GB991367A - Process for de-inking printed waste paper - Google Patents

Abstract

Printed paper is de-inked by pulping it in an alkaline aqueous solution comprising an anionic detergent and a non-ionic wetting agent. The water used in the treating solution may be freed of impurities, e.g. iron, by treatment with a zeolite to reduce its iron content to less than 1 p.p.m. The alkali, e.g. sodium or potassium hydroxide, may be added to the solution in an amount sufficient to bring the pH up to 7-10 or higher. The anionic detergent may be a water-soluble alkyl aryl sulphonate in which the alkyl chain contains 9-19 carbon atoms, alkali metal alkyl aryl sulphonates having builders, e.g. alkali metal phosphates, polyphosphates and sulphates, incorporated therein being preferred. The non-ionic wetting agent may be a water-soluble alkyleneoxide-alkyl phenolic compound adduct containing a polyoxyalkylene chain of at least two alkenoxy groups, the alkyl phenolic compound used in forming the adduct preferably containing a total number of alkyl carbon atoms of 4-24, examples of which are given. 0.1-2% by weight of the dry paper of each of the anionic detergent and nonionic wetting agent are preferably used. Below 10% by weight of the solution of the dry printed paper, which may or may not be shredded, is preferably added to the alkaline solution and pulping may be carried out at a temperature of from room temperature up to the cloud point or decomposition temperature of the anionic detergent and non-ionic wetting agent, e.g. 110 DEG -140 DEG F., for 10-30 minutes. The pulp may then be diluted with water to a solid content of 0.5-1.5% based on the weight of the solution, separated from the solution, e.g. by screening, washed, acidified to a pH of 4-7, with for example sulphuric acid or SO2, bleached if necessary, thickened and formed into a web. The recovered pulp may be blended with fresh sulphate or sulphite stock.