| 摘要 |
A process for bleaching mechanical pulp in at least two stages, of which the first stage is carried out at the same time as the wood raw material is broken down mechanically, comprises the following two stages: (1) a bleaching stage including at least one partial bleaching step carried out in combination with a refining step in a refiner, or during processing of the ground pulp, by adding 0.1-1.5 % bisulphite (equivalent to 1-15 kg/ADMT), with either the diluting water for the refiner or the spray water for grinding, so that bisulphite is present in the fibre liberation or processing step at a pH of 4-6.5 and a temperature less than 200 deg. C ; and (2) an oxidative or reductive bleaching stage. - Preferably peroxide or more preferably dithionite is added in stage (2). |
