Aqueous compositions comprising blocked isocyanate crosslinking agent.

摘要

Compsn. comprises (1) a film-forming resin bearing reactive functionality and (2) a blocked polyisocyanate crosslinking agent (I) capable of reacting with the reactive functionality at elevated temp. The improvement is that (I) is a diisocyanate in which one NCO gp. has been blocked with an agent (II) contg. reactive hydrogen and the other NCO gp. has been reacted with an OH gp. of an amine (III) contg. at least two OH gps. and at least one tert nitrogen; and (I) is at least partially solubilised or dispersed in the aq. coating compsn. by an organic acid which protonated at least some of the tert. N atoms of (I). The compsn. is for application to a substrate cathode by electrodeposition. By using (I) contg. ionisable gps. (as a result of protonation of the amine N by the organic acid), the aq. coating can exist at higher solids in the form of an uninverted dispersion due to the system holding greater amts. of (I) and still remaining stable. Greater crosslinking efficiency can be achieved, and cathodic electrodeposition systems can be formed which are capable of curing at reduced temps.