| 摘要 |
<p>1. A process for selective bleaching of paper pulp, consisting of submitting a pulp, obtained by making a suspension of fibrous materials and especially of old paper, to mechanical separation into two or more fractions differing in the length of fibres of which they are composed, then submitting each of the fractions produced to a type of bleaching specific to the type of fibres of the said fraction, characterised by the following stages : a) a raw material consisting of illustrated magazines and periodicals is submitted to a suspension treatment, ink-removal and elimination of objectionable contamination (adhesive tapes, metallic fragments, plastics material, etc...) ; b) the pulp obtained from stage a) is centrifugally separated into a first fraction corresponding to 30 to 70% by weight of the total of the raw material introduced and consisting of a majority of long fibres, the fibre length of this first fraction being between 1,5 and 4,5 mm, and into a second fraction corresponding to 70 to 30% by weight of the total of the raw material introduced and consisting of a majority of short fibres, the fibre length of this second fraction being between 0.3 and 2.5 mm ; c) the said first fraction is submitted to bleaching in a descending tower (6) in an oxidizing environment in the presence of an oxygenated compound ; d) the second fraction is first acidified to raise its pH to between 6 and 7 and is then submitted to bleaching in an ascending tower in a reducing medium in the presence of sodium hydrosulphite.</p> |
