Abstract: The object of the present invention is to provide a process for producing deinked pulp from recovered paper containing stickies while preventing excessive reduction in the size of stickies, lowering the COD of effluents, and producing deinked pulp with a smaller residual ink content. In the ink detachment stage of the process for producing deinked pulp from recovered paper containing stickies, an anhydride of crystalline layered silicate is added, preferably in an amount of 0.1-1.5 weight % of absolute-dry pulp, and a deinking treatment is performed at a pH of 7.0-9.9. In the present invention, the deinking treatment is performed in a weakly alkaline to neutral region which is generally said to be effective in reducing the amount of stickies but less effective in ink detachment and, yet, deinked pulp having a smaller amount of residual ink can be produced.

Abstract: The object of the present invention is to provide a process for producing deinked pulp from recovered paper containing stickies while preventing excessive reduction in the size of stickies, lowering the COD of effluents, and producing deinked pulp with a smaller residual ink content. In the ink detachment stage of the process for producing deinked pulp from recovered paper containing stickies, an anhydride of crystalline layered silicate is added, preferably in an amount of 0.1-1.5 weight % of absolute-dry pulp, and a deinking treatment is performed at a pH of 7.0-9.9. In the present invention, the deinking treatment is performed in a weakly alkaline to neutral region which is generally said to be effective in reducing the amount of stickies but less effective in ink detachment and, yet, deinked pulp having a smaller amount of residual ink can be produced.

Abstract: Wood chips having low bleachability are impregnated with a chemical liquor at a pH range of 7-12 in aqueous solution and the chemical liquor from the impregnated chips is drained, whereby extractives contained in the chips and consuming bleaching agents can be removed to improve the effect of bleaching agents in a subsequent bleaching step. Bleached mechanical pulp is prepared by defibration by primary refining—bleaching—beating by secondary refining wherein pulp fibers are washed after defibrating wood chips having low bleachability and before bleaching the pulp fibers, whereby the amount of bleaching agents used can be reduced and bleached mechanical pulp having a Hunter brightness of 45-65% after secondary refining can be obtained.

Abstract: The present invention aims firstly to provide a novel technique capable of preparing bleached pulp having high brightness from materials having low bleachability containing high levels of extractives and secondly to provide a technique capable of reducing the amount of bleaching agents used in processes for preparing bleached mechanical pulps.