Patent ID: 7052578

Claim:
A process of making a bleached mechanical wood pulp comprising: providing an aqueous slurry of mechanical wood pulp; providing an aqueous bleaching mixture consisting essentially of water and hydrogen peroxide; providing an aqueous magnesium hydroxide slurry consisting essentially of water and magnesium hydroxide; combining together the aqueous slurry of mechanical wood pulp, the aqueous slurry consisting essentially of magnesium hydroxide and the aqueous bleaching mixture, to form a bleaching pulp mixture, the bleaching pulp mixture having a pH of from about 5.0 to 8.5, the initial ratio of magnesium hydroxide to hydrogen peroxide in said bleaching mixture being about 25 parts to about 75 parts of magnesium hydroxide to about 100 parts of hydrogen peroxide, and the magnesium hydroxide having an initial concentration in the bleaching pulp mixture of at least about 0.5 wt. %, based on pulp dry mass; and bleaching the bleaching pulp mixture consisting essentially of mechanical pulp, hydrogen peroxide, magnesium hydroxide and water for a time sufficient to produce bleached mechanical wood pulp, the bleached mechanical wood pulp having an ISO brightness of more than about 65%, and the magnesium hydroxide having a BET surface area of about 7 to about 15 m 2 /g.