Patent ID: 6679972
Filing Date: 2004-01-20
Classification: D21C,D21H

Abstract:
A process for producing paper or board comprising providing a chemical pulp suspension and cellulosic fibers and calcium containing lignin in an aqueous environment, bleaching said suspension in a bleaching stage, and processing the bleached suspension into paper or board, characterized by providing in said bleaching stage carbonic acid or a salt thereof as the only bleaching chemical provided in said stage, said acid or salt being provided in said suspension or in a stream of water entering said suspension for causing a substantial bleaching by separating calcium from said calcium containing lignin present in said suspension and facilitating the freeing of lignin from the fibers in said suspension, whereby paper or board processed from said suspension will have an increased brightness and/or a reduced kappa number compared to a similar product produced without said carbonic acid or its salt.