PURPOSE: To obtain the titled resin, uniformly coatable and having improved adhesion to undercoats without skinning on coating, by copolymerizing a specific polyurethane resin with an acrylic monomer having the quaternary ammonium salt structure.

CONSTITUTION: A polyurethane resin is first obtained by using a polyester, containing double bonds and having diols at both ends, an organic diisocyanate, e.g. 2,4-tolylene diisocyanate, etc., and chain extender, e.g. ethylene glycol, etc. The resultant resin is then copolymerized with an acrylic monomer having the quaternary ammonium salt structure, e.g. dimethylaminoethyl acrylate, to afford the aimed resin. Preferably, the above-mentioned acrylic monomer is quaternized normally by adding benzyl chloride to a reaction mixture during or after completing the grafting reaction.