PURPOSE: To obtain a resin hardened with a multifunctional cross-linking agent and useful for coating agents by containing an acrylate copolymer containing a water-soluble semi-ester of dicarboxylic acid as a pendant group.

CONSTITUTION: This resin contains (A) A pendant group containing a water-soluble semi-ester of dicarboxylic acid; and (B) an acrylate copolymer containing a pendant group containing activated ethylenic unsaturation. The semi-ester of the component A preferably contains ethylenic unsaturation. Further, the acrylate copolymer is preferably manufactured from (C) 5-70 (wt.)% of one or more epoxy-containing (meta)acrylate compounds, (D) 3-30% of one or more hydroxy-functional (meth)acrylate compounds, and (E) 0-92% of one or more monomers copolymerizable with the component C and the component D.