Coating composition for an optical article, comprising a colloidal suspension of zirconia particles

1. A transparent coating composition comprising:

(a) a transparent colloidal suspension of zirconia nano-particles comprising mainly single monoclinic rod-shaped crystallites, which particles represent from 10 to 85 dry wt. % of the dry weight of the composition,

(b) at least one epoxysilane hydrolyzate,

(c) optionally, at least one alkoxysilane which does not contain any reactive functional group, and

(d) a curing catalyst,

wherein the composition does not contain any other metal oxide than zirconia.

2. The composition according to claim 1 , wherein the colloidal suspension has a pH of from 2 to 6.

3. The composition according to claim 1 , wherein the colloidal suspension is prepared by a process comprising the following successive steps:

a) subjecting a mixture of zirconium oxychloride and an alkali metal halide in an aqueous solvent to hydrothermal treatment at a temperature above 150° C.,

b) desalting said slurry, so as to form a colloidal suspension of zirconia, and

c) optionally substituting at least one alcoholic solvent, for part or all of the aqueous solvent.

4. The composition according to claim 1 , wherein dimensions of the crystallites range from 1 to 15 nm, along the crystallites' short axis and from 3 to 30 nm, along the crystallites' long axis.

5. The composition according to claim 1 , wherein the epoxysilane is γ-glycidoxypropyl trimethoxysilane (GLYMO).

6. The composition according to claim 1 , wherein the catalyst is aluminium acetyl acetonate.

7. The composition according to claim 1 , which also comprises an organic solvent, an alcohol solvent, a wetting agent or a mixture thereof.

8. A method for preparing the composition of claim 1 , comprising:

1—hydrolyzing the epoxysilane by means of a strong acid in a concentration of between 0.005 N and 0.1N,

2—introducing the zirconia colloid into the epoxysilane hydrolyzate after the start of the hydrolysis, and

3—adding the curing catalyst to the mixture resulting from step 2.

9. A method for coating a transparent optical substrate, comprising:

directly applying the composition of claim 1 to said substrate.

10. A method for manufacturing an optical article, comprising:

providing a transparent polymer substrate,

applying a coating prepared from the composition of claim 1 directly onto said substrate, without first subjecting said substrate to any physical pre-treatment suitable for activating a surface of the substrate.

11. The composition according to claim 1 , wherein the colloidal suspension has a pH of from 3 to 5.

12. The composition according to claim 1 , wherein dimensions of the crystallites range from 1 to 4 nm, along the crystallites' short axis and from 5 to 15 nm, along the crystallites' long axis.

13. The composition according to claim 1 , wherein the epoxysilane has formula (I):

(R 1 O) 3-n Si(R 3 ) n —W   (I)

wherein:

R 1 is a linear or branched alkyl group with 1 to 6 carbon atoms, an acetyl group, or a hydrogen atom,

R 3 is a non-hydrolyzable group, or a linear or branched alkyl group having from 1 to 6 carbon atoms,

n is 0 or 1, and

W is an organic group containing at least one epoxy group.

14. The composition according to claim 1 , wherein the epoxysilane has formula (II):

wherein:

R 1 is a linear or branched alkyl group with 1 to 6 carbon atoms an acetyl group, or a hydrogen atom,

R 2 is a methyl group or a hydrogen atom,

a is an integer from 1 to 6, and

b is 0, 1 or 2.

15. The composition according to claim 1 , wherein the alkoxysilane has formula (III):

wherein each of the two groups T1 and T2 bonded to the silicon may be hydrolyzed to a hydroxy group and are independently selected from linear or branched alkoxy groups with 1 to 10 carbon atoms, and

Z1 and Z2 are selected independently of each other from linear or branched alkoxy groups with 1 to 10 carbon atoms, linear or branched alkyl groups with 1 to 10 carbon atoms and aryl groups with 6 to 10 carbon atoms.

16. The composition according to claim 1 , wherein the catalyst is an aluminium chelate having formula (IV)

AlX V Y 3-V   (IV)

wherein X is an OL group where L is a linear or branched alkyl group with 1 to 10 carbon atoms,

Y is at least one coordinating product obtained from a compound having formula M 1 COCH 2 COM 2 or M 3 COCH 2 COOM 4 , wherein M1, M2, M3 and M4 are linear or branched alkyl groups with 1 to 10 carbon atoms, and

v takes the value 0, 1 or 2.

17. The method according to claim 10 , wherein the substrate is an acrylic substrate.