Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Patent
1998-07-30
2000-08-15
Nguyen, Dean T.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
162 5, D21B 108
Patent
active
061030562
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase under 35 U.S.C. .sctn.371 of prior PCT International Application No., PCT/JP97/01794, which has an International filing date of May 27, 1997, which designated the United States of America, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a deinking method for deinking wastepapers such as newspapers, leaflets and magazines to reclaim them. More particularly, the present invention relates to a deinking process according to which bulkier pulp sheets can be obtained.
2. Prior Arts
Wastepapers are reclaimed by stripping ink from the wastepapers by a deinking treatment to prepare reclaimed pulp and manufacturing reclaimed paper from the reclaimed pulp. The conventional deinking methods generally comprises a step of stripping ink from wastepapers and a step of discharging the stripped ink.
More specifically, the deinking method comprises as main steps: physically and chemically (or biochemically) stripped therefrom to thereby separate the ink from the fibers. Thus, reclaimed pulp is obtained.
The foregoing ink stripping in the conventional deinking treatment is generally carried out at a high pH (pH: 10 to 9), followed by the removal of the ink under the same conditions in the flotation step.
In recent years, the properties of wastepapers which are used as the starting material have been varied because of an increase in a demand for a beautiful and stable printing and a progress in printing techniques. Besides, the degree of bond of ink to paper is widely varied from a mild to strong one. Under these circumstances, it is demanded to improve the quality and the recovery (i.e., productivity) of deinked pulp. In order to attain these purposes, various proposals are offered from various field including deinking processes, deinking agents and apparatuses used for deinking.
However, most of the techniques heretofore proposed are directed to an improvement in the whiteness of deinked pulp. Thus, it cannot be said that sufficient investigations have been made on the strength and bulk density of pulp sheets. Although the pulping step and the flotation step in the conventional deinking method are generally carried out at a pH value on the alkaline side such as a pH of 10 to 9 as described hereinbefore, it cannot be said that the paper strength and bulk density of the resulting pulp sheets are satisfactory. Although there are known some deinking methods wherein the pulping step and the flotation step are carried out at a pH of at most 9 (JP-A 54-23705, JP-A 59-53532 and U.S. Pat. No. 4,043,908), these methods are not necessarily effective as measures for improving the strength and bulk density of pulp sheets.
DISCLOSURE OF THE INVENTION
SUMMARY OF INVENTION
As a result of detailed investigations on the removal of ink by flotation, the inventors of the present invention have found out that the interfacial potentials of ink and pulp in the flotation step exert great influences on the bulk density of pulp sheets. The present invention has been completed based on this finding.
The present invention provides a deinking process comprising at least the step of stripping ink from a pulp slurry formed from wastepaper as the starting material, wherein at least one surfactant is used for ink stripping, and the step of removing the stripped ink by flotation, characterized by controlling before or in the flotation step the interfacial potential (.xi. potential) of ink particles in said pulp slurry containing the stripped ink to be in the range of -5 mV to -60 mV and that of pulp in said pulp slurry containing the stripped ink to be in the range of -15 mV to +15 mV with a difference of at least 10 mV between the interfacial potential (.xi. potential) of said ink particles and said pulp. The adjustment of the .xi. potential may be conducted before or in the flotation step. It may be conducted during or at least at a point in time of the flotation step.
The present invention further provides a
REFERENCES:
patent: 4043908 (1977-08-01), Roberts et al.
A New Approache To The Selective Removal of Ink Particles By Flotation, Hiromichi Takahashi et al, Performance Chemical Research Lab., 1996 Pulping Con. 811-812.
Characterization and Flotation Studies of Electrostatic Inks, Bret A. Snyder, et al, Progress in Paper Recycling--Nov. 1993, pp. 17-26.
Irinatsu Yuichi
Miyauchi Yoshitaka
Takahashi Hiromichi
Kao Corporation
Nguyen Dean T.
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