An object to be achieved by the present invention is to provide a
bookbinding adhesive which is excellent in high-speed application properties,
cutting properties, book opening properties, and
bookbinding strength. The present invention is directed to a
bookbinding adhesive characterized by having a
melt viscosity in the range of from 1,000 to 10,000 mPa·s, as measured at 120° C. by means of a cone plate
viscometer, exhibiting a JIS A
hardness of 20 or more, as measured with respect to the
adhesive which is applied and allowed to stand for 30 minutes, in an
atmosphere at 23° C., and exhibiting a JIS A
hardness of 95 or less, as measured with respect to the adhesive which is applied and allowed to stand for 30 minutes, in an
atmosphere at 23° C., and is then allowed to stand in an
atmosphere at 23° C. and at a
humidity of 50% for one week, wherein a cured film of the adhesive has an upper yield stress of 7 MPa or less. The bookbinding adhesive is preferably a
moisture-curing
polyurethane hot-melt adhesive containing an urethane
prepolymer having an
isocyanate group which is obtained by reacting a
polyol (A), which contains a crystalline
polyester polyol (a-1) and a polyether
polyol (a-2), with a polyisocyanate (B).