Method of making cathode-depositing binder dispersions with cross-linkers based on hydroxy group-blocked polyisocyanates

摘要

PCT No. PCT/EP88/00998 Sec. 371 Date Jun. 13, 1990 Sec. 102(e) Date Jun. 13, 1990 PCT Filed Nov. 3, 1988 PCT Pub. No. WO89/04353 PCT Pub. Date May 18, 1989.The invention relates to a process for the preparation of aqueous dispersions to be further processed to electrocoating paints with baking temperatures below 160 DEG C. and baking times/=30 minutes, which dispersions contain modified epoxide-amine adducts as binders and polyisocyanates blocked by hydroxyl groups as cross-linking agents. In this process polyepoxides and compounds containing one or more, preferably 2, hydroxyl groups per molecule are reacted at elevated temperatures in the presence of catalysts to furnish epoxide-containing intermediates. A solvent or a mixture of solvents is then added with external cooling ahd the solution is boiled under reflux, if necessary in vacuo, until the temperature of the solution drops to 95 DEG C. to 20 DEG C. Amines are then added onto the epoxide groups which are still present in a free state in the epoxy resin and a dispersion is prepared by adding a water/acid mixture after adding the crosslinking agent or the dispersion is first prepared and the crosslinking agent is added subsequently.