Method for bleaching mechanical pulp
CA 2270475 A1 · Owner: Depew, M. Catherine · Inventors: Depew, M. Catherine; Wan, Jeffrey K.-S.
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
A method for reducing brightness reversion and yellowness (b*) of a bleached mechanical wood pulp is described. The pulp is digested in an aqueous formaldehyde solution containing carbonate preferably magnesium or calcium , carbonate preferably in an amount up to 30 % by weight of pulp and at a temperature in the range of 15 to 60 ~C. Paper made from the digested pulp can be further improved by treating with a reversion inhibitor such as a polyethylene glycol bisthiol. A method for bleaching unbleached softwood or hardwood pulps using hydrogen peroxide without added alkali for activation is also described. The aqueous hydrogen peroxide solution preferably contains magnesium or …
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Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Filed September 21, 1998. No grant is recorded for it in Canada; had it been granted, its 20-year term would have ended September 21, 2018.
- A certificate of supplementary protection adds at most two years for a drug, so even that would have ended by September 21, 2020.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.