Composition for transparent antistatic coating

1. A curable composition providing, upon curing, a transparent antistatic coating, said curable composition comprising:

at least one binder comprising at least one silane of formula (I)

wherein n=2 or 3, p=1 or 2, q=0 or 1 and n+p+q=4

X, identical or different, is a hydrogen atom, alkoxy group, halogen atom, siloxy group or silazane group;

R 1 , identical or different, is a C1-C10 linear or branched alkyl group wherein:

the alkyl group is substituted with a monocyclic or bicyclic heterocycle at a carbon atom, the heterocycle having a hetero atom selected from oxygen or sulphur,

a carbon atom of the alkyl group may be replaced by an oxygen atom;

the alkyl group may be further substituted with an organic functional group;

R 2 , identical or different, is a C1-C10 linear or branched divalent alkylene group linked to the silicon atom and R 1 , in which a carbon atom of R 2 may be replaced by an oxygen atom; and

R 3 represent an alkyl group, an alkenyl group or an aryl group;

a salt (II) comprising an alkali cation and a counter ion which is the conjugate base of a superacid

Alkali + Superacid −   (II);

and

a Brønsted acid of molecular weight greater than or equal to 200 g/mol.

2. The curable composition of claim 1 , wherein the molecular weight of Brønsted acid is lower than 2000 g/mol.

3. The curable composition of claim 2 , wherein the molecular weight of Brønsted acid is lower than 1000 g/mol.

4. The curable composition of claim 1 , wherein the Brønsted acid is a surfactant of formula (III)

R 4 —(R 5 ) r —ZH  (III)

wherein:

R 4 represents a linear or branched alkyl group;

R 5 represents an arylene group; and

Z represents a Brønsted acid function selected from the group consisting of sulphate, sulfonate, carboxylate, phosphate, phosphonate or phosphinate;

r=0 or 1.

5. The curable composition of claim 1 , wherein the Brønsted acid represents less than 5% in weight, relative to the dry weight of the curable composition.

6. The curable composition of claim 5 , wherein the Brønsted acid represents less than 1% in weight, relative to the dry weight of the curable composition.

7. The curable composition of claim 1 , wherein the alkali cation of salt (II) is lithium.

8. The curable composition of claim 1 , wherein the counter ion of compound (II) is bis(trifluoromethanesulfonimide) or a derivative of trifluoromethanesulfonic acid.

9. The curable composition of claim 1 , wherein the compound (II) represents less than 5% in weight, relative to the dry weight of the curable composition.

10. The curable composition of claim 9 , wherein the compound (II) represents less than 1% in weight, relative to the dry weight of the curable composition.

11. The curable composition of claim 1 , wherein the binder further comprises fillers chosen among mineral oxides.

12. The curable composition of claim 11 , wherein the fillers are silicon dioxide nanoparticles.

13. The curable composition of claim 1 , wherein the binder further comprises a solvent.

14. The curable composition of claim 13 , wherein the solvent is methylethylketone.

15. An optical article comprising a substrate, wherein the substrate is at least partially coated with a transparent antistatic coating formed by depositing onto the substrate and curing a curable composition of claim 1 .

16. The optical article of claim 15 , further defined as an ophthalmic lens.

17. The optical article of claim 15 , wherein the thickness of the antistatic coating ranges from 5 to 5000 nm.

18. The optical article of claim 15 , further defined as having a decay time lower than 500 ms.

19. A process for preparing a transparent antistatic optical article comprising:

providing an optical substrate having at least one main surface;

applying onto at least part of said main surface a composition of claim 1 ; and

curing said composition.