Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1998-02-12
2001-03-06
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C210S358000, C210S358000, C210S360200
Reexamination Certificate
active
06197157
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related to, and claims priority under 35 U.S.C. § 119 of, German Application No. 197 05 360.2, filed Feb. 12, 1997, the disclosure of which is expressly incorporated herein in its entirety by reference thereto.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and a process, particularly a press device and a pressing process. The device and process of the invention are for use on a fibrous web or fibrous pulp web, such as a cellulosic fibrous web or cellulosic fibrous pulp web, having a surface weight of about 100 g/m
2
or less, or under about 100 g/m
2
; graphic papers are particularly preferred. The device and process of the invention are utilized for treating—e.g., for draining (particularly dewatering) and/or for smoothing—and particularly for pressing the indicated material, and for controlling its surface properties and sheet structure.
The device and process of the invention employ a press area which comprises or consists of at least one press nip. During operation of the device and practice of the process, the fibrous pulp web is fed through the press area at a speed of at least about 1200 m/min, while simultaneously being subjected to pressure.
2. Discussion of Background Information
Press devices of the type as discussed above, for the production of high-grade, graphic papers, usually are composed of compact presses, comprising or consisting of a press with 3 or 4 rolls, followed by at least one supplementary laying press. Such a relatively large number of essential roll openings, which is necessary due to the high operating velocity used in producing high-grade graphic papers, results in a large space requirement for these devices, because of the correspondingly large number of rolls needed. Despite this relatively high expenditure, only a limited draining capacity is attained because of the high operating velocity.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a press device and a pressing process of the type as mentioned initially above, but which have as small a space requirement as possible, while at the same time both displaying a high capacity for draining at high operational speeds, and also avoiding a loss of quality, such as from crumpling the paper web. This object is achieved by providing that the press area of the indicated press device and pressing process comprises at least two press zones in succession, and also providing that the device and process attain a K value of at least 2.5 kPa·s·m, or at least about 2.5 kPa·s·m. Preferably, the device and process of the invention attain a K value of at least 2.6 kPa·s·m, or at least about 2.6 kPa·s·m, or at least 2.8 kPa·s·m, or at least about 2.8 kPa·s·m, or at least 3.0 kPa·s·m, or at least about 3.0 kPa·s·m.
The indicated K value is the product of L
1
and I
tot
. L
1
is the length of the first press zone, measured along the direction in which the web runs, and I
tot
is the total press impulse operating on the fibrous pulp web in the entire press area.
With press devices of the prior art, usually the fibrous pulp web is first drained intensively with roll presses, with a high line force, and then drained gently with extended nip presses. Pressure peaks with large gradients accordingly appear at high velocities. As a result, large quantities of water are pressed out of the loosely bound, wet paper web in a short amount of time, so that the paper web can be damaged, for example by crumpling.
However, for the present invention, it is guaranteed that a sufficient pressing time in the first press zone, as well as a sufficient press impulse for as high a draining or dewatering capacity as possible, are provided for the fibrous pulp web. If the draining or dewatering is not gentle, then twosidedness increases; however, the use of gentle draining or dewatering has the desirable effect of minimizing twosidedness. A gentle draining or dewatering is achieved by means of the length of the first press zone as well as the total press impulse operating on the fibrous pulp web.
It is understood that twosidedness, with reference to a particular property or properties, pertains to a variation in that property or properties between the top side and the bottom side of the fibrous web, for example, paper or liner. If the difference between the top and the bottom side is small for a particular property, then twosidedness for that property is small.
For instance, twosidedness in ash content refers to a difference in ash content distribution, from the top to the bottom of the web or paper product; correspondingly, minimizing twosidedness in ash content means minimizing the difference in ash content distribution between the top side and the bottom side. Accordingly, twosidedness in filler content refers to a difference in filler content distribution, from the top to the bottom of the web or paper product; correspondingly, minimizing twosidedness in filler content means minimizing the difference in ash content distribution between top and bottom.
There is also twosidedness with respect to the properties of structure and roughness. Minimizing structural twosidedness means minimizing the difference in the structural arrangement of fibers between the top and bottom sides. Minimizing twosidedness as to roughness means minimizing the difference between the roughness of the surface of the top side and the roughness of the surface of the bottom side.
As indicated herein, gentle dewatering minimizes twosidedness generally. Among the specific properties for which gentle draining diminishes twosidedness are structural twosidedness, twosidedness in ash content, twosidedness in filler content, and twosidedness as to roughness.
Because the amount of fluid is highest at the point where the fibrous pulp web is fed into the press device, or where the fibrous pulp web is first subjected to the pressing process, significantly more fluid must be diverted at the beginning of the pressing than at the end of the pressing. Therefore, a gentle draining in the first press zone is especially important at the machine velocities which are necessary for treating graphic papers. Because of the length of the first press zone in accordance with the invention, and accordingly the extent of the time period during which the fibrous pulp web is inside this zone, the essential gentle draining is accomplished in the first press zone.
The pressure pries of the various press zones can be the same, or substantially or essentially the same. However, it is advantageous for various press zones to have differing pressure profiles. For example, after the first, gentle draining in the first press zone, there can follow a gentle draining in the second press zone, with the pressure profile of this second zone demonstrating a pressure gradient larger than that of the pressure profile of the first press zone.
In a preferred and advantageous embodiment of the invention, the press zones of the press area are formed by several presses, such as shoe presses, roll presses, and extended nip presses. Preferably a shoe press is used to form the first press zone, because the distinguishing features of the invention can be especially easily attained with a shoe press. Thus it is especially simple to adjust the essential, gentle draining in the first zone by means of a shoe press. The reason for this ease of adjust is that, on the one hand, long duration of the web in the zone, and on the other hand, a moderate increase in pressure via a corresponding length and shape of the press shoe as well as a corresponding impingement of the press shoe, can be achieved with pressure.
The present invention may employ two or two or more press zones, or three or three or more press zones. Assuming that the first press zone is formed by a shoe press or a part of a shoe press, the most diverse embodiments of the remaining press zones are conceivable. For example, the entire press area can encompass two press zones, whereby the first press zone is formed by a
Grabscheid Joachim
Hasenfuss Rudolf
Schiel Christian
Schuwerk Wolfgang
Greenblum & Bernstein P.L.C.
Nguyen Dean T.
Voith Sulzer Papermaschinen GmbH
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