Silica-based coating composition and its use for coating cement-bonded objects
The invention relates to a composition comprising a binder, filler particles and water, wherein the binder comprises amorphous silica and a vinyl-functional silicone polymer. The invention also relates to a method of making this composition as well as to a method of coating a substrate comprising applying the composition onto the substrate.
1. A composition comprising a binder, filler particles and water,
wherein the binder comprises amorphous silica and a vinyl-functional silicone polymer, wherein the amorphous silica comprises a combination of colloidal silica particles and precipitated silica, the colloidal silica particles comprising a first group of particles having a size of more than 20 nm and a second group of particles having a size of less than 20 nm, as determined by laser particle size analysis, and wherein the second group contains 10 to 50 wt % of all colloidal silica particles;
and wherein the filler particles have a BET specific surface area in the range of 0.1 to 5 m 2 /g and/or a D50 in the range of 1 to 100 μm.
2. The composition of claim 1 , wherein the binder additionally comprises a crosslinker and a catalyst.
3. The composition of claim 2 , wherein the binder additionally comprises one or more alkali silicates.
4. The composition of claim 3 , wherein the alkali silicate is potassium silicate.
5. The composition of claim 2 , wherein the cross linker is a reactive organofunctional siloxane or polysiloxane.
6. The composition of claim 2 , wherein the catalyst is an organoplatinum complex.
7. The composition of claim 1 , wherein:
the colloidal silica particles of the first group have a D50 in the range of 30 to 200 nm and the colloidal silica particles of the second group have a D50 in the range of 3 to 20 nm; and the colloidal silica particles of the first group have a BET specific surface area in the range of 30 to 100 m 2 /g and the colloidal silica particles of the second group have a BET specific surface area in the range of 200 to 600 m 2 /g.
8. The composition of claim 1 , wherein the precipitated silica is in the form of precipitated silica particles having:
a BET specific surface area in the range of 75 to 500 m 2 /g; and a D50 in the range of 1 to 50 μm.
9. The composition of claim 1 , wherein the filler particles are selected from the group consisting of glass powder particles, zirconia particles, titania particles, alumina particles, crystalline silica particles and mixtures thereof.
10. The composition of claim 1 comprising one or more additives selected from the group consisting of thickeners, dispersing agents, defoaming agents, and mixtures thereof.
11. The composition of claim 1 , wherein:
the filler particles-to-amorphous silica weight ratio is in the range of 0.8 to 10; and
the silicone polymer weight content, expressed relative to the weight of the composition, is in the range of 0.5 to 15%; and
the amorphous silica weight content, expressed relative to the weight of the composition, is in the range of 10 to 50%.
12. The composition of claim 1 , wherein the filler particles have a BET specific surface area in the range of 0.4 to 2 m 2 /g.
13. The composition of claim 1 , wherein the filler particles have a BET specific surface area in the range of 0.8 to 1 m 2 /g.
14. The composition of claim 1 , wherein the filler particles have a D50 in the range of 8 to 50 μm.
15. The composition of claim 1 , wherein the filler particles have a D50 in the range of 12 to 20 μm.
16. A cement bonded article comprising the composition of claim 1 and a substrate therefor.
17. The cement bonded article of claim 16 , which is a roofing tile.