Modified aminoplast crosslinkers and powder coating compositions containing such crosslinkers

A multilayer composite coating composition comprising a base coat deposited from a film-forming coating base coating composition and a top coat over at least a portion of the base coat deposited from a curable powder top coating composition comprising a solid particulate film-forming mixture of the following components:

• (1) a polymer containing reactive functional groups, said polymer having a glass transition temperature of at least 30° C.;
• and
• (2) a crosslinking agent having functional groups reactive with the functional groups of the polymer (1), said crosslinking agent comprising an ungelled reaction product of the following reactants:
• (a) at least one aminoplast resin;
• and
• (b) at least one compound having active hydrogen-containing groups reactive with aminoplast resin (a), said compound selected from at least one of:
• (i) compounds having the following structure (I):
• wherein X is aromatic;
• R1, R2, and R3 can be the same or different and each independently represents H, (cyclo)alkyl having from 1 to 12 carbon atoms, aryl, alkaryl, aralkyl, or an active hydrogen-containing group,
• provided that at least one of R1, R2, and R3 represents an active hydrogen-containing group which is reactive with the aminoplast resin (A);
• (ii) compounds having the following structure (II) or (III):
• where R′ and R″ are the same or different and each independently represents an aromatic group or an alkyl group having 1 to 12 carbon atoms;
• and p3 (iii) compounds different from (i) and (ii) and having a melting point of at least 80° C.,
• wherein said crosslinking agent has a glass transition temperature of at least 10° C. and is essentially free of functional groups which are reactive with aminoplast resin.