The invention discloses a waterborne
polyurethane binder. The preparation method of the waterborne
polyurethane binder comprises the following steps of: reacting 20-50 parts of diisocyanate, 80-140 parts of
polymer polyol, 0.5-2 parts of trihydric
alcohol, 0.5-2 parts of dihydric
alcohol, 4-10 parts of hydrophilic chain
extender, 10-30 parts of cosolvent and 0.01-0.1 part of catalyst under the protection of
nitrogen gas at 75-90 DEG C for 2-4 hours; then, adding 10-30 parts of amine terminated polyether chain
extender for reacting at 70-80 DEG C for 2-3 hours; cooling to 30-40 DEG C, and then, adding 3-6 parts of neutralizing agent for reacting for 5-7 minutes; adding 200-500 parts of dispersing agent at the
room temperature, and dispersing for 10-20 minutes while stirring at a high speed; and adding 1-2 parts of small molecular chain
extender for reacting for 1-2 hours to obtain the waterborne
polyurethane binder. The waterborne polyurethane binder disclosed by the invention has the advantages of better mechanical performance,
water resistance and
adhesive force, good low-temperature performance, high gloss and good gloss retention, is used for waterborne ink and acquires an excellent effect.