Abstract: A method of producing a paper board comprising: a pulping step of disintegrating and beating fibers from a pulp raw material containing waste paper as a main raw material to obtain pulping process water; a stock preparation step of adding an additive containing a paper strength additive to the obtained pulping process water to obtain a prepared pulp raw material; and a paper-making step of making the obtained prepared pulp raw material into a paper board, wherein the paper board is produced by adding (a) an aqueous solution of hypochlorite and (b) an aqueous solution of water-soluble inorganic ammonium salt or ammonia water to the pulping process water to reduce the amount of the paper strength additive added in the stock preparation step.

Abstract: A method of producing a paper board comprising: a pulping step of disintegrating and beating fibers from a pulp raw material containing waste paper as a main raw material to obtain pulping process water; a stock preparation step of adding an additive containing a paper strength additive to the obtained pulping process water to obtain a prepared pulp raw material; and a paper-making step of making the obtained prepared pulp raw material into a paper board, wherein the paper board is produced by adding (a) an aqueous solution of hypochlorite and (b) an aqueous solution of water-soluble inorganic ammonium salt or ammonia water to the pulping process water to reduce the amount of the paper strength additive added in the stock preparation step.