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: POST-FUNCTIONALIZED ROOFING GRANULES, AND PROCESS FOR PREPARING SAME

Inventors:  Keith C. Hong  Greogry F. Jacobs  Van Nhan Nguyen
Agents:  PAUL AND PAUL
Assignees:
Origin: PHILADELPHIA, PA US
IPC8 Class: AB32B702FI
USPC Class: 428216

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Abstract:
 

Roofing granules having a color coating layer are covered with a clear, transparent or translucent outer coating composition including a functional material, such nanoparticles of anatase titanium dioxide.

Claims:
 

1. A process for preparing functionalized roofing granules, the process comprising:(a) providing base roofing granules having a first coating layer, the first coating layer including at least one coloring material;(b) coating the base roofing granules with a clear, transparent or translucent outer coating composition, the outer coating composition comprising an outer coating binder and at least one functional material; and(c) curing the outer coating composition to form a transparent or translucent outer coating layer on the base roofing granules.

2. A process according to claim 1 wherein the outer coating binder is selected from the group consisting of binders including at least one alkali metal silicate, binders including at least one alkaline earth metal silicate, binders including colloidal silica, binders including at least one metal phosphate, binders including at least one titanate, binders including at least on zirconate, and binders including at least one organic polymer.

3. A process according to claim 1 wherein the at least one functional material is a particulate having an average particle size less than 0.2 microns.

4. A process according to claim 3 wherein the at least one functional particulate material has biocidal activity.

5. A process according to claim 3 wherein the at least one functional particulate material imparts a solar reflectance to the granules of greater than about 25 percent.

6. A process according to claim 1 wherein the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature.

7. A process according to claim 2 wherein the at least one organic polymer is selected from the group consisting of polyurethane polymers, acrylic polymers, polyurea polymers, silicone polymers, siliconized polymers, and sulfo-urethane silanol-based polymers, and their respective copolymers or mixtures hereof.

8. A process for preparing functionalized roofing granules, the process comprising:(a) providing base roofing granules having a first coating layer, the first coating layer including at least one coloring material;(b) coating the base roofing granules with a second coating composition to form a second coating layer over the first coating layer;(c) curing the second coating composition having a second coating layer on the base roofing granules to form intermediate granules;(d) coating the intermediate granules with a transparent or translucent outer coating composition, the outer coating composition comprising an outer coating binder and at least one functional material; and(e) curing the outer coating composition to form a transparent or translucent outer coating layer on the base roofing granules.

9. A process according to claim 8 wherein the second coating composition provides a second coating layer comprising silicon dioxide.

10. A process according to claim 8 wherein the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature.

11. Functionalized roofing granules comprising:(a) base roofing granules having a first coating layer, the first coating layer including at least one coloring material; and(b) a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one functional material.

12. Functionalized roofing granules according to claim 11 wherein the outer coating binder is selected from the group consisting of binders including at least one alkali metal silicate, binders including at least one alkaline earth metal silicate, binders including colloidal silica, binders including at least one metal phosphate, binders including at least one titanate, binders including at least on zirconate, and binders including at least one organic polymer.

13. Functionalized roofing granules according to claims 11 wherein the at least one functional material is a particulate having an average particle size less than 0.2 microns.

14. Functionalized roofing granules according to claim 13 wherein the at least one functional particulate material has biocidal activity.

15. Functionalized roofing granules according to claim 11 wherein the at least one functional particulate material imparts a solar reflectance to the granule of greater than about 25 percent.

16. Functionalized roofing granules according to claim 11 wherein the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature.

17. Functionalized roofing granules according to claim 12 wherein the at least one organic polymer is selected from the group consisting of polyurethane polymers, acrylic polymers, polyurea polymers, silicone polymers, siliconized polymers, and sulfo-urethane silanol-based polymers, and their respective copolymers or mixtures hereof.

18. Functionalized roofing granules comprising:(a) base roofing granules having a first coating layer, the first coating layer including at least one coloring material;(b) a second coating layer over the first coating layer;(c) a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one functional material.

19. Functionalized roofing granules according to claim 18 wherein the second coating layer comprises silicon dioxide.

20. Functionalized roofing granules according to claim 19 wherein the outer coating layer comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder

21. Functionalized roofing granules comprising:(a) base roofing granules; and(b) a coating layer comprising a coating binder, at least one coloring material, and at least one functional material.

22. Functionalized roofing granules comprising:(a) base roofing granules having a first coating layer, the first coating layer including at least one coloring material including an organic compound or ligand;(b) a second coating layer over the first coating layer;(c) a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one photocatalytic functional material.

Description:
 

CROSS-REFERENCE TO RELATED APPLICATION

[0001]The present application claims the priority of provisional application Ser. No. 60/912,830 filed Apr. 19, 2007.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present application relates to roofing granules and roofing products including roofing granules.

[0004]2. Brief Description of the Prior Art

[0005]Asphalt shingles are conventionally used in the United States and Canada as roofing and siding materials. Roofing granules are typically distributed over the upper or outer face of such shingles. The roofing granules, in general formed from mineral materials, serve to provide the shingle with durability. They protect the asphalt from the effects of the solar radiation (in particular from the degradative effects of ultraviolet rays) and of the environment (wind, precipitation, pollution, and the like), and contribute to better reflection of incident radiation. The granules moreover are typically colored, naturally or artificially by way of the application of pigments, to meet the aesthetic requirements of the user.

[0006]However, it is not unusual to see unattractive green, brown or black spots appearing on the surface of asphalt shingles of buildings located in temperate climates. These spots are due to micro-organisms, mainly algae of the Gloeocapsa genus which benefit from conditions favorable to their growth found in temperate climates. These conditions include heat, moisture and nutrients. The essential biogenic salts may be provided by the mineral granules themselves, but also may be supplied by organic matter which settles on the shingles. The unattractiveness of these spots, all the more noticeable when the color of the shingle is a light one, is not the only disadvantage. In addition, the resulting darkening of the surface causes an increase in the absorption of the solar radiation, which in turn reduces the effectiveness of the shingles as thermal insulation, and decreases their service life.

[0007]To address this problem, algae-contaminated shingles can be treated with suitable biocides. However, the complete elimination of the algae is difficult, and requires the treatment of the entire building, including seemingly healthy surfaces. Even by using a powerful biocide such as sodium hypochlorite, the prophylactic effect is not permanent, because the roof is subsequently scrubbed by weather-borne water. Moreover, certain green algae particularly resistant to biocides can re-colonize previously treated surfaces, thus requiring additional treatments, at regular intervals, to limit their reappearance.

[0008]Other methods known to prevent the appearance of the undesirable algae growth are based on the incorporation of algaecide in the shingle. For example, it has been suggested that granules include metal compounds in the form of zinc oxide or sulfide (U.S. Pat. No. 3,507,676), or copper oxide (U.S. Pat. No. 5,356,664), or that a mixture copper oxide and zinc oxide (U.S. Patent Publication 2002/0258835 and U.S. Patent Publication 2002/0255548) be incorporated in the asphalt.

[0009]It has also been suggested to disperse a granular or pulverulent material containing an algaecide on the surface of the shingle (JP-A-2004162482).

[0010]U.S. Pat. No. 6,245,381 suggests adding a biocide in the form of salt or of chelate starting from Cu.sup.2+, Zn.sup.2+ and Sn.sup.2+ ions complexed with an organic binder anion in asphalt during the manufacture of the shingle.

[0011]Another approach has been to employ photocatalytic particles as biocidal agents. The photocatalytic effect has been employed to provide self-cleaning glass and other ceramic materials. For example, U.S. Pat. No. 6,037,289 discloses a substrate provided with photocatalytic anatase titanium dioxide that is at least partially crystalline, and has a mean size of between 5 and 80 nm. The coating can include an inorganic binder, such as an amorphous or partially crystalline oxide, or mixture of oxides, such as oxides of silicon, titanium, tin, zirconium or aluminum, which can serve as a matrix for the photocatalytic titanium oxide. Alternatively, a partly organic binder can be used, such as a binder based on epoxide-containing alkoxysilanes. Similarly, U.S. Pat. No. 6,465,088 discloses a substrate such as a glass or acrylate glazing material covered with a photocatalytic coating including crystallized particles having photocatalytic properties and a mineral binder comprising at least one oxide of a metal having photocatalytic properties. U.S. Pat. Nos. 6,569,520 and 6,881,702 disclose a photocatalytic composition and method for preventing algae growth on building materials such as roofing granules. A plurality of photocatalytic particles, such as anatase titanium dioxide, is dispersed in a silicate binder to form an exterior coating for a substrate such as a roofing granule or concrete surface. At least a portion of some of the photocatalytic particles is exposed on the surface of the coating.

[0012]In general all these approaches aim to provide biocide at the surface of the roofing granules, but also require significant deviations from the conventional techniques for producing such granules, such as formulating, applying and curing one or more interior coatings including biocidal materials, adding functional components such as various biocidal materials to the exterior color coating composition used to provide color to the granules and the roofing shingles formed with such granules, and the like.

[0013]Functional materials are substances that confer special or desirable properties when added to a composition, such as coating composition. Biocides are an example of one class of functional materials. Another type of functional material encountered in the roofing granule art enhances the solar reflectance of the roofing granules. Some materials may have multiple functional characteristics.

[0014]Colored granules have been modified using functional materials to provide special functions to the granules and the shingles or membranes that contain these granules. The most common feature is algae resistance which relies on the metal oxides, such as cuprous oxide, to serve as the algaecides. Solar reflectance is another feature that has been added to the roofing granules by incorporating solar reflective or solar transparent pigments. The major disadvantage of these types of functionalized colored granules is the high cost--usually 10 to 20-fold more expensive than the standard colored granules. The main reason is a combination of complicated manufacturing processes in order to achieve the desired colors and properties, plus the high costs of raw materials (algaecides and/or solar reflective pigments).

[0015]There is a great need for roofing granules to possess an appealing color appearance and to increase functionalities, but remain cost effective.

[0016]Further, there is a continuing need to prevent the appearance of undesirable algae growth on roofing shingles and other roofing materials in an efficient and cost-effective manner.

SUMMARY OF THE INVENTION

[0017]The present invention provides for the addition of special functionalities to standard "commodity" colored granules. In the process of the present invention, colored roofing granules prepared by the conventional coloring process, commonly referred as the "pan coating process," are used as starting core materials. A functionalized outer coating layer that is clear, transparent, or translucent is applied over the colored granules, preferably without significantly altering the original color of the granules. As a result, the costly color matching process that would be otherwise required can be avoided. The conventional pan coating coloring process can be used to apply the outer layer. However, other coating process, such as fluidized bed coating processes, can be used to provide the outer coating layer, but with greater coating coverage and efficiency than the conventional pan coating process. Different coating or binder materials such as those based on siliceous materials (alkali metal silicate, alkali earth metal silicate and various silica chemistries), titanates, zirconates, metal phosphates or polymers can also be used to provide the outer layer.

[0018]Thus, in one aspect, the present invention provides a process for preparing functionalized roofing granules. This process comprises providing base roofing granules having a first coating layer which includes at least one coloring material. The process further comprises coating the base roofing granules with outer coating composition that provides a clear, transparent or translucent outer coating. The outer coating composition comprises an outer coating binder and at least one functional material. The process also comprises curing the outer coating composition to form a clear, transparent or translucent outer coating layer on the base roofing granules. Preferably, the outer coating binder is selected from the group consisting of binders including at least one alkali metal silicate, binders including at least one alkaline earth metal silicate, binders including colloidal silica, binders including at least one metal phosphate, and binders including at least one organic polymer. Preferably, the at least one organic polymer is selected from the group consisting of polyurethane polymers, silane or siliconized polymers, sulfo-urethane silanol-based polymers, and acrylic polymers. In addition, when a particulate material is employed as the at least one functional material, in order to minimize light scattering and increase the transparency or translucency of the outer coating layer, it preferred that the at least one functional material be a particulate having an average particle size less than 0.2 microns. Alternatively, the at least one functional material can have a refractive index near the refractive index of the binder in the wave length range of the visible spectrum. In one presently preferred embodiment, it is preferred that the at least one functional particulate material have biocidal activity, such as nano titanium dioxide materials. In another presently preferred embodiment, it is preferred that the at least one functional particulate material has a solar reflectance greater than about 25 percent, more preferably greater than about 35 percent, and even more preferable greater than about 50 percent. Preferably, in one presently preferred embodiment of the process of the present invention, the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature.

[0019]In another aspect, the present invention provides a process for preparing functionalized roofing granules in which the process comprises two additional steps. In this aspect, the process steps include providing base roofing granules having a first coating layer wherein the first coating layer includes at least one coloring material. However, in this aspect the process also includes the step of coating the base roofing granules with a second coating composition to form a second coating layer over the first coating layer, and the step of curing the second coating composition having a second coating layer on the base roofing granules to form intermediate granules. In this aspect, the process of the present invention also includes coating the intermediate granules with an outer coating composition that provides a clear, transparent or translucent outer coating, wherein the outer coating composition comprises an outer coating binder and at least one functional material, and curing the outer coating composition to form a clear, transparent or translucent outer coating layer on the base roofing granules. In this aspect, the first coating composition preferably provides a first coating layer comprising silicon dioxide. Preferably, the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature.

[0020]The present invention in one aspect also provides functionalized roofing granules comprising base roofing granules having a first coating layer, the first coating layer including at least one coloring material; and a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one functional material. Preferably, the outer coating binder is selected from the group consisting of binders including at least one alkali metal silicate, binders including at least one alkaline earth metal silicate, binders including colloidal silica, binders including at least one metal phosphate, binders including at least on titanate, binders including at least one zirconate, and binders including at least one organic polymer. Preferably, the at least one functional material is a particulate having an average particle size less than 0.2 microns. In one presently preferred embodiment, the at least one functional particulate material has biocidal activity. In another presently embodiment, the at least one functional particulate material imparts a solar reflectance greater than about 25 percent, preferably greater than about 35 percent, and more preferably greater than about 50 percent, to the finished covering on the granule. Preferably, the outer coating composition comprises a colloidal silica binder and photocatalytic anatase titanium dioxide dispersed in the binder, and the outer coating composition is cured at an elevated temperature. Preferably, the at least one organic polymer is selected from the group consisting of polyurethane polymers, acrylic polymers, polyurea polymers, silicone polymers, siliconized polymers, and sulfo-urethane silanol-based polymers.

[0021]In another aspect, the present invention provides functionalized roofing granules comprising base roofing granules having a first coating layer, the first coating layer including at least one coloring material, a second coating layer over the first coating layer, and a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one functional material. Preferably, the first coating layer comprises silicon dioxide. It is also preferred in this aspect of the functionalized roofing granules of the present invention that the outer coating layer comprises a silica binder and photocatalytic anatase titanium dioxide dispersed in the binder.

[0022]In another aspect, the present invention provides functionalized roofing granules comprising base roofing granules, and a coating layer over the base roofing granules, the coating layer comprising a coating binder, at least one coloring material, and at least one functional material.

[0023]In yet another aspect, the present invention provides functionalized roofing granules comprising base roofing granules having a first coating layer, the first coating layer including at least one coloring material including an organic compound or ligand. The functionalized roofing granules further comprise a second coating layer over the first coating layer, as well as a clear, transparent or translucent outer coating layer comprising an outer coating binder and at least one photocatalytic functional material. The second coating layer is preferably formulated as a barrier coating between the first coating layer and the outer coating layer. The at least one coloring material can be a phthalocyanine derivative such as a phthalocyanine blue or phthalocyanine green.