Anti-scratch coating composition containing anisotropic particles, a corresponding coated substrate and its application in ophthalmic optics

1. An anti-scratch coating polymerisable composition comprising:

a) at least one alkoxysilane and/or at least one hydrolysate thereof; and

b) anisotropic particles of at least one metal oxide and/or of at least one metal oxyhydroxide, having a main axis and a length D1 following this main axis, smaller than or equal to 400 nm and whereof the sizes vary, in a direction transversal to said main axis, between a minimum dimension D2 and a maximum dimension D3, with D3≧D2;

wherein the ratios F=D1/D2 and f=D1/D3 defining the form factors of said anisotropic particle verify the relation F>10 and f≧10, and

wherein said metal oxide and/or metal oxyhydroxide is selected from the group consisting of oxides and oxyhydroxides of aluminum, zirconium, titanium, iron, tungsten, vanadium, and mixtures thereof.

2. The composition of claim 1 , further defined as comprising a polymerisation catalyst.

3. The composition of claim 1 , wherein 10<F≦50 and 10<f≦50.

4. The composition of claim 3 , wherein F≧15.

5. The composition of claim 4 , wherein F≧20.

6. The composition of claim 5 , wherein F≧25.

7. The composition of claim 5 , wherein F≧30.

8. The composition of claim 7 , wherein F≧35.

9. The composition of claim 3 , wherein f≧20.

10. The composition of claim 9 , wherein f≧25.

11. The composition of claim 1 , wherein D1 varies from 100 to 300 nm.

12. The composition of claim 11 , wherein D1 varies from 140 to 300 nm.

13. The composition of claim 12 , wherein D1 varies from 140 to 200 nm.

14. The composition of claim 1 , wherein F and f are substantially identical.

15. The composition of claim 14 , wherein the anisotropic particles are in the form of needles.

16. The composition of claim 1 , wherein the anisotropic particles are in the form of laths.

17. The composition of claim 1 , wherein said metal oxide is an aluminum oxide.

18. The composition of claim 1 , wherein said metal oxyhydroxide is an aluminum oxyhydroxide AlOGH.

19. The composition of claim 1 , wherein the anisotropic particles have been surface-treated in order to increase their solubility in alkoxysilane and/or hydrolysate thereof.

20. The composition of claim 19 , wherein the surface treatment of the anisotropic particles comprises a grafting step of at least one organo-functional alkoxysilane.

21. The composition of claim 20 , wherein the organo-functional alkoxysilane is an epoxysilane and/or a (meth)acryloxysilane.

22. The composition of claim 21 , wherein the organo-functional alkoxysilane is γ-glycidoxypropyltrimethoxysilane and/or (3-methacryloxypropyl)trimethoxy silane.

23. The composition of claim 1 , wherein the anisotropic particles are in the form of a colloidal solution.

24. The composition of claim 1 , wherein the anisotropic particles are obtained by hydrolysis of a hydrolysable metal precursor and hydrothermal treatment.

25. The composition of claim 24 , wherein the hydrolysable metal precursor is aluminum acrylate.

26. The composition of claim 24 , wherein the hydrothermal treatment is performed in acid medium, in an autoclave, at a temperature comprised between 150° C. and 200° C.

27. The composition of claim 1 , wherein the theoretic dry extract of said composition comprises from 0.1 to 39% in mass of anisotropic particles of metal oxide and/or of metal oxyhydroxide.

28. The composition of claim 27 , wherein the dry extract of said composition comprises from 3 to 35% in mass of anisotropic particles of metal oxide and/or of metal oxyhydroxide.

29. The composition of claim 28 , wherein the dry extract of said composition comprises from 10 to 35% in mass of anisotropic particles of metal oxide and/or of metal oxyhydroxide.

30. The composition of claim 1 , wherein the alkoxysilane and/or the hydrolysate thereof is an epoxysilane.

31. The composition of claim 1 , comprising at least one other globally isotropic metal oxide.

32. The composition of claim 1 , wherein the composition is a coating on a substrate.

33. The composition of claim 32 , wherein the coating has a thickness of 1 to 10 microns.

34. The composition of claim 33 , wherein the coating has a thickness of 2 to 5 microns.

35. The composition of claim 32 , wherein the coating has a critical load greater than or equal to 7N, when scratched by a diamond tip with a tip radius of 100 micrometers.

36. The composition of claim 35 , wherein the coating has a critical load greater than or equal to 9N, when scratched by a diamond tip with a tip radius of 100 micrometers.

37. The composition of claim 36 , wherein the coating has a critical load greater than or equal to 11N, when scratched by a diamond tip with a tip radius of 100 micrometers.

38. The composition of claim 32 , wherein the substrate is an ophthalmic lens.

39. The composition of claim 32 , wherein the substrate is a spectacle glass.

40. A method of preparing a substrate coated with a film comprising:

Obtaining a composition comprising:

At least one alkoxysilane and/or at least one hydrolysate thereof; and anisotropic particles of at least one metal oxide and/or of at least one metal oxyhydroxide, having a main axis and a length D1 following this main axis, smaller than or equal to 400 nm and whereof the sizes vary, in a direction transversal to said main axis, between a minimum dimension D2 and a maximum dimension D3, with D3≧D2 wherein said metal oxide and/or metal oxyhydroxide is selected from the group consisting of oxides and oxyhydroxides of aluminum, zirconium, titanium, iron, tungsten, vanadium, and mixtures thereof;

wherein the ratios F=D1/D2 and f=D1/D3 defining the form factors of said anisotropic particle verify the relation F>10 and f≧10;

obtaining a substrate;

coating the substrate with the composition; and

hardening the composition into a film.

41. The method of claim 40 , wherein said film has a thickness of from 1 to 10 microns.

42. The method of claim 41 , wherein said film has a thickness of from 2 to 5 microns.

43. The method of claim 40 , wherein said film shows, when scratched by a diamond tip with a tip radius of 100 micrometers, a critical load greater than or equal to 7 N.

44. The method of claim 43 , wherein said film shows a critical load greater than or equal to 9 N.

45. The method of claim 43 , wherein said film shows a critical load greater than or equal to 11 N.

46. The method of claim 40 , wherein said substrate is an ophthalmic lens.

47. The method of claim 46 , wherein said ophthalmic lens is a spectacle glass. respectively.

48. An anti-scratch coating polymerisable composition comprising:

a) at least one alkoxysilane and/or at least one hydrolysate thereof; and

b) anisotropic particles of at least one metal oxide and/or of at least one metal oxyhydroxide, having a main axis and a length D1 following this main axis, smaller than or equal to 400 nm and whereof the sizes vary, in a direction transversal to said main axis, between a minimum dimension D2 and a maximum dimension D3, with D3≧D2;

wherein the ratios F=D1/D2 and f=D1/D3 defining the form factors of said anisotropic particle verify the relation F>10 and f≧10, and

wherein the anisotropic particles are in the form of laths.