GB441331A - Process for de-inking imprinted paper - Google Patents

Abstract

Mechanically disintegrated waste paper is de-inked by cooking with detergents to free the ink particles, an alkaline flocculating agent added if the pH value of the pulp is above 7, or an acid if below 7, the ink being then floated by adding a frothing agent, and the froth separated. Waste paper from magazines, books, &c. is sorted, dusted, preferably shredded, e.g. in a hammer mill and sent to a broke beater, cooked 3--4 hours in a circulating type cooker using lime, and caustic soda or sodium silicate, or soda ash. The pulp may then be reduced in consistency, agitated, burnt lime, or magnesium oxide added or alternatively sulphuric acid or alum &c., to precipitate soaps formed in the alkaline cooking; mineral fillers may be dispersed using sodium silicate or soluble starch. The volume of froth may be reduced by kerosene, a light frothing agent, e.g. cresylic acid, pine oil, or a high boiling point alcohol may also be added, heavier frothing agents, e.g. coal tar oil, pine tar oil may be added during cooking. Sodium oleate, amyl acetate, butyl alcohol, and potassium ethyl xanthate dissolved in ethyl chlor carbonate may be used as collectors of ink. The pulp is passed through successive compartments of a flotation machine, and froth from certain compartments returned to the primary pulp feed, remaining froth being washed and used in making board &c. The pulp may then be filtered, washed, and bleached, and the filtrate used to dilute cooked pulp. In a similar process for newspaper, the pulp, at 3 per cent consistency may be beaten 45--60 mins. at 140--160 DEG F. in water containing caustic soda and sodium silicate.