To recover the ash content including fillers from the pulp slurry at the deinking process in high yield and utilizes the ash content effectively.
In the method for producing deinked pulp by adding an additive for producing deinked pulp to the pulp slurry at the deinking step, the additive for producing deinked pulp is a water-soluble amphoteric copolymer from (a) (meth)acrylamide, (b) a cationic monomer and (c) an anionic monomer having a weight-average molecular weight of 500,000 to 10,000,000. The additive is added after the flotation step and before the dewatering step for the pulp slurry from which the ink is removed. As the water-soluble amphoteric copolymer having a proper size of molecular weight is added after the flotation step, it can strongly be aggregated to pulp fiber correspondingly to the filler having all kinds of charging whereby the filler originating from the used paper can be fed to the papermaking step in high yield.
COPYRIGHT: (C)2006,JPO&NCIPI
Tomohiko Nakata
Yoshiharu Hashiguchi
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