Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1998-06-29
2001-01-30
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S005000, C162S006000
Reexamination Certificate
active
06179957
ABSTRACT:
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 in order to recycle them. More particularly, the present invention relates to a deinking process according to which good-quality pulp sheets reduced in sad color can be obtained.
2. Prior Arts
Wastepapers are recycled by stripping ink from the wastepapers by a deinking treatment to prepare recycled pulp and manufacturing recycled paper from the recycled pulp. The conventional deinking methods generally comprise a step of stripping ink from wastepapers and a step of discharging the stripped ink.
More specifically, the deinking method comprises as main steps:
(1) a step of pulping (disintegrating) wastepapers,
(2) a step of aging, i.e., leaving the disintegrated paper as it is,
(3) a step of flotation, and
(4) a step of washing.
That is, in deinking treatment, ink bound to the fibers of wastepapers is physically and chemically (or biochemically) stripped therefrom to thereby separate the ink from the fibers. Thus, recycled 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.
A deinking agent for use in the ink stripping step and the ink removal step has hitherto been required to have different properties for the respective steps. Specifically, a deinking agent for use in the ink stripping step is required to improve the wettability and permeability of pulp with ink and increase the ink-stripping power while having excellent ink-dispersing properties in order to prevent redeposition. On the other hand, a deinking agent for use in the ink removal step is required to have a foaming power and foam-breaking properties in the course of washing.
It has been believed that improvements in such performances can generally be attained by lowering the surface tension and hence, increasing the hydrophilicity of ink interfaces, i.e., lowering the contact angle of the aqueous solution of a deinking agent (aqueous solution portion of slurry) with ink interfaces is a matter of necessity for improvements in performances.
From the viewpoint of ink removal, however, a deinking agent having good ink-stripping and ink-dispersing properties involves a particular problem of “sad color” because the ink is excessively dispersed such that the ink is insufficiently adsorbed on the bubbles, thus failing to provide satisfactory whiteness. This “sad color” deteriorates the appearance of printed matter prepared by using recycled paper. Thus, in order to prevent this problem, a large amount of virgin pulp must be added. In other words, the problem of “sad color” cannot well be solved with any approach from the viewpoint of an improvement in the wettability of ink interfaces or an increase in the hydrophilicity of ink interfaces as has hitherto been proposed.
DISCLOSURE OF THE INVENTION
Summary of Invention
As a result of detailed investigations on how to remove fine particles of ink from pulp after sufficient ink stripping, the inventors of the present invention have found out that the foregoing problem of “sad color” can be solved so as to provide good-quality pulp sheets when the contact angle of the aqueous solution of a deinking agent with ink interfaces, on which investigations have hitherto been made with the aim of more lowering the contact angle, is heightened in the flotation step to the contrary. More specifically, they have found out that the removal of fine particles of ink proceeds to remarkably decrease the appearance of sad color particularly when the contact angle of the aqueous solution portion of a slurry containing stripped ink with ink interfaces in a flotator is at least 70°. The present invention has been completed based on these findings.
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 contact angle of the aqueous solution portion of said pulp slurry containing said stripped ink with the interfaces of ink particles to be at least 70°.
The present invention further provides a method for controlling the deinking performance in a deinking process comprising at least the step of stripping ink from a pulp slurry formed from wastepaper as the starting material, and the step of removing the stripped ink by flotation, characterized by measuring before or in the flotation step the contact angle of the aqueous solution portion of said pulp slurry containing said stripped ink with the interfaces of ink particles and adjusting the contact angle to a value of at least 70°. The adjustment of the contact angle 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.
Thus the present invention provides a deinking process at least comprising the step of stripping ink from wastepaper as the starting material and the step of removing the stripped ink by the flotation method, characterized by using at least one surfactant for ink stripping and controlling the contact angle of the aqueous solution portion of a slurry containing the stripped ink with the interfaces of ink particles in the flotation step to be at least 70°.
The deinking process of the present invention is characterized by controlling the contact angle of the aqueous solution portion of the slurry containing the stripped ink with the interfaces of ink particles in the flotation step to be in the range of at least 70°, preferably 70 to 100°, further preferably 70 to 90°. Furthermore, it is possible to control this contact angle to be in the above-mentioned range before entering the flotation step. Also it is permissible to examine a method of controlling the contact angle to be in the above-specified range in the flotation step separately on a laboratory scale and apply this method to the operation on a real equipment level in factories or the like. In this case, the contact angle control method found out preliminarily may be applied to the operation of real equipment.
The contact angle is measured in the following manner.
<Contact Angle Measurement>
A glass plate is coated with a resin component obtained by removing the liquid component of a newspaper ink to form an ink plate. Alternatively, an ink plate may be formed by adding water to wastepaper for use in deinking to prepare an aqueous solution of 5% in pulp concentration, subjecting the solution to disintegration with a bench disintegrator, subjecting the resulting solution to Soxhlet extraction with chloroform for 48 hours to obtain an extract as an ink composition, subjecting the ink composition to GPC preparatory column chromatography of 100,000 in exclusion limit molecular weight to separate and collect a resin component of at least 1,000 in molecular weight in the ink composition, and coating a glass plate with the resin component. An aqueous solution obtained by filtration of a slurry in a flotator before the flotation step of the deinking process is dropped on an ink plate formed according to one of the foregoing procedures to measure the contact angle therebetween. The use of the resin component as an ink sample is based on a belief that the ink portion removed by deinking is a solid portion, while drying oil, semidrying oil and mineral oil are not involved in ink removal.
The contact angle of the aqueous solution portion of a slurry with ink interfaces in a flotator is about 60° in conventional deinking methods. There is even a deinking agent capable of further lowering this contact angle from the viewpoint of the aforementioned direction of development of a deinking agent. Even in the deinking process of the present invention, the contact angle of the aqueous solution portion of a s
Irinatsu Yuichi
Miyauchi Yoshitaka
Takahashi Hiromichi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Nguyen Dean T.
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