Primer composition

Abstract

A primer coating composition for a metal substrate is described. The primer has a suitable binder and is characterized in that there is at least one semiconductor photocatalyst dispersed throughout the primer coating composition. A process of coating a metal substrate is also described. The invention extends to the use of a semiconductor photocatalyst as a top-coat to primer adhesion promoter or as a primer to top-coat delamination inhibitor in a primer coating composition.

1 . A primer coating composition for a metal substrate comprising a suitable organic binder, wherein at least one semiconductor photocatalyst is dispersed throughout the primer coating composition. 
   
   
       2 . A process of coating a metal surface comprising the following steps:
 a) applying a primer coating composition of  claim 1  to the metal substrate;   b) exposing the primer coating composition to UV radiation to at least partially effect photocatalytic degradation of the organic binder;   c) optionally washing an exposed surface of the primer coating composition; and   d) applying a top-coat directly to the exposed surface of the primer coating composition.   
   
   
       3 . A method of improving adhesion of a top-coat to a primer coating composition by a process comprising providing a primer coating composition comprising at least one semiconductor photocatalyst. 
   
   
       4 . The primer coating composition of  claim 1 , wherein the semiconductor photocatalyst is in the form of particles. 
   
   
       5 . The primer coating composition of  claim 1 , wherein the semiconductor photocatalyst is selected from a group consisting of anatase TiO 2 , brookite TiO 2 , strontium titanate, tin oxide, zinc(II) oxide, iron oxide, and mixtures thereof. 
   
   
       6 . The primer coating composition of  claim 1 , wherein the semiconductor photocatalyst is anatase TiO 2 . 
   
   
       7 . The primer coating composition of  claim 1 , wherein the organic binder is selected from alkyd, polyester, urethane, acrylic or epoxy resin binder. 
   
   
       8 . The primer coating composition of  claim 1 , wherein the semiconductor photocatalyst in the composition is in the range 1-40% w/w total dry composition. 
   
   
       9 . A coated substrate comprising a metal substrate, a primer coating composition according to  claim 1  located on the substrate and at least one top-coat. 
   
   
       10 . A coated substrate comprising a substrate and a series of coatings on at least one surface of the substrate including one or more inner coatings and an outer coating, at least one of the said inner coatings being a primer coating composition of  claim 1 . 
   
   
       11 . The primer coating composition of  claim 1 , further comprising additional ingredients selected from the group consisting of solvents, colorants, mineral oils, fillers, elastomers, antioxidants, stabilizers, defoamers, extenders, plasticizers, catalysts, pigments, pigment pastes, reinforcing agents, flow control agents, thickening agents, flame-retarding agents, additional hardeners and additional curable compounds. 
   
   
       12 . The process according to  claim 2 , wherein the primer coating composition is applied directly to an un-primed metal substrate. 
   
   
       13 . A two layer coating system for a metal substrate comprising a first primer coat comprising the primer coating composition of  claim 1  and a second top-coat wherein the top-coat is selected from:
 a) an epoxy based top-coat,   b) a polyurethane based top-coat,   c) an alkyd/polyester resin based top-coat, or   d) an acrylic resin based top-coat.   
   
   
       14 . The process according to  claim 2 , wherein step (b) lasts for an interval of 10-500 days before applying the top-coat in step (d). 
   
   
       15 - 18 . (canceled) 
   
   
       19 . The primer coating composition of  claim 1 , wherein the semiconductor photocatalyst is a photocatalytic metal oxide. 
   
   
       20 . A method of inhibiting delamination of a top-coat from a primer coating composition by a process comprising providing the primer coating composition comprising at least one semiconductor photocatalyst dispersed throughout the primer coating composition. 
   
   
       21 . The primer coating composition of  claim 1 , wherein the metal is steel. 
   
   
       22 . The process of  claim 2 , wherein the metal is steel. 
   
   
       23 . The process of  claim 2 , wherein the UV radiation is sunlight. 
   
   
       24 . The process of  claim 2 , wherein the semiconductor photocatalyst is in the form of particles. 
   
   
       25 . The process of  claim 2 , wherein the semiconductor photocatalyst is selected from a group consisting of anatase TiO 2 , brookite TiO 2 , strontium titanate, tin oxide, zinc(II) oxide, iron oxide, and mixtures thereof. 
   
   
       26 . The process of  claim 2 , wherein the semiconductor photocatalyst is anatase TiO 2 . 
   
   
       27 . The process of  claim 2 , wherein the organic binder is selected from alkyd, polyester, urethane, acrylic or epoxy resin binder. 
   
   
       28 . The process of  claim 2 , wherein the semiconductor photocatalyst in the composition is in the range 1-40% w/w total dry composition. 
   
   
       29 . The process of  claim 2 , further comprising additional ingredients selected from the group consisting of solvents, colorants, mineral oils, fillers, elastomers, antioxidants, stabilizers, defoamers, extenders, plasticizers, catalysts, pigments, pigment pastes, reinforcing agents, flow control agents, thickening agents, flame-retarding agents, additional hardeners and additional curable compounds. 
   
   
       30 . The process of  claim 2 , wherein the semiconductor photocatalyst is a photocatalytic metal oxide. 
   
   
       31 . The two layer coating system of  claim 13 , wherein the metal substrate is a ship's hull.