Chlorine free pulping and bleaching sequence
CA 2089516 A1 · Owner: Vilpponen, Aki · Inventors: Vilpponen, Aki; Henricson, Kaj; Phillips, Joseph R.
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
Kraft pulp is bleached to acceptable brightness without the use of chlorinated organic compounds yet, it still has commercially acceptable strength properties. During production of the kraft pulp it is subjected to extended delignification by adding, kraft white liquor to a first recirculation loop in the digester, and a second, wash, recirculation loop in the digester. Then the pulp is subjected to hot alkali extraction; followed by two oxygen stages; then preferably acid washing to prevent the buildup of heavy metals; and then is subjected to ozone bleaching at medium consistency. The bleaching sequence after acid washing may be ZEZPZ and the E, stage may be an oxidative peroxide …
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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 February 15, 1993. No grant is recorded for it in Canada; had it been granted, its 20-year term would have ended February 15, 2013.
- A certificate of supplementary protection adds at most two years for a drug, so even that would have ended by February 15, 2015.
- 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.