Photocatalytic Roofing Granules, Photocatalytic Roofing Products, and Process for Preparing Same

Abstract

Photocatalytic roofing granules include a binder and inert mineral particles, with photocatalytic particles dispersed in the binder.

1 - 30 . (canceled) 
     
     
         31 . Photocatalytic roofing granules comprising:
 (a) a binder that is a chemically-bonded phosphate cement;   (b) inert mineral particles; and   (c) photocatalytic particles; the inert mineral particles and the photocatalytic particles being dispersed in the binder.   
     
     
         32 . Photocatalytic roofing granules according to  claim 31  wherein the photocatalytic particles are particles of zinc oxide. 
     
     
         33 . Photocatalytic roofing granules according to  claim 31 , wherein the photocatalytic particles are particles of anatase titanium oxide or vanadium oxide. 
     
     
         34 . Photocatalytic roofing granules according to  claim 31  wherein the photocatalytic particles have an average particle size from about 5 nanometers to 100 nanometers. 
     
     
         35 . Photocatalytic roofing granules according to  claim 31  wherein the inert mineral particles have an average particle size from about 0.1 micrometers to 40 micrometers. 
     
     
         36 . Photocatalytic roofing granules according to  claim 31  having an average particle size from about 0.1 mm to 3 mm. 
     
     
         37 . Photocatalytic roofing granules according to  claim 31 , wherein the chemically-bonded phosphate cement is a cured product of a cementitious exterior coating composition including at least one metal oxide or a metal hydroxide slightly soluble in an acidic aqueous solution to provide metal cations and a source of phosphate anions. 
     
     
         38 . Photocatalytic roofing granules according to  claim 37 , wherein relative quantities of the at least one metal oxide or metal hydroxide and at least one source of phosphate anion are selected to provide a cured coating having a neutral pH, the coating composition being cured by the acid-base reaction of the at least one metal oxide or hydroxide and the source of phosphate anions. 
     
     
         39 . Photocatalytic roofing granules according to  claim 37 , wherein the cementitious exterior coating composition comprises at least one metal oxide or metal hydroxide as a source of metal cations and at least one phosphate. 
     
     
         40 . Photocatalytic roofing granules according to  claim 37 , wherein the at least one metal oxide or metal hydroxide comprises at least one clay. 
     
     
         41 . Photocatalytic roofing granules according to  claim 37 , wherein the at least one metal oxide or metal hydroxide is selected from the group consisting of magnesium oxide, calcium oxide, iron oxide, copper oxide, aluminum oxide, cobalt oxide, zirconium oxide and molybdenum oxide. 
     
     
         42 . Photocatalytic roofing granules according to  claim 41 , wherein the at least one metal oxide or metal hydroxide is zinc oxide and wherein the photocatalytic particles are particles of anatase titanium oxide or vanadium oxide. 
     
     
         43 . Photocatalytic roofing granules according to  claim 37 , wherein the at least one phosphate is selected from the group consisting of phosphoric acid and acid phosphate salts. 
     
     
         44 . Photocatalytic roofing granules according to  claim 37 , wherein the at least phosphate is selected from the group consisting of phosphoric acid, and acid salts of phosphorous oxo anions, 
     
     
         45 . Photocatalytic roofing granules according to claim  18 , wherein the at least one phosphate is selected from salts including at least one cation selected from the group consisting of ammonium, calcium, sodium, potassium, and aluminum cations. 
     
     
         46 . Photocatalytic roofing granules according to  claim 37 , wherein the at least one phosphate is selected from the group consisting of phosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate, magnesium hydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, aluminum hydrogen phosphate, aluminum dihydrogen phosphate, and mixtures thereof. 
     
     
         47 . Photocatalytic roofing granules according to  claim 37 , wherein binder further comprises colloidal silica. 
     
     
         48 . A process for preparing photocatalytic roofing granules according to  claim 31 , the process comprising:
 (a) providing a cementitious exterior coating composition comprising at least one metal oxide or metal hydroxide as a source of metal cations and at least one phosphate, inert mineral particles, and photocatalytic particles;   (b) dispersing the inert mineral particles and the photocatalytic particles in the cementitious exterior coating composition to form a mixture;   (c) forming the mixture into granules; and   (d) curing the cementitious exterior coating composition.   
     
     
         49 . Photocatalytic roofing granules, each comprising:
 a base particle having an outside surface; and   disposed on the outside surface of the base particle, a coating of photocatalytic particles dispersed in a binder that is a chemically-bonded phosphate cement.   
     
     
         50 . A process for making photocatalytic particles according to  claim 49 , the process comprising:
 (a) providing a cementitious exterior coating composition comprising at least one metal oxide or metal hydroxide as a source of metal cations and at least one phosphate, and photocatalytic particles;   (b) dispersing the photocatalytic particles in the cementitious exterior coating composition to form a mixture; and   (c) coating the mixture on outside surfaces of base particles; and   (d) curing the cementitious exterior coating composition.