Algae resistant roofing granules with controlled algaecide leaching rates, algae resistant shingles, and process for producing same

Abstract

Algae-resistant roofing granules are formed by extruding a mixture of mineral particles and a binder to form porous granule bodies, and algaecide is distributed in the pores. Release of the algaecide is controlled by the structure of the granules.

We claim: 
     
         1 . An algae-resistant roofing shingle, the shingle being produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a shingle stock material, the algae-resistant roofing granules being produced by a process comprising:
 (a) providing porous, inert base particles; and   (b) providing at least one inorganic algaecide on or within the base particles to form algaecide-bearing particles.   
     
     
         2 . An algae-resistant roofing shingle according to  claim 1 , wherein the base particles are prepared from a mixture including stone dust and a binder. 
     
     
         3 . An algae-resistant roofing shingle according to  claim 2  wherein the binder comprises an aluminosilicate material. 
     
     
         4 . An algae-resistant roofing shingle according to  claim 3  wherein the mixture is formed into base particles by a forming process selected from press molding, cast molding, injection molding, extrusion, spray granulation, gel casting, pelletizing, compaction and agglomeration. 
     
     
         5 . An algae-resistant roofing shingle according to  claim 1  wherein the at least one inorganic algaecide is provided on the base particle by coating the base particle with the at least one inorganic algaecide. 
     
     
         6 . An algae-resistant roofing shingle according to  claim 3  wherein the base particles are fired in a kiln to insolubilize the binder. 
     
     
         7 . An algae-resistant roofing shingle according to  claim 1  wherein the at least one inorganic algaecide is selected from the group consisting of copper materials, zinc materials, and mixtures thereof. 
     
     
         8 . An algae-resistant roofing shingle according to  claim 7  wherein the inorganic algaecides are cuprous oxide and zinc oxide. 
     
     
         9 . An algae-resistant roofing shingle according to  claim 7  wherein the at least one inorganic algaecide is provided in the base particles after the base particles are fired, an algaecide-forming compound being dissolved in a fluid to form a solution, the solution being drawn into the pores in the base particles by capillary action to form solution-laden particles, the solution-laden particles being subsequently treated to convert the algaecide-forming compound to an inorganic algaecide. 
     
     
         10 . An algae-resistant roofing shingle according to  claim 9  wherein the algaecide-forming compound is a soluble copper salt, and the solution-laden particles are subsequently treated by heating the particles to convert the soluble copper salt to cuprous oxide. 
     
     
         11 . An algae-resistant roofing shingle according to  claim 7  wherein the at least one inorganic algaecide is provided in the base particles after the base particles are fired, an algaecide-forming compound being mixed with a binder and a fluid to form a slurry, the slurry being drawn into the pores in the base particles by capillary action to form slurry-laden particles, the slurry-laden particles being subsequently treated to convert the algaecide-forming compound to an inorganic algaecide. 
     
     
         12 . An algae-resistant roofing shingle according to  claim 11  wherein the algaecide-forming compound is a soluble copper salt, and the slurry-laden particles are subsequently treated by heating the particles to convert the soluble copper salt to cuprous oxide. 
     
     
         13 . An algae-resistant roofing shingle according to  claim 1  further comprising coating the algaecide-bearing particles with a colorant composition. 
     
     
         14 . An algae-resistant roofing shingle according to  claim 13  wherein the colorant composition includes a fusible binder, and further comprising heating the colorant-coated algaecide-bearing particles to fuse the binder. 
     
     
         15 . An algae-resistant roofing shingle, the shingle being produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a shingle stock material, the algae-resistant roofing granules being produced by a process comprising:
 (a) mixing stone dust, a binder and at least one inorganic algaecide; and   (b) forming the mixture into particles by a forming process selected from press molding, cast molding, injection molding, extrusion, spray granulation, gel casting, and pelletizing.   
     
     
         16 . An algae-resistant roofing shingle according to  claim 15  wherein the at least one inorganic algaecide is selected from the group consisting of copper materials, zinc materials, and mixtures thereof. 
     
     
         17 . An algae-resistant roofing shingle according to  claim 16  wherein the inorganic algaecides are cuprous oxide and zinc oxide. 
     
     
         18 . An algae-resistant roofing shingle according to  claim 15 , wherein the binder comprises an aluminosilicate material, and the process further comprises firing the particles in a kiln to insolubilize the binder.