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  Colored roofing granules with increased solar heat reflectance, solar heat-reflective shingles, and process for producing sameRelated Patent Categories: Coating Processes, Particles, Flakes, Or Granules Coated Or EncapsulatedThe Patent Description & Claims data below is from USPTO Patent Application 20080008832. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application is a division of U.S. application Ser. No.10/679,898 filed Oct. 6, 2003. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to asphalt roofing shingles, and protective granules for such shingles, and processes for makings such granules and shingles. [0004] 2. Brief Description of the Prior Art [0005] Pigment-coated mineral rocks are commonly used as color granules in roofing applications to provide aesthetic as well as protective functions to the asphalt shingles. Roofing granules are generally used in asphalt shingle or in roofing membranes to protect asphalt from harmful ultraviolet radiation. [0006] Roofing granules typically comprise crushed and screened mineral materials, which are subsequently coated with a binder containing one or more coloring pigments, such as suitable metal oxides. The binder can be a soluble alkaline silicate that is subsequently insolubilized by heat or by chemical reaction, such as by reaction between an acidic material and the alkaline silicate, resulting in an insoluble colored coating on the mineral particles. Preparation of colored, coated roofing granules is disclosed for example, in U.S. Pat. No. 2,981,636 of Lodge et al. The granules are then employed to provide a protective layer on asphaltic roofing materials such as shingles, and to add aesthetic values to a roof. [0007] U.S. Pat. No. 2,732,311 of Hartwright discloses a method for preparing roofing granules having metal flakes, such as aluminum flakes, adhered to their surfaces, to provide a radiation-reflective surface. Rock granules are first mixed with kaolin clay, and then a stream of sodium silicate solution is added. A tacky viscous film is developed on the surface of the granules by passing air through the mixture while it is being mixed, and a fine grade of metal flakes are added, and the flake-coated granules are subsequently fired to cure the clay-silicate binder. [0008] Pigments for roofing granules have usually been selected to provide shingles having an attractive appearance, with little thought to the thermal stresses encountered on shingled roofs. However, depending on location and climate, shingled roofs can experience very challenging environmental conditions, which tend to reduce the effective service life of such roofs. One significant environmental stress is the elevated temperature experienced by roofing shingles under sunny, summer conditions, especially roofing shingles coated with dark colored roofing granules. Although such roofs can be coated with solar reflective paint or coating material, such as a composition containing a significant amount of titanium dioxide pigment, in order to reduce such thermal stresses, this utilitarian approach will often prove to be aesthetically undesirable, especially for residential roofs. [0009] Asphalt shingles coated with conventional roofing granules are known to have low solar heat reflectance, and hence will absorb solar heat especially through the near infrared range (700 nm-2500 nm) of the solar spectrum. This phenomenon is increased as the granules covering the surface become dark in color. For example, while white-colored asphalt shingles can have solar reflectance in the range of 25-35%, dark-colored asphalt shingles can only have solar reflectance of 5-15%. Furthermore, except in the white or very light colors, there is typically only a very small amount of pigment in the conventional granule's color coating that reflects solar radiation well. As a result, it is common to measure temperatures as high as 77.degree. C. on the surface of black roofing shingles on a sunny day with 21.degree. C. ambient temperature. Absorption of solar heat may result in elevated temperatures at the shingle's surroundings, which can contribute to the so-called heat-island effects and increase the cooling load to its surroundings. [0010] There is a continuing need for roofing materials, and especially asphalt shingles, that have improved resistance to thermal stresses while providing an attractive appearance. In particular, there is a need for roofing granules that provide increased solar heat reflectance to reduce the solar absorption of the shingle, while providing a wide range of colors including deep-tone colors to maintain the aesthetic value of the system. SUMMARY OF THE INVENTION [0011] The present invention provides roofing granules that provide increased solar heat reflectance, while providing deep-tone colors, as well as a process for preparing such roofing granules, and asphalt shingle roofing products incorporating such roofing granules. [0012] In one aspect of the present invention, roofing granules are colored by the combination of a binder, for example, a metal silicate binder or polymeric binder suitable for outdoor exposure, and special pigments that have high reflective properties towards the solar heat radiation while simultaneously serving as a colorant. Specifically, colored, infrared-reflective pigments, such as those disclosed in U.S. Pat. No. 6,174,360 and comprising a solid solution including iron oxide, can be employed in producing the colored infrared-reflective roofing granules of the present invention. The colored, infrared-reflective pigment can also comprise a near infrared-reflecting composite pigment such as disclosed in U.S. Pat. No. 6,521,038. Composite pigments are composed of a near-infrared non-absorbing colorant of a chromatic or black color and a white pigment coated with the near infrared-absorbing colorant. [0013] In addition to or in the alternative to employing colored, infrared-reflective pigments selected from the group consisting of a solid solution including iron oxide and near infrared-reflecting composite pigments, infrared-reflective roofing granules of the present invention can be prepared using infrared-reflective "functional" pigments. Infrared-reflective functional pigments include light-interference platelet pigments including titanium dioxide, light-interference platelet pigments based on metal oxide coated-substrate, mirrorized silica pigments based upon metal-doped silica, and alumina. Such infrared-reflective functional pigments have been found to enhance the solar heat reflectance when incorporated in roofing granules. [0014] Thus, in one aspect, the process of the present invention provides roofing granules colored by light-interference platelet pigments and/or infrared ("IR")-reflective color pigments to achieve higher solar heat reflection. These "pearlescent" pigments based on metal oxide-coated substrates allow additional solar reflection to achieve both colors and increased solar heat reflection. Light-interference platelet pigments based on metal oxide coated-substrates are preferably selected from those pigments constructed from partially opaque substrates, such as mica, alumina, or silica, and metal-oxide coatings having light-interference properties. [0015] In another aspect of the present invention, colored infrared-reflective roofing granules are provided by coating inert mineral particles with a first coating composition including a binder and at least one reflective white pigment, and curing the first coating composition on the inert mineral particles to form base particles. The base particles are then coated with a second coating composition including a binder and at least one colorant selected from the group consisting of uv-stabilized dyes and granule coloring pigments, and the second coating composition is then cured. The granule coloring pigments can be conventional granule coloring pigments based on metal oxides, or colored infrared-reflective pigments. Optionally, the second coating composition can include at least one infrared-reflective functional pigment. [0016] In yet another aspect of the present invention, colored infrared-reflective roofing granules are provided by a process comprising providing an inert mineral particle and coating the inert mineral particles with a first coating composition including a base particle binder, and at least one colorant selected from the group consisting of uv-stabilized dyes and granule coloring pigments, and curing the first coating composition on the inert particles to form base particles. The base particles are then coated with a second coating composition including a coating binder, and at least one infrared-reflective functional pigment selected from the group consisting of light-interference platelet pigments including mica, light-interference platelet pigments including titanium dioxide, mirrorized silica pigments based upon metal-doped silica, and alumina, and the second coating composition is then cured. [0017] Coating compositions employed by the present invention can include metal-silicate binders or organic polymeric binders. Organic binders advantageously permit lower curing temperatures than metal-silicate binders, and do not require additional surface treatment for water repellency and staining resistance, and/or slate oils to reduce dusting during transportation. [0018] The process of the present invention produces colored infrared-reflective roofing granules that have a higher solar heat reflectance than colored roofing granules prepared using conventional metal oxide colorants, which typically have a solar heat reflectance of from about 12 percent to about 20 percent. Thus, it is preferred that the colored infrared-reflective roofing granules of the present invention have a solar heat reflectance greater than about 20 percent. It is especially preferred that the colored infrared-reflective roofing granules according to the present invention have a solar heat reflectance of at least about 25 percent, and that bituminous roofing products, such as asphaltic roofing shingles, made with such colored infrared-reflective roofing granules have a solar heat reflectance of at least about 20 percent, more preferably at least about 25 percent, with a solar heat reflectance of at least about 30 percent being especially preferred. [0019] The present invention also provides a process for increasing the solar or infrared reflectance of a colored roofing granules by at least about 20 percent, more preferably at least about 25 percent, while substantially maintaining the color of the roofing granules, such that the value of the total color difference .DELTA.E* is no more than 10 units, more preferably no more than 5 units, and even more preferably no more than 3 units. [0020] In general, the process of the present invention for producing colored, infrared-reflective roofing granules comprises (a) providing base particles; (b) coating the base particles with a coating composition including (i) a coating binder, and (ii) at least one infrared-reflective pigment, and (c) curing the coating composition to form coated granules. As noted above, the colored, infrared-reflective roofing granules of the present invention can be colored in a variety of different ways. First, the infrared-reflective pigment itself can be colored. Alternatively, the infrared-reflective pigment can be a "functional" pigment that contributes to the color of the granules, but may be supplemented by other colorants. Finally, the color of the granules can be supplied largely by conventional colorants, with the infrared-reflectance being attributable to other materials. [0021] The colored, infrared-reflective granules of the present invention preferably have a relatively dark shade, characterized by a value of L* of less than 85, more preferably, less than 55, and even more preferably less than about 45. Continue reading... Full patent description for Colored roofing granules with increased solar heat reflectance, solar heat-reflective shingles, and process for producing same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Colored roofing granules with increased solar heat reflectance, solar heat-reflective shingles, and process for producing same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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