Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With classifying – separating or screening of pulp
Patent
1981-08-12
1982-12-07
Smith, William F.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With classifying, separating or screening of pulp
162 5, 162190, 162191, 209 5, D21C 900
Patent
active
043626009
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to chemical separation of cellulose fibres and more particularly it relates to the use of high molecular weight polyalkylene oxides for separation of unbleached sulphate fibres from mixed cellulose pulps. The invention can be applied in connection with recycling of secondary fibres, broke etc., for subsequent production of paper, board, paperboard and similar products.
Paper, board, paperboard etc. is for the most part manufactured from the following kinds of pulps: mechanical pulp--including both pulp prepared by purely mechanical means and thermomechanical pulp--, sulphite and sulphate pulps, and semi-chemical sulphite pulp, e.g. NSSC-pulp. Mechanical and thermomechanical pulps contain substantially all of the original components of the wood or the raw material, but for the other kinds of pulp, lignin and other non-cellulosic components have been removed to a varying extent by pulping. Depending on the intended field of use, the pulps are subjected to further treatment in the form of bleaching. Bleaching is the term used for chemical treatment of pulps with different kinds of chemicals, e.g. chlorine, chlorine dioxide, hypochlorite, peroxide, oxygen, dithionite etc., to produce a brighter pulp and it involves mainly a removal and/or a chemical modification of the lignin.
At the production of e.g. multi-layer paper or paper board, different pulps are used for the different layers, and broke and white water from these processes will thus contain mixtures of fibres. Mixed pulps are also obtained in the increased handling of waste paper. According to the invention mixed pulps from such processes can be worked up to different fractions and thereafter be utilized with improved economy and in an improved technical manner.
Broke and reclaimed fibres from the production of paper, paper board and similar products including different kinds of pulps are generally utilized in integrated systems without preceding separation. Large quantities of originally high quality pulp suited for the production of products with high economic value are hereby utilized in a very uneconomical manner. Considerable economic advantages can be gained by converting pulp blends into pure pulp fractions. Upgrading pulp mixtures also gives advantages in that the subsequent production of paper products can be controlled in a better way as far as chemicals and process variables are concerned than for systems of unspecific and varying mixtures. As examples of systems wherein different pulps are used and wherein reclaiming of broke and fibre alurry is valuable can be mentioned e.g. the production of corrugated fibreboard where the corrugated layer is made up from NSSC and/or recycled fibre pulp, while the facings (linerboard) are made up from unbleached sulphate pulp. Further, there can be mentioned multi-layer products wherein one or more layers have been produced from bleached pulp, to obtain a better appearance or to improve the printability, but which contain layers of unbleached sulphate in order that they will possess the required strength.
In the handling of waste paper, in which paper or board after use, is reclaimed and after slushing and optionally de-inking, is re-used for the production of paper products, the incoming waste material contains mixtures of pulps of different types and it is here highly desirable that the material, to the greatest possible extent, can be sorted and classified to give the best utilization. The sources of the waste material vary to a great extent, e.g. from households, where the largest part is made up from newsprint and magazine paper, to industries and offices, where the waste is a mixture of printing and writing paper, paperboard, sacks, newsprint etc. Collected waste paper is--if sorted at all--sorted manually and it is evident that this sorting cannot give a total grading of all the material in uniform groups. A large part of the material will be classified as "mixed" and used for, or as part of, products with lower quality requirements, e.g. as middle-layer in paperboard
REFERENCES:
patent: 3141816 (1964-07-01), Manley
patent: 3884750 (1975-05-01), Iannazzi
Lindstrom Tom S. C.
Westman Lennart H.
AB Casco
Philpitt Fred
Smith William F.
Svenska Traforskningsinstitutet
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