Highly reflective cool roof granule having improved opacity

Abstract

The present disclosure is directed to reflective granules including: at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder, a hardening additive; and a reflective opacifying agent. The present disclosure is also directed to an architectural material, a method for making reflective granules, and a method for making a cool roof substrate.

Description

HIGHLY REFLECTIVE COOL ROOF GRANULE HAVING IMPROVED OPACITYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 677,568, filed on July 31 , 2024, and U.S. Provisional Application No. 63 / 725,276, filed on November 26, 2024, the disclosures of which are hereby incorporated by reference in their entireties.BACKGROUNDField

[0002] The present disclosure relates to reflective granules suitable for use in cool roof applications, the granules having improved opacity.Technical Considerations

[0003] Commercial and residential roofs are continuously exposed to the outside elements, which are often harsh or extreme. Even under moderate external conditions, these roofs are exposed to environmental or weather conditions that affect the ability of the roofs to insulate the building or residence interiors from the effects of the environmental or weather conditions. In many parts of the world, during the summer months, roofs are continuously exposed to high heat and sunny conditions under which the roofing materials absorb solar energy and retain high levels of heat. As the roofs absorb the solar energy and retain heat, the conditions inside the underlying buildings or residences suffer adversely, which often causes the interiors to heat up to uncomfortable conditions.

[0004] In order to remedy these conditions, the buildings or residences often resort to increased amounts of internal insulation, or increased use of artificial cooling systems (e.g., HVAC equipment). However, increasing the amount of insulation has a limited ability to reduce heat transfer, and increasing energy costs make the increased use of artificial cooling systems undesirable or even cost prohibitive.

[0005] Reflective granules have been developed for use as the top covering of roofing systems for buildings to reflect a high percentage of solar radiation to reduce the cooling energy demand. These solar radiation reflective granules, or cool roof granules (CRGs) are commonly applied over and adhere to a modified asphalt substrate as part of a roofing system. The CRG layer not only reflects a largepercentage of solar energy from entering the building but also protects the asphalt substrate from degradation by solar radiation, especially UV lights.

[0006] Total solar reflectance (TSR) of a solar reflective granular product is commonly measured over a thick layer of the granules which may include multiple reflection of multiple layers of the granules. However, in practice, the granules are normally applied to and / or coated over an asphalt substrate as a single layer. The TSR of a product of solar reflective granules measured at the thickness of a single layer represents much better the true reflective performance of the granules. Granules based on silica sand alone (e.g., with a binder and hardening additive) can demonstrate significantly lower TSRs when measured at a single layer thickness than the TSRs measured at multiple layer thickness, due to their partially transparent nature. The application of these materials to an asphalt substrate to form a cool roof shingle can diminish the reflectiveness of the granules due to the transparency of the reflective granules and the absorbing nature of the asphalt substrate.SUMMARY

[0007] The present disclosure relates to reflective granules including: at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent.

[0008] In some non-limiting embodiments or aspects, the binder and the hardening additive may be the same substance.

[0009] In some non-limiting embodiments or aspects, the silica sand-based material may at least partially convert into cristobalite upon kilning.

[0010] In some non-limiting embodiments or aspects, the hardening additive may include a sodium salt or another salt.

[0011] In some non-limiting embodiments or aspects, the binder and the hardening additive may be sodium silicate and / or sodium aluminate.

[0012] In some non-limiting embodiments or aspects, the reflective opacifying agent may include at least one of the following: kaolin clay, aluminum trihydrate (ATH), colloidal silica, nanoparticulate silica different from the silica sand-based mineral, and / or any combination thereof.

[0013] In some non-limiting embodiments or aspects, the reflective granules at a 2 mm thickness may have a total solar reflectance of at least 85%.

[0014] In some non-limiting embodiments or aspects, an asphalt substrate may be coated by a single layer of the reflective granules to form a cool roof substrate, and the cool roof substrate may have a total solar reflectance of at least 65%.

[0015] In some non-limiting embodiments or aspects, the reflective granules may have a transparency index of up to 5%, the transparency index defined by: 1 - (TSR2mm / TSR20mm).

[0016] In some non-limiting embodiments or aspects, the binder and hardening additive may include at least 9 wt-% of the reflective granules, based on total dry weight of the reflective granules.

[0017] In some non-limiting embodiments or aspects, the reflective granules may have an anti-staining coating.

[0018] In some non-limiting embodiments or aspects, the reflective granules may exhibit an L* value of at least 90.

[0019] The present disclosure also relates to an architectural material including the reflective granules as described herein.

[0020] In some non-limiting embodiments or aspects, the architectural material may include an asphalt substrate coated by the reflective granules.

[0021] In some non-limiting embodiments or aspects, the asphalt substrate may be coated by a single layer of the reflective granules to form a cool roof substrate, and the cool roof substrate may have a total solar reflectance of at least 65%.

[0022] In some non-limiting embodiments or aspects, the architectural material may include a roofing material.

[0023] The present disclosure also relates to a method for making reflective granules, the method including mixing at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent.

[0024] The present disclosure also relates to a method for making a cool roof substrate, the method including applying the reflective granules as described herein to an asphalt substrate.

[0025] The present disclosure also includes the following clauses.

[0026] Clause 1 : Reflective granules, comprising: at least 50 wt-% of a silica sandbased mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent.

[0027] Clause 2: The reflective granules of clause 1 , wherein the binder and the hardening additive are the same substance.

[0028] Clause 3: The reflective granules of clause 1 or 2, wherein the silica sandbased material converts at least partially into cristobalite upon kilning.

[0029] Clause 4: The reflective granules of any of clauses 1 -3, wherein the hardening additive comprises a sodium salt or another salt.

[0030] Clause 5: The reflective granules of any of claims 1 -4, wherein the binder and the hardening additive are an alkali metal silicate and / or alkali metal aluminate.

[0031] Clause 6: The reflective granules of any of clauses 1 -5, wherein the reflective opacifying agent comprises at least one of the following: kaolin clay, aluminum trihydrate (ATH), colloidal silica, nanoparticulate silica different from the silica sandbased mineral, and / or any combination thereof.

[0032] Clause 7: The reflective granules of any of clauses 1 -6, wherein the reflective granules at a 2 mm thickness have a total solar reflectance of at least 85%.

[0033] Clause 8: The reflective granules of any of clauses 1 -7, wherein an asphalt substrate coated by a single layer of the reflective granules forms a cool roof substrate, the cool roof substrate having a total solar reflectance of at least 65%.

[0034] Clause 9: The reflective granules of any of clauses 1 -8, the reflective granules having a transparency index of up to 5%, the transparency index defined by: 1 - (TSR2mm / TSR20mm).

[0035] Clause 10: The reflective granules of any of clauses 1 -9, wherein the binder and hardening additive comprise at least 9 wt-% of the reflective granules, based on total dry weight of the reflective granules.

[0036] Clause 11 : The reflective granules of any of clauses 1 -10, wherein the reflective granules exhibit an L* value of at least 90.

[0037] Clause 12: The reflective granules of any of clauses 1 -11 , wherein the reflective granules have an anti-staining coating.

[0038] Clause 13: An architectural material comprising the reflective granules of any of clauses 1 -12.

[0039] Clause 14: The architectural material of clause 13, comprising an asphalt substrate coated by the reflective granules.

[0040] Clause 15: The architectural material of clause 14, the asphalt substrate coated by a single layer of the reflective granules to form a cool roof substrate, the cool roof substrate having a total solar reflectance of at least 65%.

[0041] Clause 16: The architectural material of any of clauses 13-15, wherein the architectural material comprises a roofing material.

[0042] Clause 17: A method for making reflective granules, such as the granules of any of clauses 1 -12, comprising mixing at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent.

[0043] Clause 18: A method for making a cool roof substrate comprising applying the reflective granules of any of clauses 1 -12 to an asphalt substrate.DETAILED DESCRIPTION

[0044] For purposes of the following detailed description, it is understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0045] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in its respective testing measurement.

[0046] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0047] In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in thisapplication, the use of “or” means “and / or” unless specifically stated otherwise, even though “and / or” may be explicitly used in certain instances. Further, in this application, the use of “a” or “an” means “at least one” unless specifically stated otherwise.

[0048] As used herein, the transitional term “comprising” (and other comparable terms, e.g., “containing” and “including”) is “open-ended” and open to the inclusion of unspecified matter. Although described in terms of “comprising”, the terms “consisting essentially of” and “consisting of” are also within the scope of the disclosure.

[0049] As used herein, the term “granular roofing material,” “particulate roofing material,” and like terms, refer to solar reflective particulates or granules that are useful in so-called “cool roof” applications, and these terms are used interchangeably with the terms “solar reflective particulates,” “solar reflective granules,” “reflective particulates,” “reflective granules,” and like terms. Additionally, while the particulates and granules described herein are described in terms of their efficacy in “cool roof” applications, it is understood that the described particulates and granules may have other uses and applications, and that the described embodiments are not limited to use in “cool roof” applications. For example, in some non-limiting embodiments, the particulate roofing materials described herein may be useful on any exterior surface, for example, as a filler in an exterior paint, or like application.

[0050] Reflective granules may include: at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent. Total dry weight of the reflective granules may refer to dry weight of the materials included in the pre-granulation and / or prekilning composition.

[0051] The silica sand-based mineral may comprise a silica sand-based material that converts at least partially into cristobalite upon kilning. For example, in response to the granules undergoing a kilning process, the silica sand-based mineral may undergo a transformation to cristobalite. As used herein, “cristobalite” refers to a crystalline polymorph of silica. The silica sand-based mineral may comprise a powdered material.

[0052] The silica sand-based mineral may comprise at least 50 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as at least 60 wt- %, at least 70 wt-%, at least 75 wt-%, at least 80 wt-%, or at least 85 wt-%.

[0053] The silica sand-based mineral may have a d90 particle size of up to 50 pm, such as up to 25 pm, up to 20 pm, up to 12 pm, up to 10 pm, up to 5 pm, or up to 3 pm, as measured by a laser diffraction particle size analyzer. The silica sand-basedmineral may have a d90 particle size of from 3-50 pm, such as from 5-30 pm, and / or from 10-20 pm. Without being bound to a particular theory, such finer average particle sizes of the silica sand-based mineral are believed to increase reflectivity of a thin layer of the reflective granules applied to a substrate (e.g., an asphalt substrate) due to additional multi-refraction at the air-solid interfaces.

[0054] In order to bind the particles (e.g., granulation) of the materials, a binder may be added. Suitable binders for binding silica sand material may include the class of alkali-metal silicate, such as sodium silicate of various modulus or the wt-% ratios of SiO2 / Na2O. Suitable binders may also include aluminates of alkali metals, specifically sodium silicate of various wt-% ratios of A Oa / SiC . Silicates or aluminates of some other alkali metals or their combinations may also be included in the binder system. Suitable additional binders may also include the class of water-soluble polymers, such as water-soluble synthetic polymers. Water-soluble synthetic polymers may contain hydrophilic functional groups, such as ethers, alcohols, amides, and pyrrolidones. In some non-limiting embodiments or aspects, the binder may comprise polyvinyl alcohol.

[0055] The binder may be added to the raw feed mixture in an amount of from 1 to 20% by weight, such as from 5 to 15% by weight, based on the total dry weight of constituent raw materials.

[0056] The hardening additive may comprise a sodium salt or another salt. Exemplary sodium salts that may form the hardening additive may include sodium silicate, sodium carbonate, sodium hydroxide, or a mixture thereof. In further exemplary embodiments, the sodium salts that may form the hardening additives may include sodium chloride, sodium polyacrylate, sodium sulfate, sodium thiosulfate, sodium phosphate, or a mixture thereof any of the foregoing salts of barium, potassium, calcium, and lithium may alternatively be employed, in embodiments. Hydrated forms of any of the foregoing salts are additionally suitable. Sodium (and other) salts of the foregoing varieties are typically commercially supplied in either a powder or granular / crystalline form. The hardening additive may further function as a fluxing agent for whitening and brightening the reflective granules in some non-limiting embodiments. Some of the alkali metal silicates and / or alkali metal aluminates binders described above may also function in silica sand as a hardening additive during kilning.

[0057] The hardening additive (e.g., and binder) may comprise at least 9 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as atleast 10 wt-%, or at least 12 wt-%. The hardening additive (e.g., and binder) may comprise up to 20 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as up to 18 wt-%, or up to 15 wt-%. The hardening additive (e.g., and binder) may comprise from 9-20 wt-% of the reflective granules, based on total dry weight of the reflective granules, such from 10-18 wt-%, from 9-15 wt-%, or from 12-15 wt-%.

[0058] In some non-limiting embodiments or aspects, the binder and the hardening additive may be the same substance. In some non-limiting embodiments or aspects, the binder and the hardening additive may be different substances.

[0059] The reflective opacifying agent may make the reflective granules opaquer compared to the same granules but without the reflective opacifying agent. The reflective opacifying agent may comprise at least one of the following: kaolin clay, aluminum trihydrate (ATH), colloidal silica, nanoparticulate silica different from the silica sand-based mineral, and / or any combination thereof. The reflective opacifying agent may reduce the transparency of the reflective granules applied over substrate (e.g., an asphalt substrate) while also not reducing or significantly reducing the total solar reflectance of the granules.

[0060] The type or source of the kaolin clay used as the reflective opacifying agent is not particularly limited in the present disclosure. Non-limiting examples of kaolin clay materials include EPK kaolin (e.g., having an Fe content of about 0.93 wt-%, where the reported Fe content is adjusted to exclude loss-on-ignition (LOI) and normalized to a total oxide content of 100%) available from Edgar Minerals (Edgar, FL), MCNAMEE kaolin (e.g., having an Fe content of about 0.38 wt-%, where the reported Fe content is adjusted to exclude LOI and normalized to a total oxide content of 100%) available from Vanderbilt Minerals, LLC (Norwalk, CT), Kingsley kaolin (e.g., having an Fe content of about 0.45 wt-%, where the reported Fe content is adjusted to exclude LOI and normalized to a total oxide content of 100%) available from Kentucky- Tennessee Clay Company (Roswell, GA), 6 TILE kaolin (e.g., having an Fe content of about 0.4 wt-%, where the reported Fe content is adjusted to exclude LOI and normalized to a total oxide content of 100%) available from Kentucky-Tennessee Clay Company (Roswell, GA), optiKasT kaolin (e.g., having an Fe content of about 0.58 wt- %, where the reported Fe content is adjusted to exclude LOI and normalized to a total oxide content of 100%) available from Kentucky-Tennessee Clay Company (Roswell, GA), lone Airfloated Kaolin (e.g., having an Fe content of about 0.7 wt-%, where thereported Fe content is adjusted to exclude LOI and normalized to a total oxide content of 100%) available from lone Minerals, Inc. (lone, CA), kaolin-containing products available from Thiele Kaolin Company (Sandersville, GA), kaolin-containing products available from Imerys S.A. (Paris, France), and kaolin-containing products available from KaMin (Macon, GA). The kaolin clay may comprise calcined kaolin clay. The kaolin clay may be used as a finely milled powder or as a well dispersed slurry for example in an aqueous medium. In response to the granules undergoing the kilning process, the kaolin may undergo a transformation to form a mixture of mullite and amorphous silica.

[0061] The type or source of the aluminum trihydrate (ATH) used as the reflective opacifying agent is not particularly limited in the present disclosure. The ATH may be used as a finely milled powder or as a well dispersed slurry such as in an aqueous medium. In response to the granules undergoing the kilning process, the ATH may undergo a transformation to form dehydrated alumina.

[0062] The type or source of the colloidal silica used as the reflective opacifying agent is not particularly limited in the present disclosure. The colloidal silica may comprise amorphous silica particles of between 10 to 1000 nm and dispersed in a liquid medium such as an aqueous medium through stabilization by various stabilizing agents. In response to the granules undergoing the kilning process, the colloidal silica may undergo a transformation to form amorphous or crystalline silica.

[0063] The type or source of the nanoparticulate silica used as the reflective opacifying agent is not particularly limited in the present disclosure. The nanoparticulate silica used as the reflective opacifying agent may be different from the silica sand-based mineral of the reflective granule. By different is meant that the nanoparticulate silica may be compositionally different, different with respect to one or more physical property, differently prepared, and / or the like compared to the silica sand-based mineral of the reflective granule. For example, the nonparticulate silica may be compositionally the same as the silica sand-based mineral but different with respect to one or more physical properties (e.g. particle size). For example, the nonparticulate silica may be compositionally different from the silica sand-based mineral but the same with respect to one or more physical properties (e.g. particle size). The nanoparticulate silica may comprise nanoparticulate quartz and / or nanoparticulate cristobalite and / or form such material upon kilning. The nanoparticulate silica may comprise precipitated silica and / or silica gels that are non-crystalline. The nanoparticulate silica may havea d50 particle size of less than 1 pm, as measured by a laser diffraction particle size analyzer. The nanoparticulate silica may be prepared as a wet nanoparticulate silica, such as in an aqueous slurry comprising the nanoparticulate.

[0064] The reflective opacifying agent may comprise at least 5 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as at least 10 wt- % or at least 15 wt-%. The reflective opacifying agent may comprise up to 30 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as up to 25 wt-% or up to 20 wt-%. The reflective opacifying agent may comprise from 5-30 wt-% of the reflective granules, based on total dry weight of the reflective granules, such as from 10-25 wt-% or from 10-20 wt-% or from 5-20 wt-%.

[0065] The reflective granules may be prepared from a mixture of dry powder of constituent raw materials, which may contain a varied amount of moisture brought in by the binder system. One or multiple raw materials may also contain some amount of moisture. The raw constituents may be added and mixed with the binder system to form granules of desired sizes, and the thus formed granules are then dried, sized and crushed if necessary. The granulator may be a mechanical mixer, such as a mixer from Eirich Machines. For the bench study listed in this application, a KitchenAid mixer was also used as the granulator.

[0066] The reflective granules may also be prepared from a slurry. The slurry may include a liquid media (e.g., water) in addition to the binder.

[0067] The granules may be dried. In some non-limiting embodiments, a method may further include extruding the wet mixture, or spray granulating the mixture, and drying the extruded or sprayed product. The drying may be performed at any suitable temperature to substantially drive off the liquid media. As used herein, the term “substantially” is a term of approximation, and not a term of degree, and the phrase “substantially drive off the liquid media” is intended to account for inherent deviations in the measurement, calculation or observation of the amount of the liquid media remaining in the mixture after drying. For example, the liquid media would be considered substantially driven off if the amount of liquid media remaining in the mixture is either not detectable or is otherwise negligible, as would be understood by those of ordinary skill in the art.

[0068] The temperature for drying the wet granule is not particularly limited, and it may vary depending on the liquid media selected. However, the temperature should be high enough to substantially drive off the liquid media, but not high enough to constitutea heat treatment or kilning procedure. For example, drying may be performed at a temperature of from 100 °C to 800 °C, such as from 100 °C to 700 °C, from 120 °C to 160QC, or from 130 °C to 150QC. Additionally, the time needed to dry the wet mixture is not particularly limited, and it may vary depending on the consistency of the wet mixture, the liquid media used in the wet mixture, the temperature used to perform the drying, and the amount of the liquid media in the wet mixture. In some non-limiting embodiments, drying is performed for from 10 minutes to 90 minutes, such as from 20 minutes to 70 minutes, or from 30 minutes to 60 minutes.

[0069] In some non-limiting embodiments or aspects, the dried granules may be kilned. The kilning process may be performed at any suitable temperature and for any suitable length of time. For example, in some non-limiting embodiments, the dried mixture may be kilned (or fired) at a temperature of from 900 °C to 1500 °C, such as from 1000 °C to 1300QC, from 1025 °C to 1275QC, or from 1050 °C to 1250QC.

[0070] The reflective granules may have a total solar reflectance (TSR) of at least 85%, when measured by building a 20 mm thick layer of the granules in a cup (TSFfcomm), such as or at least 90%. The reflective granules may have a total solar reflectance of at least 85%, when measured by building a 2 mm thick layer of the granules in a cup (TSFfcmm), such as at least 90%. For example, the 410-Solar visible / NIR Portable Reflectometer from Surface Optics Corporation (San Diego, CA) may be used, which measures reflectance over 7 wavelength bands and uses an algorithm to calculate the TSR. A benchtop reflectometer, Model SSR-R from Devices and Services Co (Dallas, TX), which produces the same data, may also be used.

[0071] The reflective granules may have a transparency index of up to 7%, the transparency index defined by: 1 -(TSR2mm / TSR20mm), such as up to 6% or up to 5% or up to 3% or up to 1 % or 0%.

[0072] The reflective granules may exhibit an L* value (CIELAB Colorspace) of at least 90, such as at least 91 or at least 92, as measured using a colorimeter.

[0073] In some non-limiting embodiments or aspects, a coating and / or surface treatment that does not significantly decrease the reflectance of the granules may be applied to the granules. For example, many suitable coatings and / or surface treatments may be sealants or otherwise clear coatings that do not adversely affect the overall solar reflectance of the granules. In some non-limiting embodiments, the granules may be treated with an emulsion of silicones, silanes, and siloxanes withoutadded solvents. The coating may decrease staining of the granules (e.g., by the asphalt content of the substrate).

[0074] The surface treatments and / or coatings can be applied to the granules using a variety of methods and processes known to those of skill in the art. For example, in one exemplary embodiment, after the raw material has been sized according to the preferred screen size and packaged, the particles can be treated by adding the particles to an aqueous solution, fully saturating the particles with the treatment, and then immediately drying the particles to drive off excess moisture at a temperature not exceeding 600 °F (316°C). In another exemplary embodiment, after the raw material has been sized according to the preferred screen size and packaged, the particles can be post-treated by spraying the particles with an aqueous solution and then immediately drying the particles to drive off excess moisture at a temperature not to exceed 600 °F (316 °C). In yet another exemplary embodiment, after the raw material has been sized according to the preferred screen size, the particles can be treated by spraying the particles with an aqueous solution and then immediately kiln drying the particles to drive off excess moisture at a temperature not to exceed 600 °F (316°C) after which time they can be packaged. In still yet another embodiment of coating and / or treating the surface of granules, after the raw material has been sized according to the preferred screen size, the particles are treated by spraying with an aqueous solution followed by immediately aerating the particles to drive off excess moisture after which time the particles can be packaged. The coatings and / or surface treatments may be applied as delivered (e.g., off the shelf) or from aqueous dilutions. The dilution ratio may range from 1 :5 to 1 :200. The dilutions may be prepared from demineralized water.

[0075] For example, the reflective granules may be treated by applying an anti-staining agent thereto, to coat the reflective granules. The anti-staining agent may protect the reflective granules from being stained by one or more asphalt components, such as when applied to an asphalt substrate to form an architectural material. The antistaining agent may comprise an emulsion of silicones, silanes, and / or siloxanes, such as a modified silicone aqueous emulsion. The anti-staining agent may comprise a fluoropolymer.

[0076] The reflective granules may be used to form an architectural material. The architectural material may comprise a roofing material or other building material. The architectural material may be positioned in an outdoor environment.

[0077] The roofing material may be formed by applying the reflective granules to an asphalt layer to adhere the granules thereto. The asphalt layer may comprise bitumen or modified bitumen, modified with at least one reinforcing material, such as polyester or fiberglass. Such roofing material having the reflective granules applied to an asphalt layer may constitute a cool roof system.

[0078] In some non-limiting embodiments or aspects, the reflective granules may be applied to the asphalt layer in order to adhere the reflective granules thereto. Subsequently, further reflective granules may be applied to the asphalt layer in order to adhere the further reflective granules thereto. The further reflective granules may have a smaller average particle size compared to the reflective granules. The application of the further reflective granules having a smaller average particle size (being finer in particle size) over the reflective granules (being coarser in particle size) may result in better coverage over the asphalt layer by reflective granules, due to the smaller further reflective granules filling in the gaps over the asphalt layer left by the initial application of the larger reflective granules. Thus, the roofing material as a whole may have a higher TSR compared to a roofing material using only a single layer of the coarser solar reflective granules.

[0079] An asphalt substrate coated by a single layer of the reflective granules may form a cool roof substrate. By a “single layer” is meant that the reflective granules are applied over and adhered to the asphalt substrate, forming a single layer of reflective granules over the asphalt substrate, with the remainder of non-adhered reflective granules being cleared away from the resulting cool roof substrate. In some nonlimiting examples, only a single layer of reflective granules may form on the substrate because the reflective granules can adhere to the surface of the substrate but cannot adhere only to other reflective granules. The cool roof substrate having the single layer of granules may have a total solar reflectance of at least 65%.

[0080] The present disclosure is also directed to a method for making reflective granules. The method may include mixing at least 50 wt-% of the silica sand-based mineral, based on total dry weight of the reflective granules; the binder; the hardening additive; and the reflective opacifying agent. The mixture may be granulated to form the granules by building up the materials into granules within or having approximately the desired particle size distribution.

[0081] The granules may be sieved to obtain granules within the desired particle size range and / or distribution. The granules may be sieved to remove undersizedparticulate below the particle size range and / or distribution and / or removing oversize particulate above the particle size range and / or distribution.

[0082] The present disclosure is also directed to a method for making a cool roof substrate comprising applying the reflective granules to the asphalt substrate.EXAMPLES

[0083] The following examples are presented to demonstrate the general principles of the disclosure. The disclosure should not be considered to be limited to the specific examples presented.Examples 1-6 Preparation of Reflective Granules and Cool Roof Substrates

[0084] Reflective granules according to Examples 1 -6 were prepared by mixing the components according to Table 1 . Granulation was mostly carried out in a KitchenAid 4.5 Qt. mixer or in an Eirich L10 mixer. The wet granules made from the mixer were dried in an oven at about 120°C for about 80-90 minutes. The dried granules were sieved at 8 thru 40 mesh US standard. On certain occasions if the yield of the oversize (+8 mesh) fraction was too high, such as more than 10%, the oversize fraction was crushed through a small lab jaw crusher and re-sieved. The combined -8 mesh (-2.36 mm)+40 mesh (+0.425 mm) mesh dry granules were than kilned in a muffle furnace at a temperature between 1 150 to 1190°C for 2 hours. The kilned granules were then surface coated with a modified silicone aqueous emulsion, Silres® BS 5160 from Wacker Chemical Corp. (Munich, Germany) at the dosage of 0.75 wt-%, excluding water in the emulsion. The prepared reflective granules were applied by sprinkling or dropping action over and adhered to a heat-softened atactic polypropylene (APP) modified asphalt substrate in a single layer of about 2 mm thickness to form the cool roof substrate.

[0085] The kilned granules were measured for CIE color space, with the L* component being listed in Table 1 . The granules were also measured for Total Solar Reflectance (TSR) using the benchtop reflectometer, Model SSR-R from Devices and Services Co (Dallas TX). The TSR measurements were carried out with a granule sample packed in a sample cup at a thickness of 20 mm and 2 mm, respectively, with a piece of black paper backing and inside a black cup cover. A transparency index was calculated for each type of granule according to the formula described above. The cool roof substrates (prepared by sprinkling or dropping a single layer of Silres® BS 5160- coated granules onto an APP asphalt substrate) were also measured for TSR. Eachgranule-coated asphalt substrate was measured for TSR on 18 locations and their average values are listed in Table 1 .Table 11 . Calculated from specific surface area listed in the supplier’s tech data sheet.2. Products of PQ Corp. (Malvern, PA)

[0086] As the results from Table 1 indicate, the reflective granules according to the present disclosure have reduced transparency or improved opacity while also maintaining a high TSR at a single layer or 2-mm thickness, both as granules and as a granule coated asphalt substrate. The single layer TSR reflects the actual performance of a highly reflectance cool roof granule product since the common present practice of making a cool roof asphalt substrate is to apply a single layer of the granules.

[0087] It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detailherein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

WHAT IS CLAIMED IS1 . Reflective granules, comprising: at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder; a hardening additive; and a reflective opacifying agent.

2. The reflective granules of claim 1 , wherein the binder and the hardening additive are the same substance.

3. The reflective granules of claim 1 or 2, wherein the silica sandbased material converts at least partially into cristobalite upon kilning.

4. The reflective granules of any of claims 1 -3, wherein the hardening additive comprises a sodium salt or another salt.

5. The reflective granules of any of claims 1 -4, wherein the binder and the hardening additive are an alkali metal silicate and / or alkali metal aluminate.

6. The reflective granules of any of claims 1 -5, wherein the reflective opacifying agent comprises at least one of the following: kaolin clay, aluminum trihydrate (ATH), colloidal silica, nanoparticulate silica different from the silica sandbased mineral, and / or any combination thereof.

7. The reflective granules of any of claims 1 -6, wherein the reflective granules at a 2 mm thickness have a total solar reflectance of at least 85%.

8. The reflective granules of any of claims 1 -7, wherein an asphalt substrate coated by a single layer of the reflective granules forms a cool roof substrate, the cool roof substrate having a total solar reflectance of at least 65%.

9. The reflective granules of any of claims 1 -8, the reflective granules having a transparency index of up to 5%, the transparency index defined by:1 -(TSR2mm / TSR20mm).

10. The reflective granules of any of claims 1 -9, wherein the binder and the hardening additive comprise at least 9 wt-% of the reflective granules, based on total dry weight of the reflective granules.1 1. The reflective granules of any of claims 1 -10, wherein the reflective granules exhibit an L* value of at least 90.

12. The reflective granules of any of clauses 1 -1 1 , wherein the reflective granules have an anti-staining coating.

13. An architectural material comprising the reflective granules of any of claims 1 -12.

14. The architectural material of claim 13, comprising an asphalt substrate coated by the reflective granules.

15. The architectural material of claim 14, wherein the asphalt substrate is coated by a single layer of the reflective granules forming a cool roof substrate, the cool roof substrate having a total solar reflectance of at least 65%.

16. The architectural material of any of claims 13-15, wherein the architectural material comprises a roofing material.

17. A method for making reflective granules, comprising mixing at least 50 wt-% of a silica sand-based mineral, based on total dry weight of the reflective granules; a binder, a hardening additive; and a reflective opacifying agent.

18. A method for making a cool roof substrate comprising applying the reflective granules of any of claims 1 -12 to an asphalt substrate.

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