Sacrificial anode coating containing a fugitive colorant

Claim 1

A COATING COMPOSITION FOR THE PROTECTION OF A FERROUS METAL SURFACE COMPRISING AN ADMIXTURE BASED UPON 100 PERCENT BY WEIGHT OF THE COATING COMPOSITION OF 5075 PERCENT BY WEIGHT OF AN ANODE METAL POWDER SELECTED FROM THE CLASS CONSISTING OF ZINC DUST AND MAGNESIUMZINC ALLOY PARTICLES HAVING BETWEEN 70 AND 85 WEIGHT PERCENT OF ZINC AND BETWEEN 30 AND 15 WEIGHT PERCENT OF MAGNESIUM; A BINDER CONSISTING ESSENTIALLY OF 10 TO 25 PERCENT OF AN ALKALI SILICATE SOLUTION, 2 TO 10 PERCENT OF AN ACRYLIC RESIN EMULSION WHEREIN THE RESIN IS AN INTERPOLYMER COMPRISED OF: (1) UNITS HAVING CARBOXYLATE GROUPS FROM AT LEAST ONE POLYMERIZABLE ALPHA, BETA-UNSATURATED VINYLIDENE CARBOXYLIC ACID, (2) UNITS FROM AT LEAST ONE POLYMERIZABLE ESTER WHICH BY ITSELF FORMS SOFT POLYMERS AND WHICH IS SELECTED FROM THE CLASS CONSISTING OF ESTERS OF ACRYLIC ACID AND PRIMARY ALKANOLS OF 1 TO 18 CARBON ATOMS, ESTERS OF ACRYLIC ACID AND SECONDARY ALKANOLS OF 1 TO 18 CARBON ATOMS, ESTERS OF METHACRYLIC ACID AND PRIMARY ALKANOLS OF 5 TO 18 CARBON ATOMS, ESTERS OF METHACRYLIC ACID AND SECONDARY ALKANOLS OF 5 TO 18 CARBON ATOMS, AND (3) UNITS FROM AT LEAST ONE POLYMERIZABLE MONOVINYLIDENE COMPOUND WHICH BY ITSELF FORMS A HARD POLYMER AND WHICH IS SELECTED FROM THE CLASS CONSISTING OF ALKYL METHACRYLATES IN WHICH THE ALKYL GROUP HAS 1 TO 4 CARBON ATOMS, TERT-AMYL METHACRYLATE, TERTBUTYL ACRYLATE, TERT-AMYL ACRYLATE, CYCLOHEXYL ACRYLATE, AND CYCLOHEXYL METHACRYLATE WITH THE CARBOXYLATE UNITS CONSTITUTING BETWEEN 0.5 TO 2.5% OF THE INTERPOLYMER AND THE PROPORTION OF UNITS FROM THE SOFT POLYMER-FORMING ESTER BEING SUFFICIENT TO CAUSE THE DISPERSION OF INTERPOLYMER TO FORM ADHESIVE AND COHESIVE FILMS AT AN APPLICATION TEMPERATURE OF ABOUT 35*C. AND THE RATIO OF UNITS FROM SAID ESTER TO UNITS FROM THE VINYLIDENE COMPOUND BEING BETWEEN 9:1 AND 1:20, AND SUFFICIENT WATER TO ADJUST THE VISCOSITY TO THAT DESIRED FOR THE MODE OF APPLICATION OF THE COATING TO THE SURFACE; AND A FUGITIVE TRIPHENYLMETHANE COLORANT IN AN AMOUNT BETWEEN 0.1 AND 2.0 PERCENT SUFFICIENT TO IMPART A DISCERNIBLE COLOR TO THE COATING COMPOSITION, SAID COLORANT BECOMING COLORLESS UPON EXTENDED EXPOSURE.