Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Patent
1995-02-13
1999-04-20
Chin, Peter
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
162 6, 162 8, 162 13, 162147, 162 72, 162189, D21C 502
Patent
active
058955569
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for the treatment of waste paper pulps, and in particular to a process for the treatment of waste paper pulps in a repulping stage.
DESCRIPTION OF THE RELATED ART
Because of increasing public demand, the use of recycled paper has steadily increased. To recover the fibres used for papermaking from wastepaper, a waste paper deinking operation must generally be carried out to remove the inks used in printing, and thus create a wastepaper with suitable appearance for re-use. Traditionally, deinking has been conducted by either washing, or flotation deinking.
Wastepaper may contain a mixture of newspapers, magazines, telephone directories, printed advertising material, corrugated containers and the like. The paper fibres used to produce these materials may be chemically pulped materials, such as Kraft pulps, or may be mechanical produced pulps such as groundwood. Much of this wastepaper has undergone some form of printing operation, which printing operation leaves a deposit of ink on the paper. To date, wastepaper recycling has concentrated on removal of the ink, prior to re-use of the recycled waste paper for further printing.
The basic stages in a typical washing or flotation deinking process are: repulping the wastepaper in a repulper; coarse cleaning and screening of the repulped material; deinking; fine cleaning and screening; post-bleaching, and finally, storage.
A key component in a typical old newspaper (ONP) deinking operation is treatment of the waste paper in the repulper. In the repulper, the wastepaper is typically treated in water with chemicals such as caustic soda, sodium silicate and hydrogen peroxide, as described hereinbelow. A metal chelating agent may also be included.
The repulping stage may degrade the resin surrounding the ink particles, while the physical action of the repulper helps to separate the ink from the fibres.
Repulping is followed by a series of coarse cleaners and screens to remove large particles, like staples and plastics from the pulp. The cleaned pulp is passed to either a wash or a flotation deinking stage.
In wash deinking, a large volume of water is passed through the repulped wastepaper which wastepaper is supported on a mesh screen. The ink and other particles are washed through, and away from the pulp.
In flotation deinking, chemicals designed to collect the ink particles together are employed while air bubbles are introduced to the repulped wastepaper. The hydrophobic nature of the ink particles treated with collector chemicals promotes the adherence of the ink to the air bubbles, so that the ink is lifted to the surface of the repulped wastepaper, where it can be removed.
Typically, only one type of deinking is utilized. However, some waste paper treatment mills may employ both washing and flotation deinking processes.
After either process, the deinked, repulped wastepaper is subsequently passed through a series of fine cleaners and screens where the small particles, like sand and grit, are removed.
Additional processing stages may be required, such as for example, dispersion, to reduce the particle size of any contaminants, or a special cleaning stage with special cleaners designed to remove specific contaminants. Further, the repulped wastepaper may also be treated with bleaching chemicals to increase the whiteness and brightness of the pulp.
The deinked wastepaper is then held in storage until it is eventually fed to a paper-making machine. The deinked wastepaper thus provides a furnish of pulp which furnish may be combined with other paper furnishes to produce the saleable paper product.
The chemistry involved in traditional deinking is well known. Caustic soda is used in the repulper to increase the pH and, in some cases, to saponify the resin surrounding the ink particles. Increasing the pH above 7.0, however, will cause yellowing and darkening of the wastepaper stock that contains paper made from groundwood or mechanical pulps. To counteract the undesirable darkening effect, a bleaching agent i
REFERENCES:
patent: 3098784 (1963-07-01), Gorman
patent: 5055161 (1991-10-01), Hoffman
patent: 5061345 (1991-10-01), Hoffman
patent: 5141598 (1992-08-01), Richmann et al.
patent: 5200034 (1993-04-01), Richmann et al.
patent: 5234543 (1993-08-01), Markham et al.
Database WPI, Week 7944, Derwent Publications Ltd., AN 79-79671B & JP, A,54 120 705, Sep. 1979, see abstract.
Blain Terrence J.
Ferguson Loreen D.
Grant Jeanette E.
Parent Christine M.
Chin Peter
ICI Canada Inc.
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