Process for impregnating supports

Abstract

An impregnation process of a porous support including immersing the support in an aqueous colloidal dispersion of ionomeric (per)fluorinated polymer, containing sulphonyl fluoride groups and having a concentration greater than 15% by weight, thermal treatment at 200° C. or less, conversion of the ionomer sulphonyl groups into the corresponding salts, ionomer crosslinking when ionomer equivalent weight is less than 650 g/eq.

1 . An impregnation process of a porous support, formed by a polymer compound inert under use conditions, carried out by using colloidal dispersions in water of thermoplastic (per)fluorinated polymers containing functional groups convertible into —SO 3 H said aqueous dispersions of thermoplastic (per)fluorinated polymers obtainable by polymerization in emulsion of the following monomers: 
 (A) one or more (per)fluorinated monomers, containing at least one ethylene unsaturation, and    (B) one or more (per)fluorinated comonomers containing functional groups convertible into the above acid groups,    said process comprising the following steps:    1) preparation of an aqueous colloidal dispersion of thermoplastic (per)fluorinated polymers by polymerization in emulsion of at least the following monomers: 
 (A) one or more (per)fluorinated monomers, containing at least one ethylene unsaturation, and  
 (B) one or more (per)fluorinated comonomers containing functional groups convertible into the above acid groups;  
   2) a) concentration or dilution of the dispersion obtained in 1) having a solid content in the latex greater than 20% by weight; 
 b) optional addition of surfactants to obtain a dispersion surface tension lower than 40 mN/m;  
   3) impregnation of the porous support with the latex obtained in 2b);    4) thermal treatment at a temperature of 20° C. higher than the glass transition temperature of the thermoplastic ionomeric polymers and lower or equal to 200° C.;    5) a) ionomer crosslinking when the equivalent weight is lower than 650 g/eq, 
 b) conversion of the functional groups of the thermoplastic ionomeric polymers into the corresponding salts, by contacting the membrane with a basic aqueous solution, at temperatures comprised between 60° C. and the boiling temperature of the aqueous solution, and subsequent washings by immersion of the membrane in deionized water at room temperature, until obtaining an almost neutral pH of the washing waters;  
   6) optionally, membrane treatment by immersion at room temperature in an acid aqueous solution of an inorganic strong acid, and subsequent washings by immersion in deionized water up to an about neutral pH of the washing waters.    
   
   
       2 . The process according to  claim 1 , wherein the crosslinking of step 5a) is optional when the polymer has equivalent weight higher than 650 g/eq.  
   
   
       3 . The process according to  claim 1 , wherein steps 3) and 4) are repeated until obtaining a completely occluded membrane with Gurley number>10,000 (ASTM D726-58).  
   
   
       4 . (canceled)  
   
   
       5 . The process according to  claim 1 , wherein the porous support is a membrane having (a) a porous structure containing knots linked to each other by fibrils, and/or (b) a porous structure formed by only interconnected fibrils, or (c) a tissue.  
   
   
       6 . The process according to  claim 1 , wherein the thermoplastic (per)fluorinated polymers have equivalent weight from 380 to 1,800.  
   
   
       7 . The process according to  claim 1 , wherein in thermoplastic polymers the (per)fluorinated monomers of type (A) are selected from the following: 
 vinylidene fluoride (VDF);    C 2 -C 8  perfluoroolefins;    C 2 -C 8  chloro- and/or bromo- and/or iodo-fluoroolefins;    (per)fluoroalkylvinylethers (PAVE) CF 2 ═CFOR f , wherein R f  is a C 1 -C 6  (per)fluoroalkyl;    perfluoro-oxyalkylvinylethers CF 2 ═CFOX, wherein X is a C 1 -C 12  perfluorooxyalkyl having one or more ether groups;    the fluorinated monomers of type (B) are selected from one or more of the following:    F 2 C═CF—O—CF 2 —CF 2 —SO 2 F;    F 2 C═CF—O—[CF 2 —CXF—O] n —CF 2 —CF 2 —SO 2 F;    wherein X=Cl, F or CF 3 ; n=integer from 1 to 10;    F 2 C═CF—O—CF 2 —CF 2 —CF 2 —SO 2 F;    F 2 C═CF—Ar—SO 2 F wherein Ar is an aryl ring.    
   
   
       8 . (canceled)  
   
   
       9 . The process according to  claim 7 , wherein the fluorinated ionomers comprise: 
 monomeric units deriving from TFE;    monomeric units deriving from CF 2 ═CF—O—CF 2 CF 2 SO 2 F;    optionally, monomeric units deriving from the bis-olefin of formula (I);    optionally, iodine atoms in terminal position.    
   
   
       10 . The process according to  claim 1 , wherein the crosslinking of step 5a) can take place out by both ionic and radical route.  
   
   
       11 . (canceled)  
   
   
       12 . The process according to  claim 10 , wherein the crosslinking composition contains: 
 (a) a crosslinking co-agent, in an amount in the range 0.5-10% by weight with respect to the polymer;    (b) a metal compound, in amounts in the range 1-15% by weight with respect to the polymer, selected from oxides or hydroxides of divalent metals, optionally combined with a weak acid salt;    (c) other conventional additives;    (d) inorganic or polymer reinforcing fillers, optionally fibrillable.    
   
   
       13 . The process according to  claim 1 , wherein the latexes contain particles having a diameter from 5 to 400 nm.  
   
   
       14 . The process according to  claim 1 , wherein in step 1) in the colloidal aqueous dispersion of the ionomeric thermoplastic polymers fluorinated surfactants are present, of formula:  
       R f —X − M +   
     wherein R f  is a C 5 -C 16  (per)fluoroalkyl chain or a (per)fluoropolyoxyalkylene chain, X −  is —COO −  or —SO 3   − , M +  is selected from: H + , NH 4   + , an alkaline metal ion.  
   
   
       15 . The process according to  claim 1 , wherein the surfactants used in step 2b) are non-ionic, ionic or amphoteric surfactants or mixtures thereof, wherein the hydrophobic portion of the surfactant molecule can be of hydrocarbon, fluorocarbon, fluoropolyether or silicone type.  
   
   
       16 . The process according to  claim 15 , wherein the surfactant is the octylphenoxypolyethoxyethanol compound with a number of ethoxylic units comprised between 9 and 10, in an amount from 1% to 20% with respect to the latex.  
   
   
       17 . The process according to  claim 1 , wherein after step 6 a further heating step is effected at temperatures from 150° C. to 210° C.