Solar-reflective granules and process for producing same

Abstract

The reflective particulate material comprises a particulate substrate having high total solar reflectance, bulk density, apparent density, and toughness, and a low dust index. The reflective particulate has a total solar reflectance of 80% to 87%, a fine particle toughness of 1% or less, and a dust index of 2.75 g / cm. 3 The reflective particulate material may have an apparent density of 100 MPa or more and a dust index of 1 or less. A method for producing the reflective particulate material includes preparing a slurry of a particulate substrate, spray drying the slurry to form spray-dried particulates, grinding the spray-dried particulates to form ground particulates, and heating / calcining the ground particulates. The heated ground particulates can be further coated to form coated roofing granules.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 16 / 911,073, filed June 24, 2020, and to U.S. Provisional Patent Application No. 62 / 866,790, filed June 26, 2019, the entire contents of which are incorporated herein by reference.

[0002] (Technical field) FIELD OF THE DISCLOSURE The present disclosure relates to particulate materials and processes for making same, which are useful as solar-reflective granules or granule layers in roofing materials. [Background technology]

[0003] (background) This section provides background information related to the present disclosure that is not necessarily prior art.

[0004] Commercial and residential roofs are continuously exposed to harsh or extreme environmental conditions. Even under less extreme external conditions, roofs are subject to environmental and weather conditions that affect their ability to protect the interior of a building or home from the effects of environmental or weather conditions. During the summer months in many parts of the world, roofs are continuously exposed to high heat and sun conditions, under which roofing materials absorb solar energy and retain high levels of heat. As roofs absorb solar energy and retain heat, conditions within the building or home below deteriorate, often resulting in overheated and uncomfortable interiors. To remedy these conditions, buildings or homes often rely on increased interior insulation or the increased use of engineered cooling systems (e.g., HVAC equipment). However, increased insulation has limited ability to reduce heat transfer, and higher energy costs lead to increased use of engineered cooling systems, which are undesirable and sometimes prohibitive.

[0005] To address this concern and satisfy California government regulations, roofing material manufacturers strive for high total solar reflectance to maintain cooler roof temperatures. However, state-of-the-art roofing materials (such as asphalt and modified bitumen) are black in color and have correspondingly low solar reflectance. To compensate for this shortcoming, some roofing material manufacturers apply light-colored granules to the asphalt or modified bitumen to increase solar reflectance. Unfortunately, to date, many of these light-colored granules or granule layers have only slightly improved solar reflectance, and the solar reflectance of the system is still below the minimum total solar reflectance value for California cool roofs. Summary of the Invention [Means for solving the problem]

[0006] (overview) This section provides a general overview of the disclosure, but is not an exhaustive disclosure of its full scope or of all of its features.

[0007] This disclosure describes particulate materials useful as solar-reflective granules or granule layers in roofing materials and processes for making the same. The particulate or granule materials include solar-reflective granules or particulates having a bulk total solar reflectance (also referred to herein as "total solar reflectance" or simply "solar reflectance") of 70% or greater, as measured using a reflectometer from Surface Optics Corporation (San Diego, California).

[0008] In one aspect, the present disclosure provides a reflective coating having a total solar reflectance of 80% to 87%, a toughness as measured according to ASTM D1865M-09 of 1% or less fine particles, and a glass fiber optics performance of 2.75 g / cm 3 A reflective particulate material is provided that includes a particulate substrate having an apparent density of at least 100 MPa and a dust index of 1 or less.

[0009] In another aspect, the present disclosure provides a process for producing a reflective particulate material. A slurry including a particulate mixture is spray dried to form spray-dried particulates. The spray-dried particulates are milled to form ground particulates. The ground particulates are heated and calcined.

[0010] Further areas of applicability will become apparent from the description provided herein. This summary description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0011] (drawing) The drawings described herein are only for purposes of illustrating selected embodiments rather than all possible implementations and are not intended to limit the scope of the present disclosure.

[0012] These and other features and advantages of embodiments of the present disclosure will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating a system and method for producing uncoated microparticles according to an embodiment of the present disclosure.

[0014] [Figure 2] FIG. 2 is a graph illustrating the effect of mill gap setting on the toughness of uncoated particulates, according to an embodiment of the present disclosure.

[0015] [Figure 3] FIG. 3 is a graph illustrating the effect of kiln temperature on the total solar reflectance (or reflectance) of uncoated microparticles according to an embodiment of the present disclosure.

[0016] [Figure 4] FIG. 4 is a graph showing the correlation between bulk density and toughness (ie, percent fines).

[0017] [Figure 5] FIG. 5 is a graph showing the correlation between reported bulk density and total solar reflectance.

[0018] [Figure 6] FIG. 6 is a schematic diagram showing a conventional process in which granules are extruded, dried, and heated before milling. DETAILED DESCRIPTION OF THE INVENTION

[0019] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

[0020] (Detailed explanation) Exemplary embodiments will now be described more fully with reference to the accompanying drawings.

[0021] As the cost of energy increases, reducing heat transfer from the external environment to the interior working or living spaces of a building becomes increasingly important. The interior spaces of a home or building can generally be kept comfortable by engineered cooling systems (e.g., HVAC systems), but as energy costs rise, so too does the cost of maintaining a comfortable working or living space. As a result, methods for reducing the transfer of heat from the external environment to the interior spaces of a building or residence are desirable. In effect, such reduced heat transfer would reduce the run time of the engineered cooling systems required to maintain a comfortable interior space, thereby reducing the amount of energy consumed by those cooling systems.

[0022] According to embodiments of the present invention, particulate materials are useful as solar-reflective granules or granule layers in roofing materials. The particulate or granule materials include solar-reflective granules or particulates having a bulk total solar reflectance (also referred to herein as "total solar reflectance" or simply "solar reflectance") of 70% or greater as measured using a reflectometer from Surface Optics Corporation (San Diego, California). For example, the 410-Solar visible / NIR portable reflectometer from Surface Optics Corporation (San Diego, California) can be used, which measures reflectance across seven different wavelength bands and then calculates the total solar reflectance using an algorithm. In some embodiments, the particulate or granule material has a solar reflectance of at least 60%, e.g., at least 70% or at least 80%. In some embodiments, coated particulate materials can have a solar reflectance of at least 80%, and in some embodiments, the coated particulate materials can have a total solar reflectance of at least 85% or at least 90%. For example, in some embodiments, the particulate material can have a total solar reflectance of 90% or greater, e.g., in some embodiments, the coated particulate material has a solar reflectance of 60%-95%, 70%-95%, 80%-95%, 70%-90%, 80%-90%, 85%-95%, or 90%-95%.

[0023] In some embodiments, particulate materials can be coated to improve hydrophobicity, stainability, and other performance characteristics. Particulate materials according to embodiments of the present invention can have a total solar reflectance within the ranges described above, regardless of whether the material is coated. However, in some embodiments, uncoated particulate materials can have a total solar reflectance that is different from the corresponding reflectance of a coated counterpart. For example, in some embodiments, uncoated particulate materials can have a total solar reflectance that is higher than the corresponding reflectance of a coated counterpart. Coated and uncoated types of particulate materials can both have total solar reflectances within the same range (described above), or the coated and uncoated types of materials can have different total solar reflectance values ​​within the same range. Indeed, in some embodiments, for example, uncoated particulate materials can have a total solar reflectance of 80% or 90% or more, while coated particulate materials can have a total solar reflectance of 60% or 70% or more.

[0024] As used herein, terms such as “particulate material,” “granular material,” “solar-reflective particulate,” “solar-reflective granules,” “reflective particulate,” and “reflective granules” are used interchangeably and refer to particles or granules of uncoated material described herein. Similarly, terms such as “coated particulate material,” “coated granular material,” “coated solar-reflective particulate,” “coated solar-reflective granules,” “coated reflective particulate,” and “coated reflective granules” are used interchangeably and refer to particles or granules of material described herein after coating. Additionally, while the particulates and granules described herein are promoted for their effectiveness in “cool roof” applications, it should be understood that the described particulates and granules may have other uses and applications, and the described embodiments are not limited to “cool roof” applications. For example, in some embodiments, the particulate or granular material described herein may be useful on any exterior surface, for example, as a filler in exterior paints, or in similar applications.

[0025] According to embodiments of the present invention, the (uncoated) reflective particulate or granule comprises a particulate (or granule) substrate having high total solar reflectance and improved hardness and dust index properties. In some embodiments, the reflective particulate or granule can also have a coating on the particulate substrate, which can provide further improvements in dust index and toughness, as well as improved hydrophobicity and dyeability. The (uncoated) reflective particulate or granule can be coated by any suitable means using any suitable coating material. For example, in some embodiments, the granules may be coated with any of the coatings described in U.S. patent application Ser. No. 16 / 370,303, filed March 29, 2019, entitled "COATED SOLAR REFLECTIVE GRANULES AND METHODS OF MANUFACTURING THE SAME," U.S. Patent No. 10,501,636, filed February 12, 2018, entitled "SOLAR REFLECTIVE PARTICULATES," U.S. Patent No. 10,253,493, filed August 29, 2016, entitled "PARTICULATES HAVING HIGH TOTAL SOLAR REFLECTANCE," and U.S. Patent No. 10,253,493, filed December 8, 2015, entitled "SOLAR REFLECTIVE PARTICULATES," each of which is incorporated herein by reference in its entirety. The coating may be performed using any of the methods and materials disclosed in U.S. Pat. No. 9,890,288 entitled "Polyester-Based Fluorescent Particulates."

[0026] To prepare a final coated microparticle having the above solar reflectance values, the uncoated microparticle substrate must have a relatively high total solar reflectance (i.e., before coating). However, the microparticle substrate is not particularly limited and can include any suitable microparticle substrate having a suitable total solar reflectance value before coating. For example, the substrate should have a sufficiently high solar reflectance when uncoated so that the total solar reflectance of the corresponding coated substrate falls within the above range. For example, in some embodiments, the substrate can include any material that (by itself, i.e., before coating) exhibits a total solar reflectance of 80% or greater. Non-limiting examples of suitable such substrates include transition metal oxides, clays, calcium silicates (e.g., wollastonite), and pyrophyllite. For example, in some embodiments, the substrate can include transition metal oxides, calcium silicates (e.g., wollastonite), pyrophyllite, and / or kaolin clay. In some embodiments, for example, the substrate can include titanium dioxide, pyrophyllite, calcium silicate (e.g., wollastonite), hydrous kaolin clay, and / or calcined kaolin clay. In some embodiments, for example, the substrate can include clay, such as hydrous kaolin clay or calcined kaolin clay, one non-limiting example of which is calcined kaolin chamotte. Non-limiting examples of suitable substrates include calcium silicate (e.g., wollastonite), AS 45 chamotte (e.g., having an SiO content of about 54.9%, an AlO content of about 42.4%, and a KO content of about 1.4%) available from Amberger Kaolinwerke Eduard Kick GmbH & Co. ("AKW") (a subsidiary of Quarzwerke GmbH) (Hirschau, Germany), EPK kaolin (e.g., having an SiO content of about 54.9%, an AlO content of about 42.4%, and a KO content of about 1.4%) available from Edgar Minerals (Edgar, Florida), and EPK kaolin (e.g., having an SiO content of about 54.9%, an AlO content of about 42.4%, and a KO content of about 1.4%) available from Edgar Minerals (Edgar, Florida).93 wt% Fe content, with the reported Fe content adjusted to exclude loss on ignition (LOI) and normalized to 100% total oxide content), MCNAMEE® kaolin available from Vanderbilt Minerals, LLC (Norwalk, Connecticut) (e.g., having an Fe content of about 0.38 wt%, with the reported Fe content adjusted to exclude LOI and normalized to 100% total oxide content), Kingsley kaolin available from Kentucky-Tennessee Clay Company (Roswell, Georgia) (e.g., having an Fe content of 0.45 wt%, with the reported Fe content adjusted to exclude LOI and normalized to 100% total oxide content), 6 TILE® kaolin available from Kentucky-Tennessee Clay Company (Roswell, Georgia) (e.g., having an Fe content of about 0.4 wt% Fe content, with the reported Fe content adjusted to eliminate LOI and normalized to 100% total oxide content), optiKasT kaolin available from Kentucky-Tennessee Clay Company (Roswell, Georgia) (e.g., having an Fe content of about 0.58 wt%, with the reported Fe content adjusted to eliminate LOI and normalized to 100% total oxide content), Ione Airfloated kaolin available from Ione Minerals, Inc. (Ione, California) (e.g., having an Fe content of about 0.7 wt%, with the reported Fe content adjusted to eliminate LOI and normalized to 100% total oxide content), the ASP® product line (e.g., ASP G90 and ASP G92), M17-052 available from BASF Corporation (Florham Park, New Jersey), RT Vanderbilt Company, Inc.(Norwalk, Connecticut) available PYRAX® product line (e.g., Pyrax HS), and the TK product line (e.g., including TK1827, TK1828, TK1912, TK1913, TK1914, TK1915, TK1916, and TK1917, with Fe + Ti contents ranging from 0.5% to 1.8%) available from Thiele Kaolin Company (Sandersville, Georgia).

[0027] The particle size and particle size distribution of the substrate are not particularly limited. Thus, the substrate can have any suitable average particle size and any suitable particle size distribution, and these values ​​can vary depending on the intended use of the granules (e.g., as a cool roof material for commercial or residential roofs, or as a filler in paints). Indeed, in embodiments in which the substrate is a mineral, for example, in embodiments in which the substrate comprises clay (e.g., kaolin clay or calcined kaolin clay), the average particle size and particle size distribution can vary depending on the source or supplier of the substrate.

[0028] According to embodiments of the present disclosure, the uncoated particulate substrate also has high toughness, as well as high total solar reflectance and a smoother surface, a combination of characteristics that is generally difficult to obtain with such uncoated particulates, as increasing bulk density and toughness typically reduces total solar reflectance.

[0029] The toughness of uncoated particulates can be determined by any suitable standard. In some embodiments, for example, toughness is determined according to ASTM D1865M-09, the disclosure of which is incorporated herein by reference. Generally, ASTM D1865M-09 describes a method for determining toughness by comparing the initial particle distribution to the particle distribution after multiple 1.2-meter drops. More specifically, the difference in the percentage of fine particles measured before and after multiple drops indicates how well the particulate withstands the stress of multiple drops; therefore, fewer fine particles after multiple drops (or a smaller difference in the number of fine particles before and after drops) indicates a tougher material (i.e., a higher toughness value). According to some embodiments, for example, the difference in the percentage of fine particles before and after drops (after 100 drops from a height of 1.2 meters), as measured by ASTM D1865M-09, is 0-3%, 0-2%, 0-1.5%, or 0-1%. In some embodiments, the difference in the percentage of fine particles before and after dropping (after 100 drops from a height of 1.2 meters), as measured by, for example, ASTM D1865M-09, can be 0%, 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, or 1.7%.

[0030] In some embodiments, the uncoated microparticles have a bulk density of 1.00 to 2.00 g / cm 3 , 1.00~1.50g / cm 3 , 1.00~1.40g / cm 3 , 1.00~1.30g / cm 3 , or 1.00 to 1.20 g / cm 3 For example, in some embodiments, the bulk density may be 1.05 g / cm 3 , 1.06 g / cm 3 , 1.07 g / cm 3 , 1.08 g / cm 3 , 1.09 g / cm 3 , 1.11 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3, 1.16 g / cm 3 , 1.17 g / cm 3 , 1.18 g / cm 3 , 1.19 g / cm 3 , or 1.20 g / cm 3 Additionally, in some embodiments, the uncoated microparticles may have a density of 2.75 g / cm 3 or more, for example, 2.76 g / cm 3 More than 2.77 g / cm 3 More than 2.78 g / cm 3 or more than 2.79 g / cm 3 In some embodiments, the uncoated microparticles may have an apparent density of 2.79 g / cm or greater. 3 In fact, uncoated microparticles according to embodiments of the present disclosure may have an apparent density of 2.66 g / cm 3 or 2.72 g / cm 3 The apparent density is higher than that of currently available products, which have an apparent density of 1000 .mu.m.

[0031] According to some embodiments, the uncoated microparticles can have a total solar reflectance as described above. In some embodiments, for example, the total solar reflectance (measured using a 410-Solar visible / NIR portable reflectometer from Surface Optics Corporation (San Diego, CA)) can be 80% or greater, e.g., 80% to 95%, 80% to 90%, 80% to 89%, 83% to 90%, 83% to 89%, 84% to 90%, 84% to 89%, 85% to 90%, 85% to 89%, 86% to 90%, 86% to 89%, 87% to 90%, 87% to 89%, 88% to 90%, or 88% to 89%. In some embodiments, for example, the total solar reflectance (measured using a 410-Solar visible / NIR portable reflectometer from Surface Optics Corporation (San Diego, Calif.)) can be 84.8%, 85.3%, 85.7%, 85.9%, 86.5%, 87.2%, 87.3%, 88.0%, 88.1%, 88.2%, 88.3%, 88.4%, 88.5%, or 88.7%.

[0032] In some embodiments, uncoated particulates may also have a lower dust level. The amount of dust in a sample of uncoated substrate particles can be represented by a dust index, which measures the amount of dust in the sample. The dust index can be measured using a DustMon dust measurement device (available from Microtrac Inc., Montgomeryville, PA). The dust index is a measure of the amount of suspended dust in a particle sample. To determine the dust index, particles are dropped into a sample container at the top of a length of pipe, and the particles fall into a sample collector at the other end of the pipe. When the particles land in the sample collector, the airflow and impact force move the sample dust upward and back into a measurement area containing a light source and a detector. The detector observes the change in light intensity from the light source. The sample dust blocks some of the light from the light source, and the detector detects the decrease in light intensity and outputs a dust index based on the decrease in light intensity. The dust index is the sum of the maximum dust concentration and the dust concentration after 30 seconds. Dust concentration is reported as a percentage (%), with 100% meaning complete blockage of light from the source at the detector.

[0033] In some embodiments, the uncoated particulates have a dust index (as measured by DustMon) of less than 3, and in some embodiments, less than 2, or less than 1. For example, in some embodiments, the uncoated particulates may have a dust index of 0.3 to 1.5, e.g., 0.3 to 1.0, 0.4 to 0.9, or 0.5 to 0.8. In some embodiments, the uncoated particulates may have a dust index of 0.5, 0.6, 0.7, or 0.8.

[0034] As a point of comparison, conventional uncoated particulates (e.g., prepared according to conventional processes discussed below) may have a dust index greater than 14; for example, some uncoated clay particles have a dust index of 14.9 to 27.4. Indeed, some coated particulates may have a higher dust index than uncoated particulates according to embodiments of the present disclosure. For example, particulates coated by conventional processes may have a dust index greater than 3, e.g., 3 to 5, 3 to 4, 3.4 to 3.8, or 3.5. As can be seen from this comparison, uncoated particulates according to embodiments of the present disclosure have a significantly reduced dust index compared to both conventional uncoated particulates and some conventional coated particulates.

[0035] According to some embodiments, as generally shown in Figure 1, a system 100 for preparing uncoated particulates described herein includes a slurry mixer 20, a spray dryer 30, a particle mill 40, a first screen 50 (or other particle filter), a kiln 60 (or other heating device), and a second screen 70 (or other particle filter). As shown in Figure 1, the system 100 for preparing uncoated particulates can directly or indirectly deliver the as-prepared uncoated particulates to another system or device 200 for coating the particulates. The slurry mixer 20 is not particularly limited and can be any device or chamber capable of holding and mixing the components of a slurry (discussed further below) and delivering the slurry to the dryer 30.

[0036] According to embodiments of the present disclosure, drying apparatus 30 is a spray dryer. Any suitable spray dryer capable of atomizing the slurry (discussed further below) or thermally spray drying the slurry can be used. Non-limiting examples of suitable spray dryers include those available from GEA Process Engineering A / S Corporation (Denmark). For example, in some embodiments, the spray dryer can be one of the NIRO® line of spray dryers available from GEA Process Engineering A / S Corporation (Denmark).

[0037] Similarly, any suitable particle crushing device can be used as the particle mill. In some embodiments, for example, the crushing device can be a roll mill, although the present disclosure is not limited thereto. Non-limiting examples of suitable particle crushers include those available from JC Steele & Sons Inc. (Statesville, North Carolina), Sturtevant Inc. (Hanover, Maryland), TerraSource Global Corp. (St. Louis, Missouri, e.g., the Gundlach crusher line), Metso Corp. (Finland), and McLanahan Corp. (Holidaysburg, Pennsylvania). However, in some embodiments, the gap setting of the particle crusher can be adjusted to produce uncoated particulates having the toughness and dust index properties described herein. For example, while any suitable gap setting can generally be used, if the gap is set too narrow, additional dust may be generated during toughness testing, increasing the amount of fine particles and decreasing the toughness rating. According to embodiments of the present disclosure, even relatively small or very slight changes in the gap setting of the particle crusher can significantly affect the toughness of the resulting uncoated particulates. In fact, as shown in the graph of FIG. 2, the difference between a wide gap of 0.065 inches and a narrow gap of 0.045 inches results in significantly different fine particle production. For example, as shown in FIG. 2, at the same kiln temperature of 1,250°C, the narrow gap (0.045 inches) produced 8.98% fine particles, while the wide gap (0.065 inches) produced only 2.87% fine particles. As can be seen, even slight adjustments to the mill gap setting can have very beneficial or detrimental effects on the toughness of the resulting uncoated particulates. Therefore, while the gap setting can be adjusted as needed depending on the particles being crushed, in some embodiments, the particle crusher can have a gap setting of 0.06 inches to 0.07 inches.

[0038] The first and second screens (or other particle filters) are not particularly limited and can be any suitable screen or filter capable of retaining larger particles and allowing smaller particles to pass through. One of ordinary skill in the art would be able to select an appropriate screen or filter from the many commercially available options available. However, in some embodiments, both the first and second screens (or filters) 50 and 70 can be double screens (or double screen shakers), with the larger screen retaining particles larger than mesh 8 (i.e., 2,380 microns) and the smaller screen retaining particles larger than mesh 100 (150 microns). Particles that fall between the larger and smaller screens of the first screen 50, i.e., particles smaller than mesh 8 but larger than mesh 100, are delivered directly from the double screen shaker to the kiln 60. Small particles that pass through the smaller screen of the first screen 50, i.e., particles smaller than mesh 100, are returned to the spray dryer 30, where they can be resized and then re-delivered to the mill 40. The larger particles retained on the larger screen of the first screen 50 are returned to the slurry mixer 20 .

[0039] The kiln is also not particularly limited and can be any suitable rotary kiln or similar device. Non-limiting examples of suitable kilns include kilns manufactured by and / or available from Feeco International Inc. (Green Bay, Wisconsin), FLSmidth A / S (Denmark), Claudius Peters AG (Germany), IKD Processing Machinery (Louisville, Kentucky), and Allis-Chalmers Manufacturing Corp. (Milwaukee, Wisconsin). In some embodiments, the kiln may be directly fired or indirectly fired, and in some embodiments, the kiln can be directly fired. Additionally, the kiln can be fired by electricity, natural gas, propane, or other fuel sources. In some embodiments, for example, the kiln can be fired by natural gas as an economical fuel option.

[0040] The kiln temperature can be adjusted to produce uncoated particulates having the total solar reflectance values ​​described herein. For example, while any suitable temperature can generally be used, if the temperature is set too high, the total solar reflectance may be adversely affected, as shown in Figure 3. Indeed, from a morphological standpoint, the particulates may be more susceptible to further drying, metakaolin (2.6 g / cm 3 ) form, spinel transformation (3.58 g / cm 3 ), and the final platelet mullite (3.05 g / cm 3 (TTL) structure under heat. Upon reaching a certain (or critical) temperature, the particulates darken, resulting in increased toughness but decreased total solar reflectance. Therefore, the rotary kiln temperature should be adjusted or set at a threshold or critical temperature to achieve the desired balance between total solar reflectance and toughness. In some embodiments, for example, the kiln temperature can be between 1,050°C and 1,250°C, or between 1,100°C and 1,200°C.

[0041] Kiln temperature and mill settings can also affect the apparent density and bulk density of uncoated particulates according to embodiments of the present disclosure. For example, the bulk density of the resulting uncoated particulates increases with increasing kiln temperature, which leads to the correlation between bulk density and toughness (i.e., percent fines) reported in Figure 4 and the correlation between bulk density and total solar reflectance reported in Figure 5.

[0042] After the rotary kiln, the uncoated particulates are cooled and then passed through the second screen 70 (described above) for further screening. As with the first screen 50, particles separated by the second screen 70 can be recycled back to the slurry mixer 20 or the spray dryer 30. In particular, particles falling between the larger and smaller screens of the second screen 70, i.e., particles smaller than mesh 8 but larger than mesh 100, are delivered directly from the double screen shaker 70 to the coating operation / system 200. Small particles passing through the smaller screen of the second screen 70, i.e., particles smaller than mesh 100, can be returned to the spray dryer 30, where they can be resized and then passed back through the mill 40, the first screen 50, and the kiln 60. Larger particles retained by the larger screen of the second screen 70 can be returned to the slurry mixer 20. It should be understood that while particles exiting the kiln can be recycled in this manner, particles exiting the kiln 60 and the second screen 70 do not necessarily need to be recycled. Indeed, reintroducing the selected fines into the slurry mixer or spray dryer via the return stream for multiple cycles can darken the product, although this risk poses only minor losses.

[0043] According to an embodiment of the present disclosure, a method for preparing uncoated particulates having high total solar reflectance, high bulk and apparent densities, high toughness, and a low dust index includes preparing a particulate slurry, spray-drying the particulate slurry to obtain dried uncoated particulates, grinding the dried uncoated particulates to obtain ground uncoated particulates, and heating (or calcining) the ground uncoated particulates. After heating (or calcining) the ground uncoated particulates, the particulates can be cooled and then coated to form coated solar-reflective granules. As noted above, any suitable coating process and coating material may be used, such as, for example, U.S. Patent Application No. 16 / 370,303, filed March 29, 2019, entitled "COATED SOLAR REFLECTIVE GRANULES AND METHODS OF MANUFACTURING THE SAME"; U.S. Patent Application No. 10,501,636, filed February 12, 2018, entitled "SOLAR REFLECTIVE PARTICULATES"; U.S. Patent Application No. 10,253,493, filed August 29, 2016, entitled "PARTICULATES HAVING HIGH TOTAL SOLAR REFLECTANCE"; and U.S. Patent Application No. 10,253,493, filed December 8, 2015, entitled "SOLAR REFLECTIVE PARTICULATES HAVING HIGH TOTAL SOLAR REFLECTANCE." No. 9,890,288, entitled "Synthetic Methods for Implanting Microorganisms and Microorganisms," entitled "Synthetic Methods for Implanting Microorganisms and Microorganisms," entitled "Synthetic Methods for Implanting Microorganisms and Microorganisms," entitled "Synthetic Methods for Implanting Microorganisms and Microorganisms," and ...For example, in some embodiments, uncoated particulates can be coated using the processes and methods described in U.S. patent application Ser. No. 16 / 370,303, filed March 29, 2019, and entitled "COATED SOLAR REFLECTIVE GRANULES AND METHODS OF MANUFACTURING THE SAME."

[0044] In some embodiments, the slurry can be prepared by mixing the particulate substrate described herein with a suitable dispersant and / or binder. Any suitable dispersant and / or binder can be used without limitation. In some embodiments, for example, the dispersant and / or binder can include anionic polyacrylamides, polyacrylates, polymethacrylates, polyvinyl alcohols, starches, methylcellulose, and the like. As will be appreciated by those skilled in the art, dispersants and binders can have similar chemical structures, but they can differ in their function within the slurry composition and in their molecular size or molecular weight. For example, in some embodiments, the binder can include long-chain polyacrylates, polyalkene carbonates, or polyacrylamides for thickening and / or solidifying the slurry composition, while the dispersant can be a relatively short-chain charged species that can surround particles in the slurry and prevent aggregation due to charge repulsion. The amount of dispersant and / or binder is not particularly limited, but in some embodiments, it can be included in an amount of 0.7 to 1.7% by dry weight. Water is used to adjust the solid content of the slurry, which can be 35% to 65% or 40% to 50%.

[0045] The particulate substrate is mixed with a dispersant and / or binder in a slurry mixer 20 and then delivered to a spray dryer 30. In the spray dryer 30, the slurry can be heated. The slurry can be heated to any suitable degree and / or to any suitable temperature. For example, in some embodiments, the slurry can be heated to a suitable temperature in the spray dryer 30. In some embodiments, the slurry can be at least partially heated using recycled flue gas heat to reduce energy costs and cool the flue gas before environmental treatment. The spray dryer 30 can then thermally spray the slurry onto "seed" particles of the substrate particulate. In this process, the spray dryer 30 sprays layers of slurry onto the seed particles, increasing the diameter or particle size of the uncoated particulate with each layer.

[0046] The particles / particulates output by the spray dryer 30 are typically spherical. However, spherical particles may not be ideal for roofing applications. For example, spherical particles require more weight to be added to the particles to fully cover the surface (compared to more plate-like particles). Spherical particles may also have reduced solar reflectance due to poor packing and may cause safety hazards (e.g., slippage) that could lead to undesirable litigation. Therefore, according to an embodiment of the present disclosure, the spray-dried particles are delivered from the spray dryer 30 to a grinder 40, where the spray-dried particulates are ground and flattened into more plate-like, highly angular particles / granules, and the spherical particles are broken down to a distribution of more plate-like particles that promotes better surface coverage. The grinder and grinder settings are discussed in more detail above, for example, the grinder gap setting is 1.524 mm to 1.778 mm (6 / 100 inch (0.06 inch) to 7 / 100 inch (0.07 inch)).

[0047] According to some embodiments, after milling, the particles can be filtered or screened through a first screen 50 to adjust particle size before being sent to a kiln. As generally discussed above in connection with the structure of the first and second screens 50 and 70, the first screen 50 can separate the particles into three fractions: a first fraction containing particles larger than mesh 8 (i.e., 2,380 microns), a second fraction containing particles smaller than mesh 100 (150 microns), and a third fraction containing particles larger than mesh 100 but smaller than mesh 8. According to embodiments of the present disclosure, the third fraction (i.e., particles smaller than mesh 8 but larger than mesh 100) is delivered directly to the kiln 60, the second fraction (i.e., particles smaller than mesh 100) is returned to the spray dryer 30 where particle size can be obtained and then returned through the mill 40, and the first fraction (i.e., particles larger than mesh 8) is returned to the slurry mixer 20.

[0048] After filtering / screening, the filtered particles are delivered to a kiln where they are heated / calcined at an appropriate temperature. As generally discussed above, the kiln temperature can be selected according to the desired total solar reflectance, bulk density, apparent density, toughness, and dust characteristics. For example, in some embodiments, as also described above, the particles can be heated in a kiln at temperatures between 1,050°C and 1,250°C or between 1,100°C and 1,200°C.

[0049] After heating in the kiln, the particulates are allowed to cool and then filtered / screened again before being delivered to the coating system / operation. As generally discussed above in connection with the first screening, the second screening also separates the particles (from the kiln) into three fractions: a first fraction containing particles larger than mesh 8 (i.e., 2,380 microns), a second fraction containing particles smaller than mesh 100 (150 microns), and a third fraction containing particles larger than mesh 100 but smaller than mesh 8. According to an embodiment of the present disclosure, the third fraction (i.e., particles smaller than mesh 8 but larger than mesh 100) is delivered directly to the coating system / operation 200, the second fraction (i.e., particles smaller than mesh 100) is returned to the spray dryer 30 where particle size can be obtained and then returned via the mill 40 and kiln 60, and the first fraction (i.e., particles larger than mesh 8) is returned to the slurry mixer 20.

[0050] As shown in Figure 1, a method according to an embodiment of the present invention involves spray drying a slurry and milling the spray-dried particulates before delivering the particles to a kiln. In contrast, as shown in Figure 6, conventional methods instead extrude and dry the granules before milling, and then firing them in a kiln. As generally discussed above, particles prepared according to methods according to the present disclosure (i.e., milled, etc., prior to kiln firing) exhibit significantly improved properties and characteristics, including improved total solar reflectance, bulk density, apparent density, toughness, and dust level.

[0051] While various embodiments of the present disclosure have been described, additional modifications and variations will be apparent to those skilled in the art. For example, the compositions and microparticles can have additional components, such as other additives suitable for improving strength, reducing odor, and / or otherwise modifying the properties of the resulting compositions and microparticles, which can be present in various suitable amounts. Similarly, the methods for preparing the compositions and microparticles described herein by way of example embodiments can be modified in accordance with the knowledge of the art to which the various embodiments pertain. For example, the methods for preparing the compositions and microparticles can include additional steps, can be performed at various temperatures, and / or can be otherwise appropriately modified (e.g., as described with respect to the compositions and microparticles). Accordingly, the present disclosure is not limited to the specifically disclosed embodiments, and the compositions, microparticles, and methods for preparing the compositions and microparticles can be modified without departing from this disclosure, limited only by the scope of the appended claims and their equivalents.

[0052] Throughout the text and claims, any use of the word "about" reflects the ambiguity of variations associated with measurement, significant figures, and interchangeability, as will all be understood by one of ordinary skill in the art to which this disclosure pertains. Furthermore, as used herein, the term "substantially" is used as a term of approximation, not as a term of degree, and is intended to account for normal variations and deviations in measurements or evaluations related to compositions, microparticles, and methods of preparing the compositions and microparticles (e.g., in describing the physical or chemical properties of various ingredients or compositions, and describing the amounts of various ingredients). The foregoing description of embodiments is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment generally do not limit that particular embodiment, but are interchangeable where applicable and can be used in selected embodiments even if not specifically shown or described. They are also susceptible to various modifications. Such variations should not be considered a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. The present application provides the following aspects of the invention. (Aspect 1) 80%-87% total solar reflectance, 1% or less fine particles as measured per ASTM D1865M-09, toughness 2.75 g / cm 3 A reflective particulate material comprising a particulate substrate having an apparent density of at least 1000 nm and a dust index of 1 or less. (Aspect 2) 1. A method for producing a reflective particulate material, comprising: preparing a slurry containing the particulate mixture; spray drying the slurry to form spray-dried microparticles; milling the spray-dried microparticles to form milled microparticles; and The method further comprising heating and calcining the ground particulates. (Aspect 3) The method of aspect 2, wherein the heating and calcining of the pulverized particulates comprises heating the pulverized particulates at a temperature of 1,050°C to 1,250°C. (Aspect 4) 3. The method of claim 2, wherein the heating and calcining of the pulverized particulates comprises heating the pulverized particulates at a temperature of 1,100°C to 1,200°C. (Aspect 5) 3. The method of embodiment 2, wherein milling the spray-dried microparticles comprises milling with a mill having a gap setting of 0.06 inches to 0.07 inches. (Aspect 6) 6. The method of claim 5, wherein the heating and calcining of the pulverized particulates comprises heating the pulverized particulates at a temperature of 1,050°C to 1,250°C. (Aspect 7) The method of embodiment 5, wherein the heating and calcining of the pulverized particulates comprises heating the pulverized particulates at a temperature of 1,100°C to 1,200°C.

Claims

1. 1. A method for producing a reflective granule material, comprising: preparing a slurry comprising a particulate mixture, the particulate mixture comprising an uncoated particulate substrate selected from the group consisting of transition metal oxides, clay, calcium silicate, pyrophyllite, and combinations thereof; mixing the slurry with a dispersant and / or binder; spraying the mixed slurry onto seed granules and drying them to form spray-dried granules; milling the spray-dried granules to form milled granules, wherein milling the spray-dried granules comprises milling with a roll mill having a gap setting of 1.524 mm to 1.778 mm (0.06 inch to 0.07 inch); and heating and calcining the ground granules; The method, wherein the reflective granular material has a total solar reflectance of 80% or greater.

2. 10. The method of claim 1, wherein heating and calcining the ground granules comprises heating the ground granules at a temperature of 1,050°C to 1,250°C.

3. 10. The method of claim 1, wherein heating and calcining the ground granules comprises heating the ground granules at a temperature of 1,100°C to 1,200°C.

4. 10. The method of claim 1, wherein the uncoated particulate substrate is selected from transition metal oxides, calcium silicate, and pyrophyllite.

5. 10. The method of claim 1, wherein after the milled uncoated granules are heated and calcined, the granules are cooled and then coated to form coated solar-reflective granules.

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