D - Textiles – Paper – 21 – C
Patent
D - Textiles, Paper
21
C
9/1
D21C 5/02 (2006.01)
Patent
CA 1335687
According to the method of deinking and bleaching waste paper, operation in a stock pulper is carried out without chemicals or with only minimum quantities of chemicals, particularly alkali. Subsequent to a first or initial printing ink removal, for instance, in a washing process, a two-stage bleaching process is effected, preferably by adding peroxide and then formamidine sulfinic acid. Subsequent to the first bleaching stage using peroxide as the bleaching agent, the pH value is in the alkaline range of approximately pH 8.5 to 9.5. In the case of approximately stoichiometric ratios of alkali and formamidine sulfinic acid there exists, subsequent to the second bleaching stage, a medium in the neutral range of pH 6.5 to 7.5, without the need for additional acidification. In this manner, purification of circulating or recycle water in closed circuits, for instance, by means of flotation by expansion, is essentially facilitated. Two-stage bleaching is accomplished, for example, in the combination of a disperser bleaching process and a bleaching process carried out at a medium pulp consistency. Subsequent to the disperser treatment or subsequent to the bleaching process, a further removal of ink and dirt is effected, for example, by flotation or washing, whereby also non-ionic frothing or collecting agents have proven useful. Residual peroxide from the first bleaching stage, which peroxide would decompose formamidine sulfinic acid used in the second bleaching stage, can be not only rendered harmless by the addition of thiourea, but also advantageously converted into additional formamidine sulfinic acid.
609695
Maier Josef
Matzke Wolfgang
Selder Harald
Sulzer-Escher Wyss Gmbh
Swabey Ogilvy Renault
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