Coating compositions for roofing granules, dark colored roofing granules with increased solar heat reflectance, solar heat-reflective shingles, and process for producing the same

Abstract

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.