PHOTOCATALYTIC COMPOSITION BASED ON AN AERIAL BINDER AND USE THEREOF FORTHE PRODUCTION OF WATER-BASED PAINTS, IN PARTICULAR FOR INTERIOR APPLICATIONS

Abstract

A photocatalytic composition comprising: (a) at least one aerial binder; (b) at least one photocatalyst; (c) at least one cellulose ether; (d) at least one fluidizing agent; (e) at least one pumice in the form of micronized powder; (f) at least one barite in the form of micronized powder. This composition can be used as water-based paint for preparing wall coatings having a very low thickness, in particular for interior applications, which guarantee a high photocatalytic effect and stable with time, even with relatively low quantities of photocatalyst, normally lower than 10% by weight. This coating also has marked inhibitory properties with respect to the growth of mold and bacteria on wall surfaces.

Claims

1. A photocatalytic composition comprising: (a) at least one aerial binder; (b) at least one photocatalyst; (c) at least one cellulose ether; (d) at least one fluidizing agent; (e) at least one pumice in the form of micronized powder; (f) at least one barite in the form of micronized powder.

2. The photocatalytic composition according to claim 1, comprising: (a) from 15 to 60% by weight, of at least one aerial binder; (b) from 0.5 to 12% by weight, of at least one photocatalyst ; (c) from 0.02 to 3% by weight, of at least one cellulose ether; (d) from 0.05 to 5% by weight, of at least one fluidizing agent; (e) from 5 to 40% by weight, of at least one pumice in the form of micronized powder; (f) from 1 to 20% by weight, of at least one barite in the form of micronized powder.

3. The photocatalytic composition according to claim 1, wherein the aerial binder (a) is selected from: hydrated lime, chalk or mixtures thereof .

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

5. The photocatalytic composition according to claim 4, wherein the photocatalytic titanium dioxide has a particle-size which is such that at least 95% by weight has a dimension not exceeding 50 nm.

6. The photocatalytic composition according to claim 4, wherein the photocatalytic titanium dioxide is mixed with non-photocatalytic titanium dioxide.

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

8. The photocatalytic composition according to claim 1, wherein the pumice (e) is a noncrystalline silica (NCS), in the form of particles of which at least 95% by weight has a dimension not exceeding 100 ?m.

9. The photocatalytic composition according to claim 1, wherein the barite (f) is in the form of micronized powder, of which at least 95% by weight has a dimension not exceeding 80 ?m.

10. The photocatalytic composition according to claim 1, which also comprises: (g) at least a first calcareous filler in particle form, of which at least 95% by weight has a dimension not exceeding 100 ?m; (h) at least a second calcareous filler in particle form, of which at least 95% by weight has a dimension not exceeding 30 ?m.

11. The photocatalytic composition according to claim 10, wherein the first calcareous filler (g) is in particle form, at least 95% by weight of which has a dimension not exceeding 70 ?m whereas the second calcareous filler (h) is in particle form, of which at least 95% by weight has a dimension not exceeding 20 ?m.

12. The photocatalytic composition according to claim 10, wherein the calcareous fillers (g) and (h) are present in a weight ratio (g)/(h) ranging from 0.2 to 2.0.

13. The photocatalytic composition according to claim 1, which also comprises at least one vinyl versatate polymer (i).

14. he photocatalytic composition according to claim 1, which also comprises: (j) at least a salt of a long-chain carboxylic acid.

15. Use of a photocatalytic composition according to claim 1, for the internal coating of building components, in order to reduce the presence of polluting agents, to abate the total bacterial count and to eliminate unpleasant odours.

16. The photocatalytic composition according to claim 1, comprising: (a) from 20 to 50% by weight, of at least one aerial binder; (b) from Ito 8% by weight, of at least one photocatalyst ; (c) from 0.05 to 1.5% by weight, of at least one cellulose ether; (d) from 0.1 to 2% by weight, of at least one fluidizing agent; (e) from 10 to 30% by weight, of at least one pumice in the form of micronized powder; (f) from 3 to 15% by weight, of at least one barite in the form of micronized powder.

17. The photocatalytic composition according to claim 4, wherein the photocatalytic titanium dioxide has a particle-size which is such that at least 95% by weight has a dimension not exceeding 20 nm.

18. The photocatalytic composition according to claim 5, wherein the photocatalytic titanium dioxide is mixed with non-photocatalytic titanium dioxide.

19. The photocatalytic composition according to claim 1, wherein the cellulose ether (c) has a Brookfield RVT viscosity at 20? C. ranging from 100 to 30,000 mPa.Math.s.

20. The photocatalytic composition according to claim 1, wherein the cellulose ether (c) has a Brookfield RVT viscosity at 20? C. ranging from 200 to 10,000 mPa.Math.s

21. The photocatalytic composition according to claim 1, wherein the pumice (e) is a noncrystalline silica (NCS), in the form of particles of which at least 95% by weight has a dimension not exceeding 80 ?m.

22. The photocatalytic composition according to claim 1, wherein the pumice (e) is a noncrystalline silica (NCS), which is an amorphous aluminium silicate, in the form of particles of which at least 95% by weight has a dimension not exceeding 100 ?m.

23. The photocatalytic composition according to claim 1, wherein the pumice (e) is a noncrystalline silica (NCS), which is an amorphous aluminium silicate, in the form of particles of which at least 95% by weight has a dimension not exceeding 80 ?m.

24. The photocatalytic composition according to claim 10, wherein the calcareous fillers (g) and (h) are present in a weight ratio (g)/(h) ranging from 0.5 to 1.5.

25. The photocatalytic composition according to claim 11, wherein the calcareous fillers (g) and (h) are present in a weight ratio (g)/(h) ranging from 0.2 to 2.0.

26. The photocatalytic composition according to claim 11, wherein the calcareous fillers (g) and (h) are present in a weight ratio (g)/(h) ranging from 0.5 to 1.5.

27. The photocatalytic composition according to claim 1, which also comprises at least one vinyl versatate polymer (i) in a quantity ranging from 1 to 20% by weight.

Description

EXAMPLE 1

[0057] A photocatalytic composition according to the present invention was prepared by mixing the following components in the quantities indicated in Table 1.

TABLE-US-00001 TABLE 1 Quantity Component Characteristics (% weight) Hydrated lime 20 Photocatalytic titanium Surface area: 350 m.sup.2/g 5 dioxide Particle-size <50 nm (min. 95%) Cellulose ether Brookfield viscosity RVT at 0.8 (methylhydroxypropyl 20? C.: cellulose) 400-600 mPa .Math. s Super-fluidizing agent Polycarboxylic polyether 0.5 Calcareous micronized filler ?95% with dimensions 20 ?60 ?m Calcareous ultra-filler ?95% with dimensions 20 ?20 ?m Micronized pumice Average particle-size: 15 ?m 20 Micronized barite D.sub.90: 37 ?m 3 Non-photocatalytic titanium Average particle-size: 0.3 ?m 4.7 dioxide Vinyl versatate polymer 4 Antifoaming agent 1.5 Calcium stearate 0.5

[0058] A water-based paint was prepared by mixing the above-mentioned composition with water in a weight ratio of 60%. The water-based paint was applied on a sample with an average thickness of 0.3 mm and the characteristics relating to the reflectance of solar light and heat emittance were measured. The results are indicated in Table 2

TABLE-US-00002 TABLE 2 Measured Property Standard value Solar reflectance index (SRI) ASTM E1980-11 109 Solar reflectance ASTM C1549-09 88.4% Heat emittance ASTM C1371-04a 0.83

[0059] The solar reflectance is the fraction of incident solar radiation which is reflected by an irradiated surface; the same ranges from zero for a totally absorbing surface, to 1 (i.e. 100%), for a perfectly reflecting surface. The heat emittance is the ratio between the thermal radiation actually emitted by a surface and the maximum theoretical heat emission at the same temperature; this also ranges from 0 to 1. A covering surface having a high solar reflectance absorbs only a small part of the incident solar radiation. Furthermore, most of the solar energy that has been absorbed is returned to the outside environment if the covering surface has an equally high thermal emittance.

[0060] A high reflectance index of surfaces coated with the photocatalytic composition according to the present invention allows a saving of electric energy for illumination, in houses, offices, schools, etc. To obtain the same luminosity, in fact, the energy consumption of the light sources (lamps and similar) is reduced.

[0061] The photocatalytic composition according to the present invention has also been evaluated with respect to the capacity of hindering the growth of mold and bacteria. [0062] (a) Resistance to the Growth of Mold

[0063] A sample of the composition described above was dispersed in deionized water (water 60%, powder 40%). After careful mixing, the product was applied with a brush on a panel of inert polyester, so as to obtain a thin layer which was dried in the air for 24 h. After drying, three samples of the treated panel were collected under aseptic conditions (dimensions: 3 inches?4 inches) (samples 1, 2 and 3). The capacity of hindering the growth of mold was evaluated on the three samples according to the method ASTM D 3273-12 Standard Test method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber.

[0064] Contrary to what is envisaged by the above standard, the samples were subjected to UV radiation with an intensity of about 0.1 mW/cm.sup.2 for the whole incubation period of four weeks. The incubation chamber contained a bed of soil strewn with spores of Aspergillus niger ATCC*6275, Penicillium citrinum ATCC*9849 and Aureobasdium pullulans ATCC*9348. The chamber was kept at 32.5?1? C. with a relative humidity of 95?3%. The three samples of treated panel (Samples 1, 2 and 3) were hung inside the chamber, together with a further three comparative samples of the same non-treated panel (Samples 4, 5 and 6). The samples were kept in the chamber for four weeks under UV radiation, as indicated above. The samples were examined every week to verify the fungal growth on their surface. A score was attributed with each test, based on the area percentage of the sample that was visually altered due to fungal growth, according to the following Table 3:

TABLE-US-00003 TABLE 3 % of altered Score surface 10 0 9 1-10 8 11-20 7 21-30 6 31-40 5 41-50 4 51-60 3 61-70 2 71-80 1 81-90 0 91-100

[0065] The results are indicated in the following Table 4:

TABLE-US-00004 TABLE 4 Sample 1? week 2? week 3? week 4? week 1 10 10 10 10 2 10 10 10 9 3 10 10 10 9 4 * 10 8 7 4 5 * 10 8 7 4 6 * 10 8 7 5 * comparison

[0066] The results obtained show a high capacity of the photocatalytic composition according to the present invention of preventing the growth of fungi, keeping its surface unaltered even after exposure to fungal spores for four weeks in a humid environment at a high temperature. It should be noted that the photocatalytic effect on the fungal growth is also exerted with a relatively low UV irradiation intensity (around 0.1 Mw/cm.sup.2). [0067] (b) Resistance to Bacterial Growth

[0068] Three samples (50 mm?50 mm) of the same treated panel according to what is described above, were used for evaluating the resistance to the growth of bacteria, compared with three samples having the same dimensions without treatment. The evaluation was made according to standard ISO 27447:2009(E), Test Method for Antibacterial Activity of Semiconducting Photocatalytic Materials.

[0069] The samples were exposed to the attack of Escherichia coli ATCC*8739 (initial inoculum equal to 4.2?10.sup.5 CFU/mL) and Staphylococcus aureus ATCC*6538P (initial inoculum equal to a 3, 6?10.sup.5 CFU/mL). The tests were carried out separately for each microorganism. The initial amount of inoculum was equal to 0.3 mL. The chamber was kept at 35? C. The three samples of the treated panel (Samples 1, 2 and 3) were hung inside the chamber into which the bacterium was inoculated, the bacterial growth was verified at time zero and after eight hours, under UV radiation (0.109 mW/cm.sup.2) using a sterile adhesive film Whirlpak? (40 mm?40 mm?0.05 mm).

[0070] For both bacteria, the reduction in the population after eight hours of UV radiation was equal to 99.998%.