Disbondment resistant epoxy powder coating composition

A thermosetting epoxy powder coating composition, which is a composition in particulate form that comprises a blend of:

• (a) an epoxy resin comprising a diglycidyl ether of bisphenol A having a weight per epoxide between about 700 and 1,200;
• (b) a curing agent for said epoxy resin comprising a bisphenol A endcapped diglycidyl ether of bisphenol A having a hydroxy equivalent weight between about 350 and 450;
• and,
• (c) from about 4 to about 10 phr of a cure catalyst comprising an imidazole adduct with a diglycidyl ether of bisphenol A;
• (d) up to about 60 phr of pigments;
• (e) up to about 2 phr of an acrylic flow modifier;
• (f) up to about 4 phr of a fumed silica;
• and,
• (g) up to about 100 phr of a filler,
• in which the stoichiometry of said curing agent to said epoxy resin is provided in an effective amount at or below about 60% stoichiometry.

A thermosetting epoxy powder coating composition, which is a composition in particulate form that comprises a blend of:

• (a) an epoxy resin which is a diglycidyl ether of a dihydric phenol having a weight per epoxide between about 650 and about 2,000;
• (b) a phenolic curing agent for said epoxy resin which is a bisphenol A endcapped diglycidyl ether of bisphenol A having a hydroxy equivalent weight between about 180 and about 450;
• and,
• (c) an effective amount of a cure catalyst which is selected from the group consisting of an imidazole and an imidazole adduct with a diglycidyl ether of bisphenol A,
• in which the stoichiometry of said curing agent to said epoxy resin is provided in an effective amount at or below about 60% stoichiometry.

A method of powder coating, which comprises:

• a) electrostatically applying a thermosetting epoxy powder coating composition partially or completely over steel strapping at ambient temperature, in which said composition is in particulate form and comprises a blend of:
• i) an epoxy resin which is a diglycidyl ether of a dihydric phenol having a weight per epoxide between about 650 and about 2,000;
• ii) a phenolic curing agent for said epoxy resin which is a bisphenol A endcapped diglycidyl ether of bisphenol A having a hydroxy equivalent weight between about 180 and about 450;
• and,
• iii) an effective amount of a cure catalyst which is selected from the group consisting of an imidazole and an imidazole adduct with a diglycidyl ether of bisphenol A,
• in which the stoichiometry of said curing agent to said epoxy resin is provided in an effective amount at or below about 60% stoichiometry;
• b) heating said steel strapping to a substrate temperature sufficient to melt, flow and cure said composition over said steel strapping and form a smooth, dry, continuous film finish thereon;
• and,
• c) cooling said steel strapping to ambient temperature.