Roofing granules with high solar reflectance, roofing products with high solar reflectance, and process for preparing same

Abstract

A solar heat-reflective roofing product includes a base sheet, and solar heat-reflective roofing granules on top of the base sheet. The granules have a base particle with a flake-like geometry covered by a uniform coating layer. The coating layer has a thickness of at least one mil and includes a coating binder and at least one solar heat-reflective pigment. The solar heat-reflective pigment provides a solar heat reflectance of greater than 70 percent to the granules and the roofing product. Roofing products including roofing shingles and roofing membranes are described.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the priority of U.S. Provisional Patent Application No. 61 / 313,911 filed Mar. 15, 2010, and incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present application relates to roofing granules and roofing products including roofing products, such as roofing shingles and roofing membranes.[0004]2. Brief Description of the Prior Art[0005]Asphalt shingles or bitumen roofing membranes are conventionally used in the United States and Canada as roofing and siding materials. Roofing granules are typically distributed over the upper or outer face of such shingles. The roofing granules, in general are formed from mineral materials, and serve to provide the shingle with durability. They protect the asphalt from the effects of the solar radiation (in particular from the degradative effects of ultraviolet rays) and of the environment (wind, precipitation, pollution, and the like),...

AI Technical Summary

Benefits of technology

[0020]The present invention provides asphalt-based roofing membranes with solar reflectance greater than 70 percent. The present invention also provides roofing granules having a solar heat reflectance of a...

Problems solved by technology

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.

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.

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.

To achieve such high level of solar reflectance, it has been proposed to coat the roof with a reflective coating over granulated roofing products, since the granules with current commercially available coloring technology are not capable of achieving such high levels of solar reflectance.

However, polymeric coatings applied have only a limited amount of service life and will require re-coat after certain years of service.

Also, the cost of adding such a coating on roof coverings can be relatively high.

Unfortunately, these granules have a “washed-out” color appearance due to the partially revealed white base coat.

However, there is no control of color blends and the novel granules are typically available only in white or buff colors.

Furthermore, these novel granules tend to have high UV transmittance and hence are not suitable for roofing applications in bitumen based products.

However, the addition of kaolin clays, which are used to make the metal-silicate binder durable through heat curing, inevitably reduce the color strength or the color intensity of the pigment.

However, these alternatives require either very high temperatures, or the use of corrosive chemicals, and in many cases could result in loss of color due to pigment degradation by the acid.

However, the long-term durability and cost for polymeric coatings are not as advantageous as the silicate binders.

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