Coating system for cement composite articles

Abstract

A substrate may be coated with a various combinations of a water-dispersible polyisocyanate, a water-soluble acid or salt thereof, and/or an isocyanate-reactive compound. The resulting coated article has improved coating adhesion, especially near coated burnished surfaces such as sawn edges or grooves.

1 . An aqueous coating composition comprising an aqueous mixture of water-dispersed polyisocyanate, a water-soluble inorganic or water-soluble monomeric or oligomeric organic acid or water-soluble salt thereof in an amount that affords improved coating adhesion on a cementitious substrate, and an optional isocyanate-reactive compound. 
     
     
         2 . (canceled) 
     
     
         3 . A method for preparing a coating, which method comprises providing a cementitious substrate having at least one outer surface; applying to such surface an aqueous solution of an acid or salt thereof, which acid or salt affords improved coating adhesion on a cementitious substrate, together with or followed by an aqueous coating composition comprising water-dispersible polyisocyanate; exposing the surface of the thus-applied coating to steam, ammonia, an amino compound or other isocyanate-reactive compound, thereby providing a coating having reduced surface tack, and overcoating such reduced surface tack coating with one or more of a sealer, primer or topcoat. 
     
     
         4 . (canceled) 
     
     
         5 . A coated article comprising a cementitious substrate having at least one outer surface at least a portion of which is coated with an aqueous mixture comprising water-dispersed polyisocyanate, water-soluble acid or water-soluble salt of such an acid, and an optional isocyanate-reactive compound. 
     
     
         6 . A coated article according to  claim 5  wherein the substrate is cement fiberboard. 
     
     
         7 . A composition according to  claim 1  wherein the acid is inorganic. 
     
     
         8 . A composition according to  claim 1  wherein the acid is a monomeric or oligomeric organic acid. 
     
     
         9 . A composition according to  claim 1  wherein the acid or salt comprises a phosphorus acid or salt. 
     
     
         10 . A composition according to  claim 1  wherein the salt comprises a sodium, potassium or ammonium salt. 
     
     
         11 . A composition according to  claim 1  wherein the salt comprises a silicate salt. 
     
     
         12 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains about 60 to about 99 wt. % water-dispersible polyisocyanate and about 1 to about 40 wt. % water-soluble acid or salt. 
     
     
         13 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains the isocyanate-reactive compound. 
     
     
         14 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains an isocyanate-reactive emulsion polymer. 
     
     
         15 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains an isocyanate-reactive emulsion polymer comprising isocyanate-reactive hydroxyl groups. 
     
     
         16 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains an isocyanate-reactive acrylic latex. 
     
     
         17 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains an isocyanate-reactive emulsion polymer stabilized by an alkali-soluble polymer. 
     
     
         18 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains about 1 to about 75 wt. % water-dispersible polyisocyanate and about 99 to about 25 wt. % isocyanate-reactive compound. 
     
     
         19 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains about 5 to about 40 wt. % water-dispersible polyisocyanate, about 1 to about 40 wt. % water-soluble acid or salt and about 95 to about 20 wt. % isocyanate-reactive compound. 
     
     
         20 . A method according to  claim 3  wherein the substrate is cement fiberboard, and the method further comprises at least partially drying the aqueous solution prior to applying such aqueous mixture coating composition. 
     
     
         21 . A method according to  claim 3  wherein the aqueous coating composition is applied to one or more burnished regions on the substrate and at one or more edges, corners or grooves proximate such burnished regions. 
     
     
         22 . A composition according to  claim 1  wherein the aqueous mixture or aqueous coating composition contains an isocyanate-reactive compound comprising acetoacetoxy groups.