METHOD OF BLEACHING CHEMICAL PULP FOR MAKING PAPER

摘要

PROBLEM TO BE SOLVED: To increase the whiteness of the chemical pulp for paper, as the amount of chemical for ECF bleaching is reduced in the chemical pulp for paper making. SOLUTION: The chemical pulp for paper making is subjected to the digesting treatment and to the oxygen delignification, followed by chlorine dioxide step- chlorine dioxide step-four step bleaching sequence. Further, the resultant pulp is bleached in the 4-step chlorine dioxide sequences of the chlorine dioxide step-alkali extraction/oxygen/peroxide step-chlorine dioxide step-chlorine dioxide step. In this case, the pH after the third chlorine dioxide treatment step is maintained at 6-8 and the pH at the final step is kept at 4.5-5.5.