A water-based electrodeposition dispersion for forming an insulating film includes: polymer particles; an organic solvent; a basic compound; and water, wherein the polymer particles include polyamic acid having a predetermined structural unit, and a volume-based median diameter (D.sub.50) of the polymer particles is 0.08 m to 0.7 m.

A water-dispersed electrodeposition solution (11) for forming an insulating film includes: polymer particles; an organic solvent; a basic compound; and water. The polymer particles are made of: any one of; or both of polyamide-imide and polyester-imide, main chains thereof being free of an anionic group, a number-based median diameter D.sub.50 of the polymer particles is 0.05 m to 0.5 m, and polymer particles having a particle size within 30% to +30% of the number-based median diameter D.sub.50 are 50% or more of all of the polymer particles on a number basis.

The present invention is related to a polyurethane dispersant and a preparation method thereof. The polyurethane dispersant is terminated by a nitrogen-containing heterocyclic compound during synthesis. The nitrogen-containing heterocyclic compound is prepared by subjecting anhydride and a compound containing a primary amine and a secondary amine or a hydroxyl or mercapto group to dehydration condensation. The condensed product is the nitrogen-containing heterocyclic compound, containing a reactive hydrogen. The structural formula of the compound containing the primary amine and the secondary amine or hydroxyl or mercapto group is shown as follows: ##STR00001##
wherein n=1 to 5, and preferably 2 to 4, R.sup.1 and R.sup.2 are respectively alkyls containing 1 to 8 carbons, R.sup.1 and R.sup.2 are independent of each other or connected by a chemical bond to form one or more saturated or unsaturated 4-member to 8-member rings, and X represents N, O, or S.