| abstract |
According to the present invention, the addition amount of persulfate in a polymerization initiator from a polymerizing step before a drying step is reduced to the total amount of 0-0.04 mol% (with respect to a monomer during polymerization), and a gel particle size of a water-containing gel-like polymer before the drying step and a drying condition are controlled, thereby suppressing the decomposition of a chelating agent in the drying step. |