A COATED GRANULE, AND A BITUMINOUS ROOFING MEMBRANE COMPRISING A PLURALITY OF THE COATED GRANULES

Abstract

A coated granule that is suitable for use in a bituminous roofing membrane. The coated granule comprises: i) a granule, the granule comprising cristobalite, ii) a first coating on the surface of the granule, the coating comprising TiO2 in its anatase form and a binder, and iii) an oil barrier coating on the first coating, the oil barrier coating being a compound which will form a bond with a bituminous material, the oil barrier degrading upon exposure to the ultra violet radiation in sunlight and/or the action of rainwater to thereby expose the first coating.

Claims

1. A coated granule suitable for use in a bituminous roofing membrane, said coated granule comprising: i) a granule having a solar transmittance of less than 3% for wave-lengths less than 1400 nm, said granule comprising 20%-100% by weight of cristobalite, ii) a first coating on the surface of the granule, said coating comprising TiO.sub.2 in anatase form and a binder, and iii) a transparent or translucent oil barrier coating on said first coating, said oil barrier coating being an organo-silicon compound which will form a bond with a bituminous material, said oil barrier degrading upon exposure to the ultra violet radiation in sunlight and the action of rainwater to thereby expose said first coating.

2. The coated granule of claim 1, said granule comprising 50%-90% by weight of cristobalite, the balance preferably including another crystalline phase of silica.

3. The coated granule of according to claim 1, the compound defining said oil barrier being polymethylhydrogensiloxane, which may be mixed with an acrylic resin.

4. The coated granule according to claim 1, said binder being a silicate or phosphate binder.

5. The coated granule according to claim 5, said binder comprising monoaluminiumphosphate.

6. The coated granule according to claim 1, said granule having a size in the range 0.325 mm to 2.5 mm.

7. The coated granule according to claim 1, said first coating covering at least 50%, preferably at least 70% of the surface of said granule.

8. The coated granule according to claim 1, said first coating covering at least 60% and at most 90% of the surface of said granule.

9. The coated granule according to claim 1, said first coating having an average thickness in the range of 10 m to 20 m, preferably 5 to 15 m.

10. The coated granule according to claim 1, said first coating having a maximum thickness at any place of 100 m.

11. The coated granule according to claim 1, said first coating comprising said anatase TiO.sub.2 in the form of particles having a size in the order of 0.2 m-0.4 m.

12. A bituminous roofing membrane comprising a bituminous web having a first side, coated granules according to claim 1 being spread over said first side to define a surface of said membrane.

13-15. (canceled)

Description

BRIEF DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0036] An embodiment of the invention will now be described in further details, with reference to FIGS. 1 and 2a and 2b.

[0037] FIG. 1 shows schematically in cross-section and enlarged a portion of a bituminous roofing membrane 1 comprising a bituminous web 11 having on a side thereof a coated granule 10 of the present invention. It will be understood that the shown granules 10 with coating are distributed evenly and densely on the bituminous web 11 to effectively define the visible appearance of the roofing membrane 1.

[0038] Each shown granule 10 is a cristobalite granule/core having a size in the order of 1 mm and carrying directly thereon a first covering or coating layer 5 in the form of a composition comprising or consisting of i) TiO.sub.2 in its anatase form and ii) a binder, such as a monoaluminiumphosphate binder. In this embodiment the thickness of this layer 5 is in the range of 10 to 20 m, with particles of anatase TiO.sub.2 having a size in the order of 0.2 m-0.4 m, such as around 0.3 m, so that the bituminous roofing membrane 1 provides a depolluting effect and at the same time highly desirable TSR and SRI values. Preferably, no granules of other type and no granules having any first coating layer 5 of other composition are distributed onto the bituminous web 11. Specifically, the first coating layer 5 may in one embodiment have the following composition:

TABLE-US-00001 Recipe Recipe 1 Rock raw material Cristobalite in g 1000 Colouration treatment Anatase TiO2 52 White extender (alumino-silicate) 10 Phosphate binder 30 Water 10

[0039] During manufacture of the coated granule 10 an additional second layer is applied directly onto the first coating layer 5 to form an oil barrier defining the outer surface of the coated granule 10. In the membrane 1 a portion 12 of this second layer will be in contact with the bituminous material of the web 11 by the coated granule 10 being partially embedded therein through a rolling procedure during the final steps of the manufacturing of the membrane 1. Another portion 13 of the second layer is exposed to the environment. The second layer forms a firm bond to the first layer 5 and to the bituminous material of the web 11 on the other hand. Specifically, the second layer forms an oil barrier coating, which may be transparent, preventing or restricting migration of oil components of the bituminous web towards the surface of the membrane 1. At the same time the aforementioned portion 13 of the oil barrier (defined by the second layer) is by selection of the compound for the oil barrier, degradable upon exposure to UV-radiation, such as typically after a few days or weeks after application of the membrane on a building roof/building surface, such as after 4 weeks, to thereby expose the first layer 5 and, hence, the titanium dioxide TiO.sub.2 containing first layer to the environment, allowing the anatase TiO.sub.2 to act as a depollutant. In some cases this degradation/exposing of the first layer 5 is assisted by photocatalytic action of the titanium dioxide TiO.sub.2 of the first layer.

[0040] The compound defining the oil barrier may by way of example be an organosilicon compound, such as polymethylhydrogensiloxane, which may be mixed with an acrylic resin. The acrylic resin has the further advantageous effect of binding any free dust particles to the surface of the granules with the oil barrier during the process of manufacturing the coated granules. Such free dust would be of disadvantage when the coated granules are applied to the bituminous web on manufacturing the roofing membrane in causing problems with the adhering of the coated granules to the bituminous web as well as causing possible respiratory health problems to workers making the roofing membrane ; an increased resistance against staining of the roofing membrane may also obtained by this binding, in the case of dust having bitumen oil absorption properties. Examples of useful acrylic resins are compounds having a glass transition temperature of the order of 20 C.-0 C., or chosen in the family of polyacrylate polymers, styrene-acrylic copolymers, or the like.

[0041] FIG. 2a shows a curve representing the reflectance as a function of solar spectrum wavelengths ranging from 200 to 2500 nm, for a bituminous roofing membrane with alumino-silicate granules carrying an anatase TiO.sub.2-containing coating.

[0042] FIG. 2b, on the other hand, shows two curves representing the solar reflectance for a bituminous roofing membrane of the present invention, with granules comprising more than 20% cristobalite and carrying the same coating applied to the granules subject to the analysis in FIG. 2a, i) without any further oil barrier coating and ii) with an oil barrier coating for preventing migrating oil and having the following composition:

TABLE-US-00002 Recipe Recipe 1 Recipe 2 Rock raw material Cristobalite Cristobalite in g 1000 1000 Colouration treatment Anatase TiO2 Anatase TiO2 52 52 White extender White extender (alumino-silicate) (alumino-silicate) 10 10 Phosphate binder Phosphate binder 30 30 Water Water 10 10 Surface treatment Polymethylsiloxane Polymethylsiloxane 0 2.73 Water Water 0 68.63

[0043] Using an oil barrier with an acrylic resin composition has no significant effect on the Total Solar Reflectance as depicted in FIG. 2b; where acrylic resin is used then for the example of recipe 2 the amount of polymethylsiloxane would be as above and water amounting to 65.72 and acrylic resin 2.91.

[0044] As can be seen from the figures, including the blueish TiO.sub.2 in its anatase form in the coating composition defining the first coating layer 5 on granules 10 comprising a relatively high % by weight of cristobalite, allows for a high reflectance, i.e. higher values of the SRI, compared to FIG. 2a, thereby effectively decreasing the temperature of a building onto which the membrane is applied. In this manner a long life bituminous roofing membrane resistant to migrating oil and having depolluting properties and a high SRI is obtained.

[0045] FIG. 3 shows a curve representing the transmittance of several granulates as a function of solar spectrum wavelengths ranging from 200 to 1500 nm. As can be seen, the transmittance of cristobalite raw material is lower than natural sand but higher than natural alumina-silicate such as kaolinite. This means that the cristobalite raw material granules are not fully opaque to solar wavelengths, therefore the total solar reflectance is reduced. The first coating comprising TiO.sub.2 in anatase form (referred to in FIG. 3 as colored cristobalite) allows for a reduction of the transmittance to a lower level than the natural kaolinite granules and similar level as the treated kaolinite granules.