Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Mechanical defibration in the presence of heated gas or gas...
Patent
1991-03-22
1992-05-12
Hastings, Karen M.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Mechanical defibration in the presence of heated gas or gas...
2412613, 241296, D21B 114, B02C 712
Patent
active
051124432
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to methods for making fiber pulp from lignocellulose-containing material. More particularly, the present invention relates to methods for making fiber pulp from lignocellulose-containing material at torr solids contents of greater than about 15%.
Still more particularly, the present invention relates to apparatus for making fiber pulp from lignocellulose-containing material.
BACKGROUND OF THE INVENTION
The manufacture of fiber pulp from lignocellulose-containing material is generally carried out in a refiner comprising two grinding discs, at least one of which is rotary. This is generally accomplished in a manner such that the material is fed in through a central opening in one disc and disintegrated in the gap between the discs, while water is simultaneously being supplied thereto. Conventionally, the grinding discs are provided with raised bars and intermediate grooves, which extend from the center outwardly to the periphery of the grinding discs. Such methods for the manufacture of mechanical cellulose pulp have been known for a considerable period of time.
The pulps which are manufactured in such a conventional manner, however, generally contain a large fraction of relatively long fibers. In certain applications, such as for use as newsprint, this can be of value, primarily because it results in high strength, especially tear resistance, which is essential in view of the high machine speeds used during the manufacture and printing of same.
In other quality papers, such as magazine paper and LWC (light weight coated) paper, however, the printability of these papers is of greater importance, and the necessary strength in these cases is generally achieved by admixing chemical pulp therein.
Thermomechanical pulp (TMP) and chemi-mechanical pulp (CTMP) are pulps which are produced in very high yields, e.g., 90 to 95%. This implies that substantially all of the lignin remains in the pulp. The long fibers thus become rigid, and the smoothness of the paper is considerably deteriorated.
SUMMARY OF THE INVENTION
In accordance with the present invention these and other problems have been overcome by the invention of a method and apparatus which enables the manufacture of a pulp with a lower portion of long fibers, which, at the same time, is well defibered and fibrillated, and has low shives content and high bonding strength. It is thus not possible to achieve these results by the use of conventional refiner techniques. Thus, in order to reduce the long fiber content conventionally, the pulp must be reground in a separate step, at low concentration. In accordance with the present invention, however, these problems have been overcome by the cellulosic material being defibered and fibrillated by a shears-like effect between opposed bars in the two grinding discs. This is achieved in accordance herewith by the fact that the bars in the two grinding discs are arranged in both directions at a definite angle with respect to the radius of the grinding segments. Experimental evidence has thus shown that this angle should be between about 5.degree. and 30.degree., preferably between about 7.5.degree. and 22.5.degree..
Furthermore, in addition to the above-noted requirements with respect to pulp quality, a grinding segment is also required which can yield high production. This, in turn, requires a high capacity for transporting pulp and generating steam through the grinding zone. Furthermore, it must also be possible for rotation to take place in both directions in order to reduce the trueing of the leading bar edge by wear. It is therefore necessary for the pattern on the grinding segments to be reversible. Another requirement for the grinding segments is to contribute to the reduction of the otherwise high energy consumption by means of the pattern design itself.
There has been considerable study of the refining procedures which take place in the grinding zone itself. According to one opinion, this treatment takes place in a manner such that the chips in the grin
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Haven Anders E. E.
Virving Nils
Hastings Karen M.
Sunds Defibrator Industries Aktiebolag
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