COATING COMPOSITIONS FOR ROOFING GRANULES, DARK COLORED ROOFING GRANULES WITH INCREASED SOLAR HEAT REFLECTANCE, SOLAR HEAT-REFLECTIVE SHINGLES, AND PROCESS FOR PRODUCING THE SAME
Dark colored roofing granules include an inert base particle coated with a composition including a metal silicate, a non-clay latent heat reactant, and a dark colored but solar reflective pigment.
1 . A method of making roofing granules, the method comprising:
(a) providing inert base particles;
(b) coating the inert base particles with a coating composition to form at least one coating layer on the inert base particles, the coating composition comprising:
a metal silicate coating binder comprising an alkali metal silicate and at least one non-clay latent heat reactant; and
at least one solar reflective pigment;
the at least one solar reflective pigment being selected to provide roofing granules having an L* less than 30 and solar reflectance of at least 20 percent;
(c) curing the coating composition at an elevated temperature less than the glass sintering temperature of silica.
2 . A method according to claim 1 wherein the coating composition is cured between about 200 degrees C. and 1100 degrees C.
3 . A method according to claim 2 wherein the coating composition is cured between about 500 degrees C. and 1000 degrees C.
4 . A method according to claim 1 in which at least two coating layers are formed.
5 . A method according to claim 1 wherein the at least one non-clay latent heat reactant is selected from the group consisting of Portland cement, aluminum fluoride, ammonium silicofluoride, alkali metal silicofluorides, and alkaline earth metal silicofluorides.
6 . A method according to claim 5 wherein the at least one non-clay latent heat reactant comprises Portland cement, aluminum fluoride and at least one alkali metal silicofluoride.
7 . A method according to claim 6 wherein the at least one alkali metal silicofluoride is sodium silicofluoride.
8 . A method according to claim 6 wherein the at least one non-clay latent heat reactant comprises from about 3 to 15 weight percent of the coating composition of aluminum fluoride, from about 0.5 to 5 weight percent of the coating composition of sodium silicofluoride, and from about 0.5 to 5 weight percent of the coating composition of Portland cement.
9 . A coated substrate comprising:
a substrate having a surface;
a cured coating on the surface, the cured coating comprising
a reaction product of a coating composition, the coating composition comprising
a metal silicate;
at least one non-clay latent heat reactant; and
at least one solar reflective pigment.
10 . A coated substrate according to claim 9 wherein the coated substrate has an L* less than about 30 and a solar reflectance of at least about 20 percent.
11 . A coated substrate according to claim 9 wherein the coated substrate comprises an architectural material.
12 . A coated substrate according to claim 9 wherein the at least one non-clay latent heat reactant is selected from the group consisting of Portland cement, aluminum fluoride, ammonium silicofluoride, alkali metal silicofluorides, and alkaline earth metal silicofluorides.
13 . A coated substrate according to claim 12 wherein the at least one non-clay latent heat reactant comprises Portland cement, aluminum fluoride and at least one alkali metal silicofluoride.
14 . A coated substrate according to claim 13 wherein the at least one alkali metal silicofluoride is sodium silicofluoride.
15 . A coated substrate according to claim 13 wherein the at least one non-clay latent heat reactant comprise from about 3 to 15 weight percent of the coating composition of aluminum fluoride, from about 0.5 to 5 weight percent of the coating composition of sodium silicofluoride, and from about 0.5 to 5 weight percent of the coating composition of Portland cement.
16 . A coating composition comprising:
a metal silicate;
at least one non-clay latent heat reactant; and
at least one solar reflective pigment.
17 . A coating composition according to claim 16 wherein the at least one non-clay latent heat reactant is selected from the group consisting of Portland cement, aluminum fluoride, ammonium silicofluoride, alkali metal silicofluorides, and alkaline earth metal silicofluorides.
18 . A coating composition according to claim 16 wherein the at least one non-clay latent heat reactant comprises Portland cement, aluminum fluoride and at least one alkali metal silicofluoride.
19 . A coating composition according to claim 18 wherein the at least one alkali metal silicofluoride is sodium silicofluoride.
20 . A coating composition according to claim 18 wherein the at least one non-clay latent heat reactant comprise from about 3 to 15 weight percent of the coating composition of aluminum fluoride, from about 0.5 to 5 weight percent of the coating composition of sodium silicofluoride, and from about 0.5 to 5 weight percent of the coating composition of Portland cement.