Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1999-04-29
2001-07-10
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S266000, C162S202000, C162S308000, C162S265000, C162S182000, C162S102000, C162S203000, C162S208000, C162S322000, C162S300000
Reexamination Certificate
active
06258212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and device for applying a liquid or paste-like medium onto a traveling material web made of paper or cardboard.
2. Description of Background Information
The inventors regard German Patent DE 194 23 48 as the most closely related prior art. As shown in FIG. 1 of this document, a fibrous suspension is deposited on a base (e.g., lower) endless wire or screen 3 by means of a headbox 1. A set of drainage elements 2 are disposed on the side of the wire or screen 3 opposite the side on which the fibrous suspension is deposited (e.g., on the inner side of the wire). A fibrous web 8 is formed along the lower wire or screen 3.
After the initial drainage zone, a second endless wire or screen 10 is arranged on the opposing (e.g., upper) side of the fibrous web 8. The base endless wire 3 has not been covered by an upper wire or screen up to this point. A second set of drainage elements 11 (suction devices) is disposed on the inner side of this second wire or screen 10, e.g., the side that does not touch the fibrous web 8. Consequently, drainage of the fibrous web 8 occurs in the opposing (e.g., upper) direction in this second region.
Opposing the second set of drainage elements 11, a set of application devices 7 (applicators) are associated with the wire surface on the underside of the base wire or screen 3. These application devices 7 introduce an application medium (additive) through the lower or base wire 3 into the fibrous web (borne on the upper side of the lower or base web 3). The drainage elements 11 (suction devices) on the inner side of the second wire 10 encourage the penetration of the application medium into the fibrous web 8. In the twin wire region (e.g., where the fibrous web is between the upper and lower endless wires or screens), essentially only drainage elements 11 are disposed on the inner side of one wire or screen 10, 3, and only application devices 7 are disposed on the inner side the other wire or screen. That is, with this arrangement, the application medium is applied to only one side of the fibrous web 8.
This structure and process are disadvantageous and use a relatively coarse wire structure. Due to the application of the application medium, the papers produced have coarse wire marks. Consequently, the resulting paper web has raised areas and recesses in the web that reduce the quality of the paper.
SUMMARY OF THE INVENTION
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.
An object of the invention, therefore, is to find a process and device that produce an improved surface quality in the resulting paper web.
According to a first aspect of the invention, a process for applying an application medium onto a material web includes forming the material web in a first twin wire zone between a first opposing pair of driven endless wires, transferring the material web to a second twin wire zone between a second opposing pair of driven endless wires, and applying the application medium onto the material web through one or both of the second opposing pair of driven endless wires.
In this manner, the application process is embodied so that the first fibrous web is produced in a first twin wire zone, which is optimally designed for drainage. Then, the fibrous web is transferred to a second twin wire zone, which is optimally designed, in terms of mechanical properties, for the application of the application medium in the wire region.
Preferably, the application of the application medium is through a different, finer mesh structure (in the second opposing pair of driven endless wires) than the first opposing pair of driven endless wires.
This improvement particularly addresses the problem that wire marks are produced because the strands of the wire cover a part of the fibrous web and therefore, the application medium does not travel well between the fibrous web and the strands at the covered regions. On the other hand, during the application of the application medium, a build-up occurs in the region of a mesh. When the wire is removed from the fibrous web surface that is coated with the application medium, small, undesirable raised areas are produced in the region of the wire meshes. The larger the wire meshes, the larger the raised areas become. These raised areas lead to problems in the further treatment of the fibrous web. It can also be advantageous if the wire mesh or web (disposed opposite the application device) is mechanically designed for an optimal supporting role so that a very smooth application is produced over the entire width of the wire.
More particularly, wire that is used both for drainage and for supporting the fibrous web during the application of the application medium actually can be optimally designed for only one of the two objects. If the wire is optimally designed for drainage, then it has a relatively large mesh width so that an effective and rapid drainage is produced in the beginning region of the wire section. Accordingly, in the invention, one or both of the second opposing pair of endless wires (through which the application medium is applied to the material web) can be embodied as a porous belt or as a more finely structured mesh than the first opposing pair of endless wires, which are used for the drainage of the wire web.
Optionally, the application medium may be applied to only one side of the material web through one of the second opposing pair of driven endless wires. Alternatively, the application medium may be applied to both sides of the material web through both of the second opposing pair of driven endless wires.
In this manner, in the second twin wire zone, it is possible to provide the fibrous web with an application medium from both sides. This has the further advantage that the respective opposite wires support the application devices. However, as noted, the application medium may be optionally applied from only one side. In this instance, only the wire disposed on the application side needs to be finely structured.
When the application medium is applied onto a first side of the material web through one or both of the second opposing pair of driven endless wires, the second side of the material web, opposite the first side of the material web, may be drained via suction. Further, after the draining, an additional application of the application medium to the second side through the remaining one of the second opposing pair of driven endless wires may be performed, along with an additional draining via suction on the first side of the material web. Alternatively, an additional draining via suction on the second side of the material web (without additional application of the medium) may be performed.
In this manner, especially when the wires are finely meshed, the draining leads to an increase in the dry matter content of the fibrous web without leaving behind wire marks of any consequence.
According to another aspect of the present invention, a process for forming a material web and applying an application medium onto the material web includes introducing a fibrous suspension into at least one twin wire zone between at least one opposing pair of driven endless wires, draining the material web in the twin wire zone to form the material web from the fibrous suspension, applying the application medium onto the material web on a first side of the material web, draining the application medium from the material web from a second side of the material web opposite the first side, applying the application medium onto the material web on the second side of the material web, and draining the application medium from the material web from the first side of the material web.
In this manner, it is possible to provide the material web with an application medium from both sides, and the disposition of the drainage elements on opposite sides prevents asymmetry in the material web surface.
Optionally, all of the applying and draining of the application medi
Greenblum & Bernstein P.L.C.
Halpern Mark
Silverman Stanley S.
Voith Sulzer Papiertechnik Patent GmbH
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