Process for bleaching chemical pulp

Details Process for bleaching chemical pulp Process for bleaching chemical pulp

D - Textiles, Paper

21

C

8/79

D21C 9/14 (2006.01) D21C 9/10 (2006.01)

Patent

CA 1192704

ABSTRACT OF THE DISCLOSURE A process of bleaching chemical pulp without loss of pulp strength is disclosed. In the manufacture of printing paper furnish, small quantities of chemical pulp are mixed with mechanical pulp to provide a fur- nish with the necessary physical strength properties resulting in papers with better tear resistance. The bleaching process includes first treating a chemical pulp with chlorine under aqueous conditions, followed by an alkaline extraction step, wherein the chlorinated pulp is treated with an alkali, and in a third step treated with sodium or calcium hypochlorite at a pH above about 8.5. The improvement for retaining the physical strength properties of the chemical pulp com- prises the steps of adding urea or urea derivatives in an amount of about 0.05% to 0.2% by weight of oven dry fiber to the chemical pulp prior to or simultaneously with the addition of chlorine in the first step.

416149

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