Roof surfacing having increased reflectance

Abstract

A roof surfacing having increased reflectance comprises a roof membrane with a bituminous layer and a layer of generally flat particles placed in a generally overlapping geometry so as to substantially cover the bituminous layer. The composition of the particles includes a polymer and a filler. The polymer may be polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, or methylmethacrylate (MMA). The filler may be calcium carbonate, dolomite, or barium sulfate. The particles may further include a pigment, fire retardant, and/or anti-microbial agent. A method of creating a roof surfacing having increased reflectance includes creating a thin sheet of material having increased reflectance, dividing that sheet into multiple particles, feeding the particles through a hopper onto a curved directional plate, and placing the particles on a roof membrane having a molten bituminous layer in a generally horizontal direction to create an overlapping, scaled appearance.

Description

FIELD OF THE INVENTION

This invention relates to roofing materials and surfaces, and more particularly to a roof surfacing having increased solar reflectance.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a top view of a roof surfacing in accordance with the present invention.

FIG. 2 is a cross-sectional view of a roof surfacing in accordance with the present invention, taken along line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of a prior art granular surfaced roof membrane.

FIG. 4 is a detail view of an individual, exemplary particle in accordance with the present invention.

FIG. 5 is a schematic diagram illustrating a method of constructing the roof surfacing in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and to FIGS. 1 and 2 in particular, a roof surfacing 16 in accordance with one embodiment of the present invention is illustrated. The roof surfacing 16 includes a roof membrane 14 having a bituminous layer 15, and a plurality of generally flat particles 10 overlying the roof membrane 14, secured to the roof membrane 14 by the bituminous layer 15. The roof membrane 14 is of well-known construction and typically comprises a woven, nonwoven, or composite fabric coated in a bituminous layer 15. The bituminous layer 15 can be any of the water-resistant materials known in the roofing industry, including, but without limitation, those materials containing or derived from bitumen, modified bitumen, tar, pitch, or asphalt.

Turning now to FIGS. 2 and 3, the particles 10 preferably overlap each other to cover the bituminous layer 15 more completely than can be achieved with irregularly shaped granules 27. Also, the generally flat surfaces of the particles 10 reduce the amount of incident energy 22 that is trapped between particles 10, allowing more energy 22 to be effectively reflected away from the surface 16. The combination of greater coverage of the bituminous layer 15 and a more uniform surface increases reflectance and minimizes the amount of solar energy that is transferred to the bituminous layer 15 of the roof surfacing 16. The reduced effect of solar energy 22 on the bitumen 15 can be seen in an increased lifespan of the roof membrane 14, lowered energy costs to cool the enclosed structure, and a cooler roof surface 16.

As shown in FIG. 5, the inventive roof surfacing 16 is manufactured by beginning with a thin sheet 51 of the highly reflective material. The thickness 33 of this sheet preferably ranges from about 4 to about 15 mils (about 0.1 to about 0.4 mm). This sheet 51 of material is divided into multiple particles 10. The particles 10 need not be identical in size or shape or of any particular size or shape. The preferred width 32 of these particles is about ⅛ inch, but a mean width 32 to thickness 33 ratio of about 2:1 to about 50:1 produces the desired improvements of the present invention, independent of any particular width 32 of the particles 10. The generally flat particles 10 are placed in a hopper 53 for eventual deposition onto the roof membrane 14. The flat particles 10 are fed from the hopper 53 onto a curved directional plate 56, which serves to orient the particles 10 in a generally horizontal direction. The generally flat geometry of the particles 10 allows for some degree of overlap between the particles 10 as they are deposited onto the bituminous layer 15 of the roof membrane 14. This results in a horizontally scaled appearance. The particles 10 are not deposited in any particular vertical configuration. Because the particles 10 are deposited on the bituminous layer 15 while the bituminous layer 15 is in its warm, molten state, the particles 10 become partially embedded in the bituminous layer 15. Upon solidification of the bituminous layer 15, the particles 10 are securely adhered to the roof membrane 14.

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.

Claims

1. A roof surfacing having increased reflectance, comprising:

a roof membrane, having a bituminous layer; and

a layer of generally flat particles placed in generally overlapping relationship to each other so as to substantially cover said bituminous layer.

2. The roof surfacing of claim 1, wherein said particles are adhered to said roof surfacing by said bituminous layer.

3. The roof surfacing of claim 1, wherein said bituminous layer comprises a material selected from the group of bitumen, modified bitumen, tar, pitch, or asphalt.

4. The roof surfacing of claim 1, wherein said particles have a mean width to thickness ratio of about 2:1 to about 50:1.

5. The roof surfacing of claim 1, wherein said particles have a mean width of about ⅛ inch.

6. The roof surfacing of claim 1, wherein said particles comprise a material having increased reflectance, comprising:

a polymer selected from the group consisting of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, and methylmethacrylate (MMA); and

a filler selected from the group consisting of calcium carbonate, dolomite, and barium sulfate.

7. The roof surfacing of claim 6, wherein said particles further comprise a pigment.

8. The roof surfacing of claim 6, wherein said particles further comprise a fire retardant.

9. The roof surfacing of claim 6, wherein said particles further comprise an anti-microbial agent.

10. The roof surfacing of claim 7, wherein said pigment comprises titanium dioxide.

11. A roof surfacing having increased reflectance, comprising:

a roof membrane, having a bituminous layer; and

a layer of particles, having a mean width of about ⅛ inch and a mean width to thickness ratio of about 2:1 to about 50:1, placed in generally overlapping relationship to each other so as to substantially cover said bituminous layer.

12. The roof surfacing of claim 11, wherein said particles comprise a material having increased reflectance, comprising:

a polymer selected from the group consisting of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, and methylmethacrylate (MMA); and

a filler selected from the group consisting of calcium carbonate, dolomite, and barium sulfate.

13. The roof surfacing of claim 12, wherein said particles further comprise a pigment.

14. The roof surfacing of claim 12, wherein said particles further comprise a fire retardant.

15. The roof surfacing of claim 12, wherein said particles further comprise an anti-microbial agent.

16. The roof surfacing of claim 13, wherein said pigment comprises titanium dioxide.

17. A method of making a roof surfacing having increased reflectance, comprising the steps of:

creating a sheet of material having an increased reflectance;

dividing said sheet into a plurality of generally flat particles;

feeding said particles through a hopper onto a curved directional plate;

depositing said particles onto a molten bituminous layer of a roof membrane in a generally horizontal direction to create an overlapping, scaled appearance.

18. The method of claim 17, wherein said directional plate orients said particles in a generally horizontal direction.

19. The method of claim 17, further comprising the step of solidifying said bituminous layer to adhere said particles to said roof surfacing.

20. The method of claim 17, wherein said particles have a mean width to thickness ratio of about 2:1 to about 50:1.

21. The method of claim 17, wherein said particles have a mean width of about ⅛ inch.

22. The method of claim 17, wherein said sheet has a thickness of about 0.1 to about 0.4 mm.

23. The method of claim 17, wherein said sheet comprises:

a polymer selected from the group consisting of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, and methylmethacrylate (MMA); and

a filler selected from the group consisting of calcium carbonate, dolomite, and barium sulfate.

24. The method of claim 23, wherein said sheet further comprises a pigment.

25. The method of claim 23, wherein said sheet further comprises a fire retardant.

26. The method of claim 23, wherein said sheet further comprises an anti-microbial agent.

27. The method of claim 24, wherein said pigment comprises titanium dioxide.

28. A composition of matter suitable for forming particles for use in a roof surfacing having increased reflectance, comprising:

a polymer selected from the group consisting of polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyester, acrylic, polymethylmethacrylate, and methylmethacrylate (MMA); and

a filler selected from the group consisting of calcium carbonate, dolomite, and barium sulfate.

29. The composition of matter of claim 28, wherein said composition is about 10 to about 100 percent by weight polymer and about 0 to about 90 percent by weight filler.

30. The composition of matter of claim 28, further comprising a pigment.

31. The composition of matter of claim 28, further comprising a fire retardant.

32. The composition of matter of claim 28, further comprising an anti-microbial agent.

33. The composition of matter of claim 30, wherein said pigment comprises titanium dioxide.

34. The composition of matter of claim 30, wherein said composition is about 10 to about 100 percent by weight polymer, about 0 to about 90 percent by weight filler, and about 0 to about 10 percent by weight pigment.

35. The composition of matter of claim 30, wherein said composition is about 10 to about 15 percent by weight polymer, about 75 to about 85 percent by weight filler, and about 5 to about 10 percent by weight pigment.