Controlled time-release algae resistant roofing system

Abstract

Time-release algae-resistant roofing granules have a base particle including an algaecide and an outer coating layer including another algaecide. The at least two algaecides are released over different predetermined periods. The outer layer protects the base particle from exposure to the environment for a predetermined period, then fails catastrophically so that the interior algaecide can be released.

1 . A process for producing time-release algae-resistant roofing granules, the process comprising:
 (a) providing base particles comprising at least one first algaecidal material; and   (b) encapsulating the base particles with an outer coating composition including at least one second algaecidal material to form an outer layer, the at least one second algaecidal material differing from the at least one first algaecidal material, the encapsulating outer layer protecting the base particles from exposure to the environment, the outer coating composition being selected such that the outer layer fails catastrophically after a predetermined period thereby exposing at least a portion of the base particles to the environment, the at least one second algaecidal material being releasable from the outer layer during the predetermined period.   
   
   
       2 . A process according to  claim 1  further comprising;
 (a) providing inert core particles; and   (b) forming the base particles by coating the inert core particles with an inner coating composition to form an inner layer on the inert core particles, the inner coating composition including the at least one first algaecidal material.   
   
   
       3 . A process according to  claim 2  wherein the inner coating composition includes a binder comprising an aluminosilicate material and an alkali metal silicate. 
   
   
       4 . A process according to  claim 1  wherein the at least one first algaecidal material is selected from the group consisting of copper compounds, zinc compounds, and mixtures thereof. 
   
   
       5 . A process according to  claim 1  wherein the outer coating composition includes a binder comprising a material selected from the group consisting of an organic polymeric material or/and an inorganic material. 
   
   
       6 . A process according to  claim 1  further comprising providing base particles comprising metallic granules. 
   
   
       7 . A process according to  claim 1  further comprising providing an interlayer on the base particles, the interlayer enhancing the release of the at least one first algaecidal material under predetermined conditions. 
   
   
       8 . A process according to  claim 7  wherein the interlayer includes a UV degradable material selected from the group consisting of virgin and recycled natural or synthetic polymers and copolymers and combinations thereof. 
   
   
       9 . A process according to  claim 7  wherein the interlayer includes a photocatalytic material. 
   
   
       10 . Time-release algae-resistant roofing granules, each granule comprising:
 (a) a base particle comprising at least one first algaecidal material; and   (b) at least one outer coating layer formed from an outer coating composition including at least one second algaecidal material and encapsulating the base particle, the at least one second algaecidal material differing from the at least one first algaecidal material, the encapsulating at least one outer layer protecting the base particle from exposure to the environment, the outer coating composition being selected such that the outer layer fails catastrophically after a predetermined period thereby exposing the base particles to the environment, the at least one second algaecidal material being releasable from the outer layer during the predetermined period.   
   
   
       11 . Time-release algae-resistant roofing granules according to  claim 10  wherein the base particles comprise inert core particles coated with an inner coating composition to form an inner layer on the inert core particles, the inner coating composition including the at least one first algaecidal material. 
   
   
       12 . Time-release algae-resistant roofing granules according to  claim 10  wherein the at least one first algaecidal material is releasable from the granule during a second predetermined period. 
   
   
       13 . Time-release algae-resistant roofing granules according to  claim 10  wherein the inner coating composition includes a binder comprising an aluminosilicate material and an alkali metal silicate. 
   
   
       14 . Time-release algae-resistant roofing granules according to  claim 10  wherein the at least one first algaecidal material is selected from the group consisting of copper compounds, zinc compounds, and mixtures thereof. 
   
   
       15 . Time-release algae-resistant roofing granules according to  claim 14  wherein the at least one first algaecidal material is cuprous oxide. 
   
   
       16 . Time-release algae-resistant roofing granules according to  claim 10  wherein the outer coating composition includes a binder comprising a material selected from the group consisting of an organic polymeric material and an inorganic material. 
   
   
       17 . Time-release algae-resistant roofing granules according to  claim 16  wherein the at least one second algaecidal material is initially uniformly dispersed in the binder, and subsequently diffuses to the exterior surface of the outer layer. 
   
   
       18 . Time-release algae-resistant roofing granules according to  claim 10  wherein the at least one second algaecidal material is an organic biocide. 
   
   
       19 . Time-release algae-resistant roofing granules according to  claim 16  wherein the binder is selected from the group consisting of poly(meth)acrylate, polyurethanes and polyureas; and the inorganic materials include, aluminosilicate, silica and phosphate binders. 
   
   
       20 . Time-release algae-resistant roofing granules according to  claim 10  wherein the outer layer has a thickness of from about 5 micrometers to about 200 micrometers. 
   
   
       21 . Time-release algae-resistant roofing granules according to  claim 10  wherein the base particles comprise metallic granules. 
   
   
       22 . Time-release algae-resistant roofing granules according to  claim 10  further comprising an interlayer coated on the base particles, the interlayer enhancing the release of the at least one first algaecidal material under predetermined conditions. 
   
   
       23 . Time-release algae-resistant roofing granules according to  claim 10  wherein the base particles comprise microshells encapsulating the at least one first algaecidal material, each microshell having a wall enclosing an interior cavity, the interior cavity containing the at least one first algaecidal material, the microshell wall being permeable to the at least one first algaecidal material. 
   
   
       24 . A sheet roofing product including a bituminous base and time-release algae-resistant roofing granules, each granule comprising:
 (a) a base particle comprising at least one first algaecidal material; and   (b) at least one outer coating layer formed from an outer coating composition including at least one second algaecidal material and encapsulating the base particle, the at least one second algaecidal material differing from the at least one first algaecidal material, the encapsulating at least one outer layer protecting the base particle from exposure to the environment, the outer coating composition being selected such that the outer layer fails catastrophically after a predetermined period thereby exposing the base particles to the environment, the at least one second algaecidal material being releasable from the outer layer during the predetermined period.   
   
   
       25 . A sheet roofing product according to  claim 24  wherein the base particles comprise inert core particles coated with an inner coating composition to form an inner layer on the inert core particles, the inner coating composition including the at least one first algaecidal material.