PAPER STRENGTH INTENSIFIER FOR NEUTRAL PAPERMAKING AND ITS APPLICATION

PURPOSE: To obtain the subject intensifier exhibiting an excellent paper strength intensifying effect without reducing optical properties in a neutral papermaking condition by including (meth)acrylamide and a specific polymer. CONSTITUTION: This paper strength intensifier in a neutral papermaking contains a copolymer comprising (A) (meth)acrylamide and (B) a vinyl compound expressed by formula I (R is H, a 1-3C alkyl) or its salt as constituting components. Furthermore, a paper strength intensifier in a neutral papermaking is obtained which contains a copolymer comprising 60-98.95mol% of the component A, 0.5-20mol% of the compound B, (C) 0.05-10mol% of a vinyl compound expressed by formula II (R is H or a 1-3C alkyl; (n) is 1-5) or its salt, and (D) 0.5-10mol% of an α,β-unsaturated monocarboxylic acid or a polycarboxylic acid or a salt thereof as constituting components. The intensifiers exhibit a superior paper strength intensifying effect than usual intensifiers as for a specific bursting strength and a Z-direction tensile strength.