Cathodic corrosion protection powder coating composition and method

Abstract

The present invention provides a curable cathodic corrosion protection powder coating, which comprises a thermosetting resin, a zinc borate compound, a curing agent in an amount effective to cure the coating. Further, the present invention also provides a method of cathode corrosion protection which includes the steps of subjecting the substrate to a mechanical treatment, applying to said treated steel surface, the cathodic protective coating, and polarizing the coated material as a cathode.

We claim:  
     
         1 . A curable coating composition comprising: 
 (a) a thermosetting resin, or mixture of thermosetting resins;    (b) from about 0.5 to 4.75% by weight, based upon total solids weight, of a zinc borate compound; and    (c) a curing agent, or mixture of curing agents, capable of curing said coating composition in an amount effective to cure the coating.    
     
     
         2 . The coating composition of  claim 1  wherein said composition is a powder coating composition.  
     
     
         3 . The coating composition of  claim 1  wherein said thermosetting resin is at least one resin selected from (a) epoxy resins and epoxy curing agents, (b) polyol resins and isocyanates, (c) acryl modified epoxy resins and polymerization initiators, (d) alkyd resins, (e) humidity curing type urethane resins, and (f) phenoxy resins.  
     
     
         4 . The coating composition of  claim 1  wherein said thermosetting resin is a bisphenol A/epichlorohydrin epoxy functional resin.  
     
     
         5 . The coating composition of  claim 1  which comprises from about 25 to 90% by weight, based upon total solids weight, of said thermosetting resin, or mixtures thereof.  
     
     
         6 . The coating composition of  claim 1  which comprises from about 60 to 80% by weight, based upon total solids weight, of said thermosetting resin, or mixtures thereof.  
     
     
         7 . The coating composition of  claim 1  which comprises from about 1.5 to 2.5% by weight, based upon total solids weight, of said zinc borate compound.  
     
     
         8 . The coating composition of  claim 1  wherein said zinc borate compound is at least one compound selected from the group consisting of zinc methaborate, basic zinc borate and zinc borate.  
     
     
         9 . The coating composition of  claim 1  wherein said zinc borate compound is zinc borate, as represented by the formula:  
       2ZnO.3B 2 O 3 .3.5H 2 O  
     
     
         10 . The coating composition of  claim 1  wherein the said curing agent is an epoxy curing compound selected from the group consisting of aliphatic diamines, aromatic diamines, heterocyclic diamines and the modified products of the above-mentioned diamines, polyamide resins reacted with aliphatic acids or the dimers thereof, acid anhydrides, thiols, phenols, dicyandiamide derivatives having an addition reactivity and self-polyaddition catalytic activity, and imidazoles.  
     
     
         11 . The coating composition of  claim 1  wherein said curing agent is an accelerated dicyandiamide functional epoxy curing compound.  
     
     
         12 . The coating composition of  claim 1  wherein said curing agent is a phenolic functional epoxy curing compound.  
     
     
         13 . The coating composition of  claim 1  which comprises from about 1 to 35% by weight, based upon total solids weight, of said curing agent, or mixtures thereof.  
     
     
         14 . The coating composition of  claim 1  which comprises from about 2 to 20% by weight, based upon total solids weight, of said curing agent, or mixtures thereof.  
     
     
         15 . The coating composition of  claim 1  which further comprises a calcium oxide filler, silicate filler, or mixture thereof.  
     
     
         16 . The coating composition of  claim 1  which further comprises a pigment selected from the group consisting of titanium dioxide, iron oxide, aluminum, bronze or phthalocyanine blue.  
     
     
         17 . The coating composition of  claim 1  which further comprises an additive, or mixture of additives selected from the group consisting of dyes, flow control agents, dispersants, thixotropic agents, adhesion promoters, antioxidants, light stabilizers, curing catalysts, anticorrosion agents, and substituted benzotriazoles.  
     
     
         18 . The coating composition of  claim 1  which comprises from about 0 to 55% by weight, based upon total solids weight, of fillers, pigments, additives, or any mixtures thereof.  
     
     
         19 . The coating composition of  claim 1  which comprises from about 20 to 35% by weight, based upon total solids weight, of fillers, pigments, additives, or any mixtures thereof.  
     
     
         20 . An epoxy powder coating composition comprising a thermosetting epoxy resin and curing agent for said epoxy resin, wherein the improvement is the addition of from about 0.5 to 4.75% by weight, based upon total solids weight, of a zinc borate compound for improved resistance to cathodic disbandment.  
     
     
         21 . A method of cathode protection for a steel material, comprising the steps of: 
 (a) subjecting the steel surface to a mechanical treatment,    (b) applying to said treated steel surface, the coating composition of  claim 1 , and    (c) polarizing the coated steel material as a cathode.    
     
     
         22 . The method of cathode protection claimed in  claim 21  wherein a heavy duty protective film and/or a finishing layer is further applied to the surface of the coated film.