To provide an internally adding self-fixing starch having high fixity to pulp fiber and having high surface strength-improving effect and vessel pick- suppressing effect for printing paper.
This internally adding paper strengthening agent for producing printing paper comprises a self-fixing starch obtained by absorbing a high molecular weight cationic polymer on the surface of a low viscous anionic starch powder at a rate of 400-7,000 ppm as the solid component based on the starch solid component, wherein the 0.2 wt.% aqueous solution of the cationic polymer has ≥30 mPa.s Type B viscosity at 20°C and 60 rpm and a 7-25 wt.% solid concentration solution of the low viscous anionic starch powder has 50 mPa.s Type B viscosity at 50°C and 60 rpm. And the agent is used by being internally added to paper stock in paper making.
KIMURA TORU
ASHIKAWA MASATAKA
