Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1999-09-23
2001-10-09
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S336000, C162S258000, C162S259000
Reexamination Certificate
active
06299731
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 198 43 727.7, filed Sep. 24, 1998, 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 process and headbox system for improving the consistency cross-direction profile of a fiber web, e.g., a paper or cardboard web, in a wet process. The process includes distributing, via the headbox, a fiber suspension across a width of the machine onto either a wire or between two wires, and at least partially adjusting a cross-direction basis weight that is sectionally variable across the machine width. The adjustment of the cross-direction basis weight includes mixing a first suspension having a first solid content and a first percentage composition of solids content with a second suspension having a second solid content, which is lower or higher than the first solid content. A second percentage composition of the solids content of the second suspension is different from the first percentage composition.
2. Discussion of Background Information
U.S. Pat. No. 5,560,807 discloses sectionally feeding a suspension with additives, chemical admixtures, or weighting agents in a regulated manner in a diaphragm-controlled headbox in the area of a lateral distributor. In this manner, with respect to the z-direction of the resulting web or paper, the concentration of admixtures can be adjusted and the feed of the admixtures can take place as close as possible to the outlet of the headbox. Thus, a change in the admixtures due to an excessively long dwell time in the pulp slurry can be prevented.
Commonly assigned German patent disclosure document DE 40 19 593 A1 discloses a sectional consistency-regulated headbox having two sets of individual feeds for two pulp slurries of differing solids content which are distributed across the machine width. Preferably, pulp stock and backwater are used in this process. When the basis weight cross-direction profile of the paper web deviates at a specific position of the web width, the concentration CM of the sectional flow corresponding to this specific position is corrected by changing the quantitative proportion of the regulating flows of differing solids content Q
H
/Q
L
fed to a mixer. This type of basis weight cross-direction profile regulation is very advantageous with respect to a simultaneously good fiber orientation cross-direction profile, and yields very good results with regard to basis weight cross-direction profile. However, as requirements concerning paper quality are constantly increasing, it is clear that papers manufactured in this way can exhibit striped wild formations with respect to their printability despite even fiber orientation and even basis weight. Detailed studies have shown that this uneven printability is attributable to an uneven composition of the paper.
U.S. Pat. No. 5,401,363 and its counterpart European patent document EP 0600 251 B1 discloses sectionally feeding differing quantities of a retention agent to the headbox across the machine width to eliminate an uneven consistency crossdirection profile of a paper web arising through wear on the wires of differing intensity. However, a process of this type is unsuccessful if the original consistency of the pulp slurry is already uneven across the machine width.
SUMMARY OF THE INVENTION
Therefore, the present invention provides a process and a headbox system that improves the consistency cross-direction profile of a fiber web, e.g., a paper or cardboard web.
The process, according to the present invention, includes sectionally admixing, across the machine width, at least a third suspension having a third solids content, which has either a lower or higher solids content than the first and/or second suspensions. Moreover, a third percentage composition of the solids content of the third suspension differs from the first and/or second percentage compositions.
The headbox system of the present invention includes at least a third set of individual feeds with flow regulating elements for feeding the third suspension, the at least a third set of individual feeds being positioned upstream from a turbulence generator and/or to act equally per section in a z-direction of the fiber web. The third percentage composition of solids of the third suspension can differ from the first and/or second percentage compositions.
Accordingly, the present invention provides a process for manufacturing a fiber web, e.g., a paper or cardboard web, in a wet process in which the fiber suspension is distributed by a headbox across the width of the machine onto a wire or between two wires. The basis weight cross-direction profile, which is sectionally variable across the machine width, is at least partly influenced or adjusted by a mixture of the first suspension Q
1
having a first solids content and a first percentage composition of the first solids content, and the second suspension Q
2
having a second solids content which is lower or higher than the first solids content. A second percentage composition of the second solids content differs from the first percentage composition. At least a third suspension Q
3
, having a third solids content which is lower or higher than the first and/or second solids content, is sectionally admixed across the machine width. The third percentage composition of the third solids content differs from the first and/or second percentage composition.
Through a corresponding variation of the mixture of at least three suspensions of differing compositions, the process of the present invention enables influencing or adjustment of a sectional overall volume flow that, despite a reduction or increase in the overall solids content in the section, maintains a constant percentage composition of individual solid components. However, the influence or adjustment of a specific retention, which changes with respect to the individual solids content based on the differing overall solids content in the suspension, can be offset by targeted influencing or adjustment of the initial composition of the fed pulp slurry.
In a particularly advantageous embodiment of the instant invention, normal pulp slurry (pulp stock) can be utilized as first suspension Q
1
, backwater can be utilized as second suspension Q
2
, and clarified filtrate, clarified water, diluted retention agent, backwater from other parts of the wire section, first suspension Q
1
, and/or any combinations thereof can be utilized as third suspension Q
3
.
Moreover, the suspensions may also differ in content of weighting agent and/or fiber content. It is also possible that the suspensions may differ in content of fibers of different lengths and/or content of fibers having a different shrinkage effect on the fiber web in the subsequent manufacturing process. In this context, reference is made to commonly owned German patent application 198 43 729.4 and counterpart U.S. patent application Ser. No. 09/401,952 filed Sep. 23, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety.
In an exemplary embodiment of the process, second suspension Q
2
can be structured or formed to mainly or exclusively include fiber content, and third suspension Q
3
can be structured or formed to mainly or exclusively include weighting agent content. In this manner, at a specific mixing ratio of the second and third suspensions, i.e., Q
2
/Q
3
, a composition of solids can be achieved that corresponds to the composition of solids of first suspension Q
1
, but which has a different concentration of solids. Thus, by simply maintaining the mixing, ratio, the composition of solids can be kept constant while enabling different quantitative proportions to be set with respect to first suspension Q
1
. Therefore, a targeted shifting, of the mixing, ratio of the second and third suspensions Q
2
/Q
3
can cause a shift in the composition of solids toward weighting, agents or fibers.
Addit
Begemann Ulrich
Thomas Dirk
Greenblum & Bernstein P.L.C.
Hug Eric
Silverman Stanley S.
Voith Sulzer Papiertechnik Patent GmbH
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