Coating and coating formulation
A coated substrate comprising a coating layer with inorganic oxide and pores, the coating layer demonstrates improved anti-soiling properties. The coated substrate may for example be used in solar modules. Further a coating formulation and use of the coating formulation are disclosed.
1. A 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, and having a porosity of less than 5 vol. %;
ii. a porogen capable of forming pores with a diameter in the range of 10 to 120 nm;
iii. an inorganic oxide binder; and
iv. a solvent,
wherein the coating formulation comprises between 0.6 to 28.6 wt-% aluminium oxide equivalents of aluminium containing compound.
2. The coating formulation according to claim 1 , wherein the porogen comprises—core-shell nanoparticles where the core comprises an organic compound or a polymer with a boiling point below 200° C., and the shell comprises an inorganic oxide; and—hollow inorganic nanoparticles.
3. The coating formulation according to claim 1 , wherein the porogen accounts for 10 to 75 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
4. The coating formulation according to claim 1 , wherein the inorganic oxide binder comprises inorganic oxide nano particles with an average diameter in the range of 0.1 to 7 nm.
5. The coating formulation according to claim 1 , wherein the elongated dense inorganic oxide particles account for 5 to 70 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
6. A method of preparing a coated substrate comprising the steps of
providing a substrate having a first surface;
providing a coating formulation according to claim 1 ;
applying the coating formulation on the first surface of the substrate;
drying the applied coating formulation; and
converting the substrate with dried coating formulation into a coated substrate comprising a coating layer on the first surface.
7. A coated substrate comprising a substrate, and a coating comprised of the coating formulation of claim 1 on the substrate.
8. The coated substrate according to claim 7 , wherein the substrate comprises a transparent solid sheet member, and a base coating layer interposed between the first surface and the coating layer on the first surface.
9. The coated substrate according to claim 7 , wherein a substrate-coating anti-soiling ratio, ASR, with
ASR
=
(
T
Substrate
,
0
-
T
Substrate
,
soil
)
-
(
T
Coating
,
0
-
T
Coating
,
soil
)
(
T
Substrate
,
0
-
T
Substrate
,
soil
)
×
100
%
is at least 50%, wherein T is the average transmittance from 400-1200 nm, Substrate refers to substrate without coating, Coating refers to the substrate with double sided coating, 0 refers to before soil test and soil refers to after soil test.
10. The coated substrate according to claim 7 , wherein the coated substrate has a substrate-coating anti-reflective effect, ARE, with
ARE= T Coatedsubstrate,0 −T Substrate,0
of at least 2%, where T is the average transmittance from 400-1200 nm, Substrate refers to substrate without coating, Coated substrate refers to the substrate with double sided coating and 0 refers to before soil test.
11. The coated substrate according to claim 7 , wherein the coated substrate has an Antisoiling gain, ASG, with
ASG
=
[
1
-
(
T
coated
substrate
with
Al
,
0
-
T
coated
substrate
with
Al
,
soil
)
(
T
coated
substrate
without
Al
,
0
-
T
coated
substrate
without
Al
,
soil
)
]
×
100
%
of at least 50%, where T is the is the average transmittance from 400-1200 nm, Coated Substrate with Al refers to a double side coated substrate with the coating with alumina and elongated particles and Coated Substrate without Al refers to a double side coated substrate with same coating where the alumina and dense inorganic oxide particles are excluded, 0 refers to before soil test and soil refers to after soil test.
12. The coated substrate according to claim 7 , wherein the mass ratio of inorganic oxide originating from the elongated dense inorganic oxide particles to total inorganic oxide of the coating is higher in a 20 nm thick top layer of the coating closest to the outer surface of the coated substrate than the average mass ratio of the inorganic oxide originating from dense inorganic oxide particles to total inorganic oxide of the coating.
13. The coated substrate according to claim 7 , wherein the onset dust removal is below 5.5 m/s.
14. A coated substrate according to claim 7 , wherein the substrate is a cover glass for a solar module.
15. A solar module comprising a coated substrate according to claim 7 .
16. The coating formulation according to claim 1 , wherein the coating formulation comprises between 1.2 to 16.6 wt-% aluminium oxide equivalents of aluminium containing compound.
17. The coating formulation according to claim 3 , wherein the porogen accounts for 20 to 50 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
18. The coating formulation according to claim 5 , wherein the elongated dense inorganic oxide particles account for 5 to 50 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
19. The coating formulation according to claim 5 , wherein the elongated dense inorganic oxide particles account for 10 to 45 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
20. The coating formulation according to claim 5 , wherein the elongated dense inorganic oxide particles account for 12 to 30 wt-% of the total amount of inorganic oxide equivalents in the coating formulation.
21. The coated substrate according to claim 8 , wherein, the base coating is selected from the group of barrier coatings and anti-reflective coatings.
22. The coated substrate according to claim 9 , wherein the substrate-coating ASR is at least 90%.
23. The coated substrate according to claim 10 , wherein the ARE is at least 4%.
24. The coated substrate according to claim 11 , wherein the ASG is at least 75%.
25. The coated substrate according to claim 12 , wherein the mass ratio of inorganic oxide originating from the elongated dense inorganic oxide particles to total inorganic oxide of the coating is at least twice as high in the top layer of the coating than the average mass ratio of the inorganic oxide originating from dense inorganic oxide particles to total inorganic oxide of the coating.
26. The coated substrate according to claim 13 , where the onset dust removal is between 5.5 m/s and 4 m/s.