Method for producing fluoropolymers

Abstract

The present invention relates to a method for producing semi-crystalline fluoropolymers, to the fluoropolymers obtainable by said method, and to the use of said fluoropolymers in various applications. [Selection diagram] None

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application Publication No. 17165867.7, filed April 11, 2017, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a process for the preparation of fluoropolymers, to fluoropolymers obtainable by said process and to the use of said fluoropolymers in various applications. [Background technology]

[0003] Fluoropolymers are known in the art and are preferred for use in a variety of applications because they have both high mechanical and chemical resistance.

[0004] Various attempts have been made in the art to obtain fluoropolymer compositions suitable for use in various applications, such as coating applications.

[0005] JP 2017-057379 (Daikin Industries, Ltd.) (March 23, 2017) relates to a method for polymerizing tetrafluoroethylene and vinylidene fluoride in an aqueous medium in the presence of at least one surfactant selected from fluorinated and non-fluorinated surfactants. In all instances, JP 2017-057379 discloses the polymerization of tetrafluoroethylene and vinylidene fluoride in the presence of reactive fluorine-containing allyl ether anionic surfactants, i.e. compounds of the formula CH2=CFCF2-O-(CF(CF3)CF2O)-CF(CF3)-COONH4 and short-chain fluorine-containing anionic surfactants of the formula F(CF2)-COONH4. Polymerization in the presence of reactive ionic surfactants results in polymers containing multiple ionic pendant groups. A serious drawback of having those ionic groups attached to the polymer backbone is the reduced thermal stability of the resulting polymer.

[0006] However, there remains a need in the art for melt-processible fluoropolymers and compositions thereof that have low melting points and high thermal stability that can be obtained in an efficient and cost-effective manner. Summary of the Invention

[0007] It has now surprisingly been found that the process of the present invention advantageously makes it possible to provide fluoropolymers which are generally easy to process in the melt phase.

[0008] The fluoropolymers of the present invention advantageously have high molecular weights and are suitable for use in a variety of applications requiring excellent mechanical properties, especially at elevated temperatures.

[0009] In particular, it has been found that the process of the present invention advantageously operates without the use of surfactants while providing an aqueous latex that can be advantageously concentrated into an aqueous dispersion suitable for use in a variety of applications, particularly coating applications. In addition to environmental benefits, the absence of surfactants, particularly reactive fluorinated surfactants, in the polymerization process results in polymers having improved thermal stability when compared to polymers obtained by polymerization processes in the presence of reactive surfactants having ionic pendant groups.

[0010] It has also been found that the aqueous latexes of the present invention advantageously provide coatings having high hardness at relatively low film formation temperatures, in combination with high chemical and heat resistance, when compared to aqueous latexes containing fully fluorinated fluoropolymers, such as tetrafluoroethylene homopolymers and copolymers with perfluoroalkyl vinyl ethers.

[0011] In a first embodiment, the present invention relates to a method for producing a semicrystalline fluoropolymer [polymer (F)], the polymer comprising: - more than 50 mol%, preferably from 51 mol% to 70 mol%, more preferably from 55 mol% to 65 mol%, even more preferably from 60 mol% to 65 mol% of repeat units derived from tetrafluoroethylene (TFE); - less than 50 mol%, preferably 49 mol% to 30 mol%, more preferably 45 mol% to 35 mol%, and even more preferably 40 mol% to 35 mol% of repeating units derived from vinylidene fluoride (VDF); Including, the molar amount of said repeating units being relative to the total moles of repeating units in said polymer (F), and said process being carried out by emulsion polymerization in an aqueous polymerization medium without the addition of one or more surfactants.

[0012] The method of the present invention typically comprises: at least one radical initiator, optionally with at least one chain transfer agent; The reaction is carried out in the presence of

[0013] The process of the present invention is typically initiated by at least one radical initiator without the addition of one or more surfactants.

[0014] Also, no surfactants are added during the process of the present invention.

[0015] The process of the invention is usually carried out at a pressure comprised between 10 bar and 35 bar, preferably between 11 bar and 25 bar.

[0016] The person skilled in the art will choose the polymerization temperature taking into account, inter alia, the radical initiator used. The process of the invention is usually carried out at a temperature comprised between 50°C and 135°C, preferably between 55°C and 130°C.

[0017] The choice of radical initiator is not particularly limited, but 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.

[0018] Inorganic radical initiators can be used, including, but not limited to, persulfates, such as sodium persulfate, potassium persulfate, and ammonium persulfate, and permanganates, such as potassium permanganate.

[0019] Additionally, organic radical initiators may be used, including, but not limited to, the following: acetylcyclohexanesulfonyl peroxide; diacetyl peroxydicarbonate; dialkyl peroxydicarbonates such as diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate; tert-butyl perneodecanoate; 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile; tert-butyl perpivalate; dioctanoyl peroxide; dilauroyl peroxide; 2,2'-azobis(2,4-dimethylvaleronitrile); tert-butyl azo -2-cyanobutane; dibenzoyl peroxide; tert-butyl-per-2-ethylhexanoate; tert-butyl permaleate; 2,2'-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane; tert-butylperoxyisopropyl carbonate; 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.

[0020] Other suitable radical initiators include, in particular, halogenated free radical initiators, such as trichloroacetyl peroxide, bis(perfluoro-2-propoxypropionyl) peroxide, [CF3CF2CF2OCF(CF3)COO]2, perfluoropropionyl peroxide, (CF3CF2CF2COO)2, (CF3CF2COO)2, {(CF3CF2CF2)-[CF(CF3)CF2O] m-CF(CF3)-COO}2 (wherein m=0 to 8), [ClCF2(CF2) n COO]2, and [HCF2(CF2) n chlorocarbon and fluorocarbon acyl peroxides, such as [(CF3)2CFN=]2, where n=0-8; perfluoroazoisopropane, [(CF3)2CFN=]2, TIFF0007657022000001.tif7161 (in the formula, TIFF0007657022000002.tif7161 is a linear or branched perfluorocarbon group having 1 to 8 carbons); perfluoroalkylazo compounds such as hexafluoropropylene trimer radical, [(CF3)2CF]2(CF2CF2)C ● radicals and perfluoroalkane radicals, and stable or hindered perfluoroalkane radicals.

[0021] Redox systems, which include at least two components that form a redox pair, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide, and diphenylamine-benzoyl peroxide, may also be used as radical initiators to initiate the polymerization process.

[0022] Among the inorganic radical initiators, ammonium persulfate is particularly preferred.

[0023] Among the organic radical initiators, peroxides having a self-accelerating decomposition temperature (SADT) higher than 50° C., such as, for example, di-tert-butyl peroxide (DTBP), di-tert-butylperoxyisopropylcarbonate, tert-butyl(2-ethyl-hexyl)peroxycarbonate, tert-butylperoxy-3,3,5-trimethylhexanoate, are particularly preferred.

[0024] One or more radical initiators as defined above may be added to the aqueous polymerization medium of the aqueous emulsion polymerization process of the present process in an amount advantageously ranging from 0.001% to 20% by weight, based on the weight of the aqueous polymerization medium.

[0025] The polymerization process of the present invention is usually carried out in the presence of a chain transfer agent.

[0026] The chain transfer agent is generally selected from those known in the polymerization of fluorinated monomers, such as ethane, ketones, esters, ethers, or aliphatic alcohols having 3 to 10 carbon atoms, e.g., acetone, ethyl acetate, diethyl ether, methyl-tert-butyl ether, isopropyl alcohol; chloro(fluoro)carbons having 1 to 6 carbon atoms, optionally containing hydrogen, e.g., chloroform, trichlorofluoromethane; bis(alkyl)carbonates, in which the alkyl has 1 to 5 carbon atoms, e.g., bis(ethyl)carbonate, bis(isobutyl)carbonate, etc. The chain transfer agent can be fed to the aqueous medium at the start, continuously or in discrete amounts (stepwise) during the polymerization, with continuous or stepwise feeding being preferred.

[0027] The aqueous emulsion polymerization processes detailed above have been described in the art (see, for example, U.S. Pat. No. 4,990,283, filed Feb. 5, 1991 (AUSIMONT SPA), U.S. Pat. No. 5,498,680, filed Mar. 12, 1996 (AUSIMONT SPA), and U.S. Pat. No. 6,103,843, filed Aug. 15, 2000 (AUSIMONT SPA)).

[0028] In a second embodiment, the invention relates to a semicrystalline fluoropolymer [polymer (F)] obtainable by the process of the invention.

[0029] The polymers (F) of the present invention are advantageously melt-processible. The term "melt-processible" is intended herein to mean a fluoropolymer which can be processed by conventional melt processing techniques.

[0030] The polymer (F) of the present invention usually has a melting point (T m ).

[0031] The semicrystalline polymer (F) is usually recovered from the aqueous latex obtainable by the process of the invention.

[0032] The semi-crystalline polymer (F) of the present invention may further comprise repeat units derived from at least one fluorinated monomer different from tetrafluoroethylene (TFE) and vinylidene fluoride (VDF).

[0033] For the purposes of the present invention, the term "fluorinated monomer" is intended to mean an ethylenically unsaturated monomer containing at least one fluorine atom.

[0034] When the fluorinated monomer contains at least one hydrogen atom, it is referred to as a hydrogen-containing fluorinated monomer.

[0035] If the fluorinated monomer does not contain any hydrogen atoms, it is referred to as a per(halo)fluorinated monomer.

[0036] The fluorinated monomer may further contain one or more other halogen atoms (Cl, Br, I).

[0037] Non-limiting examples of suitable fluorinated monomers include, among others, the following: - C3-C8 perfluoroolefins, for example hexafluoropropene (HFP); - C2-C8 hydrogenated fluoroolefins such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene; - Formula CH2=CH-R f0 (In the formula, R f0 is a C1-C6 perfluoroalkyl group; - chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins, such as chlorotrifluoroethylene; - Formula CF2=CFOR f1 (In the formula, R f1is a C1-C6 fluoro- or perfluoroalkyl group, for example, CF3, C2F5, C3F7), (per)fluoroalkyl vinyl ethers; - CF2 = CFOX0 (per)fluoro-oxyalkyl vinyl ether (wherein X0 is C1-C 12 Alkyl groups, C1-C 12 C1-C having one or more ether groups, such as an oxyalkyl group or a perfluoro-2-propoxy-propyl group 12 (per)fluorooxyalkyl group; - Formula CF2=CFOCF2OR f2 (In the formula, R f2 is a C1-C6 fluoro- or perfluoroalkyl group, for example a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as CF3, C2F5, C3F7, or -C2F5-O-CF3; - Formula CF2 = CFOY0 (wherein Y0 is C1 to C 12 Alkyl group or (per)fluoroalkyl group, C1-C 12 Oxyalkyl group or C1-C having one or more ether groups 12 (per)fluorooxyalkyl group, and Y0 contains a carboxylic or sulfonic acid group in the form of its acid, acid halide or salt); - Formula R A R B =CR C -T-CR D =R E R F (In the formula, R A , R B , R C , R D , R E and R F are equal to or different from each other and are selected from the group consisting of H, F, Cl, a C1-C5 alkyl group and a C1-C5 (per)fluoroalkyl group, and T is a linear or branched C1-C alkyl group optionally containing one or more ethereal oxygen atoms, preferably at least partially fluorinated.18 an alkylene or cycloalkylene group, or a (per)fluoropolyoxyalkylene group; Bisolefins such as CH2=CH-(CF2)6-CH=CH2; - (per)fluoro-bis-vinyl ethers; and - Fluorodioxoles, preferably perfluorodioxoles Examples include:

[0038] The semicrystalline polymer (F) of the present invention generally has the formula (I): CF2=CF-OR f (I) (In the formula, R f is a C1-C6 alkyl group or a C1-C6 (per)fluoroalkyl group. The polymer further comprises a repeating unit derived from at least one perfluoroalkyl vinyl ether (PAVE).

[0039] The semi-crystalline polymer (F) of the present invention is 0.1 mol % to 5 mol %, preferably 1 mol % to 5 mol %, more preferably 1.5 mol % to 3.5 mol % of a compound represented by the formula (I): CF2=CF-OR f (I) (In the formula, R f is a C1-C6 alkyl group or a C1-C6 (per)fluoroalkyl group. The molar amount of said repeating units is based on the total molar amount of repeating units of said polymer (F).

[0040] The semicrystalline polymer (F) of the present invention comprises: - more than 50 mol %, preferably between 55 mol % and 65 mol %, of repeat units derived from tetrafluoroethylene (TFE), - less than 50 mol %, preferably between 40 mol % and 30 mol %, of repeat units derived from vinylidene fluoride (VDF), and optionally 0.1 mol % to 5 mol %, preferably 1 mol % to 5 mol %, more preferably 1.5 mol % to 3.5 mol % of formula (I) CF2=CF-OR f (I) (In the formula, R f is a C1-C6 alkyl group or a C1-C6 (per)fluoroalkyl group. and more preferably consists of the repeating units derived from at least one perfluoroalkyl vinyl ether (PAVE), the molar amount of said repeating units being based on the total molar amount of repeating units of said polymer (F).

[0041] The perfluoroalkyl vinyl ether (PAVE) of formula (I) is usually selected from the group consisting of perfluoromethyl vinyl ether (PMVE) of formula CF2=CF-O-CF3, perfluoroethyl vinyl ether (PEVE) of formula CF2=CF-O-CF2-CF3, and perfluoropropyl vinyl ether (PPVE) of formula CF2=CF-O-CF2-CF2-CF3.

[0042] In a third embodiment, the present invention relates to an aqueous latex comprising at least one semicrystalline polymer (F) as defined above, said polymer (F) being: - more than 50 mol%, preferably from 51 mol% to 70 mol%, more preferably from 55 mol% to 65 mol%, even more preferably from 60 mol% to 65 mol% of repeat units derived from tetrafluoroethylene (TFE); - less than 50 mol%, preferably 49 mol% to 30 mol%, more preferably 45 mol% to 35 mol%, and even more preferably 40 mol% to 35 mol% of repeating units derived from vinylidene fluoride (VDF); wherein the molar amount of said repeating units is relative to the total moles of repeating units of said polymer (F), and wherein polymer (F) in the aqueous latex is in the form of primary particles having an average primary particle size, measured according to ISO 13321, of less than 1 μm, preferably less than 600 nm.

[0043] The aqueous latex of the present invention preferably contains 1% to 25% by weight, preferably 5% to 20% by weight, of at least one semi-crystalline polymer (F) relative to the total weight of said aqueous latex.

[0044] The aqueous latex of the invention advantageously comprises at least one semicrystalline polymer (F), preferably in the form of primary particles, having an average primary particle size, measured according to ISO 13321, comprised between 50 nm and 450 nm, preferably between 200 nm and 300 nm.

[0045] For the purposes of the present invention, "average primary particle size" is intended to mean the average size of the primary particles of polymer (F) obtained by aqueous emulsion polymerization.

[0046] For the purposes of the present invention, "primary particles" of polymer (F) are intended to be distinguishable from agglomerates of primary particles.

[0047] The aqueous latex comprising the primary particles of polymer (F) is advantageously obtained by aqueous emulsion polymerization. The agglomerates of the primary particles of polymer (F) are usually obtained by recovery and conditioning steps of the polymer (F) production, such as concentration and / or coagulation of the aqueous polymer (F) latex and subsequent drying and homogenization, thereby providing a solid powder of polymer (F).

[0048] The aqueous latex obtainable by the process of the present invention is therefore intended to be distinguishable from an aqueous slurry prepared by dispersing a polymer (F) powder in an aqueous medium. The average particle size of the polymer (F) powder dispersed in the aqueous slurry is typically greater than 1 μm, measured according to ISO 13321.

[0049] The aqueous latex obtainable by the process of the invention advantageously has uniformly dispersed therein primary particles of at least one polymer (F) having an average primary particle size, measured according to ISO 13321, comprised between 50 nm and 450 nm, preferably between 200 nm and 300 nm.

[0050] The aqueous latex of the present invention can be concentrated, thereby providing an aqueous dispersion.

[0051] The present invention relates to a method for producing an aqueous dispersion, said method comprising concentrating the aqueous latex of the present invention.

[0052] The aqueous latex of the present invention is typically concentrated by any of the techniques known in the art, such as, for example, via clouding, usually in the presence of a salt such as KNO3.

[0053] The method for producing the aqueous dispersion of the present invention typically comprises: - providing a mixture comprising the aqueous latex of the present invention and at least one hydrogenated surfactant [surfactant (H)], and - concentrating the mixture so obtained, thereby providing an aqueous dispersion. Includes.

[0054] The aqueous dispersion of the present invention typically comprises: up to 35% by weight, preferably between 1% and 35% by weight, of at least one semicrystalline polymer (F), relative to the total weight of said aqueous dispersion, optionally with at least one hydrogenated surfactant [surfactant (H)] Includes.

[0055] The aqueous dispersion of the present invention usually contains 1 wt % to 5 wt % of at least one hydrogenated surfactant [H] relative to the total weight of the aqueous dispersion.

[0056] For purposes of this invention, "hydroxylated surfactant [H]" is intended to mean an amphoteric organic compound that contains both hydrophobic and hydrophilic groups.

[0057] The surfactant (H) may be an ionic hydrogenated surfactant [surfactant (IS)] or a non-ionic hydrogenated surfactant [surfactant (NS)].

[0058] Non-limiting examples of suitable surfactants (IS) include 3-allyloxy-2-hydroxy-1-propanesulfonates, polyvinylphosphonates, polyacrylates, polyvinylsulfonates, and alkylphosphonates, among others.

[0059] The surfactant (H) is preferably the surfactant (NS).

[0060] Non-limiting examples of suitable surfactants (NS) include, inter alia, octylphenol ethoxylates and fatty alcohol polyethers containing repeat units derived from ethylene oxide and / or propylene oxide.

[0061] The surfactants (NS) generally have a cloud point, advantageously greater than or equal to 50° C., preferably greater than or equal to 55° C., measured according to the EN 1890 standard (Method A: 1% by weight aqueous solution).

[0062] The surfactant (NS) is preferably selected from the group consisting of non-ionic hydrogenated surfactants commercially available under the trade names TERGITOL®, TRIXON® X and PLURONIC®.

[0063] In further examples, the present invention relates to the use of the aqueous latex or dispersion of the present invention in various applications.

[0064] In particular, the aqueous latexes or dispersions of the present invention are particularly suitable for use in processes for producing films.

[0065] The films of the invention usually comprise at least one semicrystalline polymer (F) as defined above.

[0066] According to a first embodiment, the present invention relates to a method for producing a film according to the invention, said method comprising processing an aqueous latex or dispersion according to the invention, usually by casting, spraying or dipping. The film so obtained is then usually dried.

[0067] According to a second embodiment of the invention, the invention relates to a method for producing a film of the invention, said method comprising: - coagulating and then drying the aqueous latex or dispersion of the invention, thereby obtaining a solid powder of polymer (F); - processing the solid powder of polymer (F) thus obtained, optionally in the presence of at least one lubricant, thereby providing a film; Equipped with.

[0068] The processing of the solid powder of polymer (F) is usually carried out by ram extrusion, preferably by paste extrusion or by calendering.

[0069] The processing of the solid powder of polymer (F) can be carried out in the melt phase.

[0070] The processing of the solid powder of polymer (F), usually by ram extrusion or calendering, is advantageously carried out at temperatures below the melting point of the polymer (F) of the invention.

[0071] The method according to this second embodiment of the invention comprises the steps of: - expanding the inventive film, typically in one or more directions, thereby providing an expanded film; - optionally, heat treating the expanded film thus obtained. The device may further include:

[0072] The spreading of the film of the invention is advantageously carried out at a temperature below the melting point of the polymer (F) of the invention.

[0073] The heat treatment of the film of the present invention can be carried out at a temperature above the melting point of the polymer (F) of the present invention.

[0074] The expanded films of the present invention are typically porous.

[0075] The expanded films of the present invention have been found to advantageously have excellent mechanical properties.

[0076] The films of the present invention are suitable for use in a variety of applications, such as in the oil and gas industry, in the automotive industry, and in coating applications.

[0077] The expanded films of the present invention are suitable for use in a variety of applications such as water filtration, dialysis, battery separators, venting, desalination and gas separation. The expanded films of the present invention are also suitable for use in woven fabrics.

[0078] To the extent that the disclosures of any patents, patent applications, and publications incorporated herein by reference conflict with the statements of this application to the extent that the term may be unclear, this statement shall control.

[0079] The invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not limiting the scope of the invention.

[0080] raw materials Polymer (F-1): TFE (60 mol%)-VDF (40 mol%) copolymer.

[0081] Determination of second melting point The melting points were measured by differential scanning calorimetry (DSC) according to the ASTM D 3418 standard method. The endothermic peak observed during the first heating was integrated to obtain the melting enthalpy of the polymer, DH. The second melting temperature, defined as the maximum of the endothermic peak observed during the second heating period, was recorded and is referred to herein as the melting point (T m )

[0082] General procedure for preparing polymer (F-1) In a 90 liter vertical autoclave made of AISI 316 steel, equipped with baffles and a stirrer operating at 170 rpm, 66 liters of demineralized water were introduced. The temperature was then brought to the reaction temperature of 80° C., and when this temperature was reached, 2 bar of vinylidene fluoride was introduced.

[0083] A gaseous mixture of TFE-VDF in a nominal molar ratio of 60:40 was then added via a compressor until a pressure of 12 bar was reached. 500 ml of a 6% by weight aqueous solution of sodium persulfate (NaPS) was then fed as initiator. The polymerization pressure was kept constant by feeding the above TFE-VDF mixture. When 8000 g of the mixture had been fed, the reactor was cooled at room temperature and the latex was discharged. The latex was then frozen for 48 hours and, upon thawing, the coagulated polymer was washed with demineralized water and dried at 160° C. for 16 hours. The melting temperature Tm and melting enthalpy DH of the obtained semi-crystalline polymer were Tm=225 and DH=35 J / g, respectively.

[0084] Example 1 The aqueous latex obtained by the above detailed method for preparing polymer (F-1) is treated by adding TERGITOL® TMN-100X branched secondary alcohol ethoxylate surfactant followed by concentration via clouding in the presence of KNO3, thereby providing an aqueous dispersion comprising 46.9 wt. % of polymer (F-1) and 2.8 wt. % of TERGITOL® TMN-100X branched secondary alcohol ethoxylate surfactant based on the total weight of the aqueous dispersion. The aqueous dispersion does not contain one or more fluorinated surfactants.

[0085] The aqueous dispersion thus obtained is cast onto a substrate, dried at room temperature, and then heat-treated at 260° C. for 10 minutes to obtain a film.

[0086] Comparative Example 1 The film is obtained by casting an aqueous dispersion containing HYFLON® D5510 TFE / PMVE copolymer onto a substrate, drying at room temperature, and then heat treating at 320° C. for 10 minutes.

[0087] Hardness Measurement The pendulum damping test was used according to the ASTM D4366 standard procedure (Test Method A - Koenig Pendulum Hardness) to detect differences in the coating hardness of the films. Hardness is defined as its resistance to deformation. The amplitude of oscillation of a pendulum in contact with a surface decreases more rapidly the softer the surface of the film.

[0088] Measuring the film formation temperature The water-based latex was cast onto a substrate, dried at room temperature, and then baked at elevated temperatures for 10 minutes. Various tests were performed, starting at 200°C and increasing the baking temperature until good film formation was achieved, i.e. no cracks or particle coalescence was detected.

[0089] Measurement of chemical resistance to HCl Ten drops of a 10% by volume solution of 37% hydrochloric acid in tap water were applied and covered with a watch glass, and after 15 minutes of exposure, the specimen was washed with running tap water to ensure that no blistering or other visual changes had occurred.

[0090] Measurement of chemical resistance to HNO3 The test panel was placed in a jar filled halfway up with 70% nitric acid, completely covering the opening, for 30 minutes. The sample was rinsed with tap water and after a 1 hour recovery period was examined for any visual changes.

[0091] The results are shown in Table 1 herein below.

[0092] TIFF0007657022000003.tif53170

[0093] In view of the above, it has been found that the aqueous latex of the present invention advantageously does not contain one or more surfactants and advantageously provides coatings having high hardness at relatively low film formation temperatures in combination with high chemical resistance to acids when compared to aqueous latexes comprising fully fluorinated fluoropolymers such as HYFLON® D5510 TFE / PMVE copolymer.

Claims

1. A method for producing a semicrystalline fluoropolymer [polymer (F)], comprising the steps of: - 55% to 65% by mole of repeat units derived from tetrafluoroethylene (TFE); - 40 mol % to 30 mol % of repeat units derived from vinylidene fluoride (VDF), optionally from 0.1 mol % to 5 mol %, preferably from 1 mol % to 5 mol %, more preferably from 1.5 mol % to 3.5 mol % of formula (I) CF 2 =CF-O-R f (I) (wherein R f is a C 1 -C 6 alkyl group or a C 1 -C 6 (per)fluoroalkyl group). and a repeating unit derived from at least one perfluoroalkyl vinyl ether (PAVE) of It consists of: the molar amount of the repeating unit is based on the total moles of the repeating units of the polymer (F), The process is carried out by emulsion polymerization in an aqueous polymerization medium without the addition of one or more surfactants.

2. The method according to claim 1, wherein the method is carried out at a pressure comprised between 10 bar and 35 bar, preferably between 11 bar and 25 bar.

3. The perfluoroalkyl vinyl ether (PAVE) of formula (I) is represented by the formula CF ２ =CF-O-CF ３ Perfluoromethyl vinyl ether (PMVE), of formula CF ２ =CF-O-CF ２ -CF ３ Perfluoroethyl vinyl ether (PEVE), of formula CF ２ =CF-O-CF ２ -CF ２ -CF ３ 3. The method according to claim 1 or 2, wherein the perfluoropropyl vinyl ether (PPVE) is selected from the group consisting of:

4. 4. The process according to any one of claims 1 to 3, wherein the polymer (F) has a melt flow index, measured according to ASTM D1238 at 300°C under a load of 5 Kg, of less than 5 g / 10 min, preferably less than 2 g / 10 min, more preferably less than 1 g / 10 min.

5. A method for producing an aqueous latex, the aqueous latex comprising a semi-crystalline fluoropolymer [polymer (F)], the polymer (F) comprising: - 55% to 65% by mole of repeat units derived from tetrafluoroethylene (TFE); - 40 mol % to 30 mol % of repeating units derived from vinylidene fluoride (VDF); optionally from 0.1 mol % to 5 mol %, preferably from 1 mol % to 5 mol %, more preferably from 1.5 mol % to 3.5 mol % of formula (I) CF 2 =CF-O-R f (I) (wherein R f is a C 1 -C 6 alkyl group or a C 1 -C 6 (per)fluoroalkyl group). and a repeating unit derived from at least one perfluoroalkyl vinyl ether (PAVE) of It consists of: the molar amount of said repeating units is relative to the total moles of repeating units of said polymer (F), and the polymer (F) in the aqueous latex is in the form of primary particles having an average primary particle size, measured according to ISO 13321, of less than 1 μm, preferably less than 600 nm, The process is carried out by emulsion polymerization in an aqueous polymerization medium without the addition of one or more surfactants.

6. 10. A method for producing an aqueous dispersion, said method comprising concentrating the aqueous latex obtained by the method of claim 5.

7. 13. A method for producing a film, said method comprising processing an aqueous latex obtained by the method of claim 5 or an aqueous dispersion obtained by the method of claim 6, typically by casting, spraying or dipping.

8. 1. A method of making a film, the method comprising: - coagulating the aqueous latex obtained by the process according to claim 5 or the aqueous dispersion obtained by the process according to claim 6, and then drying, thereby obtaining a solid powder of polymer (F). - processing the solid powder of polymer (F) thus obtained, optionally in the presence of at least one lubricant, thereby providing a film; A method for providing the above.

9. The method further comprising: - expanding said film, typically in one or more directions, thereby providing an expanded film; - optionally, heat treating the expanded film thus obtained. The method of claim 8 further comprising:

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