POLYURETHAN-MIKROGEL

Production of an aqueous polyurethane dispersion comprises reacting methyl ethyl ketoxime-blocked 1,3-bis(1-isocyanato-1-methylethyl)benzene with a polyol and an anionic hydroxy compound, adding water and neutralizing agent to form a stable dispersion, and crosslinking the product at 30-100[deg]C. Production of polymer microparticles dispersed in an aqueous phase comprises: (a) reacting 1,3-bis(1-isocyanato-1-methylethyl)benzene with methyl ethyl ketoxime to give a reaction product with an isocyanate (NCO) content of at least 13%; (b) reacting the product with a polyol having at least three hydroxy groups and a compound having at least one anionic group and at least one hydroxy group to give a reaction mixture with an NCO content of less than 0.1%; (c) adding water and neutralizing agent to form a stable dispersion; and (d) stirring the reaction mixture at 30-100[deg]C until the proportion of crosslinked particles is more than 60% with respect to the total content of nonvolatile components of the reaction mixture. An independent claim is also included for polymer microparticles dispersed in an aqueous phase, obtainable by: (a) dispersing in an aqueous phase a polyurethane precursor that comprises methyl ethyl ketoxime-blocked isocyanate groups based on 1,3-bis(1-isocyanato-1-methylethyl)benzene and has a weight-average molecular weight of 2000-150000, an acid number of 10-50, a hydroxyl number of 25-250 and a statistical mean ratio of blocked isocyanate groups to hydroxy groups of less than 1; and (b) crosslinking the precursor in the aqueous phase in the presence of a catalyst under atmospheric pressure at a temperature below 100[deg]C so that the hydroxy groups react with the blocked isocyanate groups to form urethane linkages by cleavage of methyl ethyl ketoxime.