Papermaking internal sizing agent and use thereof

Abstract

To provide a papermaking internal sizing agent capable of efficiently imparting sizing performance even in neutral papermaking which uses calcium carbonate as filler, and uses no aluminum sulfate or uses a small amount of aluminum sulfate, and also provide a paper or a paperboard obtained by using the papermaking internal sizing agent. The papermaking internal sizing agent comprises as an effective ingredient an amphoteric copolymer having hydrophobic groups and cationic groups, at least a part of the cationic groups being quaternized. Preferably, the amphoteric copolymer is obtained by polymerizing monomer ingredients that it essentially contain a hydrophobic monomer (A), a cationic monomer (B), and an anionic monomer (C) and that an anion equivalent of the monomer (C) is 0.1 to 90% of a cation equivalent of the monomer (B), in which a rate of quaternizing of the cationic groups is not less than 40% by mole. The paper or the paperboard contains the above papermaking internal sizing agent.