Process for making an anti-reflective coating composition and a porous coating made therefrom
The invention relates to a process of making an anti-reflective coating composition comprising the steps of 1) preparing an oil-in-water emulsion by mixing an apolar organic compound A; a cationic addition copolymer C as emulsion stabilizer; and aqueous medium of pH 2-6; at a mass ratio C/A of 0.1 to 2, to result in 1-50 mass % (based on emulsion) of emulsified droplets of average particle size 30-300 nm; and 2) providing an inorganic oxide shell layer to the emulsified droplets by adding to the emulsion obtained in step 1) at least one inorganic oxide precursor, to result in organic-inorganic core-shell nano-particles with mass ratio core/shell of from 0.2 to 25. An advantage of this process is that the dispersion of nano-particles obtained is stable under different conditions, and allows altering its concentration and solvent system, and addition of different binders and auxiliary components. The invention also relates to a coating composition as obtained with said process, and to a process of applying a porous anti-reflective-coating on a substrate using such composition, and to the resulting coated substrate.
1. An anti-reflective coating composition comprising organic-inorganic core-shell nano-particles having a particle size of 35-300 nm, wherein
the particle size is a Z-averaged hydrodynamic diameter measured by DLS, the organic-inorganic core-shell nano-particles having a mass ratio of core/shell of from 0.2 to 25, wherein
the core is a sum of an organic compound A and an emulsion stabilizer C at a mass ratio C/A of 0.1 to 2, and wherein
the shell is formed of a metal oxide equivalent consisting of a mass of metal oxide resulting from complete conversion of at least one inorganic metal oxide precursor selected from the group consisting of metal salts, metal chelates and organo-metallic compounds, and wherein
the compound A is an apolar non-polymeric organic compound having a solubility in water of at most 5 kg/m 3 , and wherein
the emulsion stabilizer C is a cationic addition copolymer having an overall positive zeta potential which is comprised of at least one monomer unit having a cationic charge and at least one monomer unit being neutral or non-ionic.
2. The anti-reflective coating composition according to claim 1 , wherein the compound A has a boiling point of at least 10° C. and at most 300° C.
3. The anti-reflective coating composition according to claim 1 , where the compound A has a solubility in water at room temperature of at most 3 kg/m 3 .
4. The anti-reflective coating composition according to claim 1 , wherein the compound C is a copolymer of:
(i) at least cationic or basic monomer (M1),
(ii) at least one neutral or non-ionic monomer (M2); and
(iii) at least one polar, anionic or acidic monomer (M3).
5. The anti-reflective coating composition according to claim 4 , wherein copolymer C is a copolymer of:
(i) 1-25 mole % of the at least one cationic or basic monomer M1;
(ii) 50-99 mole % of the at least one non-ionic apolar monomer M2; and
(iii) 0-25 mole % of the at least one polar, anionic or acidic monomer M3; wherein
the monomers M1, M2, and M3 sum to 100 mole %.
6. The anti-reflective coating composition according to claim 5 , wherein the at least one cationic or basic monomer M1 comprise vinyl monomers with a tertiary amine group.
7. The anti-reflective coating composition according to claim 5 , wherein copolymer C is a copolymer of:
(i) 5-15 mole % of the at least one monomer M1;
(ii) 75-95 mole % of the at least one monomer M2; and
(iii) 0-10 mole % of the at least one monomer M3.
8. The anti-reflective coating composition according to claim 5 , wherein copolymer C is obtained from:
5-15 mole % of the at least one monomer M1 which is selected from the group consisting of amino-functional (meth)acrylates and (meth)acrylamides; and
85-95 mole % of the at least one monomer M2 which is selected from the group of C1-C18 alkyl (meth)acrylates.
9. The anti-reflective coating composition according to claim 1 , wherein a mass ratio C/A of the copolymer C to the compound A is 0.15-1.0.
10. The anti-reflective coating composition according to claim 1 , wherein the composition further comprises a binder.
11. The anti-reflective coating composition according to claim 10 , wherein the binder comprises an inorganic oxide precursor.
12. The anti-reflective coating composition according to claim 1 , wherein the at least one inorganic metal oxide precursor comprises at least one metal selected from the group consisting of Si, Al, Be, Bi, B, Fe, Mg, Na, K, In, Ge, Hf, La, lanthanoids, Sb, Sn, Ti, Ta, Nb, Y, Zn and Zr.
13. The anti-reflective coating composition according to claim 1 , wherein the at least one inorganic metal oxide precursor comprises a metal alkoxide.
14. The anti-reflective coating composition according to claim 1 , wherein the at least one inorganic metal oxide precursor comprises an alkoxy silane.
15. An anti-reflective coated transparent substrate comprising a substrate and a coating on a surface of the substrate, wherein the coating comprises the anti-reflective coating composition according to claim 1 .
16. A substrate comprising a surface, wherein the surface comprises the anti-reflective coating composition according to claim 1 .