Process for the preparation of polyisocyanates with a biuret structure

A process for the continuous preparation of polyisocyanates with a biuret structure comprising the steps of continuously reacting excess amounts of organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups with organic diamines having exclusively aliphatically and/or cycloaliphatically bound primary amino groups at temperatures above 170° C. and adding acid to the diisocyanate before the diamine feed;

• wherein the organic diisocyanates are selected from the group consisting of 1,4-diisocyanatobutane, hexamethylene diisocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,4-diisocyanatohexane, 1,5-diisocyanatohexane, 2,6-diisocyanatohexanoic acid ethyl ester, 1,12-diisocyanatododecane, 1,4-diisocyanatocyclohexane, 2,4- and/or 2,6-diisocyanato-1-methylcyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 1,3-bis-(isocyanatomethyl)cyclohexane, 1,4-bis-(isocyanatomethyl)cyclohexane, 4,4′-diisocyanatodicyclo-hexylmethane, 6-isocyanatohexanoic acid-2-isocyanatoethyl ester, and mixtures thereof;
• and
• wherein the organic diamines are selected from the group consisting of 1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,6-diamino-2,2,4-trimethylhexane, 1,6-diamino-2,4,4-trimethylhexane, 1,4-diaminohexane, 1,5-diaminohexane, 2,4-diamino-1-methylcyclohexane, 2,6-diamino-1-methylcyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 4,4′-diaminodicyclohexylmethane and mixtures thereof.