Coating and coating formulation

1. A kit of parts for providing an antireflective coating having an improved property on a cover glass for use in a solar module, comprising

(a) A first container comprising a first coating formulation comprising an inorganic oxide binder and a solvent; and

(b) A second container comprising a second coating formulation comprising

i. at least 2 wt-% based on inorganic oxide equivalents of elongated dense inorganic oxide particles with an aspect ratio of at least 2 and a smaller diameter in the range of 3 to 20 nm;

ii. a porogen capable of forming pores with a diameter in the range of 10 to 120 nm, wherein the porogen comprises core-shell nanoparticles wherein the core comprises an organic compound which organic compound comprises a polymer, and the shell comprises an inorganic oxide;

iii. an inorganic oxide binder; and

iv. a solvent,

wherein the second coating formulation comprises 0 to 30 wt-% aluminium oxide equivalents of aluminium containing compound, based on total ash rest after combustion at 600° C., 2 min in air.

2. The kit according to claim 1 , wherein the second coating formulation comprises 0.1 to 25 wt-% aluminium oxide equivalents of aluminium containing compound.

3. The kit according to claim 1 , wherein the first coating formulation comprises the porogen capable of forming pores with a diameter in the range of 1 to 120 nm and wherein the porogen comprises an amount of organic porogen material, expressed as a wt % organic porogen material, in the range from 1 to 30 wt %.

4. The kit according to claim 1 , wherein the second coating formulation comprises the porogen capable of forming pores with a diameter in the range of 10 to 120 nm and wherein the porogen comprises an amount of organic porogen material, expressed as a wt % organic porogen material, in the range from 20 to 50 wt %.

5. The kit according to claim 1 , wherein wt % organic porogen material in the first coating formulation is less than the wt % organic porogen material in the second coating formulation.

6. The kit according to claim 1 , wherein the porogen has an average size of 20-150 nm as measured using DLS.

7. A method of preparing a coated substrate using the kit according to claim 1 comprising the steps of:

providing a substrate having a first surface;

applying the first coating formulation on the first surface of the substrate;

drying the applied first coating formulation to obtain the substrate comprising an at least partially covered first surface;

applying a the second coating formulation on the at least partially covered first surface;

optionally drying of the applied second coating formulation; and

converting the substrate into a coated substrate.

8. Use of the kit as defined in claim 1 to improve the durability of an AR coated substrate, preferably an AR coated glass substrate.

9. A coated substrate, comprising a substrate, and an anti-reflective coating provided on a surface of the substrate, wherein the anti-reflective coating comprises a first coating layer provided on the surface of the substrate, a second coating layer contacting a surface of the first layer at a side opposite to the substrate, wherein the first layer comprises:

an inorganic oxide binder; and

wherein the second layer comprises:

elongated dense inorganic oxide particles with an aspect ratio of at least 2 and a smaller diameter in the range of 3 to 20 nm;

0 to 30 wt-% aluminium oxide equivalents of aluminium containing compound;

an inorganic oxide binder; and

pores with a diameter in the range of 10 to 120 nm as measured using ellipsometry and/or electron microscopy, formed by a porogen comprising core-shell nanoparticles wherein the core comprises an organic compound which organic compound comprises a polymer, and the shell comprises an inorganic oxide.

10. The coated substrate according to claim 9 , wherein the first layer comprises pores with a diameter in the range of 10 to 120 nm as measured using ellipsometry and/or electron microscopy.

11. The coated substrate according to claim 9 , wherein the first layer has a lower porosity than the second layer.

12. The coated substrate according to claim 9 , wherein the second coating layer comprises between 0.5 to 25 wt-% aluminium oxide equivalents of aluminium containing compound.

13. The coated substrate according to claim 9 , wherein

the substrate is a glass substrate having a refractive index n0;

the first layer has a first layer thickness in the range from 50 to 180 nm, as measured using ellipsometry, and a refractive index n1 at an optical wavelength of 600 nm in the range of 1.50-1.30 as measured using ellipsometry an a coated substrate;

the second layer has a second layer thickness in the range from 50 to 180 nm, as measured using ellipsometry, and a refractive index n2 at an optical wavelength of 600 nm in the range of 1.35-1.20 as measured using ellipsometry an a coated substrate;

and n0<n1<n2.

14. The coated substrate according to claim 9 , wherein the substrate demonstrates a reduction in transmission of less than 0.25% as determined in a PCT-48 hr pressure cooker test.

15. An article comprising the coated substrate according to claim 9 .

16. A solar module comprising the coated substrate according to claim 9 .