.

Claim 7. The process according to claim 5 or 6, said process being carried out by aqueous emulsion polymerization or by aqueous suspension

polymerization.

Claim 8. The process according to any one of claims 5 to 7, said process

being carried out by aqueous emulsion polymerization in an aqueous medium comprising:

- at least one surfactant [surfactant (S)],

- at least one radical initiator, - optionally, at least one non-functional perfluoropolyether (PFPE) oil, and

- optionally, at least one chain transfer agent.

Claim 9. The process according to any one of claims 5 to 8, wherein the

surfactant (F) is a cyclic fluorocompound of formula (II):

wherein Xi , X2 and X3, equal to or different from each other, are independently selected from the group consisting of H, F and C1 -C6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms, L is a bond or a divalent group, RF is a divalent fluorinated C1-C3 bridging group, and Y is an anionic functionality.

Claim 10. A composition [composition (C)] comprising at least one polymer (F) according to any one of claims 1 to 4.

Claim 1 1. The composition (C) according to claim 10, said composition (C) further comprising one or more additives.

Claim 12. A fluoropolymer film [film (F)] comprising the composition (C)

according to claim 10 or 1 1.

Claim 13. A process for manufacturing the film (F) according to claim 12, said process comprising processing the composition (C) into a film.

Claim 14. Use of the polymer (F) according to any one of claims 1 to 4 or the film (F) according to claim 12 in electric and/or electronic devices.