To obtain the subject agent that is excellent in sizing effect and can improve the printability and defibrillability the paper by forming a polyionic complex comprising a specific grafted starch polymer and a specific hydrophobic group-bearing anionic copolymer.
In an aqueous solution countering 20-80 pts.wt. of cationic starch, 20-80 pts.wt. of a monomer mixture comprising 50-98 mol% of (meth)acrylamide, 1-30 mol% of an anionic vinyl monomer such as acrylic acid and 1-20 mol% of a cationic vinyl monomer such as N,N-dialkylamino-alkyl (meth)acrylamide are polymerized as the essential components to prepare shaft starch polymer A. In the meantime, a hydrohobic vinyl monomer such as styrene and an anionic vinyl monomer such as acrylic acid are used as essential components to prepare a hydrohobic group-bearing anionic copolymer B. These copolymers A and B are used as main components to prepare a polyionic complex containing the component A and B at a ratio of 70/30-30/70 thereby giving the objective surface treatment agent.
TAKEUCHI KUNIO
OWATARI JUNYA
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