Blocked isocyanate crosslinker solution
View Patent ↗A low viscosity blocked isocyanate solution can be made by reacting together a polymeric isocyanato compound and propylene glycol, or a polymeric primary or secondary amine and propyl carbonate. The resulting beta-hydroxypropyl urethane polymer can be combined with propylene glycol monomethyl ether as a reducing solvent to form a pourable high-solids solution with good flow properties at room temperature. The solution has lower viscosity than is obtained using ethylene glycol as a blocking agent or using several non-HAPS reducing solvents that are similar to propylene glycol monomethyl ether. The solution can readily be combined with electrodepositable paint ingredients to form a curable coating composition.
1. A method for preparing a blocked isocyanate solution comprising:
a) reacting together a polymeric isocyanato compound and propylene glycol, or a polymeric primary or secondary amine and propyl carbonate, to provide a beta-hydroxypropyl urethane polymer; and
b) combining the beta-hydroxypropyl urethane polymer with propylene glycol monomethyl ether to provide a pourable blocked polymeric isocyanate solution.
2. A method according to claim 1 wherein the isocyanato compound comprises a diphenylmethane diisocyanate polymer.
3. A method according to claim 1 wherein the isocyanato compound comprises an isocyanate-terminated prepolymer formed by reacting a polyol, polyether polyol or polyester polyol with a stoichiometric excess of one or more polyisocyanates.
4. A blocked polymeric isocyanate solution comprising a pourable mixture of beta-hydroxypropyl urethane polymer and propylene glycol monomethyl ether.
5. A solution according to claim 4 wherein the isocyanato compound comprises a diphenylmethane diisocyanate polymer.
6. A solution according to claim 4 containing about 50 to about 75 weight percent solids.
7. A waterborne coating composition comprising an isocyanate solution according to claim 4 , an active hydrogen-containing material and a cure catalyst, wherein the composition when stripped of propylene glycol monomethyl ether and applied to a substrate will form a film that upon drying will cure at a temperature below about 175° C.
8. A waterborne coating composition according to claim 7 wherein the active hydrogen-containing material comprises a water dispersible polyepoxide.