As the chain expansion medicine (d

摘要

PROBLEM TO BE SOLVED: To obtain a binder for water-based printing ink, good in re-dissolution of ink, excellent in resistance of the coated layer to oil with reduced smell by converting a polyurethane resin bearing isocyanate groups on its chain terminals and anionic groups on the side chains into a water-based polymer by a specific treatment. SOLUTION: This binder comprises a water-based polyurethane resin which is derived from (A) an organic isocyanate, (B) a polyester polyol, (C) a compound having anionic groups (preferably carboxyl) and at least 2 groups bearing active hydrogen atoms (for example, hydroxyacid, hydroxysulfonic acid, aminosulfonic acid and the like) and, when necessary, (D) a chain extender and whose chain terminal is blocked with ammonia and its anionic groups are neutralized, and then the product is dissolved in an aqueous medium. The isocyanate concentration of the polyurethane resin is preferably 0.1-1.5wt.%.