Process for Preparing Membranes

Abstract

A process for preparing an ion-exchange membrane having a textured surface profile comprising the steps (i) and (ii): (i) applying a radiation-curable composition to a membrane in a patternwise manner; and (ii) irradiating and thereby curing the radiation-curable composition present on the membrane; wherein the radiation-curable composition comprises: a) 10 to 65 wt % of curable ionic compound(s) comprising one ethylenically unsaturated group; b) 3 to 60 wt % of crosslinking agent(s) comprising at least two ethylenically unsaturated groups and having a number average molecular weight below 800; c) 0 to 70 wt % of inert solvent(s); d) 0 to 10 wt % of free-radical initiator(s); and e) 0.5 to 25 wt % of thickening agent(s).

1 .- 21 . (canceled) 
     
     
         22 . An ion-exchange membrane having a textured surface profile obtained by a process comprising the steps (i) and (ii):
 (i) applying a radiation-curable composition to a membrane in a patternwise manner; and   (ii) irradiating and thereby curing the radiation-curable composition present on the membrane;   wherein the radiation-curable composition comprises:   a) 10 to 65 wt % of curable ionic compound(s) comprising one ethylenically unsaturated group;   b) 3 to 60 wt % of crosslinking agent(s) comprising at least two ethylenically unsaturated groups and having a number average molecular weight below 800;   c) 0 to 70 wt % of inert solvent(s);   d) 0 to 10 wt % of free-radical initiator(s); and   e) 0.5 to 25 wt % of thickening agent(s) comprising a particulate solid in a form which has a specific surface area as determined by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas of greater than 50 m 2 /g.   
     
     
         23 . The ion-exchange membrane according to  claim 22  which further comprises a porous support and a cured radiation-curable curable composition present in the porous support. 
     
     
         24 . The ion-exchange membrane according to  claim 22  wherein the radiation-curable composition applied to the membrane forms the textured surface profile. 
     
     
         25 . The ion-exchange membrane according to  claim 22  wherein the particulate solid is in a form which has a BET surface area greater than 150 m 2 /g. 
     
     
         26 . The ion-exchange membrane according to  claim 22  wherein the particulate solid is in a form which has a BET surface area greater than 250 m 2 /g. 
     
     
         27 . The ion-exchange membrane according to  claim 22  wherein the curable ionic compound(s) comprises an acidic group selected from the group consisting of a sulpho, carboxy and/or phosphato group. 
     
     
         28 . The ion-exchange membrane according to  claim 22  wherein the curable ionic compound(s) comprises a quaternary ammonium group. 
     
     
         29 . The ion-exchange membrane according to  claim 22  wherein the radiation-curable composition used in step (i) has a viscosity of 30 to 1000 Pa·s at a shear rate of 0.1 s −1  and a viscosity of <20 Pa·s at a shear rate of 1000 s −1 , when measured at 20° C. 
     
     
         30 . The ion-exchange membrane according to  claim 22  wherein the ratio of the viscosity of the radiation-curable composition used in step (i) when measured at a shear rate of 0.1 s −1  at 20° C. to the viscosity when measured at a shear rate of 1000 s −1  at 20° C. is between 1.5 and 5000. 
     
     
         31 . The ion-exchange membrane according to  claim 22  wherein step i) comprises rotary screen-printing, flatbed screen-printing or rotary-stop-cylinder screen-printing of the radiation-curable composition onto the membrane in a patternwise manner. 
     
     
         32 . The ion-exchange membrane according to  claim 22  wherein the textured surface profile comprises protrusions which have an average height of 5 to 500 μm. 
     
     
         33 . The ion-exchange membrane according to  claim 22  wherein the (Area of Texture/Total Membrane Area)×100% is 2 to 40%. 
     
     
         34 . The ion-exchange membrane according to  claim 22  wherein the textured surface profile comprises protrusions which have an average length to average width ratio of 10:1 to 1:10. 
     
     
         35 . The ion-exchange membrane according to  claim 22  wherein the textured surface profile comprises protrusions which are separated from each other by an average of at least 0.5 mm. 
     
     
         36 . The ion-exchange membrane according to  claim 22  wherein the thickening agent e) comprises a rheology modifier. 
     
     
         37 . The ion-exchange membrane of  claim 22  wherein the particulate solid comprises an inorganic filler selected from crystalline and amorphous silica, carbon black, clay particles, aluminum silicate, metal oxides and metal carbonates. 
     
     
         38 . The ion-exchange membrane according to  claim 22  wherein the radiation-curable composition comprises:
 a) 12 to 60 wt % of curable ionic compound(s) comprising one acrylic group and one or more acidic or basic group selected from sulfo, carboxy, phosphato, quaternary amino and tertiary amino groups; 
 b) 4 to 45 wt % of crosslinking agent(s) comprising at least two ethylenically unsaturated groups and having a number average molecular weight below 800; 
 c) 5 to 50 wt % of inert solvent(s); 
 d) 0.01 to 10 wt % of free-radical initiator(s); 
 e) 1 to 15 wt % of thickening agent comprising an inorganic filler selected from the group consisting of hydrophilic metal oxides, carbon black, clays and calcium carbonate; and 
 f) 1 to 15 wt % of crosslinking agent(s) comprising at least two ethylenically unsaturated groups and having a number average molecular weight of 800 to 8,000 Daltons. 
 
     
     
         39 . The ion-exchange membrane according to  claim 22  which further comprises a porous support and a cured radiation-curable curable composition present in the porous support and wherein:
 (i) the particulate solid is in a form which has a BET surface area greater than 150 m 2 /g; 
 (ii) the curable ionic compound(s) comprises an acidic group selected from the group consisting of a sulpho, carboxy and/or phosphato group or a quaternary ammonium group; and 
 (iii) the particulate solid comprises an inorganic filler selected from crystalline and amorphous silica, carbon black, clay particles, aluminum silicate, metal oxides and metal carbonates. 
 
     
     
         40 . The ion-exchange membrane according to  claim 22  wherein:
 (i) the textured surface profile comprises protrusions which have an average height of 5 to 500 μm; 
 (ii) the (Area of Texture/Total Membrane Area)×100% is 2 to 40%; and 
 (iii) the textured surface profile comprises protrusions which are separated from each other by an average of at least 0.5 mm. 
 
     
     
         41 . The ion-exchange membrane according to  claim 39  wherein:
 (i) the textured surface profile comprises protrusions which have an average height of 5 to 500 μm; 
 (ii) the (Area of Texture/Total Membrane Area)×100% is 2 to 40%; and 
 (iii) the textured surface profile comprises protrusions which are separated from each other by an average of at least 0.5 mm. 
 
     
     
         42 . An electrodialysis or reverse electrodialysis unit, an electrodeionization module, a capacitive deionization device, a diffusion dialysis apparatus or a membrane distillation module, comprising one or more ion exchange membranes according to  claim 22 .