Sulfonamide modified aminoplast crosslinkers and powder coating compositions containing such crosslinkers

Abstract

A crosslinking agent that is an ungelled reaction product of (a) an aminoplast resin and (b) a compound having active hydrogen groups reactive with the aminoplast resin such that the crosslinking agent is essentially free of functional groups reactive with an aminoplast resin and has a glass transition temperature of at least 10° C. is disclosed. Compound (b) is, more specifically, a monofunctional sulfonamide having only one active hydrogen. Methods for preparing crosslinking agents are also disclosed. Further provided is a curable powder coating composition including a polymer having a glass transition temperature of at least 30° C. containing reactive functional groups and the present crosslinking agent; a multilayer composite coating compositions and substrates coated therewith are also disclosed. Methods for modifying aminoplasts are also disclosed.

1 .- 14 . (canceled)  
   
   
       15 . 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 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:                          wherein R 15-19  are the same or different and are selected from H, C 1-4  alkyls, C 1-4  alkoxys and NO 2 , and at least one of R 15-19  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 compound is a reactive polyhydric compound, the aminoplast is not an alkoxylated aldehyde condensate of glycoluril.    
   
   
       16 . The method of  claim 15 , wherein said aminoplast resin is solid.  
   
   
       17 . The method of  claim 15 , wherein said aminoplast resin is liquid.  
   
   
       18 . The method of  claim 15 , wherein said appropriate ratio is a ratio of aminoplast to modifying compound of from 1:0.2 to 1:1.  
   
   
       19 . The method of  claim 17 , wherein said modifying compound is a monofunctional sulfonamide having only one active hydrogen.  
   
   
       20 . The product prepared by the method of  claim 15 .  
   
   
       21 .- 24 . (canceled)  
   
   
       25 . 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:                          wherein R 15-19  are the same or different and are selected from H, C 1-4  alkyls, C 1-4  alkoxys and NO 2 , and at least one of R 15-19  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.    
   
   
       26 . A crosslinking agent comprising an ungelled reaction product of the following reactants: 
 (a) an aminoplast resin; and    (b) a compound having the structure (I):                          wherein X is a cycloaliphatic group; R 1 , R 2 , and R 3  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 R 1 , R 2 , and R 3  is an active hydrogen-containing group that is reactive with the aminoplast resin.    
   
   
       27 . The crosslinker of  claim 26 , wherein X is a cyclohexyl group.