This invention relates to roofing materials and surfaces, and more particularly to a roof surfacing having increased solar reflectance.
It has become desirable in recent years to create roof surfaces having increased solar reflectance to reduce the temperature of roofs, reduce the amount of energy required to cool the enclosed facility, and reduce ambient heat in densely populated areas. In fact, various jurisdictions have enacted laws and ordinances setting mandatory levels of roof surface reflectance. Traditional roofing materials are comprised of a roof membrane containing bitumen and granules embedded in the surface of the membrane to protect the bitumen from damaging ultraviolet radiation. The bituminous layer is naturally black, making it necessary to cover as much of the bituminous layer as possible to create a reflectance of 0.70 or greater, as defined by ASTM methods E 903 and E 1918. Even using white granules in manufacturing a traditional granular surfaced roof membrane creates a reflectance value no greater than 0.32. The difficulty is that traditional roofing granules are processed from naturally occurring minerals that are crushed and sized, resulting in irregular surfaces and shapes. These irregular shapes make complete coverage of the black bituminous layer of the roof membrane virtually impossible. Further, the irregular surfaces of the granules result in some incident light energy being reflected between the granules, thereby trapping incident energy in the roof surfacing, decreasing reflectance, and damaging the underlying bituminous layer.
Complete, or near-complete, coverage of the black bituminous layer is currently achieved by various methods, all of which have significant drawbacks. Roofing material manufacturers have achieved a high level of reflectance by applying a white film to the surface of the roof membrane, by applying a reflective coating either in the field or at the factory, or by applying a coated fiberglass mat to the surface of the roof membrane. These methods all call for extra production steps, either at the manufacturing facility or in the field, which significantly increase labor and raw materials costs. Further, because these continuous coatings or films are applied to an underlying roof membrane with different physical properties, adhesion problems frequently occur between the coatings or films and the underlying roof membrane. For example, the coating or film and the roof membrane may have different coefficients of thermal expansion, meaning that the two materials will expand and contract at different rates when subjected to thermal oscillations. This disparity causes stress at the bond plane between the two materials, which may eventually cause the two materials to separate, or delaminate.
Adhesion problems are also brought about because roof membranes are typically stored and transported in a rolled, cylindrical form. When a coated roof membrane is wound around a cylindrical core, the coating or film and the underlying roof membrane are at different radii from the center. This means that the coating or film and the underlying roof membrane will have different circumferences, causing at least one of the materials to stretch or compress in order to maintain the bond between the two. This stretching or compression creates stress at the bond plane between the two materials, which may eventually lead to delamination of the two materials in storage.
Various roof surfaces have been proposed to increase reflectance without the delamination problems detailed above. By way of example, published U.S. patent application Ser. Nos. 10/421,386 and 10/683,536, both assigned to The Garland Company, disclose a granular material and method of applying the granular material to the surface of roofing materials resulting in increased reflectivity. But the irregularities in the granular shape of The Garland Company's surface material prevents complete coverage of the underlying bituminous layer of the roof membrane, thereby limiting the reflectance this material can achieve.
Flat particles have been used in roof surfacing to effect a more complete coverage of the bituminous layer for purposes other than increasing reflectance. For instance, published U.S. patent application Ser. No. 10/274,717 by Kiik et al. discloses the use of metal flakes on a roof surface to improve durability and aesthetic qualities of the roof. But metal is susceptible to oxidation upon exposure to various weather conditions, leading to sometimes drastic changes in the appearance of the roof surface, and metal is a relatively expensive roofing material. Further, metal is a good thermal conductor, meaning that solar energy not reflected by the metallic flakes will likely be transferred to the underlying bituminous layer as heat, which can accelerate the destruction of the bitumen and shorten the useful life of the roof membrane.
What is needed in the roofing industry is a roof surfacing having increased reflectance, reduced incidence of delamination, low thermal conductance, high opacity to ultraviolet radiation, reduced weight, and good weathering characteristics.
In accordance with one aspect of the present invention, a roof surfacing comprises a roof membrane and a plurality of generally flat particles overlying the roof membrane. The roof membrane has a bituminous layer to which the flat particles are adhered. The discontinuous roof surfacing material provided by the present invention avoids the delamination problems noted in the prior art. The flat particles may be arranged in a generally overlapping geometry to substantially cover the bituminous layer. The roof surfacing exhibits increased reflectance because the flat particles have a regular surface and an increased ability to cover the black bituminous layer.
In accordance with a further aspect of the present invention, the flat particles comprise a composition exhibiting a high reflectance, namely a polymer and a filler, wherein the polymer may be selected from the group consisting of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, and methylmethacrylate (MMA) and the filler may be selected from the group consisting of calcium carbonate, dolomite, and barium sulfate. Advantageously, the particles may further comprise a pigment, which is preferably titanium dioxide. In an even more beneficial aspect of the invention, the particles may further comprise a fire retardant.
In accordance with an even further aspect of the invention, a method for constructing a roof surfacing comprises forming a sheet of material having an increased reflectance; dividing the sheet into generally flat particles; feeding the particles through a hopper onto a curved directional plate; and depositing the particles onto a molten bituminous layer of a roof membrane. Preferably, the particles may be deposited in an overlapping, generally horizontal geometry, creating a scaled appearance. It may also be advantageous for the particles to have a mean width to thickness ratio of about 2:1 to about 50:1.
The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, three embodiments that are presently preferred are shown in the drawings. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
Referring now to the drawings, and to
Turning now to
As shown in
The flat particles 10 may comprise any combination of a polymer and a filler, where the polymer may be polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, or methylmethacrylate (MMA) and the filler may be calcium carbonate, dolomite, or barium sulfate. Additionally, the particles 10 may contain one or more pigments. Currently, the preferred pigment is titanium dioxide for its ultraviolet protective properties, but any other pigment may be added to the particles 10 in lieu of or in addition to titanium dioxide to impart various colors to the reflective roof surface. Further, the particles 10 may contain other beneficial additives, such as, but not by way of limitation, fire retardants or anti-microbial agents.
A currently preferred embodiment combines PVA, barium sulfate, and titanium dioxide, with PVA comprising about 10 to about 15 percent of the composition by weight, barium sulfate comprising about 75 to about 85 percent of the composition by weight, and titanium dioxide comprising about 5 to about 10 percent of the composition by weight. The PVA compound is currently preferred due to its ready availability and low cost. It is believed that MMA may be an even more preferable polymer component due to its ability to withstand harsh weather conditions.
Another currently preferred embodiment exhibits improved weathering properties by combining acrylic, calcium carbonate, and titanium dioxide, with acrylic comprising about 10 to about 15 percent of the composition by weight, calcium carbonate comprising about 75 to about 85 percent of the composition by weight, and titanium dioxide comprising about 5 to about 10 percent of the composition by weight.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. By way of example, the flat particles could be of uniform size and shape. Alternatively, the flat particles could be adhered to roof surfaces other than traditional roof membranes having a bituminous layer, using any adhesion method known in the art. It will be understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.