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.

1 . Solar heat-reflective roofing granules comprising:
 a) a base particle having a flake-like geometry, and an average particle size from #5 US mesh to #50 US mesh,   b) a uniform coating layer on the base particle, the coating layer having a thickness of at least one mil, the coating layer comprising a coating binder and at least one solar heat-reflective pigment, the solar heat-reflective pigment providing a solar heat reflectance of greater than 70 percent to the granules.   
     
     
         2 . Solar heat-reflective roofing granules according to  claim 1 , wherein the roofing granules have an aspect ratio of at least 3. 
     
     
         3 .- 4 . (canceled) 
     
     
         5 . Solar heat-reflective roofing granules according to  claim 1 , wherein the coating layer has a thickness of at least 2 mils. 
     
     
         6 . Solar heat-reflective roofing granules according to  claim 1 , wherein the base particles are selected from the group consisting of crushed slate, slate granules, shale granules, mica granules, metal flakes, and flake-like synthetic particles. 
     
     
         7 . Solar heat-reflective roofing granules according to  claim 1 , wherein the coating binder is selected from the group consisting of metal silicates, fluoropolymers, metal phosphates, silica coating binders, sol-gel coating binders, polysiloxanes, silicones, polyurethanes, and polyacrylates. 
     
     
         8 . Solar heat-reflective roofing granules according to  claim 1 , wherein the at least one solar heat-reflective pigment is selected from the group consisting of titanium dioxide, calcium carbonate, zinc oxide, lithopone, zinc sulphide, white lead, glass microspheres, glass microbubbles, microvoid pigments, and synthetic polymeric opacifiers. 
     
     
         9 . Solar heat-reflective roofing granules according to  claim 1 , which have (a* 2 +b* 2 ) 1/2  less than 6. 
     
     
         10 . A solar heat-reflective roofing product comprising:
 a) a base sheet, and   b) solar heat-reflective roofing granules on top of the base sheet, the granules comprising:
 1) a base particle having a flake-like geometry, and an average particle size from #5 US mesh to #50 US mesh, 
 2) a uniform coating layer on the base particle, the coating layer having a thickness of at least one mil, the coating layer comprising a coating binder and at least one solar heat-reflective pigment, the solar heat-reflective pigment providing a solar heat reflectance of greater than 70 percent to the granules. 
   
     
     
         11 . A solar heat-reflective roofing product according to  claim 10  wherein the granules cover at least 85 percent of the surface area of the base sheet. 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . A solar heat-reflective roofing product according to  claim 10 , wherein the roofing granules particles have an aspect ratio of at least 3. 
     
     
         15 .- 20 . (canceled) 
     
     
         21 . A solar heat-reflective roofing product according to  claim 10  wherein the solar heat-reflective roofing granules have (a* 2 +b* 2 ) 1/2  less than 6. 
     
     
         22 . A solar heat-reflective roofing product according to  claim 10 , the solar heat-reflective roofing granules comprising primary roofing granules, the shingle further comprising secondary roofing granules interspersed among the primary roofing granules. 
     
     
         23 . A solar heat-reflective roofing product according to  claim 22 , the secondary roofing granules including at least one algaecide. 
     
     
         24 . A process for preparing solar heat reflective roofing granules, the process comprising:
 a) providing base particles having a flake-like geometry, and an average particle size from #5 US mesh to #50 US mesh,   b) providing a coating composition including a coating binder and at least one solar heat-reflective pigment; and   c) coating the base particles with the coating composition to provide a uniform coating layer on the base particles, the solar heat-reflective pigment providing a solar heat reflectance of greater than 70 percent to the granules.   
     
     
         25 . A process for preparing solar heat reflective roofing products, the process comprising:
 a) providing base particles having a flake-like geometry, and an average particle size from #5 US mesh to #50 US mesh,   b) providing a coating composition including a coating binder and at least one solar heat-reflective pigment;   c) coating the base particles with the coating composition to provide a uniform coating layer on the base particles, the solar heat-reflective pigment providing a solar heat reflectance of greater than 70 percent to the granules, thus providing solar heat-reflective roofing granules;   d) providing a bituminous base sheet having an upper surface; and   e) applying the solar heat-reflective roofing granules to the upper surface of the base sheet, the solar heat heat-reflective roofing granules being applied to at least 85 percent of the upper surface.   
     
     
         26 . A process according to  claim 25  wherein the solar heat-reflective roofing granules are applied to at least 90 percent of the upper surface. 
     
     
         27 . (canceled) 
     
     
         28 . Solar heat-reflective roofing granules according to  claim 9 , having a value of L* of at least one of greater than about 80, greater than about 85 or greater than about 90. 
     
     
         29 .- 31 . (canceled) 
     
     
         32 . A solar heat-reflective roofing product according to  claim 10 , wherein the roofing product is a roofing membrane. 
     
     
         33 . (canceled) 
     
     
         34 . A solar heat-reflective roofing product according to  claim 10 , wherein the roofing product is a shingle. 
     
     
         35 .- 38 . (canceled) 
     
     
         39 . A process according to  claim 24 , wherein the coating layer has an average coating thickness, and the coating thickness does not vary by more than about 25 percent of the average coating thickness. 
     
     
         40 . A process according to  claim 25 , wherein the solar heat-reflective roofing granules comprise a first class of granules, and a second class of granules are provided, the second class of granules having a smaller average dimension than the first class of granules, and granules of the second class of granules are applied to the upper surface of the base sheet. 
     
     
         41 . A process according to  claim 40 , wherein the granules of the second class have a size and a shape selected so that granules of the second class of granules will tend to lie in interstitial spaces between granules of the first class of granules.