Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1999-04-28
2001-02-13
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S007000, C162S008000
Reexamination Certificate
active
06187135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to the paper making arts, more particularly to a process for the manufacture of a recycled kraft paper having improved strength properties comparable to that made from virgin pulps. Such papers find particular application in the inexpensive substitutes for papers made from expensive virgin pulps. The container making arts, particularly, in the field of kraft paper sacks and plastic laminated sheets for containers, had to use kraft papers made from virgin pulps because the strength properties of recycled papers deteriorate fast as the number of recycling increases. But the use of virgin pulps consumes much of the natural timber resources. Thus, it would be beneficial to improve strength properties of recycled papers and replace much of the kraft papers made from virgin pulps.
2. Description of the Related Art
A typical stock preparation process for recycled paper stocks is roughly described by the
FIG. 1. A
high consistency furnish (4~8%) is formed at the pulper where waste paper is defibered by water. Heavy contaminants in furnish are eliminated by high-consistency cleaners and large size but relatively light contaminants in furnish are eliminated by turbo-separators. In addition to cleaning and screening, the pulper, high-consistency cleaners and turbo-separators perform dispersing of fibers in waste papers.
This is the reason why the process is called by another name, primary dispersion process.
More water is added to the high-consistency furnish at the low-consistency chest (below 1%) and transmitted to low-consistency cleaners and pressure screens for additional cleaning and screening to eliminate small size contaminants from furnish.
At the final stage of low-consistency cleaning and screening process, contaminated water in furnish is replaced with fresh water by an extractor. Then the out put of cleaned furnish undergoes refining process where mechanical beating and kneading on cellulose fibers in furnish is done.
Then the refined furnish is transported to a mixing chest where chemical additives are added and mixed. The machine chest receives furnish from mixing chest and stores it until it is sent to paper machine.
Although refining is essential for virgin fibers, refining recycled fibers that went through refining process already at the first occasion deteriorates fiber quality because refining will easily tear fibrils apart from fiber bodies turning them into fibril fragments. This results in the deterioration of strength properties of recycled paper. But they keep refining recycled fibers simply because it is recognized as the only means to control the freeness of furnish.
In the art of paper recycling, deterioration in strength properties of recycled paper has been taken as unavoidable and, therefore, more attention has been given to immediate problems such as de-inking and stickies control than to restoration of strength properties.
Moreover, the need for improving the strength properties of recycled paper has not been so serious. It is because either it has been tolerable in most cases of recycled paper usage or surmountable by the use of virgin pulps and dry-strength additives in paper manufacturing process. But this means that the strength of paper has been achieved at the cost of high priced natural resources such as virgin pulps.
SUMMARY OF THE INVENTION
In one embodiment the invention is directed to a stock preparation process for recycled paper wherein a furnish is prepared by pulping, cleaning, screening, extracting, and refining recycled fibers, characterized in:
Removing refiners, eliminating fibril fragments from furnish, adding dispersion aids to the pulper, maintaining a pH of furnish at least 5.5 and at highest 6.5, and applying dry strength additives to furnish.
In another embodiment, the invention is directed to a stock preparation process for recycled paper, separation of hydrogen bonds of recycled fibers is achieved by replacing refiners with ultrasonic and/or mechanical furnish agitators.
In still further embodiment, the invention is directed to a stock preparation process for recycled paper, elimination of fibril fragments from furnish is accomplished by enlarging holes and controlling the rotating speed of screens used in extractors.
A further embodiment discloses a process of stock preparation for recycled fibers characterized in the following steps:
(a) adding effective amount of NaOH to pulper,
(b) eliminating fibril fragments from furnish by extractor,
(c) removing refiners from the stock preparation process,
(d) employing ultrasonic and/or mechanical furnish agitators,
(e) applying appropriate amount of ALUM to the mixing chest to control the pH of furnish, and
(f) applying dry strength additives to the mixing chest.
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Lavigne. J.R. “Instrumentation...Paper Industry”, Miller McFreeman Publications, pp. 207-208, 1979.
Arent Fox Kintner Plotkin & Kahn
Nguyen Dean T.
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