Coating powders, methods of manufacture thereof, and articles formed therefrom

#This disclosure relates to coating powders, and methods for the enhanced storage and cure of coating powders.

#Coating powders are dry, finely divided, free-flowing solid materials at room temperature. Conventional coating powders require high temperatures to fuse and cure, and are thus limited to substrates such as metals that can withstand high temperatures. A number of coating powders for heat-sensitive substrates such as wood, fiberboard, and some plastics have been developed, for example that disclosed in U.S. Pat. No. 6,294,610 to Daly et al.

#A particular challenge in the manufacture and use of coating powders for heat-sensitive substrates is that the difference between the extrusion temperature of the coating powder and the curing temperature of the powder is small, which can result in some curing during extrusion. Another drawback is that when one-part coating powders contain catalysts to decrease curing time and temperature, solid-state reaction between the catalyst and resin particles can lead to decreased storage stability. Accordingly, there remains a need for coating powders with increased storage stability, particularly for coating powders that cure at low temperature.

#As used herein, a coating powder means a solid, particulate, film-forming composition, whereas a powder coating means the film formed on a substrate by curing a coating powder. Coating powders usually comprise a solid thermoplastic or thermosetting film-forming polymer resin. A number of different thermoplastic resins for coating powders are known, for example vinyl chloride, polyamides, celluloses, polyolefins, polyethylene, and polyesters. Thermosetting film-forming resins contain reactive functional groups, an optional curing agent (crosslinking agent) having functional groups reactive with the functional groups of the polymer resin (and which may itself be another film-forming polymer), and an optional catalyst. Known thermosetting resins include but are not limited to acid-functional polyester resins, acid-functional acrylic resins, epoxy resins, and hydroxy-functional polyester resins.

#Preferred polymer resins are low temperature cure thermosetting resins suitable for use with heat-sensitive substrates such as wood, fiberboard, and some plastics. Low temperature cure compositions generally cure at temperatures less than 325° F. (163° C.), preferably less than 300° F. (149° C.), most preferably less than 275° F. (135° C.). Cure is also generally greater than about 100° F. (39° C.), more preferably greater than 200° F. (93° C.) to provide storage and processing stability.

#One example of a suitable coating powder composition capable of cure at low temperatures comprises an acid functional polymer such as carboxylic acid functional polyester or a carboxylic acid functional acrylic resin, a polyepoxy compound, and an optional catalyst. As described in U.S. Pat. No. 6,294,610 to Daly, et al., the combined functionality comprising the carboxylic acid functionality of the carboxylic acid polymer and the epoxy functionality of the polyepoxy compound is preferably at least five, more preferably at least 7.