Dai-ichi Kogyo Seiyaku Co., Ltd.

Masahiro Kouchi

Takeshi Doi

Takeshi Miyamura

Naofumi Saiuchi

For use as a wet strength agent, a water-soluble blocked urethane prepolymer having a hydrophilic group and a blocked isocyanate group is combined with a cationic charge-adjusting agent. The adsorption and retention of the water-soluble blocked urethane prepolymer to cellulosic fiber are promoted by virtue of the cationic charge adjusting agent when the wet strength agent is added to a paper-making stock.

Composition for increasing wet strength of paper including water-soluble blocked urethane prepolymers

Paper with increased wet strength is produced by adding to the stock a water soluble blocked urethane prepolymer having a plurality of blocked isocyanate groups and hydrophilic groups. The blocking agent is a phenol compound having an electron-attracting group at the ortho- or para-position. The blocked urethane prepolymer is capable of unblocking under such conditions that encounter in the drying part of conventional paper making machines.

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Nara, Japan

Masahiro Kouchi