Solar heat-reflective roofing granules, solar heat-reflective shingles and process for producing the same

Abstract

A process for preparing roofing granules includes forming kaolin clay into green granules and sintering the green granules at a temperature of at least 900 degrees Celsius to cure the green granules until the crystalline content of the sintered granules is at least ten percent as determined by x-ray diffraction.

1 . Synthetic roofing granules comprising at least one sintered aluminosilicate, the granules having a crystalline content of at least 70 percent as determined by x-ray diffraction. 
     
     
         2 . Synthetic roofing granules according to  claim 1  having a crystalline content of at least 90 percent. 
     
     
         3 . Synthetic roofing granules according to  claim 1  comprising sintered bauxite. 
     
     
         4 . Synthetic roofing granules according to  claim 1  comprising sintered kaolin clay. 
     
     
         5 . Synthetic roofing granules according to  claim 1  wherein the amorphous content is greater than about five percent. 
     
     
         6 . Synthetic roofing granules according to  claim 1  containing less than three percent silica. 
     
     
         7 . A roofing product with high solar heat reflectance prepared according the process comprising:
 (a) providing a ceramic-forming material comprising at least one aluminosilicate;   (b) forming the ceramic-forming material into green granules;   (c) sintering the green granules at a temperature of at least 900 degrees Celsius until the crystalline content of the sintered granules is at least ten percent as determined by x-ray diffraction;   (d) providing a roofing material having an upper surface; and   (e) applying the sintered granules to the upper surface of the roofing material.   
     
     
         8 . A roofing product according to  claim 7  wherein the roofing material is a roofing sheet. 
     
     
         9 . A roofing product according to  claim 8  wherein the roofing sheet is a bituminous roofing sheet. 
     
     
         10 . A roofing product according to  claim 7 , wherein the green granules are sintered until the crystalline content of the granules is at least 70 percent. 
     
     
         11 . A roofing product according to  claim 10 , wherein the granules are sintered at a temperature of at least 1450 degrees Celsius until the crystalline content of the granules is about 100 percent as determined by x-ray diffraction. 
     
     
         12 . A roofing product according to  claim 7 , wherein the ceramic-forming material is formed into green granules by mixing the ceramic-forming material with a liquid to form a mixture, the mixture being formed into pellets, and the pellets being screened to provide green granules. 
     
     
         13 . A roofing product according to  claim 7 , wherein the ceramic-forming material is formed into green granules having a predetermined particle-size distribution. 
     
     
         14 . A roofing product according to  claim 13  wherein the ceramic-forming material is formed into at least two different classes of green granules, each class of green granule being characterized by a predetermined average particle size, the green granules being sintered to provide at least two size classes of sintered granules. 
     
     
         15 . A roofing product according to  claim 7 , wherein the shape of the granules and the granule particle-size distribution are selected to provide at least 85 percent surface coverage when the roofing granules are applied to the upper surface of the roofing material. 
     
     
         16 . A roofing product according to  claim 7  wherein the process further comprises selecting sintered granules from at least two different classes prior to applying the sintered granules in the upper surface of the roofing material, the sintered granules being selected to provide a predetermined surface coverage of the roofing material. 
     
     
         17 . A roofing product according to  claim 16  wherein at least two different classes of sintered granules are applied sequentially to the upper surface of the roofing material. 
     
     
         18 . A bituminous roofing product according to  claim 7  wherein the process further comprises applying conventional colored roofing granules to the roofing material. 
     
     
         19 . A roofing product according to  claim 7  wherein the process further comprises applying a liquid binder composition to the upper surface of the roofing material after the sintered granules have been applied, the liquid binder composition being selected from the group consisting of acrylic emulsions, acrylic solutions, thermoplastic polymers, fluoropolymer emulsions, epoxy resins, UV curable resins, radiation curable resins, alkaline metal silicates, sol-gel solutions, silicone resins, and silica binders. 
     
     
         20 . A process for forming bituminous roofing products with high solar heat reflectance, the process comprising:
 (a) providing a ceramic-forming material comprising at least one aluminosilicate;   (b) providing base particles comprising material thermally stable up to a temperature of at least 900 degrees Celsius;   (c) applying the ceramic-forming material to the base particles to form a green coating layer on the base particles to form green granules;   (d) sintering the green granules at a temperature of at least 900 degrees Celsius until the crystalline content of the coating layer of the granules is at least ten percent as determined by x-ray diffraction;   (e) providing a bituminous roofing sheet material having an upper surface; and   (f) applying the sintered granules in the upper surface of a bituminous roofing sheet material.