| 摘要 |
PROBLEM TO BE SOLVED: To regulate heat discoloration properties of kraft pulp bleached by an ECF (elementary chlorine-free) bleaching method without containing elementary chlorine and hypochlorous acid and having 82-90% Hunter brightness to that equal to or less than conventional chlorine bleached pulp. SOLUTION: Chlorine-free bleached kraft pulp having the improved heat discoloration properties is obtained as follows. A pulp component prepared by digesting a lignocellulose substance by a kraft digesting method is successively subjected to alkali oxygen delignification and washing screening. The pulp is bleached according to the ECF bleaching method without containing the elementary chlorine and hypochlorous acid by carrying out or without carrying out an acid treatment in an acidic aqueous solution. In the chlorine-free bleaching method, ozone or chlorine dioxide is used in the initial stage and the chlorine dioxide or hydrogen peroxide is used in the final stage. The final brightness after the bleaching is within the range of 82-90% Hunter. The residual iron content is≤25 ppm and the residual copper content is≤1 ppm. The residual manganese content is≤3 ppm. Hardwood chips, coniferous wood chips or nonwood is preferably used. COPYRIGHT: (C)2005,JPO&NCIPI
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