Patent attributes
A composition is provided which comprises amphoteric polymers comprising, as constituent monomer units, a cationic monomer unit, an anionic monomer unit, and optionally a nonionic monomer unit and having a 0.5% salted viscosity of 10 to 120 mPa·s, wherein said amphoteric polymers comprise a first amphoteric polymer satisfying the following expression (1) and a second amphoteric polymer satisfying the following expression (2) or a third amphoteric polymer satisfying the following expressions (3) and (4):Ca1/An1≧1 (1)Ca2/An2<1 (2)Ca3/An3≧1 (3)|(Ca1−An1)−(Ca3−An3)|≧1.5 (4)wherein Ca1 and An1 respectively represent the total mole number of the cationic monomer units and the total mole number of the anionic monomer units in the first amphoteric polymer on a condition that the total mole number of all the constituent monomer units in the first amphoteric polymer is converted to be 100 mol; on a condition similar to the above, Ca2 and An2, and Ca3 and An3, respectively represent the total mole number of the cationic monomer units and the total mole number of the anionic monomer units in the second and third amphoteric polymers. The composition is excellent in various flocculation and dewatering performances for various types of sludge, in particular, for sludge high in ratio of excess sludge, and can be used for process yield improvement in papermaking process.
