Patent ID: 7008508

Claim:
A composition for increasing the wet strength of paper comprising: (a) a water-soluble blocked urethane prepolymer having a hydrophilic group and a blocked isocyanate group capable of thermally unblocking; wherein the water-soluble blocked urethane prepolymer is produced by blocking a urethane prepolymer having a plurality of free isocyanate groups and at least one tertiary amino group with a phenolic compound having an electron-attracting group of trifluoromethyl, nitro, cyano, acetyl, alkoxycarbonyl, carboxyl or alkylsulfonyl at the ortho- or para-position followed by quaternizing or neutralizing the tertiary amino group, the water-soluble urethane prepolymer is free of a reversibly blocked isocyanate group other than those derived from the phenolic compound; and (b) a cationic compound or polymer effective for enhancing the cationic charge of the blocked urethane prepolymer in an aqueous solution.