DISPERSIBLE IONOMER POWDER AND METHOD OF MAKING THE SAME

Abstract

The present invention relates to certain dispersible ionomer powders made of particles consisting in quasi-spherical hollow agglomerates of elementary particles, to a method for their manufacture involving spray-drying of a latex of said ionomer, and to methods of using the same, notably for coating applications.

Claims

1-15. (canceled)

16. A powdery material [material (P)] composed of a plurality of particles of at least one fluorinated ionomer comprising a plurality of ionisable groups selected from the group consisting of —SO.sub.3X.sub.a, —PO.sub.3X.sub.a and —COOX.sub.a, wherein X.sub.a is H, an ammonium group or a metal, said particles consisting in quasi-spherical hollow agglomerates of elementary particles, said hollow agglomerates possessing an average particle size of 1 to 150 μm; and said elementary particles possessing an average diameter of 15 nm to 150 nm.

17. The material (P) of claim 16, wherein ionomer (I.sub.X) comprises recurring units derived from ethylenically unsaturated monomer comprising at least one fluorine atom, and optionally further comprises recurring units derived from at least one hydrogenated monomer, and/or wherein ionomer (I.sub.X) comprises said ionisable groups as pendant groups covalently bound to hydrolysed recurring units derived from a functional monomer (monomer (X), herein below), and optionally consists essentially of a sequence of hydrolysed recurring units derived from one or more than one monomer (X), or can be a copolymer comprising hydrolysed recurring units derived from one or more than one monomer (X) and recurring units derived from one or more than one additional monomer different from monomer (X), wherein monomer (X) is a fluorinated monomer.

18. The material (P) of claim 16, wherein ionomer (I.sub.X) is an ionomer (I.sub.SO3X) comprising a plurality of —SO.sub.3X.sub.a groups, and either consists essentially of a sequence of a plurality of recurring units derived from one or more than one monomer (X.sub.SO3X) comprising at least one group of formula —SO.sub.3X.sub.a, wherein X.sub.a is H, an ammonium group or a metal, or comprises a plurality of recurring units derived from one or more than one monomer (X.sub.SO3X) and recurring units derived from one or more than one additional monomer different from monomer (X.sub.SO3X).

19. The material (P) of claim 18, wherein monomer (A) is selected from the group consisting of: sulfonyl halide fluoroolefins of formula: CF.sub.2═CF(CF.sub.2).sub.pSO.sub.2X.sub.X, with X.sub.X being a halogen, preferably, F or Cl, more preferably F, wherein p is an integer between 0 and 10; sulfonyl halide fluorovinylethers of formula: CF.sub.2═CF—O—(CF.sub.2).sub.mSO.sub.2X.sub.X, with X.sub.X being a halogen, preferably, F or Cl, more preferably F, wherein m is an integer between 1 and 10; sulfonyl fluoride fluoroalkoxyvinylethers of formula: CF.sub.2═CF—(OCF.sub.2CF(R.sub.F1)).sub.w—O—CF.sub.2(CF(R.sub.F2)).sub.ySO.sub.2X.sub.X, with X.sub.X being a halogen; wherein w is an integer between 0 and 2, R.sub.F1 and R.sub.F2, equal or different from each other, are independently F, Cl or a C.sub.1-C.sub.10 fluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6; preferably w is 1, R.sub.F1 is —CF.sub.3, y is 1 and R.sub.F2 is F; sulfonyl halide aromatic fluoroolefins of formula CF.sub.2═CF—Ar—SO.sub.2X.sub.X, with X.sub.X being a halogen, preferably, wherein Ar is a C.sub.5-C.sub.15 aromatic or heteroaromatic group.

20. The material (P) of claim 18, wherein monomer (B) is selected from the group consisting of: C.sub.2-C.sub.8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene; C.sub.2-C.sub.8 hydrogen-containing fluoroolefins; C.sub.2-C.sub.8 chloro- and/or bromo- and/or iodo-containing fluoroolefins; fluoroalkylvinylethers of formula CF.sub.2═CFOR.sub.f1, wherein R.sub.f is a C.sub.1-C.sub.6 fluoroalkyl, e.g. —CF.sub.3, —C.sub.2F.sub.5, —C.sub.3F.sub.7; fluorooxyalkylvinylethers of formula CF.sub.2═CFOX.sub.0, wherein X.sub.0 is a C.sub.1-C.sub.12 fluorooxyalkyl group comprising one or more than one ethereal oxygen atom, —CF.sub.2CF.sub.2—O—CF.sub.3 and —CF.sub.3 fluorodioxoles, of formula: ##STR00009## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different each other, is independently a fluorine atom, a C.sub.1-C.sub.6 fluoro(halo)fluoroalkyl, optionally comprising one or more oxygen atom, e.g. —CF.sub.3, —C.sub.2F.sub.5, —C.sub.3F.sub.7, —OCF.sub.3, —OCF.sub.2CF.sub.2OCF.sub.3.

21. The material (P) of claim 20, wherein at least one monomer (B) is tetrafluoroethylene (TFE) and wherein ionomer (I.sup.TFE.sub.SO3X) is selected from polymers consisting essentially of: (1) recurring units derived from tetrafluoroethylene (TFE), these recurring units (1) being in an amount of 50 to 99% moles, with respect to total moles of recurring units of ionomers (I.sup.TFE.sub.SO3X); (2) hydrolysed recurring units comprising at least one —SO.sub.3X.sub.a group and derived from at least one monomer selected from the group consisting of: (j) sulfonyl halide fluorovinylethers of formula: CF.sub.2═CF—O—(CF.sub.2).sub.mSO.sub.2X.sub.X, with X.sub.X being a halogen; wherein m is an integer between 1 and 10; (jj) sulfonyl fluoride fluoroalkoxyvinylethers of formula: CF.sub.2═CF—(OCF.sub.2CF(R.sub.F1)).sub.w—O—CF.sub.2(CF(R.sub.F2)).sub.ySO.sub.2X.sub.X, with X.sub.X being a halogen; wherein w is an integer between 0 and 2, R.sub.F1 and R.sub.F2, equal or different from each other, are independently F, Cl or a C.sub.1-C.sub.10 fluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6; and (jjj) mixtures thereof; these recurring units (2) being in an amount of 1 to 50% moles, with respect to total moles of recurring units of ionomers (I.sup.TFE.sub.SO3X); and (3) optionally, recurring units derived from at least one hydrogenated and/or fluorinated monomer different from TFE; these recurring units (3) being in an amount of 0 to 45% moles, with respect to total moles of recurring units of ionomers (I.sup.TFE.sub.SO3X); (3) from 0 to 25% moles of recurring units derived from fluorinated monomer(s) different from TFE (3), as above detailed, based on the total moles of recurring units of said ionomers (I.sup.TFE.sub.SO3X).

22. The material (P) of claim 20, wherein at least one monomer (B) is vinylidene fluoride (VDF), and wherein ionomer (I.sup.VDF.sub.SO3X) is selected from polymers consisting essentially of: (1) recurring units derived from vinylidene fluoride (VDF), these recurring units (1) being generally in an amount of 55 to 99% moles, with respect to total moles of recurring units of ionomers (I.sup.VDF.sub.SO3X); (2) hydrolysed recurring units comprising at least one —SO.sub.3X.sub.a group and derived from at least one monomer selected from the group consisting of: (j) sulfonyl halide fluorovinylethers of formula: CF.sub.2═CF—O—(CF.sub.2).sub.mSO.sub.2X.sub.X, with X.sub.X being a halogen, wherein m is an integer between 1 and 10; (jj) sulfonyl fluoride fluoroalkoxyvinylethers of formula: CF.sub.2═CF—(OCF.sub.2CF(R.sub.F1)).sub.w—O—CF.sub.2(CF(R.sub.F2)).sub.ySO.sub.2X.sub.X with X.sub.X being a halogen, wherein w is an integer between 0 and 2, R.sub.F1 and R.sub.F2, equal or different from each other, are independently F, Cl or a C.sub.1-C.sub.10 fluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6; and (jjj) mixtures thereof; these recurring units (2) being in an amount of 1 to 45% moles, with respect to total moles of recurring units of ionomers (I.sup.VDF.sub.SO3X); and (3) optionally, recurring units derived from at least one hydrogenated monomer or fluorinated monomer different from VDF; these recurring units (3) being in an amount of 0 to 30% moles, with respect to total moles of recurring units of ionomers (I.sup.VDF.sub.SO3X).

23. The material (P) of claim 16, wherein the amount of said ionisable groups in ionomers (I.sub.X) is at least 0.55, and/or of at most 3.50 meq/g with respect to the total weight of ionomers (I.sub.X).

24. The material (P) of claim 16, wherein said material (P) is composed of particles consisting of hollow agglomerates which have an average particle size of at least 3 μm and/or is of at most 100 μm; and/or said material (P) is composed of particles consisting in agglomerates of elementary particles possessing an averaged diameter of at least 30 nm and/or of advantageously at most 140 nm.

25. A method for making a powdery material [material (P)] composed of a plurality of particles of at least one ionisable polymer comprising a plurality of ionisable groups selected from the group consisting of —SO.sub.3X.sub.a, —PO.sub.3X.sub.a and —COOX.sub.a, wherein X.sub.a is H, an ammonium group or a monovalent metal [ionomer (I.sub.X)], said method comprising: Step (1): providing an as-polymerized aqueous latex [latex (I.sub.p)] comprising particles of at least one ionomer precursor comprising a plurality of hydrolysable groups selected from the group consisting of —SO.sub.2X.sub.X, —PO.sub.2X.sub.X and —COX.sub.X, wherein X.sub.X is a halogen [precursor (I.sub.p)]; and Step (2): contacting said as-polymerized aqueous latex [latex (I.sub.X)] with a basic hydrolysing agent [agent (B)], in conditions such as to at least partially convert said groups —SO.sub.2X.sub.X, —PO.sub.2X.sub.X and —COX.sub.X, wherein X.sub.X is F or Cl, into corresponding groups —SO.sub.3X.sub.a, —PO.sub.3X.sub.a and —COOX.sub.a, wherein X.sub.a is H, an ammonium group or a monovalent metal, without causing any significant coagulation, so as to obtain an aqueous latex of particles of ionomer (I.sub.X); optionally, Step (3): contacting said latex (I.sub.X) with at least one ion exchange resin, so as to at least partially remove residues of agent (B) and/or other contaminants; and Step (4): spray drying the latex (I.sub.X), so as to obtain the said material (P).

26. The method of claim 25, wherein material (P) is according to claim 1.

27. The method of claim 25, wherein latex (I.sub.p) comprises at least one fluorinated emulsifier, selected from the group consisting of: (a′) CF.sub.3(CF.sub.2).sub.n0COOM′, wherein no is an integer ranging from 4 to 10 and M′ represents NH.sub.4, Na, Li or K, preferably NH.sub.4; (b′) [R.sub.1—O.sub.n-L-A.sup.−]Y.sup.+ wherein: R.sub.1 is a linear or branched partially or fully fluorinated aliphatic group which optionally contains ether linkages; n is an integer; L is a linear or branched alkylene group which is optionally nonfluorinated, partially fluorinated or fully fluorinated and which optionally contains ether linkages; A.sup.− is an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion, and phosphonate; and Y.sup.+ is hydrogen, ammonium or alkali metal cation;

28. The method of claim 25, wherein in Step (2), the latex (I.sub.p) is contacted with a basic hydrolysing agent [agent (B)], selected from inorganic bases and/or wherein Step (2) optionally further comprises, after effecting contact between agent (B) and latex (I.sub.p), contacting the resulting latex (I.sub.X) with at least one neutralizing agent [agent (N)], different from the agent (B).

29. The method of claim 25, said method comprising a Step (3) of contacting said latex (I.sub.X) with at least one ion exchange resin, so as to at least partially remove said residues of agent (B) and/or other contaminants; and wherein said ion-exchange resin comprises at least one anion exchange resin, wherein positively charged ion exchange sites of the said anion exchange resin are selected from the group consisting of: ##STR00010## wherein, R, equal or different at each occurrence, is independently a C.sub.1-C.sub.12 hydrocarbon group or a hydrogen atom and E, equal or different at each occurrence, is independently a divalent hydrocarbon group comprising at least one carbon atom.

30. The method of claim 29, wherein Step (3) includes a step of contacting the latex (I.sub.X) with a cation exchange resin before, or after contacting with anion exchange resin, and wherein negatively charged ion exchange sites of cation exchange resins are selected from the group consisting of: ##STR00011##

Description

MATERIALS

Preparative Example 1—Manufacture of TFE-VEFS Polymer Latex in —SO.SUB.2.F Form

[0180] In a 22 L autoclave the following reagents were charged: [0181] 9.3 L of demineralized water; [0182] 700 g of the monomer with formula: CF.sub.2═CF—O—CF.sub.2CF.sub.2—SO.sub.2F (VEFS); [0183] 650 g of a 5 wt % aqueous solution of CIF.sub.2O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOK (averaged molecular weight=521, ratio n/m=10).

[0184] The autoclave, stirred at 470 rpm, was heated at 66° C. A water based solution with 9 g/L of potassium persulfate was added in a quantity of 170 ml. The pressure was maintained at a value of 14.4 bar (abs.) by feeding tetrafluoroethylene (TFE). During polymerization, aliquots of 100 g of VEFS were repeatedly added every 160 g of tetrafluoroethylene in the reactor. The reaction was stopped after 240 min by interrupting the stirring, cooling the autoclave and reducing the internal pressure by venting TFE; the total mass of TFE fed into the reactor was 3200 g. So obtained precursor latex had a solid content of 30 wt %.

[0185] A small sample of the latex thus obtained was then coagulated by freezing and thawing and the recovered polymer was washed with water and dried at 80° C. for 48 hours. The equivalent weight (EW) of the corresponding polymer was determined to be 967 g/mol through FT-IR measurement. Particles of polymer dispersed in the obtained latex were found to possess particle sizes of from 50 to 100 nm.

Preparative Example 2—Preparation of TFE-VEFS Water-Based Dispersion

[0186] Precursor latex of Preparative Example 1 was coagulated by freezing and thawing and the recovered powder was extensively washed with water and then dried at 80° C. for 48 hours.

[0187] A portion of so obtained precursor ionomer powder (100 g) was first treated with a solution (1 L) of 14 wt % of potassium hydroxide, 30 wt % dimethyl sulfoxide and 56 wt % of demineralized water at 80° C. for 8 h under stirring. After several washings with demineralized water the solid polymer so recovered was acidified with 1 L of a 20 wt % nitric acid solution at room temperature for 2 h. The powder thus obtained was washed again with demineralized water and eventually dried in a vent oven at 80° C. for 8 h.

[0188] The quantitative conversion of —SO.sub.2F to —SO.sub.3H functional group was confirmed through FT-IR analysis.

[0189] Such hydrolyzed ionomer powder (60 g) was mixed with demineralized water (160 g) in a titanium 250 ml autoclave. The mixture was heated at a temperature above 180° C. and stirred at 750 rpm. After 4 h the mixture was cooled down and the water dispersion was purified by centrifugation (10,000 rpm) for 2 h. The clear and transparent dispersion of ionomer had a solid content of 22.7 wt %.

Preparative Example 3—Hydrolysis of TFE-VEFS Precursor Latex and Provision of Ionomer Latex

[0190] One litre of precursor latex prepared in Pr. Ex. 1 was contacted with 73.5 g of NaOH/H.sub.2O 2 wt % solution at room temperature for 5 days and then with 73.5 g of NaOH/H.sub.2O 20 wt % for two day at room temperature. Conversion of the pristine —SO.sub.2F group into —SO.sub.3Na was assessed through solid state nuclear magnetic resonance (NMR). The mixture is then treated in a purification column having Lewatit Monoplus M800 OH anion exchange resin as stationary phase followed by a final treatment in a column having Lewatit Monoplus S 108 H cation exchange column as stationary phase. Complete transformation of ionisable —SO.sub.3Na groups to —SO.sub.3H was confirmed by ICP-OES analysis. A purified latex of ionomer in —SO.sub.3H was hence recovered, possessing a solids content of 15% wt. Particles of ionomer dispersed in the obtained latex were found to possess particle sizes of from 50 to 100 nm.

Comparative Example 4—Spray Drying of TFE-VEFS Dispersion from Example 2

[0191] Ionomer dispersion prepared in Preparative Example 2 (200 g), by re-dispersion in water of previously coagulated ionomer precursor, submitted to hydrolysis in solid phase, was spray dried in a spray drier device having a heated air inlet temperature of about 190° C., leading to a drying chamber averaged temperature of about 100° C. and co-current double-fluid nozzle with diameter of 0.7 mm to provide a dry powder (about 44 g).

[0192] Upon microscopy analysis, particles of the powder obtained were found to be spherical and had an average size of about 30 μm. Said particles showed no structuration as agglomerate of elementary particles: rather they were found as continuous homogeneous particles.

Example 5—Spray Drying of Latex of Ionomer from Example 3

[0193] Ionomer latex prepared in Example 3 (200 g) was spray dried in a spray drier device having a heated air inlet temperature of about 190° C., leading to a drying chamber averaged temperature of about 100° C. and an integrated co-current double-fluid nozzle with diameter of 0.7 mm in to provide a dry powder (about 30 g).

[0194] The particles of the powder obtained were spherical and had an average size of about 10 μm; said particles were found to be hollow. Further, each particle was constituted by smaller elementary particles having averaged diameter of about 80 nm, and diameters ranging from about 60 to about 100 nm.

[0195] Re-Dispersion in Water and Viscosity Measurement of Powders from Comparative Example 4 and Example 5

[0196] Powders obtained as described in Comparative Example 4 and Example 5 were dissolved in demineralized water at room temperature and under stirring affording two water-based formulations having solid content of 25 wt %.

[0197] In both cases, the powders were easily and quickly solubilized, with no measurable solid residue. The water-based formulations were submitted to liquid viscosity measurements at room temperature (23° C.), using a viscometer with Couette geometry, with a shear rate sweep of from 100 to 1000 s.sup.−1. Results are summarized in table below.

TABLE-US-00001 TABLE 1 Shear Rate (s.sup.−1) Ex. 4C (Pa × s) Ex. 5 (Pa × s) 100 0.07 0.13 500 0.01 0.02 1000 0.007 0.01

[0198] Data summarized in Table above well demonstrate that the method of the invention provide inventive powders which are easily re-dispersible notably in an aqueous medium, and which possess ability to deliver liquid formulations possessing increased liquid viscosity in particular at low shear rate, so as to render the same compatible with typical coating techniques, without requiring the addition of thickeners or other viscosity enhancers, which may compromise, generally, the overall performances of coatings/impregnated articles obtained therefrom.