Process for preparing membranes

1. A process for preparing a composite membrane comprising the steps of:

a) applying a radiation-curable composition to a porous support;

b) irradiating the composition and thereby forming a layer of cured polymer of thickness 20 to 400 nm on the support;

c) forming a discriminating layer on the layer of cured polymer; and

d) optionally forming a protective layer on the discriminating layer;

wherein the radiation-curable composition comprises a partially crosslinked, radiation-curable polymer comprising dialkylsiloxane groups.

2. The process according to claim 1 wherein the partially crosslinked, radiation-curable polymer is free from phenyl siloxane groups.

3. The process according to claim 1 , which further comprises the step of preparing the partially crosslinked, radiation-curable polymer by thermally curing a composition comprising one or more curable components, at least one of which comprises a dialkylsiloxane group.

4. The process according to claim 1 , wherein the discriminating layer comprises a polyimide, cellulose acetate, polyethyleneoxide or polyetherimide.

5. The process according to claim 1 , wherein the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

6. The process according to claim 1 , wherein the radiation-curable composition comprises a cationic photoinitiator.

7. The process according to claim 1 , which further comprises the step of preparing the partially crosslinked, radiation-curable polymer by a process comprising the reaction of epoxy groups with a crosslinking agent thereby forming the partially crosslinked, radiation-curable polymer.

8. The process according to claim 1 , wherein the radiation-curable composition comprises an epoxy-modified polydimethyl siloxane.

9. The process according to claim 1 , which further comprises the step of treating the cured polymer with corona discharge or a plasma treatment before forming the discriminating layer thereon.

10. The process according to claim 1 , wherein:

the radiation-curable composition is applied continuously to the porous support in step a) by means of a manufacturing unit comprising a radiation-curable composition application station, step b) is performed using an irradiation source located downstream from the radiation-curable composition application station, the discriminating layer is formed on the layer of cured polymer in step c) by a discriminating layer application station, and the resultant composite membrane is collected at a collecting station, wherein the manufacturing unit comprises a means for moving the porous support from the radiation-curable composition application station to the irradiation source and to the discriminating layer application station and to the composite membrane collecting station.

11. The process according to claim 10 wherein step a) and/or step b) is or are performed by curtain coating, meniscus type dip coating, kiss coating, pre-metered slot die coating, reverse or forward kiss gravure coating, multi roll gravure coating, spin coating and/or slide bead coating.

12. The process according to claim 1 , wherein step a) and/or step b) is or are performed by curtain coating, meniscus type dip coating, kiss coating, pre-metered slot die coating, reverse or forward kiss gravure coating, multi roll gravure coating, spin coating and/or slide bead coating.

13. The process according to claim 1 wherein:

(i) the partially crosslinked, radiation-curable polymer is free from phenyl siloxane groups; and

(ii) the discriminating layer comprises a polyimide comprising trifluoromethyl groups;

which process further comprises the step of preparing the partially crosslinked, radiation-curable polymer by thermally curing a composition comprising one or more curable components, at least one of which comprises a dialkylsiloxane group.

14. The process according to claim 13 wherein:

the radiation-curable composition is applied continuously to the porous support in step a) by means of a manufacturing unit comprising a radiation-curable composition application station, step b) is performed using an irradiation source located downstream from the radiation-curable composition application station, the discriminating layer is formed on the layer of cured polymer in step c) by a discriminating layer application station, and the resultant composite membrane is collected at a collecting station, wherein the manufacturing unit comprises a means for moving the porous support from the radiation-curable composition application station to the irradiation source and to the discriminating layer application station and to the composite membrane collecting station.

15. The process according to claim 14 wherein step a) and/or step b) is or are performed by curtain coating, meniscus type dip coating, kiss coating, pre-metered slot die coating, reverse or forward kiss gravure coating, multi roll gravure coating, spin coating and/or slide bead coating.

16. A composite membrane comprising:

a. a porous support;

b. a layer of radiation-cured polymer of thickness 20 to 400 nm present on the porous support;

c. a discriminating layer present on the layer of radiation-cured polymer; and

d. optionally a protective layer present on the discriminating layer;

wherein the layer of radiation-cured polymer comprises dialkylsiloxane groups.

17. The composite membrane according to claim 16 wherein the discriminating layer comprises a polyimide, cellulose acetate, polyethyleneoxide or polyetherimide.

18. The composite membrane according to claim 16 wherein the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

19. The composite membrane according to claim 16 wherein the layer of radiation-cured polymer is free from phenyl siloxane groups.

20. A cartridge comprising the composite membrane according to claim 16 wherein the cartridge is of plate-and-frame, spiral-wound, hollow-fibre, tubular or envelope type.