FLUOROPOLYMER FILM

Abstract

The present invention pertains to a fluoropolymer film comprising at least one fluoropolymer hybrid organic/inorganic composite [polymer (FH)], to a process for the manufacture of said fluoropolymer film and to uses of said fluoropolymer film in various applications, in particular in electrochemical applications.

Claims

1. A fluoropolymer film comprising at least one fluoropolymer hybrid organic/inorganic composite [polymer (FH)] obtainable by hydrolysis and/or condensation of at least one grafted fluoropolymer [polymer (FG)], said polymer (FG) comprising: a fluorinated main chain comprising recurring units derived from at least one fluorinated monomer (F) and at least one hydrogenated monomer (H), at least one pendant side chain comprising an end group of formula —O-AY.sub.m-1X.sub.4-m (I-M1), wherein m is an integer from 1 to 3, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group and X is a hydrocarbon group comprising at least one sulphonic group in its acid, ester, salt or halide form, and at least one pendant side chain comprising an end group of formula —O-A′Y′.sub.m′-1X′.sub.4-m′ (II-M2), wherein m′ is an integer from 1 to 4 and, according to certain embodiments, from 1 to 3, A′ is a metal selected from the group consisting of Si, Ti and Zr, Y′ is a hydrolysable group and X′ is a hydrocarbon group.

2. The fluoropolymer film according to claim 1, wherein the mole ratio of the end groups of formula —O-AY.sub.m-1X.sub.4-m (I-M1) to the end groups of formula —O-A′Y′.sub.m′-1X′.sub.4-m′ (II-M2) in polymer (FG) is at most 2.0.

3. The fluoropolymer film according to claim 1, wherein the mole ratio of the end groups of formula —O-AY.sub.m-1X.sub.4-m (I-M1) to the end groups of formula —O-A′Y′.sub.m′-1X′.sub.4-m′ (II-M2) in polymer (FG) is at least 0.01.

4. The fluoropolymer film according to claim 1, wherein the fluorinated main chain of the polymer (FG) comprises recurring units derived from vinylidene fluoride (VDF), at least one monomer (H) and, optionally, at least one monomer (F) different from VDF.

5. A process for the manufacture of the fluoropolymer film according to claim 1, to said process comprising: applying, by spray coating onto at least one surface of a substrate, a composition [composition (C)] comprising: at least one fluoropolymer [polymer (F)] comprising recurring units derived from at least one fluorinated monomer (F) and at least one hydrogenated monomer comprising at least one hydroxyl group [monomer (OH)], at least one functional metal compound [functional compound (M1)] of formula (I):
X.sub.4-xAY.sub.m   (I) wherein m is an integer from 1 to 3, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group and X is a hydrocarbon group comprising at least one sulphonic group in its acid, ester, salt or halide form, at least one non-functional metal compound [non-functional compound (M2)] of formula (II):
X′.sub.4-m′A′Y′.sub.m′  (II) wherein m′ is an integer from 1 to 4, A′ is a metal selected from the group consisting of Si, Ti and Zr, Y′ is a hydrolysable group and X′ is a hydrocarbon group, and a liquid medium (L); thereby providing a coated substrate; and drying the coated substrate.

6. The process according to claim 5, wherein the mole ratio of the functional compound (M1) to the non-functional compound (M2) in the composition (C) is at most 2.0.

7. The process according to claim 5, wherein the mole ratio of the functional compound (M1) to the non-functional compound (M2) in the composition (C) is at least 0.01.

8. The process according to claim 1, wherein the monomer (OH) of the polymer (F) is selected from the group consisting of (meth)acrylic monomers of formula (III): ##STR00012## wherein each of R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.X is a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group.

9. The process according to claim 5, wherein polymer (F) in the composition (C) is selected from the group consisting of polymers (F-1) comprising recurring units derived from: vinylidene fluoride (VDF), at least one monomer (OH) of formula (III): ##STR00013## wherein each of R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.X is a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group, and optionally, at least one monomer (F) different from VDF.

10. The process according to claim 5, wherein composition (C) comprises at least one polymer (F) in an amount comprised between 2% and 30% by weight, based on the total weight of said at least one polymer (F) and the medium (L).

11. The process according to claim 5, wherein the functional compound (M1) in the composition (C) is of formula (I-A):
R.sup.A.sub.4-mA(Y.sup.A).sub.m   (I-A) wherein m is an integer from 1 to 3, A is a metal selected from the group consisting of Si, Ti and Zr, R.sup.A, equal to or different from each other and at each occurrence, is a C.sub.1-C.sub.12 hydrocarbon group comprising at least one —SO.sub.2M functional group, wherein M is selected from the group consisting of halogen atoms, such as F, Cl, Br and I, and —O.sup.−T.sup.+ groups, wherein T.sup.+ is selected from the group consisting of H.sup.+, NH.sub.4.sup.+, K.sup.+, Li.sup.+ and Na.sup.+, and Y.sup.A, equal to or different from each other and at each occurrence, is selected from the group consisting of halogen atoms, and —OR.sup.B groups, wherein R.sup.B is a C.sub.1-C.sub.5 linear or branched alkyl group.

12. The process according to claim 5, wherein the substrate comprises a composition comprising: from 70% to 99.9% by weight, based on the total weight of the composition, of at least one polymer (F) selected from the group consisting of polymers (F-2) comprising recurring units derived from at least one per(halo)fluoromonomer selected from the group consisting of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), at least one hydrogenated monomer (H) selected from ethylene, propylene and isobutylene, and, optionally, or more additional monomers, and from 0.1% to 30% by weight, based on the total weight of the composition, of mica.

13. The process according to claim 5, wherein the substrate is a separator for an electrochemical device.

14. The process according to claim 5, wherein the substrate is an electrode for an electrochemical device.

15. A separator for an electrochemical device comprising the fluoropolymer film according to claim 1.

16. The fluoropolymer film according to claim 2, wherein the mole ratio of the end groups of formula —O-AY.sub.m-1X.sub.4-m (I-M1) to the end groups of formula —O-A′Y′.sub.m′-1X′.sub.4-m′ (II-M2) in polymer (FG) is at most 1.5 and at least 0.2.

17. The process according to claim 6, wherein the mole ratio of the functional compound (M1) to the non-functional compound (M2) in the composition (C) is at most 1.5 and at least 0.2.

18. The process according to claim 10, wherein composition (C) comprises at least one polymer (F) in an amount comprised between 5% and 15% by weight, based on the total weight of said at least one polymer (F) and the medium (L).

19. The process according to claim 12, wherein the substrate comprises a composition comprising: from 90% to 99% by weight, based on the total weight of the composition, of at least one polymer (F) selected from the group consisting of polymers (F-2) comprising recurring units derived from at least one per(halo)fluoromonomer selected from the group consisting of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), at least one hydrogenated monomer (H) selected from ethylene, propylene and isobutylene, and, optionally, or more additional monomers, and from 1% to 10% by weight, based on the total weight of the composition, of mica.

Description

EXAMPLES 1 TO 7

Manufacture of a Fluoropolymer Film by Spray Coating

[0249] Films were prepared via sol-gel procedure in N,N-dimethyl formamide (DMF) by processing by using a spray-coating technique a composition comprising a 1 g of a polymer (F-1) dissolved at room temperature in 9 g of previously dried DMF under vigorous stirring. After complete dissolution, TEOS was added under magnetic stirring followed by addition thereto of a solution of CSPTC in methylene chloride. After complete dissolution of TEOS and CSPTC, the mixture was left under stirring for one hour in a closed glass vial. This final solution was spray-coated onto a substrate made from an ECTFE polymer having a molar ratio of CTFE and ethylene of 50:50 and containing 3% by weight of mica, said ECTFE polymer having a melting point of 240° C. The substrate of about of 64 cm.sup.2 is used (8 cm×8 cm). After 30 minutes drying at room temperature, the films so obtained were transferred to an oven at 70° C. and kept overnight. The spray coating deposition was carried out by using a double action airbrush from Iwata connected to a pump. The main characteristics of the airbrush used in the process of the invention are the followings:

[0250] 1. Needle and fluid nozzle: 0.20 mm;

[0251] 2. Distance between the needle and the substrate equal to 20 cm;

[0252] 3. Main lever tension adjusted to its maximum;

[0253] 4. Pump capacity adjusted to 0.2 mPa.

[0254] For instance, a fluoropolymer hybrid organic-inorganic composite [polymer (FH)] having nominally 30% by weight of SiO.sub.2 (assuming complete condensation) and a molar ratio CPSTC:TEOS of 2:1 was manufactured by using 0.15 g of TEOS and 1 g of a solution of CSPTC in methylene chloride.

COMPARATIVE EXAMPLE 1

[0255] The same procedure as detailed for Examples 1 to 6 was followed but using only TEOS.

COMPARATIVE EXAMPLES 2 TO 4

[0256] The same procedure as detailed for Examples 1 to 8 was followed but using polymer (A).

[0257] As can be seen in Table 1 here below, the fluoropolymer films obtainable by the process according to the invention as notably embodied by the films of Examples 1 to 7 according to the invention are advantageously endowed with good or higher ionic conductivity values as compared to fluoropolymer films according to Comparative Examples 1 to 4.

[0258] In particular, it has been surprisingly found that the ionic conductivity values of the fluoropolymer films obtainable by the process of the invention are advantageously increased by increasing the molar ratio of the functional compound (M1) to the non-functional compound (M2) up to a molar ratio of at most 2.0, preferably of at most 1.5.

[0259] On the contrary, the ionic conductivity values of the fluoropolymer films according to Comparative Examples 2 to 4 are disadvantageously decreased by increasing the molar ratio of the functional compound (M1) to the non-functional compound (M2) up to a molar ratio of at most 1.5.

[0260] Also, the fluoropolymer films obtainable by the process according to the invention as notably embodied by the films of Examples 1 to 7 according to the invention are advantageously endowed with good or higher ionic conductivity values, while having a high thickness, as compared to fluoropolymer films according to Comparative Examples 1 to 4.

TABLE-US-00001 TABLE 1 Ionic (M1-A)/(M2-A) conductivity Thickness Run Polymer molar ratio [mS/cm] [μm] Ex. 1 (F-1A) 0.25 0.65 80 Ex. 2 (F-1A) 0.5 0.65 105 Ex. 3 (F-1A) 0.75 2.36 100 Ex. 4 (F-1A) 1.5 3.07 85 Ex. 5 (F-1A) 2.0 0.33 60 Comp. Ex. 1 (F-1A) 0 0.25 25 Ex. 6 (F-1B) 0.5 0.90 105 Ex. 7 (F-1B) 0.75 0.90 65 Comp. Ex. 2 (A) 0.5 0.22 50 Comp. Ex. 3 (A) 1.0 0.17 70 Comp. Ex. 4 (A) 1.5 0.15 30

[0261] In view of the above, it has been found that the fluoropolymer films obtainable by the process of the invention are particularly suitable for use as separators for electrochemical devices.