Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1997-09-30
2001-11-06
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S008000, C162S190000
Reexamination Certificate
active
06312559
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a deinking process for deinking wastepapers such as newspapers, inserts, magazines, woodfree for reclamation thereof. More particularly, the present invention relates to a deinking process excellent in running ability, according to which deinked pulp having a higher whiteness and a smaller number of residual ink fines can be obtained while keeping a proper pulp yield even when washing white water is reused in the flotation step.
BACKGROUND ART
Although newspapers, magazines, office automation wastepapers, etc. have been recycled from of old, effective utilization of wastepapers has particularly recently become increasingly important in connection with global environmental problems such as protection of forest resources and refuse disposal. In addition, the use of deinked pulp has advanced to the utilization thereof as a higher-rank pulp, as exemplified by the use of deinked waste newspaper pulp for making printing paper B glade. Meanwhile, recent wastepapers have been getting into more and more severe circumstances from the standpoint of deinking in keeping with changes in printing techniques, printing methods, printing ink components, etc. Thus, it has been desired to develop a deinking process comprising a proper yield, a high whiteness and little residual ink. Accordingly, for example, improvements in a variety of chemicals have hitherto been made.
Meanwhile, as a decrease in the amount of treatment water for use in a deinking process is also desirable in aspects of the source of supply and environmental protection, white water is circulated and utilized, in general. White water refers to treatment water subjected to drainage and filtration in various steps of the deinking process. Specifically, in the flotation step, white water subjected to drainage in the washing or papermaking step after the flotation step is usually circulated and used as diluent water or the like before flotation for pulp slurry after the aging or bleaching step. Since, however, such circulation of white water gives rise to accumulation of ink fines and fibers in white water, the whiteness of deinked pulp is lowered as the circulation of white water is repeated. Further, used chemicals such as the deinking agent in particular are also concentrated to extremely increase foamability in the flotation step, thus causing a great decrease in the yield. The concentration of inorganic salts mainly comprising calcium ions and the like derived from a filler and the like is also not negligible as a cause of increasing foamability. In any event, the circulation of white water lowers the performance of deinked pulp and the efficiency of deinking. Despite the foregoing circumstances, there have surprisingly been made scarcely any investigations on the deinking agent and the deinking system that can maintain a deinking performance even in a white water circulation or recycling system. Thus, the fact is that a suitable amount of fresh water is used for dilution, or that additional waste water treatment equipment is operated.
JP-A 8-337085 discloses a deinking method in which floatation is conducted in the presence of a cationic compound, an amine compound, an acid salt of an amine compound or an amphoteric compound, but fails to use such a compound in floatation step using a white water.
Although circulation and reuse of white water in the deinking process are desirable in aspects of resources conservation, operation, etc., circulation of white water without causing decreases in the whiteness and yield has been getting into difficult circumstances. Accordingly, solution to this has been desired.
DISCLOSURE OF THE INVENTION
As a result of intensive investigations made in view of the foregoing circumstances with a view to providing a deinking system causing no decreases in the whiteness and the areal ratio of residual ink fines while maintaining a proper yield even in a white water circulation system, the inventors of the present invention have confirmed that the deinking performance that can be seen in respects of the whiteness and the areal ratio of residual ink fines can be improved without causing any decrease in the performance as can be seen in conventional deinking processes, when white water is rather positively circulated and reused in the presence of a cationic compound, an amine compound, an acid salt of amine compound, or an ampholytic compound in the flotation step wherein use is made of treatment water containing white water. The present invention has been completed based on this confirmation.
The present invention provides to a deinking process comprising a flotation step using treatment water containing white water, wherein during or at least at a point in time of the flotation step it is effected in the presence of at least one compound selected from the group consisting of (1) cationic compounds, (2) amine compounds and acid salts of amine compounds, and (3) ampholytic compounds.
Further, the present invention provides a deinking process wherein at least one compound of (1) cationic compounds, (2) amine compounds and acid salts of amine compounds, and (3) ampholytic compounds may be used in combination with an organic compound.
In other words, the invention is a method for deinking wastepaper which comprises the step of conducting at least part of floatation step in the presence of at least one addtive compound selected from (1) a cationic compound, (2) an amine compound, an acid salt of an amine compound or (3) an amphoteric compound, characterized by conducting floatation with a treating water including a white water.
It is preferable that the white water is repeatedly circulated into the floatation system while further portions of the addtive compound(s) are added so that a given content of the addtive compound(s) may be maintained. It is preferable to add the addtive compound(s) every circulation. The addition may be conducted during or at a point in time of the floatation step. It may be conducted also just before floatation. It is preferable that the amount in total of the addtive compounds ranges from 0.001 to 5.0 percent by weight based on the weight of the wastepaper.
In the deinking process of the present invention, the flotation step is preferably effected using treatment water containing white water discharged in the steps following the flotation step. White water discharged in the steps preceding the flotation step, e.g., in the step of disintegrating wastepaper, is unsuitable for use in the flotation step because it contains a considerable amount of ink.
The steps following the flotation step include the washing step, the draining step, and the papermaking step. In general, at least 50%, preferably at least 70%, of white water discharged in these steps is mixed with fresh water if necessary to be circulated as treatment water for use in the flotation step.
In the present invention, although the circulation of white water is done at least once, it is desirably at least three times since the difference of the present invention from the prior art becomes remarkable in respects of the whiteness and the areal ratio of residual ink fines.
Further, according to the present invention, at least part of the flotation step is effected in the presence of at least one compound selected from the group consisting of cationic compounds, amine compounds, acid salts of amine compounds, and ampholytic compounds. The amount of such a compound(s) to be added is preferably 0.001 to 5.0 wt. %, especially preferably 0.05 to 2 wt. %, based on the weight of wastepaper.
Further, in the present invention, the pH value of the system in the flotation step is desirably set to be 4 to 12, preferably 6 to 11, further preferably 6 to 9. When the flotation step is carried out at a pH falling within this range, a better deinking effect can be secured.
As used in the present invention, the term “pH value of the system” in the flotation step refers to the pH of the aqueous solution portion of a water-pulp slurry during the flotation step. It is desirable to adjust the pH in t
Irinatsu Yuichi
Miyauchi Yoshitaka
Takahashi Hiromichi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Nguyen Dean T.
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