CEMENT-BASED PHOTOCATALYTIC COMPOSITION, AND USE THEREOF FOR OBTAINING WATER PAINTS, IN PARTICULAR FOR OUTDOOR APPLICATIONS

Abstract

Cement-based photocatalytic composition, which comprises: (a) at least one cement binder; (b) at least one photocatalyst; (c) at least one cellulose ether; (d) at least one fluidizing agent; (e) at least one first calcareous filler in the form of particles of which at least 95% by weight has a size not greater than 100 m; (f) at least one second calcareous filler in the form of particles of which at least 95% by weight has a size not greater than 30 m; (g) at least one silane supported on an inorganic support in the form of powder. Such composition can be employed as a water paint for obtaining wall coatings with very low thickness, in particular the outdoor applications, which ensure a high and stable photocatalytic effect over time even with relatively low quantities of photocatalyst, generally lower than 10% by weight, with optimal results in terms of uniformity of the coating and resistance of the same to weathering agents.

Claims

1. Cement-based photocatalytic composition, which comprises: (a) at least one cement binder; (b) at least one photocatalyst; (c) at least one cellulose ether; (d) at least one fluidizing, agent; (e) at least one first calcareous filler in the form of particles of which at least 95% by weight has a dimension not greater than 100 m; (f) at least one second calcareous filler in the form of particles of which at least 95% by weight has a dimension not greater than 30 m; (g) at least one silane supported on an inorganic support in the form of powder.

2. Photocatalytic composition according to claim 1, which comprises: (a) from 15 to 60% by weight, preferably from 20 to 50% by weight, of at least one cement binder; (b) from 0.5 to 12% by weight, preferably from 1 to 8% by weight, of at least one photocatalyst; (c) from 0.02 to 3% by weight, preferably from 0.05 to 1.5% by weight, of at least one cellulose ether; (d) from 0.05 to 5% by weight, preferably from 0.1 to 2% by weight, of at least one fluidizing agent; (e) from 10 to 50% by weight, preferably from 15 to 35% by weight, of at least one first calcareous filler in the form of particles of which at least 95% by weight has a dimension not greater than 100 m; (f) from 10 to 50% by weight, preferably from 15 to 35% by weight, of at least one second calcareous filler in the form of particles of which at least 95% b weight has a dimension not greater than 30 m; (g) from 0.05 to 5% by weight, preferably from 0.01 to 3% by weight, of at least one silane supported on an inorganic support in the form of powder.

3. Photocatalytic composition according to claim 1, wherein the cement binder (a) is a Portland cement.

4. Photocatalytic composition according to claim 1, wherein the photocatalyst (b) is photocatalytic titanium dioxide, mainly in anatase crystalline form.

5. Photocatalytic composition according to claim 4, wherein the photocatalytic titanium dioxide has a granulometry such as at least 95% by weight has a dimension not higher than 50 nm, preferably not higher than 20 nm.

6. Photocatalytic composition according to claim 4, wherein the photocatalytic titanium dioxide is in admixture with a non-photocatalytic titanium dioxide.

7. Photocatalytic composition according to claim 1, wherein the cellulose ether (c) has a Brookfield viscosity RVT at 20 C. from 100 to 70, 000 mPa.Math.s, preferably from 100 to 30, 000 mPa.Math.s, more preferably from 200 to 10,000 mPa.Math.s.

8. Photocatalytic composition according to claim 1, wherein the first calcareous filler (e) is in the form of particles of which at least 95% by weight has a dimension not greater than 70 m, while the second calcareous filler (f) is in the form of particles of which at least 95% by weight has a dimension not greater than 20 m.

9. Photocatalytic composition according to claim 1, wherein the first calcareous filler (e) is in the form of particles of which not more than 5% by weight has a dimension not greater than 30 m, preferably not greater than 20 m.

10. Photocatalytic composition according to claim 1, wherein the calcareous fillers (e) and (f) are present in a weight ratio (e)/(f) from 0.2 to 2.0, preferably from 0.5 to 1.5.

11. Photocatalytic composition according to claim 1, wherein the supported silane (g) is in the form of particles of which at least 95% by weight has a dimension not greater than 100, preferably not greater than 80.

12. Photocatalytic composition according to claim 1, further comprising: (h) at least one hydrophohized vinyl polymer, preferably a terpolymer of vinylchloride, ethylene and a vinyl ester CH.sub.2COC(O)R, wherein R is an alkyl, linear or branched, C.sub.4-C.sub.24.

13. Photocatalytic composition according to claim 1, further comprising: (i) at least one salt of a long chain carboxylic acid.

14. Use of a cement-based photocatalytic composition according to claim 1, for coating building artifacts in order to reduce the presence of polluting agents.

15. Use according to claim 14, wherein water is added to the photocatalytic composition in a predetermined proportion, by mixing until a homogeneous and fluid product is obtained.

16. Use according to claim 15, wherein the weight ratio between water and cement binder (a) is from 0.2 to 0.8.

17. Use according to claim 14, wherein, after application and drying, the photocatalytic composition forms a coating layer having a thickness from 0.05 mm to 1 mm, preferably from 0.1 to 0.5 mm.

18. Use of a cement-based photocatalytic composition according to claim 1, for coating surfaces made of metal, wood or plastic material, e.g. polyvinylchloride (PVC).

Description

EXAMPLE 1

[0049] A photocatalytic composition was obtained in accordance with the present invention by mixing the following components in the quantities reported in Table 1.

TABLE-US-00001 TABLE 1 Quantity (% by Component Commercial name weight) Portland cement 40 Photocatalytic CristalActiv PC500 5 titanium dioxide Cellulose ether Culminal MHPC 500 0.8 (methylhydroxypropyl- PF cellulose) Superfluidizing agent Melflux 2651 F 0.5 Micronized calcareous Lithos Mineraria 20 filler Lithocarb GR60 (95% with size 60 m) Calcareous Imerys #10 white 20 ultrafiller (95% with size 20 m) Silane in powder form Protectosil 851 0.5 Metakaolin 2.2 Non-photocatalytic Tioxide R-XL 5 titanium dioxide Hydrophobized vinyl Vinnapas 8034 H 4 polymer Anti-foaming agent Defomex AP 199 1.5 Calcium stearate 0.5

[0050] A water paint was prepared by mixing the aforesaid composition with water in a 60% weight ratio. The water paint was applied on a sample with an average thickness equal to 0.3 mm, and solar light reflectance and heat emittance characteristics thereof were measured. The results are reported in Table 2.

TABLE-US-00002 TABLE 2 Property Standard Measured value Solar reflectance ASTM E1980-11 112 index (SRI) Solar reflectance ASTM C1549-09 88.8% Thermal emittance ASTM C1371-04a 0.86

[0051] The solar reflectance is the fraction of the incident solar radiation that is reflected by an irradiated surface; it can vary from zero for a totally absorbent surface, to 1 (i.e. 100%), for a perfectly reflecting surface. The thermal emissivity is the ratio between the thermal radiation actually emitted by a surface and the maximum theoretical emission at the same temperature; this also varies from 0 to 1. A cover surface with high solar reflectance absorbs only a small part of the incident solar radiation. In addition, most of the solar energy that was absorbed is returned to the outside environment if the cover surface has equally high thermal emissivity.

[0052] The obtained product can thus be labelled Energy Star, ensuring a solar reflectance greater than 65%, placing itself as one of the best products currently on the market.