Patent ID: 6147155
Filing Date: 2000-11-14
Classification: C08F,C08G,C08L

Abstract:
A multi-step process for preparing an aqueous polyurethane dispersion which comprises forming an NCO prepolymer bya) reacting a cyclic diisocyanate with a compound containing one or two isocyanate-reactive groups and at least one carboxylic acid or carboxylate group at a molar ratio of cyclic diisocyanate to compound containing one isocyanate-reactive group of at least 1:1 or a molar ratio of cyclic diisocyanate to compound containing two isocyanate-reactive groups of at least 1.5:1,b) adding a non-cyclic diisocyanate having 4 to 12 carbon atoms, a high molecular weight polyol having a number average molecular weight of 400 to 6000, optionally an isocyanate-reactive compound containing non-ionic groups and optionally an at least difunctional isocyanate-reactive compound having a number average molecular weight of less than 400 in amounts such thati) the molar ratio of cyclic diisocyanate to non-cyclic diisocyanate is 4:6 to 9:1 andii) the overall equivalent ratio of isocyanate groups to isocyanate-reactive groups to prepare the NCO prepolymer is 1.1:1 to 2:1,c) dispersing the NCO prepolymer in water,d) neutralizing at least a portion of any carboxylic acid groups either before, during or after step c) ande) optionally adding a polyamine chain extender that contains a maximum of one unblocked primary or secondary amino group to the water either before, during or after the addition of the NCO prepolymer.