Solar heat-reflective roofing granules, solar heat-reflective shingles, and process for producing same
Solar-reflective roofing granules having improved solar heat-resistance are formed by coating colored mineral particles with a coating composition including titanium dioxide nanoparticles.
1. Solar heat-reflective roofing granules comprising:
(a) a base particle comprising an inert mineral;
(b) a first coating on the base particle, and
(c) a second coating on the first coating, wherein the second coating comprises a plurality of infrared-reflective metal films.
2. Solar heat-reflective roofing granules according to claim 1 wherein the second coating has an average incident radiation transmission coefficient of at least 80 percent in the range of 400 nanometers to 800 nanometers.
3. Solar heat-reflective roofing granules according to claim 1 wherein the first coating on the base particle comprises a metal oxide colorant.
4. Solar heat-reflective roofing granules according to claim 1 wherein the second coating comprises at least one film formed from a metal selected from the group consisting of silver, gold and copper.
5. Solar heat-reflective roofing granules according to claim 4 wherein the thickness of the second coating is less than about 50 nanometers.
6. Roofing shingles comprising roofing granules according to claim 1 .
7. A sheet roofing product comprising:
a bituminous base; and
solar heat reflective roofing granules according to claim 1 .