De-inking waste paper, e.g. from offset printing - which is hard to de-ink, by long term treatment with cheap de-inking agent

摘要

waste paper which is difficult to de-ink, esp. from the offset printing process, is carried out by prolonged treatment with suitable, cheap de-inking chemical(s) (I) after pulping, preliminary purificn. and thickening. (I) can be e.g., NaOH, KOH and/or NH3. Pref. de-inking is carried out for 7-50 (20-48)h at 20- 100 (40-60)deg.C. It can be followed by washing and/or brief (2-5h)treatment with bleach and/or flotation agent at high pulp density. The wash liquor obtd. is clarified with flocculants and collectors, e.g. H2SO4, alum or other flocculants, e.g. electrolytes, and retention aids, e.g. polyamine, and used for diluting the pulp from the long term treatment tower The de-inked paper can be combined with other waste paper. The process is effective and economical.