Abstract:
The retention of roofing granules on bituminous roofing products is enhanced by providing an adherent material in the interstices between the exterior surface of the roofing granules and the exposed upper surface of the base sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates to bituminous roofing products such as asphalt-based roofing membranes and processes for making such roofing products. 
     2. Brief Description of the Prior Art. 
     Asphalt-based roofing membranes are excellent waterproofing materials that have been extensively used in low-slope roofing systems to provide long-lasting and satisfactory roof coverings. Low-slope roofing systems are extensively used for commercial and industrial buildings. Examples of low-slope roofing systems are built-up roofs (BUR), modified bitumen roofs, and single-ply or membrane roofing systems. Asphalt-based roofing membranes are frequently used as waterproofing underlayment in low-rise roofing systems, as well as the uppermost or finish layer in built-up-roofs. Built-up roofs are sometimes covered with a layer of gravel or granular mineral material to protect the roofing membrane against mechanical damage. 
     Mineral-surfaced asphalt shingles, such as those described in ASTM D225 or D3462, are generally used for steep-sloped roofs to provide water-shedding function while adding aesthetically pleasing appearance to the roofs. Conversely, roll goods such as asphalt-based roofing membranes are generally used for low-slope roofs. Pigment-coated mineral particles are commonly used as color granules in roofing applications to provide aesthetic as well as protective functions. Roofing granules are generally used in asphalt shingles or in roofing membranes to protect asphalt from harmful ultraviolet radiation. 
     Roofing products such as asphalt shingles and roll stock are typically composite articles including a non-woven glass fiber or felt web covered with a coating of water repellent bituminous material, and optionally surfaced with protective mineral-based roofing granules. The bituminous material is characteristically black in color, and is strongly absorptive of incident solar radiation. Thus, asphalt-based roofing membranes can absorb significant amounts of solar radiation, which can result in elevated roof temperatures. This can contribute to the increase of energy usage for indoor air-conditioning, especially in a hot climate. 
     Asphalt shingles are generally constructed from asphalt-saturated roofing felts and surfaced by pigmented color granules. Asphalt-based roofing membranes are similarly constructed; except that roofing granules are not frequently employed. However, both asphalt shingles and asphalt-based roofing membranes are known to have low solar reflectivity and hence will absorb solar heat especially through the near-infrared range of the solar spectrum. 
     This phenomenon increases as the surface becomes dark in color. For example, white-colored asphalt shingles with CIE L* greater than 60 can have solar reflectance greater than 25% (ASTM E1918 method), whereas non-white asphalt shingles with L* less than 60 typically have solar reflectance in the range of only 5-20%. As a result, it is common to measure temperatures as high as 71-77 degrees C. (160-170 degrees F.) on the surface of dark roofing shingles on a sunny day with 27 degree C. (80 degrees F.) ambient temperature. 
     Reduced energy consumption is an important national goal. For example, the State of California has a code requirement that all commercial roofing materials in low-slope applications need to exceed a minimum of 70% solar reflectance in order to meet California&#39;s energy budget code. Also, in order to qualify as Energy Stare® roofing material, a roofing membrane needs to exceed 65% solar reflectance. 
     Typically, even a white mineral-surfaced, asphalt-based roofing membrane has only 30-35% solar reflectance. 
     In order to address this problem, externally applied coatings have sometimes been applied directly onto the shingle or membrane surface on the roof. White pigment-containing latex coatings have been proposed. Similarly, aluminum-coated asphalt roofing membranes have been employed to achieve solar heat reflectivity. U.S. Pat. No. 6,245,850 discloses a reflective asphalt emulsion for producing a reflective asphalt roofing membrane. 
     The use of exterior-grade coatings colored by infrared-reflective pigments has also been proposed for spraying onto the roof in the field. U.S. Patent Application Publication No. 2003/0068469A1 discloses an asphalt-based roofing material comprising a mat saturated with asphalt coating and a top coating having a top surface layer that has a solar reflectance of at least 70%. 
     U.S. Patent Application Publication No. 2002/0160151A1 discloses an integrated granule product comprising a film having a plurality of ceramic-coated granules bonded to the film by a cured adhesive and the cured adhesive or the film can have pigments. Such integrated granule product can be directly bonded to an asphalt-based substrate as roofing products. 
     In order to increase solar reflectance of built-up roofs, reflective coatings have been applied directly onto the surface of the roofing membrane. For example, white pigment containing latex coatings have been proposed and evaluated by various manufacturers. In addition, white single-ply roofing membranes formed from thermoplastic elastomers, PVC, or EPDM, etc., have been developed to achieve the required solar reflectance. Performance Roof Systems (Kansas City, Mo.) has also developed an asphalt-based roofing membrane having a white acrylic pre-impregnated mat on the top surface. 
     Laminated single-ply roofing membranes are known, such as those disclosed in U.S. Pat. Nos. 6,502,360; 5,456,785; 5,620,554; and 5,643,399. U.S. Pat. No. 6,296,912 discloses a roofing membrane having a fibrous layer on top for providing a secure surface for roof installation personnel. 
     There is a continuing need for roofing materials that have improved resistance to thermal stresses while providing an attractive appearance. Further, there is a continuing need to develop asphalt-based roofing membranes with solar reflectance greater than 70%. 
     SUMMARY OF THE INVENTION 
     The present invention provides a roofing membrane with high solar heat reflectance. The roofing membrane comprises a bituminous base sheet; a tie-layer comprising a reinforcement material; and a solar heat-reflective upper layer comprising a powder coating. Preferably, the reinforcement material comprises a non-woven web of fibers. Preferably, the nonwoven web comprises fibers selected from the group of glass fibers, polymeric fibers and combinations thereof. Preferably, the powder coating comprises at least one polymeric binder, such as a powder coating binder, and at least one solar heat reflective pigment. 
     The polymeric binder is preferably selected from the group consisting of acrylic copolymers, polyesters, polyamides, epoxies, nonacid-containing polyolefins, polyolefin alloys, polypropylene, acid-containing polyolefins, polyvinyl chloride, polyester block amide, ethylene-chlorotrifluorethylene, and polyvinylidene fluoride. Preferably, the acid-containing polyolefin is selected from polyethylene acrylic acid and polyethylene methacrylic acid. In a presently preferred embodiment, the polymeric binder is polyamide 11. In another presently preferred embodiment, the polymeric binder is an acrylic copolymer. Preferably, the at least one solar heat reflective pigment is titanium dioxide. 
     The present invention also provides a process for preparing a roofing membrane with high solar heat reflectance. The preparative process of the present invention comprises laminating a tie-layer to a bituminous base sheet to form an intermediate sheet; depositing a powder coating composition on the intermediate sheet; and fusing the powder coating composition. Preferably, the tie-layer is laminated to the bituminous base sheet by heating the surface of the base sheet to above the softening temperature of the bituminous material, and adhering the tie-layer to the base sheet by contacting the base sheet with the tie-layer and permitting the bituminous material to partially saturate the tie-layer. Preferably, the preparative process further comprises applying pressure while fusing the powder coating composition. 
     The present invention further provides a roof having high solar heat resistance. The roof comprises a roofing deck and a roofing membrane with high solar heat resistance according to the present invention adhered to the roofing deck. In addition, the present invention provides a method of constructing a roof having high solar heat resistance. The construction method comprises adhering to a roofing deck a roofing membrane with high solar heat resistance according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of the structure of solar-reflective roofing membrane according to a first embodiment of the present invention. 
         FIG. 2  is a schematic illustration of the structure of solar-reflective roofing membrane according to a second embodiment of the present invention. 
         FIG. 3  is a schematic illustration of a process according to the present invention for preparing a roofing membrane with high solar reflectance. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the process of the present invention, roofing membranes with high solar heat reflectance are formed by combining a reinforcement material as a tie-layer between the substrate of suitable bituminous membrane and a solar heat-reflective upper layer formed by melting or fusing a suitable powder coating material in place during manufacturing. 
     Referring now to the figures in which like reference numerals represent like elements in each of the several views, there is shown in  FIG. 1  a schematic illustration of a first embodiment of a solar heat-reflective roofing membrane  10  according to the present invention. The solar heat-reflective roofing membrane  10  is comprised of three layers  12 ,  14 ,  16 . The first layer  16  is a bituminous membrane, such as an asphalt-based roofing base sheet with a self-adhering backing. Adhered to the upper surface of the base sheet  16  is a tie-layer  14  formed from a reinforcement material such as mineral particles. A solar heat-reflective coating  12 , preferably formed from a powder coating composition, is provided on the tie-layer  14 , to form an upper surface layer. 
     A schematic illustration of a second embodiment of a solar heat-reflective roofing membrane  20  according to the present invention is shown in  FIG. 2 . The solar heat-reflective roofing membrane  20  is also comprised of three layers  22 ,  24 ,  26 . The first layer  26  is also bituminous membrane, such as an asphalt-based roofing base sheet with a self-adhering backing. However, adhered to the upper surface of the base sheet  26  is a tie-layer  24  comprising a fibrous mat, such as a non-woven glass fiber mat. A solar heat-reflective coating  22 , preferably formed from a powder coating composition, is also provided on the tie-layer  24 , to form an upper surface layer. 
     The solar heat-reflective roofing products of the present invention, such as solar-reflective roofing membranes, can be manufactured using conventional roofing production processes, with the addition of a powder coating process step. Typically, bituminous roofing products are sheet goods that include a non-woven base or scrim formed of a fibrous material, such as a glass fiber scrim. The base is coated with one or more layers of a bituminous material such as asphalt to provide water and weather resistance to the roofing product. A self-adhering backing can also be applied to the lower or rear surface of the base, and covered with a suitable release sheet. The upper surface of the base layer is covered with a tie-layer, and a powder coating is then applied to the exposed surface of the tie-layer. 
     The solar heat-reflective roofing membrane is subsequently employed in constructing a solar heat-reflective roof according to the present invention. The roof is constructed by applying a solar-reflective roofing membrane according to the present invention to a suitable subroof in the case of new construction, or a suitably prepared roofing surface in the case of an existing structure. In constructing the roof, the upper surface of the solar-reflective roofing membrane can be covered with mineral granules to provide durability, reflect heat and solar radiation, and to protect the powder coating binder from environmental degradation. Optionally, a further protective coating (not shown) could be applied over the heat reflective coating  22  to protect the powder coating binder from the environment. 
       FIG. 3  schematically illustrates a presently preferred process according to the present invention for preparing a roofing membrane  50  with high solar reflectance. A continuous web of bituminous membrane  30 , such as an asphalt-based roofing base sheet with a self-adhering backing, is provided as the base layer of the roofing membrane  50 . The web of bituminous membrane  30  is fed to the processing apparatus in the direction shown by the arrows  32 . A tie-layer web  34 , such as a non-woven web of glass fiber, is fed to the processing apparatus in the direction shown by the arrow  35 . The tie-layer web  34  is adhered to the upper surface of the base layer  30  by pressure applied by a first set of heated pressure rollers  36  to form an intermediate web  37 . Next, a solar heat-reflective coating composition powder  38  is deposited from a hopper  40  on the upper surface of the intermediate web  37 . Alternatively, other methods of applying the coating composition powder  38  to the intermediate web  37 , such as spray application, can be employed (not shown). As the intermediate web  37  next passes under an infrared heater  42 , the powder  38  is fused to form a continuous coating  43  on the top of the intermediate web  37 . The intermediate web  37  then passes through a second set of heated pressure rollers  44  which press the coating composition  43  and tie-layer  34  and bituminous membrane  30  to provide a uniform, predetermined thickness to the roofing membrane  50 . 
     Bituminous roofing products, such as the base sheet  30 , are typically manufactured in continuous processes in which a continuous substrate sheet of a fibrous material such as a continuous felt sheet or glass fiber mat is immersed in a bath of hot, fluid bituminous coating material so that the bituminous material saturates the substrate sheet and coats at least one side of the substrate. The reverse side of the substrate sheet can be coated with an anti-stick material such as a suitable mineral powder or a fine sand. Alternatively, the reverse side of the substrate sheet can be coated with an adhesive material, such as a layer of a suitable bituminous material, to render the sheet self-adhering. In this case the adhesive layer is preferably covered with a suitable release sheet. 
     The solar-reflective roofing membrane can be formed into roll goods for commercial or industrial roofing applications. Alternatively, the solar-reflective roofing membrane can be cut into conventional shingle sizes and shapes (such as one foot by three feet rectangles), slots can be cut in the shingles to provide a plurality of “tabs” for ease of installation or for aesthetic effects, additional bituminous adhesive can be applied in strategic locations and covered with release paper to provide for securing successive courses of shingles during roof installation, and the finished shingles can be packaged. 
     The bituminous material used in manufacturing roofing products according to the present invention is derived from a petroleum processing by-product such as pitch, “straight-run” bitumen, or “blown” bitumen. The bituminous material can be modified with extender materials such as oils, petroleum extracts, and/or petroleum residues. The bituminous material can include various modifying ingredients including polymeric materials such as, for example, SBS (styrene-butadiene-styrene) block copolymers, resins, flame-retardant materials, oils, stabilizing materials, anti-static compounds, and the like. Preferably, the total amount by weight of such modifying ingredients is not more than about 15 percent of the total weight of the bituminous material. The bituminous material can also include amorphous polyolefins, up to about 25 percent by weight. Examples of suitable amorphous polyolefins include atactic polypropylene, ethylene-propylene rubber, etc. Preferably, the amorphous polyolefins employed have a softening point of from about 130 degrees C. to about 160 degrees C. The bituminous composition can also include a suitable filler, such as calcium carbonate, talc, carbon black, stone dust, or fly ash, preferably in an amount from about 10 percent to 70 percent by weight of the bituminous composite material. 
     Examples of suitable bituminous membranes for use as base sheets in the process of the present invention include asphalt roofing membranes such as asphalt-based, self-adhering roofing base sheet available from CertainTeed Corporation, Valley Forge, Pa., for example, WinterGuard™ shingle underlayment, a base sheet which is impregnated with rubberized asphalt. 
     Preferably, the reinforcement material comprises a non-woven web of fibers. Preferably, the nonwoven web comprises fibers selected from the group of glass fibers, polymeric fibers and combinations thereof. Examples of suitable reinforcement material for use as a tie-layer include, but not limited to, non-woven glass fiber mats, non-woven polyester mats, composite non-woven mats of various fibers, composite woven fabrics of various fibers, industrial fabrics such as papermaker&#39;s forming fabrics and papermaker&#39;s canvasses, polymer netting, screen, and mineral particles. The fibers employed in preparing the reinforcing material can be spun, blown or formed by other processes known in the art. Yarn for forming the reinforcement material can include mono-filament yarn, multi-filament yarn, spun yarn, processed yarn, textured yarn, bulked yarn, stretched yarn, crimped yarn, chenille yarn, and combinations thereof. The cross-section of the yarn employed can be circular, oval, rectangular, square, or star-shaped. The yarn can be solid, or hollow. The yarn can be formed from natural fibers such as wool and cotton; synthetic materials such as polyester, nylon, polyethylene, polypropylene, polyvinylidene fluoride, ethylene tetrafluroethylene copolymer, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, poly(meth)acrylates, aramide, polyetherketone, polyethylene naphthalate, and the like, as well as non-organic materials such as spun glass fibers and metallic materials, or combinations thereof. 
     Non-woven glass fiber mats for use in the process of the present invention preferably have a weight per unit area of from about 40 to 150 g/m 2 , more preferably form about 70 to 120 g/m 2 , and still more preferably from about 80 to 100 g/m 2 , and a thickness of from about 0.01 to 1 mm. Non-woven glass mats having a weight per unit area of about 90 g/m 2  (0.018 lb/ft 2 ) are typically employed. 
     Preferably, the tie-layer has sufficient thickness so that an adequately thick layer of solar heat-reflective coating composition can be adhered thereto to provide effective solar heat reflectance. Preferably, the tie layer has a thickness of from about 0.001 cm to about 0.1 cm, more preferably from about 0.001 cm to about 0.03 cm. 
     Examples of mineral particles that can be used as tie layer materials include conventional roofing granules. In the present invention, colored, infrared-reflective granules, such as disclosed in U.S. patent application Ser. No. 10/679,898, filed Oct. 6, 2003, can be mixed with conventional roofing granules. Alternatively, colored, infrared-reflective granules can be substituted for conventional roofing granules to enhance the solar-heat reflectance of the solar-reflective roofing membranes of the present invention. When mineral particles are employed as the reinforcement material, it is preferred that the mineral particles have an average particle size of from about 180 to about 850 μm. Mineral particles may function as a tie layer for holding the powder coating on the roofing sheet. For example, the powder coat may adhere better to the granules than to the bituminous base sheet and the mineral particles may adhere to both the bituminous base sheet and to the powder coating. In this sense the tie layer is not necessarily a reinforcement material in the sense of reinforcing the sheet, but rather the tie layer tends to enhance the holding power of the powder coat to the surface of the bituminous sheet. 
     In contrast to conventional liquid coating materials, powder coating materials are typically dry, solid powder materials that include a polymeric resinous binder with a melting temperature above ambient temperature and optional pigments, extenders, flow control agents, and/or other additives. Powder coating materials or compositions for use in the present invention preferably include both a polymeric binder and a solar-reflective pigment. 
     Suitable powder coating material should have excellent outdoor durability; a melting temperature for application of between 66 degrees C.-204 degrees C. (150 degrees F.-400 degrees F.); and low viscosity upon melting to completely impregnate the tie-layer in a relatively short period of time. By “low viscosity” is meant a viscosity of from about 50 centipoise to 3000 centipoise. 
     Examples of suitable powder coating compositions include thermoplastic and thermoset powder coating compositions. Thermoplastic powder coating compositions are frequently employed to provide coating of at least about 250 microns. Thermosetting powder coating compositions are frequently employed to provide thinner coatings, such as coatings with a thickness of from about 20 to 80 microns. Suitable powder coating polymeric materials include, but are not limited to, acrylic and related copolymers, polyesters, polyamides, epoxies, polyolefin and its alloys, polypropylene, acid containing polyolefins such as polyethylene acrylic acid or polyethylene methacrylic acid, polyvinyl chloride, polyester block amide, ethylene chlorotrifluorethylene, or polyvinylidene fluoride. Examples of thermosetting materials include epoxy, polyester, and acrylic thermosetting materials. Examples of thermoplastic materials include polyamide, polyethylene, polypropylene, polyvinyl chloride, polyester, and polyvinylidene fluoride thermoplastic materials. 
     Preferably, a powder coating composition having good exterior durability and weatherability characteristics is employed. Examples of powder coating compositions providing coatings with good exterior durability include thermoplastic polyester compositions, thermoplastic polyvinylidene fluoride compositions, thermosetting polyester compositions such as hydroxyalkylamide polyesters, thermosetting epoxy resin compositions, thermosetting epoxy-polyester hybrid coating compositions, thermosetting polyester-triglycydyl isocyanurate compositions, thermosetting GMA acrylic compositions, thermosetting acrylic urethane compositions, and thermosetting polyester urethane compositions. 
     Powder coating compositions for use in the present invention are preferably pigmented with solar heat-reflective pigments or fillers in order to produce an upper surface coating of high solar reflectance. Examples of suitable heat-reflective pigments have been disclosed in the commonly assigned U.S. patent application Ser. No. 10/679,898, filed Oct. 6, 2003, incorporated herein by reference. 
     In addition, powder coating compositions for use in the preparative process of the present invention can include other components, such as curing agents or hardeners, extenders, and additives such as thixotropes, flow modifiers, and the like. 
     Examples of heat- or infrared-reflective pigments that can be employed include colored infrared-reflective pigments and white infrared-reflective pigments. 
     Upper surface coatings for use in preparing roofing membranes according to the present invention preferably include at least one infrared-reflective pigment. The at least one infrared-reflective pigment can be a colored infrared-reflective pigment, a white infrared-reflective pigment, or a mixture of two or more infrared-reflective pigments. 
     Preferably, the at least one colored infrared-reflective pigment is selected from the group consisting of (1) infrared-reflective pigments comprising a solid solution including iron oxide and (2) near infrared-reflecting composite pigments. 
     Preferably, in the upper surface coating composition, when a colored infrared-reflective pigment is employed, the colored infrared-reflective pigment comprises from about 2 percent by weight to about 40 percent by weight of the coating composition. More preferably, the colored infrared-reflective pigment comprises about 5 percent by weight to about 35 percent by weight of the coating composition. 
     Preferably, in the upper surface coating composition, when a white infrared pigment, such as titanium dioxide, is employed, the white infrared-reflective pigment comprises from about 2 percent by weight to about 40 percent by weight of the coating composition. More preferably, the white infrared-reflective pigment comprises about 10 percent by weight to about 35 percent by weight of the coating composition. Still more preferably, the white infrared-reflective pigment comprises from about 25 percent by weight to about 35 percent by weight of the coating composition. 
     Preferably, in the upper surface coating composition, when a combination of a white infrared-reflective pigment, such as titanium dioxide, and a colored infrared-reflective pigment, is employed, the combination of the white infrared-reflective pigment and the colored infrared-reflective pigment comprises form about 2 percent by weight to about 40 percent by weight of the coating composition. Preferably, the colored infrared-reflective pigment comprises from about 2 percent by weight to about 10 percent by weight of the coating composition, and the white infrared-reflective pigment comprises from about 25 percent by weight to about 35 percent by weight of the coating composition. 
     Preferably, the upper surface coating composition further comprises 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. 
     When alumina is employed as the at least one infrared-reflective pigment, the alumina (aluminum oxide) preferably has a particle size less than #40 mesh (425 microns), preferably between 0.1 micron and 5 microns, and more preferably between 0.3 micron and 2 microns. It is preferred that the alumina includes greater than 90 percent by weight Al 2 O 3 , and more preferably, greater than 95% by weight Al 2 O 3 . 
     Optionally, the upper surface coating composition can include at least one coloring material selected from the group consisting of granule coloring pigments and UV-stabilized dyes. 
     Preferably, the at least one colored, infrared-reflective pigment comprises a solid solution including iron oxide, such as disclosed in U.S. Pat. No. 6,174,360, incorporated herein by reference. 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, incorporated herein by reference. 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. Near-infrared non-absorbing colorants that can be used in the present invention are organic pigments such as organic pigments including azo, anthraquinone, phthalocyanine, perinone/perylene, indigo/thioindigo, dioxazine, quinacridone, isoindolinone, isoindoline, diketopyrrolopyrrole, azomethine, and azomethine-azo functional groups. Preferred black organic pigments include organic pigments having azo, azomethine, and perylene functional groups. 
     Examples of near infrared-reflective pigments available from the Shepherd Color Company, Cincinnati, Ohio, include Arctic Black 10C909 (chromium green-black), Black 411 (chromium iron oxide), Brown 12 (zinc iron chromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chrome antimony titanium). 
     Light-interference platelet pigments are known to give rise to various optical effects when incorporated in coatings, including opalescence or pearlescence. Surprisingly, light-interference platelet pigments have been found to provide or enhance infrared-reflectance of roofing granules coated with compositions including such pigments. 
     Examples of light-interference platelet pigments that can be employed in the process of the present invention include pigments available from Wenzhou Pearlescent Pigments Co., Ltd., No. 9 Small East District, Wenzhou Economical and Technical Development Zone, Peoples Republic of China, such as Taizhu TZ5013 (mica, rutile titanium dioxide and iron oxide, golden color), TZ5012 (mica, rutile titanium dioxide and iron oxide, golden color), TZ4013 (mica and iron oxide, wine red color), TZ4012 (mica and iron oxide, red brown color), TZ4011 (mica and iron oxide, bronze color), TZ2015 (mica and rutile titanium dioxide, interference green color), TZ2014 (mica and rutile titanium dioxide, interference blue color), TZ2013 (mica and rutile titanium dioxide, interference violet color), TZ2012 (mica and rutile titanium dioxide, interference red color), TZ2011 (mica and rutile titanium dioxide, interference golden color), TZ1222 (mica and rutile titanium dioxide, silver white color), TZ1004 (mica and anatase titanium dioxide, silver white color), TZ4001/600 (mica and iron oxide, bronze appearance), TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance), TZ1001/80 (mica and titanium dioxide, off-white appearance), TZ2001/600 (mica, titanium dioxide, tin oxide, off-white/gold appearance), TZ2004/600 (mica, titanium dioxide, tin oxide, off-white/blue appearance), TZ2005/600 (mica, titanium dioxide, tin oxide, off-white/green appearance), and TZ4002/600 (mica and iron oxide, bronze appearance). 
     Examples of light-interference platelet pigments that can be employed in the process of the present invention also include pigments available from Merck KGaA, Darmstadt, Germany, such as Iriodin® pearlescent pigment based on mica covered with a thin layer of titanium dioxide and/or iron oxide; Xirallic™ high chroma crystal effect pigment based upon Al 2 O 3  platelets coated with metal oxides, including Xirallic T 60-10 WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold, and Xirallic F 60-50 WNT fireside copper; Color Stream™ multi color effect pigments based on SiO 2  platelets coated with metal oxides, including Color Stream F 20-00 WNT autumn mystery and Color Stream F 20-07 WNT viola fantasy; and ultra interference pigments based on TiO 2  and mica. 
     Examples of mirrorized silica pigments that can be employed in the process of the present invention include pigments such as Chrom Brite™ CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge, N.Y. 11788. 
     Upper surface coatings can include at least one infrared-reflective white pigment. Examples of white pigments that can be employed in the process of the present invention include rutile titanium dioxide, anatase titanium dioxide, lithopone, zinc sulfide, zinc oxide, lead oxide, and void pigments such as spherical styrene/acrylic beads (Ropaque® beads, Rohm and Haas Company), and hollow glass beads having pigmentary size for increased light scattering. Preferably, the at least one reflective white pigment is selected from the group consisting of titanium dioxide, zinc oxide and zinc sulfide. 
     It is preferred that the at least one reflective white pigment comprises from about 10 percent by weight to about 40 percent by weight of the upper surface coating composition. It is more preferred that the at least one reflective white pigment comprises from about 20 percent by weight to about 30 percent by weight of the upper surface coating composition. 
     The powder coating compositions of the present invention are prepared by admixing the solar heat-reflective pigment(s) with the polymeric resinous binder and other optional additives and then subsequently extruding and milling the mixture. Alternatively, the powder coating compositions of the present invention can be prepared by blending the solar heat-reflective pigment(s) with the polymeric resinous binder after the binder and other optional additives have been mixed, extruded and milled. In the alternative, the powder coating compositions of the present invention can be prepared by blending the solar heat-reflective pigment(s) with the polymeric resinous binder after the powder and other optional additives have been mixed, extruded and milled, and subsequently subjecting the blend to compressive forces to bond the solar heat-reflective-pigment(s) to the surface of the milled particles of the polymeric resinous binder. 
     Preferably, the infrared-reflective upper surface coating is provided in a thickness effective to render the coating opaque to infrared radiation, such as a coating thickness of at least about 75 microns. However, advantageous properties of the present invention can be realized with significantly lower coating thicknesses, such as at a coating thickness of from about 2 micrometers to about 25 micrometers, including at a coating thickness of about 5 micrometers. 
     Optionally, the upper surface coating composition includes at least one extender pigment such as barium sulfate, wollastonite, talc, calcium carbonate, or clay. 
     In a presently preferred process of the present invention, a roofing membrane of the present invention is produced by first laminating a tie-layer onto a hot asphaltic surface of a membrane substrate to adhere the tie-layer. 
     In the case of a fibrous web tie-layer, the lamination to the asphaltic surface serves to partially impregnate the tie-layer with material from the substrate layer. It is preferred that the tie-layer is well adhered to the substrate membrane and the asphalt coating does not over-saturate the tie-layer in order that the upper layer can be properly adhered to the tie-layer. 
     In another presently preferred process of the present invention, a roofing membrane of the present invention is produced by first forming a tie-layer comprised of particulate material on a hot asphaltic surface of a membrane substrate to adhere the tie-layer. The particulate material, such as roofing granules, is deposited on the hot asphaltic surface such that the particulate material at least partially penetrates into the asphaltic surface such that a secure mechanical bond is formed when the heated surface cools. It is preferred that the particles of the tie-layer be well adhered to the substrate membrane and the asphalt coating are not too far embedded in the asphaltic surface in order that the upper layer can be properly adhered to the tie-layer. 
     Subsequently, a suitable amount of powder coating material is deposited onto the upper surface of the tie-layer, followed by heating to melt or fuse the powder coat in place. This can be accomplished by direct infrared heat lamps, localized microwave irradiation, direct application of hot air by passage through a convection oven or the like, impingement heating, or by heated hot press rolls, or a combination thereof. 
     In general, the method of application depends upon the chemical and physical characteristics of the polymeric powder coating composition. In the case of thermosetting polymer systems, fine-particle sized powder can be applied to the tie-coat surface by suitable spray equipment or by gravity deposition from a suitable reservoir or hopper. In the case of thermoplastic materials, fluidized bed application of the web can be used, although in general it is preferred to coat only one side of the bituminous membrane with the powder coating material. 
     Conventional powder coating application equipment can be used to apply the polymeric powder, such as electrostatic spray equipment employing corona charging or triboelectric charging of the powder coating particles. Alternatively, an air spray system that delivers the powder onto the substrate having sufficient heat to soften the polymeric powder for enabling sticking onto the surface can be used. Preferably, the application equipment includes provisions for precision application of the powder coating composition to the tie layer, and collection and recycling of excess powder coating composition in order to increase the efficiency and lower the cost of the process. When electrostatic spray equipment is employed to deliver the polymeric powder composition to the tie layer, it is preferred that a suitable electrical charge be provided on the tie layer or that the tie layer be electrically grounded so as to increase electrostatic attraction between the tie layer and the polymeric powder composition. For example, the tie layer can be formed from a non-woven material that includes electrically conductive fibers. 
     Preferably, the powder coating is applied to the intermediate web or substrate in sufficient quantity so as to completely cover the surface, while forming a thin coating film after the powder coating is fused. Preferably, the powder coating material is applied to the intermediate substrate in sufficient quantity to provide a coating of from about 25 to about 300 microns in thickness, more preferably from about 50 to about 200 microns, with a thickness of from about 75 to about 175 microns being especially preferred. 
     The method of fusing and/or curing the powder coating composition depends on the chemical and physical properties of the polymeric powder, including the average particle size of the powder and particle size distribution, and the chemical properties of the crosslinking agent, if any, present in the material. If the powder coating composition includes a suitable heat-activated crosslinking agent, infrared heat can be used. Similarly, if the powder coating composition includes a UV-activated crosslinking agent or photoinitiator, ultraviolet radiation can be used to cure the powder coating composition. In some other instances, a higher energy actinic radiation source such as an electron beam or gamma source can be used to impart cure to the powder coating composition. 
     A protective overcoat can also be applied over the powder coating composition. The solar heat-reflective upper layer in this case thus comprises an overcoat applied to the powder coating. For example, in order to help protect the fused powder coating composition from environmental degradation, an overcoat of a suitable coating material can be applied to the fused powder coating composition. Examples of protective overcoat compositions include fluoropolymer coating, acrylic modified fluoropolymer emulsion, all-acrylic coating materials, and in particular solvent-based and water-based acrylic coating materials with good adhesion to the powder coating composition employed. The overcoat composition includes a suitable binder, and optional pigment, such as a suitable infrared-reflective pigment. 
     The present invention also provides an improved roof having high solar heat resistance. The roof comprises a roofing deck, and a roofing membrane with high solar heat resistance, according to the present invention, adhered to the roofing deck. Conventional roofing decks, such as decks formed from plywood, steel, cement, et al. can be covered with a roofing membrane according to the present invention. In addition, the present invention provides a method of constructing a roof having high solar heat resistance. The roof construction method comprises adhering to a roofing deck a roofing membrane with high solar heat resistance according to the present invention. 
     The following examples are provided to better disclose and teach processes and compositions of the present invention. They are for illustrative purposes only, and it must be acknowledged that minor variations and changes can be made without materially affecting the spirit and scope of the invention as recited in the claims that follow. 
     EXAMPLE 1 
     A 12.7 cm by 12.7 cm (5 inch×5 inch) piece of an asphalt-based, self-adhering roofing base sheet (WinterGuard, commercially available from CertainTeed Corporation, Valley Forge, Pa.) is first heated to about 50 degree C. and then a non-woven glass fiber mat (1.8 lb. mat available from Johns Manville Corp.) is laminated onto the self-adhering side of the base sheet using a 12.3 kg (27 lb.) roller. A white powder coat mixture consisting of 6.05 g clear acrylic powder (Ultra Detail from Mark Enterprises, Anaheim, Calif.) and 2.66 g of TiO 2  white pigment (TiPure R-102 from DuPont Corp.) is then deposited onto the surface of the glass fiber mat using a perforated hand shaker until the surface is covered with a uniform layer of the power coat. The resultant sheet is then heated under infrared heat lamps to a surface temperature of 116-121 degrees C. (240-250 degrees F.) until the powder coat is completely melted and the tie-layer filled to form a uniform white coating. The resultant sample of roofing membrane has an averaged solar reflectance of 76.5% as measured by the ASTM C-1549 method. 
     EXAMPLE 2 
     A 12.7 cm by 12.7 cm (5 inch×5 inch) of an asphalt-based, self-adhering roofing base sheet (WinterGuard, commercially available from CertainTeed) is first heated to about 50° C. and then a non-woven glass fiber mat (1.81lb. mat available from Johns Manville Corp.) is laminated onto the self-adhering side of the base sheet using a 12.3 kg (27 lb) roller. A white powder coat of nylon 11 with melting temperature of about 186 degrees C. (Rilsan 11 polyamide from Atofina Chemicals, Inc., Philadelphia, Pa.) is then deposited onto the surface of the glass mat using a perforated hand shaker until the surface is covered by a uniform layer of the powder coat. The resultant sheet is then pressed under a hot plate with the top plate set at 193 degrees C. (380 degrees F.) and bottom plate set at room temperature using pressing load of 3630 kg (8000 lb.), holding time of 15 seconds, and a gauge bar of 0.24 cm ( 3/16 inch) to prevent over-press. The resultant sample of roofing membrane has a very smooth surface finish and an averaged solar reflectance of 77.6%. 
     Various modifications can be made in the details of the various embodiments of the processes, compositions and articles of the present invention, all within the scope and spirit of the invention and defined by the appended claims.