Sulfonamide modified aminoplast crosslinkers and powder coating compositions containing such crosslinkers

A method for modifying an aminoplast comprising:

• (a) mixing together:
• (i) an aminoplast resin;
• and
• (ii) a modifying compound in an appropriate ratio;
• (b) heating the mixture of step (a) to a temperature ranging from 90° C. to 160° C.;
• and
• (c) maintaining the temperature achieved in step (b) for a time sufficient to obtain an ungelled reaction product that has a glass transition temperature of at least 10° C. and that is substantially free of active hydrogen-containing groups as determined by analytical methods;
• and
• but when the modifying compound is a polyester polyol comprising the reaction product of a cycloaliphatic polyol and a cyclic polycarboxylic acid or anhydride, and the aminoplast is an aminotriazine compound having one or is less non-alkylated NH bond per triazine ring, the aminotriazine is present in a weight ratio excess as compared to the polyol;
• and
• when the modifying compound is a monohydroxy single ring aromatic compound having the formula:
• 8
• wherein R15-19 are the same or different and are selected from H, C1-4 alkyls, C1-4 alkoxys and NO2, and at least one of R15-19 is H, and the aminoplast is an aminotriazine compound having one or less non-alkylated NH bond per triazine ring, the ratio of aromatic compound to aminotriazine is from 1.0 to less than 1.8:1 to greater than 2.2 to 3:1;
• and
• when the modifying copound is a reactive polyhydric compound, the aminoplast is not an alkoxylated aldehyde condensate of glycoluril.

A method for converting a liquid aminoplast into an ungelled crosslinking agent comprising:

• a) mixing together:
• i) an aminoplast resin;
• and
• ii) a powder forming compound in an appropriate ratio;
• (b) heating the mixture of step (a) to a temperature ranging from 90° C. to 160° C.;
• and
• (c) maintaining the temperature achieved in step (b) for a time sufficient to obtain an ungelled reaction product that has a glass transition temperature of at least 10° C. and that is substantially free of active hydrogen-containing groups as determined by analytical methods;
• but when the modifying compound is a polyester polyol comprising the reaction product of a cycloaliphatic polyol and a cyclic polycarboxylic acid or anhydride, and the aminoplast is an aminotriazine compound having one or less non-alkylated NH bond per triazine ring, the aminotriazine is present in a weight ratio excess as compared to the polyol;
• and
• when the modifying compound is a monohydroxy single ring aromatic compound having the formula:
• 9
• wherein R15-19 are the same or different and are selected from H, C1-4 alkyls, C1-4 alkoxys and NO2, and at least one of R15-19 is H, and the aminoplast is an aminotriazine compound having one or less non-alkylated NH bond per triazine ring, the ratio of aromatic compound to aminotriazine is from 1.0 to less than 1.8:1 to greater than 2.2 to 3:1.

A crosslinking agent comprising an ungelled reaction product of the following reactants:

• (a) an aminoplast resin;
• and
• (b) a compound having the structure (I):
• 10
• wherein X is a cycloaliphatic group;
• R1, R2, and R3 are the same or different and are selected from the group consisting of 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 is an active hydrogen-containing group that is reactive with the aminoplast resin.