Paper making and fiber liberation – Processes and products – Reclamation – salvage or reuse of materials
Reexamination Certificate
2000-05-12
2002-12-24
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
Reclamation, salvage or reuse of materials
C162S264000, C162S186000, C162S335000
Reexamination Certificate
active
06497788
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 22 391.2, filed on May 14, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a backwater cycle of a paper machine that has at least one application device for applying a composition containing pigment and/or filler onto a fiber web that has not yet been completely dewatered in the wet zone. The backwater cycle includes a first backwater cycle that supplies a stock inlet with backwater, and a second backwater cycle that forms the remainder of the backwater cycle. The present invention further relates to a process for circulating water of a paper machine having a wet zone in which a composition containing pigment and/or filler is applied onto at least one surface of a fiber web being formed, and backwater is extracted from the fiber web being formed.
2. Discussion of Background Information
It is known from U.S. Pat. No. 5,152,872 to apply a pigment or filler onto a paper web that has not yet been completely dewatered, in order to produce thereby a multilayer paper whose outer layers have a pigment content considerably higher than that of the inner layer.
When such a pigment application or filler application technique is used in a conventional paper machine on a paper web that has not yet been completely dewatered, a problem arises that, after the paper machine has been running for a certain time, the wire cycle in which the stock inlet is included becomes enriched with filler or pigment. The result of such an enrichment is that the inner paper layer, which is initially low-filler, becomes likewise enriched with filler or pigments as the production process continues. This result runs counter to the desired distribution of the filler in the paper. In fact, an advantageous filler distribution in the paper is considered to be a state in which the filler or the pigments are essentially situated in the outer layers of the paper, while the inner layer is chiefly loaded with fiber components in order to achieve a high breaking strength. The chief advantage of such a steep filler distribution in the paper is the leveling of the surface structure that is decisive for the printing process, and homogenization thereof.
SUMMARY OF THE INVENTION
The present invention provides a backwater cycle of a paper machine and a process for circulating water of a paper machine that prevents the inner layer of the produced paper from being enriched with filler and/or pigment, even when the paper machine has been operated for a lengthy period.
During the paper production process, the amounts of water removed in a wire section of the paper machine are separated into two fractions, backwater I and backwater II. In modern paper machines, backwater I refers to the part of the backwater that accumulates on a forming roll, an upper wire suction box, a forming shoe, and/or other suction elements, in which the possibility of an upstream application of filler and/or pigment is not being taken into consideration. Backwater I is conducted in a short cycle without treatment and is utilized for thinning the slush of a machine vat immediately upstream of the stock inlet.
The water that accumulates at the wet suction elements, flat suction elements, and suction wire rolls are typically collected as backwater II. The clear water is then used for spray pipes and the like.
However, when filler and/or pigment is applied in the wire section of a paper machine, a portion of the applied filler and/or pigment can be removed by a subsequent vacuum suction element. Thus, re-using such water without intermediate treatment causes the thin pulp, which is initially distributed in a crosswise manner by the stock inlet and dewatered via a forming roll and wire suction box, to be enriched with filler and/or pigment. It is not possible to adjust a very steep filler distribution in the Z direction of the paper.
Therefore, in order to solve the above-described problem, the backwater cycle of a paper machine and the process for water circulation of the paper machine can be designed so that the water cycle in which the stock inlet of the paper machine is included is loaded from dewatering units that dewater the fiber web at a stage at which no composition containing pigment and/or filler has been applied onto the fiber web that is being formed. Each dewatering element that extracts moisture from the web subsequent to the application of filler and/or pigments can be consequently enriched with high pigment or filler components, so that this water would lead to a constant increase in the filler and/or pigment content of the layer formed by the stock inlet. Other units which would be undesirable to use for delivering backwater to the stock inlet include devices for catching cleaning liquid for wires which have come into contact with the pigment and/or filler application. This is because these wires are likewise charged with an increased filler and/or pigment content.
Thus, the present invention develops a backwater cycle of a paper machine that has at least one application device for applying a composition containing pigment and/or filler onto a fiber web that has not yet been completely dewatered in the wet zone. The backwater cycle includes a first backwater cycle that supplies a stock inlet with backwater and a second backwater cycle that accepts the remainder of the backwater. In this manner, the first backwater cycle is fed exclusively by dewatering elements that are arranged in the production process upstream, relative to a wire travel direction, of the application of a composition containing pigment and/or filler.
In this manner, the first backwater, which is returned to the stock inlet, is charged with lower or substantially lower filler concentrations or pigment concentrations than the pulp suspension that is fed to the stock inlet. This avoids the problem of the first backwater cycle, in which the stock inlet is included, being increasingly enriched with filler and/or pigment. Finally, in this way, a high portion of pigment and/or filler can be present in the outer layers of the produced paper web, while the fiber component maintains a constantly high value in the inner layer, and while the filler and/or pigment portion remains low.
The advantageous design of the backwater cycle of the present invention includes that the backwater of the second backwater cycle serves to feed the application of the composition containing pigment and/or filler. Since the second backwater cycle of the invention is fed at least chiefly by units that deliver water with a high pigment and/or filler content, this cycle is particularly well-suited to serve the water cycle for the applicator or applicators of the pigment and/or filler-containing composition.
It may furthermore be advantageous for the remaining backwater of the second backwater cycle, which is not being used to feed the application of the composition containing pigment and/or filler, to be processed with a depulping device, e.g., a microflotation device, to produce a clear filtrate. The clear filtrate formed from the second backwater cycle can be used later at any desired point in the production process of the paper web.
The presence of a depulping device, e.g., a microflotation device, is particularly advantageous when the backwater of the second backwater cycle is provided with a binder, e.g., starch, since this binder can then be carried out from the backwater by the depulping device and thereby avoid an enrichment of binder in the middle fiber layer of the finished paper.
Moreover, it is advantageous to introduce a disk decker upstream of a microflotation device, since a considerable portion of the remaining substances is removed from the backwater and the necessary filter area of the microflotation device can be reduced at the same water flow-through amount, thereby reducing costs.
It is also advantageous when a microflotation
Cedra Ingolf
Prechtel Klaus
Greenblum & Bernstein P.L.C.
Griffin Steven P.
Hug Eric
Voith Sulzer Papiertechnik Patent GmbH
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